Post-processing of Drive Test Data &

Analysis of W-CDMA Networks (Internship Report)

SUBMITTED BY:

YOUR NAMEGraduate Student

INTRODUCTION:

First Generation and Second Generation Wireless Systems have enabled voice

communications to go wireless in many of the leading markets. But customers are

increasingly finding value in other services such as Text Messaging, Video and access to

Data Networks. Thus there is a huge demand for networks that support these services.

Third generation systems are specifically designed for enabling multimedia

communications.

Multimedia communication includes:

Person to person communication with enhanced high quality images and video.

Access to information on public and private networks.

High data rate access and new flexible communication capabilities

With such a high demand for 3rd Generation wireless communication networks, all

the telecom vendors are vying for a piece of the 3G Cellular Networks Market. Ericsson

is one of the vendors that is ahead of the race and is all set to launch Cingular’s

WCDMA based 3G Wireless Cellular Communication System.

During the course of internship at Ericsson the job description was to support the

Launch of Cingular`s WCDMA Network for the various markets.

Responsibilities included:

1) Processing Drive Test Data using Ericsson In-house Tools.

2) Ensuring that the generated KPI`s were accurate.

3) Analyzing Drop Calls and Call Setup Failures

4) Analyzing the ThroughPut for Packet Calls.

5) Running Macros on the Results to ensure proper results

6) Coordinating with Market personnel to ensure proper availability of Resources.

7) Support the development of Omega Tool by giving feedback on the tool to the

developers.

Introduction to 3G WideBand-CDMA Technology:

Worked on UMTS (Universal Mobile Telecommunication Systems) .UMTS is

based on WCDMA technology. WCDMA is called UTRA (Universal Terrestrial Radio

Access) FDD (Frequency Division Duplex) and TDD(Time Division Duplex).

SUMMARY of the Main Parameters of WCDMA:

WCDMA is a wideband Direct-Sequence Code Division Multiple Access(DS-

CDMA) system. The Duplexing method used is Frequency division duplexing/Time

division duplex ( the user information are spread over a wide bandwidth by multiplying

the user data with quasi-random bits).Thus in order to support very high bit rates upto

2Mbps, the use of a variable spreading factor and multicode connections are supported.

The Chip rate of 3.84Mcps is used which leads to a carrier bandwidth of approximately 5

MHz . WCDMA supports two basic modes of operation: Frequency Division

Duplex(FDD) and Time Division Duplex(TDD).

FDD Mode: A separate 5MHz carrier frequencies are used for the uplink and

downlink respectively.

TDD Mode: Only one 5MHz is time shared between the uplink and downlink.

Uplink is the connection from the mobile to the base station, and downlink is that from

the base station to the mobile.

WCDMA supports the operation of asynchronous base stations, so that there is no

need for a global time reference such as GPS. Deployment of indoor and micro

base stations is easier when no GPS signal needs to be received.

WCDMA employs coherent detection on uplink and downlink based on the use of

pilot symbols or common pilot.

WCDMA air interface has been crafted in such a way that multi-user detection

and smart adaptive antennas can be deployed by the network operator as a system

option to increase capacity and/or coverage.

WCDMA is designed to be deployed in conjuction with GSM. Therefore

handovers between GSM and WCDMA are supported in order to be able to

leverage the GSM coverage for the introduction of WCDMA.

1.2 Generic Principles of WCDMA operations:

1.2.1. Spreading and De-spreading:

User data is assumed to be a BPSK-modulated bit sequence of rate R, the user

data assuming the values of +1or -1.The spreading operation, is the multiplication of each

user data bit with a sequence of 8 code bits, called chips. Thus the resulting spread data is

at the rate of 8*R and has the same random appearance as the spreading code. Here the

spreading factor is considered to be 8. This wideband signal would then be transmitted

across a wireless channel to the receiving end.

During de-spreading we multiply the spread user data/chip sequence, bit duration

by the bit duration, with the very same 8 code chips as we used the spreading of these

bits. Thus the original user bit sequence has been recovered perfectly, provided we have

the perfect synchronization between the spread user signal and the de-spreading code.

Fig 1: Spreading and De-spreading

1.2.2. Multipath Radio Channels:

Radio propagation in the land mobile channel is characterized by the multipath

reflections, diffractions and attenuation of the signal energy. These are caused by natural

obstacles such as buildings, hills etc which results in so-called multipath propagation.

There are two effects resulting from multipath propagation .

1) The signal energy may arrive at the receiver across clearly distinguishable

instants. The arriving energy is smeared into a certain multipath delay profile.

2) Also for a certain time delay position there are usually many paths nearly equal in

length along which the radio signal travels. This may result into signal

cancellation which is called fast fading. Thus the signal power may drop

considerably 20-30 dB when phase cancellation of multipath reflection occurs.

Fig 2: Multipath Propogation

1.2.3. Rake Receiver Principle:

The delay dispersive energy is combined by utilizing multiple RAKE fingers

allocated to those delay positions on which significant energy arrives.

Each RAKE finger tracks a different multipath component

– Also used to track other cells during soft handover

Sliding correlator used to obtain a correlation peak for each multipath

component

– 1 to 2μs delay between multipaths in urban/suburban

1 0

2

3

– 20μs delay in rural/hilly

– Most RAKE receivers can handle up to 30μs delay

Searcher finger is used to measure other cells

– Used to determine when to perform handovers

1.2.4. Different type of Handovers:

Hard Handover:

Hard handover means that all the old radio links in the UE are removed before the

new radio links are established. Hard handover can be seamless or non-seamless.

Seamless hard handover means that the handover is not perceptible to the user. In

practice a handover that requires a change of the carrier frequency (inter-

frequency handover) is always performed as hard handover

.

Soft Handover:

Soft handover means that the radio links are added and removed in a way that the

UE always keeps at least one radio link to the UTRAN. Soft handover is

performed by means of macro diversity, which refers to the condition that several

radio links are active at the same time. Normally soft handover can be used when

cells operated on the same frequency are changed.

Softer handover:

Softer handover is a special case of soft handover where the radio links that are

added and removed belong to the same Node B (i.e. the site of co-located base

stations from which several sector-cells are served. In softer handover, macro

diversity with maximum ratio combining can be performed in the Node B,

whereas generally in soft handover on the downlink, macro diversity with

selection combining is applied.

2. UMTS Radio Access Network Architecture:

2.1. System Architecture:

The System architecture consists of logical network elements and the interfaces.

The network elements are grouped into Radio Access Network(RAN,UMTS Terestrial

RAN=UTRAN) that handles all radio-related functionality and the Core Network which

is responsible for switching and routing calls and data connections to user and radio

interfaces.

UMTS network elements consists of sub-networks and it is possible to have

several network elements of the same type so UMTS system is called modular. Thus

having sub-networks , are distinguished from each other with unique identities. Such a

network is called UMTS PLMN(Public Land Mobile Network) ..Typically one PLMN is

operated by a single operator and is connected to other PLMNs as well as to other types

of network, such as ISDN, PSTN, the internet .

The network elements in a PLMN are shown in the figure as follows:

Fig 3: Network elements in a PLMN

The brief description of the network elements is described as follows:

2.1.1. UE: The UE consists of two parts

The Mobile Equipment (ME) is the radio terminal used for radio communication

over the Uu interface.

The UMTS Subscriber Identity Module (USIM) is a smartcard that holds the

subscriber identity, performs authentication algorithms, and stores authentication

USIM

ME

Node B

Node B

Node B

Node B

RNC

RNC SGSN

GMSC

HLR

GGSN

PLMN, PSTNetc

Internet

UEUTRAN CN

External Networks

MSC/VLR

and encryption keys and some subscription information that is needed at the

terminal.

2.2.2. UTRAN: The UTRAN consists of two distinct elements:

The Node B converts the data flow between the Iub and Uu interfaces. It also

participates in radio resource management.

The Radio Network Controller (RNC) is the service access point for all services

UTRAN provides the CN.

2.1.3. HLR: (Home Location Register) is a database located in the user’s home system

that stores the master copy of the user’s service profile. The service profile consists of,

for example, information on allowed services, forbidden roaming areas, and

supplementary service information such as status of call forwarding and the call

forwarding number. It is created when a new user subscribes to the system, and remains

stored as long as the subscription is active.

2.1.4. MSC/VLR(Mobile Services Switching Centre/Visiting Location Register) is

the switch (MSC) and database(VLR) that serves the UE in its current location for circuit

Switched(CS) services. The MSC function is used to switch the CS transactions, and the

VLR function holds a copy of the visiting user’s service profile as well as more precise

information on the UE’s location within the serving system.

2.1.5. GMSC(Gateway MSC) is the switch at the point where UMTS PLMN is

connected to external CS networks. All incoming and outgoing CS connections go

through GMSC.

2.1.6. SGSC(Serving GPRS(General Packet Radio Service Support Node)

functionality is similar to that of MSC/VLR but is typically used for packet switched(PS)

services. The part of the network that is accessed via the SGSN is often referred to as the

PS domain.

2.1.7. GGSN (Gateway GPRS Support Node) functionality is close to that of GMSC

but is in relation to PS services.

The external networks can be divided into two groups:

2.1.8. CS networks: These provide circuit-switched connections, like the existing

telephony service. ISDN and PSTN are examples of CS networks.

2.1.9. PS networks: These provide connections for packet data services. The internet is

one example of a PS network.

Interfaces in UMTS system:

2.1.10. Cu interface: This is the electrical interface between the USIM smartcard and

ME.

2.1.11. Uu interface: This is WCDMA radio interface.The Uu is the interface which the

UE accesses the fixed part of the system.

2.1.12. Iu interface: This connects UTRAN to the CN.

2.1.13. Iur interface: The open lur interface allows soft handover between RNCs from

different manufacturers

2.1.14. Iub interface: The Iub connects a Node B and an RNC.

2.2 UTRAN Architecture

UTRAN consists of one or more Radio Network Sub-systems (RNS). An RNS is

a sub-network within UTRAN and consists of one Radio Network Controller (RNC) and

one or more Node Bs. RNCs may be connected to each other via an Iur interface. RNCs

and Node Bs are connected with an Iub interface.

The radio Network Controller: The RNC is the network responsible for the control of

radio resources of the UTRAN. It interfaces the CN (normally to one MSC and one

SGSN) and also terminates the RRC (Radio Resource Control) protocol that defines the

messages and procedures between the mobile and UTRAN.

2.3 Channels:

2.3.1.Downlink Logical Channels(L3:

a) Control Logical Channels:

BCCH(Broadcast Control Channel): Broadcasts cellsite and system

information to all UE

PCCH(Paging Control Channel): Transmits paging information to a UE when

the UE’S location is unknown.

CCCH(Common Control Channel): Transmits control information to a UE

when there is no RRC Connection

DCCH( Dedicated Control Channel): Transmits control information to a UE

when there is a RRC connection.

b) Traffic Logical Channels:

CTCH(Common Traffic Channel): Traffic channel for sending traffic to a

group of UEs

DTCH(Dedicated traffic Channel): Traffic Channel dedicated to one UE.

2.3.2. Downlink Transport Channels (L2):

a) Common Transport Channels:

BCH(Broadcast Channel): Continous transmission of system and cell

information

PCH (Paging Channel): Carries control information to UE when location is

unknown.

PICH (paging indication channel): Pending activity indicated

FACH (Forward Access Channel): Used for transmission of idle-mode control

information to a UE.

b) Dedicated Transport Channels:

DCH(Dedicated Channel): Carries dedicated traffic and control data to one

UE .Used for BLER measurements.

2.3.3. Downlink Physical Channels (L1)

a) Common Physical Channels:

P-CCPCH Common Control Physical Channel (Primary): Broadcasts cell site

information. Timing reference for all DL.

SCH (Synchronization Channel): Fast Synch. Codes 1 and 2: time-multipleded

with P-CCPCH.

S-CCPCH Common Control Physical Channel(Secondary): Transmits idle-

mode signaling and control information to UEs.

CPICH: Common Pilot Channel.

b) Dedicated Physical Channels:

DPDCH: Dedicated Downlink Physical Data Channel

DPCCH: Dedicated Downlink Physical Control Channel: Transmits connection-

mode signaling and control to UEs.

c) Indicator Physical Channels:

AICH: (Acquisition Indicator Channel): Acknowledges that BS has acquired a

UE Random Access attempt.

AP-AICH(Access Preamble Indicator Channel): Acknowledges that BS has

acquired a UE Packet access attempt

CD/CA-ICH: Confirms that there is no ambiguity between UE in a Packet

Access attempt. Optionally provides available Packet Channel assignments

CSICH: Broadcasts status information regarding packet channel availability.

3. Description of the software used at Ericsson:

Responsible for Austin Market for the post processing of Scanner data and UE

information which were being used for the initial tuning of the Cingular UMTS network

and is due to be launched in December 2005.

The Austin market basically used to give me Clusters in the form of log files.

These log files contained the drive test information collected by the Drive test engineers.

There were two types of drive one was Voice Drive (AMR loaded) and Packet Drive (PS

loaded). In Voice Drive there were long calls and short calls. Short calls were made for

30 seconds approximately and long calls were calculated from 30 minutes to 1 hour.

Voice Drive consists of information regarding call setup, call set-up timing,

dropped call, time for the call, end messages, layer3 messages, event data information,

scanner data, BLER, EC/Io, Ec, RSCP.

These log files were exported into FMT files with the help of TEMS Investigation

Version 6.0 Software. The details what the TEMS investigation Ver 6.0 Software is as

below,

3.1. TEMS Investigation 7.0 version :

It is a leading air-interface test tool for UMTS networks.

The tool allows operators to monitor radio parameters, speech quality and decode air

interface messages efficiently and easily.

TEMS Investigation tool is used to

1) Track poorly defined neighbor relations

2) detect a wide range of radio network configuration errors.

3) Simulate and verify network changes

4) Decode Layer 3 messages and display network data on map line charts or status

monitor.

5) Identify coverage, quality and capacity measurements

6) Perform system testing

7) Perform fault-tracing and troubleshooting

8) Verify perdiction

9) Tuning

10) Active Set Distribution

This tool automatically collects correlated data from follow phones, scanners and

GPS. It measures and analyze parameters such as throughput , call setup success, drop

call rate, pilot pollution and missing neighbors. Captures and displays handoff.

3.2. Omega tool:

The Omega Tool is an in house tool used to post-process drive test data and

produce outputs useful in Initial tuning and Report generation.

Omega Tool is used for post-processing the TEMS log files from a cluster drive to derive

the KPIs from the drive and to extract meaningful data for analysis

The Omega Tool performed various functions like

1) Input Consolidation

2) Post-Processing

3) Data analysis

4) Report Generation

5) Data export

6) Input Adaptation

The processed data was stored in an MS access database. A drive test consists of

several individual files. The first task of omega tool is to extract data from individual text

and put in a single database. All the data from one drive test instance will be stored in

that database.

The post-processing, analysis, export and Report Generation consists of following

calculations

1) UE Call Sequence:

Call Sequence were needed for the evaluation of drop call rate and call success rate.

The Layer3 messages gave the information regarding the call setup and dropped call.

The sequence followed was as follows:

a) RRC Connection Request

b) RRC Connection Setup complete

c) RRC Connection Reject

d) Alerting

e) Connect

f) Disconnect

g) Dropped Call

h) Activate PDP Context Accept

i) Session Start

j) Session End

k) Session Error

A Call sequence has to start and end normally. A call sequence always starts with

an RRC Connection Request message. The end sequence is signaled by the message

Disconnect or event Dropped call.

For Packet calls, the end of the sequence is indicated by session end or session

error messages. It is possible not to receive the end of Sequence indications. This can

happen because of UE or drive test software bugs. All such sequence will be marked as

incomplete. Incomplete sequences will not be used for calculations.

Fig 4: Voice Call sequence

RRC Connection Request RRC

Connection Setup Complete

Alerting

Disconnect or Dropped Call

Paging Type 1

CS Voice Call Sequence

Fig 5: Packet sequence

3.3. LAYER-3 Messages in TEMS Investigation 7.0 Software

Fig 5: Layer 3 messages on TEMS

RRC Connection Request RRC

Connection Setup Complete

Activate PDP Context Accept

Session Start

Paging Type 1

Session End OR Session Error

PS Call Sequence

3.4. UE KPI(Keys Process interface) Evaluation:

KPIs will be compiled from the call sequences as shown in the figure. Incomplete

call sequences will not be considered during the KPI evaluation.

3.4.1. AMR voice Dropped Call Rate

a) Discrete Calls: Discrete calls last for a fixed duration and are either dropped or ended

normally

Voice Dropped Call Rate= Total number of Dropped Call events from complete

sequences/Total number of alerting messages

b) Long Calls: A long call is maintained until the time the call is either dropped or is

normally ended at the time of the completion of the route. To calculate the drop rate of

a long call drive test, the mean call duration must be given. The call sequences have to

divided into two groups.

Sequence that result in a dropped call-Sequence A

Sequence that are terminated normally with a Disconnect message-Sequence B

Dropped Call Rate= Number of sequence a calls/ Total effective number of calls.

3.4.2. AMR Voice Call Success Rate

For voice call success rate , the following need to be calculated.

Total Attempts= Total number of the last RRC connection Request message in the

RRC Connection procedure with cause code for voice call origination.

Voice call success rate= 1- Total Failures/Total Attempts

3.4.3. Bler Calculation= Errored/ (Errored blocks+ Good blocks)

3.4.4. PS Dropped Call Rate = number of session errors/ number of Activate PDP

Context Accept messages.

3.4.5. PS Call Success Rate= 1- total failures/total attempts

3.4.6. Transport channel throughput= (1-BLER)* RLC throughput

3.4.7. Scanner Data Evaluation:

UMTS scanner data is used for examining the RF environment. The scanner

measures CPICH, Ec/Io and Ec. This information is used for the further improvement of

the radio environment. For every scanner sample point, the scanner samples points are

arranged in the descending order i.e the strongest server will have the best Ec. Each

scrambling code has the information regarding Ec/Io, Ec, cell name and rank. The rank

determines the position of the scrambling code. Scanner sample points are assigned to

bins and a list of scrambling codes present in the bin is made and Median Ec, Median

Ec/Io, average rank and number of samples reported. If the number of samples for the

scrambling code is <X% of the total samples in the bin that server is discarded. X% is the

settable parameter.

For every bin total samples in the bin, scrambling code of the server, cell name of

the server, Median Ec of the server, median Ec/Io of the server, average rank of the

server, number of samples of the server is exported into Mapinfo files.

3.4.8. Pilot Pollution Analysis for the scanner:

Pilot pollution will be analysed to determine which areas have the pilot pollution

and which cell causes pollution. The first “active set size” scrambling code are assigned

to be active, the remaining scrambling are assigned to be polluters if their median Ec is

within the pilot pollution threshold dB. If more than maximum number of polluters are

found, then only first maximum number of polluters are retained.

3.4.9. Neighbor Analysis:

The purpose of neighbor analysis is to determine missing UTRAN neighbor from

the scanner data For every scanner sample point, the scanner samples are arranged in the

order of the strongest server (highest Ec) to the weakest server (lowest Ec).

Each scrambling code has the information about the Ec, Ec/Io, Cell name and the

rank. The rank determines if the position of the scrambling code (SC) in the sorted list

indicated above. Scanner samples points are assigned to bins.

A list of all SCs present in the bin is determined. For every SC in the bin, the

following values are calculated: Median Ec, Median Ec/Io, Average rank, Number of

samples reported. For every bin, all the SCs within “active set threshold” of each other

are separated. The process is repeated for all the bins. A list of all the neighbors from all

the bins is compiled. This list is called the Feasible Neighbor List. Feasible neighbor list

is checked against the neighbor list in TEMS Investigation cell file. Neighbor relations

are checked in both directions. A list of all the neighbors present in the feasible neighbor

list but missing tin the TEMS Investigation cell file is compiled. This list is called the

Missing Neighbor List.A list of all the neighbors absent in the feasible neighbor list but

present in the TEMS Investigation cell file is compiled. This list is called the Additional

Neighbor List.

4. Conclusion:

It was a great learning experience working with Ericsson in the UMTS team for

Post-Processing of Drive Test Data and help in the Launch of the Cingular network at

Austin .Learnt about the existing and the new recent technologies used in wireless

cellular systems. Looking Forward to learn more and as Ericsson’s LOGO says “Taking

you Forward”. I believe that it has really taken me forward and I am looking forward to

move more forward.

5. References:

WCDMA for UMTS Radio access for 3G Mobile Communication

Third Edition by Harri Holma and Antti Toskala.

Reference material provided by Ericsson.