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

Figure 6:  Radio interface

Downlink PowerThe 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.

3. Reactive

Counter/KPI Name, unit Description

monitoring 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.

M1002C602 DL DCH This counter is updated when the HS-DSCH cannot be

SELECTED FOR STREAMING DUE TO HSDPA POWER [#]

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 DLThe 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 ACAdmission 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 downgradesCounters 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 PowerThe 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 the level 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 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-DCH established 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 level indicates an increase in interference in the cell.

2. Proactive monitoring

Counter/KPI

Name, unit Target

Red 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

Counter/KPI

Name, unit Description

M1000C147

RB DOWNGRADE BY PBS DUE TO INTERFERENCE CONGESTION [#]

The number of RB downgrades by priority-based scheduling (PBS) due to interference congestion.

M1000C159

RB RELEASE BY 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.

M1000C164

RB RELEASE BY 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 Access Failure Rate due to UL DCH [%]

HSDPA access failure rate due to the associated UL DCH.

4. Analysis1. Total Interference in UL

The primary indication for a highly loaded BTS.

2. Service RejectionsCounters 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 DCHAn increase in the HSDPA Access FR due to the UL DCH indicates 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 CapacityThe 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), and PCH. FACH and PCH are multiplexed into the same SCCPCH (see Figure 7 Common channels mapped to one SCCPCH).

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 PRACH preambles. There is no overload control algorithm for RACH, but the RACH load measurements are 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

Counter/KPI

Name, unit Target

Red flag

Description

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

Counter/KPI

Name, unit Description

- - -

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 carrier5. Using the 24 kbps Paging Channel feature if the PCH is loaded.

Channelization Code TreeThe 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 the cell. 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 cell’s 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 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

Counter/KPI Name, unit Targe Red Description

monitoring t flag

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 the code tree situation of a cell is measured.

3. Reactive monitoring

Counter/KPI Name, unit Description

M1000C248-258

DURATION OF HSDPA xx(5-15) CODES RESERVATION

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 TO RT [#]

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 RT-over-HSDPA prioritization.

M1000C267 HSDPA CH CODE DOWNGRADE DUE TO

The number of HSDPA channelization code downgrades due to congestion of NRT DCH

NRT DCH [#] requests. It is updated when the code downgrade is started due to an NRT DCH-over-HSDPA prioritization.

M1000C148 RB DOWNGRADE BY PBS DUE TO SPREADING CODE CONGESTION [#]

The number of RB downgrades by priority-based scheduling (PBS) due to spreading code congestion.

M1000C153 RB DOWNGRADE BY PREEMPTION DUE TO SPREADING CODE CONGESTION [#]

The number of RB downgrades by pre-emption due to spreading code congestion.

M1000C165 RB RELEASE BY PRE-EMPTION DUE TO SPREADING CODE CONGESTION [#]

The number of radio bearers released by pre-emption due to spreading code congestion.

M1000C160 RB RELEASE BY PBS DUE TO SPREADING CODE CONGESTION [#]

The number of radio bearers released by priority-based scheduling (PBS) due to spreading code congestion.

4. Analysis1. 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 occupancyThe 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 occupancyThe user can use the Maximum code tree occupancy KPI as a triggering point to upgrade (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 <1%. Therefore, the user can use the 85-90% limit.

4. HSDPA channelization code downgrades RT (NRT)This counter indicates the code tree congestion related to simultaneous REL99 and

HSDPA traffic in the cell. Because of congestion, the system frees the codes allocated to HSDPA, when required by the RT/NRT DCH allocation. Cells with HSDPA reserve a minimum of five SF16 codes for HSDPA at the start. If there is HSDPA traffic, and there is no need for R99 codes, the system will try to use up to fifteen SF16 codes for HSDPA. The RT traffic (normal voice) has the highest priority, so high voice traffic can keep the number of SF16 codes for HSDPA at the minimum of five codes.

5. Overload With the increase of code occupancy (that is, the R99 traffic increase) the throughput per user decreases.

6. Upgrade Two basic solutions for avoiding the effect of code congestion are:

1. Reduce the code usageReduce the initial R99 bit rate from 128 kbps to 64 kbps or even 16 kbps. Allow R99 NRT to take codes from HSDPA, for example, allow two SF16 codes to be taken. It is not recommended to enable the high rate features if there are no 15-code UEs in the network, or if there are other limits (for example, in the BTS or Iub).

2. Add new codes with new carrierTo obtain more codes, install an additional carrier.

= 6]> Id: 0900d805807a3fd0 ©2010 Nokia Siemens Networks

DN0972569