01 GO_NA08_E1_1 GSM Basic Radio Parameters-60

8/10/2019 01 GO_NA08_E1_1 GSM Basic Radio Parameters-60

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GSM Basic Radio parameters

ZTE University


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Objectives

At the end of this course, you will be able to:Understand the meaning of various radio parametersGrasp the setting of radio parametersState the effect to radio network performance of variouskind of radio parameters


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Content

Netw ork id ent i f ica t ion parametersSystem control parametersCell selection parameters

Network function parameters


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Roles of identification parameters

Enable the MS to correctly identify the ID of the currentnetwork

Enable the network to be real time informed of the correct

geographical location of the MS

Enable the MS to report correctly the adjacent cellinformation during the conversation process


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MCC LAC

Cell Global Identi ty

MNC

3 Digi t s 2-3 Digi ts Max 16 Bits

CI

Max 16 bi ts

LAI

CELL GLOBAL IDENTITY (CGI)

Cell Global Identity (CGI) It is used for identifying individual cells within an LA


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ROLES OF CGI

The CGI information is sent along the system broadcastinginformation in every cell.

When the MS receives the system information, it will

extract the CGI information from it and determines whetherto camp on the cell according to the MCC and MNCspecified by the CGI.

It judges whether the current location area is changed,then determines whether to take the location updatingprocess.


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SETTING OF CGI

MCC Mobile Country Code :consists of 3 decimal digits, and the value range is the decimal000 999.

MNC Mobile Network Code :consists of 3 decimal digits, and the value range is the decimal00 999.

LAC Location Area Code : The range is 1-65535.

CI Cell Identity :The range is 0-65535.


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NCC BCC

3 Bi t s 3 Bi t s

BSIC

NCC Network/ National Color Code Value Range: 0~7

BCC Base Station Color Code Value Range: 0~7

BASE STATION IDENTITY CODE (BSIC)

Base Station Identity Code (BSIC) It enables MSs to distinguish betweenneighboring base stations


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NCC and BCC ROLES

NCC:In the connection mode (during conversation), the MSmust measure the signals in the adjacent cells andreport the result to the network. As each measurement

report sent by the MS can only contain the contents ofsix cells, so it is necessary to control the MS so as toonly report the information of cells factually related tothe cell concerned. The high 3 bits (i.e. NCC) in theBSIC serve this purpose.

BCC:The BCC is used to identify different BS using the sameBCCH in the same GSMPLMN.


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CBA

FED

BSIC CONFIGURATION PRINCIPLE

In general, it is required that Cells A, B, C, D, E andF use different BSIC when they have same BCCH

frequency. When the BSIC resources are notenough, the cells close to each other may take thepriority to use different BSIC.


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ROLES OF BSIC

Inform the MS the TSC used by the common signalingchannel of the cell. As the BSIC takes part in the decoding process of therandom access channel (RACH), it can be used to preventthe BS from mis-decoding the RACH, sent by the MS toan adjacent cell, as the access channel of this cell.When the MS is in the connection mode (duringconversation), it must measure the BCCH level of adjacentcells broadcasting by BCCH and report the results to theBS. In the uplink measurement report, MS must showBSIC of this carrier it has measured to every frequencypoint.


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BA LIST (BCCH ADJACENT LIST)

Adjacent cell BCCH table At most 32 adjacent cellCarried by BCCH when MS is idle, by SACCHwhen MS is dedicatedThe MS will first search carriers from this tableand if none is found it will turns to find any of 30carriers with highest levels.


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Content

Network identification parametersSys tem co n t ro l p aram eter s

Cell selection parameters



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RANDOM ACCESS

Random access is the process that messagesbeing transmitted on RACH when a MS turnsfrom idle to dedicate mode. The mainparameters includes:

MAXRETRANSTx_Integer

AC


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MAX RETRANS

When starting the immediate assignment process(e.g, when MS needs location updating,originating calls or responding to paging calls), theMS will transmit the "channel request" message

over the RACH to the network. As the RACH is an ALOHA channel, in order to enhance the MSaccess success rate, the network allows the MS totransmit multiple channel request messagesbefore receiving the immediate assignmentmessage. The numbers of maximumretransmission (MAX RETRANS) are determinedby the network.


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MAX RETRANS

The MAX RETRANS is often set in the following ways:For areas (suburbs or rural areas) where the cell radius is more

than 3km and the traffic is smaller, the MAX RETRANS can beset 11 (i.e. the MAX RETRANS is 7).

For areas (not bustling city blocks) where the cell radius is lessthan 3km and the traffic is moderate, the MAX RETRANS can beset 10 i.e. the MAX RETRANS is 4).

For microcellular, its recommend that the MAX RETRANS beset 01 i.e. the MAX RETRANS is 2).

For microcellular areas with very high traffic and cells withapparent congestion, its recommend that the MAX RETRANSbe set 00 i.e. the MAX RETRANS is 1).


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Transmission Distribution Timeslots(Tx_integer)

The Tx_integer parameter is the interval in timeslots at whichthe MS continuously sends multiple channel request messages.

The parameter S is an intermediate variable in the accessalgorithm, and is to be determined by the Tx_integer parameterand the combination mode of the CCCH and SDCCH


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Format of Tx_Integer

MS starts the first channel request message : {0, 1, ...,MAX (Tx_integer, 8)-1}The number of timeslots between any two adjacentchannel request messages {S, S+1, ..., S+Tx_integer-1}

The Tx_integer is a decimal number, which can be 3~12,14, 16, 20, 25, 32 and 50 (default). The values of theparameter S are shown as below:

Tx_integerCCH Combination Mode

CCCH Not Shared with SDCCH CCCH Shared with SDCCH

3, 8, 14, 50 55 41

4, 9, 16, 76 52

5, 10, 20, 109 58

6, 11, 25, 163 86

7, 12, 32, 217 115


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ACCESS CONTROL AC

The access levels are distributed as follows:C 0 C9: ordinary subscribers;C11: used for PLMN management;C12: used by the security department;

C13: public utilities e.g. water, gas ;C14: emergency service;C15: PLMN staff.


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SETTING OF AC

In the BS installation and commissioning process or in theprocess of maintaining or testing some cells, the operatorcan set C0 C9 as 0 to forcedly forbid the access ofordinary subscribers so as to reduce the unnecessaryeffects on the installation or maintenance work.In some cells with very high traffic, the congestion willoccur in busy hours. For example, the RACH conflicthappens frequently, the AGCH is overloaded and the Abisinterface flow is overloaded. The network operator can set

proper access control parameters C0 C15 to controlthe traffic of some cells.


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CCCH_CONFCoding

MeaningsCCCH messageblocks in one

BCCH0 CCCH use one basic physical channel, not shared with SDCCH 91 CCCH use one basic physical channel, shares with SDCCH 3

10 CCCH use two basic physical channels, not shared with SDCCH 18100 CCCH use three basic physical channels, not shared with SDCCH 27110 CCCH use 4 basic physical channels, not shared with SDCCH 36

Others Reserved

CCCH_CONF

The CCCH can be one or more physical channels. TheCCCH and SDCCH can share the same physical channel.The combination mode of the common control channel in acell is determined by the CCCH_CONF


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CCCH_CONF

The CCCH_CONF is determined by the telecomoperation department according to the trafficmodel of a cell.

If a cell has 1 TRX, we recommend that the CCCH

uses one basic physical channel and shares it with theSDCCH If a cell has 2 ~ 8 TRX, we recommend that the CCCHuses one basic physical channel but does not share it

with the SDCCH.


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AGBLK

Since the CCCH consists of the access grantchannel (AGCH) and paging channel (PCH), it isnecessary to set how many blocks of the CCCHinformation blocks are reserved and dedicated to

the AGCH, the access grant reserve blocks(AGBLK).

AGBLK is represented in decimal numerals, andits value range is:

CCCH is not combined with SDCCH: 0 7.CCCH is combined with SDCCH: 0 2.


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AGBLK

SETTING AND IMPACT OF AGBLKThe AGBLK setting principle is: given that the AGCH isnot overloaded, try to reduce the parameter as much aspossible to shorten the time when the MS responds to

the paging and improve the quality of service of thesystem.The recommended value of AGBLK is usually 1 (whenthe CCCH is combined with the SDCCH), 2 or 3 (whenthe CCCH is not combined with the SDCCH).


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BS-PA-MFRMS

According to the GSM specifications, every mobilesubscriber belongs to a paging group. the MS calculatesthe paging group to which it belongs by its own IMSI. In an actual network, the MS only "receives the contentsin the paging subchannel to which it belongs but ignoresthe contents in other paging subchannels. (i.e. DRXsource). The BS-PA-MFRMS refers to how many multi-frames areused as a cycle of a paging subchannel. This parameter infact determines how many paging sub-channels are to bedivided from the paging channels of a cell.


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BS-PA-MFRMS

Multiframes of the same

paging group that cycleon the paging channel2 2

3 3

4 4

5 56 6

7 7

8 8

9 9

BS-PA-MFRMS (2)

BS-PA-MFRMS is represented in decimalnumerals and its value range is 2 9, its unit ismultiframe 51 frames , its default value is 2


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PERIODIC UPDATING TIMER (T3212)

The frequency of periodic location update iscontrolled via the network and the period length isdetermined by the parameter T3212. The T3212 is a decimal number, within the rangeof 0~255, in the unit of six minutes (1/10 hours).If the T3212 is set to 0, it means that the cellneeds no periodical location update.


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NCCPERM

In the connection mode (during the conversation),the MS will report the measured signals of theadjacent cells to the BS, but each report maycontain at most 6 adjacent cells.

Therefore, let the MS only report the information ofthe cells that may become the hand-over targetcells.The above functions can be fulfilled by limiting the

MS to merely measure the cells whose NCC havebeen specified. The NCCPERM lists the NCCs ofcells to be measured by the MS.NCCPERM will affect handover


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RADIO LINK TIMEOUT (RLT)

GSM specification stipulates that the MS must have a timer(S), which is assigned with an initial value at the start ofthe conversation, that is, the downlink radio link timeoutvalue.Every time the MS fails to decode a correct SACCHmessage when it should receive the SACCH, the S isdecreased by 1. On the contrary, every time the MSreceives a correct SACCH message, the S is increased by2, but the S should not exceed the downlink radio link

timeout value. When the S reaches 0, the MS will reportthe downlink radio link failure.The radio link timeout is a decimal number, within therange of 4 ~ 64, at the step of 4, defaulted to 16.


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MBCR (1)

The parameter "multiband indication (MBCR)" isused to notify the MS that it should report themultiband adjacent cell contents.

The value is 0-3


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MBCR (2)

0: Based on the signal strength of adjacent cells, the MS reports themeasurement results of 6 adjacent cells whose signals are the strongest,whose NCC are known and allowed no matter in which band the adjacentcells lie. The default value is 0

1: The MS should report the measurement result of one adjacent cell ineach band (not including the band used by the current service area) in theadjacent table, whose signal is the strongest and whose NCC is alreadyknown and allowed.


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MBCR (3)

2: The MS should report the measurement results of two adjacent cellsin each band (not including the band used by the current service area)in the adjacent table, whose signals are the strongest and whose NCC

are already known and allowed.

3: The MS should report the measurement results of three adjacent cells

in each band (not including the band used by the current service area)in the adjacent table, whose signals are the strongest and whose NCCare already known and allowed.


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Application of MBCR


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Content

Network identification parametersSystem control parametersCell select ion param eters



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CELL SELECTION C1

When the MS is turned on, it will try to contact apublic GSM PLMN, so the MS will select a propercell and extract from the cell the control channelparameters and prerequisite system messages.

This selection process is called cell selection.

The quality of radio channels is an important factor

in cell selection. The GSM Specifications definesthe path loss rule C1. For the so-called proper cell,C1>0 must be ensured.


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C1 = RXLEV - RXLEV_ACCESS_MIN- Max(MS_TXPWR_MAX_CCH - P ,0)

CELL SELECTION C1

where:RXLEV_ACCESS_MIN is the minimum received level theMS is allowed to access the network

MS_TXPWR_MAX_CCH is the maximum power level ofthe control channel (when MS sending on RACH);

RXLEV is average received level;

P is the maximum TX power of MS; MAX X, Y X; if X Y.

MAX X, Y Y; if Y X.


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RxLevAccessMin

The RXLEV_ACCESS_MIN is a decimal number,within the range of -110dBm ~ -47dBmDefault value is 0 (-110dBm).

RXLEV_ACCESS_MIN Meaning-47 dBm > -48 dBm (level 63)

-46 dBm -49 ~ -48 dBm (level 62)

... ...

-108 dBm -109 ~ -108 dBm (level 2)

-109 dBm -110 ~ -109 dBm (level 1)

-110 dBm


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Setting and Influence

For a cell with traffic overload, you can appropriatelyincrease the RXLEV_ACCESS_MIN

RXLEV_ACCESS_MIN value cannot be set to too high a

value. Otherwise, blind areas will be caused on theborders of cells.

It is suggested that the RXLEV_ACCESS_MIN value

should not exceed -90 dBm.


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CELL RESELECTION C2

Cell Reselection (C2) is a process when MS change itsservice cell in idle mode.

When the MS selects a cell it will begin to measure the

signal levels of the BCCH TRX of its adjacent cells (atmost 6)

When given conditions are met, the MS will move from the

current cell into another one. This process is called cellreselection.


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When C2 Parameter Indicator (PI) indicates YES the MS

will get parameters (CRO, TO and PT) , from BCCH, to beused to calculate C2(channel quality criterion), which serves

as cell reselection norm. The equation is as follows:

Where T is a timer. When a cell is recorded by MS as one

of the six strongest cells, timer starts counting, otherwise, T

is reset to zero.

C2 C1 CRO H

PT T

TO, whenPT

31C2 C1 CRO , when PT= 31

CELL RESELECTION C2


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PARAMETER INDICATOR (PI)

PI is used to notify the MS whether to use C2 as the cellreselect parameter and whether the parameters calculatingC2 exist.

PI consists of 1 bit. 1means the MS should extractparameters from the system message broadcasting in thecell to calculate the C2 value, and use the C2 value as thestandard for cell reselect; 0 means the MS should useparameter C1 as the standard for cell reselect (equivalentto C2 C1 .


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CRO, PT AND TO

The cell reselection initiated by the radio channel quality regards C2as the standard. C2 is a parameter based on C1 plus some artificial

offset parameters.

The artificial influence is to encourage the MS to take the priority inaccessing to some cells or prevent it from accessing to others. These

methods are often used to balance the traffic in the network.

In addition to C1, there are three other factors influencing C2, namely:

CELL_RESELECT_OFFSET (CRO), TEMPORARY_OFFSET (TO)

and PENALTY_TIME (PT).


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Format of CRO, PT and TO

The CRO is a decimal number, in dB, within the rangeof 0 ~ 63, meaning 0 ~ 126 dB, at the step of 2 dB.

The TO is a decimal number, in dB, within the range of

0 ~ 7, meaning 0 ~ 70 dB, at the step of 10 dB, where70 means infinite.

The PT is a decimal number, in seconds, within the

range of 0 ~ 31, meaning 20 ~ 620 seconds for 0 ~ 30,and at the step of 20 seconds. The value of 31 isreserved to change the direction of effect that the CROworks on the C2 parameter.


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C2 TYPICAL APPLICATIONS

For cells where the traffic is very heavy or thechannel quality is very low. the PT may be set 31,making TO invalid, so C2=C1-CRO.

For cells where the traffic is moderate, therecommended value for CRO is zero and PT=31,thus causing C2=C1, i. e. no artificial impact willbe imposed.


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C2 TYPICAL APPLICATIONS

For cells with light traffic, its recommended that CRObe ranged from 0 to 20dB. The greater the CRO, themore possible the cells will be reselected ,and viceversa. Its also suggested that TO is equal or a littlehigher than CRO. PT , whose main role is to avoidfrequent cell reselection by MS, is generallyrecommended to be set at 20 seconds or 40 seconds .


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CELL SELECTION HYSTERESIS (1)

When a MS reselects a cell, if the old cell and the targetcell are in different locations, then the MS must initiate alocation updating process after cell reselection.Due to the fading features of the radio channel, the C2values of two adjacent cells measured along their borderswill fluctuate greatly.MS will frequently conduct the cell reselection, which willnot only increase the network signaling flow and lead tolow efficiency use of radio resources, but reduces theaccess success rate of the system, as the MS cannotrespond to paging calls in the location updating process.


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CELL SELECTION HYSTERESIS (2)

To minimize the influence of this issue, the GSMspecifications put forward a parameter calledReselHysteresis,

The cell selection hysteresis is represented indecimal numerals, its unit is dB, its range is 0 14,its step length is 2dB, and its default value is 4.


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CELL RESELECTION PRINCIPLE

If the MS calculates that the C2 value of anadjacent cell (Same location area) surpasses theC2 value of the serving cell and maintains for 5sor longer, the MS will start cell reselection .

If the MS detects a cell that is not in the samelocation area with the current cell, the calculatedC2 value surpasses the sum of the C2 value of thecurrent cell and the ReselHysteresis parameterand if it remains for 5s or longer, the MS will startthe cell reselection .The cell reselection caused by C2 should beoriginated at least at the interval of 15s.


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In the system message broadcasting in each cell, there is a bit

information indicating whether to allow the MS to access to it, which

is called cell bar access (CBA). The parameter CBA is to indicate

whether the cell bar access is set in a cell.

The CBA bit is a parameter for the network operator to set. Usuallyall the cells are allowed to be accessed by MS , so the bit is set

NO. However, in special cases, the telecom operator may want to

assign a certain cells for handover service only, then the bit can be

set YES.

CELL BAR ACCESS (CBA)


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Area A

MS A

BTS B

BTS C

CELL BAR ACCESS (CBA)


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CELL BAR QUALIFY (CBQ)

In areas where the cells overlay with eachother and differ in capacity, traffic andfunctions, the telecom operator often hopesthat the MS can have priority in selecting

some cells, that is, the setting of cell priority.This function is set by way of the parameter"Cell Bar Qualify" (CBQ).


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C1 and C2 States with CBA and CBQ Configurations

CBQ CBA Cell SelectionPriority Cell ReselectionState

No No Normal Normal

No Yes Barred Barred

Yes No Low Normal

Yes Yes Low Normal

CELL BAR QUALIFY (CBQ) 2


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B

EXAMPLE OF CBQ SETTING

For some reasons, the traffic of Cells A and B is apparently higherthan that of other adjacent cells. To balance the traffic in the wholearea, you can set the priority of Cells A and B as low, and set thepriority of the rest cells as normal so that the traffic in the shadearea will be absorbed by adjacent cells. It must be noted that theresult of this setting is that the actual coverage of Cell A and Cell Bis narrowed. However, this is different from reducing the transmittingpower of Cell A and Cell B, the latter may cause blind areas of thenetwork coverage and the reduction of communication quality.


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Content

Network identification parametersSystem control parametersCell selection parameters

Netwo rk fun c t ion param eters


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Value Range Specified dBm Level0


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INTAVE

Due to the randomness of the radio channelinterference, the BTS must average the measureduplink interference levels within the specifiedperiod, and this average cycle is determined by

the INTAVE parameter.This parameter is a decimal number, in SACCHmulti-frames, within the range of 1 ~ 31.


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New Cause Indication (NECI)

The NECI is a decimal number, within the range of0 ~ 1, with the meaning described as below:When the NECI is 0, it means that the cell does notsupport the access of half-rate services.

When the NECI is 1, it means that the cell supports theaccess of half-rate services.


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RE-ESTABLISHMENT ENABLE (RE)

For the drop calls caused by the radio link fault, the MScan start the call reestablishment process to resume theconversation, but the network is entitled to determinewhether the call reestablishment is allowed or not.

0=Yes, 1=No. In some special circumstances, the drop call may occurwhen the MS goes through a blind area during theconversation. If the call reestablishment is allowed, themean drop call rate will be reduced. However, the callreestablishment process will occupy a longer period oftime, most of the subscribers have hung up before thereestablishment process is over, as a result, the callreestablishment failed to achieve its purpose and wastedmany radio resources. We recommend that the callreestablishment be not allowed in the network except forsome individual cells.


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01 GO_NA08_E1_1 GSM Basic Radio Parameters-60