86233221 Radio Interface Capacity

7/29/2019 86233221 Radio Interface Capacity

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Radio Interface CapacityThe main bottlenecks in the radio interface are the downlink power, uplink interference, radiobearers, common channels, and the channelization code tree.

Figure 6: Radio interface

Downlink Power

The BTS controls the amount of HSDPA DL transmission power, after the powers for DCH,

HSUPA control channels, and common channels have been set up. The BTS can measure the

total power, NonHSDPA power, and HSDPA power.

1.

Monitored

capacity

item

Transmitted Total Carrier Power

The total transmitted power includes the downlink power allocated to the downlink DPCH, the

common channels, and the E-RGCH, E-AGCH, E-HICH, HS-SCCH, and HS-PDSCH. The BTS

reports the Transmitted Carrier Power in absolute units. The classification depends on the cell

size setting (PRACHDelayRange parameter). A proactive KPI has been defined, based on the

M1000C342 - M1000C353 classification counters.

2.

Proactive

monitoring

Counter/KPI Name, unit Target Red

flag

Description

RNC_5201a Marginal

Transmitted Carrier

Power Time Share

DL [%]

20 >50 Share of time when the Transmitted

Carrier Power (TxCrPwr) is in classes

7-8. The mapping to power value

depends on the PRACHDelayRange

WCEL parameter settings.


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3. Reactive

monitoring

Counter/KPI Name, unit Description

RNC_5202a Overload

Transmitted Carrier

Power Time Share

DL [%]

Share of time when the Transmitted Carrier Power

(TxCrPwr) is in classes 9-10. The mapping to power value

depends on the PRACHDelayRange WCEL parameter

settings.

RNC_964a RRC Setup FR due

to AC [%]

RRC setup failure ratio caused by Admission Control.

M1000C155 RB RELEASE BY

DYN LINK OPT

DUE TO RL

POWER

CONGESTION [#]

The number of radio bearers released by the dynamic link

optimization for NRT traffic because of RL power

congestion.

M1000C166 RB RELEASE DUE

TO ENH

OVERLOAD

CONTROL USING

RL RECONF [#]

The number of radio bearer releases by the enhanced

overload control using the radio link reconfiguration

method.

M1000C149 HS-DSCH

RELEASE DUE TO

DL OVERLOAD [#]

The number of HS-DSCH allocation releases due to

downlink overload. This counter includes both interactive

and background class connections. It is updated when the

user's HS-DSCH allocation is released due to the

PtxNonHSDPA >=

PtxTargetHSDPA+PtxOffsetHSDPA condition. This

counter is updated only when the HSDPA Static Resource

Allocation is used.

M1000C142 RB DOWNGRADE

BY ENH

OVERLOAD

CONTROL USING

TFC SUBSET [#]

The number of radio bearer downgrades by the enhanced

overload control using the TFC subset method.


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M1002C602 DL DCH

SELECTED FOR

STREAMING DUE

TO HSDPA

POWER [#]

This counter is updated when the HS-DSCH cannot be

selected as a downlink transport channel due to

PtxTotal>PtxTargetHSDPA or

PtxNC>PtxTargetHSDPA conditions.

RNC_969b DL DCH Selected

due to the HSDPA

power [#]

The number of times when the HS-DSCH downlink

transport channel cannot be selected for an interactive or

background class connection due to downlink power

limits.

4. Analysis

1. Marginal (Overload) Transmitted Carrier Power Time Share DL

The primary indication for highly loaded sites is the percentage of time when these sites are

in marginal and overload power classes.

2. RRC setup failure rate due to AC

Admission control may reject setup, cell change, or handover (excluding frozen BTS failure).

Increase of failures, indicated by the RRC setup failure rate due to AC, means that the

WBTS has used all available downlink power in order to maintain the connection for the

users.

3. RB releases and downgrades

Counters M1000C155, M1000C166, M1000C149, M1000C142, and M1002C602 react in

overload situation.

Note that the average available power for HSDPA influences the CQI seen by the UE. If the

downlink quality is bad, there is not enough power to serve the users. However, high power for

HSDPA does not necessarily mean high throughput (or low power - low throughput).

5.

Overload

The system can downgrade or release a dedicated channel of a non-real-time RAB, due to

excessive downlink power.

6. Upgrade With the 40 W LPAs, the maximum HSDPA power can increase to 45 dBm (also concerns the

average power). High DL power levels, together with a low throughput, indicate low coverage for

UEs. Improve the coverage by adding sites.

Received Total Wideband Power

The power control allows access to as many users as possible while minimizing the interference

caused by these users. At the same time, the capacity of a WCDMA system is proportional to thelevel of interference in the system.

The cell-specific load control in the RNC maintains the estimated received wideband power

value for the resource allocation of the RNC. The estimated received wideband power value


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represents the received interference of transferred active bearers, which are allocated in the RNC

(such as DCHs). It does not include the contribution of the bearers, which have an E-DCHestablished with the scheduled transmission, as follows:

If the HSUPA has not been configured in the cell, the estimated received wideband power

value represents the received total wideband power (PrxTotal), measured and reported by

the BTS. If the HSUPA has been configured in the cell, the estimated received wideband power

value represents the received total non-E-DCH scheduled transmission wideband power

(PrxNonEDCHST). The PrxTotal is not estimated in the HSUPA cell.

1.

Monitored

capacity

item

Received Total Wideband Power

The Received Total Wideband Power (RTWP) reflects the total noise level within the UMTS

frequency band of one single cell. This is measured by the BTS.

The RNC limits the uplink noise using the PrxTarget parameter, which defines the maximum

allowed increase in uplink noise in relation to the background noise floor. A high RTWP levelindicates an increase in interference in the cell.

2.

Proactive

monitoring


flag

Description

RNC_5203a Percentage of RTWP

in marginal area [%]

10 - Share of time when the received total

wideband power is in classes 13-16.

The KPI is based on the M1000C320-41 counters. The total uplink power

(RTWP) measurement report samples

the power values that are within a

particular class range. The counter

takes into account the whole received

power, including HSDPA and Common

Channels.

3. Reactive

monitoring


M1000C147 RB DOWNGRADE BY

PBS DUE TO

INTERFERENCE

CONGESTION [#]

The number of RB downgrades by priority-based

scheduling (PBS) due to interference congestion.


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PBS DUE TO

INTERFERENCE

CONGESTION [#]

The number of radio bearers released by priority-based

scheduling (PBS) due to interference congestion.

M1000C152 RB DOWNGRADE BY

PRE-EMPTION DUE

TO INTERFERENCE

CONGESTION [#]

The number of RB downgrades by pre-emption due to

interference congestion.


PRE-EMPTION DUE

TO INTERFERENCE

CONGESTION [#]

The number of radio bearers released by pre-emption

due to interference congestion.

RNC_970a SRB Reject Rate UL

[%]

The number of SRB requests that have been rejected

on the UL.

RNC_972a AMR Service Reject

Rate UL [%]

The number of voice call requests that have been

rejected on the UL.

RNC_974a CS Data Service

Reject Rate UL [%]

The number of video call requests that have been

rejected on the UL.

RNC_976a PS Data Service

Reject Rate UL [%]

The number of PS data call requests that have been

rejected on the UL.

RNC_661d HSDPA AccessFailure Rate due to UL

DCH [%]

HSDPA access failure rate due to the associated ULDCH.

4. Analysis

1. Total Interference in UL

The primary indication for a highly loaded BTS.

2. Service Rejections


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Counters M1000C147, M1000C159, M1000C152, M1000C164 and KPIs RNC_970a,

RNC_972a, RNC_974a, and RNC_976a react in overload situation.

3. HSDPA Access FR due to the UL DCH

An increase in the HSDPA Access FR due to the UL DCHindicates that there is no room for

more UEs to be connected to that particular cell due to UL power congestion.

There are no predefined thresholds for the frequency of rejections, downgrades, or releases.

5. Overload The system can downgrade or release a dedicated channel of a non-real-time RAB (controllable

load), due to excessive uplink congestion situations. When the load is still too high, the power

control cannot mitigate failures due to non-controllable load.

6. Upgrade -

Common Channel Capacity

The air interface physical channels map to transport channels in UTRAN:

1. PCCPCH (Primary Common Control Physical Channel), mapped to the BCH (Broadcast Channel)

2. SCCPCH (Secondary Common Control Physical Channel), mapped to the PCH (Paging Channel) or

FACH (Forward Access Channel). There can be up to three SCCPCH channels configured in the cell.

3. PRACH (Physical Random Access Channel), mapped to the RACH (Random Access Channel)

These channels are not the subject of the dynamic power control. The transmission powers of the

downlink common physical channels are determined during radio network planning, and their bit

rates are not configurable by the user. The system measures the loads indirectly, by measuring

the loads on corresponding transport channels (RACH, FACH, PCH, and BCH).Common channel load consists mainly of FACH, RACH, and PCH loads on the SCCPCH

channel(s). RACH and FACH load have separate control plane and user plane load: RACH-u,RACH-c, FACH-u, and FACH-c. The total load of the common channels is thus the sum of these

loads.

There can be up to three SCCPCHs configured in the cell. If only one SCCPCH is used in a cell,

it will carry FACH-c (containing DCCH/CCCH/BCCH), FACH-u (containing DTCH), andPCH. FACH and PCH are multiplexed into the same SCCPCH (see Figure 7 Common channels

mapped to one SCCPCH).


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Figure 7: Common channels mapped to one SCCPCH

If the user configures two SCCPCHs in a cell, the primary CCPCH will always carry PCH only

and the second SCCPCH will carry FACH-u and FACH-c (see Figure 8 Common channels

mapped to two SCCPCHs).

Figure 8: Common channels mapped to two SCCPCHs

The system measures the RACH load in the NBAP interface in terms of acknowledged PRACHpreambles. There is no overload control algorithm for RACH, but the RACH load measurementsare used by the RNC for load control, when the downlink channel type (common or dedicated) is

selected.

1. Monitored

capacity

item

Common Channel Capacity

The main proactive KPI for the common channel load is the average SCCPCH channel load,

calculated indirectly from the transport channels, which map to it. Assuming fixed transmit rates

for each transport channel, the user can follow the load proactively.

Additionally, the user can monitor each common transport channel proactively.

2. Proactive

monitoring


flag

Description


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RNC_979a SCCPCH

Average

Load [%]

- - Average SCCPCH channel load - including the

PCH in the measurement period.

Average PCCPCH load: if one SCCPCH is used

in a cell, it will carry FACH-c (containing

DCCH/CCCH/BCCH), FACH-u (containing

DTCH), and PCH.

RNC_2029a FACH-u

Load Ratio

[%]

- - FACH-u Load Ratio provides information about

the FACH transport channel user plane data

load (the FACH channel throughput is divided by

the corresponding transport channel maximum

bit rate to get the load ratio).

RNC_2030a FACH-c

Load Ratio

[%]

- - FACH-c Load Ratio provides information about

the FACH transport channel control plane data

load (the FACH channel control data throughput

is divided by the corresponding transport

channel maximum bit rate to get the load ratio).

RNC_2032a RACH-u

Load Ratio

[%]

- - RACH-u Load Ratio provides information about

the RACH transport channel user plane data

load (the RACH channel user data throughput is

divided by the corresponding transport channel

maximum bit rate to get the load ratio).

RNC_2033a RACH-c

Load Ratio

[%]

- - RACH-c Load Ratio provides information about

the RACH transport channel control plane data

load (the RACH channel control data throughput

is divided by the corresponding transport

channel maximum bit rate to get the load ratio).

3. Reactive

monitoring


- - -


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4. Analysis You can use RNC_979a to see how loaded the physical channel (SCCPCH) is in this

configuration. When two SCCPCHs are used, this will contain all other transport channels

except PCH.

5. Overload If there is only one SCCPCH, the system gives PCH traffic a higher priority compared to the

FACH. When the system notices congestion on this channel, it is likely that the FACH channel

will suffer.

6. Upgrade The SCCPCH load (PCH+FACH, or PCH only) can be reduced by:

1. Increasing the number of available SCCPCHs (for example, by introducing a second

SCCPCH)

2. Evaluating whether there is a high level of signaling generated by cell, URA, location area,

or routing area updates. If so, consider adjusting the area boundaries or reducing the size

of the location and routing areas.

3. Evaluating whether there is excessive user plane data transfer within the CELL_FACH. If

so, consider reducing the RLC buffer thresholds that trigger the transition to CELL_DCH.

4. Upgrading the Node B configuration with an additional carrier

5. Using the 24 kbps Paging Channelfeature if the PCH is loaded.

Channelization Code Tree

The available codes in the Channelization Code Tree in the BTS can become a capacity

bottleneck in the downlink direction, especially when HSDPA and HSUPA are enabled in thecell. There is a fixed number of codes reserved for Common Channels. REL99 services require a

certain number of codes, depending on the service bit rate. HSDPA can reserve 5, 10, or 15

codes.

In uplink, the code tree is arranged per each UE; therefore no capacity bottleneck is expected.

1.

Monitored

capacity

item

Channelization Code Tree

Channelization Code Occupancy provides an indication of the percentage of codes, that the

system uses or blocks. The channelization codes, which the system assigns to both common

and dedicated downlink channels, are included in the KPI. Furthermore, there are also counters

to monitor the maximum and minimum code occupancy. This can be used to detect the cells

busy and non-busy hours.

Channelization Code Blocking is the percentage of code allocation attempts, that block because

of code tree congestion.

When a user enables HSDPA, the system can dynamically adjust the number of SF16 codes

reserved for HSDPA, depending on the R99 usage of codes. There are counters for monitoring

the number of HSDPA channelization code downgrades due to congestion of the RT or NRT


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DCH.

The user can monitor the impact of code tree congestion reactively, using counters related to

HSDPA code and radio bearer downgrades/releases.

2.

Proactive

monitoring


flag

Description

RNC_113a Average code tree

occupancy [%]

70 80 Average code tree occupancy

RNC_519b Min code tree

occupancy [%]

- - Minimum code tree occupancy

RNC_520b Max code tree

occupancy [%]

80 90 Maximum code tree occupancy

RNC_949b Spreading code

blocking rate in DL

[%]

5 >5 Spreading Code Blocking rate of a

cell over the reporting period. This

measurement is based on Cell

Resource Measurement, where thecode tree situation of a cell is

measured.

3. Reactive

monitoring


M1000C248-

258

DURATION OF

HSDPA xx(5-15)

CODESRESERVATION

It is possible to calculate the average number of

reserved SF16 codes for HSDPA, based on the

duration counters for each code (original transmitted xy(5-15) codes with QPSK or 16QA, M5000).

M1000C266 HSDPA CH CODE

DOWNGRADE DUE

The number of HSDPA channelization code

downgrades due to congestion of RT DCH requests. It

is updated when the code downgrade is started due to a


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TO RT [#] RT-over-HSDPA prioritization.

M1000C267 HSDPA CH CODE

DOWNGRADE DUE

TO NRT DCH [#]

The number of HSDPA channelization code

downgrades due to congestion of NRT DCH requests. It

is updated when the code downgrade is started due to

an NRT DCH-over-HSDPA prioritization.


BY PBS DUE TO

SPREADING CODE

CONGESTION [#]

The number of RB downgrades by priority-based

scheduling (PBS) due to spreading code congestion.


BY PREEMPTION

DUE TO

SPREADING CODE

CONGESTION [#]

The number of RB downgrades by pre-emption due to

spreading code congestion.


PRE-EMPTION DUE

TO SPREADING

CODE

CONGESTION [#]

The number of radio bearers released by pre-emption

due to spreading code congestion.


PBS DUE TO

SPREADING CODE

CONGESTION [#]

The number of radio bearers released by priority-based

scheduling (PBS) due to spreading code congestion.

4. Analysis

1. Average code tree occupancy

At the average code occupancy of 70%, code blocking can start to affect the QoS at the

level of 70%. At the level of 80%, service blocking can start.

2. Min code tree occupancy

The minimum code occupancy is 3%, when the common channels are active. When HSDPA

is active, but there are no users, the system reserves five codes, bringing the total

occupancy to 35%.

3. Max code tree occupancy

The user can use the Maximum code tree occupancyKPI as a triggering point to upgrade


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(second carrier). The occupancy ranges from 35% to 100%. When the maximum code

occupancy is less than 80%, the code allocation failure rate still remains close to 0% and

less than approximately 90% of maximum code occupancy means that the code allocation

failure rate is

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86233221 Radio Interface Capacity