المـــــدرســــــة العليـــــا للمـــــواصــــالت بتــــونــــــس
High School for Communications of Tunis
Telecommunication Engineering
Major: Mobile Services and Networks
Graduation Project Report
Topic:
Ericsson 3G Trial Network Optimization
Realized by:
Sofien Jouini
Supervisors:
Mr. Sami Tabbane
Mr. Mohamed Tahar Ferchichi
Project carried out within:
Academic year: 2006-2007
Dedication
Dedication
To my Parents
Acknowledgment
Acknowledgment
First and foremost, I would like to express my deep gratitude and appreciation to
my training supervisor Mr Mohamed Tahar Ferchichi (N&TC Manager in Ericsson)
for his efforts, his consistent and generous support during the project schedule as well
as my recognition for offering me the opportunity to carry this work at Ericsson
Tunisia.
I’m also grateful for Mr Sami Tabbane, my supervisor at Sup’com for all the
help he gave me, his encouragement and advises in both technical and non-technical
matters.
I would like also to express my sincerely thanks for all the working team at the
ELS department of Ericsson Tunisia for their precious help and documentation they
provided me with, Special thanks for Mr Tahar Labidi (N&TC Consultant in
Ericsson).
I also take the opportunity to mention my respect and gratitude for the members
of my PFE evaluation committee for their acceptance to asses my work.
Abstract
Sofien Jouini - iv - PFE 2006/2007
Abstract This project was elaborated in the purpose to optimize Ericsson 3G trial
network in Tunisia and study the impact of its HSDPA upgrade in later phases.
Optimization activity deals with two main issues that were marginalized during
the first and second phases of Ericsson 3G project, neighbours list optimization and
isolation between coexisting antennas (2G/3G and 3G/3G). Likewise, a baseline drive
test was conducted to asses the network performance and propose the required
changes.
The study of HSDPA impact aims to predict the network performance after
HSDPA upgrade, to define the key network performances that will be impacted, and
finally to propose an optimum strategy to deploy HSDPA.
Key Words; UMTS, Neighbours list, Co-existence, Initial tuning, HSDPA impact
Summary
Sofien Jouini - v - PFE 2006/2007
Summary
Acknowledgement Abstract General introduction ……………………………………………………………………….…1
I. Chapter 1: Overview to 3G....................................................................................3
I.1. Introduction .............................................................................................................3
I.2. R99 Networks...........................................................................................................3
I.2.1. Architecture & Interfaces ...............................................................................3
I.2.2. Functionalities of RAN Elements....................................................................5
a) NodeB ............................................................................................................5
b) Radio Network Controller (RNC)..................................................................6
c) RXI .................................................................................................................6
I.3. Migration to HSDPA ...............................................................................................6
I.3.1. R99 to R4 to R5 migration ..............................................................................6
I.3.2. HSDPA Definition ..........................................................................................7
I.3.3. HSDPA features..............................................................................................7
a) Short Transmission Time Interval (TTI) ........................................................8
b) Fast radio-dependent scheduling ..................................................................8
c) High-order modulation ..................................................................................9
d) Fast link adaptation.....................................................................................10
e) Fast hybrid ARQ with soft combining .........................................................10
f) Efficient Cell Power Utilization ...................................................................11
I.3.4. HSDPA channels ..........................................................................................11
I.3.5. SW/HW upgrade for HSDPA introduction ...................................................12
a) RBS...............................................................................................................12
b) RNC .............................................................................................................13
I.4. Ericsson 3G Project...............................................................................................13
I.4.1. Architecture ..................................................................................................13
I.4.2 .Coverage.......................................................................................................15
I.4.3. Services .........................................................................................................16
Summary
Sofien Jouini - vi - PFE 2006/2007
a) Traffic classes ..............................................................................................16
b) Radio Access Bearers (RABs)......................................................................17
c) Mapping of 3G services in RABs .................................................................18
d) Services offered by Ericsson 3G Network in Tunisia ..................................19
I.5.Conclusion ..............................................................................................................19
II.Chapter 2: Network optimization ...........................................................................20
II.1. Introduction ..........................................................................................................20
II.2. Neighbors list optimization ..................................................................................20
II.2.1. Definitions ...................................................................................................21
a) Compressed mode algorithm .......................................................................21
b) Generated list by TCPU ..............................................................................22
II.2.2. Problem study..............................................................................................23
II.2.3. Conclusion...................................................................................................24
II.3. Co-existence problems .........................................................................................25
II.3.1. Definitions ...................................................................................................25
a) Spurious emissions ......................................................................................25
b) Receiver blocking ........................................................................................26
c) Isolation .......................................................................................................26
d) RBS sensitivity degradation.........................................................................28
II.3.2. Problem study..............................................................................................29
a) Spurious emission: GSM TX into WCDMA RX ...........................................29
b) Spurious emission: WCDMA TX into WCDMA RX.....................................30
c) WCDMA Receiver blocking .........................................................................31
II.3.3. Conclusion...................................................................................................31
II.4. Initial tuning .........................................................................................................32
II.4.1. Definition and Purpose ...............................................................................32
II.4.2. Process ........................................................................................................32
a) Preparation phase .......................................................................................33
b) Radio Network (RN) audit ...........................................................................33
c) Data collection.............................................................................................34
d) Post processing............................................................................................34
e) Analysis ........................................................................................................34
II.4.3. Encountered problems.................................................................................35
a) Poor coverage..............................................................................................35
Summary
Sofien Jouini - vii - PFE 2006/2007
b) Missing neighbor .........................................................................................36
c) Pilot pollution and wrong parameters configuration ..................................37
d) Not allowed PLMN ......................................................................................38
II.5. Conclusion............................................................................................................39
III. Chapter 3: HSDPA impact...................................................................................40
III.1. Introduction.........................................................................................................40
III.2. Impact of HSDPA; theoretical study...................................................................41
III.2.1. Impact on Ec/No values .............................................................................41
III.2.2. Impact on coverage....................................................................................42
III.2.3. Impact on capacity .....................................................................................44
III.2.4. Impact on traffic distribution .....................................................................44
III.3. Practical study; Simulation with TCPU .............................................................45
III.3.1. TCPU and Monte Carlo method ................................................................46
a) TCPU ...........................................................................................................46
b) Monte Carlo method....................................................................................46
c) Process of Monte Carlo Simulation in WCDMA Analysis .........................46
III.3.2. Simulation process .....................................................................................49
a) Setup common channel power .....................................................................49
b) Setup HSDPA enabled cells.........................................................................50
c) Define HSDPA related RABs .......................................................................50
d) Define WCDMA Bearer Rate Sets ...............................................................51
e) Define HSDPA capable terminal .................................................................52
f) Run network analysis ...................................................................................53
III.3.3. Simulation result ........................................................................................53
a) Impact on coverage......................................................................................53
b) Impact on capacity.......................................................................................56
c) Traffic distribution .......................................................................................57
d) Quality .........................................................................................................59
III.4. Proposal for HSDPA deployment strategy .........................................................60
III.4.1. Proposal 1 ..................................................................................................60
III.4.2. Proposal 2 ..................................................................................................63
III.5. Conclusion ..........................................................................................................64
Figures list
Sofien Jouini - viii - PFE 2006/2007
Figures list
Figure1. 1 : UMTS networks architecture .....................................................................5
Figure1. 2 : MSC architecture evolution from R99 to R4 .............................................7
Figure1. 3 : Downlink data throughput improvement ...................................................7
Figure1. 4 : proportional fair scheduling algorithm......................................................9
Figure1. 5 : QPSK and 16 QAM....................................................................................9
Figure1. 6 : fast link adaptation ...................................................................................10
Figure1. 7 : Fast hybrid ARQ with soft combining .....................................................10
Figure1. 8 : Efficient Cell Power Utilization in HSDPA.............................................11
Figure1. 9 : HSDPA channels......................................................................................12
Figure1. 10 : HS-TX board ..........................................................................................12
Figure1. 11 : Software and hardware upgrade of RNC ...............................................13
Figure1. 12 : Ericsson 3G network architecture ..........................................................14
Figure1. 13 : Grand Tunis area coverage.....................................................................15
Figure1. 14 : Highway and Hammamet Areas coverage .............................................16
Figure1. 15 : UMTS and Radio Access Bearer Service...............................................17
Figure2. 1 : Compressed Mode algorithm impact .......................................................21
Figure2. 2 : 2G-3G neighbours list generation ............................................................22
Figure2. 3 : neighbours list details...............................................................................23
Figure2. 4 : optimized neighbours’ list ........................................................................24
Figure2. 5 : Inter-modulation product..........................................................................26
Figure2. 6 : Wide Band Noise......................................................................................26
Figure2. 7 : Isolation; co-area case ..............................................................................27
Figure2. 8 : Isolation; co-site case ...............................................................................27
Figure2. 9 : Initial tuning activity process ...................................................................32
Figure2. 10 : poor coverage .........................................................................................36
Figure2. 11 : Missing neighbour..................................................................................37
Figure2. 12 : Pilot pollution and wrong parameters configuration..............................38
Figure2. 13 : PLMN not allowed .................................................................................39
Figures list
Sofien Jouini - ix - PFE 2006/2007
Figure3. 1 : Power consumption in RBS .....................................................................41
Figure3. 2 : Coverage reduction ..................................................................................43
Figure3. 3 : IRAT-H & CM area moving ....................................................................45
Figure3. 4 : simulation flowchart with Monte Carlo algorithm...................................47
Figure3. 5 : setup common channel power ..................................................................49
Figure3. 6 : Setup HSDPA enabled cells .....................................................................50
Figure3. 7 : Define HSDPA related RABs ..................................................................50
Figure3. 8 : Define WCDMA bearer rate sets .............................................................51
Figure3. 9 : Defining HSDPA capable terminals.........................................................52
Figure3. 10 : Run network analysis .............................................................................53
Figure3. 11 : Impact on coverage; simulation result....................................................54
Figure3. 12 : Top 10 cells coverage.............................................................................55
Figure3. 13 : Downlink maximum delivered power from RBS...................................56
Figure3. 14 : Average CE consumption in downlink ..................................................57
Figure3. 15 : Number of blocked users due to lack of code resources ........................57
Figure3. 16 : Average number of users in CM (per cell).............................................58
Figure3. 17 : UEs in IRAT handover (per cell) ...........................................................58
Figure3. 18 : Call setup Success Rate..........................................................................59
Figure3. 19 : Downlink Noise Rise..............................................................................59
Figure3. 20 : CPICH power increasing........................................................................60
Figure3. 21 : Total RBS power increasing...................................................................61
Figure3. 22 : Increase CPICH power with constant power for CCHs and DCHs .......61
Figure3. 23 : Uplink / downlink out of synchronization..............................................62
Figure3. 24 : Soft handover area moving.....................................................................62
Figure3. 25 : HsPowerMargin parameter.....................................................................63
Tables list
Sofien Jouini - x - PFE 2006/2007
Tables list Table1. 1 : RABs provided by Ericsson in P4 .............................................................18
Table1. 2 : Mapping of UMTS Service to RABs.........................................................19
Table2. 1 : WBN effect from GSM; calculating minimum distance ...........................29
Table2. 2 : WBN effect from GSM; calculating maximum filter size.........................30
Table2. 3 : WBN effect from WCDMA; calculating minimum distance ....................30
Table2. 4 : Initial tuning prerequisites and results. ......................................................32
Table2. 5 : Data analysis..............................................................................................35
Table3. 1 : Coverage reduction calculation .................................................................43
Abbreviations
Sofien Jouini - xi - PFE 2006/2007
Abbreviations
A A-DCH : Associated Dedicated Channel
ARQ : Automatically request
ASE: Air Speech Equivalent
ATM : Asynchronous Transfer Mode
B BLER : Block Error Rate
BSC : Base Station Controller
BTS : Base Transceiver Station
C CCH : Common Channel
CM : Compressed Mode
CN : Core Network
CQI : Channel Quality Indicator
CSR : Cell Selection / Reselection
CSSR : Call Setup Success Rate
CTR : Cell Traffic Recording
D DCH : Dedicated Channel
G GSM : Global System for Mobile
GRAN : GSM Radio Access Network
GGSN : Gateway GPRS support Node
H HDSL : High Speed Digital Subscriber
Line
HSDPA : High Speed Data Packet Access
HS-DSCH : High Speed Downlink
Shared Channel
HS-SCCH : High-Speed Shared Control
Channels
HS-TXB : HSDPA Transmitter Board
I IF : Inter-Frequency
IM : Inter-modulation
IRATH : Inter Radio Access Technology
Handover
ITU-R : International Telecommunication
Union – Radio communication sector
K KPI : Key Performance Indicator
M MGW : Media Gateway
MSC : Mobile Switch Center
MSS : Mobile Soft Switch
Abbreviations
Sofien Jouini - xii - PFE 2006/2007
O O&M : Operating and Maintenance
(O&M)
OSS : Operating Service and System
P PLMN : Public Land Mobile Network
R RAB : Radio Access Bearer
RBS : Radio Base Station
R99 : Release 99
RX : Receiver
S SC : Scrambling Code
SGSN : Server GPRS Support Node
SHO : Soft Handover
T TCPU : TEMS Cell Planner Universal
TTI : Transmission Time Interval
TX : Transmitter
TXB : Transmitter Board
U UARFCN : UTRA Absolute Radio
Frequency Channel Number
UE : User Equipment
UETR : User Equipment Traffic
Recording
UMTS : Universal Mobile Terrestrial
System
URAN : UMTS Radio Access Network
UTRAN : UMTS Terrestrial Radio
Access Network
W WCDMA: Wideband Code Division
Multiple Access
General introduction
Sofien Jouini - 1 - PFE 2006/2007
General introduction
The increasing demand for wireless data services and continuous growth of
multimedia applications made straightforward the evolution to third generation
networks, named UMTS (Universal Mobile Terrestrial System). Soon after its first
commercial launch in 2002, UMTS has been successfully adopted by wireless
operators to be in service now by 169 operators worldwide, where 69 others are in
planning, deploying or trial phase. This rapid growth of UMTS led to a focus on its
significant evolutionary phase, named HSDPA (High Speed Data Packet Access). As
HSDPA is a simple upgrade to the existing system that results in a significant increase
in data capacity and throughput, 70% of UMTS networks have been upgraded by
HSDPA. [1]
To meet the perception of those operators, optimization is fundamental for
UMTS as any other radio mobile system. However, optimization is much more
complicated with UMTS. In fact;
UMTS is an interfered system based on WCDMA (Wideband Code Division
Multiple Access) access technology that brought a set of new sophisticated algorithms
such as admission / congestion control, inner / outer loop power control, soft / softer
handover and compressed mode.
In addition, operators chose often to reuse 2G sites for 3G antennas deploying,
making cost efficient the evolution toward 3G. This leads to co-existence problems
that result in High degradation of 3G receivers sensitivity and therefore 3G services
quality.
Likewise, to exploit the spectrum (frequencies band) and the remaining resources
from R99 (first release of UMTS) traffic such as codes, power and load, HSDPA is
being deployed in the same carrier with R99 traffic, highly impacting the network
performance such as coverage, capacity and traffic distribution.
General introduction
Sofien Jouini - 2 - PFE 2006/2007
Within this context, my graduation project aims to highlight this complexity in
3G networks optimization dealing mainly with 2G–3G neighbours list optimization,
2G-3G antennas isolation, network performance analysis through drive test activity
and HSDPA impact on R99 traffic.
The report is divided into three chapters;
The first chapter depicts the UMTS architecture, interfaces and network
elements functionalities as well as HSDPA features and Ericsson 3G project
proprieties such as coverage, architecture and services.
The second chapter discusses, in first step, the importance of 2G-3G neighbours
list optimization and propose a methodology for this task. In second step, we will deal
with various problems due to co-existence between either (2G and 3G sites) or (3G
and 3G sites) of different manufactures (Ericsson, Alcatel, …). Finally, we will
analyse the network performance through a drive test performed on “on air” sites.
In the last chapter, we will start by a theoretically study of HSDPA impact.
After, we will simulate the HSDPA upgrade of Ericsson network by the planning tool
of Ericsson, TEMS Cell Planner Universal (TCPU). Finally, we will discuss the
efficiency of two strategies of HSDPA deployment.
Chapter 1 Overview to 3G
Sofien Jouini - 3 - PFE 2006/2007
I. Chapter 1
Overview to 3G
I.1. Introduction
This first chapter is an overview to UMTS networks, migration to R5 and
Ericsson 3G trial project in Tunisia. It depicts the architecture as well as the main
proprieties of Ericsson project such as coverage, capacity and offered services.
Not all UMTS features are discussed here because it is beyond the scope of my
report. However, HSDPA features are depicted in more details to make easier the
understanding of the last chapter (HSDPA impact).
I.2. R99 Networks
I.2.1. Architecture & Interfaces
The Base Transceiver Station (BTS) and Base Station Controller (BSC) in GSM
are replaced respectively by NodeB and Radio Network Controller (RNC) in UMTS.
So, the GSM Radio Access Network (GRAN) is replaced by UMTS Radio Access
Network (URAN) (Figure 1.1). Likewise, this new architecture has brought a set of
new interfaces that follow the GSM naming convention, where applicable;
Chapter 1 Overview to 3G
Sofien Jouini - 4 - PFE 2006/2007
a) Iu Interface
This interface connects the Core Network (CN) and the URAN. The Iu can have
two different physical instances, Iu-CS and Iu-PS. The Iu-CS connects the radio
access network to a circuit-switched core network, that is, to Mobile Switch Center
(MSC). The Iu-PS connects the access network to a packet-switched core network,
which in practice means a connection to an SGSN (Server GPRS Support Node) [2].
b) Iub Interface
This interface is situated between the RNC and the NodeB in the UTRAN. In
GSM terms this corresponds to the A-bis interface between the BTS and the BSC.
The RNC manages NodeB over the Iub interface. The following functions are
performed over the Iub interface;
Logical Operating and Maintenance (O&M) functions of Node B
System information management
Traffic management of common, dedicated and shared channels
Timing and synchronization management [2]
c) Iur Interface
The Iur interface connects two RNCs. This interface can support the exchange
of both signaling information and user data. All RNCs connected via the Iur must
belong to the same Public Land Mobile Network (PLMN). The Iur interface exists to
support macro-diversity so that the URAN can manage the problem of soft handovers
by itself.
There is always only one RNC in control of a UE connection which is the
Serving RNC (SRNC). Any other RNC involved in the connection is a slave RNC or
a Drift RNC (DRNC). The connection to MSC is routed via the SRNC (figure 1.1) [2]
Chapter 1 Overview to 3G
Sofien Jouini - 5 - PFE 2006/2007
Figure1. 1 : UMTS networks architecture
I.2.2. Functionalities of RAN Elements
a) NodeB
NodeB is the UMTS equivalent of BTS in GSM and is called often Radio Base
Station (RBS). Functions that are performed by a NodeB include the following:
Transmitting of system information messages according to scheduling
parameters given by the RNC
Macro diversity combining and splitting of data streams internal to
NodeB
Reporting of uplink interference measurements and Downlink power
information
Radio measurements and indication to higher layers
Inner loop power control
RF processing [2]
RNS BSS
CN
Chapter 1 Overview to 3G
Sofien Jouini - 6 - PFE 2006/2007
b) Radio Network Controller (RNC)
The RNC controls one or more Node Bs. It may be connected via the Iu
interface to an MSC (via Iu-CS) or to an SGSN (via Iu-PS). The interface between
RNCs (Iur) is a logical interface, and a direct physical connection doesn’t necessarily
exist. An RNC is comparable to a BSC in GSM networks.
Functions that are performed by the RNC include the following:
Iub transport resources management
Control of NodeB logical O&M resources
System information management and scheduling of system information
Traffic management of common and shared channels
Modifications to active sets (in soft handover)
Allocation of Downlink channelization codes
Downlink and Uplink outer loop power control
Admission control
Reporting Management [2]
c) RXI
The RAN aggregator, RXI, is perfectly similar to the HUB for local area
networks. In fact, its role results in aggregating the backhaul traffic from a large set of
RBSs depending on its capacity. It can either be co-located with the RNC for port
expansion or be remotely located for regional transport concentration. [3]
I.3. Migration to HSDPA
I.3.1. R99 to R4 to R5 migration
3G network evolution results in CN architecture change and downlink data
throughput improvement. The 3G MSC (in R99) was divided (in R4) into MSC
Server and Media Gateway (MGW) (Figure 1.2). Data throughput reaches 14.4 Mbps
in 3GPP specifications but the implemented version of equipments (terminals) support
only 1.6 Mbps (terminal category 12) and 3.6 Mbps (terminal category 5). (Figure
1.3)
Chapter 1 Overview to 3G
Sofien Jouini - 7 - PFE 2006/2007
Figure1. 2 : MSC architecture evolution from R99 to R4
Figure1. 3 : Downlink data throughput improvement
I.3.2. HSDPA Definition
The High Speed Data Packet Access (HSDPA) is a downlink channel concept
that employs:
Radio channel quality-dependent fast link adaptation
Hybrid ARQ
A higher modulation scheme of 16 QAM
Radio resources sharing between users in the time and code domains
On the new downlink channel, defined in 3GPP as the HS-DSCH - High Speed
Downlink Shared Channel, the theoretical maximum bit rate that can be achieved
reaches up to 14.4 Mbps. [4]
I.3.3. HSDPA features
HSDPA supports a set of new features that enables higher capacity, reduced
delay and significantly higher data rates than for ordinary Radio Bearers (RBs);
Short Transmission Time Interval (TTI)
Fast radio-dependent scheduling
2000(R99) 2001(R4) 2002(R5) 2003 2004(R6) 2005 2006(R7)
3GPP 1st Specification Version of HSDPA
1st Commercial launch for HSDPA
1st Commercial launch for WCDMA
Downlink peak data rate
384 Kbps 3.6 Mbps
MSC
MSC Server
MGW
In charge of the processing of the user data
In charge of call control and Mobile Management (MM)
R99 R4
Chapter 1 Overview to 3G
Sofien Jouini - 8 - PFE 2006/2007
High-order modulation
Fast link adaptation
Fast hybrid ARQ with soft combining
Efficient Cell Power Utilization
a) Short Transmission Time Interval (TTI)
One of the main features of HSDPA is the introduction of a shorter TTI in the
WCDMA air interface of just 2 ms. The TTI for HSDPA is short when compared to
DCH, where it is between 10 – 40 ms.
A shorter TTI allows adjusting the properties of the transmission on the HSDPA
downlink channel 500 times per second and has the following advantages:
Fast changing radio channel conditions (mainly due to fading and
multi-path propagations) can be tracked by the radio functions more
accurately.
Scheduling of users and data packets can be realized much more
efficiently, since it is now possible to receive a fast feedback on the
instantaneous radio channel conditions for individual users.
By reducing the round-trip time for packets in the air interface, the
application response time is perceived as improved service quality and
as a higher data throughput for the application in the terminal
equipment.
The short delays are also beneficial to TCP when downloading many
relatively small objects (like a web page), since TCP round trip time is
also reduced.
b) Fast radio-dependent scheduling
Scheduling is the method to determine which UE to transmit at a given time
instant. One of the basic ideas is to transmit to UEs only at fading peaks, thus
improving the C/I conditions for the radio channel and thereby improving the cell
throughput. The consequence of such solution is that the data rate for different users
may vary greatly.
Another method is to give all users the same priority, but this reduces the cell
throughput. In other words there is a trade-off between fairness for the individual user
and cell throughput. In P4 two scheduling algorithms are implemented:
Chapter 1 Overview to 3G
Sofien Jouini - 9 - PFE 2006/2007
Round Robin scheduling;
Is a simple scheduler giving each user the same amount of radio resources
(TTIs) and does not take into account the possibility to transmit on only fading peaks.
The algorithm is fair for all users from a resource point of view. All users are given
the same amount of radio resources, but the bit rate will vary depending on
momentary radio conditions.
Proportional fair scheduling;
It utilizes information about the fading peaks to prioritize users with good radio
conditions. It also takes delay into account promoting users that have not been given
any data for a long time. In this way, both user fairness and cell throughput is taken
into account (Figure 1.4).
Figure1. 4 : proportional fair scheduling algorithm
c) High-order modulation
HS-DSCH is able to use 16 QAM if the UE category permits, which allows
twice as high data rates to be transmitted as compared to QPSK (which is used for the
DCH).
Since 16 QAM is more sensitive to interference, the channel conditions need to be
good (high C/I). Once the conditions are fulfilled very high data rates can be
accomplished.
Figure1. 5 : QPSK and 16 QAM
High data rate
Low data rate Time
#2 #1 #2 #2 #1 #1 #1
User 2
Scheduled user
16QAM
2 bits 4 bits
QPSK
Chapter 1 Overview to 3G
Sofien Jouini - 10 - PFE 2006/2007
d) Fast link adaptation
Based on the 2 ms TTI and new feedback channel from the UE to the system for
reporting of the instantaneous radio channel quality CQI (Channel Quality Indicator),
the transmission parameters, such as error correction coding scheme and modulation
scheme, can be adjusted so as to track fast varying radio channel conditions.
Figure1. 6 : fast link adaptation
e) Fast hybrid ARQ with soft combining
The fast changing quality of any radio channel introduces bit errors in data
packets sent between the transmitter and the receiver of a packet transmission.
In traditional error correction schemes for interactive and best effort data
transmissions, the main solution is to automatically request a re-transmission (ARQ)
of the erroneously received packets. Expecting the retransmitted packet to arrive
without bit errors, the previously received erroneous packet is discarded. In HSDPA
both the erroneous packet and the retransmitted packet are soft-combined together by
the error correction algorithm to more efficiently use earlier sent packets and air
interface resources. By deploying Hybrid ARQ with soft combining the air interface
capacity can be increased while still keeping a high robustness of the error correction
schemes.
Figure1. 7 : Fast hybrid ARQ with soft combining
High data rate
Low data rate
NodeB
Chapter 1 Overview to 3G
Sofien Jouini - 11 - PFE 2006/2007
f) Efficient Cell Power Utilization
Fast link adaptation considers the cell power available for HSDPA downlink
transmissions. Rather than deploying power control for compensating adverse radio
channel conditions, the HSDPA downlink shared channel is rate controlled. This
allows use of all remaining power of a cell for HSDPA transmission after that the R99
traffic demand has been satisfied. Consequently, no urgent requirement exists to
deploy a second or separate carrier for HSDPA.
As the traffic demand on HSDPA channels increases, WCDMA deployment
strategy will be revised due to a high load on the HSDPA channels having an impact
on the existing R99 traffic channel coverage and capacity.
Figure1. 8 : Efficient Cell Power Utilization in HSDPA
I.3.4. HSDPA channels
HSDPA channels consist of the following:
One High-Speed Downlink Shared Channel (HS-DSCH), used for
downlink data transmission,
One High-Speed Shared Control Channels (HS-SCCH), used for
downlink control signaling,
One Associated Dedicated Channel (A-DCH) pair (UL & DL) per
HSDPA user in connected state, used for control signaling and uplink
data transmission.
Chapter 1 Overview to 3G
Sofien Jouini - 12 - PFE 2006/2007
Figure1. 9 : HSDPA channels
I.3.5. SW/HW upgrade for HSDPA introduction
The upgrade from WCDMA to HSPA requires a new software package and,
potentially, some new pieces of hardware in the base station and in RNC to support
the higher data rates and capacity.
a) RBS
RBS needs to be equipped with HSDPA capable TXB (Transmitter Board) and
new software which is remotely loaded. Dedicated Channel (DCH) and HSDPA share
the same hardware resources and the hardware is separate for downlink and uplink.
This new generation of TXB card, HSTXB, can be configured to meet either R99
traffic only, HSDPA traffic only or a mix of both traffic types. HS-TXB supports up
to 5 codes per cell carrier and up to 16 HSDPA simultaneous users per cell carrier in
P4 (Figure 1.10)
Figure1. 10 : HS-TX board
Chapter 1 Overview to 3G
Sofien Jouini - 13 - PFE 2006/2007
b) RNC
RNC capacity has to be increased according to the estimated added traffic on
Iub interface, so one or more sub-racks may be added (Figure 1.11). Also a new
software package must be installed to enable HSDPA related algorithms such as
scheduling and ARQ soft combining
Figure1. 11 : Software and hardware upgrade of RNC
I.4. Ericsson 3G Project
I.4.1. Architecture
The network is composed of 61 sites, whose 44 are located in Grand Tunis area,
10 sites in Highway (fast route to Hammamet) and 7 sites in Hammamet city. The
network reaches now its second phase (P2) and is still not fully deployed with nearby
26 sites in pending phase (figure 1.2).
The Operating Service and System-Radio Control (OSS-RC 2.2) will be
upgraded in the next phase (to be RC 3.1) and moved to Hached Centre. The RNC,
RXI, (SGSN), Gateway GPRS support Node (GGSN) and the Mobile Soft Switch
(MSS) are installed in Hached Centre.
The Technopole Centre contains 1 RBS, the OSS-RC container and the mini-
link traffic node that is directly related, by FH, to mini-link traffic node in Marsa
Centre where another RBS are located too.
The transmission lines between different RBSs and the RXI are HDSL (High
Speed Digital Subscriber Line) with Asynchronous Transfer Mode (ATM) Protocol.
Sub-rack
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Figure1. 12 : Ericsson 3G network architecture
OSS-RC 3.1Technopole
Minilink Traffic Node
MSS R4.1
RXI 820
RNC 3810
SGSN / GGSN
Marsa minilink TN
Marsa MSC
Hammamet Area
(7RBS)
Highway Area
(10 RBS)
Grand Tunis Area
(43 RBS)
RBS 3100
FH
FH
HDSL
Hached C
enter
Technopole Center
Marsa C
enter
RBS
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I.4.2. Coverage
The project was designed to cover three areas; Grand Tunis, Highway and
Hammamet as it are depicted on the following snapshots from TEMS Cell Planner
Universal (TCPU) (Ericsson tool for WCDMA planning). The plots are a prediction
made with TCPU using the RF propagation model “Ericsson 9999” (modified
“Okurama Hata” model for WCDMA networks).
Figure1. 13 : Grand Tunis area coverage
HSDPA
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Figure1. 14 : Highway and Hammamet Areas coverage
I.4.3. Services
a) Traffic classes
From end-user and application point of view four major traffic classes can be
identified as illustrated in the following.
Real time applications:
o Streaming class; preserve time relation between entities of the
stream, e.g. Video
o Conversational class; preserve time relation of the entities with
low delay, e.g. Voice.
Non real time applications:
o Background class; destination is not expecting data, preserve
payload, e.g. email
o Interactive class; request and response pattern with preserved
payload, e.g. Internet browsing
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b) Radio Access Bearers (RABs)
3GPP has defined a Radio Access Bearer (RAB) as “The service that the access
stratum provides to the non-access stratum to transfer user data between User
Equipment and Core Network”. [5]
In UMTS Terrestrial Radio Access Network (UTRAN) a RAB is defined as the
logical connection between the CN and UE and is used to provide a connection for a
UMTS service via UTRAN as it is describing below.
TETE MTMT WCDMARAN
WCDMARAN CN Iu
edgenode
CN Iuedgenode
CNGateway
CNGateway
TETE
UMTS
End-to-End Service
TE/MT LocalBearer Service
ExternalBearer Service
UMTS Bearer Service
Radio Access Bearer Service CN BearerService
Backbone BearerService
Iu BearerService
Radio BearerService
UTRA FDD/TDDService
PhysicalBearerService
Figure1. 15 : UMTS and Radio Access Bearer Service
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The Radio Access Bearers provided by Ericsson are listed in the table1.1. [6]
Radio Access Bearers Description
PS Interactive 64/64
Implemented with a 64 kbps uplink DCH and 64 kbps downlink DCH.
PS Interactive 64/128
Downlink DCH with 128 kbps.
PS Interactive 64/384
Downlink DCH with 384 kbps.
PS Interactive 64/HS (HSDPA)
Implemented with an uplink DCH and downlink HS-DSCH. The DCH has the capacity of 64 kbps and the TTI is 20 Ms. the HS-DSCH has the capacity of 3.6 Mbps and the TTI is 2 ms.
PS Interactive 384/HS (HSDPA)
The DCH has the capacity of 384 kbps and the TTI is 10 ms.
PS Streaming 16/64 + PS Interactive 8/8
The multi RAB consists of a streaming (16/64) and interactive RAB (8/8). The streaming one has a guaranteed bit rate of 56 kbps in downlink (64 Kbps as maximum)
PS Streaming 16/128 + PS Interactive 8/8
The streaming RAB has a guaranteed bit rate of 112 Kbps in downlink (with 128 Kbps as Max)
CS Conversational Speech 12.2/12.2 + PS Interactive 64/64
The interactive RAB implemented with 64 Kbps in uplink/downlink
CS Conversational Data 64/64 + PS Interactive 8/8
Same proprieties with a difference in traffic type which is data here and the bit rate as it is 64/64 for conversational and 8/8 for interactive RAB.
Table1. 1 : RABs provided by Ericsson in P4
c) Mapping of 3G services in RABs
The Core Network maps the UMTS service on the Radio Access Bearer
according to the table 1.2.
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UMTS Service Type of Radio Access Bearer Speech(AMR codec) + Emergency call Conversational/speech RAB Internet access Interactive or Background PS RAB Modem V.90 Streaming 57.6 Kbps Circuit Switched (CS) RAB H.324M multimedia Conversational 64 Kbps CS RAB SMS Signalling Radio Bearer(SRB) Table1. 2 : Mapping of UMTS Service to RABs
d) Services offered by Ericsson 3G Network in Tunisia
Voice call
o 3G to 3G within Ericsson Network
o 3G to 2G and vice versa (Ericsson – Alcatel)
Video Call
o 3G to 3G within Ericsson Network
Data Services
o MMS
o Video streaming
o Mobile Positioning
o Internet browsing
o E-post cards
o Multiplayer games
I.5. Conclusion
We have seen in this chapter the architecture, interfaces and RAN elements
functionalities of R99 networks as well as the upgrade from R99 to HSDPA and
finally the different proprieties of Ericsson 3G project and requirements. The whole
of this bibliography is important to understand the next chapter where we will explain
the performed tasks during network troubleshooting activity.
Chapter 2 Network Optimization
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II. Chapter 2
Network Optimization
II.1. Introduction
Optimize a network is to tune its design and configuration parameters to meet its
predefined target performance. Network optimization can be either before commercial
launch or after. When it is before, it is called “Initial Tuning”.
Several tasks have to be performed before initial tuning activity. We will focus
mainly on the two most critical tasks that haven’t been achieved for Ericsson 3G
project, neighbors’ list optimization and antennas isolation.
The importance of neighbors’ list optimization will be discussed in the first
section of this chapter. The second section depicts the methodology of calculating the
required isolation between antennas and stresses its impact on network performance.
The last section is a description of the performed initial tuning activity for the on air
sites of the studied network.
II.2. Neighbors list optimization
Neighbor list definition is a basic activity in the planning phase to ensure a good
mobility within the radio mobile network. 3G-3G neighbor’s list definition is easy to
perform in our case because of the weak density of 3G sites in the total area (Grand
Tunis, Hammamet). However, 2G-3G neighbor’s list is much more critical because of
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the compressed mode algorithm that has a great impact on network performance as it
will be explained in the following paragraphs.
Nevertheless, we can generate such lists automatically by TCPU but the result
needs to be well reviewed and verified (during drive test). The problem is perfectly
like the frequency planning task in GSM that may be performed automatically by
some tools but result is usually inaccurate.
II.2.1. Definitions
a) Compressed mode algorithm
In GSM, the mobile disposes of an idle frame to perform measurements on other
frequencies (26th frame in dedicated mode and 51st frame in idle mode). However, in
WCDMA, the UE transmits continuously and has no possibility to conduct such
measurements. Thus, it is necessary to give a gap of time for the UE to achieve this
task.
The RNC reserves 7 slots within each frame during a period called compressed
mode period (Figure 2.1). This period of time depends on the number of frequencies
that have to be measured. The UE achieves the measurements on one frequency
within 3 slots, and then 2 frequencies may be measured during one compressed frame.
The algorithm that runs in RNC and monitors such function is named as
compressed mode algorithm.
Figure2. 1 : Compressed Mode algorithm impact
1…………15
1
2
3
4
12
13
1………..15
14
15
Gap of 7 slots
Normal frame (SF =16) Normal frame (SF=16)Compressed frame (SF = 8)
UE performs measurement on other frequencies (IF or IRAT handover)
RBS Total power
RNC CPU load
38 dbm 41 dbm 38 dbm
60 % 65 % 60 %
Lost codes = 16 codes of SF = 256
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b) Generated list by TCPU
We may generate the 3G-3G and 2G-3G neighbors’ list by TCPU, following the
two steps described in figure 2.2 and figure 2.3.
A short description of the ambiguous parameters of TCPU windows is set below
each figure.
Figure2. 2 : 2G-3G neighbours list generation
1. Define the candidate neighbor cells (for GSM and WCDMA)
2/3. The maximum/minimum neighbors allowed for origin GSM cells
4. GSM handover margin in dB.
5/6. The maximum/minimum length of the neighbor list generated
between cells using different frequencies (GSM and other WCDMA
frequencies). (Max = 32)
7. The minimum signal quality of the pilot required for a target cell
using WCDMA
1
2
3
4
5
6
7
1
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Figure2. 3 : neighbours list details
II.2.2. Problem study
When we define a neighbors’ list, we may fall in one of the following cases:
Case1; Setting a low number of 2G neighbors for 3G candidate cells
may lead to high drop or handover failure rate because of the missing
neighbors problem.
Case2; Defining a high number of 2G neighbors may contribute to a
long Compressed Mode (CM) period because of the long time needed
to achieve all measurements.
Long CM period leads to a high power consumption in downlink to keep the
same quality of connection (bit rate, Eb/No…) and therefore a high lost power in RBS
as well as interference in downlink. Likewise, CM algorithm is performed in RNC
consuming a great amount of resources like CPU load and channelization codes.
(Figure2.1)
Defining a low or high number of 2G neighbors is a tradeoff. Thus, the best
method to get an optimized neighbors’ list is to scan the GSM frequencies during
Serving cell
Candidate neighbours
Generated neighbours
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drive test activity and rank them for each candidate cell according to their signal
strength. Next, we compare the generated list by TCPU and the scanning result. The
intersection between two lists will be the primarily optimized neighboring cell list (no
more than 6 neighbors as start number) (Figure 2.4). This list may be modified next
time according to drive test result or data recording functions in OSS-RC. For
example, if we record a high drop rate where GSM covers the overall area (like
“Tunis Center”) we must add another set of 2G neighbors in the same way as in the
first. A good number of GSM neighboring cells that we may start with, is no more
than 6 (this takes more than 15 ms in CM).
Figure2. 4 : optimized neighbours’ list
II.2.3. Conclusion
We didn’t get to implement this method because we didn’t dispose of a scanner
when we performed the drive test activity. As an instantaneous remedy, we defined
the 6 strongest neighbors generated by TCPU as neighboring cells for each 3G
candidate cell.
During the drive test activity that we performed, the UE achieved successfully
the IRAT handovers in areas covered by GSM. But this cannot reflect the reliability
of the generated list (by TCPU) because, simply, the drive routes didn’t mach all the
covered area where any UE can experience a bad 3G coverage at the moment when
GSM covers well the area.
List from scanning result
TCPU generated list
Primarily optimized list
Cell 1.1
Cell 2.1
Cell 3.2
Cell 4.2
Cell 5.1
Cell 5.3
Cell 1.3
Cell 1.1
Cell 5.3
Cell 7.1
Cell 1.3
Cell 2.1
Cell 7.2
Cell 8.1
Cell 1.1
Cell 5.3
Cell 1.3
Cell 2.1 < >
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II.3. Co-existence problems
Coexistence problems result from either the transmitter or receiver
imperfections. 3GPP and GSM specifications guarantee a minimum performance that
should be respected by both WCDMA and GSM product vendors. However, these
specifications cannot often resolve the problem. Thus, we must isolate the coexisting
antennas by ensuring a sufficient separation distance between them or adding filters in
the critical cases.
In this project, we are interested in the effect of GSM / WCDMA transmitter
(TX) on WCDMA receiver (RX) and Ericsson WCDMA RBS receiver blocking.
Otherwise, we will not discuss the effect of WCDMA TX on GSM RX or GSM RX
blocking because it is beyond the scope of this project.
II.3.1. Definitions
a) Spurious emissions
ITU-R Recommendation M.329-7 defines spurious emissions as “Emission on
frequencies which are outside the necessary bandwidth and the level of which may be
reduced without affecting the corresponding transmission of information.
Spurious emissions include harmonic emissions, parasitic emissions, inter-modulation
products and frequency conversion products but exclude out-of-band emissions.” [7]
Inter-modulation (IM) products:
They are created when two or more frequencies mix in non linear devices in the
transmit path or the receive path. IM products of order n are the sums and differences
in n terms of the original frequencies. The strengths of the IM products decline with
higher orders (we consider only the third order). (Figure 2.5)
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Figure2. 5 : Inter-modulation product
Wide Band Noise (WBN) (harmonic or parasitic emission).
Figure2. 6 : Wide Band Noise
b) Receiver blocking
Receiver blocking is the effect of a strong out of band signal, present at the input
of the receiver, on the receiver’s ability to detect an in-band wanted signal. The
blocking signal reduces the specified receiver sensitivity by a certain value of dB. [7]
c) Isolation
Isolation between systems is defined as attenuation between transmitter port in
the interfering system and receiver port (victim). It is the total path loss due to feeder
losses, propagation and attenuation in any extra filter or other devices.
Antennas can be either co-sited or co-area case as it is explained below ( Figure
2.7, Figure2.8).
P1P2
M3
M5M7
M3
M5
Power
Frequency
f1f2 2f1-f2
Frequency
Power
Out of the wanted band emission (WBN)
Wanted band (Normal emission)
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Figure2. 7 : Isolation; co-area case
Figure2. 8 : Isolation; co-site case Isolation = ∑ losses between RBS and BTS = Lfi + Lfj + Lt + Lpath - Gai - GASC - Gaj (2.1)
Lpath = 32.4 + 20log (d) +20log (f) (2.2)
Where;
f: the frequency of transmitter
d: the distance between antennas
3G RBS
GSM BTS
ASC gain GASC
Path-Loss (Lpath) Distance > 10m
Gai Gaj
Isolation
RBS port
Feeder Loss Lfi Feeder Loss
Lfj
3G RBS
GSM BTS
Isolation = 30 db Distance < 10m
TMAASC
TMA loss Lt
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Ericsson recommends a minimum isolation of 30 db for co-sited antennas to
guarantee its RBS performance. This isolation is achieved by a minimum separation
distance between antennas depending on their proprieties (beamwidth, tilt,
azimuth…).
d) RBS sensitivity degradation
The RBS sensitivity can be expressed as: [5]
RBSSens = Nt + Pint + Nf + 10 log (RUser) + Eb/No [db] (2.3)
Where;
Nt : the thermal noise power density = -174dBm/Hz
Pint : the received level of the external interferer [dBm]
Nf : the noise figure (3 dB with TMA, 4 dB without)
RUser : the user bit rate
Eb/No : the required bit energy above the noise spectral density for
minimum call quality [dB]
RBS sensitivity degradation is expressed as following;
RBS sensitivity degradation = ∆ RBSSens = 10log (1+ Pint / N) [dB] (2.4)
Where;
N = kTBNf [W]
k : Boltzman constant (1.38·10-23 J/K)
T: the thermal noise temperature (290 ºK)
B : the receive bandwidth [Hz]
The maximum allowed sensitivity degradation which corresponds to the noise
rise caused by an external source has to be specified. Ericsson recommends (0.11 db)
as maximum degradation of RBS sensitivity to keep its network performance [8]. This
means that the maximum allowed external power (Pint) due to either spurious
emission or blocking is (-120 dbm / 3.84 MHz).
This value will be taken into consideration during the following study.
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II.3.2. Problem study
a) Spurious emission: GSM TX into WCDMA RX
Inter-modulation (IM) effect from DCS 1800;
The Downlink maximum frequency for GSM 1800 is Fmax =1880 MHz, and the
minimum frequency is Fmin = 1805 MHz. Thus, (2Fmax – Fmin) = 1955 MHz.
Ericsson 3G system operates on 2100 band (2130 MHz in uplink) and therefore
there is no problem of inter-modulation (1955 << 2130).
Wide Band Noise effect from GSM 900 and 1800;
GSM specifications limited the spurious emission from GSM BTS as following
[9];
o Co-area case; -62 [dBm / 100 kHz] = -46 [dBm / 3.84 MHz]
o Co-site case; -96 [dBm / 100 kHz] = -80 [dBm / 3.84 MHz]
To keep a certain performance of RBS receiver, Ericsson proposes
[-120dbm/3.84 MHz] as maximum allowed power coming from spurious emission.
o Required Isolation (co-area) = -46 – (-120) = 74 dB
o Required Isolation (co-site) = -80 – (-120) = 40 dB
Co-area isolation:
Considering our case where we have feeders (of 20 m), TMA losses in GSM
sites and no losses in 3G sites due to the using of ASC in uplink.
Isolation = Lfi + Lfj + Lt + Lpath - Gai - GASC - Gaj = Lfi + Lfj + Lt + [32.4 + 20log
(d) + 20log (f)] - Gai - GASC - Gaj (2.5)
Lfi
(db)
Lfj(db) Lt(db) f(MHz) Gai(dbi) GASC(db) Gaj(dbi) d(Km)
GSM900 0.8 1.5 0.2 2130 18 1.5 18 3.174 GSM1800 1.3 1.5 0.2 2130 18 1.5 18 2.996
Table2. 1 : WBN effect from GSM; calculating minimum distance
For the reason that we are studying dense urban areas (Grand Tunis,
Hammamet), we cannot fulfill this condition (d= 2 or 3 Km). Thus we need to
determine the size of filters that must be added to meet the isolation requirements. We
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consider d = 1Km (average distance between GSM and 3G sites in “Grand Tunis”
area).
Lfi
(db)
Lfj(db) Lt(db) f(MHz) Gai(dbi) GASC(db) Gaj(dbi) Filters(db)
GSM900 0.8 1.5 0.2 2130 18 1.5 18 10 GSM1800 1.3 1.5 0.2 2130 18 1.5 18 9.5
Table2. 2 : WBN effect from GSM; calculating maximum filter size Co-site isolation:
We guarantee, as I explained previously, 30 db of isolation between co-sited
antennas. As the required isolation is 40 db, we must add filters of 10 db (40-30).
b) Spurious emission: WCDMA TX into WCDMA RX
Some Ericsson 3G sites are co-existed with Alcatel ones and therefore we shall
study this case.
3GPP specifies that the power of any spurious emission (of WCDMA
transmitter) shall not exceed - 96 dBm/100 kHz (= -80 dBm/3.84 MHz). [9]
To ensure -120 dbm as maximum spurious emission at WCDMA RX we need an
isolation of 40 db (-80 – (-120)).
Co-area isolation:
We consider the following values which are the same for GSM case (LASC is
ASC insertion loss in downlink).
Lfi
(db)
Lfj(db) LASC(db) f(MHz) Gai(dbi) GASC(db) Gaj(dbi) d(Km)
WCDMA 1.5 1.5 0.2 2130 18 1.5 18 0.06
Table2. 3 : WBN effect from WCDMA; calculating minimum distance
60 m is the minimum required distance to overcome the spurious emission
problem coming from 3G transmitters. This value (60 m) is easily to reach in reality
(d > 400m in “Grand Tunis” and “Hammamet” areas) and therefore there is no
harmful effect of others 3G sites operating in the same area.
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Co-site isolation:
With a guaranteed isolation of 30 db, we must add filters (in WCDMA TX) of
10 db (40-30).
It is important to note that we are studying the worst case. In fact, the WCDMA
RBS performance is better than 3GPP specifications due to high competence between
3G products vendors. Ericsson, for example, designs its RBS to a spurious emission
35 db lower than that required by 3GPP. Thus, if ALCATEL, ZTE and HUWAWI
RBSs were designed with an equivalent performance of Ericsson RBS or at least
guarantee a maximum spurious emission 10 db lower than 3GPP specifications (- 90
dbm/3.84 MHz), we will not need to add filters. However, we have no information
about RBS performance of these vendors (ALCATEL…). Thus, we achieve our
calculations according to3GPP specifications.
c) WCDMA Receiver blocking
According to the WCDMA specifications, the WCDMA RBS has to be designed
to cope with GSM 900 1800 TX signals of up to –15 dBm. [9]
The installed Ericsson RBSs (3000 family) has been designed to cope with
GSM900 and GSM1800 TX signals of up to +20 dBm. If GSM RBS is transmitting at
its maximum power: 25W (44dBm), the isolation needed is 24 dB (44-20). This value
of isolation is guaranteed even in the near field zone of the antenna just with the
coupling loss of the antennas, and the feeder and jumper losses. In case of far field
zone, the propagation loss is enough to fulfill this requirement. Thus, we don’t need
filters.
II.3.3. Conclusion
According to the previous study, it is clear that the coexistence problems result
in spurious emission from either ALCATEL GSM 900/1800 TX or WCDMA TX of
other 3G sites (ALCATEL, HUWAWI and ZTE). Otherwise, there is no harmful
effect of GSM 1800 inter-modulation products or the high transmitted power from 2G
antennas that leads to WCDMA receiver blocking.
To overcome these problems, we recommend the installing of filters of 10 db in
2G / 3G transmitters (not receivers!) co-existing with Ericsson 3G sites.
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II.4. Initial tuning
II.4.1. Definition and Purpose
The purpose of the Initial Tuning is to make sure the radio network works well
after the network has been built. The service verifies that the radio network design
and the corresponding network data have been implemented correctly, that the
implemented design is consistent with the proposed design.
Prerequisites and results of Initial tuning activity are given by table 2.2.
INITIAL TUNING
PREREQUISITES ACTIVITIES RESULTS
- Cluster plan completed
- All planned sites
integrated, tested and in
working condition per
cluster
- Radio Network Design
and Network Data
implemented
- Network not in
commercial service
- Preparation
- Radio Network Auditing
- Drive test route plan
- Data Collection
- Post-processing
- Analyzing/Change proposal
Report
- Verification that the
critical items have been
cleared.
- Initial Tuning Analysis
report/Verification report
- Presentation of results
RND Acceptance
Table2. 4 : Initial tuning prerequisites and results.
II.4.2. Process
Figure2. 9 : Initial tuning activity process
Preparation RN audit Post processing Analysis
Fulfil Requirements
Final Report
Change proposal
NO
YES
Data collection
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a) Preparation phase
During the preparation phase a couple of activities are carried out such as:
Definition of Clusters; As a start, the total area to be covered according
to service requirements will be divided into small areas called clusters.
Each cluster is aiming to contain 10-15 sites that are located close to
each other. Each cluster can then be separately tuned in different time
frame
Definition of Drive Test Routes; It is essential that the drive test routes
are well planned, excessive duplication of drive routes or missing major
roads as well as driving too much outside the cluster will potentially
confuse the performance statistics. The routes shall be planned so that
soft/softer handover can be observed in important areas and overlapping
between them be as minimum as possible.
Collect radio network design information; The 3G project is wholly
designed and configured by Ericsson. Thus, we dispose of all required
design and configuration information for network audit.
Preparing equipment; The following set of equipments is required for
drive test activity:
o TEMS Scanner (including GPS)
o 2 TEMS UEs (one for long call, one for short call)
o 2 SIM card for the UEs
o TEMS hardware key.
o Data collection PC (PC with TEMS Data Collection)
b) Radio Network (RN) audit
Since all results of the initial tuning are highly depending on a well implemented
network, a radio network audit should be done before starting the initial tuning to
ensure a good result of the service.
The purpose of consistency check is to find inconsistencies in the network and
fix them prior to drive testing. By fixing inconsistencies we save time and speed up
the tuning process. In order to perform the design/consistency check, network
configuration data should be collected through OSS-RC (installed in OSS-HACHED
center).
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c) Data collection
Data collection can be retrieved from two different sources: TEMS Investigation
(drive testing) and Traffic Recording (UETR/GPEH/CTR).The General Performance
Event Handling (GPEH), Cell Traffic Recording (CTR) and User Equipment Traffic
Recording (UETR) functions are useful for an advanced problem analysis. In this
activity, we will be closed to TEMS investigation only. Two types of measurements
can be performed:
For scan mode, the PSCH, the SSCH and the CPICH of the sites in the
cluster shall be scanned.
For dedicated mode, two types of calls should be performed for both
speech and video:
o Long calls to evaluate the coverage, quality and retain-ability
performance of the cluster. Long calls will be measured as
continuous calls. As soon as a dropped call occurs a new call
will be placed. Also calls of 10 minutes duration can serve this
purpose.
o Short periodic calls to evaluate the accessibility performance.
The purpose of this test is to ensure that calls can be originated
from all cells on the network and to measure the Call Setup
Success Rate (CSSR) as well as the Call Complete Success Rate
(CCSR). A speech call can be set up every 90-130 seconds, and
there will be a pause of 10 seconds.
d) Post processing
The collected data will be processed in order to simplify analysis and to extract
field measurement performance statistics for reporting. In Ericsson, we dispose of
TEMS Investigation Root Analysis tool 6.0 that provides us with the required
information.
e) Analysis
Among others the following criteria will be analyzed:
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RF analysis UE analysis
- SC plan verification
- Coverage
- Pilot pollution
- Neighbors’ list
- Accessibility
- Retain-ability
- Throughput (packet)
- PDP context activation failure
(packet)
- Session error (packet)
Table2. 5 : Data analysis
II.4.3. Encountered problems
During drive test activity, we didn’t face an ambiguous problem. All
encountered problems are classic. Below, we describe briefly each problem.
a) Poor coverage
Problem description: This Drop occurs in region where CPICH RSCP and/or
CPICH Ec/No are measured in critical values not suitable for a proper connection.
TEMS investigation shows a poor coverage with CPICH RSCP = -127 dbm and
Ec/No = -28 db. As it is shown in figure 2.10, the UE experiences a bad radio
condition before the drop call and enters in idle mode after (it receives system
information type 3 which is broadcast in idle mode).
Chapter 2 Network Optimization
Sofien Jouini - 36 - PFE 2006/2007
Figure2. 10 : poor coverage
Change proposal: in this case we recommend tilting up the antenna to cover the
hall of coverage (Tunis Center). There is no need to add a new site because of the
short distance between cells.
b) Missing neighbor
Problem description: The drop occurs when the signal quality is bad on the Best
Serving cell with the contemporary possibility for the UE to perform a SHO on a
better cell that is not declared as a Neighbor. The Active Set best server is cell of SC
= 248. During the call, cell of SC = 464 becomes the strongest cell but is not added to
the active set, as it is not defined as neighboring cell (Figure 2.11). The cell of SC =
464 acts as an increasing interferer until eventually the call is released.
Chapter 2 Network Optimization
Sofien Jouini - 37 - PFE 2006/2007
Figure2. 11 : Missing neighbour
Change proposal: simply, we have to declare the cell of SC = 464 as
neighboring cell for cell of SC = 248.
c) Pilot pollution and wrong parameters configuration
Problem description: The following snapshot shows 3 problems (figure2.12).
Pilot pollution; we have more than 3 strong cells (active set size = 3)
where the difference between the measured values of Ec/No is less than
5db.
Wrong parameter configuration; the cell of SC = 184 is stronger than
that of SC = 0 (Ec/No [184] = -7 > Ec/No [0] = -14). However, the
serving cell hasn’t been replaced. This due to the parameter “individual
offset” that was set higher than 7 db!
Missing neighbor; it is clear that cells of SC = 280, 424 and 304 have to
be declared as neighboring cells for the serving cell (SC = 0)
Chapter 2 Network Optimization
Sofien Jouini - 38 - PFE 2006/2007
Figure2. 12 : Pilot pollution and wrong parameters configuration
Change proposal: we recommend 3 changes.
Setting “Individual offset” value to 0 db (recommended by Ericsson)
Declare cells of SC 280, 424 and 304 as neighboring cells for cell of SC
0
Tilt down the antennas of all these sites to overcome the problem of
pilot pollution
d) Not allowed PLMN
Problem description: The UE tries to camp on other PLMN (UARFCN =
10768) as it shown in Figure 2.13. There is no roaming between Ericsson 3G network
(UARFCN = 10663) and Alcatel 3G network (UARFCN = 10768). This is why the
UE failed in location area update.
Chapter 2 Network Optimization
Sofien Jouini - 39 - PFE 2006/2007
Figure2. 13 : PLMN not allowed
II.5. Conclusion
In this chapter, we have seen the different tasks conducted during the
optimization activity of the studied network.
We highlighted the importance of 2G–3G neighbor’s list and its impact on
network performance as well as we proposed a simple method to optimize it.
We have also depicted the coexistence problems such as inter-modulation
products, Wide Band Noise effect and WCDMA receiver blocking. We reached
defining the required isolation between antennas (2G-3G and 3G-3G) and then the
required filters sizes.
Likewise, we have shown the “initial tuning” process and analyzed the
encountered problems during such activity (drive testing). All problems we have
detected through TEMS investigation are classic. Otherwise, there weren’t an
ambiguous reason for any problem.
Chapter 3 HSDPA impact
Sofien Jouini - 40 - PFE 2006/2007
III. Chapter 3
HSDPA Impact
III.1. Introduction
Evolution to HSDPA is a mandatory step to make the difference between second
and third generation networks. In fact, the maximum theoretically bit rate in 3G is 384
Kbps which is the same given by EDGE.
For operators, HSDPA upgrade is smooth and cost-efficient regarding WCDMA
deployment cost. These reasons make straightforward the upgrade from WCDMA to
HSDPA for the most 3G operators.
Ericsson has prepared its trial network for this step by installing a scalable RBSs
and upgrading its RNC to P4 (corresponds to R5 in 3GPP). However, the network
performance may be highly impacted by HSDPA and we will come back again to
dimensioning, planning and optimization phases.
In this chapter, we will study this perceived impact of HSDPA on Ericsson 3G
network. The study is divided in two parts. In the first part, we study theoretically the
issue. In the second part, we will simulate the HSDPA upgrade to prove the expected
results from first part. At the end of chapter, we will propose two strategies of
HSDPA deployment and discuss their efficiency.
Chapter 3 HSDPA impact
Sofien Jouini - 41 - PFE 2006/2007
III.2. Impact of HSDPA; theoretical study
III.2.1. Impact on Ec/No values
HSDPA traffic consumes all the remaining power in RBS after serving R99
traffic. It is the best effort traffic regarding the R99 one (Figure 3.1).
Figure3. 1 : Power consumption in RBS
Giving the following expression; Ec/No = PCPICH / (PIntra + PExtra + Noise) (3.1)
Where;
PIntra : the internal power delivered by RBS
PExtra : the external power received by UE from other cells
Noise : the interference caused by environment and other systems
Thus, the increasing of PIntra from 75 % of RBS total power (as maximum
power at antenna for R99 traffic only), to 100 % (full power) in HSDPA case will
reduce the Ec/No value.
If we ignore the term (PExtra+ Noise) against PIntra, we obtain Ec/No = PCPICH /
PIntra. (3.2)
Considering;
X1 = (PCPICH / 0.75*PTot) : the value of Ec/No in R99 only.
X2 = (PCPICH / PTot) : the value of Ec/No in (R99 + HSDPA) case.
PTot : the total power delivered by the RBS.
X2/X1 = 0.75, and thus the difference in Ec/No = 10* log (0.75)
CS traffic
Best effort traffic
Admission Control limit (For R99 traffic)
Best effort traffic (PS)
CS traffic
HSDPA traffic 100%
75%
0%
∆ Ec/No = -1.25 db
RBS power
Chapter 3 HSDPA impact
Sofien Jouini - 42 - PFE 2006/2007
III.2.2. Impact on coverage
We separate the impact on coverage from that on Ec/No value due to fact that
the cell coverage reduction can be only calculated from the delta of downlink
interference margin and not the difference in Ec/No value we have calculated
previously (-1.25 db).
Following the below procedure to calculate the reduced coverage for a
maximum loaded cell: (Equation (3.3) is the downlink budget of CPICH channel). [5]
Lpmax = PCPICH– SUE – BPC – BIDL – BLNF – LBL – LCPL – LBPL +Ga – LJ (3.3)
Where;
Lpmax : the maximum path loss due to propagation in the air [dB]
PCPICH : CPICH power at antenna [dBm]
SUE : the UE sensitivity [dBm]
BPC : the power control margin [dB]
BLNF : the log-normal fading margin [dB]
BIDL : the noise rise or the downlink interference margin [dB]
LBL : the body loss [dB]
LCPL : the car penetration loss [dB]
LBPL : the building penetration loss [dB]
Ga : the sum of RBS antenna gain and UE antenna gain [dBi]
LJ : the jumper loss [dB]
So, the only term related to RBS transmitted power is BIDL. = 1+ K * Ptot,ref /Lsa
Where;
K = (µ + Fc) / (Nt*Nf*Rchip)
Lsa = Lpmax + BPC + BLNF + LBL + LBPL – Ga + LJ : signal attenuation
µ : the non-orthogonality factor at the cell border
Fc : the ratio between the received inter-cell and intra-cell interference
Ptot,ref : the total transmitted power of RBS at antenna
If Ptot,ref passes from 75% to 100% of to the total RBS power, BIDL increases by
X = K * 0.25* Pnom,ref / Lsa . We calculate the X value in the below table (Table 3.1)
using Ericsson project inputs.
Chapter 3 HSDPA impact
Sofien Jouini - 43 - PFE 2006/2007
Term µ Fc Nt (dbm/Hz) Nf (db) Rchip K
value 0.64 2.1 -174 7 3.84*10^6 1.75*10^13
Lpmax(db) BPC(db) BLNF(db) LBL(db) LBPL(db) Ga(db) LJ(db) Lsa(db) Lsa(linear)
130 0 4.9 0 18 18 0.2 135.1 3.23*10^13
Pnom(W) Pnom(dbm) LASC(db) Lj (db) Lf(db) Pnom,ref(dbm) Pnom,ref(W) X
17.5 42.43 0.2 0.2 2 40 10 1. 36
Table3. 1 : Coverage reduction calculation
Considering (L1, R1) and (L2, R2) the (path loss, cell range) respectively of
R99 loaded cell (75 % of total power) and HSDPA loaded cell (100%);
L1 = 134 + 35.22log (R1)
L2= 134 + 35.22 log (R2)
The reduction in coverage is calculated through the difference in path loss
values for the 2 cases: L1-L2=35.22 log (R1/R2) = X = 1.36
Figure 3.2 illustrates the cell breathing effect due to a high HSDPA traffic.
`
Figure3. 2 : Coverage reduction
R1/R2 = 12 %
HSDPA enabled cell (Maximum load)
HSDPA disabled cell (Maximum load) R1
R2 12%
Chapter 3 HSDPA impact
Sofien Jouini - 44 - PFE 2006/2007
III.2.3. Impact on capacity
HSDPA has brought a significant improvement for 3G networks capacity by:
Efficient usage of all the remaining power from R99 traffic.
Good monitoring of system resources by means of its new features such
as fast scheduling algorithm and short TTI.
Increasing the cell throughput as 3 or 4 times as in the R99 case.
However, R99 traffic will be limited as much higher as the HSDPA user’s
number in the cell. In fact;
The power admission threshold for R99 traffic should be decreased to a
value that allows an acceptable throughput for HSDPA users. This has a
direct impact on the blocking and down switching rate of R’99 traffic in
the cell.
Introduction of the HS-DSCH requires all remaining cell power after
serving all R99 users; this is why all HSDPA enabled cells transmit
close to their maximum power limit. This raises the downlink
interference in the cell and leads to a higher blocking rate.
HS-DSCH shares orthogonal code resources with R99 traffic using
codes of spreading factor (SF) 16. The deployed release of HSDPA
may use up to 5 codes with SF 16 which means that 82 codes with SF
256 may be reserved to HSDPA traffic.
HSDPA impacts Ec/No values that trigger the Compressed Mode (CM)
algorithm. This one has an intensive impact on system capacity by
consuming power, channelization codes (in RBS) and CPU load (in
RNC) as twice as the simple mode do.
III.2.4. Impact on traffic distribution
Three Mobility Management (MM) algorithms depend on Ec/No thresholds:
Inter Radio Access Technology Handover (IRAT-H)
Inter-Frequency (IF) handover
Cell Selection / Reselection (CSR)
Chapter 3 HSDPA impact
Sofien Jouini - 45 - PFE 2006/2007
Such algorithms handle the traffic distribution within radio mobile system;
either between 3G network layers, by means of IF and CSR thresholds, or between
Radio Access Technologies (RATs) (GSM – UMTS), through IRAT and CSR
parameters. The following figure shows an example of traffic distribution change due
to Ec/No varying.
`
Figure3. 3 : IRAT-H & CM area moving
III.3. Practical study; Simulation with TCPU
After explaining how HSDPA impacts R99 traffic, we are going to see such
impact on the studied project of Ericsson.
We keep the same inputs that had been used in the planning phase of Ericsson
3G network (antenna type, tilt, azimuth, propagation model, powers configuration,
RBS type…). However, we will configure 2 HSDPA terminals and enable HSDPA
for all cells by a process that I will depict in details in next paragraphs.
Before starting the simulation on TCPU, we have to get the background
information about TCPU and Monte Carlo algorithm by which TCPU is running.
CM starts
IRAT- H starts-16 db
-12 db
No Coverage
Ec/No values
Area enters in CM
UE moves from UMTS to GSM
Area enters in IRAT-H
Ec/N0=-12db
Ec/No= -18 db
RBS
Chapter 3 HSDPA impact
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III.3.1. TCPU and Monte Carlo method
a) TCPU
TEMS Cell Planner Universal is a GSM / WCDMA planning tool that provides
an advanced and accurate analysis with flexible parameter settings to support different
planning methods, with or without Monte Carlo simulations. Depending on the design
stage and level of detail of a network plan, TCPU permits us selecting different levels
of calculation speed and accuracy for the predictions and simulations.
b) Monte Carlo method
“Monte Carlo methods” are a widely used class of computational algorithms for
simulating the behaviour of various physical and mathematical systems, and for other
computations. They are distinguished from other simulation methods by being
stochastic (nondeterministic), usually by using random numbers (in practice, pseudo-
random numbers),as opposed to deterministic algorithms. Because of the repetition of
algorithms and the large number of calculations involved, Monte Carlo is a method
suited to calculation using a computer, utilizing many techniques of computer
simulation. [10]
c) Process of Monte Carlo Simulation in WCDMA Analysis
The Monte Carlo simulator of TEMS Cell Planner Universal is designed to
reflect as closely as possible the UTRAN behaviour in terms of setting up, managing,
and cancelling user connections. It simulates all UTRAN algorithms such as
admission and congestion control. Below is the flowchart of Monte Carlo algorithm
used by TCPU simulations: [11]
Chapter 3 HSDPA impact
Sofien Jouini - 47 - PFE 2006/2007
Figure3. 4 : simulation flowchart with Monte Carlo algorithm.
Step1: Generating users
Depending on the traffic demand defined for each WCDMA bearer, users are
generated at random locations. For the whole trial the user distribution is kept
constant. The probability of occupying a certain location in the network (bin) with a
specific traffic (WCDMA bearer) depends on the traffic demand in the network. Over
time, the user distribution is Poisson distributed with a mean number of users equal to
the specified traffic demand.
Step 2: Sorting Cells According to Selected Ranking Algorithm
For each bin occupied with traffic, all cells covering the bin are ranked in
priority for connection attempts. A best server list is generated for each bin. The
selected ranking algorithm defines the order of the cells for which the connection
attempt is made from a specific bin and WCDMA bearer.
WCDMA analysis input parameters
Generate users for all WCDMA bearers
Connect users to cells
Calculate achieved C/I
Modified Tx power in uplink & downlink
Disconnect users (admission & congestion
control)
Converged ?
Output DL power & UL load
Collect statistics for all trials
Generate plots
Generate statistic reports
Resort cells (if applicable)
Num
ber of random trials
Sort cells according to the ranking algorithm
YesNo
Chapter 3 HSDPA impact
Sofien Jouini - 48 - PFE 2006/2007
Step 3: Connection attempts
Starting with the highest ranked cell, each cell is checked to see if a user can
connect. During the connection attempt the following constraints are tested:
o Downlink CPICH quality
o Required uplink UE TX power
o Required downlink RBS TX power
To meet the criteria, each cell must exceed the minimum threshold by at least
the fading margin for the radio link to be available.
Step 4: Calculate Achieved C/I for All Connected Users
For each mobile, the achieved C/I is calculated based on the uplink and
downlink power settings and the interference known from the previous iteration. For
mobiles in soft or softer handover, maximum ratio combining is performed on the
downlink. For users in softer handover, maximum ratio combining is performed on
the uplink, and for all users in soft handover, selection combining is performed on the
uplink.
Step 5: Modify Tx powers on UL and DL
Over several iterations the transmit power for all cells and all user terminals is
modified to match as closely as possible the achieved C/I to the target C/I. The target
C/I is calculated from the user-defined uplink and downlink Eb/Io values and the
spreading factors used for the respective WCDMA bearer.
Step 6: Disconnect Users - Admission and Congestion Control
The next algorithm checks capacity resources for all cells and disconnects users
that would exceed the user-defined thresholds for the following parameters:
o Maximum number of UL / DL Air Speech Equivalent (ASE)
o Maximum UL interference (noise rise)
o Maximum downlink power limit
o Maximum number of users on spreading factor 8/16/32
When any of these thresholds is exceeded, users are disconnected from cells in
overload based on their QoS criteria and the priority class defined for the WCDMA
bearer. In general, packet switched WCDMA bearers (Interactive and Background
class) are disconnected before the circuit switched WCDMA bearers (Conversational
and streaming class).
Chapter 3 HSDPA impact
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Step 7: Convergence check
Once a possible overload situation is resolved for all cells, the system must
verify if the network has achieved a stable state, in which the power changes are
minimal between the iterations. One of the following three criteria can be chosen for
decision;
o UL noise rise (cell based) convergence
o UL noise rise and DL power (cell based) convergence
o UL and DL C/I (user based); System converges both on the
uplink and downlink for each user connection.
III.3.2. Simulation process
This paragraph describes the process of HSDPA configuration in the studied
network. We start by configuring HS-SCCH power, HSDPA RAB (A-DCH),
enabling HSDPA for all cells and so on. The ambiguous parameters are referred to by
a number and brief explanation according to that number is set below each window.
a) Setup common channel power
Figure3. 5 : setup common channel power
1. HS-SCCH (db): difference between HS-SCCH and PCPICH power.
1
Chapter 3 HSDPA impact
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b) Setup HSDPA enabled cells
Figure3. 6 : Setup HSDPA enabled cells
1. Maximum orthogonal codes for HSDPA. Refers to SF 256 codes.
2. Maximum HSDPA users allowed in the cell.
3. Maximum users with SF=4 on uplink allowed for the cell.
c) Define HSDPA related RABs
Figure3. 7 : Define HSDPA related RABs
1. In cases of congestion, congestion control disconnects users first on
bearers with low priority. Priority 1 = highest
2. Options include: Background, Conversational, Interactive or
Streaming
3. Options include: Average or Peak
4. Indicates if uplink and downlink rate switching is handled
simultaneously.
1
2
3
1
23
4
Chapter 3 HSDPA impact
Sofien Jouini - 51 - PFE 2006/2007
d) Define WCDMA Bearer Rate Sets
Figure3. 8 : Define WCDMA bearer rate sets
1. The maximum DL / UP bit rate of the rate set.
2. Used to calculate the interference in DL (UP) generated by the bearer
3. Maximum power that can be allocated for A-DCH ( in DL)
1
2
3
Chapter 3 HSDPA impact
Sofien Jouini - 52 - PFE 2006/2007
e) Define HSDPA capable terminal
Figure3. 9 : Defining HSDPA capable terminals
1. The sum of losses in reception / transmission such as body loss,
building penetration loss, and feeder loss
2. Maximum power available for terminal type
3. Maximum / Minimum output power of terminal type.
4. Maximum codes with SF = 16 that can be allocated for terminal
5. Shortest time interval for scheduling between users
6. Physical layer throughput (effective throughput)
Category 12
parameters
Category 5
parameters
3
4
5 6
Chapter 3 HSDPA impact
Sofien Jouini - 53 - PFE 2006/2007
f) Run network analysis
Figure3. 10 : Run network analysis
1. The minimum required pilot channel quality in dB of the HS-SCCH
required by the terminal to detect the HS-SCCH correctly and to be able
to set up a connection on the HSDPA channels.
2. Select one of the 3 defined scheduling methods
3. Defined in comparison with general Round Robin method
III.3.3. Simulation result
a) Impact on coverage
1
2
3
Chapter 3 HSDPA impact
Sofien Jouini - 54 - PFE 2006/2007
Figure3. 11 : Impact on coverage; simulation result
R99 T
raffic only R
99 + HSD
PA T
raffic
Chapter 3 HSDPA impact
Sofien Jouini - 55 - PFE 2006/2007
Figure 3.11 shows the studied network both before and after deploying HSDPA.
We depict the two snapshots from TCPU in the same page and with no
separation space or paragraph to make clearer the impact of HSDPA traffic on
network coverage.
For legend, we have chosen to separate Ec/No values into 4 ranges because of
the following;
Ec/No < -8 db: good quality of signal and no of the already discussed
algorithms (IRATH, CM, and CSR) may be triggered in this interval.
-12 db < Ec/No < -8 db: acceptable quality of signal, UE enters in
compressed mode when Ec/No = -12 db
-18 db < Ec/No < -12 db: signal can be decoded with a modest quality.
UE is in compressed mode. UEs existing in this area consume a great
amount of resources (power, codes …)
Ec/No < -18 db: signal cannot be decoded. UE moves to GSM (if it is
possible)
The coverage regression of each area, which corresponds to one of the above
four ranges of Ec/No values, meets our expectations from the theoretical study in the
first part of this chapter. Figure 3.12 depicts the top 10 cell coverage percentile (10
cells among 126). This chart stresses the previous study and the above snapshots
(figure3.11)
0%10%20%30%40%50%60%70%80%90%
100%
Coverage (%)
1 2 3 4 5 6 7 8 9 10
Top 10 Cells
Coverage per Cell
HSDPA R99
Figure3. 12 : Top 10 cells coverage
Chapter 3 HSDPA impact
Sofien Jouini - 56 - PFE 2006/2007
b) Impact on capacity
Resources that I got to evaluate their consumption during simulation, are RBS
total delivered power (Figure 3.13) and downlink Channel elements (CE)
(Figure3.14). As HS-DSCH uses SF 16 (up to 5 codes per user), the number of
blocked users due to the lack of SF 16 codes reflects well the HSDPA impact
(Figure3.15).
I see that it is not significant to compare the amount of used codes in the two
cases (R99 traffic only, R99 + HSDPA). In fact, it is obvious to say that the number
of users using codes of SF 16 increases with HSDPA deployment because HSDPA
uses codes of SF 16. And thus, it is better to show the blocked users number in each
case.
The difference between the average consumed power in the two cases is about
3db, which means that HSDPA traffic consumes as twice as R99 one (figure 3.13).
According to the Channel Element concept, an increasing in this resource (CE)
consumption reflects an increasing in hardware and software consumption in RBS
(figure 3.14).
Downlink Max Power (dbm)
32
34
36
38
40
42
44
1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106 113 120All cells
Pow
er (d
b)
HSDPA R99
Figure3. 13 : Downlink maximum delivered power from RBS
3db
Chapter 3 HSDPA impact
Sofien Jouini - 57 - PFE 2006/2007
Figure3. 14 : Average CE consumption in downlink
Blocked user ( SF = 16)
0
2
4
6
8
10
12
14
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Top 50 Cells
bloc
ked
user
s
HSDPA R99
Figure3. 15 : Number of blocked users due to lack of code resources
c) Traffic distribution
The number of users in CM increases with HSDPA traffic (figure3.16). The
probability to camp on other layer (frequency) or Radio Access Technology (RAT)
increases as larger as the CM area.
05
10152025303540
CE
1 2 3 4 5 6 7 8 9 10Top 10 Cells
Average Downlink CE
HSDPA R99
Chapter 3 HSDPA impact
Sofien Jouini - 58 - PFE 2006/2007
0
1
2
3
4
5
6
7
Average users number
1 2 3 4 5 6 7 8 9 10Top 10 Cells
Avearage number of users in CM
HSDPA R99
Figure3. 16 : Average number of users in CM (per cell)
The growing up of UEs in IRAT Handover (due to coverage regression) that is
depicted in figure 3.17 confirms well our expectation (in part one of this chapter). So,
users in cell border experience a bad quality of connection (Ec/No < -16) and attempt
to camp on other layer or GSM. In this simulation, we have not configured a
multilayer system (more than one frequency. Thus, the UE tries directly to camp on
GSM cells (defined in neighbors’ list).
0
2
4
6
8
10
12
Number of UEs
1 2 3 4 5 6 7 8 9 10
Top 10 Cells
UEs in IRAT Handover
HSDPA R99
Figure3. 17 : UEs in IRAT handover (per cell)
Chapter 3 HSDPA impact
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d) Quality
The Call Setup Success Rate (CSSR) reflects the subscriber perception about
network availability. Decreasing in this KPI (Key Performance Indicator) means
degradation in network performance and therefore a bad user perception (figure 3.16).
Downlink Noise Rise (NR) degrades the UE receiver sensitivity leading to high
Block Error Rate (BLER) that reduces the downlink data throughput and therefore the
service quality (especially multimedia services) (figure 3.17).
0.00
20.00
40.00
60.00
80.00
100.00
CSSR (%)
Bardo Soukra jamil Phénix Gammarth R-V-TTop 10 Cells
Call Setup Success Rate (%)
HSDPA R99
Figure3. 18 : Call setup Success Rate
00.5
11.5
22.5
33.5
4
NR (db)
1 2 3 4 5 6 7 8 9 10
Top 10 Cells
Downlink Noise Rise (db)
HSDPA R99
Figure3. 19 : Downlink Noise Rise
Chapter 3 HSDPA impact
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III.4. Proposal for HSDPA deployment strategy
III.4.1. Proposal 1
Ec/No = CPICH power / PIntra , as we explained previously (paragraph III.2.1).
Thus, we can increase CPICH power by 2db to compensate Ec/ No value degradation
(-1.25 db).
This is a bad solution (at least for Ericsson) as all common and even
dedicated channels powers are configured in proportion of CPICH power (values are
put as margins). Thus, we will fall in one of the two following problems;
Case 1: Increase CPICH power and keep the same values (margins)
for other common and dedicated channels power (Figure 3.19)
Figure3. 20 : CPICH power increasing
As all power values are set relatively to CPICH power, an increase by 2db in
CPICH power will increase all common and dedicated channels power by the same
value (2db). Thus, the total power delivered by an RBS may increase above the
threshold of admission control (set for R99 traffic only and not for HSDPA)
(Figure3.20).
Total power (R99) = [CCH power] + [DCH power]
If each power threshold increases with 2 db the total power threshold increases
by 20 db! Likewise, the reserved power for HSDPA will be highly decreased that a
minimum guaranteed bit rate cannot be achieved.
+ 2db
No changes in m
argins
Chapter 3 HSDPA impact
Sofien Jouini - 61 - PFE 2006/2007
Figure3. 21 : Total RBS power increasing
Case 2: increase CPICH power and decrease the margins (difference
with DCH and CCH powers) so that only CPICH power will be increased
(Figure 3.21).
Figure3. 22 : Increase CPICH power with constant power for CCHs and DCHs
In this case many problems will occur in network such as out of synchronization
between uplink and downlink and soft handover area change as it explained in figures
3.23 and 3.24.
+ 20 db
Admission Control Threshold (R99 traffic)
DCH Power
DCH Power
CCH Powers
Maximum RBS
power HSDPA Power
HSDPA Power
100%
75 %
RBS power
- 2 db
+ 2 db
Chapter 3 HSDPA impact
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Figure3. 23 : Uplink / downlink out of synchronization
Figure3. 24 : Soft handover area moving
Ec/No = -18 db
Eb/No = 4. 8 db (Target value for speech bearer)
Area where UE can access to Speech RAB
Area where UE can camp on cell
Out of synchronization area
Cell A Cell B
Cell ACell BSoft
handover Area
CPICH power = + 2db
Chapter 3 HSDPA impact
Sofien Jouini - 63 - PFE 2006/2007
III.4.2. Proposal 2
Ericsson defines a power margin (“HsPowerMargin”) that permits us to control
the reserved power for HSDPA traffic and therefore its impact (figure 3.24).
Figure3. 25 : HsPowerMargin parameter
The maximum degradation of Ec/No value is Max (∆ Ec/No) = HSDPA power
(db).
Max (∆ Ec/No) = [ Max RBS Power (100 %) – R99 power threshold (75 %)
– HsPowerMargin ] = [ 0.25 * Max RBS Power – HsPowerMargin ]
If we increase “HsPowerMargin”, we will reduce HSDPA impact but
we will limit the data throughput and capacity in downlink.
If we decrease “HsPowerMargin”, we improve both capacity (number
of HSDPA users in cell) and data throughput but this will impact R99
traffic.
Thus, it is a tradeoff between a low and high value of “HsPowerMargin”.
Unfortunately, this parameter (“HsPowerMargin) is not configured in TCPU and
therefore we cannot simulate its impact to find its optimum value. Therefore, tests
must be performed on field when we deploy HSDPA.
HsPowerMargin
CCH power
DCH power (CS + PS traffic)
HSDPA power
RBS power
R99 power Threshold
HSDPA power Threshold
100%
75%
90%
Chapter 3 HSDPA impact
Sofien Jouini - 64 - PFE 2006/2007
Ericsson May develop a new feature that permits a dynamic change of
“HsPowerMargin” according to the R99 and HSDPA traffic on cell (like “on demand
bursts” for GPRS). This will be better for good management of network.
III.5. Conclusion
We have studied in this chapter the HSDPA impact on R99 network
performance.
We demonstrated this impact on Ericsson 3G Trial Network in Tunisia through
simulation performed with TCPU. Simulation result has confirmed the theoretical
study.
However, we didn’t get to define an exact strategy of HSDPA deployment with
no impact on R99 traffic. This may be one of the current researches of 3GPP or 3G
products vendors (like Ericsson). In my opinion, the experience on field (live traffic)
will help us to make the decision on what strategy has to be followed to minimize
such impact.
General Conclusion
Sofien Jouini - 65 - PFE 2006/2007
General Conclusion
We have studied several issues in this project wholly related to Ericsson 3G
network optimization either before deploying HSDPA or after.
In the current phase, HSDPA is not yet deployed in all sites but just three. The
performed tasks within this project are mainly; neighbor’s list optimization, isolation
between co-sited and co-area antennas and drive test performing and analyzing. These
tasks are very important for all radio mobile networks, especially for WCDMA as an
interfered and complicated system. We didn’t encounter sophisticated problems
during the drive test activity; problems are classic such as lack of coverage and pilot
pollution.
For the coming phase, where HSDPA is expected to be deployed in all sites, it is
necessary to study its impact on current network performance to realize how to
proceed to minimize the expected drawbacks. The simulation result that we got
confirms well our theoretically study. Thus, it’s necessary to keep in mind that
HSDPA impacts coverage, capacity and traffic distribution (especially between 2G
and 3G systems). In fact, if no tuning will be performed after HSDPA deployment,
R99 traffic users will experience a high degradation of services quality which is too
bad for Tunisian operator since its first experience in 3G market.
We demonstrated that the increasing of Pilot power is not a remedy for the
studied problem. However, we saw that the power margin variable defined by
Ericsson to control the amount of power reserved for HSDPA traffic can be the
appropriate solution of our issue. We didn’t get to simulate the impact of this
parameter to determinate its optimum value. This for the fact that the TCPU version
we dispose of doesn’t support this feature.
References
Sofien Jouini - 66 - PFE 2006/2007
References
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