8 OMO323000 BSC6900 GPRS EDGE Radio Network Optimization Problem Analysis ISSUE1.00

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GPRS EDGE Build-in PCU Radio Network

Optimization Problem Analysis

The formula of the TBF setup success ratio varies with the measured objects.

If the measured object is the air interface, the preceding formulas are used.

For uplink TBF assignment: If the first uplink data block from the MS is not received

at the network side after an assignment command is sent from the network side,

an uplink TBF setup failure due to no response from MS is counted.

All the preceding counters are cell-level counters. The system also supports BSC-level

counters as follows:

ZA9001: uplink GPRS TBF setup attempts within the BSC

ZA9004: uplink GPRS TBF setup failures due to no response from MS within the

BSC

ZA9201: uplink EGPRS TBF setup attempts within the BSC

ZA9204: uplink EGPRS TBF setup failures due to no response from MS within the

BSC

For particular values of the preceding counters, see the GPRS and EDGE traffic statistics.





If the measured object is the air interface, the preceding formulas are used.

For downlink TBF assignment: If no Packet Control Acknowledgement message

from the MS is received at the network side after an assignment command is sent

from the network side, a downlink TBF setup failure due to no response from MS is

counted.



ZA9101: downlink GPRS TBF setup attempts within the BSC

ZA9104: downlink GPRS TBF setup failures due to no response from MS within the

BSC

ZA9301: downlink EGPRS TBF setup attempts within the BSC

ZA9304: downlink EGPRS TBF setup failures due to no response from MS within

the BSC






If the measured object is the channel resources, the preceding formulas are used.

For uplink TBF assignment: If the network side sends an assignment rejection

message upon the channel request from the MS due to lack of channel resources

(including channels, TFI, and USF), an uplink TBF setup failure due to lack of

channel resources is counted.




ZA9003: uplink GPRS TBF setup failures due to lack of channel resources within the

BSC


ZA9203: uplink EGPRS TBF setup failures due to lack of channel resources within

the BSC






If the measured object is the channel resources, the preceding formulas are used.

For downlink TBF assignment: If the downlink TBF setup fails due to lack of

channel resources (including channels, TFI, and USF) at the network side, a

downlink TBF setup failure due to lack of channel resources is counted.




ZA9103: downlink GPRS TBF setup failures due to lack of channel resources within

the BSC


ZA9303: downlink EGPRS TBF setup failures due to lack of channel resources

within the BSC






If the measured object are the air interface and the channel resources, the preceding

formulas are used

For uplink TBF assignment: Both the uplink TBF setup failures due to no response

from MS and those due to lack of channel resources are counted as uplink TBF

setup failures.




ZA9002: uplink GPRS TBF setup successes within the BSC


ZA9202: uplink EGPRS TBF setup successes within the BSC






If the measured object are the air interface and the channel resources, the preceding

formulas are used.

For downlink TBF assignment: Both the downlink TBF setup failures due to no

response from MS and those due to lack of channel resources are counted as

downlink TBF setup failures.




ZA9102: downlink GPRS TBF setup successes within the BSC


ZA9302: downlink EGPRS TBF setup successes within the BSC





RL9A08: FER = ([L9A02: number of received out-of-synchronization frames] + [L9A03:

number of received check error TRAU frames]) x {100}/([L9A02: number of received out-of-

synchronization frames]+[L9A03: number of received check error TRAU frames] + [L9A01:

number of received normal TRAU frames] + [L9A07: number of received information TRAU

frames])

The number of received information TRAU frames equals the number of empty

TRAU frames.

1. In normal cases, the FER is lower than 10e-5 (that is, one out of ten thousand) and one

error frame occurs every four minutes in each channel. In this case, the link quality is high

and the MSs transfer data stably.

2. If the FER is lower than 10e-4 (one out of one thousand), one to three error frames

occur every minute and the link quality degrades. In this case, the affected MSs easily

suffer rate drop, longer transmission delay, or even call drops due to error frame bursts.




The transmission quality of the Abis interface can also be monitored through the

maintenance console.

Transport Resource RealTime Monitoring

This describes how to monitor the transmission resources on the Abis/Iub

interface






BERS Monitoring

This describes how to detect the BER seconds on an E1/T1 port to monitor

the transmission quality of the link corresponding to the port. If any bit

error occurs on the E1/T1 port, you can start this task to obtain data such

as BERS, critical BERS, unavailable seconds, frame errors, CRC errors. Based

on these data, you can evaluate the operating condition of the

transmission network and find out the causes for the bit errors in

combination with the performance of the peer end.






BER Monitoring

This function is used to monitor bit error rate (BER), thereby evaluating the

transport network quality.




L3188A: number of reported DELETE IND messages of the Abis interface

If the BTS deletes the IMM ASS CMD message sent by the BSC due to downlink

CCCH overload of the cell, the BTS reports a DELETE IND message to the BSC. This

counter is used to measure the number of the DELETE IND messages received by

the BSC from the measured cell.

L3188D: number of reported PACKET CCCH LOAD IND messages of the Abis interface

The BTS stores the paging messages sent through the downlink CCCH (PCH

channel) for circuit services and those for packet services in two different receive

buffer queues. If the length of either receive buffer queue exceeds the specified

threshold, it is indicated that downlink CCCH overload occurs. In this case, the

judges whether the overload is caused by excessive downlink packet services or

excessive circuit services. If the overload is caused by excessive circuit services, the

BTS reports a CCCH LOAD IND message to the BSC. If the overload is caused by

excessive packet services, the BTS reports a PACKET CCCH LOAD IND message to

the BSC. The BSC then forwards the PACKET CCCH LOAD IND message to the PCU.

This counter is used to measure the number of PACKET CCCH LOAD IND messages

received by the BSC from the BTSs within the measured cell.




Channel resources are insufficient in any of the following cases:

1. The cell is configured with a small number of channels when heave traffic of

packet services exists. As a result, the channels reach the maximum capacity of MS

multiplexing. To solve the problem, add more dynamic and static channels or set

the PDCH uplink multiplexing threshold in the PS domain channel management

parameters to a higher value.

2. Check whether the resources are insufficient because voice services preempt the

dynamic PDCHs. If counters A9343 (callbacks of dynamic PDCH) and A9344

(callbacks of loaded dynamic PDCH) record high values, in indicates that circuit

services preempt the channel resources of data services due to heavy traffic. To

solve the problem, add more dynamic PDCHs or set Dynamic Channel

Preemption Level to Control Channel Preemption Forbidden.

3. If the uplink GPRS TBF setup success ratio is low due to lack of channel

resources but the uplink EGPRS TBF setup success ratio is high, check whether the

GPRS channels are insufficient due to the configuration of dedicated or preferred

EGPRS channels. If dedicated or preferred EGPRS channels are configured, modify

some of them into common EGPRS channels and, if necessary, turn on the EGPRS

Downlink and GPRS Uplink Allowed switch.




If the air interface suffers severe interference, adjust the frequency points to improve the

quality of the air interface.




Answers:

Measurement report — interference band measurement (carrier)

Measurement report — full-rate channel Rx level measurement (carrier)

Measurement report — half-rate channel Rx level measurement (carrier)

Measurement report — Rx quality measurement (carrier)

Measurement report — radio link exception measurement (carrier)

Measurement report — measurement of TA-based distribution of radio link

exceptions (carrier)

Measurement report — measurement of TA-based RQI distribution (carrier)

Measurement report — RQI distribution measurement (carrier)

Measurement report — Rx quality distribution measurement (carrier)

……




When the radio environment is poor, the BLER is extra high and the uplink data blocks

cannot be decoded correctly at the network side if a high rate uplink coding scheme is

used.

If the uplink power control parameters are configured improperly, the MS supports low Tx

power and the uplink data blocks cannot be decoded correctly at the network side.

Other parameters that might be configured improperly are as follows:

Downlink reassignment attempts (affecting the downlink TBF setup): During the

setup process of a downlink TBF, the network side fails to receive a valid Packet

Control Acknowledge message on the reserved uplink RLC block and then re-sends

a downlink assignment message. This parameter specifies the maximum number of

downlink reassignment attempts. If the downlink reassignment attempts exceed

the value of this parameter, the network side releases the downlink TBF.

Polling retransmission times (affecting the downlink TBF setup): This parameter

specifies the maximum number of polling messages retransmitted by the network

side during the setup process of a downlink TBF.




Answers:

If a high rate uplink coding scheme is used, modify the default uplink MCS and the

maximum value of the counter N3101.

Inappropriate settings of uplink power control parameters: Modify the Alpha

parameter and the initial power class.

Inappropriate settings of other parameters: Modify the number of downlink

reassignment attempts and the number of polling retransmissions.

the Tx power of the BTS.




CQT: Call Quality Test

The CQT is often performed in a good radio environment where the C/I seldom

fluctuates. The CQT in idle hours can verify whether all NEs and transmission from

the Um interface to the Gi interface are faulty. In this case, the CQT reflects the

equipment performance directly and accurately. The CQT in busy hours can also

verify the performance of the resource (such as channels, Abis resources, and Gb

resources) management algorithms. The CQT in busy hours, however, features

randomness. For example, the tested downloading rate might be severely affected

if another subscriber is also downloading data during the CQT. In this case, the

CQT cannot reflect equipment performance accurately because the test results are

significantly related to the quantity of configured resources. Therefore, the CQT in

busy hours is used only for performance comparison before and after migration.




Differing from the CQT, the DT faces cell reselection and change of the coding scheme due

to C/I fluctuation (The link quality control algorithm achieves a compromise between

higher coding scheme and fewer retransmissions. The bandwidth of the air interface

changes as the coding scheme changes). Compared with downloading of large files, the

downloading of small files features severer influence brought by the slow start process

upon setup of the TCP connection. Therefore, to locate the cause for a low downloading

rate, download large files in idle hours at a place where the C/I is high.




Quality-of-experience (QoE) describes the system-level activities focusing on the joint

optimization of experienced multimedia quality and energy consumption in wireless

multimedia systems.




The figure on the left shows the Packet Downlink Assignment message, while that on the

right shows the Packet Timeslot Reconfiguration message.




To verify whether the channel resources are sufficient, check the channel configuration.

To verify whether the MS supports sufficient multi-slot capability, check the Packet

Resource Request massage for two-stage access or the 11-bit access request and Attach

message (for 8-bit one-stage access, the MS indicates its multi-slot capability in the Attach

request message) for one-stage access.

To verify out-of-synchronization, check the alarms by running the relevant commands. For

example, run the mt pdch show state <cell ID> all command to check the status of all

PDCHs in the specified cell if the external PCU is used. If the built-in PCU is used, run the

DSP PDCH command to check the channels status.

To verify whether the Abis interface resources are sufficient, check the idle timeslot

configurations.

To verify channel preemption of voice services, check the following traffic statistics:

R9343: callbacks of dynamic PDCH

R9344: callbacks of loaded dynamic PDCH

No channel preemption of voice services is detected during a test in idle hours.




Solutions to insufficient timeslots at the Abis interface:

If Flex Abis is not used, configure all Abis interface timeslots that are not

configured as idle timeslots.

Increase the multiplexing ratio of signaling links to improve the Abis transmission

capacity.

Use Flex Abis.

Expand the transmission capacity.

Solutions to bit errors at the G-Abis interface:

Transmission problems: Perform local loopback and remote loopback at the TMU

side to locate the problems.

Faults of the interface board




TU3: The speed is 3 km/h in typical urban scenarios.




Answers:

1. The figure in page 43 shows that the BLER/TS(%) parameter indicates the block

error rate calculated by the TEMS based on a certain number of received blocks.

2. For fixed MSs, the Packet Downlink ACK/NACK message also indicates the block

error rate.

The message shows that starting sequence number (SSN) is 64 and that a bitmap exists. This indicates that block 63 is not received. Check the blocks following block 64 (1 indicates that the block is received, while 0 indicates that the block is not received). The message shows that blocks 63, 65, 66, 68, 69, and 71 to 84 are not received.




If a large number of neighbor cells are configured, the block error rate often increases

because the MS needs to update the system messages of neighbor cells frequently.

According to the relevant protocol, the MS must decode the BCCH data of a new carrier in

30 seconds. If the signal strength fluctuates and a large number of neighboring cells are

configured, the MS has to parse the system messages of neighboring cells frequently. To

solve this problem, reduce the number of neighboring cells and eliminate unnecessary

neighboring cell configurations.




The system assigns only one bidirectional control channel for the MS. Therefore,

the same timeslot is occupied as the control channel in both the uplink and the

downlink. In this way, the control channel can be located.

The PDP context shows the contracted peak rate. As shown in the following figure,

the peak rate is 128000 octets/s = 128000 x 8/1024 = 1000 Kbit/s that exceeds the

theoretical maximum rate.

The LLC layer uses the unacknowledged mode, while the RLC layer used the acknowledged mode.

Best effort (BE) service whose peak rate exceeds 215 kbit/s




Loss of packet is not a necessary result of abnormal TBF release, because the PCU stores

the data that the MS has not transmitted and that the MS has transmitted without

acknowledgement within 30 seconds after the TBF is released exceptionally. Usually, the

MS initiates TBF re-setup soon. In this case, the TLLI remains unchanged. Therefore, the

context of the MS can be detected according to the TLLI and then the data stored by the

PCU is sent to the MS.

According to the TBF release process, the MS sets the FAI bit in the Packet Downlink

ACK/NACK message to 1 if the download TBF is released normally. The system sets the

FAI bit to 1 in the Packet Uplink ACK/NACK message if the uplink TBF is released normally.

To verify whether a TBF is released exceptionally, check whether the FAI bit in the relevant

message is set to 1. If the network side sends a Packet TBF Release message, the TBF is

released exceptionally (the TBF is released exceptionally because timer N3105 expires if the

cause value is normal release).

The abnormal TBF release decreases the rate because data transmission is not supported

during the abnormal release.




This problem often results from careless operations of the relevant test engineers. The

software applications and services (such as automatic update) that support automatic

connection to the network must be disabled during the test. If such software applications

or services are not disabled, the rate at the application layer decreases when they connect

to the network automatically.

How to identify the software applications and services that support automatic connection

to the network:

After the test, check whether all the packets captured by the Ethereal software are

the data interacted with the IP address of the server. If data interacted with

another IP address exists, enter the IP address into the IE to identify the connected

network.




8 OMO323000 BSC6900 GPRS EDGE Radio Network Optimization Problem Analysis ISSUE1.00

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