umts ps service analysis

UMTS PS Service Analysis

i

Contents

1 PS Service Data Transmission Analysis Method ........................................................................... 1

1.1 Data Collection .................................................................................................................. 1

1.1.1 DT/CQT Data Collection........................................................................................... 2

1.1.2 Collection of Other Data............................................................................................ 3

1.2 Data Analys is Method......................................................................................................... 4

1.2.1 Common Problem Analysis Method ............................................................................ 4

1.2.2 Typical NE Locating Method ..................................................................................... 6

2 Data Analysis ............................................................................................................................. 9

2.1 Basic Problem Analysis ...................................................................................................... 9

2.1.1 Access Failure.......................................................................................................... 9

2.1.2 No Traffic flow on the User Plane..............................................................................17

2.2 Problems of Data Transmission Performance ........................................................................26

2.2.1 Checking the Alarms................................................................................................28

2.2.2 Factors Affecting the Data Transmission at the lub Interface .........................................29

2.2.3 Comparison and Analysis of Operation Type ...............................................................30

2.2.4 R99 Problem...........................................................................................................32

2.2.5 HSDPA Analysis........................................................................................................38

2.2.6 Poor Data Transmission Performance at CN Side.........................................................59

1

1 PS Service Data Transmission Analysis Method

The upper layer of PS services includes FTP and HTTP services etc. Most services are

established over TCP protocol which is a reliable transmission protocol and

retransmission may occur. Retransmission will have great impact on the rate. If

parameters are improperly configured or packets are wrong or lost during the

transmission, data transmission rate will also be affected. The service quality can be

estimated by using the UE as the Modem, i.e. using UE + PC to dial. Therefore the

performance of the computer and server may also affect the data transmission. In this

case, first confirm whether the problem is caused by the network or other. Usually

methods such as exclusion, separation, and packet capture are used to locate and solve

the problem.

1.1 Data Collection

SGSN/GGSN

RNC

Node BUE

Server

Figure 1-1 End-to-end data transmission process

As shown in the above figure, data transmission optimization involves multiple NEs.

Therefore collecting complete information at different interfaces is important for

optimization and problem location. Data collection mainly includes OMC traffic

statistics collection, DT data collection, background tracking of NEs and end-to-end

data capture on the user plane. The most commonly used DT tools are ZTE CNT

network optimization tool, Qualcomm QXDM software and their corresponding

background analyzing tools of CNA and QCAT (APEX).


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1.1.1 DT/CQT Data Collection

Currently the DT/CQT is usually carried out using CNT and QXDM software

(connected to the UE, Scanner or GPS). Thus information such as pilot coverage,

signaling f low, DL BLER and UE transmission power can be obtained. Combining

with measurement tracking of users in OMC-R, UL BLER, DL code field transmission

power, UL receiving power and signaling flow at RNC side can be acquired. Use

CNA/QXTM/DT processing software to make comprehensive analysis based on data

collected by CNT, QXTM, and tracking record in OMC-R operation and maintenance

console.

Note: Time synchronization should be performed before data collection.

Information that should be collected is shown in the following table:

Table 1-1 Main Parameters that Should Be Collected through DT/CQT

Parameter Method Function

Geographic information

(longitude and latitude) CNT+GPS Record the track

Scrambling code, RSCP, Ec/Io of

cells in the active set CNT+UE Analyze the problem

UE Tx Power CNT+UE or QXDM+UE Analyze the problem and

export the report

UL BLER CNT+UE or QXDM+UE Analyze the problem and

export the report

Throughput in UL/DL application

layer and in RLC layer CNT+UE or QXDM+UE

Analyze the problem and

export the report

RRC, NAS signaling at UE side CNT+UE or QXDM+UE Analyze the problem

HSDPA CQI, HS-SCCH

scheduling success rate,

throughput at APP, RLC, MAC

layers.

QXDM+UE Analyze the problem and

export the report

HSUPA average SG, DTX%,

throughput at layers of APP, RLC

and MAC

QXDM+UE Analyze the problem and

export the report

UL BLER OMC-R Analyze the problem and

export the report

Tx code power OMC-R Analyze the problem and

export the report

RNC single user signaling OMC-R Analyze the problem

Chapter 1 PS Service Data Transmission Analysis Method

3

Parameter Method Function

tracing

Iub bandwidth OMC-B Analyze the problem

DL carrier transmission power

and non-HSDPA carrier

transmission power

OMC-R Analyze the problem and

export the report

DL throughput and bandwidth OMC-R Analyze the problem and

export the report

DL traffic volume OMC-R Analyze the problem

1.1.2 Collection of Other Data

Traffic statistics, DT/CQT and user complaints help to find faults. Apart from traffic

statistics and DT/CQT, other tools and their functions can be combined to analyze and

locate faults. Functions such as connection performance measurement and cell

performance measurement of RNC background tracking, alarm query, and status query

of NEs, and tools such as FlashGet, DU Meter can all help to locate faults. In PS

service test, to reduce the effect brought by TCP receive window of the application

layer, multi-thread downloading tool such as FlashGet is recommended and the thread

count is generally set to 5. For UL data transmission, multiple FTP processes can be

used for uploading.

Table 1-2 Data that Should Be Collected

Data Data collection

tool

Data

viewing/analyz

ing tool

Function Remark

Traffic statistics OMCR CNO

From macroscopic aspect,

monitor the network

running status and analyze

whether there is fault in the

network, and which NE has

faults.

DT/CQT testing

data

QXDM+UE/C

NT+UE QCAT/CNA Combining DT/CQT

measuring data and RNC

tracing data, make analysis

from the perspectives of call

process and coverage etc.

Connectivity

measurement,

cell

performance

OMCR

OMCR/

analysis

1.22.26/signali

ngCalDateRa

Refer to online

help on RNC O

& M console.


4

Data Data collection

tool

Data

viewing/analyz

ing tool

Function Remark

measurement

and RNC

signaling

tracing

e/runsignal

UESigStat

Alarms OMCR(OMC

B)

OMCR(OMC

B)

View the alarms and find

the abnormal NE.

Association log

Association

logs at RNC

background

Association

logs at RNC

background

It records abnormal call

history of all users, and

helps to locate the

Problem. Especially for

users’ complaints, the

problem can be located

through the analysis of

The association logs.

Upload or

download

software

FlashGet etc. null

Multi-thread downloading

to get the stable throughput

rate.

PS service test

assisted tool.

Rate monitoring

software DU Meter null

Make real-time monitoring

of the throughput rate of the

application layer, and record

total throughput, average

throughput rate and peak

throughput rate (the result

can only be recorded

through screenshots).

PS service test

assisted tool.

1.2 Data Analysis Method

1.2.1 Common Problem Analysis Method

When problems occur, make tracing of relevant equipment to make the problem recur,

and get the relevant information:

1. Collect configuration and alarm information of relevant equipment. If necessary,

get the traffic statistics of important tasks. Judge whether packets are lost and

retransmitted based on the existing information. Analyze whether there is data

transmission in the uplink and no data transmission in the downlink at SGSN side


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or whether there is great delay based on user tracing in SGSN. If the UE can’t be

located, use packet capture and exclusive methods to locate the problem.

2. PS data transmission problem mainly includes blocked data transmission,

interrupted data transmission and low data transmission rate. The universal

approach is to make tracing of related UEs or make packet capture at UE

interfaces so as to locate the problem.

3. Take low rate problem for example, it is typical and hard to be located. The

problem usually occurs when the PC accesses the network through the UE to

perform the FTP download or VOD services etc. The procedures to locate the

problem are shown below:

i. Start user tracing in the SGSN and GGSN (if the RNC has this function, initiate

the CDR function) and monitor and eliminate obvious faults in signaling plane

and user plane. Run packet capture tool (for example, Ethereal) in the PC

(connected to the UE), Gi interface or the server.

ii. After the service is stopped, analyze the captured PPP packets at Gi interface and

UE side. Monitor the UL and DL data flow and confirm whether there is packets

loss, retransmission, or out-of-order etc, which affects the rate. By data flow

comparison at different interfaces, judge which part brings the problem. (Use a

relevant tool to converts data packets of SGSN user tracing \ to files which can be

analyzed by Ethereal using a relevant tool. Refer to Commissioning Guide on

RNC User Plane in WCDMA End-to-end Data Transmission Optimization Guide).

To judge whether there is packet loss, check whether the number of UL and DL

packets captured at the UE side is consistent with that at the Gi interface. If it is

inconsistent, there must be packet lost in the WCDMA system. Analyze user

tracing in SGSN, that in GGSN and captured packets at Gi interface to see in

which NE there is incoming data packets but no outgoing packets. Then the NE in

which the packet is lost can be located. Use the relevant NE equipment fault

location method to locate the fault. If permitted, capture packets at Gn interface

and compare the captured packets at Gn and Gi to judge whether the packets are

lost at GGSM.

For data transmission rate problem, if the UL and DL packet number in the UE

and that at the Gi is consistent, there is no packet loss in the WCDMA system, and

the problem may be caused by large system delay. Capture packets at the UE and


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Gi sides, and make comparison of the UL delay and DL delay. If the delay is large

but less than 1.5 s, and the service is based on TCP protocol, enlarge the TCP

window and run the service again. If the delay is large and less than 1.5 s, and the

service is VOD (RTSP/UDP/IP), response will not affect the DL packet

transmission but may affect the VOD play effect; if VOD service is discontinuous,

set the buffering time to be longer. If the delay is larger than 1.5 s which is

considered to be too large, the problem may exist at RAN or CN side. If there is

no problem at RAN side, there may be problem at CN side. Conduct mirror packet

capture at Gn and Gi interfaces of the GGSN to judge whether there is large delay

at the CN side. By experience, if there is no hardware bug, the delay at the CN

side should be small.

If the packet number in the UL and DL of UEs and that at Gi is consistent,

conduct data packet capture at the UE side to check whether the retransmitted data

at Gi interface has been received, and whether the received packets are correct

(through TCP validation). If the packets are wrong, which is serious, locate the

problem using the method described in the following sections, or ask help from

the R & D engineers.

The above procedures are targeting at the low rate problems; the procedures to locate

data transmission problem are similar.

1.2.2 Typical NE Locating Method

Using the above exclusive method, the NE can be located. As described above, PS

networking (not including access network) mainly involves the following equipment:

the SGSN, GGSN, switch, router, and firewall. Use the following method to locate the

NE.

1. SGSN user plane

Of the equipment listed above, the SGSN is the relatively complicated equipment with

many interfaces, and the data transmission function of the user plane has its own

features. Generally, lu interface between the RNC and SGSN is the ATM port, and the

interface between the Gn and Gp is IP Ethernet port (FE or GE). The data packets of

the UL user plane is transmitted as below: the RNC sends the packets of the user plane

to the forwarding engine of the specified UHPU via the ATM (the IPOA to the RNC

has been created in the forwarding engine). If the IP address of this forwarding engine


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is the same with that of the destination of the data packet, the data packet will be

processed directly; otherwise, the forwarding engine will search for the route based on

the IP address of the data packet and send it to the destination forwarding engine (PDP

context is created on this forwarding engine). In

Figure 1-2, IPOA of the RNC is created in UHPU1, and user’s IP is created in UHPU2.

The SGSN conducts GTP processing, and then encapsulate the packets with the

destination IP address to be the IP address of Gn/Gp interface of the GGSN. Because

UHPU has routing function, and data packets can be directly sent to the Ethernet port

of the GFI board. Gn/Gp interface can also be the optical port, which is connected to

the router and then to other network equipment

EtherL

P

U

RNC

M

P

U

U

H

P

U

2

N

E

T

N

E

T

G

F

I

GGSN

Other SGSN

ATM

LPU-UHPU exchange data via 8850 NETGFI-UHPU exchange data via 8850NET

SGSN 8850 frame

U

H

P

U

1

Router

or

firewall

Router or

firewall

Figure 1-2 SGSN user plane

The procedures to handle the PS service problems relevant to the SGSN are:

Check that user tracing function is normal.

Confirm that PDP has been correctly created on the user plane.


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Check whether there is wrong statistics.

2. The packets are lost at GGSN.

If it is suspected that the packets are lost at GGSN, check it based on packet loss

statistics of the NP layer. The NP problem is caused by the product design; therefore

contact the product engineer to solve the problem.

3. Packet loss of data communication equipment.

Generally the current data communication equipment supports making packet loss

statistics. Execute commands to query the interface status, check the number of packets

received and sent to see whether there is any packet lost. It should be noted that the

packet loss of the data communication equipment does not indicate the equipment is

abnormal. For example, when filter ing rules are configured in the firewall,

unreasonable packets and attacking packets will be discarded. The configuration of the

equipment may lead to the loss of the correct packets. There are many data

communication equipment, please refer to their product command manual to see the

command to view the packet loss statistics.

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2 Data Analysis

Data analysis includes traffic statistics data analysis and DT/CQT data analysis.

Considering the practical demand of Network Planning and Optimization Dept., this

article mainly introduces the DT/CQT part. The data transmission problems of

WCDMA PS service falls into three categories in the aspect of phenomenon: access

failure (or dialing connection setup failure), successful access without the traffic flow,

and data transmission with low rate or great fluctuation. Different problems require

different analysis and handling processes.

General DT/CQT data analysis flow is shown as follows:

DT/CQT data analysis

Set up the PS service

successfully?

Data transmission

condition?

N

Y

No traffic flow on user plane

Low transmission rate and great fluctuation

Analyze the

problem of no

traffic flow on the

user plane.

Analyze poor data

transmission

performance.

Analyze data

transmission

interruption.

Data Transmission interruption

Analyze the

access failure.

Figure 2-1 Analysis flow of DT/CQT data

2.1 Basic Problem Analysis

2.1.1 Access Failure

There are two ways to launch the PS service. One is launching the PS service directly


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on the UE, and browsing the webpage and watching stream media through the UE

directly. The other is launching the service through personal computer in the method of

PC+UE, and using the UE as the Modem of the personal computer.

In the optimization test, the method of PC+UE is most commonly used. During the

DT/CQT test, the drive test tool software CNT runs on a personal computer, w hich is

usually a portable one. And this method is shortly called as CNT+UE. If the UE fails to

launch the PS service directly, the engineer can use the method of CNT+UE for further

verification to acquire more information. Therefore, the following problem analysis

focuses on CNT+UE.

2.1.1.1 UE directly launches the PS service

If the UE launches the PS service directly, the analysis flow of access failure is as

follows:

The analysis of access failure of the PS service launched by

the UE

UE fails to launch the PS servce directly?

N

Y

End

Analyze the access failure of the PS service launched in the

method of PC+UE

The PS service setup is a failure in the method of PC+UE?

Y

Check and modify the APN and the

webpage address setting of the UE.

N

Figure 2-2 Analysis flow of UE’s failure of launching the PS service directly

Chapter 2 Data Analysis

11

The process of launching the PS service directly on the UE and the process of

launching the PS service in the method of PC+UE are the same in the signaling flow,

but they have different APNs (name of the access point), and setting approaches of the

service visiting address. If the UE fails to launch the PS service directly, the engineer

can find the cause of the problem by taking the following steps.

1. Make verif ication in the method of PC+UE. If the PS service is normal, then the

system works normally. The engineer should check and modify the settings of

APN, service visiting address, Proxy and password of the UE.

2. If the access failure of PS service launched in the method of PC+UE happens, the

engineer should analyze and locate the problem according to section 2.1.1.2.

2.1.1.2 UE as the Modem of PC

If the UE is used as the Modem of the PC, the analysis flow of the access failure is

shown as follows:

The analysis of access failure

of the PS service set up in the

method of PC+UE

Port opening failure?

N

End

The signaling

process analysis

in the access

process

Access failure?

Y

YHandle the port

opening failure.

Y

Find the cause and solve the

problem?

Comparison and

analysis of the

operation type

N

N

Figure 2-3 Analysis flow of UE’s failure of launching PS service


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1. Port opening failure

The analysis flow of port opening failure is shown as follows:

Handling port opening failure

Is the status of the port in Windows

Hardware Manager abnormal?

N

End

Maybe the port is not closed

normally. Restart the CNT

and the PC.

CNT abnormal termination happened

before?

Y

Y

Y

Maybe the UE software is

abnormal. Restart the UE.

N

Check and confirm CNT PORT

Configuration.

Insert and extract the UE.

N

Solve the problem?

Reinstall the UE driver.

Figure 2-4 Handling flow of port opening failure

The main causes of the port opening failure:

i Incorrect Port Configuration in the CNT

The engineer should check the Port Configuration in the CNT, and make sure the port

No. corresponds to the Com port and the Modem port in the Windows Hardware


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Manager.

ii Abnormal port status

Wrong driver installation and abnormal termination of the drive test tool during the

test may cause the status of the port mapped by the UE to become abnormal in the

Windows Hardware Manager. For example, the yellow exclamation mark appears.

Solution: Reinstall the driver, insert and extract the data cable or data card of the UE.

iii The port is not closed after abnormal termination of the software

During the test with the drive test tool such as the CNT, the software terminates

abnormally and may not close the corresponding port.

Solution: The engineer can try to restart the CNT software. If the problem still exists,

restart the personal computer.

iv Something wrong with the UE software

Try to solve the problem by restarting the computer.

v Incomplete installation of the UE driver

It is necessary to reinstall the driver, and this problem usually happens when the

personal computer is connected with the UE for the first time.

2. The port is opened successfully, but the access is still a failure.

In this condition, the failure is usually caused by the signaling f low, and the analysis

should focus on the signaling flow during the access process. The analysis flow is

shown as follows:


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The signaling flow analysis

during the access process

End

UE does not send Service

Request?

N

N

RRC connection failure? Y Analyze the RRC connection failure.

N

Analyze the problem that the UE does not

send the Service Request.Y

Are the authentification and

encryption processes

abnormal ?

YAnalyze the authentification and encryption

problems

Is the PDP activation refused?

N

YAnalyze the problem that PDP activation is

refused

Is the RB setup process

abnormal?Y Analyze the abnormal RB setup

Comparison and

analysis of the

operation type

N

Figure 2-5 Signaling analysis flow of access failure

Trace the NAS and RRC signaling in CNT or trace the single-user signaling in the

OMCR, and analyze the problems according to the standard data service signaling flow.

The problems may be:

i RRC connection setup failure

[Description]

Problems appear during the RRC connection setup process (From UE sending the RRC

Connection Request message to RNC receiving the RRC Connection Setup Complete

message).

[Analysis]


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If the engineer finds that the UE does not send the RRC Connection Request message

from the RRC Message traced by the CNT, the possible causes may be:

The Modem port is not selected during port configuration in the CNT.

The Test Controller in the CNT is not set, or is set incorrectly.

The UE port is abnormal. Details can be checked in Port Opening Failure in the

earlier part of this guide.

If the UE does not receive any responses, or receives the RRC Connection Reject

message after sending the RRC Connection Request message, the possible causes are:

Poor coverage

Admission refusal caused by uplink/downlink overload

Illegal parameter setting

For the illegal parameter setting, the main scenario is described as follows: the uplink

subscription request of the PS service is beyond the capability of the UE, which leads

to the direct refusal from the RNC. After the RAB setup failure caused by the incorrect

parameter setting which is beyond UE's capability, SGSN will negotiate a new RAB

assignment again to launch a new RAB assignment, until the UE has the capability to

support the assignment, and finally the RAB assignment is finished.

For the users, PDP activation can be successful, and the actual maximum rate is the

maximum rate the UE can support. However, if even the minimum guaranteed bit rate

required by the QoS setting in the UE’s PDP activation request is beyond the UE’s

capability, although the network has negotiated a lower rate to accept the PDP

activation request of the UE, the UE will send a request of deactivating PDP when it

finds out that the rate negotiated by the network in the PDP activation accept request is

lower than the minimum guaranteed bit rate, and finally, the PDP activation cannot be

completed.

ii UE does not send the Service Request message.

[Description]

There is no Service Request message in the NAS message.

[Analysis]

The possible causes may be:


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UE does not open the PS function

Some UEs can be set to support CS, PS, or CS+PS. If the UE is set to support CS, the

PS service cannot be set up. And then it is necessary to check the UE setting, and

modify it to PS or CS+PS.

UE does not finish the registration in PS domain.

Viewing from the signaling flow, the engineer finds that UE receives the Attach Reject

message from the network side after sending the Attach Reject message. The CN side

engineer should check whether the PS service is supported in USIM card subscription.

iii Problems in the authentication and encryption process

[Description]

The signaling flow between NAS signaling Authentication AND Ciphering REQ and

RRC signaling Security Mode Complete is abnormal.

[Analysis]

The CN side engineer should check whether the authentication switch in the PS domain

of the core network is opened, and whether the cryptographic algorithm and integrity

protection algorithm of CS domain, PS domain and RNC of the core network are

consistent.

iv PDP activation is refused.

[Description]

The UE sends the Activate PDP Context Request message, but receives the Activate

PDP Context Reject message.

The problems fall into two categories. One is incorrect setting of APN and rate

limitation at the UE side and the other is the core network problem.

APN setting problem at the UE side.

If the cause value of the Activate PDP Context Reject message is missing or unknown

APN, the cause is usually that the APN setting is not in accordance with that of the CN

side. The engineer can check the APN setting at the CNT+UE side, and compare it with

the HLR APN. The APN setting method of CNT and UE can be checked in CNT

Online Help. The CN side engineer should check the user's APN at the HLR.

Rate setting problem at the UE side


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If the cause value of the Activate PDP Context Reject message is Service option not

supported, the cause is that the rate required by UE is higher than the subscription rate.

The engineer can check the required rate setting at the CNT+UE side, and compare it

with the HLR subscription rate. The CN side engineer should be clear about the user’s

subscription rate in the HLR. The current APN and applied rate can be checked in the

Activate PDP Context Reject message.

Core network problem

If there are other cause values, and the APN and rate limitation setting at the UE side is

correct, the problem may lie in the core network, for example, some interfaces of the

core network are not through. The engineer can work with other engineers in the PS

domain of the core network to locate the problem. What is more, if the PS service is

debugged for the first time, the problem may be caused by the case that the

subscription APN in the HLR and that used in the GGSN are different. The engineer

can ask the personnel in charge of the PS domain of the core network for confirmation.

v RB setup failure

[Description]

After the Activate PDP Context Request message is sent, the RB setup message such as

the Radio Bearer Setup message is not received, but the release message is received

instead.

vi Others

Refer to the method described in Section 2.2.3, Comparison and Analys is of Operation

Type and compare the relative parts one by one to narrow the problem range.

2.1.2 No Traffic flow on the User Plane

The PS service is set up successfully on the signaling p lane, but there is no traffic flow

on the user plane. The problem analysis flow is shown as follows:


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Analysis of no traffic flow on

the user plane

End

DCH DCH，E-DCH bearer judgment HSDPA

Find the cause of problem? Y

N

Analyze the problem

of no traffic flow on

the user plan at CN

side.

Y

Analyze the problem


user plane on the E-

DCH at the RAN

side.

Comparison and

analysis of

operation type

Find the cause of problem?

N

Solve the problem?

Use corresponding

method to solve the

problem?

Analyze the problem


user plane on the

DCH

at the RAN side.

N

Y

Figure 2-6 Analysis flow of no traffic flow on the user plane

2.1.2.1 Analysis of the Problem at the RAN Side

The successful setup of connection means there is traffic flow on the signaling plane.

But there is no traffic flow on the user plane, which may be caused by the TRB reset at

the RAN side. Especially for HSDPA, the service is borne on the HS-PDSCH, and the

signaling is borne on the associated DCH. When the HS-PDSCH does not have enough

power, there is traffic flow on the signaling plane, but no traffic flow on the user plane.

The following analysis is made from the two aspects of the PS service on the DCH and

the PS service on the E-DCH.

1. DCH Bearer


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Analysis of no traffic flow on user plane

on DCH at the RAN side.


N

End

OMCR tracing throughput

rate and bandwidth


N

Y

Analyze the problem of no

traffic flow on the user plane

at the CN side.

Y

Analyze the network coverage

Handle the problem or collect

information for feedback

Analyze whether there are

TBR reset at the association

log

Is the bandwidth normal?

Y

Figure 2-7 Analysis of no traffic flow on user plane at RAN side on DCH

i. Check the coverage

Trace the service cell pilot RSCP and Ec/Io in CNT+UE mode, and judge whether this

place is with poor coverage. If the RSCP is less than -100 dBm or the Ec/Io is less than

-18 dB, data service can hardly be finished.

Solution: If the RSCP is poor, improve the coverage angle to optimize it. If the


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RSCP is fine, but the Ec/Io is very poor, then the following checks are necessary:

Check the pilot pollution, and optimize the seriously polluted pilot.

Check the power configuration of the pilot channel, and the power is always

configured as 33 dBm.

Check and remove the outside interference.

ii. Check the call drop causes such as the TRB reset

Acquire the record of the associated log corresponding to the time point of the problem,

and check whether there is abnormal print near the time point of the problem to provide

the diagnostic message.

iii. Trace and measure the throughput rate and bandwidth of uplink/downlink.

Through monitoring the change of access layer rate and non-access layer rate of current

connected uplink/downlink data transmission, the engineer can analyze the dynamic

channel configuration function and the changing characteristic of the service source

rate conveniently. The engineer can locate the problem by checking which value is zero,

the uplink throughput rate or the downlink throughput rate. With the RNC DRBC

function open, the engineer should distinguish the bandwidth change caused by the

DRBC. If the engineer still cannot locate the problem, he needs to trace the user plane

and collect the number of the data packages received and sent by the RNC L2 and

GTPU to make sure the problem of no traffic flow on the user plane happens on the

uplink/downlink, at the CN side or the RAN side.

iv. Others

Check the problem at the CN side. Please refer to Section 2.2.3, Comparison and

Analys is of Operation Type for the operation method, and compare the relative parts

one by one to narrow the problem range. Then, make a feedback about the problem.

2. E-DCH bearer

The HSDPA feature of the cell is activated, and UE is able to support HSDPA. The rate

applied by the UE or the subscription rate is higher than the HSDPA threshold of

downlink BE service (for BE service), or the HSDPA threshold of downlink stream

service (for stream service). In this case, the PS service will be borne on the E-DCH,

and the engineer can check the following items.

i. The alarms and associated log in the RNC


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Check the alarms and the associated log record to see whether there is anything

abnormal at the time point of the problem, and provide the diagnostic information.

ii. Deactivate the HSDPA feature, and set up the PS service on DCH.

With DEA CELLHSDPA, the engineer activates the HSDPA feature of the cell, and

builds dial-up connection to set up the PS service on DCH. If the data transmission of

the PS service on DCH fails, please refer to the earlier section for the handling method.

If the data transmission of PS service on DCH is normal, the problem locates at

HSDPA, and the engineer should continue with the following steps.

iii. Check the CQI, HS-SCCH scheduling success rate, SBLER and whether GBR is

configured.

Trace and record the UE reported CQI, HS-SCCH scheduling success rate and SBLER

reported by the UE in QXDM+UM mode.

a) CQI

The UE estimates and reports the UE reported CQI on the base of Ec/Nt of PCPICH. If

the UE reported CQI is zero, the NodeB will not send any data to the UE. If the

parameter configurations of pilot Ec/Io, CellMaxPower, PcpichPower, and MPO

constant are normal, but the CQI is poor, the engineer can try to change the personal

computer. PCs with different model have different noise floors, which will influence

the reported CQI at certain degree.

b) HS-SCCH scheduling success rate

The engineer can observe the HS-SCCH success rate at the WCDMA HSDPA

Decoding Statistics dialog box and the WCDMA HSDPA Link Statistics window of

QXDM.


22

Figure 2-8 Example of dialog box showing the HSDPA parameter in QXDM

The HS-SCCH Success Rate (%) is the user’s HS-SCCH scheduling success rate which

is relative to the currently configured HS-SCCH channel number, accessed HSDPA

user number, and the scheduling algorithm parameter. If one HS-SCCH channel is

configured in the HSDPA cell, the RR scheduling algorithm is used, and all the

accessed UEs continue transferring data, then the HS-SCCH scheduling success rate of

every user is about the reciprocal of the HSDPA user number, which means all the

users share the resource of this HS-SCCH in time division.

If the user’s HS-SCCH Success Rate is about zero, then the use's data transmission rate

is about zero, which means there is no traffic flow on the user plane.

The possible reasons why the HS-SCCH Success Rate is about zero:

The MAX C/I scheduling algorithm is used, and there are more than one HSDPA


23

users accessed to this cell, with relatively low CQI.

The transmission power of the HS-SCCH is too low. Currently, the HS-SCCH

transmission power is configured as 2% of the total transmission power of the cell

in indoor scenario; and it is configured as 5% of the total transmission power of

the cell in outdoor scenario. If the transmission power of HS-SCCH is lower than

the standard mentioned above, there may be some troubles for UE to demodulate

the HS-SCCH.

There is no data to transfer on the application layer, and the engineer can confirm

this situation by checking the actual transmission data volume in RNC LMT by

choosing Connection Performance Measure -> Uplink Throughput rate and

bandwidth, Downlink Through rate and bandwidth.

The CQI reported by the UE is too low, which causes that the NodeB does not

schedule this user.

c) SBLER 100%

SBLER is the HS-DSCH block error rate. The above WCDMA HSDPA Decoding

Statistics dialog box shows the SBLER and retransmission conditions under different

TB, and in WCDMA HSDPA Link Statistics window, the HS-DSCH SBLER-Delta

and HS-DSCH SBLER-Average are shown, in which Delta is an instantaneous value,

and Average is an average value. The reason for the SBLER being 100% is that the

HS-PDSCH Ec/Nt is too low while the fundamental reason is that the HSDPA power is

not enough. The engineer can check the HSDPA power configuration which falls into

two categories: the static power configuration and the dynamic power configuration. If

this parameter is not less than the largest transmission power of the cell, this power

configuration is the dynamic configuration. Reversely, if this parameter is less than the

largest transmission power of the cell, this power configuration is the static

configuration. In the case of dynamic configuration, HS-PDSCH available power =

largest transmission power of the cell - power margin - R99 downlink load (including

common channel load) - HS-SCCH power; in the case of static configuration,

HS-PDSCH available = power of HS-PDSCH and HS-SCCH – HS-SCCH power.

From the above two formulate, in the case of dynamic configuration, the high power

margin configuration, or R99 downlink overload or high HS-SCCH power

configuration may cause the problem that the HS-PDSCH available power becomes too

low. In the case of static configuration, the insufficient power of HS-PDSCH and


24

HS-SCCH or excessive HS-SCCH power may cause the problem that the HS-PDSCH

available power becomes too low. The situation of SBLER being 100% caused by

insufficient power seldom happens, unless the CQI reported by the UE is too low. In

addition, the CQI calculated by the NodeB with insufficient power will be lower than

the normal value, and the TB scheduled by the NodeB will also be smaller than the

normal size. Therefore, the rate acquired by the UE will be reduced.

Solution: Correct the parameter configuration. If the R99 load is too high, the engineer

should consider carrier addition to solve the problem.

iv. Check the available bandwidth, the occupied bandwidth and the assigned

bandwidth of lub.

If the transmission data configuration is wrong, and the IMA group No.s of

AAL2PATH (for HSDPA) of the NodeB and the RNC are not corresponding to each

other, then the data transmission will not be through. If the product software problem

causes the problem that the HSDPA available bandwidth is insufficient, data

transmission will also be not through.

If the transmission configuration is in the ATM+IP mode, the HSDPA service is

transmitted in the IP mode, and the signaling is transmitted in the ATM mode, then the

FE interruption will cause the problem that the signaling can be transmitted, but there

is no traffic flow on the user plane.

2.1.2.2 Analysis of the Problem at the CN side

The problem at the CN side may be caused by the service server with problem, the

incorrect user name and password and so on.


25

Analysis of the problem of no traffic flow

on user plane at the CN side

Is it normal to use the service

through the LAN/other radio

networks?

N

End

Check the user name and the

password. Y

The CN side is normal.

Check whether the server

and service software operate

normally.

Figure 2-9 Analysis of the problem of no traffic flow on user plane at the CN side

The engineer can make sure that the service software server and the service software

runs normally through other access networks (or LAN).

1. LAN

Through the personal computer on the LAN, the engineer can perform the FTP or

HTTP service to make sure that the services are normal and verify the accessible user

name and password.


26

2. Other radio access networks in the same core network

Establish the PS connection on 3G access networks in the same core network or on the

GPRS, and then check whether the service is normal. If the engineer finds the service

server works normally after finishing the above step, he should analyze the problem at

the RAN side. If the engineer finds that the service server works abnormally, the

problem must lie in the CN.

i. HLR

One SIM card can be configured with multi APNs, and each APN corresponds to a

highest rate. When there is no maximum rate limit at the UE side, the RAB assignment

request message delivered by the core network carries the subscription rate of the user.

If there is no limit on the power, code resource and other resources at the RNC side, the

assigned rate will be sent to the UE through the Activate PDP content Accept message

in the NAS signaling, and the rate in the PDP activation acceptance can be viewed in

the QXDM or other drive test tools.

ii. GGSN

To modify the user’s QOS parameter on GGSN, the engineer should set the downlink

bit rate and guaranteed rate which are 384 kpbs by default. Set the maximum downlink

rate as 2048 kpbs, so that the CN allows the HSDPA downlink maximum rate to be 2

Mpbs.

iii. SGSN

The SGSN uses SET 3GSM to modify the user’s downlink maximum rate and

guaranteed rate to 2 M.

iv. Summary

The checking result shows that the cells have been established. Therefore problems at

the RAN side can be excluded. Then the engineer should check the HLR subscription

rate and the user’s QoS parameter of the SGSN and the GGSN at the CN side.

2.2 Problems of Data Transmission Performance

From the aspect of throughput rate measurement, the poor data transmission

performance is represented as unstable and low rate, and great fluctuation. From the

aspect of service quality, poor data transmission performance is represented as poor


27

stream media graphic quality, the need to buffer stream media and slow webpage

response. The PS data transmission path is shown in Appendix 8.1, and the PS data

mainly passes the internet service server, the GGSN, the SGSN, the RNC, the NodeB,

and finally arrives at the UE. During the transmission, the data passes five interfaces:

Gi, Gn, IuPS, Iub, and Uu. In this process, the internet server communicates with the

GGSN by the IP protocol, and there are one or more route equipment and firewall

between them. The PS service takes the AM mode of the RLC, and it is equipped with

the retransmission function. For the FTP and HTTP service, the TCP protocol, which

also has the function of retransmission, is used for communication. The parameters of

the two protocols (RLC/TCP) have great influence on the rate. If the parameters are

improperly configured, or packet error and packet loss happen during the transmission,

the data rate may be reduced. When observing the service quality, the engineer always

uses the application program on the computer with the UE as the MODEM to judge the

quality, then the performance of the computer and the server is involved. Therefore,

there are many factors affecting the PS data transmission performance, and these

factors fall in the categories of the access network problem, the core network

equipment problem, and the application and the service software problem. In this guide,

the application and service software problem and the core network equipment problem

are generalized as the problem at the CN side; and the access network problem is

referred as the problem at the RAN side.

The analysis flow of poor data transmission performance is shown as follows:


28

Analysis of the problem of

poor data transmission

performance

End

Find the cause of the problem?

Judge the RAN/CN problem？

Analyze the problem

of poor data

transmission

performance at the

CN side.

Comparison and

analysis of the

operation type


Solve the problem?

Check the alarm

N

Analyze the problem

of poor data

transmission

performance at the

RAN side.

RAN Problem CN Problem

Handle the problem with

effective measure.

Y

Y

Y

N

Figure 2-10 Analysis flow of data transmission performance problem

2.2.1 Checking the Alarms

After the problems appear, the engineer should check whether there is alarm appearing.

The alarms of the NodeB and the RNC at the RAN side, and the alarms of SGSN,

GGSN, LANSWITCH, ROUTER, FIREWALL and other NEs at the CN side should be

checked. The alarms of the clock problem, the transmission errors, the instantaneous

interruption of transmission and other abnormal conditions of the equipment may affect

the data transmission. If the engineer cannot locate the problem by alarms of NEs, he


29

should make comparison and analysis of the operation type, and try to screen out the

affecting factors and narrow the range of the problem. If the cause of the PS data

transmission problem can be determined to be at the RAN side, the engineer should

analyze the problem at the RAN side; If the service is established on the DCH, the

engineer should follow the procedures in section 2.2.4 “R99 Problem”; if the service is

HSDPA, the engineer should follow the procedures in section 2.2.5 “HSDPA Analys is”;

if the service is HSUPA, the engineer should follow the procedures in section. If the

cause of problem can be determined to be at the CN side, the engineer should analyze

the data transmission problem at the CN side. If the cause the problem cannot be fixed,

the engineer should analyze from both the RAN side and the CN side.

2.2.2 Factors Affecting the Data Transmission at the lub Interface

The Iub interface transmission error, delay jitter, and lub bandwidth problem will affect

the data transmission. The analysis flow is shown as follows:

Analysis of the factors

affecting data transmission at

the lub interface

Is there any alarm for abnormal

transmission/clock problem? Y Handle the problem.

End

N

Iub bandwidth congestion? YIncrease the

transmission resource.

N

Check the alarm.

Check the lub

bandwidth.

Figure 2-11 Analysis of the factors affecting the data transmission at the lub interface


30

1. Transmission error and delay jitter

The engineer can check whether the problem exists by checking the transmission alarm

and the clock alarm.

2. Iub bandwidth problem

The methods of checking whether lub congestion exists are shown as follows:

RNC probe and NodeB PM checking

Lub bandwidth performance checking

The abnormal record in the association log checking

2.2.3 Comparison and Analysis of Operation Type

Comparison and analysis of the operation type is to find out the NE on which the

problem happens, and tell where the cause of the problem is: the core network or

service software or the access network. The comparison includes the following

operations:

Changing the USIM card, the cell phone/data card and the PC;

Changing the webpage, gateway and the service mode;

Changing the networks in the same server, for example, 2G or other 3G networks

Table 2-1 Comparison and Conclusion

No. Operation Result Conclusion

1 Changing the USIM card

The data transmission

returns to normal.

The problem may relate to

the USIM card

subscription.


problem still exists.

The cause cannot be

located, and the engineer

should continue the

troubleshooting.

2 Changing the cell phone/data card


returns to normal.

This problem may relate

to UE, for example, the

compatibility or the UE

performance problem.

The data transmission The cause cannot be


31


problem still exists. located, and the engineer

should continue the

troubleshooting.

3 Changing the personal computer


returns to normal.

This problem may relate

to the drive program

installation, APN setting

in the personal computer,

rate limit setting and the

firewall.



The cause cannot be


should continue the

troubleshooting.

4

Changing the service in the same

server ( making sure that the

server is in the normal working

status, and trying the PING and

stream media service)


returns to normal.

The cause is the problem

at the CN side, and may

relate to the service

software.



The cause cannot be


should continue the

troubleshooting.

5 Changing the website (making the

download from other websites)


returns to normal.


at the CN side, and may

relate to the server

performance, TCP/IP

parameter or the service

software.



The cause cannot be


should continue the

troubleshooting.

6

Changing other access networks in

the same server, such as the GPRS

network.


returns to normal.


at the RAN side.



The cause cannot be

located.

7 Testing other NodeBs The data transmission

returns to normal.

This problem is caused by

the NodeB problem or the

improper configuration of

RNC parameters related

with the NodeB.


32




The cause cannot be

located.

What is more, for further troubleshooting, the engineer can send the data from the

upper level equipment to the UE for comparison.

Table 2-2 Packet Delivery Check and Conclusion


1 Delivering packets actively from

PDN to UE

The downloading returns

to normal

The cause is not CN and

RNC problem

The downloading problem

still exists

The cause is CN or RNC

problem.

2

Delivering packets actively from

RNC to UE.


to normal


at the RNC side.

The downloading problem

still exists


at the RAN side.

3 Delivering packets actively from

NodeB to UE


to normal


at the IUB interface.

If the engineer still cannot find out where the problem lies after making the comparison

and analysis according to the above operation step by step, he should analyze the

problems step by step in the sequence of the RAN side and the CN side.

2.2.4 R99 Problem

The analysis flow of the poor data transmission performance on DCH at RAN side:


33

End

Analysis of the problem of

poor data transmission

performance at the RAN

side.


N

N

Is there any alarm at NE? Y Handle the alarm.

Y Handle the problem.

Analyze the

factors affecting

the data

transmission at

the Uu interface.

Analyze the

factors affecting

the data

transmission at

the lub interface


N

Y Handle the problem.

Is the ratio of APP/RLC

throughput too low?Y

Check the TCP receiving

window and MTU setting.

N

Figure 2-12 Analysis flow of the problem of poor data transmission performance on the DCH at the

RAN side

2.2.4.1 Factors Affecting the Data Transmission at the Uu Interface (DCH)

If the PS service is on the DCH, the factors affecting the data transmission at the Uu

interface mainly include the allocated channel bandwidth, the state migration

occurrence and the error condition at Uu interface. The analysis flow is shown as

follows:


34

Analysis of the factors

affecting the data

transmission at the Uu

interface

Analyze the

bandwidth of the

DCH.

Analyze the error

at the Uu

interface.

Find the cause of the problem? Y Handle the problem.

End

N

Find the cause of the problem? Y Handle the problem.

N

Figure 2-13 Analysis of the factors affecting the data transmission at the Uu interface

1. DCH Bandwidth

When the PS service is on the DCH, RNC allocates certain channel bandwidth for

every accessed UE. The size of the bandwidth is decided by the spreading factor and

the coding method of the code resource. Open the uplink/downlink throughput and

bandwidth real-time measurement provided by the OMCR to see the uplink/downlink

bandwidth allocation and the throughput. Bandwidth shows the channel bandwidth of

UE allocated by the RAN, and DlThroughput is the actual downlink data transmission

rate. If bandwidth is the same as the rate when UE applies the PS service, or as the UE

subscription rate, or as the maximum rate in the case of DCH bearer, such as 384 k,

then the bandwidth allocation is normal, that is to say the allocation of code resource,

power resource and lub bandwidth is normal.

If the above measurement shows that the UE’s allocated bandwidth is lower than that


35

in expectation, there are two possible causes. One is that the channel with higher rate

cannot be allocated to the UE because of the congestion and other abnormal reasons,

which is an abnormal condition. The other is the DRBC algorithm of RNC. If the

parameter of the DRBC algorithm is reasonable, this rate decrease is normal. For the

current network, it is necessary to open the DRBC algorithm, so that the system can

reduce the allocated bandwidth to save the resource when the transmitted data is

reduced or the transmission is suspended temporarily. However, sometimes the

algorithm may be set improperly. According to the condition of the traffic volume,

coverage and soft handover, the rate can be adjusted through the DRBC algorithm.

Based on the on-site configured parameter, taking the algorithm into account, the

engineer should check whether the current bandwidth allocation and adjustment is

reasonable, whether there is anything abnormal and whether it is necessary to adjust

the parameter to solve the problem. For the low bandwidth caused by congestion and

other abnormal conditions, the engineer can make single-user tracing, check the

downlink load and code resource allocation and the size of the lub available bandwidth,

and acquire the corresponding association log to check the abnormal printing

information, then the clue of the problem can be found.

2. Error at the Uu Interface

The uplink/downlink error at the Uu interface directly affects PS throughput. If the

average values of the measured UL BLER and DL BLER during a certain period of

time are near or better than the BLER Target, the error condition at the Uu interface is

normal. Otherwise, it is necessary to analyze the factors causing the error at the Uu

interface.

DL BLER measurement: Use CNT+UE to collect the drive test file, and import CNA

analys is.

UL BLER measurement: click OMCR Connection Performance Measure -> Uplink

Transmission Channel Block Error Rate. Make comparison between the block error

rate and the CNT drive test file.

Power control and coverage are the main factors affecting the uplink/downlink BLER.

i. External loop power control switch

The engineer should make sure that the RNC external loop power control switch is

open.


36

ii. Coverage

The engineer should make sure that the uplink/downlink power is limited in the area

with poor UL BLER and DL BLER.

iii. UE performance

The engineer can try to change the UE, or compare the current UE and the UE of other

types.

3. In-sequence delivery

Setting the In-Sequence Delivery to TRUE or FALSE will affect the rate and

fluctuation of uplink data transmission. If the In-Sequence Delivery is set to TRUE,

RLC will keep the transfer order of the high-level PDUs. If it is set to FAUSE, RLC

entity which receives the data will allow the SDUs to be transferred to the high-level in

the order different from that of the sender, and then the uplink data transmission rate

will be low, with great fluctuation. It is suggested to set the In-Sequence Delivery to

True, and the setting can be modified in HLR of CN.

2.2.4.2 Comparison of the Throughputs on APP Level and RLC level

The engineer can acquire the throughputs on APP level and RCL level through

DT/CQT test.

If Throughput on APP level/ Throughput on RLC level is lower than the normal range

of theoretical analys is, it means the TCP/IP retransmission costs too much overheads.

TCP receiving window and MTU setting can be checked and modified.

2.2.4.3 Data Transmission Interruption Analysis

1. Phenomenon: Data transmission is interrupted for a period of time during the

transmission process.

2. Possible Reasons:

i. Call drop during the data transmission;

ii. The data transmission is interrupted after the handover from 3G to 2G;

iii. The state migration from CELL_DCH to CELL_FAC and CELL_PCH happens

during the data transmission. When the data transmission is recovered, the

systems cannot migrate back to CELL_DCH status, because the resource is not

enough. And the data transmission will be affected.


37

iv. Other abnormal conditions, such as transmission interruption

3. Analys is: The engineer analyzes this problem from the aspects of alarms,

signaling flow and association log.

Analysis of the data

transmission interruption

Is there any alarm? Y Handle the problem.

End

N

Is there any state migration?

N

Y

Analyze the problem that

the bandwidth can not

recover after the state

migration.

N

Is there any call drop? Y Analyze the call drop.

Is the data transmission

interrupted after the 3G/2G

handover?

N

YAnalyze the 3G/2G

handover

Figure 2-14 Analysis flow of data transmission interruption on DCH

i. Alarms

The engineer checks the alarms of CN and RAN NE, understands the abnormal

condition of the current system, and guide the problem analysis and troubleshooting.

The engineer can find out the problems such as the transmission interruption, the cell

clock asynchronizaiton and the NE congestion through the alarms.

ii. Signaling Flow

The data transmission problem location mainly depends on the signaling specific


38

analys is, for example, judging whether there is call drop, handover from 3G to 2G, and

channel state migration. There are two ways to collect the signaling: one is to use

CNT+UE to collect the signaling sent and received at the UE side, the other way is to

use the OMCR single-user tracing to collect the signaling sent and received at the RNC

side. Through the comparison of the signaling collected by the two ways, the engineer

can check whether there is message loss caused by the air interface with poor quality.

What is more, the engineer can take the association log into account to locate the

problem.

Call drop

Channel state migration

After the channel status is migrated to the common channel, the channel cannot

migrate back to the CELL_DCH status. The engineer can check the abnormal printing

of the association log to check whether the problem is caused by the downlink overload

or the lub bandwidth congestion. To solve the problem, the engineer can add the

carriers or the transmission resources.

Handover between 3G and 2G

The data transmission failure caused by the handover from 3G to 2G relates to the

coordination of the two networks. If the 2G network is HW’s network, the problem

location is even harder. Firstly, the engineer checks whether the PS service can be

normally set up on the 2G system. If the data transmission is normal when the 2G

network is accessed, and it becomes abnormal after the handover, then the engineer

should check the UE side, and the signaling flow at the 3G and 2G equipment. The

cause of the problem may be the unsuccessful update of the routing area caused by the

inconsistent cryptographic algorithm configuration of subscription and Authentication.

2.2.5 HSDPA Analysis

HSDPA schedules power and code resources among multiple users in code-division or

time-divis ion mode. Under the single-user condition (that is when there is only one

HSDPA user in the cell), the factors that affect data transmission rate are available

power for HSDPA, the number of HS-PDSCH codes (only one HS-SCCH channel is

needed under the single-user condition), the UE category (the maximum number of

codes supported by the UE and the availability of 16QAM support function), radio

signals at the location of the UE, the UE’s subscription rate, Iub bandwidth, and the


39

maximum rate supported by the RNC, NodeB, GGSN, and SGSN. Under the

multi-user condition, apart from the above factors, the algorithm used in the NodeB,

the number of HS-SCCHs configured for the cell will also affect the data transmission

rate.

2.2.5.1 HSDPA Working Process

1. The UE reports CQI on the HS-DPCCH, and the NodeB acquires the channel

quality of the location of the UE.

2. The scheduling module in Node B evaluates different UEs on the channel

condition, the data volume in each UE’s buffer area and the latest service duration

to determine the HS-DSCH parameters.

3. The NodeB sends the HS-DSCH parameters on the HS-SCCH, and then sends the

parameters on the HS-DSCH after 2 slots.

4. The UE monitors the HS-SCCH to see whether there is any information for itself.

If there is, then the UE starts receiving data from the HS-DSCH and then cache

the data.

5. According to information on the HS-SCCH, the UE can judge whether to integrate

the data received from the HS-DSCH with that in the soft buffer area.

6. The UE demodulates the data received from the HS-DSCH, and sends the

ACK/NACK in response to the uplink HS-DPCCH according to the CRC results.

7. If the NodeB receives NACK, it will resend the data until it receives ACK from

the UE or until the number of resending times reaches the maximum value.

2.2.5.2 Problem Analysis Process

To test the HSDPA performance of the system, we usually download big files in

5-thread mode from the FTP server and observe the downlink throughput rate. All the

abnormities described later in this article take place when the data at the service

resource is sufficient.


40

End

Analyzing poor data

transmission problem

at RAN side

Low Scheduled Rate

N

N

N

Is there any NE alarm? Y Handle alarms

YHandle the

problem

Low MAC Layer Rate

N

Y

Handle the

problem of high

SBLER

The throughput rate of

APP/RLC is too small?Y

Check the TCP

receiving window

and MTU setting.

N

Services based on

HSDPA?Y

Handle the

problem

Low Served Rate

N

Y

Handle the

problem of low

HS-SCCH

success rate.

Low RLC Layer Rate YHandle the

problem

N

Figure 2-15 Analysis process of poor data transmission performance on E-DCH

2.2.5.3 Whether Services are borne on HSDPA

Judge whether the services are based on HSDPA from the following aspects:

1. Whether the cell supports HSDPA: Check whether the HSDPA cell at the RNC

side has been activated, and whether the attribute of the local cell at the Node B

side has been configured to support HSDPA.


41

2. HSDPA services access failure will also cause the RNC to reconfigure HSDPA

services to 384 kbps as R99 services. Check whether the following configurations

are reasonable: the uplink and downlink load of R99 services, downlink code

resource, Iub transmission resource, the number of HSDPA services users, the

total rate threshold in the HSDPA cell, the guaranteed rate threshold and the

guaranteed power threshold of stream services.

3. The HSDPA threshold of downlink BE services is too high. The HSDPA threshold

of downlink BE services determines the rate decision threshold of the PS domain

Background/Interactive services on the HS-DSCH. Only when the maximum

downlink rate of the PS domain Background/Interactive services is not less than

this threshold, can the services be borne on the HS-DSCH; otherwise, they will be

borne on the DCH.

2.2.5.4 Locating Scheduled Rate Problem

During the NodeB scheduling process, TB size is decided by CQI, code, and power.

And TB size/2 ms are the scheduled rate. In the normal condition, scheduled rate and

the UE reported CQI are in a mapping relationship (which depends on the NodeB CQI

mapping table in practical use). Strictly speaking, because the NodeB will filter and

correct the UE reported CQI, in fact the scheduled rate may be in a mapping

relationship with the NodeB scheduled CQI, rather than with the UE reported CQI.

Therefore, the following table shows the corresponding relation between CQI and the

reference TB size according to the protocol 25.306, and the relation between CQI and

the scheduled rate can be worked out.

Table 2-3 CQI Mapping Table When UE Level is 11-12

CQI value Transport Block Size Number of

HS-PDSCH Modulation

Reference power

adjustment

0 N/A Out of range

1 137 1 QPSK 0

2 173 1 QPSK 0

3 233 1 QPSK 0

4 317 1 QPSK 0

5 377 1 QPSK 0

6 461 1 QPSK 0

7 650 2 QPSK 0


42

8 792 2 QPSK 0

9 931 2 QPSK 0

10 1262 3 QPSK 0

11 1483 3 QPSK 0

12 1742 3 QPSK 0

13 2279 4 QPSK 0

14 2583 4 QPSK 0

15 3319 5 QPSK 0

16 3319 5 QPSK -1

17 3319 5 QPSK -2

18 3319 5 QPSK -3

19 3319 5 QPSK -4

20 3319 5 QPSK -5

21 3319 5 QPSK -6

22 3319 5 QPSK -7

23 3319 5 QPSK -8

24 3319 5 QPSK -9

25 3319 5 QPSK -10

26 3319 5 QPSK -11

27 3319 5 QPSK -12

28 3319 5 QPSK -13

29 3319 5 QPSK -14

30 3319 5 QPSK -15

Table 2-4 CQI Mapping Table When UE Level is 1-6

CQI

value

Transport

Block Size

Number of

HS-PDSCH Modulation

Reference power

adjustment

0 N/A Out of range

1 137 1 QPSK 0

2 173 1 QPSK 0

3 233 1 QPSK 0

4 317 1 QPSK 0

5 377 1 QPSK 0

6 461 1 QPSK 0

7 650 2 QPSK 0

8 792 2 QPSK 0

9 931 2 QPSK 0

10 1262 3 QPSK 0


43

CQI

value

Transport

Block Size

Number of

HS-PDSCH Modulation

Reference power

adjustment

11 1483 3 QPSK 0

12 1742 3 QPSK 0

13 2279 4 QPSK 0

14 2583 4 QPSK 0

15 3319 5 QPSK 0

16 3565 5 16-QAM 0

17 4189 5 16-QAM 0

18 4664 5 16-QAM 0

19 5287 5 16-QAM 0

20 5887 5 16-QAM 0

21 6554 5 16-QAM 0

22 7168 5 16-QAM 0

23 7168 5 16-QAM -1

24 7168 5 16-QAM -2

25 7168 5 16-QAM -3

26 7168 5 16-QAM -4

27 7168 5 16-QAM -5

28 7168 5 16-QAM -6

29 7168 5 16-QAM -7

30 7168 5 16-QAM -8

The factors that affect the scheduled rate are CQI, HSPDA cell available power, and

HSDPA cell available codes. The analysis can be made from the following

perspectives:

1. CQI

i. Problem of low CQI

If the UE downlink rate is low, check whether the UE reported CQI is too low and at

the same time check the RSCP and Ec/lo of the PCPICH in the current cell. The

problem may be caused by:

The coverage is poor and the UE reported CQI is low.

Interference is relatively serious, the pilot is polluted, and the UE reported CQI is

relatively low.

If the HSDPA user changes cells frequently, he/she will be forbidden changing

cells as a punishment. Therefore the UE reported CQI will be low.


44

Poor receiving performance of some UE built- in antennas or UE individuality will

also cause low UE reported CQI and therefore affect rate.

ii. Solutions :

For the poor coverage problem, optimize RF or add sites to improve the UE

reported CQI.

For the serious interference problem, optimize RF to adjust the antenna directional

angle and the down tilt angle to provide a dominant serving cell.

For the problem of the frequent change of HSDPA cells, optimize RF to adjust the

antenna directional angle and down tilt angle or add sites to avoid frequent

handover. In addition, in our system, there is a timer (T1d), which defines the

punishment time between cell changes. This time is 4 seconds by default, but in

fact, this time is too long so that it affects the HSDPA throughput rate. Therefore,

the plan is to set it to 0 second or 2 second.

For the UE problem, it is suggested to exclude other problems before changing it.

2. HSDPA cell available power

If the available power for the HSDPA cell is too low, it will affect the TB size during

the NodeB scheduling process. HSDPA power can be configured in dynamic mode or

in static mode.

If HSDPA power is dynamic configuration, HSDPA available power = total power of

the cell x (1- power margin) - the power of R99 service channel and common channel.

Static configuration of HSDPA power means HSDPA available power is the initially

configured HSDPA power. However, the maximum power in practical use can only be

the result of the formula: total cell power x (1- power margin) - power of the common

channel. Please note that even in the static power configuration mode. R99 services

will take the power of HSDPA services because of the power control. Therefore, the

HSDPA power in practical use may not be the configured power.

The available power of HSDPA cells can be affected by the following factors:

i. HS-PDSCH MPO constant

The HS-PDSCH MPO constant can be modified in the RNC OMC. Under the

condition of HSDPA, the UE reports CQI, and according to the reported CQI, the

NodeB can judge the quality of the current radio link and adjust the TB size and the


45

power. When the UE reported CQI is less than 5, the NodeB will not send data to this

UE. And the MPO constant can adjust the UE reported CQI, which can be calculated

based on the pilot Ec/Nt. The formula is as follows:

UE reported CQI = (Ec/Nt)CPICH + 10*lg(16)+MPO+4.5

In the formula, 4.5 is a fixed constant which is obtained from simulation. 10*lg(16) is

the spreading gain used to calculate the HS-PDSCH (SF=16).

ii. HS-SCCH power

The HS-SCCH power can be configured in static mode or dynamic mode. In static

mode, the HS-SCCH power is configured to a percentage of the maximum emission

power of the cell. This percentage is 2.5% for now. In dynamic mode, the power of

the HS-SCCH can be adjusted dynamically.

3. HSDPA cell available codes

Configuration of SF for the downlink physical channel of HSDPA cells: While

configuring SF for the HSDPA cell, in addition to the common channels as for R99

cells, SF codes should also be reserved for the HS-SCCH (static configuration only)

and the HS-PDSCH (when code resource is allocated in static mode). For the

HS-SCCH, SF is fixed to 128, and for the HS-PDSCH, SF is fixed to 16. In this

condition, R99 users cannot take the code resource configured for HSDPA.

i. When the code resource is allocated in dynamic mode, usually the OMC will

assign the initial number of HS-DSCHs, the maximum number of HS-DSCHs and

the minimum number of HS-DSCHs. The number of HS-DSCHs occupied by

users should be between the maximum one and the minimum one. If more R99 CS

users need to access the network, they may take the HSDPA code resource.

ii. HSDPA accompanies the DCH code resource allocation. When a user applies the

high speed PS services, the system will bear the services on HSDPA. This user

occupies the HS-SCCH and the HS-PDSCH, and meanwhile when the services

are being established, the user will be assigned with an associated DCH (A-DPCH)

to transmit signaling at 3.4 kbps. This channel is a dedicated downlink channel

with SF256.

iii. If the codes allocated to HSDPA users are too few, the TB size scheduled by the

NodeB will also be affected.

4. HSDPA UE capacity


46

i. Protocol 25.306 specifies 12 categories of UE. In one TTI, different UE categories

obtain different maximum TB sizes. Therefore the maximum scheduled rate

obtained by the UE is different.

ii. In the message RRC Connection Setup Complete the UE will report its capacity.

The IE (information element) of HSDSCH physical layer category reflects the

UE’s ultimate capacity.

5. The data volume that can be scheduled by the UE is smaller than the largest TB.

The TB size scheduled by the NodeB depends not only on the UE available power and

codes, but also on the data volume that can be sent by the UE. If the data volume sent

by the UE is smaller than the largest TB, then the physical layer rate will be lower than

the expected value. This problem usually occurs when there is still data in the NodeB

buffer area, but the data volume is smaller than the largest TB that can be scheduled.

2.2.5.5 Locating Served Rate Problem

According to the formula: Served Rate = Scheduled Rate * HS-SCCH Success Rate,

when the scheduled rate is normal, low served rate is due to low HS-SCCH success

rate. Under the condition of single user, if the power and traffic volume of the

HS-SCCH do not have limit, the success rate of the HS-SCCH should be 100%. User’s

HS-SCCH success rate is related to the HS-SCCH power, the number of the HS-SCCH

channels, the number of users, scheduling algorithm, and the transmittable traffic

volume.

1. HS-SCCH power ratio

The HS-SCCH is a downlink common channel, which can be shared by all the users.

The UE keeps monitoring the UE ID on the HS-SCCH, and judges whether TTI directs

to itself. If it is, the UE will demodulate the HS-PDSCH data. Therefore, the HS-SCCH

must be correctly demodulated before data transmission.

2. Number of HSDPA users and number of HS-SCCHs

The success rate of the HS-SCCH is also related to the number of users. If there is only

one HSDPA user, no limit on traffic volume and the HS-SCCH power is enough, then

the HS-SCCH success rate of this user is nearly 100%. If there are multiple HSDPA

users in the cell, the HS-SCCH success rate of each user depends on the scheduling

algorithm and the number of HS-SCCHs. Usually, according to the HS-PDSCH

available power, code resource and the traffic volume at the traffic resource. it is


47

suggested to configure the HS-SCCH for UE level 12 in the following ways:

i. Configure 5 codes for the HS-PDS and two HS-SCCHs

ii. Configure 10 codes for the HS-PDSCH and three HS-SCCHs

iii. Configure 14 codes for the HS-PDSCH and four HS-SCCHs

3. Scheduling algorithm

Under the multi-user condition, the probability of each user being scheduled varies

from different algorithms. For instance, if the MaxC/I scheduling algorithm is adopted,

the user at distance will have less probability to be scheduled because its CQI is

relatively low; the probability can be 0 in this case. Scheduling algorithm is the

function of the HSDPA’s newly added function entity MAC-hs, which takes four

factors into account: CQI, length of the waiting time, priority in the queue, and length

of the queue. CQI indicates the signal quality of the UE location; length of the waiting

time (Wait_Inter_TTI) indicates the interval during which the UE waits for services.

The typical scheduling algorithms are listed below:

i. MaxC/I (taking only the CQI value into account)

ii. RR (taking only the length of waiting time into account)

iii. PF (Proportional Fair, taking all the factors above into account)

In terms of fairness, RR algorithm is the fairest way, and after it comes the RF

algorithm. Max_C/I are the most unfair way. In terms of the cell throughput rate,

MAX_C/I are the best algorithm, and PF comes after it. The worst one in this case is

the RR algorithm. In terms of commercial network, for the balance of fairness and

throughput rate, the RF algorithm is recommended. Because this algorithm takes into

account the user’s throughput rate history and the condition of channels. Operators can

choose whatever algorithm according to the actual situation.

4. Traffic volume

After parameters configuration check, if no problem is detected, the UE reported CQI

is relatively high, and neither power nor code resource nor transmission resource is the

bottleneck, but the user’s rate is still unstable, then through the UE’s HSDPA in the

PMS you can measure whether the data coming from Iub is sufficient to be scheduled.

The cause of insufficient data may be that the rate at the data resource is not stable, or

the download mode is single-line mode and meanwhile the TCP window configuration


48

is small.

5. Speed limit at UE side

The requested service type and highest downlink/uplink rate can be sent to the UE by

the command of AT, and the UE will send the information to the CN in the follow -up

signaling of Active PDP context request. When the subscription rate is not lower than

the maximum rate of this request, the CN will send RAB Assignment request at the

highest rate of the request sent in AT command. If there is no resource limit at the RNC

side, the service will be supplied at this rate. If the highest downlink rate in the RAB

assignment request is much lower than the scheduled rate, and the traffic volume in the

buffer area is insufficient to be scheduled by the NodeB, then the success rate of the

HS-SCCH will be low.

i. Setting rate by the command of AT

Click My computer -> Property (Management) -> Hardware -> Device manager

-> Demodulator -> Attribute -> Advanced, and enter AT command in the initial

command line. Apart from rate limit, usually it is also required to set APN in the AT

command. To set APN to cement, the rate limit to uplink 64 kbps, downlink 384 kbps,

the AT command should be as follows:

AT+cgdcont=1,"ip","cmnet"; +cgeqreq=1, 3, 64,384

ii. Cancel the rate limit by the command of AT

Set the rate to 0 by the AT command. That means not to apply specific rate. In this case,

the system will assign subscription rate only as possible.

AT+cgdcont=1,"ip","cmnet"; +cgeqreq=1, 3, 0, 0

6. Iub Bandwidth Limited (It is recommended to describe common problems like

bandwidth, alarm and configuration, which are not specific to DPA

independently.)

i. If the physical bandwidth of the Iub interface is limited, then the bandwidth of

AAL2PATH that can be obtained by HSDPA is small. As a result, the traffic

volume in the NodeB buffer area will be insufficient, and therefore the success

rate of the HS-SCCH will be low.

ii. If there are many R99 users in the cell, they will take the Iub bandwidth.

Therefore, the bandwidth of ALL2PATH that can be obtained by HSDPA will be


49

small. Although the R99 ALL2PATH and the HSDPA ALL2PATH are configured

separately, they share the physical bandwidth. That’s why the success rate of the

HS-SCCH will be affected.

iii. Peak traffic flow of typical E1 configurations

At present, most operators adopt the ATM (E1) transmission. The following table

shows the theoretical peak throughput rate under different typical E1 transmission

configurations at the Iub interface. (Suppose that the total bandwidth configured for the

NodeB AAL5 is 384 kbps, and the transmission efficiency of the Iub interface is 75 %.)

Table 2-5 Theoretical Peak Throughput Rate under Different Typical E1 Configurations at the Iub Interface

E1 number Total

bandwidth

(Kbps)

AAL5

bandwidth

(Kbps)

AAL2

bandwidth

(Kbps)

Theoretical

maximum

transmission rate

(Kbps)

1 1920 384 1536 1152

2 3840 384 3456 2592

3 5760 384 5376 4032

4 7680 384 7296 5472

5 9600 384 9216 6912

6 11520 384 11136 8352

7 13440 384 13056 9792

8 15360 384 14976 11232

Note: The theoretical bandwidth of one E1 is 2048 Kbps, which is equal to that of 30 DS0 standard channels. This

bandwidth is for dat a transmission. To control signaling and to perform synchronization, two non-standard channels of 64

kbps should be added. Therefore, an effective bandwidth for dat a transmission of an E1 link is 30/32*2048=1920 Kbps.

7. ACK/NACK/DTX repetition factor

The following physical layer parameters inform the UE (RB setup) and the NodeB (RL

reconfig ready) through signaling:

i. ACK/NACK repetition factor: N_acknack_transmit

ii. CQI repetition factor: N_cqi_transmit

iii. CQI feedback period: CQI Feedback Cycle k

After the UE demodulates the HS-PDSCH data, based on the CRC check result of

MAC-hs, the UE will send an ACK or NACK to the NodeB and resend


50

ACK/NACK information in N_acknack_transmit successive HS-DPCCH

subframes. If N_acknack_transmit is more than 1, in HS-DSCH+1 to n +

N_acknack_transmit - 1 subframes, the UE will not attempt to receive or

demodulate TBs from the HS-PDSCH. (n stands for the last HS-DSCH subframe

No. of the received block.) Because in the subframes from HS-DSCH n + 1 to n +

N_acknack_transmit - 1, the UE will not attempt to receive or demodulate TBs

from the HS-PDSCH, the UE acquired rate will become: (the UE rate when

ACK/NACK is not resent)*(1/N_acknack_transmit). Therefore, ACK/NACK

repetition factors can have great influence on the throughput rate of the UE. The

default configuration of the repetition factor is 1, which means resending is not

required.

CQI repetition factor means the number of the same CQIs that are sent

successively. This parameter will affect the real-time performance. For now the

default value of this parameter is 1.

CQI feedback cycle: This parameter is used to determine the time to send CQI. (When the

value is 0, the UE will not feedback the channel quality,) Because CQI takes 2 time slots

on the uplink HS-DPCCH, from some documents and other materials, the

configuration of this parameter will cause interference to the NodeB uplink

transmission. But from the actual test, compared with 2 ms, 8 ms feedback cycle

will not cause obvious interference. In our system, this parameter is set to be 2 ms

for now.

2.2.5.6 Locating MAC Layer Rate Problem

According to the formula: MAC Layer Rate = Served Rate * (1- SBLER), low MAC

Layer Rate is caused by high SBLER. In normal condition, when IBLER is set to be

10%, SBLER value tends to be lower than 15%. The factors that affect SBLER are as

follows:

1. IBLER

The setting of IBLER has a direct impact on the MAC-HS retransmission, which will

in turn affect user’s actual rate. IBLER mentioned here refers to the ratio of the number

of wrong TBs to the total number of TBs when the NodeB is sending new data. And

SBLER refers to the ratio of wrong TBs to the sum of wrong TBs and right TBs during

the transmission of new data and retransmission of data. The value of IBLER has a

direct effect on the value of SBLER.


51

At present, the default IBLER configuration is 10% (Target BLER is fixed in the code

and cannot be modified). IBLER configuration directly affects the power assigned to

each UE during the NodeB scheduling process, which, at this point, is similar to the

outer-loop power control of R99.

2. Low CQI and insufficient HSDPA power

If the UE reported CQI is low, and the available power for HSDPA is low, then SBLER

will be high. That is because one MAC-d PDU is 336 bits, and the TB size in

transmission is required to be bigger than 336 bits. As a result, CQI during the NodeB

scheduling process must be higher than a certain value to limit the IBLER at 10%.

3. UE reported CQI is higher than the actual value

When the UE reported CQI is higher than the actual value, the NodeB will make

adjustment according to the target IBLER value. However, the adjustment takes some

time, during this period, the NodeB will transmit data with low power according to the

UE reported CQI, which will result in high SBLER and thus affect the data

transmission performance.

4. Low configuration of pilot power

If the power of the other channels is 10 dB higher than the pilot power, there will be

10% error rate for HSDPA; if the power of the other channels is 13dB higher than the

pilot power, there will be 100% error rate for HSDPA. At present, the NodeB can make

some adjustment to power according to HSDPA SBLER. Therefore, if the power of the

other channels is 13 dB higher than the pilot power, the effect on throughput rate is

minor. However if the pilot power is configured too low, even after the NodeB

adjustment, the power still cannot be high enough, which will result in high SBLER

and thus affect the throughput rate.

2.2.5.7 Locating RLC Throughput Problem

The RLC AM uses “ACK/NACK acknowledgement” for ensuring reliable data

transmission, Sliding Window Protocol when performing the flow control.

Before the RLC receives the ACK/NACK messages, it can transmit the PDUs allowed

in the RLC send window. If the TX end can timely receive the ACK message, the

window will slide more quickly, and the allowable RLC TX rate will be larger.

Otherwise, the RLC TX rate will be smaller. The RLC may reset, and call drop

happens.


52

If the Scheduled Rate, Served Rate, and MAC Layer Rate are normal, check whether

the RLC Throughput is abnormal.

Relation between RLC Throughput and MAC Layer Rate:

RLC Throughput = MAC Layer Rate x (1 - MAC-hs PDU overhead proportion)

Since the proportion of overhead is small, the RLC Throughput approximates the MAC

Layer Rate.

If the RLC Throughput is obviously less than the MAC Layer Rate, it is abnormal.

1. High probability of ACK demodulated as NACK/DTX

ACK->NACK/DTX represents the proportion that the NodeB demodulates ACK as

NACK/DTX. Based on the simulation, the average ACK->NACK/DTX proportion

should be less than 1%. If the NodeB demodulates the ACK message as NACK/DTX,

it will retransmit the data which is already correctly transmitted to the UE. Then

resources will be wasted, and the UE rate will be reduced.

RLC Throughput ≈ (1 - ACK->NACK/DTX%) x MAC Layer rate (if the correctly

received blocks that are repeatedly transmitted are not counted)

i. Too low configuration of HS-DPCCH power parameters

The HS-DPCCH is the dedicated UL physical channel for transmitting ACK/NACK

and CQI signals of the physical layer. HS-DPCCH has no independent power control

mechanism, and it keeps certain power offset with the UL DPCCH. It can use different

power offsets when bearing different information. If the HS-DPCCH power offset

when bearing ACK/NACK is too low, the probability that the NodeB demodulates the

UL ACK as NACK/DTX will be high, thereby affecting the UE rate.

ii. Imbalanced UL and DL RLs in the handover area

Step1: Acquire the test data about the H <-> H handover in the whole network,

including the data at the UE and RNC sides.

Step2: Trace the signaling of a single UE, and check for the update of the serving cell

caused by UL RL Failure. If exist, check the UE APP Throughput at the corresponding

time.

Step3: Get the UL SIR, SIRtarget, UL BLER, DL throughput rate, PCPICH RSCP, and

EcNo information from the data at the RNC side. Draw all the information into one


53

figure, then you can get the SIR information in the UL associated channel.

Step4: Analyze the data acquired in Step2 and Step3 to check for imbalanced RLs in

the current network.

Step5: Locate the causes, and give the corresponding solution.

2. Impact from UL associated DCH power control

The impact of UL associated DCH power control to the rate of HSDPA users are

mainly in the following aspects:

i. The UL DCH power control does not converge, and the BLER is too high.

The HS-DPCCH has no independent power control mechanism, and it keeps certain

power offset with the UL DPCCH. If the UL DCH power does not converge, and the

BLER is too high, the HS-DPCCH power offset for bearing ACK/NACK is too low.

Then the probability that the NodeB will demodulate the UL ACK as NACK/DTX will

be high, and the RLC rate of the HSDPA users is too low.

ii. Both the TCP and RLC use the AM mode, therefore the ACK messages should be

transmitted on UL DCH.

The TCP can provide reliable transmission layer and it can confirm whether the

other end has correctly received the data through the ACK message. However,

both the data and acknowledge messages may be lost. To solve this problem, TCP

will trigger a timer when sending the data. If it fails to receive the ACK message

after the timer expires, it would retransmit the data. However, if the UL DCH

power control fails to be converged, and the BLER is too high, the TCP at the TX

end cannot receive the ACK message. Then it will retransmit the data, thereby

affecting the data transmission rate.

Similarly, the RLC also uses the AM mode. If the UL BLER fails to be converged,

which causes untimely response or no response of RLC ACK messages, the RLC

will retransmit the data after the waiting time expires. Then the data transmission

rate is affected. If the RLC still receives no response after several times of

retransmission, it will reset. The RNC send window can be set to 2047 maximally.

When the RLC TX rate is high and the state reports are not timely returned, the

RLC send window may be fully occupied, and no new data can be sent.

The UL BLER can be observed on the OMCR. Check the reasons that may cause the


54

power control convergence failure from the following two aspects:

Check whether the RTWP is abnormal, and whether the UL interference exists.

Check whether the outer loop power control parameters of the current services are

properly set, which mainly refers to the SIRTarget and BLERTarget parameters. In

addition, perform distance test for a single HSDPA user in an HSDPA single cell.

The UE may report favorable CQI at cell edges, though its rate is low or even zero.

This is mainly caused by UE UL power restriction, UL power control convergence

failure, and high UL BLER (even 100%).

3. AAL2 PATH configuration error

The configuration error refers to two conditions, one is that the configured bandwidth

at the NodeB side is larger than that at the RNC side, or the configured bandwidth is

larger than the physical bandwidth. Under both conditions, Iub packet loss may occur,

and the cell total throughput rate will be reduced.

4. High RLC retransmission rate caused by high residual BLER at the MAC layer

If the TB blocks are still not correctly transmitted at the MAC-E layer after the

retransmission time reaches the threshold, these TB blocks will be discarded. For the

RLC layer, this is packet loss. After the RLC RX end detects that some packets are lost,

it would require the TX end to retransmit the packets through the state report. The high

residual BLER of the MAC layer is usually accompanied with high SBLER at the

MAC layer.

Normally, the residual BLER (Res. BLER) of the MAC layer should be less than 1%.

Check the Res. BLER through QXDM, as shown in the following figure.


55

Figure 2-16 QXDM windows for checking residual BLER at the MACK layer

5. DL rate affected by UL rate restriction

Both the TCP and RLC use the AM mode, therefore the ACK messages should be

transmitted on UL DCH. The field test data shows that the TX rate for the feedback

information on the UL is 2% to 3% of the DL transmission rate. For example, when the

DL rate is 1.6 Mbps, the corresponding UL rate is 32 Kbps to 48 Kbps. When the DL

rate is 3.6 Mbps, the corresponding UL rate is 72 Kbps to 108 Kbps. However, if the

UL subscription rate is 64 Kbps, it cannot satisfy the DL data transmission demand. If

the HSDPA user also has the data transmission demand on the UL, three types of data

will be transmitted on the UL, which are the TCP confirmation data, RLC confirmation

data, and UL data of the user. In this condition, if the subscription rate is low, the DL

transmission will be impacted. Check the UL rate of the service through the RAB

assignment request information. If it is low, check the subscription rate in the HLR.

Check the actual UL bandwidth through the RB SETUP message.

6. Fully occupied RLC send window caused by abnormal RLC RTT (which can be

caused by improperly set TimerStatusProhibit and UL BLER convergence failure)

The RNC send window can be set to 2047 maximally (also the capacities of UE RLC

receive and send windows). When the RLC TX rate is high and the state reports are not

timely returned, the RLC send window may be fully occupied, and no new data can be

sent. For example, the rate at the air interface is 3 Mbps, and the MAC-d PDU size

equals 336 bit. Then the send window can maintain (2047 x 336)/ (3 x 1024) = 224 ms


56

of transmission. If the RNC fails to receive the state reports within 224 ms, the send

window will be fully occupied.

The time that the state reports are returned is related to the setting of

TimerStatusProhibit timer and the transmission quality of the UL air interface. If the

TimerStatusProhibit is set to a large value, or the UL BLER fails to be converged, this

problem will occur.

Solution:

Check whether the TimerStatusProhibit timer is set to the default baseline value. Check

the UL BLER convergence status, and ensure it is converged.

2.2.5.8 Locating TCP/IP Rate Problem

TCP/IP uses “inclusive acknowledgement” for ensuring reliable data transmission,

Sliding Window Protocol when performing the flow control, and congestion control

after detecting network congestion.

1. Flow control (sliding window)

It is used to prevent the problem that the buffer overflows or the buffer the portable

computer is completely full. It generates a window value for the TX end, the TX end

can send the byte number specified in the send window. After the transmitted byte

number reaches the threshold, the window will be closed, and the TX end has to stop

the transmission. The window will be reopened after the TX end receives the ACK

message from the RX end.

2. Inclusive acknowledgement

It is used to acknowledge all the transmitted bytes before the maximum byte No. For

example, 10 data packets are sent, which reach the destination out of sequence. The

TCP has to acknowledge the maximum continuous packets that are correctly received,

and it would only return the ACK message to the maximum byte No. after all

intermediate bytes are successfully received. If the ACK messages to the intermediate

bytes are not sent to the TX end, the timer at TCP of the TX end will expire, and the

TX TCP will retransmit the unacknowledged communication data.

3. Congestion control (overtime retransmission)

It can detect whether the network is congested by measuring whether the RTT delay is

overtime or by checking whether the TX end has received any repeated ACK messages.


57

Once it detects that the network is congested, it will trigger the congestion avoidance

algorithm (rate reduction and retransmission).

Therefore, factors that may affect the rate of the TCP/IP layer are as follows:

Configured TCP send/receive window

Though the size of receive window changes dynamically, which means actually

deployed window will be smaller after the RX end receives the disordered packets or

fails to forward the packets to higher levels, however, the configured window size has

determined the actual available receive window size.

Since Capacity (bit) = Bandwidth (b/s) x Round-trip time (s), if the receive/send

window size is too small, the TX rate will be affected.

Congestion caused by RTT fluctuation

You can acquire the APP and RLC throughput rate by DT/CQT tests.

If the APP throughput rate/RLC throughput rate is lower than the theoretical value, the

TCP/IP retransmission overhead is large.

2.2.5.9 Analysis of HSDPA Data Transmission Interruption

One RAB can be mapped only to the HS-DSCH of one cell, which means that it does

not support soft handover. Therefore data transmission will be interrupted when the

serving cell is changed.

The serving cell may be changed in the following scenarios:

1. Intra-NodeB: The transmission happens within one DSP of the NodeB, and no

data migration happens, therefore the data transmission will not be interrupted.

2. Inter-NodeB: The MAC-hs resets and the original buffer data of the NodeB is

discarded. The discarded data can be recovered through RNC RLC retransmission,

and the data transmission interruption duration is about 300 ms.

3. Intra-frequency & inter-frequency hard handovers: MAC-hs resets when the

serving cell is changed, and the NodeB discards the original buffer data. Though

the discarded data can be recovered through the RNC RLC retransmission, the

data interruption also happens.

4. Data transmission interruption may also happen during the H2D soft handover,

intra-frequency and inter frequency hard handovers, and D2H soft handover, etc.


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5. Data transmission interruption also happens during H to GPRS or GPRS to H

handovers.

The data transmission interruption can be divided into two types:

Serving cell remains unchanged or no handover happens.

Serving cell changes or handover happens.

Data transmission interruption happens when the serving cell remains unchanged or no

handover happens, and the possible causes are as follows:

Call drops or TRB resets.

Other problem appears, such as the breaking of transmission or complete of data

download.

Perform the following steps to locate the problem:

1. Check the alarms.

Check the alarms of different NEs of the CN and RAN to see the operating status of the

system. This can guide the troubleshooting. Check the alarms for transmission

interruption, clock synchronization failure, and NE congestion.

2. Check whether the download of the file is completed.

During the data transmission, if the data transmission is interrupted for a long period

and cannot be recovered, checked whether the FTP download is completed.

3. Check the signaling flow.

Analyze the signaling of the RNC and UE to check for call drops, H2H serving cell

changes, or H2D/D2H handovers. For the transmission interruption caused by call

drops, analyze the reasons of call drops.

4. Analyze the transmission interruption duration

There are two ways to measure the interruption duration.

Qualcomm QXDM+QCAT

Qualcomm QXDM+QCAT can measure the duration at the RX end (from the moment

that packets are discarded to the moment correct packets are received after the

retransmission). This duration is the data transmission interruption time.

Ethereal


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Use Ethereal to capture the TCP/IP packets, and analyze the transmission interval

between different TCP/IP packets.

Method one: By measuring the handover signaling one by one, you can directly get the

interruption duration. However, the result is not very accurate, and the measurement is

very laborious.

Method two : Obtain the interruption duration from the TCP rate figure, as shown in

Figure 2-17. This method is applicable to the scenario that few interruptions happen.

Figure 2-17 Interruption intervals in Ethereal TCP rate figure

From Method one: By measuring the handover signaling one by one, you can directly

get the interruption duration. However, the result is not very accurate, and the

measurement is very laborious.

We can see that two interruptions happen, and each lasts 300 ms.

2.2.6 Poor Data Transmission Performance at CN Side

2.2.6.1 Problem Analysis Flow

Figure 2-18 shows the analysis flow for poor data transmission performance at the CN

side.


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Analyze the poor data

transmission performance at

the CN side

End

Whether the operating system of the

server and test PC satisfy the

requriement?

Whether MTU is set to 1450

bytes?

N

Y

Y

Check service related issues,

such as service software, the

FTP uses Multi-thread

download method

Y

Whether the NE reports any

alarm?

Whether the TCP receive window of

the server and test PC is large

enough?

Y Handle the alarm

N

Change the operating system

to the one that meet the

requirement, e.g., the server

should be installed with

Win2000 Server

NSet the TCP receive

window to a large value,

such as 64 K

N Set MTU to 1450 bytes

Figure 2-18 Poor data transmission performance at CN side

2.2.6.2 Congestion Avoidance

The packet losses at the CN side will lead to RTT timeout, which will tr igger

congestion avoidance. The TCP can provide reliable transmission layer. One of its

functions is to acknowledge the message sent by the other end. However, both the data

and acknowledge messages may be lost. To solve this problem, the TCP will trigger a

timer when sending the data. If it fails to receive the ACK message after the timer

expires, it will retransmit the data. The TCP TX end will measure the RTT value, which

is the length of time it takes for a signal to be sent plus the length of time it takes for an

acknowledgment of that signal to be received, and will maintain an RTT timer. If the


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measured RTT has timed out, the TCP will think that the network is congested, and will

trigger congestion avoidance. Thus, the data transmission rate is affected. The IP packet

losses at the CN side will lead to RTT timeout.

2.2.6.3 Environment Issue

Rate is also related with the performance and the operating system of the computer, as

well as the installed application software, because the inner algorithm of the

application software and the TCP parameters of the operating system may have great

influence on the performance. Similarly, the PS data transmission rate of the computer

with WIN2000 operating system is better than that with WIN98 operating system.

Therefore it is recommended that the computer and server should be installed with

WIN2000 Pro and WIN2000 Server respectively or high versions. Because the portable

computer is usually installed with WINXP, the performance issue caused by the

operating system does not exist. However, the server should use WIN2000 Server

rather than WINXP, otherwise the data transmission will be serious ly affected. The

computer working as the UE background must be able to provide better performance. It

is verified that the IBM provides better performance when demonstrating the VOD. If

the CPU usage of the portable computer reaches 100% at the RX end, the TCP receive

window will be full. When the TCP receive window is full, the RX end will inform the

TCP TX end, and then the TCP TX end will stop the data transmission. As a result,

RLC BO is zero, the NodeB cannot perform the data scheduling, and the data

transmission performance is affected. Meanwhile, the performance of the server may

also affect the services, and this is another factor that we must consider.

2.2.6.4 TCP Receive and Send Windows

For services using the TCP protocol, such as VOD and FTP, the sizes of the TCP

windows on the test computer (as the Client) and the server have great influence on the

service. The window size is usually set to a large value to ensure good performance,

and the window sizes on the Client and the Server should be the same. Theoretically,

the TCP receive window should be larger than the product of bandwidth and delay.

Capacity (bit) = Bandwidth (b/s) x Round-trip time (s)

The 64-K window is sufficient for the HSDPA CAT12 1.6-MHz bandwidth, but it is

insufficient for the HSDPA CAT6 3.6-MHz bandwidth. Especially when the delay is

larger than 200 ms, the TCP window may be easily fully occupied. Then we will

observe that RLC and NodeB buffer is 0.


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Solution:

Set the TCP window size of the portable computer to 80 Kbytes.

2.2.6.5 Maximum Transmission Unit (MTU)

If there is one data packet to be transmitted at the IP layer, with its length larger than

that of the MTU at the link layer, then the IP layer will divide the packet into different

segments. Each segment is shorter than the MTU. To improve the transmission

efficiency, we should avoid the IP segmentation and regrouping and use a longer MTU

(usually does not exceed 1450 bytes). To modify the MTU length, modify the MTU at

the server and the portable testing computer. After the PS services are connected, the

Server and Client will negotiate about the MTU length. Then, the shorter MTU is used.

2.2.6.6 Service Related Problems

1. FTP

When selecting the FTP software, the commercial FTP is preferred. It usually provides

better services than the FTP software of the operating system. Besides, the FTP uses

the binary mode to download the data. Thus, you are advised to use the multi-thread

download software, such as FlashGet. If the upload rate is low, you can use multiple

FTPs to perform the transmission, or use the software to send the packets at a fixed rate

to test the bottom layer.

2. VOD

The maximum transmission rate of the RealPlay should be larger than 384 K, and the

buffering time should be short, for example, 3 s. As to some portable computers with

poor graphics cards, frequency hopping may appear. You can set the resolution ratio to

800 x 600 pixels. If the problem still exists, replace the graphics card.

3. NetTV

When the rate at the bottom layer is reduced, the performance of NetTV is hard to

recover. You must pay special attention to this point.

4. Video conference

The output rate of the video conference should be slightly less than the rate at the

bottom layer, otherwise packet losses will occur. For example, the rate for the NetTV

of one vendor is set to 128 K initially, which will be increased by 64 K every time.

Actually the recommended value for this NetTV is 320 K. If this rate is too low, the


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bandwidth cannot be fully used; otherwise, a rate higher than 320 K, such as 384 K or

higher, may lead to packet losses because the bottom layer cannot satisfy the demand.

Then the effect of video conference will be influenced. The lightning bolt on the upper

right corner of the screen indicates that there are some error codes or some packets are

lost during the transmission process.

umts ps service analysis

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