GSM Radio Network Optimization

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GSM Radio Network Optimization


INTRODUCTION


Introduction

RF people work in either

RF Planning RF Optimization

Responsibilities

Nominal Plan Design Sites Survey Validation from field Set RF design (Structure, Azimuth, Height, Tilt, Cables type) Frequency Plan Sites Acceptance

They have to provide the coverage either outdoor or indoor.

Responsibilities

Maintain the Network‘s Accessibility KPIs Maintain the Network’s Retain ability KPIs Maintain the Network’s Service Integrity KPIs Study and Apply new features Try to think of innovative solutions to maximize the Network capacity

They have to maintain the performance of the Network as good as possible.


Introduction

What will be our concern during this part of the course?

RF Optimization

How the RF Optimization people can maintain the KPIs?

By studying the different radio network features and studying the controlling parameters of each feature and how to tune them in a smart way to achieve the target KPIs.

What are we going to study during this part of the course?

Most of the Radio Network features and their controlling parameters.

KPIs monitoring and analysis.

Trouble shooting and Tuning.


COURSE OUTLINES


Course Outlines

Idle Mode Behavior. Handover. HCS (Hierarchical Cell Structure). Concentric & Multi Band Cells. CLS ( Cell Load Sharing). Frequency Hopping. Intra Cell Handover. Dynamic HR Allocation. Power Control. GSM to UMTS Cell Reselection and Handover. Trouble Shooting and KPIs monitoring.


THANK YOU


IDLE MODE BEHAVIOR


IDLE MODE BEHAVIOR

MS in Idle Mode

Doesn’t have a dedicated channel, but able to access the Network and able to be reached by the Network.

MS will always try to camp on the best cell based on the signal strength criterion.

MS will continuously monitor the serving and neighbor BCCH carriers to decide which cell to camp on.

The purpose behind studying the Idle Mode Behavior is to always ensure that the MS is camped on the cell where it has the highest probability of successful communication.


IDLE MODE BEHAVIOR

MS Tasks during Idle Mode

I. PLMN Selection.

II. Cell Selection.

III. Cell Reselection.

IV. Location Updating.

V. Monitor the Incoming Paging.


IDLE MODE BEHAVIOR

I. PLMN Selection Criterion PLMN identity is defined as “MCC+MNC” which is part of the LAI, where

LAI=MCC+MNC+LAC.

MCC: Mobile Country Code - MNC: Mobile Network Code - LAC: Location Area Code

When the MS is powered ON, it will perform a Location Update and compare the new LAI with the old stored one.

An MS will need to make a PLMN selection only incase:

1. MS is powered ON for the 1st time i.e. No PLMN was registered on before

(No Information on MCC&MNC is stored on SIM)

2. Old PLMN is not available any more.


IDLE MODE BEHAVIOR

I. PLMN Selection Criterion When the MS has to do a PLMN selection due to one of the previous cases,

the selection mode will depend on the MS settings either Automatic or Manual.

Automatic PLMN Selection Mode steps:

1. Home PLMN.

2. Each PLMN stored on the SIM card in priority order.

3. Other PLMNs have Signal Strength > -85 dBm in random order.

4. All other PLMNs in order of decreasing Signal Strength.

Manual PLMN Selection Mode:

1. Home PLMN.

2. All other available PLMNs and give the user the choice to select.


IDLE MODE BEHAVIOR

I. PLMN Selection Criterion National Roaming

If National Roaming is permitted then a MS can register on a PLMN in its home country other than its home PLMN.

National Roaming may be allowed on a certain location areas LAs of the visitor PLMN.

MS should periodically try to access back his home PLMN, but this periodic attempts will occur only on Automatic selection mode.


IDLE MODE BEHAVIOR

II. Cell Selection Criterion The Cell Selection algorithm tries to find the most suitable cell in the selected

PLMN and make the MS camp on.

Cell Selection is done by the MS itself.

During Idle Mode the Network doesn’t know the cell which the MS is camping on, it only knows the Location Area where the mobile registered himself in.


IDLE MODE BEHAVIOR

II. Cell Selection Criterion

MS will synchronize to the BCCH frequency and read system information (LAI,BA List,…etc)

Scan RF Frequencies one by one and calculates the Average received signal strength over 3 5 seconds

Tune to the RF Frequency with the highest average received signal strength

Camp on the Cell

Check if the chosen frequency is a BCCH carrier frequency or not

Check if C1 > 0 or not

Check if Cell is barred or not

Check if PLMN is desired or not

Tune to the next higher frequency that wasn’t tried before

Yes

Yes

No

Yes

No

Yes

No

No


IDLE MODE BEHAVIOR

II. Cell Selection Criterion Scanning RF Frequencies may occur in 2 ways:

1. Normal Scanning: Scan all Frequencies in the band ex:124 freq. in GSM900 Band.

2. Stored List Scanning: Scan the Frequencies in the Idle BA list (BCCH Allocation) stored on the MS SIM before being switched off.

(BA list can have maximum 32 frequencies)

If MS found cell belongs to the desired PLMN but not suitable, the MS will start to scan the Idle BA list of this cell.


IDLE MODE BEHAVIOR

II. Cell Selection Criterion Cell is said to be suitable if:

1. Cell belongs to the desired PLMN If at least 30 strongest frequencies from GSM900 band were tried and no

suitable

cell was found, then the MS will try another PLMN based on PLMN criterion.

2. Cell is not Barred ( CB = NO)

Some cells can be barred for access at selection and reselection or given lower priority based on settings of parameters: CB and CBQ

3. C1 > 0


IDLE MODE BEHAVIOR

II. Cell Selection Criterion C1 is called “Cell Selection Quantity”

It is calculated at the MS based on the below equation:

C1 = (Received SS – ACCMIN) – max (CCHPWR-P,0)

ACCMIN Minimum allowed DL received SS at the MS in order to access the system

CCHPWR Maximum allowed transmitting power by the MS in the UL.

P Maximum out put power of the MS according to its class.

N.B:

1. ACCMIN and CCHPWR are cell parameters sent to the MS at the BCCH channel.

2. If CCHPWR > P then C1 will decrease and so the Received SS should be large enough to keep C1 > 0 (May be this cell is not designed of this MS class)

3. ACCMIN, CCHPWR, P are all measured in dBm, where C1&C2 are measured in dBs


IDLE MODE BEHAVIOR

III. Cell Reselection Criterion After a cell has been selected, the MS will start the cell reselection

measurements to know if it is better to stay on the current cell or to camp on another cell.

Cell reselection measurements:

1. Monitors the SS (Signal Strength) of the BCCH carrier of the serving cell.

2. Monitors the SS of the BCCH carrier of all defined neighbors in the Idle BA list.

3. Continuously read system information sent on the serving BCCH carrier at least every 30 seconds.

4. Continuously read system information sent on the BCCH carrier for the six strongest neighbors at least every 5 minutes.

5. Try to decode BSIC of the six strongest neighbors every 30 seconds to assure that it is still monitoring the same cells.


IDLE MODE BEHAVIOR

III. Cell Reselection Criterion Cell reselection measurements summary:

BSIC BCCH Data (System Information)

Serving Cell - Every 30 Seconds

Six Strongest Neighbors Every 30 Seconds Every 5 Minutes


IDLE MODE BEHAVIOR

III. Cell Reselection Criterion When will Cell Reselection occur ?!!!

1. Serving Cell became barred ( CB = YES )

2. C1 serving cell falls below zero for more than 5 seconds.

3. MS tried to access the network through this cell unsuccessfully for the allowed no. of times defined by the parameter MAXRET

4. C2 neighbor cell ( one of the six strongest neighbors) became greater than C2 serving

cell for more than 5 seconds.

5. MS detects Downlink Signaling Failure.


IDLE MODE BEHAVIOR

III. Cell Reselection Criterion What will happen when the MS needs to make cell reselection?

The MS will camp on the cell that has the highest C2 value.

C2 is called “Cell Reselection Quantity”

C2 = C1 + CRO – TO * H( PT – T ) where PT ≠ 31

C2 = C1 – CRO where PT = 31

0 , X < 0

Where H(x)

1 , X ≥ 0 CRO Cell Reselection Offset, unit = 2 dB, value range = 0 to 63 TO Temporary Offset, unit = 10 dB, value range = 0 to 7 PT Penalty Time during which TO is valid T Initiated from zero when the MS places the neighbor in the list of the

Six Strongest


IDLE MODE BEHAVIOR

III. Cell Reselection Criterion CRO : defines a signal strength offset to encourage or discourage MSs to

reselect that cell.

TO : defines a negative temporary offset for certain time according to settings of PT (Practically this is useful to prevent fast moving MS from camping on microcells)

PT: If PT is set to 31, this means that a (–ve) SS offset “CRO” will be applied to this cell and it appears less favorite for cell reselection.


IDLE MODE BEHAVIOR

III. Cell Reselection Criterion Down Link Signaling Failure Algorithm The Algorithm of type “Leaky Bucket” and used a counter “D”, where D =

90/MFRMS

MFRMS is a cell parameter defines the no. of multi-frames between the transmission of each paging group i.e. if MFRMS=4 then a MS attached to a certain paging group will wait in sleeping mode for 4 multi-frames (4*253msec) until it is up again to listen to paging.

When the MS is up to listen to its paging group, if the message is not decoded successfully then D is decremented by 4 and if the message is decoded correctly then D is incremented by 1.

If D reaches zero, then a Down Link Signaling Failure is detected and cell reselection took place.


IDLE MODE BEHAVIOR

III. Cell Reselection Criterion Down Link Signaling Failure Algorithm

Ex: Assume that MFRMS = 4

Downlink signaling failure counter is initialized: D = round(90/MFRMS)=22.

If the MS unsuccessfully decodes a paging message, then: D = D - 4 = 18.

If the MS successfully decodes a paging message, then: D = D + 1 = 19.

If D reaches zero, then a Down Link Signaling Failure is detected and

cell reselection took place.

N.B:

D can’t exceed the bucket size given by round(90/MFRMS)


IDLE MODE BEHAVIOR

III. Cell Reselection Criterion CRH ( Cell Reselection Hysteresis ) Cell Reselection between two cells lie in two different Location Areas, will be

accompanied by Location Update.

At the border between cells the Signal level may be comparable, cell reselection may occur many times accompanied by many location updating leading to huge signaling load.

To avoid this, a parameter CRH is introduced such that a cell in another location area LA2 should have C2LA2

should greater than C2LA1 of serving cell

lie in LA1 by at least CRH in order to be selected.

If C2LA1 = 5 dB, CRH = 4 dB, then C2LA2

≥ 9 dB in order to be selected.


IDLE MODE BEHAVIOR

IV. Location Updating To make it possible for the mobile subscriber to receive a call and initiate a call

whenever needed, the network must know where the MS is located whenever it moves that’s why Location Updating is needed.

In the Idle Mode, the Network knows the location of the MS on a Location area resolution not on a cell resolution.

There are three different types of location updating defined:

1. Normal Location Updating.

2. Periodic registration.

3. IMSI attach & IMSI detach (when the MS informs the network when it enters an inactive state)


IDLE MODE BEHAVIOR

IV. Location Updating1. Normal Location Updating Initiated by the MS when it enters a cell belongs to a new Location Area

(LA).

The MS will compare the LAIold stored on the SIM with the LAInew broadcasted from the new cell and it will found them different so it’ll perform Location Update type normal.


IDLE MODE BEHAVIOR

IV. Location Updating2. Periodic Registration Regularly the MS should update the Network with its current location Area.

The Network will inform the MS how often it should report the location Area he is registering himself in.

Based on the value of the Parameter T3212 the MS will know how frequent it should make periodic registration.

T3212 take values from 1 (6min) to 255 (25.5 Hours), default = 40 (4 Hours)

MSC has a supervision time = BTDM+GTDM if it doesn’t hear from the MS during this period, the MSC will consider the MS implicitly detached.

BTDM+GTDM should > T3212, to not consider the MS detach before periodic location update is performed.


IDLE MODE BEHAVIOR

IV. Location Updating3. IMSI Attach/Detach IMSI attach/detach operation is an action taken by the MS to inform the

Network either it will go to inactive state (Power off) or it returned back to idle mode.

ATT is a cell parameter that will inform the MS whether IMSI attach/detach is operational or not.

If ATT=Yes, then before the MS will be switched off, it will send an IMSI detach request to the Network, so no paging messages will be sent to this MS while it is in this state.

When the MS is switched on again it will send an IMSI attach request to the Network so now paging messages can be sent normally to this MS.


IDLE MODE BEHAVIOR

V. Monitor the Incoming Paging Let us revise the DL logical channels and their mapping:

I) BCH(Broadcast Channels): including FCCH(Frequency Correction Channel) SCH(Synchronization Channel) BCCH(Broadcast Control Channel)

II) CCCH(Common Control Channels): including PCH(Paging Channel) AGCH(Access Grant Channel)

III) DCCH(Dedicated Control Channels): including SDCCH(Stand Alone Dedicated Control Channel) SACCH(Slow Associated Control Channel) CBCH(Cell Broadcast Channel) FACH(Fast Associated Control Channel)

May be Mapped on eitherTS1/C0 or TS0/C0

Always Mapped on TS0/C0

Always Mapped on TS0/C0

“ Work in Stealing mode by replacing the TCH time slot”


IDLE MODE BEHAVIOR

V. Monitor the Incoming Paging

CBBBBSF

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

F S F S F S F S F S I

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

Frame 1 Frame 2 Frame 3 Frame 4 Frame 5 Frame 6 Frame 7

Default Mapping on TS0/C0 (BCH+CCCH) “Non Combined Mode”51 TDMA Frames = 1 Control Multi-frame

B C C C C C C C C C


IDLE MODE BEHAVIOR


D1D1D1D0D0D0D0

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

I I I

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51

D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 A2 A3

Default Mapping on TS1/C0 (SDCCH+SACCH+CBCH(optional))

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7



IDLE MODE BEHAVIOR

V. Monitor the Incoming PagingCombination of Control channels (Different Mapping Criteria) Mapping on TS0/C0 is controlled by Parameter called BCCHTYPE

BCCHTYPE ═ NCOMB (Non Combined, BCH&CCCH) TS1/C0 will carry SDCCH+SACCH

═ COMB (Combined, BCH&CCCH&SDCCH/4) TS1/C0 will be free for TCH

═ COMBC (Combined with cell broadcast channel CBCH is in use, BCH&CCCH&SDCCH/4&CBCH) TS1/C0 will be free for TCH


IDLE MODE BEHAVIOR

V. Monitor the Incoming PagingCombination of Control channels (Different Mapping Criteria) SDCCH may have on of the following 4 configurations based on parameter

SDCCH

SDCCH ═ (i) SDCCH/8 (8 SDCCH Sub-channels i.e. make call setup for 8 users)═ (ii) SDCCH/8 including CBCH (7 SDCCH Sub-channels + 1 CBCH)

For these two cases, the BCCHTYPE=NCOMB and the mapping of the SDCCH channel is done on TS1/C0

═ (iii) SDCCH/4 (4 SDCCH Sub-channels)═ (iv) SDCCH/4 including CBCH(3 SDCCH Sub-channels + 1 CBCH)

For these two cases, the BCCHTYPE=COMB or COMBC and the mapping of the SDCCH channel is done on TS0/C0


IDLE MODE BEHAVIOR

V. Monitor the Incoming PagingCombination of Control channels (Different Mapping Criteria)

Non Default Mapping on TS0/C0 (BCH+CCCH)2*51 TDMA Frames = 2 Control Multi-frame


IDLE MODE BEHAVIOR

V. Monitor the Incoming PagingCombination of Control channels (Different Mapping Criteria) The Table below summarizes all the previous details:

Default Mapping (Non Combined) Non Default Mapping (Combined) BCH+CCCH on TS0/C0 and

SDCCH+SACCH+CBCH on TS1/C0BCH+CCCH+SDCCH+SACCH+CBCH on

TS0/C0

CBCH doesn't exist CBCH exist CBCH doesn't exist CBCH exist

1 block for BCCH 1 block for BCCH 1 block for BCCH 1 block for BCCH

9 blocks for CCCH 9 blocks for CCCH 3 blocks for CCCH 3 blocks for CCCH

8 blocks for SDDCH 7 blocks for SDDCH 4 blocks for SDDCH 3 blocks for SDDCH

1 block for CBCH 1 block for CBCH


IDLE MODE BEHAVIOR

V. Monitor the Incoming PagingPaging Groups The MS will monitor the incoming paging in only specific times, and the rest

of the time it will remain in sleeping mode. In this way we save the MS battery and we decrease the UL interference on

the system. The MS will monitor the incoming paging when the “Paging Group” assigned

for this MS is transmitted only. The CCCH block can be used by either PCH or AGCH. When the CCCH block is used for paging it will be called “Paging Block” The Paging Block consists of 4 consecutive Time slots lie in 4 consecutive

frames. The Paging Block can be used to page 4/3/2 users according to IMSI or

TMSI is used when paging the MS ( Length IMSI = 2 TS, Length TMSI=1TS) The group of users belong to the same paging block will be called “Paging

Group”


IDLE MODE BEHAVIOR


CBBBBSF

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

F S F S F S F S F S I

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7


Default Mapping on TS0/C0 (BCH+CCCH) “Non Combined Mode”51 TDMA Frames = 1 Control Multi-frame

B C C C C C C C C C


IDLE MODE BEHAVIOR

V. Monitor the Incoming PagingPaging Groups As appeared the MS will listen to paging in only specific times. The MS will utilize the time between the 4 TS that lie in 4 consecutive

frames to make the required measurements on the neighbor cells.


IDLE MODE BEHAVIOR

V. Monitor the Incoming PagingPaging Groups As we said before the no. of the CCCH blocks will depend on either non-

combined mode or combined mode is in use.

The structure of the CCCH will depend on a parameter called AGBLK. If AGBLK=1 1 CCCH block will be reserved for AGCH and we will have

either 8 or 2 blocks assigned for Paging. If AGBLK=0 No Blocks are reserved for AGCH and we will have either 9 or

3 blocks assigned for Paging.

Default Mapping(Non Combined) Non Default Mapping(Combined) BCH+CCCH on TS0/C0 and

SDCCH+SACCH+CBCH on TS1/C0BCH+CCCH+SDCCH+SACCH+CBCH on

TS0/C0CBCH doesn't exist CBCH exist CBCH doesn't exist CBCH exist

9 blocks for CCCH 9 blocks for CCCH 3 blocks for CCCH 3 blocks for CCCH


IDLE MODE BEHAVIOR

V. Monitor the Incoming PagingPaging Groups How many Paging Groups we have? This will depend on a parameter

MFRMS MFRMS is a parameter defined per cell and it defines how frequent the

paging group assigned for certain MS will be transmitted. MFRMS takes values from 1 to 9,

If MFRMS=1 then the paging group assigned for certain MS will be transmitted every 1 control Multiframes=253 msec

If MFRMS=9 then the paging group assigned for certain MS will be transmitted every 9 control Multiframes = 9*253msec=2.3 seconds.

If MFRMS is large: Positive Side: The MS battery life time will increase coz the MS

remains in sleeping mode for long time. Negative Side: Call setup time will increase coz may be paging come to

the MS while it is still in the sleeping mode.


IDLE MODE BEHAVIOR

V. Monitor the Incoming PagingPaging Strategies Paging Strategies are controlled by parameters in the MSC.

Setting of parameters will decide whether the paging will be local paging (within the LA) or global paging (within the MSC service area).

Setting of parameters will decide also whether paging will be done via IMSI or TMSI.

Using the parameters we can decide also how the second paging will be incase the first paging failed, ex: If 1st paging was local with TMSI then we can set the 2nd paging to be global with IMSI.


IDLE MODE BEHAVIOR

Related Feature to the Idle Mode BehaviorAdaptive Configuration of Logical Channels (ACLC) As we know the SDCCH channel is used for signaling i.e. call setup, while the

TCH channel is used to carry real user traffic (speech/data).

As a rule of thumb GOS for TCH=2% i.e. within 100 calls if 2 of them are blocked then this will be acceptable, for the SDCCH/8 the GOS=0.5% and for the SDCCH/4 the GOS=1%

As we know in the default settings for frequency C0, TS0 is used to carry BCH+CCCH and TS1 used to carry SDCCH+SACCH, and TS2TS7 used to carry speech/data


IDLE MODE BEHAVIOR

Related Feature to the Idle Mode BehaviorAdaptive Configuration of Logical Channels (ACLC) Now if the signaling load is high i.e. many users need to make call setup then

high blocking will occur exceeding the allowed value 0.5% To solve the blocking we have 2 ways:

i) Static Configuration of a TCH TS to be used as SDCCH forever

(Now TS1&TS2 used for SDDCH+SACCH and TS3TS7 used to carry speech/data)

But in this case we lost 1 TCH channel i.e. 5 users can talk simultaneously instead of 6

ii) Adaptive Configuration of a TCH TS to be used as SDCCH/8 when there is blocking only

(Now TS1&TS2 used for SDDCH+SACCH and TS3TS7 used to carry speech/data)

But when there is no blocking (TS2 will be configured back automatically as a TCH and used to carry speech/data)


IDLE MODE BEHAVIOR

Related Feature to the Idle Mode BehaviorAdaptive Configuration of Logical Channels (ACLC) Main Controlling Parameters: ACSTATE: Activates/Deactivates the feature on cell basis, values: ON/OFF SLEVEL: No. of Idle SDCCH sub-channels below which the feature will work.

The conditions that should be fulfilled for the ACLC feature to work:

1. ACSTATE=ON

2. No. of Idle SDCCH sub-channels < SLEVEL (This is an indication for congestion)

3. No. of Idle TCHs > 4 or no. of Idle TCHs > Total no. of TRXs (Frequencies)

4. No. of already defined SDCCH channels/8 < Max. allowed configuration of SDCCHs in the cell.


IDLE MODE BEHAVIOR

Parameters Summary

SCH ParametersParameter Name Value Range Recommended Value Unit

BSIC NCC: 0 to 7 BCC: 0 to 7 ─ ─

RACH Control ParametersParameter Name Value Range Recommended Value Unit

MAXRET 1,2,4,7 4 ─

Control Channel ParametersParameter Name Value Range Recommended Value Unit

BCCHTYPE COMB COMBC NCOMB NCOMB ─

SDCCH 0 to 16 (0: No SDCCH/8 configured-combined mode) 1 ─

IMSI Attach/Detach ParametersParameter Name Value Range Recommended Value Unit

ATT Yes, No Yes ─


IDLE MODE BEHAVIOR

Parameters Summary

Paging Parameters and Periodic UpdateParameter Name Value Range Recommended Value Unit

MFRMS 2 to 9 6 Control Channel Multi frame

AGBLK 0 or 1 0 ─

T3212 0 to 255 (0: infinite-No periodic registeration) 40 6 minutes

Cell Selection and Reselection Parameters

Parameter Name Value Range Recommended Value Unit

ACCMIN − 47 dBm to −110 dBm −110 dBm dBm

CCHPWR GSM900: 13 to 43 in steps of 2 GSM1800: 4 to 30 in steps of 2

GSM900: 33 dBm GSM1800: 30 dBm dBm

CRO 0 to 63 0 2 dBTO 0 to 7 (7:infinite) 0 10 dBPT 0 to 31 0

CRH 0 to 14 in steps of 2 dB


THANK YOU


HANDOVER (LOCATING)


Handover (Locating)

Handover (Locating) Algorithm

The Handover (Locating) Algorithm

is the basic feature to provide mobility in the Radio Network.

Aims At?

i. Keep the continuity of a current call with acceptable quality.

ii. Cell size control in-order to decrease total interference in the system.

Implemented where?

In the BSC.

Location process initiated when?

After Hand Over (HO), Assignment or Immediate Assignment.


Handover (Locating)


Inputs to the Algorithm?

Signal Strength, Quality measurements &TA for serving cell and Signal Strength measurements for neighbor cells.

Output from the Algorithm?

List of candidates which the algorithm judges to be possible candidates for HO (List of HO candidates are ranked and sorted in descending order)


Handover (Locating)


What types of Handover (locating) algorithm we have?

i. SS & Path Loss based Algorithm: Follows the GSM specifications. HO decision is taken based on both Signal Strength (SS) and Path Loss.

ii. SS based Algorithm: HO decision is taken based on Signal Strength only and this leads to better performance.

It is less complex, uses less parameters and easy to be maintained in the Radio Network.


Handover (Locating)


The main Flow of the Handover (locating) Algorithm goes as follow:

Filtering Basic Ranking Urgency Conditions HandlingInitiation

Auxiliary Radio Network Features Evaluation

Organizing the List

Sending the List & Allocation Reply


Handover (Locating)


I. Initiation.

II. Filtering.

III. Basic Ranking.

IV. Urgency Conditions Handling.

V. Auxiliary Radio Network Features Evaluation.

VI. Organizing the List.

VII. Sending the List & Allocation Reply.


Handover (Locating)

I. Initiation of the Handover (Locating) Process/Algorithm The Locating Process is initiated when one of the following occurs:

1. Handover: Normal, Intra Cell HO (IHO), Sub-cell change (OLUL or ULOL)

2. Assignment: Allocation of TCH channel after completing call setup on SDCCH.

3. Immediate assignment: You are assigned SDCCH to make call setup, or a TCH to make call setup on when no free SDCCH channels exist.


Handover (Locating)

I. Initiation of the Handover (Locating) Process/Algorithm Handover on SDCCH can be enabled/disabled based on parameter SCHO

At initiation of Locating after successful HO, Assignment or Immediate assignment a timer TINIT starts which will disable HO for some time until it expires.

The reason is to leave the connection on the current channel for some time until the locating algorithm produces reliable results we can rely on.

TINIT will disable HO only, but Assignment on own or other cell will occur normally and will not wait TINIT till expired.

TINIT is a BSC parameter not a cell parameter and it measured in SACCH periods.


Handover (Locating)

II. Filtering Simply it is the process of collecting the required data on Signal Strength

(SS), Quality and Time Advance (TA) for serving and neighbor cells and average these consecutive measurements over a specified period to rank these cells.

This is accomplished in two steps:

1. Measurements Preparation

2. SS, Quality and TA Filtering


Handover (Locating)

II. Filtering1. Measurements Preparation Data that is measured:

The MS can measure the SS of up to 32 neighbor frequencies but only the six strongest neighbors (which it succeeded to decode its BSIC over the last 10 seconds) are reported and considered candidates for HO.

Cell on which measurements are reported Measured Quantity Who makes the

measurements?

Serving Cell

SS DL MSQuality DL (rxqual_DL) MSQuality UL (rxqual_UL) BTS

TA BTS

6 Strongest neighbor cells SS DL MS


Handover (Locating)

II. Filtering1. Measurements Preparation SS measurements are delivered as integer values 0 63 corresponds to

real SS from -110 dBm - 47 dBm Quality is measured based on the BER and it may be represented in two

forms:

i. Integers 0 (Best) 7 (Worst)

ii. Deci Transformed Quality Units (dtqu) from 0 (Best) 70 (Worst)

Time Advance (TA): is reported as values between 0 63 bit period.

N.B:

If TA=1 then the MS is at nearly 0.5 km from the cell


Handover (Locating)

II. Filtering2. SS, Quality and TA Filtering: The consecutive measurements for SS, Quality and TA are averaged in

some way based on the equation of the filter used.

We’ve 5 Types of Filters that may be used, each one has its own equation or its way to produce output results from the collected consecutive measurements:

A. General FIR Filters

B. Recursive Straight Average Filter

C. Recursive Exponential Filter

D. Recursive 1st Order Butterworth Filter

E. Median Filter


Handover (Locating)

II. Filtering2. SS, Quality and TA Filtering: In addition to the way each filter use to produce output results from the

consecutive measurements, each filter has what we call filter length which is the period over which measurements are considered.

We have controlling parameters on cell basis to select the type of filter used and the length of the filter.

Also the type of the filter used in signaling (call setup) and dedicated phases may be configured separately as we’ll see.


Handover (Locating)

II. Filtering2. SS, Quality and TA Filtering:

2-i) Signal Strength Filters controlling parameters SSEVALSI Selects the Type of the filter that will be used during Signaling

phase. SSEVALSD Selects the Type of the filter that will be used during

Connection phase. SSLENSI Selects the Length of the filter that will be used during Signaling

phase. SSLENSD Selects the Length of the filter that will be used during

Connection phase.

N.B:

SSLENSI & SSLENSD are measured in the form of SACCH periods,

i.e. if SSLENSD=10, then the length of the filter during the connection phase = 10*0.48 sec = 4.8 seconds


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2-ii) Quality Filters controlling parameters QEVALSI Selects the Type of the filter that will be used during Signaling

phase. QEVALSD Selects the Type of the filter that will be used during Connection

phase. QLENSI Selects the Length of the filter that will be used during Signaling

phase. QLENSD Selects the Length of the filter that will be used during

Connection phase.

N.B:

QLENSI & QLENSD are measured in the form of SACCH periods,

i.e. if QLENSD=10, then the length of the filter during the connection phase = 10*0.48 sec = 4.8 seconds


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2-iii) Time Advance (TA) controlling parameters One single type of filters is used which is the Recursive Straight Average

Filter and the length of the filter is specified by parameter TAAVELEN which is also measured in SACCH periods.


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III. Basic Ranking It is called “Basic” coz in this stage ranking is done before handling the

urgency conditions and evaluation of the auxiliary radio network features.

As mentioned earlier, two algorithms are available for basic ranking (SS&Path loss based Algorithm and SS based Algorithm) and they’re selected according to the parameter EVALTYPE

EVALTYPE=1, SS & Path loss based Algorithm is used for basic ranking taking into consideration both Signal Strength measurements and the path loss.

EVALTYPE=3, SS based Algorithm is used for basic ranking taking into consideration Signal Strength measurements only.


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III. Basic Ranking Basic Ranking Algorithm following the SS based Algorithm will be done on

four steps:

A. Correction of Base Station output power.

B. Evaluation of the minimum signal strength condition for neighbors.

C. Subtraction of signal strength penalties.

D. Rank the Candidates after applying Offsets and Hysteresis.

Common for both

Algorithms


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III. Basic Ranking Basic Ranking Algorithm following the SS based Algorithm

A. Correction of Base Station output power The location algorithm aims at making the Pure Traffic Frequencies to control

the cell borders and not the BCCH frequencies, coz most of the time the seized TCH Time slot will be located on a TCH frequency.

BSPWR is a parameter to set the output power of the BCCH carrier

And BSTXPWR is a parameter to set the output power of the TCH frequencies.

Correction for the output power will done for both:

(A-i) Correction for Neighbor Cells.

(A-ii) Correction for Serving Cell.


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A. Correction of Base Station output power

(A-i) Correction for Neighbor Cells The MS is informed by the BCCH frequencies of the neighbors cells on

which he has to perform his measurements via Active BA list.

SS_corrected_DLneighbor = SS_measured_DLneighbor - ( BSPWR - BSTXPWR )


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A. Correction of Base Station output power

(A-ii) Correction for Serving Cell

1) TCH Time Slot (TS) is on the BCCH frequency

SS_corrected_DLservingcell = SS_measured_DLservingcell - ( BSPWR - BSTXPWR )

2) TCH TS is hopping between a BCCH frequency and a TCH frequency:

SS_corrected_DLservingcell = SS_measured_DLservingcell - ( BSPWR - BSTXPWR )/N ,

Where N is the no. of the hopping frequencies

3) TCH TS is on the OL (Over Laid sub cell)

SS_corrected_DLUnderLaid = SS_measured_DLOverLaid+ ( BSTXPWR Under Laid – BSTXPWROverLaid )


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B. Evaluation of the minimum Signal Strength condition for Neighbors Not all the neighbors are allowed to be ranked!! The neighbor should pass the minimum signal strength condition in order to

be ranked.

SS_corrected_DLneighbor will be compared with respect to parameter called MSRXMIN,

If SS_corrected_DLneighbor ≥ MSRXMIN this neighbor will be included in ranking

If SS_corrected_DLneighbor < MSRXMIN this neighbor will be excluded from ranking

If UL measurements are included then SS_corrected_ULneighbor will be compared with respect to parameter called BSRXMIN,

If SS_corrected_ULneighbor ≥ BSRXMIN this neighbor will be included in ranking

If SS_corrected_ULneighbor < BSRXMIN this neighbor will be excluded from ranking


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B. Evaluation of the minimum Signal Strength condition for Neighbors

Example:Assume that a MS is connected to cell A that has five neighbors B,C,D,E&F, theMSRXMIN for all the cells is -104 dBm and the SS_corrected_DLneighbor for each cell after

correcting the BTS o/p power is given in the below Table:

Cell C will be excluded from ranking and won’t be considered in the next stage and the MS will

never HO to it

Neighbors SS_corrected_DLneighbor

B -85 dBm

C -110 dBm

D -87 dBm

E -70 dBm

F -100 dBm


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C. Subtraction of signal strength penalties Penalties or Punishments will be applied on cells that are for some reasons

temporarily undesirable.

A Penalty value will decrease the rank of some cells for certain penalty time.

SS_punished_DL = SS_corrected_DL – Locating Penalties – HCS Penalties

In the coming slides we’ll talk about the two types of penalties:

(C-i) Locating Penalties

(C-ii) HCS Penalties


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C. Subtraction of signal strength penalties


1) Due to HO failure:

If HO to a neighbor cell failed then we’ve to apply a penalty value for some

time on this neighbor so when basic ranking is done again we don’t go back

to this cell. Penalty value will be configured using parameter PSSHF (default 63 dB) Penalty time will be configured using parameter PTIMHF (default 5 sec)


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2) Due to Bad Quality (BQ) Urgency HO:

If a cell was abandon due to BQ, then it should have been the best cell from

SS point of view so without penalties using the basic ranking we’ll be back to

this cell. Penalty value will be configured using parameter PSSBQ (default 7 dB) Penalty time will be configured using parameter PTIMBQ (default 5 seconds)

3) Due to Excessive TA Urgency HO:

Handled in the same manner like the BQ case. Penalty value will be configured using parameter PSSTA (default 63 dB) Penalty time will be configured using parameter PTIMTA

(default 30 seconds)


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(C-ii) HCS Penalties It is related to the HCS (Hierarchical Cell Structure) feature when a MS is

detected as a fast moving mobile.

A penalty will be applied on lower layer cells so in ranking we will prioritize cells in the same layer of the serving cell and cells in higher layers and in this way unnecessary HO’s are prevented ( ex: layer2 cells will be prioritized than layer1 cells)


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D. Rank the Candidates after applying Offsets and Hysteresis Ranking for neighbor cells will be done after applying Offsets and Hysteresis.

Offset: Displace the cell border as compared to

the border strictly given by SS.

Controlling parameter: OFFSET (default: zero dB)

Hysteresis: To reduce the risk of ping pong HO

a region for Hysteresis is applied

around the cell border.


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D. Rank the Candidates after applying Offsets and Hysteresis If the Hysteresis value is too high there will be a risk that the MS will be

connected to the cell of low SS for long time and if the Hysteresis is too low then there will be a risk that ping pong HO’s occur.

So the applied value of Hysteresis will be variable based on the received SS of the serving cell.

SS_corrected_DLservingcell will be compared to value HYSTSEP (default -90 dBm), If SS_corrected_DLservingcell > HYSTSEP, then the serving cell is strong

enough and high value of Hysteresis will be applied such that Hysteresis value=HIHYST (default 5 dB)

If SS_corrected_DLservingcell < HYSTSEP, then the serving cell is not strong enough and low value of Hysteresis will be applied such that Hysteresis value=LOHYST (default 3 dB)


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D. Rank the Candidates after applying Offsets and Hysteresis

HYST=LOHYSTNo

SS_corrected_DLservingcell > HYSTSEP

HYST=HIHYST

Yes

Output from Basic Ranking

Rankservingcell = SS_corrected_Dlservingcell

Rankneighbor= SS_punished_DLneighbor – OFFSETneighbor – HYSTneighbor


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IV. Urgency Conditions Handling After the Basic Ranking stage a check is made on the serving cell to know if

Urgency conditions are detected or not.

We have two types of Urgency HO:

1. Bad Quality (BQ) Urgency HO

2. Excessive Time Advance (TA) Urgency HO

If Urgency conditions are detected then the serving cell should be abandon as fast as possible, but some of the neighbors will be removed from the candidate list and the MS will not be able to HO to them as we will see later.

As seen before, cells that were abandon due to Urgency HO will be subjected to punishment/penalty.


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IV. Urgency Conditions Handling1. Bad Quality (BQ) Urgency HO The Quality measured at the DL and UL for the serving cell will be

compared with two parameters QLIMDL & QLIMUL (default 50 dtqu) and if:

rxqual_DL > QLIMDL

rxqual_UL > QLIMUL

The Quality may drop like that as a result of Co-Channel Interference or when the SS became very low.

When Urgency Condition is detected the MS has to leave the cell and make HO to other cell, but in this case the serving cell is the one that has the highest SS so the MS has to HO to a cell of worse SS, but is the MS allowed to HO to any worse cell?

Or Urgency HO due to BQ should be performed


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IV. Urgency Conditions Handling1. Bad Quality (BQ) Urgency HO Is the MS allowed to HO to any worse cell? No, this will be based on a

parameter called BQOFFSET which will ensure that far neighbors won’t be selected.

If Rankservingcell – Rankneighbor < BQOFFSET+HYST, then this neighbor is near to the serving cell and it is not much worse than the serving cell and it can be candidate for HO.

If Rankservingcell – Rankneighbor > BQOFFSET+HYST, then this neighbor is far from the serving cell and it will be removed from the candidate list.


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IV. Urgency Conditions Handling1. Bad Quality (BQ) Urgency HO

Example:If Urgency condition is detected where Rankservingcell = -75 dBm and the neighbors:

((RankB = -79 dBm , RankC = -90 dBm , RankD = -87 dBm)) and

((BQOFFSET=5dB, HYST=0 dB))

Rankservingcell – RankB = 4dB < BQOFFSET= 5dB “Cell B is kept in the candidate list” Rankservingcell – RankC = 15dB > BQOFFSET= 5dB “Cell C is removed from the

candidate list” Rankservingcell – RankD = 8dB > BQOFFSET=5dB “Cell D is removed from the

candidate list”


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IV. Urgency Conditions Handling2. Excessive Time Advance (TA) Urgency HO TA can be used as a measure for the distance between the BTS and the

MS.

If TA > TALIM (63 bit period) Urgency HO due to TA is initiated.


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After Basic Ranking and Evaluation of the Urgency Conditions, the Serving Cell and Neighbor Cells will be divided into 3 Groups:

Better Cell

Serving Cell

Worse Cell

Categorization #1


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V. Auxiliary Radio Network Features Evaluation1. Assignment to Another Cell Evaluation

2. Cell Load Sharing Evaluation

3. Over Laid/Under Laid sub-cell Evaluation

4. IHO Evaluation

5. HCS Evaluation

After these Evaluations, some candidates will be removed from the HO candidate list and Categorization#2 will be performed.


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V. Auxiliary Radio Network Features Evaluation1. Assignment to Another Cell Evaluation The Locating Algorithm may be initiated after immediate assignment to know

whether it is better for the MS to take a TCH time slot on the current cell or not.

If during the signaling phase a Better Cell was found after ranking then “Assignment to Better Cell” will be initiated.

If during the signaling phase no better cell was found, then the MS will normally be assigned a TCH time slot on the current cell.

If the Better/Serving Cells were congested then “Assignment to Worse Cell” will be done.


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V. Auxiliary Radio Network Features Evaluation1. Assignment to Another Cell Evaluation Is the MS allowed to take TCH time slot on any worse cell? No, this will be

based on a parameter called AWOFFSET which will ensure that far neighbors won’t be selected.

Only if Rankservingcell – Rankneighbor < AWOFFSET, then this neighbor is near to the serving cell and it is not much worse than the serving cell and assignment to it can be done.

If Rankservingcell – Rankneighbor > AWOFFSET, then this neighbor is far from the serving cell and it will be removed from the candidate list.


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V. Auxiliary Radio Network Features Evaluation2. Cell Load Sharing (CLS) Evaluation This feature is used to reduce congestion on the serving cell. When CLS is activated and the load on the serving cell becomes higher than

certain threshold then:

i) Valid CLS HO candidates are defined

ii) Re-calculation of their ranking values will be performed.


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V. Auxiliary Radio Network Features Evaluation2. Cell Load Sharing (CLS) Evaluation

i. Valid CLS HO candidates are defined as follow: Worse cells: coz if they were better then they’ll be chosen at Basic

Ranking Load on neighbor cells < CLS load threshold Internal cells: lies in the same BSC Same Layer

ii. Re-calculation of their ranking values will be performed: We’re going to recalculate the Ranking values of the valid CLS

neighbors with reduced Hysteresis so these worse neighbors will appear with higher SS than they really are and the MS can make HO to them and relief the congestion on the current cell.


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V. Auxiliary Radio Network Features Evaluation3. OL/UL Sub-Cell Evaluation The OL/UL feature provides a way of increasing the traffic capacity in a

cellular network without building new sites.

Since OL sub-cell serves smaller area than the corresponding UL sub-cell a smaller reuse distance can be used in in the OL sub-cell than in the under laid.

The OL/UL evaluation may result in a recommendation to change the sub-cell from the one currently in use, this evaluation is based on:

DL SS, TA Serving Cell, Distance to cell border, Traffic Load in the cell

This feature will be discussed in details afterwards.


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V. Auxiliary Radio Network Features Evaluation4. Intra Cell HO (IHO) Evaluation The IHO feature provides a way to improve the speech quality during the

conservation when bad quality is detected while the SS is high.

This is can be accomplished by changing the channel the connection is currently using within the same cell.


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V. Auxiliary Radio Network Features Evaluation5. Hierarchical Cell Structure (HCS) Evaluation The HCS feature provides the possibility to give priority to cells that are not

strongest but provide sufficient SS.

The priority of a cell is given by associating a layer to the cell.

We have 8 layers from layer 1 (Highly prioritized) to layer 8 (least prioritized).

Micro cells are prioritized than Macro cells for capacity purposes.

Cells of lower layers will be ranked higher than cells of higher layers in the HO candidate list.


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After the Auxiliary Radio Network features evaluation some candidates may be prioritized and the order of the candidate list will be modified.

The Serving Cell and Neighbor Cells will be divided into 3 Groups:

Above S

Serving Cell (SC)

Below S

Categorization #2


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VI. Organizing the List The final list will contain maximum up to Six Neighbors + The Serving Cell

and categorized as follows: Serving Cell (SC), Above S, Below S

To reach the final form before sending the list the following steps will be done:

A. Removal of Candidates

B. Ordering the Candidate List based on the Current Conditions.


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VI. Organizing the ListA. Removal of Candidates Some Candidates may be removed coz:

Some Controlling timers are active and preventing HO to certain cell: TALLOC: This timer prevents HO on a target cell for some time after

assignment/HO failure due to congestion on target cell.

(N.B: No penalties are applied on this cell)

TURGEN: This timer prevents HO on a target cell for some time after urgency HO failure due to congestion on target cell.

N.B:

TALLOC and TURGEN are BSC parameters


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VI. Organizing the ListB. Ordering the Candidate list based on the Current Conditions Means what? Means in what order the 3 categories (Above S, S, Below S)

will be arranged before sending the candidate list. This will be based on some condition flags.

Condition Flags:

1. Assignment Request Arrived

2. Assignment to Worst Cell is in Use

3. Excessive TA Detected

4. BQ Urgency HO

5. OL/UL Sub-Cell Load Change or IHO


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VI. Organizing the ListB. Ordering the Candidate list based on the Current Conditions

Condition Flags: 3 Excessive TA Detected

1 Assignment Request Arrived 4 BQ Urgency HO

2 Assignment to Worst Cell is in Use 5 OL/UL Sub-Cell Load Change or IHO

CaseCondition Flags

Ordering Comment1 2 3 4 5

1 0 x 0 0 0 Above S Normal Case

2 0 x 0 1 0 Above S Below S Serving Cell has BQ so it should be abandon either to the Above S or Below S cell

3 1 0 0 0 0 Above S S An Assignment request came and the AW flag is not raised

4 1 1 0 0 0 Above S S Below S An Assignment request came and the AW flag is raised

5 0 x 0 1 1 Above S S Below S

Serving Cell has BQ so it should be abandon but coz the OL/UL subcell change flag is raised, then

the serving cell is included coz this subcell change may solve the issue with no need to go

for a below worse cell


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VII. Sending the List & Allocation Reply The resulting candidate list will form the basis on which HO will be

performed.

Empty list means that no options are better than remaining on the current cell and no HO will occur.

The channel allocation reply may be success or failure.

Failure may be due to congestion or signaling failure on the target cell.

Based on the result of allocation either success/failure, some actions will be taken like applying some penalties or enabling of certain timers as we saw previously.


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Example:Assume that the o/p from the Filtering stage for the SS measurements is asbelow and we want to prepare the Basic Ranking Candidate list for HO:

Where,BSPWR = BSTXPWR, MSRXMIN = -90 dBm, Cell A was abandon due to BQ urgency HO (PSSBQ=7dB)SS based Algorithm is in use where OFFSET=0, HYSTSEP= -90 dBm,HIHYST= 5 dB, LOHYST= 3 dB

Cell SS(dBm)A -70

B (Serving Cell) -74C -78D -68E -80F -92G -95


Cell SS(dBm)A -70

B (Serving Cell) -74C -78D -68E -80F -92G -95

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Solution:A) Correction of Base Station output power: Since BSPWR = BSTXPWR then the current measurements will be kept as it is. SS_corrected_DLneighbor = SS_measured_DLneighbor

SS_corrected_DLserving = SS_measured_DLserving

B) Evaluation of the minimum Signal Strength condition for Neighbors: The SS for neighbors will be compared against MSRXMIN = -90 dBmCell F and Cell G have SS < MSRXMIN then they will be removed from the list and can’t be

candidates for HO.


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Solution:C) Subtraction of signal strength penalties: Since Cell A was abandon due to BQ urgency HO (PSSBQ=7dB) then it will be

punished, SS_punished_DL Cell A = SS_corrected_DL – PSSBQ = -70 – 7 = -77 dBm

The candidate list will now be in the following form:Cell SS(dBm)

A -77

B (Serving Cell) -74

C -78

D -68

E -80


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Solution:D) Rank the Candidates after applying Offsets and Hysteresis Since SSServing cell B = -74 dBm > HYSTSEP= -90 dBm, then it is better to stay on the

current cell and high Hysteresis will be applied i.e. HYST = HIHYST = 5 dB

Rankservingcell B = -74 dBm “Serving Cell” RankA= -77 dBm – OFFSET – HYST = -77 – 0 – 5 = -82 dBm “Worse Cell” RankC= -78 dBm – OFFSET – HYST = -78 – 0 – 5 = -83 dBm “Worse Cell” RankD= -68 dBm – OFFSET – HYST = -68 – 0 – 5 = -73 dBm “Better Cell” RankE= -80 dBm – OFFSET – HYST = -80 – 0 – 5 = -85 dBm “Worse Cell”

Cell SS(dBm)A -77

B (Serving Cell) -74

C -78

D -68

E -80


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Solution:Now the final list according to Categorization#1 will be arranged as follows:

Categorization#1

Cell SS(dBm) Category

D -73 Better Cell

B -74 Serving Cell

A -82 Worse Cell

C -83 Worse Cell

E -85 Worse Cell


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Disconnection Criteria

The Disconnection algorithm is not part of the locating algorithm but for completeness, the topic is treated here.

The Disconnection algorithm manages when the connection between the MS and the Network shall be dropped when signaling failure is detected.

The Disconnection criterion can be made in both the DL and the UL such that: In the DL: managed by the MS

and In the UL: managed by the BSC


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Disconnection Criteria

In DL: Controlled by a parameter RLINKT (max. bucket size) , when the MS couldn’t

decode a SACCH message (0.48 sec), the bucket will be decreased by 1 unit, when the MS successfully decodes a SACCH message, the bucket will be increased by 2 units, if the bucket reached value = Zero then disconnection will occur, recommended value RLINKT=16

In UL: The disconnection algorithm will run in the same way, the BSC will make the

evaluation, and the controlling parameter is called RLINKUP, , recommended value RLINKUP=16

N.B: The bucket can’t have values larger than the max. value given by RLINKT/RLINKUP


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Parameters Summary

Algorithm SelectionParameter Name Value Range Recommended Value Unit

EVALTYPE 1 or 3 3 ─

Flow Control ParametersParameter Name Value Range Recommended Value Unit

TINIT 0 to 120 10 SACCH period=480 msecTALLOC 0 to 120 2 SACCH period=480 msecTURGEN 0 to 120 2 SACCH period=480 msec


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Parameters Summary

Filtering Control ParametersParameter Name Value Range Recommended Value Unit

SSEVALSI 1 to 9 6 ─SSEVALSD 1 to 9 6 ─QEVALSI 1 to 9 6 ─QEVALSD 1 to 9 6 ─SSLENSI 1 to 20 4 SACCH period=480 msecSSLENSD 1 to 20 10 SACCH period=480 msecQLENSI 1 to 20 4 SACCH period=480 msecQLENSD 1 to 20 10 SACCH period=480 msec

TAAVELEN 1 to 20 4 SACCH period=480 msec


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Parameters Summary

Signal Strength based Basic Ranking ParametersParameter Name Value Range Recommended Value Unit

HYSTSEP −150 to 0 -90 dBmLOHYST 0 to63 3 dBHIHYST 0 to63 3 dBOFFSET −63 to 63 0 dB

Handover Failure Parameters (Signaling Failure)Parameter Name Value Range Recommended Value Unit

PSSHF 0 to 63 63 dBPTIMHF 0 to 600 5 Seconds


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Parameters Summary

Urgency Conditions ParametersParameter Name Value Range Recommended Value Unit

QLIMUL 0 to 100 55 dtqu

QLIMDL 0 to 100 55 dtqu

BQOFFSET 0 to 63 3 dB

PSSBQ 0 to 63 7 dB

PTIMBQ 0 to 600 15 Seconds

TALIM 0 to 63 62 Bit Period (0.577msec)

PSSTA 0 to 63 63 dB

PTIMTA 0 to 600 30 Seconds

Disconnection Algorithm ParametersParameter Name Value Range Recommended Value Unit

RLINKT 4 to 64 in steps of 4 16 SACCH period=480 msecRLINKUP 1 to 63 16 SACCH period=480 msec


THANK YOU


HIERARCHICAL CELL STRUCTURE (HCS)


Hierarchical Cell Structure (HCS)

HCS Evaluation Algorithm

HCS feature provides the ability and flexibility to give priority to cells that are not strongest but provide sufficient Signal Strength.

The priority of a cell is given by associating an HCS layer to the cell where each cell will be belonging to an HCS band.

The lower the layer ( and the HCS band), the priority is higher,

i.e. layer 1 has higher priority than layer 2, layer 3, layer 4, …..

layer 2 has higher priority than layer 3, layer 4, layer 5, …..

Up to 8 layers (in up to 8 bands) may be defined, where one or several layers can be assigned to the same HCS band.




The lower HCS bands will only include lower layers compared to a higher HCS bands.

A mixture of small micro cells (lower layers) and large macro (higher layers) cells will achieve both high capacity and good coverage.

Micro cells will be used for capacity issues while macro cells will be used to provide coverage, fill coverage holes and handle the fast moving mobiles.




With Basic Ranking only, micro cells will be ranked as the strongest server in very small area, so to let micro cells serve in an area where acceptable SS is guaranteed then HCS should be used.




The idea with a layered cell structure is to let lower layer cells serve MSs that receive sufficient SS even if there is other cells with strongest received SS in the area.

But how to decide if the lower layer cell has sufficient SS to be prioritized over strongest cells?

This will be according to two thresholds LAYERTHR (Layer Threshold) and HCSBANDTHR (HCS Band Threshold)

LAYERTHR: Decides if the cell should be prioritized over stronger cells lie in the same HCS band or not.

HCSBANDTHR: Decides if the cell should be prioritized over stronger cells from different HCS bands or not.




The input to the HCS Evaluation Algorithm is the Basic Ranking list we prepared from the locating process.

The output will be in the form of two lists: HCS prioritized list (on Top) then Basic Ranking list.

HCS prioritized list: will include cells that fulfilled the HCS conditions & rules and will be ranked according to HCS evaluation (layered ranking)

Basic Ranking list: will include cells that didn’t fulfill the HCS conditions and will be ranked according to basic ranking rules (SS ranking)


HCS Prioritized Cell List

Basic Ranking List

Basic Ranking ListInput Output



HCS Evaluation Algorithm Mechanism of the HCS Algorithm




(A) Band Evaluation: In order to be a candidate in the HCS evaluation process, then the SS of

serving and neighbor cells should be greater than their band threshold

( HCSBANDTHR )

SSservingcell > HCSBANDTHRservingcell – HCSBANDHYSTservingcell SSneigbhorcell > HCSBANDTHRneighborcell + HCSBANDHYSTneighborcell

Cells that will not fulfill the above condition will go to be sorted in the Basic Ranking list in priority order according to SS.

Cells that will fulfill the criterion will pass to the next step in the HCS Evaluation.

N.B: HCSBANDTHR and HCSBANDHYST are BSC Parameters.




(B) Define the strongest Cell (SS) in each Band Cells that passed the band evaluation in step (A) will be moved to the next

step.

In this stage, the strongest cells in each Band from SS point of view will be identified.

Strongest cells will pass direct to be HCS Ranked

The rest of cells that are not strongest within the band will be moved to Step(C)




(C) Layer Threshold Evaluation Cells that passed the band evaluation in step (A) and they are not strongest

within their own band, their SS will be checked against the Layer threshold (LAYERTHR)

SSservingcell > LAYERTHRservingcell – LAYERHYSTservingcell SSneigbhorcell > LAYERTHRneighborcell + LAYERHYSTneighborcell

Cells that will not fulfill the above condition will go to be sorted in the Basic Ranking list in priority order according to SS.

Cells that will fulfill the criterion will pass to the next step in the HCS Evaluation




(D) Identify the Strongest Cells within each layer Now we will deal with cells that passed the band evaluation (in Step A) and

they were not strongest within their own band (in Step B) and they passed the layer threshold condition (in Step C)

Cells that are strongest within their own layer will be identified and they’ll pass direct to be HCS ranked.

Cells that are not strongest within their own layer will be moved to the next step.




(E) Check how many cells from each layer are allowed to pass to be HCS ranked Now we will deal with cells that passed the band evaluation (in Step A) and

they were not strongest within their own band (in Step B) and they passed the layer threshold condition (in Step C) and they are not strongest within their own band (in step D)

MAXCELLSINLAYER: will identify how many cells from each layer can pass to be HCS ranked, ex: if MAXCELLSINLAYER = 2 then two cells only are allowed to pass to be HCS ranked.

MAXDBDEVINLAYER: will identify how the next strongest cell in the layer is far from the strongest cell in the layer.

i.e. if SS_Strongest Celllayer x - SS_next strongest celllayer x<MAXDBDEVINLAYER

then the next strongest cell is not weak and it will pass to be HCS ranked.




(F) Form the Final list Now all cells that succeeded to pass to be HCS ranked, will be sorted in

ascending order according to their layer not SS (as in Basic Ranking). i.e. layer1 cells, then layer2 cells, …… and these cells will form an HCS

Prioritized List that will lie on Top.

All cells that failed to pass to be HCS Ranking, will go to be sorted in a Basic Ranking List and this list will lie after the HCS Prioritized List.



HCS Evaluation AlgorithmExample: Assume that the output from the Basic Ranking is as below, where for all cells have HCSBANDTHR = - 90 dBm, LAYERTHR = - 80 dBm, HCSBANDHYST= LAYERHYST= 0, MAXCELLSINLAYER = 3, MAXDBDEVINLAYER = 3

Cell SS(dBm) Band LayerG -68 Band 8 Layer 7

E -72 Band 8 Layer 6

B (Serving) -73 Band 4 Layer 4

A -74 Band 4 Layer 3

C -75 Band 8 Layer 7

F -75 Band 4 Layer 4

D -95 Band 4 Layer 4



HCS Evaluation AlgorithmSolution:

(A) Band Evaluation: In order to be a candidate in the HCS Evaluation Process, then the SS of serving and neighbor cells should be greater than their band threshold(HCSBANDTHR)

SSservingcell > HCSBANDTHRservingcell – HCSBANDHYSTservingcell SSneigbhorcell > HCSBANDTHRneighborcell + HCSBANDHYSTneighborcell HCSBANDTHRservingcell = HCSBANDTHRneighborcell = -90 dBm HCSBANDHYSTservingcell = HCSBANDHYSTneighborcell = 0 dBm

Cell SS(dBm) Band LayerG -68 Band 8 Layer 7


B (Serving) -73 Band 4 Layer 4

A -74 Band 4 Layer 3




Cell D didn’t fulfill the condition (SS_CellD = -95 dBm < -90 dBm), so it will be out of the HCS evaluation and it will go to be sorted in the Basic Ranking List.




(B) Define the strongest Cell (SS) in each Band Cells that passed the band evaluation in step (A) will be moved to the next step. In this stage, the strongest cells in each Band from SS point of view will be identified. Strongest cells will pass direct to be HCS Ranked

Cell SS(dBm) Band Layer CommentG -68 Band 8 Layer 7 Strongest in Band 8 - Go direct to HCS Evaluation listE -72 Band 8 Layer 6 Will go to the next step: Layer EvaluationB -73 Band 4 Layer 4 Strongest in Band 4 - Go direct to HCS Evaluation listA -74 Band 4 Layer 3 Will go to the next step: Layer EvaluationC -75 Band 8 Layer 7 Will go to the next step: Layer Evaluation F -75 Band 4 Layer 4 Will go to the next step: Layer EvaluationD -95 Band 4 Layer 4 Out of the HCS Evaluation – Back to the Basic Ranking list

Now Cells G & B will go direct to be HCS evaluated, while cells E,A,C&F will be examined in the next steps.




(C) Layer Threshold Evaluation: Cells E,A,C&F that are not strongest within their own band, their SS will be checked against the Layer threshold (LAYERTHR) if

SSservingcell > LAYERTHRservingcell – LAYERHYSTservingcell SSneigbhorcell > LAYERTHRneighborcell + LAYERHYSTneighborcell

LAYERTHRservingcell = LAYERTHRneighborcell = - 80 dBm LAYERHYSTservingcell = LAYERHYSTneighborcell = 0 dBm

Cell SS(dBm) Band Layer CommentG -68 Band 8 Layer 7 Strongest in Band 8 - Go direct to HCS Evaluation listE -72 Band 8 Layer 6 SS > LAYERTHR = -80 dBm, Will go to the next stepB -73 Band 4 Layer 4 Strongest in Band 4 - Go direct to HCS Evaluation listA -74 Band 4 Layer 3 SS > LAYERTHR = -80 dBm, Will go to the next stepC -75 Band 8 Layer 7 SS > LAYERTHR = -80 dBm, Will go to the next stepF -75 Band 4 Layer 4 SS > LAYERTHR = -80 dBm, Will go to the next stepD -95 Band 4 Layer 4 Out of the HCS Evaluation – Back to the Basic Ranking list




(D) Identify the Strongest Cells within each layer After Cells E,A,C&F all of them passed the layer threshold condition (LAYERTHR), Cells

that are strongest within their own layer will be identified and they’ll pass direct to be HCS ranked.

Cells E&A are strongest within their own layer so they will go direct to be HCS ranked. Cells C&F are not the strongest within their own layer, so they will be examined in the next

step to know if they can pass to be HCS ranked or not.

Cell SS(dBm) Band Layer CommentG -68 Band 8 Layer 7 Strongest in Band 8 - Go direct to HCS Evaluation listE -72 Band 8 Layer 6 Strongest in Layer 6 - Go direct to HCS Evaluation listB -73 Band 4 Layer 4 Strongest in Band 4 - Go direct to HCS Evaluation listA -74 Band 4 Layer 3 Strongest in Layer 3 - Go direct to HCS Evaluation listC -75 Band 8 Layer 7 Not Strongest in Layer-Will be examined in the next stepF -75 Band 4 Layer 4 Not Strongest in Layer-Will be examined in the next stepD -95 Band 4 Layer 4 Out of the HCS Evaluation – Back to the Basic Ranking list




(E) Check how many cells from each layer are allowed to pass to be HCS ranked MAXCELLSINLAYER: will identify how many cells from each layer can pass to be HCS In

our example MAXCELLSINLAYER = 3 then three cells only are allowed to pass to be HCS ranked.

MAXDBDEVINLAYER: will identify how the next strongest cell in the layer is far from the strongest cell in the layer.

i.e. if SS_Strongest Celllayer x - SS_next strongest celllayer x< MAXDBDEVINLAYER = 3 dB,

then the next strongest cell is not weak and it will pass to be HCS ranked.




(E) Check how many cells from each layer are allowed to pass to be HCS ranked Cell C: Check1: Lies in layer 7 and ranked as the 2nd strongest cell in the layer and since 3 cells

are allowed to be ranked according to MAXCELLSINLAYER then Check1 is passed. Check2: Is SS_strongest celllayer 7-SS_next strongest celllayer 7 < MAXDBDEVINLAYER=3dB?!

SSCell G - SSCell C = -68-(-75) = 7 dB > MAXDBDEVINLAYER=3dB, then Check2 failed. Cell SS(dBm) Band Layer Comment

G -68 Band 8 Layer 7 Strongest in Band 8 - Go direct to HCS Evaluation list

E -72 Band 8 Layer 6 Strongest in Layer 6 - Go direct to HCS Evaluation list

B -73 Band 4 Layer 4 Strongest in Band 4 - Go direct to HCS Evaluation list

A -74 Band 4 Layer 3 Strongest in Layer 3 - Go direct to HCS Evaluation list

C -75 Band 8 Layer 7 Out of the HCS Evaluation – Back to the Basic Ranking list


D -95 Band 4 Layer 4 Out of the HCS Evaluation – Back to the Basic Ranking list




(E) Check how many cells from each layer are allowed to pass to be HCS ranked Cell F: Check1: Lies in layer 4 and ranked as the 2nd strongest cell in the layer and since 3 cells

are allowed to be ranked according to MAXCELLSINLAYER then Check1 is passed. Check2: Is SS_strongest celllayer 4-SS_next strongest celllayer 4 < MAXDBDEVINLAYER=3dB?!

SSCell G - SSCell C = -73-(-75) = 2 dB < MAXDBDEVINLAYER=3dB, then Check2 is passed.

Cell SS(dBm) Band Layer CommentG -68 Band 8 Layer 7 Strongest in Band 8 - Go direct to HCS Evaluation list

E -72 Band 8 Layer 6 Strongest in Layer 6 - Go direct to HCS Evaluation list

B -73 Band 4 Layer 4 Strongest in Band 4 - Go direct to HCS Evaluation list

A -74 Band 4 Layer 3 Strongest in Layer 3 - Go direct to HCS Evaluation list

C -75 Band 8 Layer 7 Out of the HCS Evaluation – Back to the Basic Ranking list

F -75 Band 4 Layer 4 2nd Strongest in Layer4-Go to HCS Evaluation list

D -95 Band 4 Layer 4 Out of the HCS Evaluation – Back to the Basic Ranking list




(F) Form the Final list Now all cells that succeeded to pass to be HCS ranked, will be sorted in ascending order

according to their layer not SS (as in Basic Ranking) i.e. layer1 cells, then layer2 cells, …… and these cells will form an HCS Prioritized List that will lie on Top.

All cells that failed to pass to be HCS Ranking, will go to be sorted in a Basic Ranking List and this list will lie after the HCS Prioritized List.

Final List

Cell SS(dBm) Band Layer CommentA -74 Band 4 Layer 3

HCS Prioritized List (Layer Ranking)

B(Serving) -73 Band 4 Layer 4



G -68 Band 8 Layer 7

C -75 Band 8 Layer 7Basic Ranking List (SS Ranking)





HCS Traffic Distribution Concept This feature is useful In order to control the traffic distribution between cells. If this feature is active then some cells that were prioritized due HCS Ranking

(layer ranking) will be removed if they already have enough traffic.

HCSTRAFDISSTATE: Is a BCS Parameter that shows if HCS Traffic Distribution is enabled within the cells in the BCS or not.

If the HCS traffic distribution is allowed then two checks will be made:

(i) Check on the serving cell’s availability vs. parameter on cell level called HCSOUT

(ii) Check on the neighbor cells’ availability vs. parameter on cell level called HCSIN

− The Availability means: the percentage of Free (non-occupied) Time Slots.




HCS Traffic Distribution Concept(i) Check on the serving cell’s availability:

If AvailabilityServingCell > HCSOUT, then this cells has too many free Time slots and it is not preferred to leave this cell.

(ii) Check on the neighbor cell’s availability: If AvailabilityneighborCell < HCSIN, then this cells has few free Time slots and it

can’t accept HO’s due to HCS prioritization.






HCS Evaluation AlgorithmI) Example:

When HCS Traffic Distribution is enabled (AvailabilityServingCell < HSCOUT) After ordinary HCS evaluation we formed the below list from the previous example. Assume HCSOUT=50%, HCSIN=30%, Availability of Cell B (serving) = 40% and

availability of Cell F (neighbor cell) = 10% only, while all other cells have availability = 45 %

What will be the final list form ?

Final List



B(Serving) -73 Band 4 Layer 4F -75 Band 4 Layer 4E -72 Band 8 Layer 6G -68 Band 8 Layer 7C -75 Band 8 Layer 7

Basic Ranking List (SS Ranking)D -95 Band 4 Layer 4




Availability of Serving Cell (B) = 40% < HCSOUT (50%), then the serving cell has few free Time Slots and we can leave this cell i.e. outgoing HO from this cell is enabled.

Availability of Neighbor Cell F=10% < HCSIN (30%), then this cell can’t accept HO’s due to HCS prioritization coz it has few free TS i.e. this cell is congested.

This cell will be removed from the HCS prioritized list and it will be moved to the Basic Ranking List.

Final List








The final list will be as below:

Final List



B(Serving) -73 Band 4 Layer 4




Basic Ranking List (SS Ranking)C -75 Band 8 Layer 7




HCS Evaluation AlgorithmII) Example:

when HCS Traffic Distribution is enabled (AvailabilityServingCell > HSCOUT)

If the serving cell has a channel availability above HCSOUT it is considered to be taking too little traffic so it is decided to not allow handovers out due to HCS from the cell.

Instead all the remaining HCS prioritized candidate cells, fulfilling the HCSIN criterion and that are in a lower layer or in the same layer as the serving cell, will be basic ranked among themselves and added to a “Prioritized basic ranked cells list” that will be put above the other basic ranked cells in the final candidate list.



HCS Evaluation AlgorithmII) Example:

when HCS Traffic Distribution is enabled (AvailabilityServingCell > HSCOUT) After ordinary HCS evaluation we formed the below list from the previous example. Assume HCSOUT=50%, HCSIN=30%, Availability of Cell B (serving) = 60% and

availability of Cell F (neighbor cell) = 10% only, while all other cells have availability = 45% What will be the final list form ?

Final List








Availability of Serving Cell (B) = 60% > HCSOUT (50%), then the serving cell has Too many Time slots and HO out from this cell due to HCS is not allowed.

Availability of Neighbor Cell F=10% < HCSIN (30%), then this cell can’t accept HO’s due to HCS prioritization coz it has few free TS i.e. this cell is congested.

This cell will be removed from the HCS prioritized list and it will be moved to the Basic Ranking List.

Cells E&G are layers 6&7 respectively i.e. they are of higher layers than the serving cells. These cells will be removed from the HCS prioritized list and it will be moved to the Basic

Ranking List. Now cells A&B will be ranked according to SS “Prioritized Basic Ranking list” cells C,D,E,F&G will be ranked according to SS “Basic Ranking list”




Final List








The final list will be as below:

Final List

Cell SS(dBm) Band Layer CommentB(Serving) -73 Band 4 Layer 4

Prioritized Basic Ranking ListA -74 Band 4 Layer 3


Basic Ranking List (SS Ranking)E -72 Band 8 Layer 6






HCS Evaluation Algorithm Optimizing a problematic Traffic Case:

Assume we have the below case with 3 Macro cells (layer 4) and 1 Micro cell (layer2) and all of them belong to the same HCS band, HCSBAND 1

One of the Macro cells carries very high traffic and it is about to congest, how could we solve this case?

Macro Cell (L4)

Macro Cell (L4)

Micro Cell (L2)

Macro Cell (L4)



HCS Evaluation AlgorithmSolution 1:

Direct more Traffic to the Micro Cell We can decrease the LAYERTHR of the Micro cell (Layer 2) from -75dBm to -

80dBm for example, so the micro cell will capture more traffic from the congested macro cell.




Direct more Traffic to the Adjacent Macro Cells We can increase the Layer of the congested Macro cell (Layer 4 Layer 5) so it

will appear less prioritized with respect to the adjacent neighbor cells and it will offload its traffic to them.




Direct more Traffic to one of the Adjacent Macro Cells We can decrease the Layer of one of the adjacent Macro cell (Layer 4 Layer 3)

so it will appear more prioritized with respect to the congested cell and it will capture some of its traffic.



HCS Evaluation AlgorithmFast Moving MSs If cell parameter FASTMSREG is “ON” and MS made no. of HOs >NHO

(default=3) in time window THO (default=30sec) then MS is considered as fast moving MS.

The stronger cells according to Basic Ranking in all higher layers within the same system type are given priority.

For Example: 1800 candidates are in Layers 1,2&3 while 900 candidates are in Layers 4&5, if

the MS is considered as fast in layer1, then candidates in layers 2&3 of higher basic ranking than the serving cell are given priority.

Highest priority is given for the strongest cell regardless of its layer. To prevent HO back to lower layer cells, a penalty PSSTEMP (0 to 63) is applied

for a time PTIMTEMP (0 to 600s) on all neighbor cells within the current system type and all cells in other system types.



Parameters Summary

For reduced HCS functionality we have only 2 bands HCS Band1 and HCS Band2 (default)

For reduced HCS functionality we have only 3 layers

HCS Algorithm Control ParametersParameter Name Value Range Default Value Recommended Value Unit

HCSBAND 1 to 8 1 2 2 ─

HCSBANDTHR 150 to 0 95 ─ dBm (–ve)HCSBANDHYST 0 to 63 2 2 dB

LAYER 1 to 8 2 2 ─ ─

LAYERTHR 150 to 0 75 ─ dBm (–ve)LAYERHYST 0 to 63 2 2 dB

MAXCELLSINLAYER 1 to 31 1 1 MAXDBDEVINLAYER 0 to 63 3 3 dBHCSTRAFDISSTATE 0,1 0 1 ─

HCSIN 0 to100 0 ─ %HCSOUT 0 to100 100 ─ %


THANK YOU


CONCENTRIC CELLS(OVER LAID UNDER LAID SUB-CELLS)

& MULTI BAND CELLS (MBC)


1ST. CONCENTRIC CELLS (OVER LAID UNDER LAID SUB-CELLS)


Concentric Cells (Over laid Under laid Sub-cells)

Traffic Capacity of a cellular network can be increased by either adding more frequencies or reducing the frequency reuse distance.

One approach is to apply a second frequency reuse pattern with a tighter frequency reuse (Overlay) on the existing pattern.

These cells should be restricted in size, so shorter reuse distance can be accomplished without causing Co-channel/Adjacent channel interference.

They are termed Overlaid (OL) Sub-cells, whereas the original cells will be called Under laid (UL) Sub-cells.

Now by having more frequencies per cell, then Network capacity is increased.




The fundamental idea behind the OL/UL sub-cells is to let the traffic close to the site to be moved to the OL sub-cell, while traffic close to the cell border to be moved to the UL sub-cell.

In that way of treading the traffic, the frequencies in the OL sub-cell can have tighter frequency reuse.




Example: Assume that cell A has frequencies: f1&f2, cell B has frequencies: f3&f4 and now cell A

has increase in the traffic, so we’re going to assign cell A frequency f4 also.

Now high Co-channel interference will occur on f4 at the border between the two cells, coz f4 is reused between two adjacent cells.




Using the OL/UL concept we can solve the case as follows:

f4 will be used in the OL sub-cell and it will be restricted to serve in a small area only near to the site so interference from the neighbor cell will be minimized and a good C/I can be enjoyed.




To maintain the service area of the OL sub-cell restricted to a certain region we have three thresholds we can play with:

A. Path Loss Threshold

B. Timing Advance Threshold

C. Distance to Cell Border Threshold

With the ordinary OL/UL sub-cells, the MS near the cell will camp on the overlaid sub-cell but even if the OL sub-cell got congested there is no way to push traffic to the UL sub-cell and blocking will occur.

Using Sub-cell Load Distribution (SCLD) Concept, we can configure the cell to use the OL as the preferred sub-cell initially and when traffic on the OL increased beyond certain load, any extra traffic will be offloaded to the UL sub-cell.



AlgorithmI. OL/UL Sub-cell Change with Sub-cell Load Distribution Deactivated As we stated before, the service area of the OL sub-cell can be defined based

on one of three criteria: Path Loss, Time Advance and Distance to cell border.

A. Path Loss Criterion: Controlling Parameters are the path Loss threshold LOL and the path Loss

hysteresis LOLHYST DL Path Loss L=(BSTXPWR - BTS power reduction) –Received_SS_DLfiltered

BSTXPWR: BTS output power for the TCH frequencies. DL Path Loss L will be checked vs. LOL (Path Loss Threshold) and

LOLHYST to know whether a sub-cell change from OLUL or ULOL is needed.



AlgorithmI. OL/UL Sub-cell Change with Sub-cell Load Distribution Deactivated

B. Time Advance Criterion: Time Advance can be used as a measure for the distance between the BTS

and MS. Controlling Parameters are the Time Advance Threshold TAOL and the Time

Advance Hysteresis TAOLHYST The “ta” of the MS will be measured via BTS and checked vs. TAOL and

TAOLHYST to know whether sub-cell change is needed or not.




C. Distance to Cell Border Criterion: DTCBSC: Is a BSC parameter that enables/disables the Distance to Cell

Border Evaluation Criterion on whole cells on the BSC.

Controlling Parameters are the Distance to Cell Border Threshold DTCB and the Distance to Cell Border Hysteresis DTCBHYST

The Cell Border is defined as the difference between the Received_SSServingCell and the Received_SSStrongest Neighbor , where this strongest neighbor should meet the following: Non Co-sited, Same System Type (900/1800), Same HCS Layer.




C. Distance to Cell Border Criterion: Received_SSServingCell - Received_SSStrongest Neighbor will be checked vs. DTCB

and DTCBHYST to see whether sub-cell change is needed or not.

But for the evaluation to be triggered (initiated), the serving cell should have number of neighbor cells > NNCELLS (if NNCELLS=2, at least 2 neighbor cells) that are measured by the MS having enough SS such that:

Received_SSServingCell - Received_SSNeighbor < DTCB+DTCBHYST+NDIST where,NDIST is a threshold measured in dBs.




OL UL Sub-cell change: for a sub-cell change from OL UL then one of the following should be fulfilled.

L (Path Loss) > LOL + LOLHYST “OR” ta (Time Advance) ≥ TAOL + TAOLHYST “OR” SSServing - SSNeighbor < DTCB - DTCBHYST


But as mentioned before, for this evaluation to be initiated then,No. of neighbor cells ≥ NNCELLS should be reported meeting the following equation:SSServing - SSNeighbor < DTCB + DTCBHYST + NDIST

Non Co-sited, Same Type, Same HCS Layer

Strongest, Non Co-sited, Same Type, Same HCS Layer



UL OL Sub-cell change: for a sub-cell change from UL OL then one of the following should be fulfilled.

L (Path Loss) ≤ LOL - LOLHYST “and” ta (Time Advance) < TAOL - TAOLHYST “and” SSServing - SSNeighbor ≥ DTCB + DTCBHYST



But as mentioned before, for this evaluation to be initiated then,No. of neighbor cells ≥ NNCELLS should be reported meeting the following equation:SSServing - SSNeighbor < DTCB + DTCBHYST + NDIST

Non Co-sited, Same Type, Same HCS Layer


AlgorithmI. OL/UL Sub-cell Change with Sub-cell Load Distribution Deactivated N.B: If parameter TAOL is set to its maximum value = 61 bit periods and DTCB is

set to its minimum value = - 63 dB then the OL/UL sub-cell change will only be controlled by the path loss using LOL coz:

OLUL: Time Advance & Distance to cell border conditions will never be met and so the Path Loss only using LOL will control the evaluation.

ULOL: Time Advance & Distance to Cell Border Conditions will always be met and so the Path Loss only LOL will control the evaluation.



AlgorithmII. OL/UL Sub-cell Change with Sub-cell Load Distribution Activated A sub-cell load distribution is used to control the traffic between the OL/UL

sub-cells, so if the initially preferred cell got congested we will try to allocate resources in the other sub-cell.

(Activated by setting cell parameter SCLD = ON) SCLDSC: Is a cell parameter used to define the preferred cell in allocation

whether UL or OL i.e. the sub-cell which will carry traffic first. But if the OL sub-cell is the preferred one, i.e. if SCLDSC=OL, then the below

conditions should be met otherwise a TCH on the UL sub-cell will be allocated. L < LOL – LOLHYST and ta < TAOL – TAOLHYST and SSServing - SSNeighbor ≥ DTCB + DTCBHYST


No. of neighbor cells ≥ NNCELLS should be reported meeting the following equation:SSServing - SSNeighbor < DTCB + DTCBHYST + NDIST



AlgorithmII. OL/UL Sub-cell Change with Sub-cell Load Distribution Activated A sub-cell change may occur due to load based on the settings of the

parameters SCLDLUL an SCLDLOL.

Example: If serving cell is the OL sub-cell and the following occur

Percentage of idle TCHs in the OL sub-cell < SCLDLOL andPercentage of idle TCHs in the UL sub-cell > SCLDLUL

then sub-cell change from OLUL due to SCLD will occur.



AlgorithmII. OL/UL Sub-cell Change with Sub-cell Load Distribution Activated A sub-cell change may occur due to load based on the settings of the

parameters SCLDLUL an SCLDLOL



AlgorithmII. OL/UL Sub-cell Change with Sub-cell Load Distribution Activated If some traffic will be moved from the OL UL sub-cell due to load

distribution, then the MSs with the high path loss will be chosen first i.e. MSs that are near to cell border.

If some traffic will be moved from the UL OL sub-cell due to load distribution, then the MSs with the low path loss will be chosen first i.e. MSs that are near to the site.

A part from the sub-cell change due to SCLD, as we mentioned before the MS can also request to move from OL UL because of path loss, TA or distance to cell border criterion and in this case the load is not checked coz the thresholds : SCLDLUL&SCLDLOL are only controlling the load incase of sub-cell change due to load distribution.



Parameters Summary


Overlaid/Underlaid Control ParametersParameter Name Value Range Default Value Recommended Value Unit

SCTYPE UL,OL − − −LOL 0 to 200 − − dB

LOLHYST 0 to 63 3 3 dBTAOL 0 to 61 − − Bit Periods (3.69 µsec)

TAOLHYST 0 to 61 − − Bit Periods (3.69 µsec)DTCBSC 0,1 0 − −

DTCB −63 to 63 -63 − dBDTCBHYST 0 to 63 2 2 dB

NDIST 0 to 63 10 − dBNNCELLS 1 to 5 3 1 −

SCLD ON,OFF OFF − −SCLDLOL 0 to 99 20 − %SCLDLUL 0 to 99 20 − %SCLDSC UL,OL UL OL −


THANK YOU


2ND . MULTI BAND CELLS (MBC)


Multi Band Cells (MBC)


A multi band network consists of cells from different frequency bands for example: 900/1800 MHz

By combining these frequencies in the same cell with 1 common BCCH, the radio performance and traffic capacity are improved where the no. of cells and neighbor relations are significantly reduced.

Using 1 BCCH instead of two will increase the no. of time slots that will be used for traffic.




Using MBC concept with only 1 BCCH, this will reduce the no. of defined neighbors to 50% leading to better accuracy for the measurement reports coz there will be more time available for measurements for each neighbor.




The Dynamic OL/UL sub-cells (Concentric Cells) is a prerequisite feature for

the Multi Band Cells.

Mostly the frequency band with “Better Coverage” (i.e. lower frequency band)

is configured as the Under laid sub-cell while the other frequency band with

“Worse Coverage” (i.e. higher frequency band) is configured as the Overlaid

Sub-cell.

Ex: 900MHz frequency band UL, while 1800MHz frequency band OL

It is recommended to select the BCCH frequency to lie in the “Better

Coverage” i.e. UL sub-cell.

For the previous example then BCCH frequency will belong to the 900MHz

band.




A parameter CSYSTYPE defines the band of the used BCCH frequency in a multi band cell.

A parameter BAND defines the band of the Channel Group, where the channel group consists of no. of frequencies as will be seen later.

As mentioned before, the Path Loss/Distance to Cell Border/Time Advance Criteria will define the coverage limit of the frequency band used in the OL sub-cell vs. UL sub-cell, (In this case the OL&UL will belong to two different bands)

Also the traffic load can be maintained between the two sub-cells (that belong to two different bands) using the sub-cell load distribution feature where the SCLD parameter will define which sub-cell is

preferred first.




The propagation of the radio waves depend on the used frequency band,

i.e. the reported signal strength from one MS will differ depending on the

frequency band used.

MS

MS

MS is in the same location but the reported SS differs depend on the used frequency band




So to locate the MS correctly regardless of the band it is using we have 2 possible ways:

1. Applying a frequency Band Offset: If OL sub-cell is on 1800MHz band and the UL is on the 900MHz band so

when the MS is located on the OL sub-cell and report a certain SS then it should be compensated for the UL sub-cell.

2. Includes the BCCH carrier frequency in the Active BCCH Allocation (BA) list: The Active BA list is the list which the serving cell uses to inform the MS the

neighbors which he has to monitor and make measurements on while it is in dedicated mode and in this way no compensation is needed.



Applying a Frequency Band Offset: FBOFFS (Frequency Band Offset): is the parameter that determines the

difference between the path loss between bands, it is measured in dBs and take values between - 40 40 dBs

If the MS is served by 1800 band frequency and reporting SS 1800 band = -85 dbm and FBOFFS=7dB then the compensated SS if the MS was served by the 900 band frequency will be SS 900 band = -85 dbm + 7 = -78 dBm

FBOFFS has to be adjusted in a correct way coz:

a. It will be used to locate the MS correctly with respect to neighbors.

b. It will be used to locate the MS correctly in the Sub-cell Change Evaluation.



Applying a Frequency Band Offset:a. FBOFFS will be used to locate the MS correctly with respect to

neighbors

Ex: MS is on the OL subcell (1800 band) and reporting SS_Serving_cellA1800 band = -85 dBm FBOFFS =7dB, and after applying the offset and HysteresisSS_neighbor_cellB900 band = -83dBm

With applying FBOFFS

SS_Serving_cellA 900band = SS_Serving_cellA1800 band+ 7 dBSS_Serving_cellA 900band = -78 dBmSS_Serving_cellA 900 band > SS_neighbor_cellB900 band

Cell A will remain the serving cell but sub-cell change may occur if needed.

Right Decision

Without applying FBOFFS

SS_Serving_cellA 1800 band < SS_neighbor_cellB900 band

HO from Cell A Cell B will occur

Wrong Decision



Applying a Frequency Band Offset:b. FBOFFS will be used to locate the MS correctly during the Sub-cell

Change Evaluation When the MS is served by the OL 1800 band sub-cell (non-BCCH Band), the

path loss in this case will be checked vs. LOL – LOLHYST + FBOFFSET

Ex: Assume a MS is served by the OL 1800 sub-cell and reporting SS1800 band = -90 dBm, BSTXPWR=46dBm, FBOFFSET=7dB, LOL=131dB, LOLHYST=zero

-85 dBm

-92 dBm

Subcell change OLUL

-90 dBm

-83 dBm



Applying a Frequency Band Offset:b. FBOFFS will be used to locate the MS correctly during the Sub-cell

Change Evaluation

Ex: Assume a MS is served by the OL 1800 subcell and reporting SS1800 band = -90 dBm, BSTXPWR=46dBm, FBOFFSET=7dB, LOL=131dB, LOLHYST=zero

Without applying FBOFFS

Path loss= BSTXPWR - SS1800 band = 46-(-90)=136 dB

Path loss=136 dB > LOL – LOLHYST=131 dB

− Sub-cell change from OL UL will occur

Wrong Decision

With applying FBOFFS

Path loss= BSTXPWR - SS1800 band = 46-(-90)=136 dB

Path loss=136 < LOL–LOLHYST+FBOFFSET=138dB

− The MS will stay on the OL sub-cell

Right Decision



Parameters Summary:

Multi Band Cells Control ParametersParameter Name Value Range Default Value Recommended Value Unit

BAND GSM800, GSM900, GSM1800, GSM1900 − − −

CSYSTYPE GSM800, GSM900, GSM1800, GSM1900 − − −

FBOFFS −40 to 40 0 − dB


THANK YOU


CELL LOAD SHARING (CLS)


Cell Load Sharing

Cell Load Sharing

The Purpose of the Cell Load Sharing Feature is to distribute some of a cells traffic load to surrounding cells during peaks in traffic.

This is achieved by moving established connections to neighboring cells that have idle resources.

Cell Load Sharing increases the number of handovers in the part of the network where the traffic load is unevenly distributed.


Cell Load Sharing

Cell Load Sharing

Cell Load Sharing is activated on the BSC level via parameter LSSTATE (Active/Inactive)

The traffic load (amount of idle full rate TCHs) on each cell is examined by the BSC every CLS time Interval defined by a parameter CLSTIMEINTERVAL (default=100msec)

If the percentage of idle full rate traffic channels is ≤ parameter CLSLEVEL, then this cell will try to get rid of some traffic by initiating cell load sharing handovers to neighbors.


Cell Load Sharing

Cell Load Sharing

For a neighbor cell to accept HOs due to cell load sharing then parameter HOCLSACC should be set to “ON”

The traffic load on the neighbor cells should also be examined so handovers due to cell load sharing will only be done to neighbors having enough idle full rate TCHs (percentage of idle full rate TCHs > CLSACC in order to accept HO due to CLS)


Cell Load Sharing

Cell Load Sharing

CLS evaluation is performed after normal locating evaluation for neighboring cells.

The normal Basic ranking evaluation was done as follows: Rankservingcell = SS_Dlservingcell

Rankneighbor= SS_DLneighbor – OFFSETneighbor – HYSTneighbor

Now when the % idle full rate TCHs < CLSLEVEL, then the HYST for neighbors will be recalculated with reduced values based on parameter RHYST

Rankneighbor= SS_DLneighbor – OFFSETneighbor – HYSTnew neighbor ,

where HYSTnew neighbor = HYSTneighbor [1-2 (RHYST/100)]


Cell Load Sharing

Cell Load Sharing

Rankneighbor= SS_DLneighbor – OFFSETneighbor – HYSTnew neighbor ,

Where HYSTnew neighbor = HYSTneighbor [1-2 (RHYST/100)]

RHYST Hysteresis Reduction

0 No reduction of the Hysteresis area

50 Cell Border is reduced to the nominal cell border

100 All the Hysteresis area is removed


Cell Load Sharing

Cell Load Sharing

For a neighbor cell to be candidate for HO due to CLS, then it should satisfy the following:

Lies in the same BSC as the source cell. Has the same HCS layer. Can Accept HO due to CLS i.e. HOCLSACC= ON % Idle full rate TCHs > CLSACC

The settings for CLSLEVEL and CLSACC should be adjusted such that CLSACC > CLSLEVEL in order to not having unstable situation.

100% idle TCHs

CLSACC=50%

CLSLEVEL=30%

Accept Incoming HOs due to CLS

Make Outgoing HOs due to CLS


Cell Load Sharing

Cell Load Sharing Parameters Summary

Parameter Default Value Recommended Value Value Range UnitCLSLEVEL 20 − 0 to 99 %CLSACC 40 − 1 to 100 %

HOCLSACC OFF ON ON/OFF RHYST 75 100 0 to 100 %

CLSTIMERINTERVAL 100 100 100 to 1000 msLSSTATE Inactive Active Active/Inactive


THANK YOU


FREQUENCY HOPPING


Frequency Hopping

Frequency Hopping

During a call connection, a time slot (burst) can easily be lost when the mobile station happens to be located in a fading dip for that particular frequency or if it is subjected to interference.

If the next time slot is sent on another frequency, there is high probability that this time slot will be received correctly and this can be done via frequency hopping.

With frequency hopping: Tighter frequency reuse can be implemented and so higher capacity can be

maintained. More robust environment can be obtained. There will be a possibility to give subscribers more uniform speech quality.


Frequency Hopping

Frequency Hopping

In frequency hopping, a set of predefined frequencies is used in each cell and the MS will be allowed to transmit on different frequency every TDMA frame (4.61 msec) i.e. The MS will change its frequency 217 times per second

With frequency hopping we can get:

i. Frequency Diversity

ii. Interference Diversity


Frequency Hopping

I. Frequency Diversity Frequency hopping can solve the multipath fading (fast fading) problem.

The multipath fading results from reflections from the surrounding buildings resulted in low signal strength fading dips.

The multipath fading is frequency and location dependent.

With frequency hopping, slow and non-moving MS won’t still in a low signal strength fading dip more than 1TDMA frame.

F1

F2

Average


Frequency Hopping

II. Interference Diversity Frequency hopping can also offer better quality when the currently used

frequency is interfered.

Interference depends on the time, frequency and the MS location.

With frequency hopping, certain MS will experience interference only for 1time during number of hops i.e. if a MS will hop on 4 frequencies one of them is interfered, then the MS will be subjected to interference1 time every 4 hops.

Using frequency hopping will result in spreading the interference on many MSs which will lead to a radio environment that is more even (symmetric).

The interference diversity can be expressed as a gain in the C/I ratio.


Frequency Hopping

Channel Group Concept (CHGR) Each number of frequencies (Transmitters) in the cell are grouped in what

we called channel group (CHGR), some parameters are defined per the CHGR and not per cell, for example: within the same cell frequency hopping can be enabled on certain CHGRs and disabled on others.

HOP: Is a parameter that is used to enable or disable frequency hopping on certain CHGR, it has two values either ON/OFF


Frequency Hopping

Frequency Hopping

Frequency Hopping is applied on Traffic channels (TCHs), on SDCCHs and packet data channels but it is not applied on Broadcast and Common control channels which are mapped on TS#0 on F0

Methods of Hopping: we have two methods of hopping:

A. Base Band Hopping (BB Hopping)

B. Synthesized frequency Hopping (SY Hopping)

FHOP: Is a parameter to specify the method of hopping, it takes values:BB/SY


Frequency Hopping

A. Base Band Hopping (BB Hopping) Each Transmitter is assigned certain frequency and connected to many MSs,

each Time slot out of the transmitter will belong to different MS but at the same frequency.

From MS prospective, each MS will transmit each TS via different transmitter and on different frequency.

Transmitter F1

Transmitter F2

Transmitter F3

Transmitter F4

TRX1

TRX2

TRX3

TRX4

TS1 TS2 TS3MS1

TS1 TS2 TS3MS2

MS1-TS1-F1

MS2-TS1-F2 MS1-TS2-F2

MS3-TS1-F3 MS2-TS2-F3 MS1-TS3-F3

TS1 TS2 TS3MS3

Bus for routing the time slots


Frequency Hopping

B. Synthesizer Frequency Hopping (SY Frequency Hopping) With Synthesized frequency hopping, the MS will transmit all its time slots via

only 1 transmitter and the transmitter will change its frequency consequently every TDMA frame based on certain sequence.

Trans F1…….Fn

Trans F1…….Fn

Trans F1……..Fn

Trans F1………Fn

TRX1

TRX2

TRX3

TRX4

TS1 TS2 TS3MS1

TS1 TS2 TS3MS2

MS3-TS1-F3 MS2-TS2-F4 MS1-TS3-F5

TS1 TS2 TS3MS3

MS1-TS1-F1 MS1-TS3-F3MS1-TS2-F2

MS2-TS1-F2 MS2-TS3-F4MS2-TS2-F3


Frequency Hopping

B. Synthesizer Frequency Hopping (SY Frequency Hopping) The Advantage of Synthesized frequency hopping is that the number of

hopping frequencies can be larger than the number of the already existing transmitters causing the hopping gain to increase without a need to use more hardware.

Modes of Hopping:

i. Cyclic Frequency Hopping

ii. Random Frequency Hopping


Frequency Hopping

Modes of Hopping i. Cyclic Frequency Hopping With this type of hopping, frequencies are changed every TDMA frame in a

consecutive order starting with the frequency of the lowest Absolute Radio Frequency Channel Number (ARFCN).

For P-GSM (UL 890-915 MHz, DL 935-960MHz), ARFCNs: 1,2,3,4,…… 124

For example for four frequencies the cyclic hopping between them will appear as follow: f1, f2, f3, f4, f1, f2, f3, f4, f1, f2, f3, f4, f1, ………

HSN (Hopping Sequence Number) : Is a parameter defined per CHGR (number of frequencies) that will be used to specify the mode of hopping with Synthesized frequency hopping, it take values from 0 63

When HSN = 0, this means that Cyclic frequency hopping will be used.


Frequency Hopping

Modes of Hoppingii. Random Frequency Hopping With this type of hopping, frequencies are changed every TDMA frame

randomly based on a pseudo-random sequence. The sequence is stored in a look-up table in the MS as well as the BTS and up to 63 independent sequences can be defined.

Based on the settings of the parameter HSN (163), one of the 63 independent random sequences will be used.

The period of the Random sequence=6 minutes, i.e. the random sequence repeats itself once every 6 minutes.


Frequency Hopping

Synthesizer Frequency Hopping (SY Frequency Hopping)MAIO Concept As we mentioned before that HSN is defined per CHGR, so if a CHGR

contains 4 Transmitters and HSN=0, then this means that cyclic hopping will be used over these 4 transmitters.

But in order for the transmitters within the same CHGR to not interfere each other they must start their hopping with different frequencies.

And in order to do so a MAIO

(Mobile Allocation Index Offset)will

Be assigned for each transmitter so

each of them will start the hopping-

sequence either cyclic/random from

a different starting point, based

the MAIO assigned to it.

Transmitter#1 (f0,f1,f2,….fn)




Same CHGR, HSN=0f0,f1,f2,f3,f4,f5,f0,….

f1,f2,f3,f4,f5,f0,f1….

f2,f3,f4,f5,f0,f1,f2….

f3,f4,f5,f0,f1,f2,f3….


Frequency Hopping

Synthesizer Frequency Hopping (SY Frequency Hopping)MAIO Concept We have different MAIOs, i.e. there are different ways through which each

transmitter will start the cyclic/random hopping. Using the default MAIO, the even MAIO values in increasing order are

picked first then the odd values, example: for a CHGR of 4 Transmitters, the default MAIO list is 0,2,4,1





Same CHGR, HSN=0

f0,f1,f2,f3,f4,f5,f0,….

f2,f3,f4,f5,f0,f1,f2….

f4,f5,f0,f1,f2,f3,f4….

f1,f2,f3,f4,f5,f0,f1….

N.B: Number of used frequencies can exceed the no. of Transmitters.


Frequency Hopping

Parameters Summary

Frequency Hopping Control ParametersParameter Name Value Range Default Value Recommended Value Unit

HOP ON,OFF OFF ON −

FHOP BB,SY − − −

HSN 0 to 63 − − −

MAIO 0 to 31 or Default Default − −


THANK YOU


INTRA CELL HANDOVER (IHO)


Intra Cell Handover

Intra Cell Handover

Intra Cell means within the same cell.

Intra Cell Handover aims at maintaining good quality of a current connection by performing handover to a new channel within the same cell when bad quality is detected.

When a connection suffers from bad quality and at the same time the Signal Strength is still high, there is a reason to believe that the bad quality is due to interference.

Channel suffering from bad quality

New channel

f1

f2

TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8

TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8

Same Cell


Intra Cell Handover

Intra Cell Handover

Changing the serving channel on a certain cell to another channel within the same cell may be useful due to the fact that most likely the interference on different channels is not the same, and the reason for this could be:

The cell that interferes a certain connection (channel/call) may be not fully loaded and not transmitting on all its channels.

If power control is in use in the interferer cell, then power used on each channel will differ based on the MS location from the BTS.

For uplink interference, the MSs connected to the interferer cell will be located in different places from the cell causing different levels of interference.


Intra Cell Handover

Intra Cell Handover

After Intra cell handover is performed, the quality of a connection will be enhanced if the radio conditions on the new channel is better than the old channel, and this may be expected when intra cell handover is performed at high signal strength while the quality (rxqual) is bad.

Intra Cell Handover can be triggered due to bad quality either in the downlink or in the uplink.

But at which conditions Intra Cell Handover will be triggered ?


Intra Cell Handover

Intra Cell Handover

At which conditions Intra Cell Handover will be triggered ? Intra cell handover is triggered/initiated when signal strength is high and at the

same time the quality is bad based on the following equation:

rxqual_DL > QOFFSETDL + FQSS (RXLEV_DL + SSOFFSETDL)

Or rxqual_UL > QOFFSETUL + FQSS (RXLEV_UL + SSOFFSETUL)

FQSS is a quality vs. signal strength function that specify at each signal level the quality beyond which an intra cell handover should be triggered.


Intra Cell Handover

Conditions at which Intra Cell Handover is initiated: rxqual_DL > QOFFSETDL + FQSS (RXLEV_DL + SSOFFSETDL) Or rxqual_UL > QOFFSETUL + FQSS (RXLEV_UL + SSOFFSETUL)

RXLEV_DL and RXLEV_UL both are

measured in rxlev units 0 63, which

corresponds to -110 dBm - 47 dBm

Example: If RXLEV_DL = 57 and

QOFFSETDL=SSOFFSETDL= zero, thenwhen rxqual_DL > 52 dtqu an intra cellhandover will be initiated.

The FQSS Table. The rxqual Values Is Given in dtqu (deci Transformed Quality Units)

RXLEV Rxqual<=30 infinity

31 6032 - 35 5936 - 38 5839 - 41 5742 - 45 5646 - 48 5549 - 52 5453 - 55 5356 - 58 5259 - 62 51>=63 50


Intra Cell Handover

Intra Cell Handover

SSOFFSETDL & SSOFFSETUL are signal strength offset parameters, increasing them will make the measured signal strength to appear better than the actual situation causing the intra cell handover to be triggered more often.

QOFFSETDL & QOFFSETUL are quality offset parameters, decreasing them will trigger the intra cell handover more often.


Intra Cell Handover

Selection of a new channel at IHO The primary target is to find a new channel that differs as much as possible

from the currently used channel.

The selection of a new channel will depend on whether frequency hopping is used or not.


Intra Cell Handover

Selection of a new channel at IHO(A) With Frequency Hopping Not Used Among the idle channels, select a channel that lies on a different frequency

than the current channel is using. If no idle channels were found then select one of the idle timeslots that are on

the same frequency as the current channel.

Interfered Channel

1st choice at IHO (Change frequency)

2nd choice at IHO (Change Time Slot on the same frequency)

f1

f2

f3


Intra Cell Handover

Selection of a new channel at IHO(B) With Frequency Hopping In Use Select one of the idle channels that belongs to a different CHGR than the

current channel. If no idle channels were found or only 1 CHGR is defined then select one of

the idle timeslots that are on the same CHGR as the current channel. If no idle channels were found select idle channels on the same CHGR and

time slot as the current channel.

1st choice at IHO(Change CHGR)

2nd choice at IHO (Change Time Slot within the same CHGR )

Interfered Channel

f2

f3

f4

f1

CHGR1

CHGR0

3rd choice at IHO (Same CHGR, same TS but different channel)


Intra Cell Handover

Intra Cell Handover

If quality is not improved after making number of consecutive IHOs, this means that all channels are suffering from poor quality and may be a part of the cell is subjected to high interference.

We can limit the number of consecutive IHOs for certain connection to certain number using parameter MAXIHO ex: If MAXIHO=3, then the maximum number of allowed consecutive IHOs=3 and if the MS tried to make the 4th IHO it will be disabled and a timer TIHO will start to inhibit any further attempts to make IHO until this timer is released.


Intra Cell Handover

Intra Cell Handover

Intra cell handover and bad quality urgency are both triggered at poor quality situations.

Intra cell handover has higher priority over bad quality urgency handover, i.e. if the criteria for both are fulfilled then IHO will be triggered/initiated first.

If the dynamic OL/UL sub-cell feature is in use and if the number of consecutive IHOs reached its maximum based on the settings of the parameter MAXIHO, then a sub-cell change from OLUL or ULOL will be attempted.


Intra Cell Handover

Parameters Summary

Intra Cell Handover Control ParametersParameter Name Value Range Default Value Recommended Value Unit

IHO ON,OFF OFF ON −

SSOFFSETDL −30 to 30 0 0 dB

SSOFFSETUL −30 to 30 0 −10 dB

QOFFSETDL −50 to 50 0 − dtqu

QOFFSETUL −50 to 50 0 − dtqu

MAXIHO 0 to 15 3 3 −

TIHO 10 to 60 10 10 Seconds


THANK YOU


DYNAMIC HR ALLOCATION


Dynamic HR Allocation


In high load situations it is important that the allocation of a traffic channel is done efficiently for a new connection.

This will result in high utilization of the channels while keeping good speech quality for the existing connections.




For a new connection the Dynamic HR Allocation Algorithm evaluates the traffic load in the cell and based on this decides the connection mode: FR, HR or AMR HR

To Activate the feature, set the parameter: DHA to “ON”

The feature differentiates between AMR and NAMR MSs and can be controlled on cell level.



Dynamic HR AllocationNew Connection

Dual Rate MS ?(Supports HR?)

Support AMR HR?

No. of Idle TCHs Total no. of TCHs

< DTHNAMR No. of Idle TCHsTotal no. of TCHs

< DTHAMR

AMR HR AllocationHR Allocation

FR/AMR FR Allocation

Yes

Yes

YesYes

No

No

No% %




DTHAMR: The threshold below which the Dynamic HR Allocation starts for AMR supported MSs

DTHNAMR: The threshold below which the Dynamic HR Allocation starts for Non AMR supported MSs



Parameters Summary

Intra Cell Handover Control ParametersParameter Name Value Range Default Value Recommended Value Unit

DHA ON,OFF OFF ON −

DTHAMR 0 to 100 30 30 %

DTHNAMR 0 to 100 15 15 %


THANK YOU


DYNAMIC POWER CONTROL


Dynamic Power Control

Dynamic Power Control

In this chapter we’ll talk on both BTS and MS Dynamic Power Control. The aim with Power Control is to increase the number of connections while

maintaining good C/I (Carrier to Interference Ratio).

Why Power Control is important ?

i. Decreases the total interference in the system ( Interference ) So when Traffic increases (no. of MSs) then good C/I can be

maintained. When Traffic is normal, C/I is improved. When Interference is low, MSs with poor quality will be able to

successfully complete their calls.

ii. Decreases the consumption of the MS battery and the BTS backup batteries when the main supply is down.


I. DYNAMIC BTS POWER CONTROL


Dynamic BTS Power Control


The Algorithms for both BTS and MS dynamic power control are the same. The below graph shows the relation between BTS o/p power and the

measured (received) signal strength at the MS vs. the path loss between BTS and MS.

12




For the area before point 1, the received power at the MS in the DL is very good and sufficient, however the BTS can’t make any sort of down regulation and sends with power less than its minimum power.

As the MS is moving away from the BTS, the received power is decreasing, so after crossing point 1, the BTS will start up regulating its power in steps to compensate for the path loss.

At point 2, the BTS can’t up regulate its power for a value above the max. allowed power level even if the received power in the MS is deteriorated or the path loss increased.




For Quality measurements the below graph shows the up regulations in the BTS o/p power when quality is deteriorated (SS is not into consideration here)

As the Quality got worse ( 0 7), the BTS will try to increase its power to compensate for the quality drop.




Algorithm: The Dynamic BTS Power Control algorithm is done on 3 stages:

1. Preparation of the Input Data.

2. Filtering of measurements.

3. Calculation of Power Order.



Algorithm: 1) Preparation of The Input Data Dynamic Power Control is made on TCHs time slots as well as on the SDCCH

time slots, while the BCCH frequency with all its time slots is sent with max. power with no power control.

Type of Measurements:

Both SS_DL and Quality_DL measurements will be used in the equation through which the next power order is calculated.

Measurement SourceSS_DL MS

Quality_DL MSpower level used by the BTS_DL BTS



Algorithm:1) Preparation of The Input Data REGINTDL: A parameter that defines the minimum time period between two

consecutive power orders in the DL. Measured in SACCH periods (0.48 Seconds) from 1 to 10 SACCH periods i.e. Regulating Interval in DL. (It is a BSC parameter)

The BTS is able to changes its output power , the resolution in o/p power is in the form of steps of 2 dBs and maximum change is 30 dBs.

(ex: 2dBs, 4dBs,………. , max to 30 dBs)

When power control is in use the BTS output power level will be given as:

Down Regulation: BTS o/p power (dBm) = BSPWRT – 2*PLused ,

Up Regulation: BTS o/p power (dBm) = BSPWRMIN – 2*PLused ,

where PLused = 0to 15

PLused is the power regulation step



Algorithm:1) Preparation of The Input Data SSDESDL: A parameter that defines the desired Signal Strength in DL which

we aim to maintain using power control. Measured in dBm

The SS measured will be checked against SSDESDL to know if Down regulation in the BTS power or up regulation is needed

QDESDL: A parameter that defines the desired Quality in DL which we aim to maintain using power control. Measured in dtqu ( 0 to 70)

The Quality measured will be checked against QDESDL to know if Down regulation in the BTS power or up regulation is needed.



Algorithm:1) Preparation of The Input Data The equation used to calculate the power order in the next SACCH period

contains information on SSDESDL−SS_DLmeasured and QDESDL−Quality_DLmeasured.

SSDESDL− SS_DLmeasured is measured in dBm, while QDESDL− Quality_DLmeasured is measured in dtqu so to be used in the same equation some sort of mapping should be done,

i.e. QDESDL−Quality_DLmeasured should be represented in the form of dBs as well.

QDESDL (dtqu) 0 10 20 30 40 50 60 70

Quality_DLmeasured 0 1 2 3 4 5 6 7

dB transformation C/I calculation (dB) 23 19 17 15 13 11 8 4



Algorithm:1) Preparation of The Input Data SS Compensation We aim to get the SS of the pure TCH time slot compensated for both

frequency hopping when BCCH frequency is included and compensated for power control.

i. Compensating for frequency hopping:

When the MS is using a TS on BCCH carrier SS_DLTCH = SS_DLMeasured – [ BSPWR – (BSTXPWR - 2*PLused) ]

SS_DLTCH = SS_DLMeasured – ( BSPWR – BSTXPWR + 2*PLused )

When the MS is using a TS on TCH frequency SS_DLTCH = SS_DLMeasured

By Averaging the results then: SS_DLTCH = SS_DLMeasured – ( BSPWR – BSTXPWR + 2*PLused )/ Nf ,

Nf = no. of hopping frequencies



Algorithm:1) Preparation of The Input Data SS Compensation

ii. Compensating for power control: SS_DLCompensated = SS_DLTCH + 2*PLused

Now in further calculations SS_DLCompensated will be used, where SSCompensated is the signal strength compensated for both frequency hopping and power regulations.

Quality Compensation Quality_DLCompensated is calculated in the same way such that:

Quality_DLCompensated = Quality_DLmeasured (in dBs) + 2*Plused

Where the Quality_DLmeasured (in dBs) is the Quality_DLmeasured (07) after transforming it into dBs



Algorithm:2) Filtering of Measurements Filtering for both SS and Quality is done with exponential non-linear filters in

order to eliminate variations of temporary nature and get partial results.

(A) Filtering of SS Measurements SS_DLFiltered (k) = b* SS_DLCompensated (k) + a* SS_DLFiltered (K-1), k is the SACCH

period

a & b (b=1-a) are the non-linear filter’s coefficients and “a” will define the length of the filter “L”, where each filter length “L” corresponds to certain value of “a” .

But how the length of the non-linear filter is calculated?



Algorithm:2) Filtering of Measurements

(A)Filtering of SS Measurements SS_DLFiltered (k) = b* SS_DLCompensated (k) + a* SS_DLFiltered(K-1),

k is the SACCH period

If SS_DLCompensated (k) < SS_DLFiltered(K-1)

then L = SSLENDL where,SSLENDL = 3 15 SACCH periods

In this case “up regulation is needed” and it should be done very fast in order to not lose the connection.

If SS_DLCompensated (k) > SS_DLFiltered(K-1)

then L = SSLENDL *UPDWNRATIO/100 where,SSLENDL = 3 15 SACCH periodsUPDWNRATIO = 100 700

In this case “Down regulation is needed” and it should be done in a smooth way, coz decreasing the power suddenly may harm the connection.




(B) Filtering of Quality Measurements Quality_DLFiltered (k) = b* Quality_DLCompensated (k) + a* Quality_DLFiltered(K-1),


If Quality_DLCompensated (k) < Quality_DLFiltered(K-1)

then L = QLENDL where,QSLENDL = 1 20 SACCH periods


If Quality_DLCompensated (k) >Quality_DLFiltered(K-1)

then L = QSLENDL *UPDWNRATIO/100 where,QSLENDL = 1 20 SACCH periodsUPDWNRATIO = 100 700





SS_DLFiltered(K-1) is set initially = SSDESDL, that will lead to start power regulations immediately after the first valid measurement report.

Also Quality_DLFiltered(K-1) is set initially = QDESDL, that will lead to start power regulations immediately after the first valid measurement report.

SSDESDL: has value range from -110 to -47 dbm and recommended value is -90 dbm

QDESDL: has value range from 0 to 70 dtqu and recommended value is 30 dtqu



Algorithm: Till now we finalized two stages from the algorithm:



SS_DLmeasured SS_DLCompensated SS_DLFiltered

Compensation Filtering

Q_DLmeasured

(Quality Units)

Q_DLCompensatedQ_DLFiltered

Compensation

Filtering

Quality units to dB transformation

Q_DLmeasured(dB)



Algorithm:3) Calculation of Power Order (PU)

This will be done on three stages:

(A) Calculating the two basic Power Orders.

(B) Applying the Power Orders constraints.

(C) Conversion of output data.




(A) Calculating the two basic Power Orders

i = 1,2 and α1 & β1 are parameters to compensate for the path loss and quality.

α1 = LCOMPDL/100, β1 = QCOMPDL/100, α2 = 0.3, β2 = 0.4

PU1 is calculated according to settings of α1 & β1 ( The operator will set the proper values from his point of view for LCOMPDL & QCOMPDL),

Default values: LCOMPDL=5 and COPMDL=55

PU2 is calculated according to recommended settings of α2 & β2 based on trials and field measurements.

pui = αi * (SSDESDL - SS_DLFiltered) + βi * (QDESDL - Q_DLFiltered)






PU1 and PU2 both of them aim to maintain the SS within the desired value defined according to SSDESDL and to maintain the Quality within the desired value defined according to QDESDL but each will calculate the path loss in different way.

PU_used = max (PU1, PU2), max of pu1 and PU2 will be used as the desired power order in the next measurement report coz the max of both of them will mean lower down regulation/higher up regulation.

pui = αi * (SSDESDL - SS_DLFiltered) + βi * (QDESDL - Q_DLFiltered)




(B) Applying Power Order constraints

The highest allowed power order PU_used = zero, which means keeping the output power at maximum value with no power control.

The lowest allowed power order is given by the minimum of the following:

PU_used= minimum (30 dB, BSPWRT- minimum BTS o/p power)

i.e. it is not allowed to decrease the o/p power or increase it by a value > 30dB




(C) Conversion of output data

pu_used will be interpreted into final form PL_used which takes values from 0 15

PL_used =Integer(-pu_used/2)

Ex: if PL_used = 3 and Down regulation for power is required, then in the next measurement report the BSC will inform the BTS to decrease its current power by 2* PL_used = 6 dBs



Parameters Summary

Dynamic BTS Power Control Parameters

Parameter Name Value Range Default Value Recommended Value Unit

SSDESDL −110 to −47 −90 −90 dBm

QDESDL 0 to 76 30 30 dtqu

SSLENDL 3 to 15 3 3 SACCH period (0.48 Seconds)

QLENDL 1 to 20 8 3 SACCH period (0.48 Seconds)

LCOMPDL 0 to 100 5 5 −

QCOMPDL 0 to 100 55 55 −

UPDWNRATIO 100 to 700 200 300 −

REGINTDL 1 to 10 1 1 SACCH period (0.48 Seconds)


THANK YOU


II. DYNAMIC MS POWER CONTROL


Dynamic MS Power Control


The Objective of the MS power control algorithm is to adjust the output power of the MS so that a desired signal strength is received in the BTS.

The below graph shows the relation between MS o/p power and the measured (received) signal strength at the BTS vs. the path loss between BTS and MS.

12




For the area before point 1, the received power at the BTS in the UL is very good and sufficient, however the MS can’t make any sort of down regulation and sends with power less than its minimum power.

As the MS is moving away from the BTS, the received power is decreasing, so after crossing point 1, the MS will start up regulating its power in steps to compensate for the path loss.

At point 2, the MS can’t up regulate its power for a value above the max. allowed power level even if the received power in the MS is deteriorated or the path loss increased.




For Quality measurements the below graph shows the up regulations in the MS o/p power when quality is deteriorated (SS is not taken into consideration here).

As the Quality got worse ( 0 7), the MS will try to increase its power to compensate for the quality drop.




Algorithm: The Dynamic MS Power Control algorithm is done on 3 stages:



3. Calculation of Power Order.



Algorithm:1) Preparation of The Input Data Dynamic Power Control is made on TCHs time slots as well as on the SDCCH

time slots, while the BCCH frequency with all its time slots is sent with max. power with no power control.

Type of measurements:

Both SS_UL and Quality_UL measurements will be used in the equation through which the next power order is calculated.

Measurement SourceSS_UL BTS

Quality_UL BTSpower level used by the MS_UL MS



Algorithm:1) Preparation of The Input Data REGINTUL: A parameter that defines the minimum time period between two

consecutive power orders. Measured in SACCH periods (0.48 Seconds) from 1 to 30 SACCH periods.

The BTS is able to changes its output power in the form of steps of 2 dBs

(ex: 2dBs, 4dBs,………. , max to 16 dBs)

When power control is in use the MS output power level will be given as:

PWR_used = min(MSTXPWR,MSPWRMAX) – 2*PLused , where PLused

= 0 to 8

and PWR_used is the power used by the MS during the connection



Algorithm:1) Preparation of The Input Data SSDESUL: A parameter that defines the desired Signal Strength in UL which

we aim to maintain using power control in the UL. Measured in dBm

The SS measured will be checked against SSDESUL to know if Down regulation in the MS power or up regulation is needed

QDESUL: A parameter that defines the desired Quality in UL which we aim to maintain using power control in the UL. Measured in dtqu ( 0 to 70)

The Quality measured will be checked against QDESUL to know if Down regulation in the MS power or up regulation is needed.



Algorithm:1) Preparation of The Input Data The equation used to calculate the power order in the next SACCH period

contains information on SSDESUL−SS_ULmeasured and QDESUL−Quality_ULmeasured.

SSDESUL− SS_ULmeasured is measured in dBm, while QDESUL− Quality_ULmeasured is measured in dtqu so to be used in the same equation some sort of mapping should be done,

i.e. QDESUL−Quality_ULmeasured should be represented in the form of dBs as well.

QDESUL (dtqu) 0 10 20 30 40 50 60 70

Quality_ULmeasured 0 1 2 3 4 5 6 7

dB transformation (dB) 23 19 17 15 13 11 8 4



Algorithm:1) Preparation of The Input Data SS Compensation Compensating for power control: SS_ULCompensated = SS_ULmeasured + 2*PLused

Now in further calculations SS_ULCompensated will be used, where SSCompensated is the signal strength compensated for power regulations.

Quality Compensation Quality_ULCompensated is calculated in the same way such that:

Quality_ULCompensated = Quality_ULmeasured (in dBs) + 2*PLused

Where the Quality_ULmeasured (in dBs) is the Quality_ULmeasured (07) after transforming it into dBs.



Algorithm:2) Filtering of Measurements Filtering for both SS and Quality is done with exponential non-linear filters in

order to eliminate variations of temporary nature and get partial results.

(A) Filtering of SS Measurements SS_ULFiltered (k) = b* SS_ULCompensated (k) + a* SS_ULCompensated(K-1), k is the

SACCH period.

a & b (b=1-a) are the non-linear filter’s coefficients and “a” will define the length of the filter “L”, where each filter length “L” corresponds to certain value of “a”

But how the length of the non-linear filter is calculated?




(A) Filtering of SS Measurements SS_ULFiltered (k) = b* SS_ULCompensated (k) + a* SS_ULFiltered(K-1), k is the SACCH

period

If SS_ULCompensated (k) < SS_ULFiltered(K-1)

then L = SSLENUL where,SSLENUL = 3 15 SACCH periods


If SS_ULCompensated (k) > SS_ULFiltered(K-1)

then L = SSLENUL *UPDWNRATIO/100 where,SSLENDL = 3 15 SACCH periodsUPDWNRATIO = 100 700





(B) Filtering of Quality Measurements− Quality_ULFiltered (k) = b* Quality_ULCompensated (k) + a* Quality_ULFiltered(K-1),


If Quality_ULCompensated (k) < Quality_ULFiltered(K-1)

then L = QLENUL where,QSLENUL = 1 20 SACCH periods


If Quality_ULCompensated (k) >Quality_ULFiltered(K-1)

then L = QSLENUL *UPDWNRATIO/100 where,QSLENUL = 1 20 SACCH periodsUPDWNRATIO = 100 700





SS_ULFiltered(K-1) is set initially = SSDESUL, that will lead to start power regulations immediately after the first valid measurement report.

Also Quality_ULFiltered(K-1) is set initially = QDESUL, that will lead to start power regulations immediately after the first valid measurement report.

SSDESUL: has value range from -110 to -47 dbm and recommended value is

-92 dbm

QDESUL: has value range from 0 to 70 dtqu and recommended value is

30dtqu



Algorithm: Till now we finalized two stages from the algorithm:



SS_ULmeasured SS_ULCompensated SS_ULFilteredCompensation Filtering

Q_ULmeasured

(Quality Units)

Q_ULCompensatedQ_ULFiltered

Compensation

Filtering

Quality units to dB transformation

Q_ULmeasured(dB)




This will be done on three stages:


(B) Applying the Power Orders constraints

(C) Conversion of output data.






α1 = LCOMPUL/100, β1 = QCOMPUL/100, α2 = 0.3, β2 = 0.4

pu1 is calculated according to settings of α1 & β1 ( The operator will set the proper values from his point of view for LCOMPUL & QCOMPUL)

pu2 is calculated according to recommended settings of α2 & β2 based on trials and field measurements.

pui = αi * (SSDESUL - SS_ULFiltered) + βi * (QDESUL - Q_ULFiltered)






pu1 and pu2 both of them aim to maintain the SS within the desired value defined according to SSDESUL and to maintain the Quality within the desired value defined according to QDESUL but each will calculate the path loss in different way.

pu_used = max (pu1,pu2), max of pu1 and pu2 will be used as the desired power order in the next measurement report coz the max of both of them will mean lower down regulation/higher up regulation

pui = αi * (SSDESUL - SS_ULFiltered) + βi * (QDESUL - Q_ULFiltered)




(B) Applying Power Order constraints

The highest allowed power order pu_used = zero, which means keeping the output power at maximum value with no power control.

The lowest allowed power order is given by the minimum of 16 dB i.e. it is not allowed to decrease the o/p power or increase it by a value > 16 dB




(C) Conversion of output data

pu_used will be interpreted into final form PL_used which takes values from 0 8

PL_used =Integer(-pu_used/2)

Ex: if PL_used = 3 and Down regulation for power is required, then in the next measurement report the BSC will inform the MS to decrease its current power by 2* PL_used = 6 dBs



Parameters Summary

Dynamic BTS Power Control Parameters

Parameter Name Value Range Default Value Recommended Value Unit

SSDESUL −110 to −47 −92 −92 dBm

QDESUL 0 to 76 30 30 dtqu

SSLENUL 3 to 15 3 3 SACCH period (0.48 Seconds)

QLENUL 1 to 20 3 3 SACCH period (0.48 Seconds)

LCOMPUL 0 to 100 6 6 −

QCOMPUL 0 to 100 75 75 −

UPDWNRATIO 100 to 700 200 300 −

REGINTUL 1 to 30 1 1 SACCH period (0.48 Seconds)


THANK YOU


GSM TO UMTS CELL RESELECTION AND HANDOVER


GSM to UMTS Cell Reselection and Handover

All 3G user equipments (UEs) can support Multi RATs(Radio Access Technology) i.e. Both GSM and UMTS.

With feature GSM-UMTS cell reselection and HO feature an operator can make use of both GSM and UMTS systems to complement each other.

Multi RAT users can have good coverage even in areas where no UMTS coverage and this can be accomplished using UMTS-GSM cell reselection and HO.

COEXUMTS: Is a BSC parameter used to activate the feature GSM-UMTS cell reselection and Handover.




New concepts will be introduced to understand how the feature works: CPICH Ec/No:

Common Pilot Channel - Energy per chip/Noise level power density. Used as a measure of the Quality of the neighbor UMTS cell.

CPICH RSCP: Common Pilot Channel - Received Signal Code Power. Used as a measure of the SS of the neighbor UMTS cell after dispreading.



Measurements on UMTS Cells In order to be able to make cell reselection or HO to a UMTS neighbor cell,

the multi RAT UE should be able to make measurements on this neighbor as well as the ordinary GSM cells.

But when or at which conditions the UE will perform measurements on the UMTS neighbors?

This will be based on the settings of the parameters QSI and QSC: QSI: used to manage the conditions of measuring the UMTS cell in Idle Mode. QSC: used to manage the conditions of measuring the UMTS cell in Active

Mode.



Measurements on UMTS Cells

Example:If QSC=8, then the UE is allowed to measure the neighbor UMTS cell only when

the SS of the serving GSM Cell > -78 dBm


SS(dBm)

time

-78 dBm

GSM&UMTS measurements

GSM measurements

GSM measurements

GSM&UMTS measurements

-90 dBm ─

When to start measuring the neighbor UMTS cell ?QSI/QSC Signal Strength of the serving GSM Cell

0 to 6 "Below" -98dBm to -74 dBm in steps of 4 dB

7 Always

8 to 14 "Above" -78dBm to -54 dBm in steps of 4 dB

15 Never


(I) GSM to UMTS Cell Reselection: This is controlled through set of parameters: QSI: Which defines at which conditions the UMTS cell will be measured in idle

mode, because there won’t be any kind of cell reselection without performing measurements.

FDDQMIN: Defines the minimum quality of a UMTS cell inorder to be candidate for cell reselection i.e. this condition should be satisfied CPICH Ec/No >FDDQMIN condition#1

default value = 5 (-10 dB)

FDDRSCPMIN: Defines the minimum SS of a UMTS cell inorder to be candidate for cell reselection i.e. this condition should be satisfied CPICH RSCP >FDDRSCPMIN condition#2

default value= 6 (-102 dBm)



(I) GSM to UMTS Cell Reselection: This is controlled through set of parameters: FDDQOFF: It is the key parameter to control the behavior of the cell

reselection provided that condition#1 and condition#2 are fulfilled.• If CPICH RSCP > RLA (S+N) + FDDQOFFS for at least 5 sec condition#3

then “Cell reselection will occur”

RLA (S+N): It is the Received Level Average of the signal strength of the serving+neighbor GSM cells measured in dBm, averaging is made on at least 5 measurements over a period of 35 seconds.

N.B: If the criteria for inter system cell reselection from GSM to UMTS is fulfilled then the multi RAT UE will perform cell reselection to the UMTS cell even if the criteria for selection another ordinary GSM cell is fulfilled.



(II) GSM to UMTS Handover: FDDMRR: The multi RAT UE is informed on how many UMTS cells (03) he

should report in the measurement report using this parameter. Upon receiving the measurements from the multi RAT UE, the BSC will handle

the GSM and UMTS cells separately by filtering out the UMTS measurements before the GSM locating algorithm.


GSM Evaluation

Sending the list and allocation

reply

Filtering

Basic Ranking

Urgency Condition

Aux. Radio features

Organizing the list

% idle TCHs ≤ ISOLEV

Ec/No > MRSL

Filtering out the UMTS cells

Add UMTS cells to Candidate list

UMTS Evaluation


(II) GSM to UMTS Handover: This is controlled through set of parameters: QSC: Which defines at which conditions the UMTS cell will be measured in

active mode, because there won’t be any kind of cell reselection without performing measurements.

MRSL: It is a BSC parameter that gives the minimum threshold for the quality (Ec/No) for a UMTS neighbor cell in order to be added to the HO candidate list, recommended value=-9dB

ISHOLEV: It is a Cell parameter. The percentage of idle TCHs in the serving GSM cell will be compared vs. ISHOLEV to decide if the UMTS will be added to the HO candidate list or not.



(II) GSM to UMTS Handover: Conditions that should be fulfilled for a UMTS cell to be added to the HO

candidate list:

(1) No. of Idle TCHsGSM ServingCell ≤ ISHOLEV, or urgency conditions are detected in the GSM serving cell either due to BQ or TA

(2) CPICH Ec/No UMTS Neighbor ≥ MRSL



(II) GSM to UMTS Handover: Now all the valid neighboring UMTS cells will be sorted in order of decreasing

CPICH Ec/No in order to form the UMTS candidate list. But how the two lists, the GSM and UMTS will be sorted? Ans.: this will depend on the urgency conditions and the load as follow:

N.B: To have balance between the behavior in the idle & active modes it is recommended to set the values for FDDQMIN (idle) = MRSL (active)


Non-Urgency HO Condition Urgency HO Condition

No Load Load No Load Load

GSM list UMTS list GSM list

GSM list UMTS list

UMTS list GSM list


Parameters Summary


GSM-UMTS Cell Reselection and HO Control ParametersParameter Name Value Range Default Value Recommended Value Unit

COEXUMTS 0(OFF),1(ON) 0(OFF) 1(ON) −

QSI0 to 6(Below:-98dBm t o -74dBm)

7(Always)8 to 14(Above:-78dBm to -54dBm)

15 (Never)

15 − −

QSC0 to 6(Below:-98dBm t o -74dBm)

7(Always)8 to 14(Above:-78dBm to -54dBm)

15 (Never)

15 − −

FDDQMIN 0 to 7 (-20dB, -6dB, -18dB, -8dB, -16dB, -10dB, -14dB, -12dB) 0 (-20dB) 5(-10dB) −

FDDRSCPMIN 0 to 15(-114 dBm to -84 dBm in steps of 2dBm) 6(-102 dBm) 6(-102 dBm) −FDDQOFF 0 to 15 (-inf, -28dB to 28dB in steps of 4 dB) 8(0 dB) 0(-inf) −

FDMRR 0 to 3 0 1 or 2 −MRSL 0 to 49 − 30 (-9 dB)

ISHOLEV 0 to 99 20 − %


THANK YOU


TROUBLE SHOOTING AND KPIS MONITORING


Trouble Shooting & KPIs monitoring


The Quality of service means that how the subscriber is satisfied with the overall service.

To keep the quality of service good as much as possible, we have to enhance the following:

(A) Accessibility: The ability of users to access the network.

(B) Retainability: The ability of users to successfully continue their connections with the network until it is terminated in a normal way.

(C) Service Integrity: The ability to keep the quality of the service good enough during the connection with the network.




KPIs: “Key Performance Indicators” it is a general term used to define the keys or observations through which you can judge if the performance is good or not.

(A) Accessibility KPIs: 1. Paging Success Rate

2. Random Access

3. SDCCH Congestion (Blocking)

4. TCH Blocking

5. SDCCH Drop




(B) Retainability KPIs: 1. TCH Drop Rate

2. Handover Success Rate

(C) Service Integrity KPIs: 3. Rxqual (Received Signal Quality)

4. SQI (Speech Quality Indicator)




(A) Accessibility KPIs: 1. Paging On MSC level there is counters to count: No. of attempts of paging to the Location Area. No. of paging response to first paging. No. of paging response to the repeated paging.

Using these counters we can form the equation to calculate the paging success rate.




(A) Accessibility KPIs:1. Paging The Paging Success rate on certain LA as appeared from the statistics:

Paging AttemptsPaging Success Rate




(A) Accessibility KPIs:1. Paging What are the causes of bad paging performance? Implicit detach is not used: parameter ATT is set to “Off” Low Signal Strength Not optimized paging strategy Use of combined BCCH mapping in high traffic location areas. Location area dimensioning Using of IMSI most of the time instead of TMSI




(A) Accessibility KPIs: 2. Random Access A failure in the random access doesn’t mean a call setup failure because the

MS sends many random access bursts each time it tries to access the network.

There are counters to count the no. of accepted random access requests, and the no. of discarded requests (incremented for random access requests that are received with too high Time Advance) through which the random access success rate can be calculated.

Causes of low random access success rate may be due to: Too high Time Advance (TA) High Interference Bad BSIC Planning




(A) Accessibility KPIs: 3. SDCCH Congestion It is the failure of call/connection setup due to high signaling load. There are counters to count the no. failed allocations due to SDCCH

congestion and the no. of call attempts through which the SDCCH congestion rate can be calculated.

Causes of high SDCCH congestion? This is may be due to: Location Area border cell. High SMS Traffic. Hardware Availability. No. of configured SDCCHs is low.




(A) Accessibility KPIs: 4. TCH Blocking It is the failure of setup a call/connection due to TCH congestion. There are counters to count the no. of released connections on SDCCH due

to TCH congestion and the no. of assignment attempts on TCH channel through which the TCH blocking rate can be calculated.

Causes of high TCH Blocking may be due to: Hardware problem. Too few TCH resources defined. Missing neighbor cell definition.




(A) Accessibility KPIs: 4. TCH Blocking

The TCH Blocking as appeared from the Statistics

TCH Blocking was solved after expansion (adding new frequency)

TCH TrafficTCH BlockingDefined TCH Channels




(A) Accessibility KPIs: 5. SDCCH Drop It is the failure of setup a call/connection due to SDCCH channel drop. N.B: when a connection is dropped at call setup it will affect the accessibility

KPIs. There are counters to count the no. of dropped connections on SDCCH and the

no. of successful MS channel establishments on SDCCH through which the SDCCH drop rate can be calculated.

Causes of high SDCCH drop rate may be due to: Bad Coverage. Interference. Hardware problems. Wrong parameters’ settings (Offsets and Hysteresis).




(B) Retainability KPIs: 1. TCH Drop It is the drop of the connection on the traffic channel which was assigned to

the MS. There are counters to count the no. of dropped connections and the initiated

connections on TCH channels through which the TCH drop rate can be calculated.

Causes of high TCH drop rate may be due to: Bad coverage. Interference. Hardware problems. Missing Neighbors. Wrong parameters' settings.




(B) Retainability KPIs: 1. TCH Drop

The TCH drop as appeared from the statistics.

High drop rate was solved after fixing a hardware problem.

TCH TrafficTCH Drop Rate





The TCH drop reasons as appeared from the statistics.

Main drop reason is due to BQ in downlink

BQ Both LinksBQ DownlinkBQ UplinkLow SS Both LinksLow SS DownlinkLow SS UplinkSudden Lost





The TCH drop reasons as appeared from the statistics.

Main drop reason is due to low SS Both link

BQ Both LinksBQ DownlinkBQ UplinkLow SS Both LinksLow SS DownlinkLow SS UplinkSudden Lost




(B) Retainability KPIs: 2. Handover Success Rate There are counters to measure the number of Handover attempts from cell to

cell and the Handover success rate.

Poor Handover Success rate may be due to: Bad Frequency plan. Wrong definitions and missing neighbors. Wrong parameters settings. Hardware problems.

Handover failure does not mean a drop call will occur.




(C) Service Integrity KPIs: 1. Rxqual It is obtained by averaging the Bit Error Rate over a certain period ~ 0.5 sec

and it is measured in both the Downlink and Uplink

Rxqual take values from 0 (Best) 7 (Worst) and gives indication for the quality of the radio environment.

There are counters to measure the no. of samples that received with Rxqual 0,1,2,….7




(C) Service Integrity KPIs: 2. SQI (Speech Quality Index) Is a good measure for the end user perceived speech quality.

The algorithm used for calculation the SQI takes into account the BER, the distribution of BER, the FER (Frame Erasure Rate) and the codec used (HR, FR, EFR). The output values are measured on a dBQ scale.

Typically, the SQI take values from 0 (Worst) 30 (Best), on HR connection SQImax=17dBQ, FR connection SQImax=22dBQ, EFR connection SQImax=30dBQ

N.B: HR ≡ Half Rate, FR ≡ Full Rate, EFR ≡ Enhance Full Rate


THANK YOU

Documents

GSM Radio Network Optimization