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1

roduction General introduction

General Introduction:

Itwould be hard to imagine a world without wireless applications and services. Around the globe,

mobile services are playing increasingly important roles in many facets of our society. Just a decade

ago, mobile services consisted primarily of basic voice communication. Today, we depend on mobile

services not only for communication, but also for education, entertainment, healthcare and location.

Mobile services have also made significant inroads into developing nations, by improving the quality

of life for many of their citizens. This evolution of service requires a very high speed data with high

quality.

For this, 3G+ radio access has evolved to support all these kinds of services.

3G+ is now able to push practical bit rates beyond 14Mbps in downlink and about 7 Mbps in uplink. In

addition to the higher peak data rate, 3G+ also reduces latency and improves network capacity.

The contents of this report are summarized as follows: In Chapter 1 we give an introduction to the

UMTS and HSPA network and we explain the main new features of UMTS and HSPA systems. The

second chapter presents design process of HSPA network and explains in detail the dimensioning part.

In The third chapter we explain the redesign and the optimization of radio network and the different

problems which occur on it .

Finally the practical part with real case study.


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UMTS & HSPA systems overview

2

apter 1

Chapter 1: UMTS and

HSPA Systems Overview


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1.1 Introduction

Since its standardization in 1990 GSM has been the predominant 2G technology around the World. In

2007, the GSM Association estimated that a whopping 82% of global market was using the GSM

standard with more than 2 billion users within 212 countries. The key success Factor of GSM has been

the open standard approach, which provided a universal technology HSPA Performance and Evolution

.platform for network operators across different regions around the world. Having an open standard

makes the network equipment from various vendors inter-operable and provides tremendous operation

benefits and cost savings for the network operators. These cost savings are in turn transferred to the

consumers, providing them with the flexibility to move from one operator to the other without

changing their handsets. In the late 1990s, with the wireless industry trends slowly shifting from voice

to data services, the GSM industry decided to design a new network technology that would support

faster and more efficient data transmissions. This new technology, called Universal Mobile

Telecommunications System (UMTS), would be based on the same open concepts as GSM and would

also benefit from the economies of scale resulting from having multiple operators around the world

agree on the same evolution path. The global success of GSM demanded that the 3G standard be

backwards compatible to ensure a smooth technology migration for both network operators and end

users. Following the trend from GSM, UMTS is today the most extended 3G technology worldwide

with 248 deployments, 223 of those including support of High Speed Data services (HSDPA or

HSDPA+HSUPA).Since the introduction of UMTS Release99, the standards have been evolving with multiple major

releases:

- Rel.5 introduced High Speed Downlink Packet Access (HSDPA), an enhancement that permits the

increase of downlink data rates, capacity and significantly reduces latency.

- Rel.6 introduced High Speed Uplink Packet Access (HSUPA), which incorporates similar

Improvements on the uplink direction.

- Rel.7 and Rel.8 provide further improvements to HSDPA and HSUPA, with a strong focus on

application performance.

1.2 UMTS Network Architecture

The UMTS network architecture bears a lot of similarities with that of GSM. The main components of

the UMTS network are the UTRAN (Radio Access) and the Core Network. The Radio Access Part

(UTRAN) takes care of the radio transmission and reception, including segmentation, error protection


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and general radio resource management, among other things. The Core Network is further divided into

Circuit Switched (CS) and Packet Switched (PS) network. The packet core network is the one involved

in data communications, and is composed of two main nodes: the Serving GPRS Support Node

(SGSN) and the Gateway GPRS Support Nodes (GGSN). The SGSN performs PS mobility

management, packet routing and transfer, authentication and charging. The GGSNs main functionality

is the routing of packets to and from external networks. It also performs authentication and charging

functions, and is the main node responsible for Quality of Service (QoS) negotiation. Within the

UTRAN, a Radio Network Subsystem (RNS) contains the Radio Network Controller (RNC) and its

corresponding Node-Bs. The RNS is equivalent to the Base Station Subsystem (BSS) in GSM. Each

RNS is hosted by the core network through the Iu interfaces (IuCS for voice and IuPS for data). Its

counterparts in a GSM system are the A and G interfaces for CS and PS respectively. Node-B and

RNC are connected through the Iub interface, which is similar to the Abis interface between the BTS

and BSC of a GSM system.

UTRAN defines a new interface between different RNCs for mobility control over the RNC

Boundaries, the Iur. The Iur interface enables soft handovers along the RNC boundaries. There is not

an equivalent interface in GSM.

Figure 1. 1: UMTS Network architecture.

1.2.1 System interfaces

The UMTS network has the following interfaces:

Cu Interface:is the electric interface between USIM card and ME.


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Uu Interface: is the radio interface of WCDMA. UE connects to the fixed network part of the

UMTS system via Uu interface. It can be said that Uu interface is the most important open

interface in the UMTS system.

Iu Interface: is interface between UTRAN and CN. Iu interface is an open standard interface.

This enables the UTRAN and CN connected by Iu interface to be provided by different equipment

manufacturers.

Iur Interface: is interface between RNCs. It is used for the mobility management of MS in the

RAN. For example, in the soft handover between different RNCs, all the data of MS are

transmitted from the working RNC to the candidate RNC via Iur interface. Iur is an open

standard interface.

Iub Interface:it connects Node B and RNC. Iub interface is also an open standard interface. This

also enables the RNC and Node B connected by Iub interface to be provided by different

equipment manufacturers .

1.2.2 Channels

Logical channel: The logical channel denes the type of information being transferred. There are

two categories of logical channel, control channels and traffic channels. Control channels are used

to transfer control plane signaling whereas traffic channels are used to transfer user plane data.

Name function

Trafic DTCH (Dedicates Traffic CHannel) for transfer date to user ; bidirectional

CTCH (Common Traffic Channel) Channel point to multipoint used to transfer

date to group of users ; DL only

Contrle BCCH (Broadcaste Control Channel) for broadcast system information ; DL only

PCCH (Paging Control Channel) For paging ; DL only

DCCH (Dedicated Control Channel) For transfer control information (call

establishment , handover, etc.) dedicated to one

user ; bidirectional.

CCCH (Common Control Channel) For transfer control information shared by

users ( initial access ) ; bidirectional

Table 1.1 : logical channels.


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Transport channel: The transport channel denes how information is transferred. There are two

categories of transport channel, common and dedicated. Common channels can be used by more

than a single UE whereas dedicated channels can be used by only a single UE.

Les canaux Description

Dedicated Channel (DCH)- bidirectional

- dedicated only for one user

Downlink channels

Broadcast Channel (BCH) Emission of system information

And specified cell

Paging Channel (PCH) Transmission of paging

Forward Access Channel (FACH) Bears small quantity of user data

Downlink shared Channel (DSCH) Used to dedicated control or traffic data

Uplink channels

Random Access Channel (RACH)Initiates Access

Common packet channel (CPCH)-only in FDD mode

-Transmission of data traffic burst

Uplink sharred channel (USCH)- only in TDD mode

-bears taffic control

Table 1.2: transport channels.

Physical channel:The Transport Channels are received by the physical layer and mapped onto

Physical Channels. Physical Channels dene how the Transport Channels use the physical medium

(i. e. chips and codes). A Physical Channel is structured in frames and slots. A frame lasts 10 ms

and consists of 15 slots. Since UMTS works with a chip rate of 3.84 Mega chips/s, this translates

into 2560 chips per slot. The frame and slot structure allows organizing the information on the

Physical Channels.


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1.3 WCDMA air interface Elements

1.3.1 User Equipment (UE)

In UMTS the term UE is the equivalent of the mobile device in GSM. Although the concept of UE is

not limited to handset or data cards. Most UMTS UEs are multi-band dual mode devices, i.e.

supporting both GSM and UMTS, to ensure backward compatibility with the 2G network. In todays

devices, a very common combination is quad band GSM, plus dual band UMTS support. This allows

users to travel from network to network without noticing the technology or the band changes, In recent

Name function

Dedicated DPDCH (Dedicated Physical data

channel)

To transport data dedicated to user ;

bidirectional

DPCCH (Dedicated Physical

control channel)

To control DPDCH ; bidirectional

Communs

PRACH (Physical random access

channel)

For initial access for mobiles to the

network ; UL only

PCPCH (Physical common packet

channel )

Shared Channel ; UL only

PDSCH (Physical downlink shared

channel)

Shared channel sporadic transmission

down s ; DL only

PCCPCH (Primary common control

Physical channel)

SCCPCH(secondary common

control Physical channel)

Broadcast system information (primary ;

DL only )

Communs

AICH (acquisition indicator

channel)

For respeonse of physical for initial

Access ; DL only

SCH (synchronization channel) Allow mobile ; DL only

CPICH (common pilotchannel) allow mobile to synchronize on cell and

and estimate the received power

Table 1. 3 :physiscal channels.


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years, there are more and more UEs supporting HSPA capability .With the increase of data traffic

demand and reduction of the chipset prices, it can be expected that most of the UMTS terminals will

support HSPA in the near future.

1.3.2 Node-B

The Node-B is the equivalent of the GSM Base Station (BTS). It hosts all base band equipment (such

as channel elements and processing boards), radio components and power system. In general, all these

are called radio resources which play a central role in the planning and optimization process of the

UMTS network. One Node-B will typically serve three sectors, and each of these can be configured

with multiple carriers (frequency channels). The Node-Bs are connected to a centralized node, called

Radio Network Controller (RNC) via the Iub interface.

1.3.3 Radio Network Controller (RNC)

The RNC is the brain of the Radio Access Network (RAN) and is responsible for the Radio Resource

Management (RRM) of the cells. The RNC performs functions such as admission control and

congestion control; it also manages the UE mobility and macro diversity combining on the uplink,

which enables soft handovers .With the support of Iur interface, one UE can be connected to more than

one RNC at a time. In such a scenario, the RNC controlling the signaling and the link radio resources

is the Serving RNC (SRNC), while the new RNC is called Drift RNC (DRNC) and will support the

Serving RNC by providing network resources through the Iur interface. Serving RNC relocation and

soft handover over Iur are the main functions for mobility control along the RNC boundaries.

Figure 1. 2: UTRANarchitecture.

1.4 Air Interface Technology:

The most important improvement introduced by UMTS is the air interface. The technology Selected

for the air interface is called Wideband Code Division Multiple Access (WCDMA).


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The following are the key characteristics of the WCDMA technology as compared to the GSM air

interface:

frequency reuse one.

spread spectrum technology.

use of fast power control.

use of soft handover.

Unlike GSM, this is based on Time Domain Multiple Access (TDMA) technology, WCDMA applies

spread-spectrum modulations schemes in which user data (typically with Small bandwidth) is spread

over a channel with large bandwidth. All users share the same Spreading spectrum and each user is

identified by a unique channelization code assigned by the system. The channelization codes are

orthogonal to each other to ensure the independency of each channel. Figure 1.3 shows the differencebetween CDMA and TDMA frequency Utilization scheme.

Figure 1. 3 CDMA vs. FDMA, TDMA different frequency utilization scheme.

1.4.1 Power Control

Since all users share the same frequency in a WCDMA system, it becomes absolutely essential to

manage interference from all radio links. A fast power control mechanism operating at 1500 Hz helps

control the power transmitted by each of the users, making sure they use just the amount of power they

need, and at the same time improving the link protection against fast fading.

1.4.2 Soft Handover

Soft handover is a unique feature in the WCDMA technology. The capability of keeping at least one

active radio link during the cell transition provides significant benefits for UE mobility performance.

Soft handover also takes advantage of macro-diversity combining of multiple radio links and improves

the capacity and performance of the system.


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1.5.1 HSDPA (High Speed Downlink Packet Access)

Rel.99 was an important milestone in the development of the 3GPP standards. It ensured a Smooth 3G

migration for the GSM network. The introduction of UTRAN provides substantial Performance

enhancements over the GSM system. However, since a lot of attention was given to the backward

compatibility with the existing GSM core network, many compromises were made in order not to

change the core network structure.

From a radio spectral efficiency standpoint, Rel.99 is very primitive because it dedicates Channel

resources to each data user, and power control mechanisms are the same between real time applications

such as voice and non real-time data. Dedicating channel resources for each data user is inefficient.

Since data is bursts in nature, implementations which can leverage the user multiplexing are more

efficient at delivering data: that is the reason why HSDPA was introduced to improve the offering of

data services on UMTS networks.

With the introduction of the High Speed Downlink Shared Channel (HS-DSCH), fast HSDPA

scheduler, adaptive modulation and coding and fast retransmission (HARQ), Rel.5 HSDPA is able to

deliver improved downlink cell throughput up to 14.4 Mbps. In addition to the Data rate improvement,

HSDPA also reduces network latency.

Main HSDPA Features :

The introduction of HSDPA represented a revolution of the existing WCDMA standards, with

Significant impacts in several parts of the Radio Access Network. The key modifications Introduced

were:

Introduction of a shared data channel, multiplexed in time (TDM).

Introduction of new modulation (16QAM) and coding schemes, with the possibility to transmit

with up to 15 parallel channelization codes.

Modification of the MAC protocol architecture to enable faster response to changes in user

demands and radio conditions.

Introduction of Adaptive Modulation and Coding (AMC) and new error correction

mechanisms in the MAC layer (HARQ).

One important improvement brought by HSDPA is the latency reduction.

We have noted that many performance managers and network designers in different wireless

companies use peak throughput when designing, evaluating or optimizing their data network. In

addition to the new traffic channel, HSDPA modifies the architecture of the radio protocols to better


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manage the resources provided by the shared channel. Adaptive modulation and coding (AMC), hybrid

automatic repeat request (HARQ) and fast packet scheduling complement the offer, taking full

advantage of the faster network dynamics to improve the efficiency of the data transmissions.

HSDPA Channel Structure:

High speed downlink packet access (HSDPA) was introduced in Rel.5 to provide enhancements over

Rel.99 to compete with EVDO and WiMAX. To increase the channel utilization efficiency, HSDPA

introduces a new physical channel called high speed downlink shared channel (HS-DSCH). This

channel is shared among all data users and uses a 2 ms frame or TTI (Transmission Time Interval), as

compared to the 10 ms radio frame used by Rel.99 channels. The shared channel is a completely new

concept compared with the conventional UMTS Rel.99 in which each user had dedicated resources. A

big shared data pipe provides the benefit of statistical multiplexing among all data users and thus

improves the overall system efficiency. Along with this new channel, there are several associated

channels defined in the standard as well. Table.1.4 lists all these channels and their functions.

Channel Description

Downlink HS-DSCH

HS-SCCH

- High Speed Downlink Shared Channel. Transport channel

carrying user plan data.

- High Speed Shared Control Channel. Common control channel

for HSDPA. Carrying information such as modulation, UE

identityetcUplink HS-DPCCH - CQI reporting, HARQ Ack/NAck

Table 1.4 : new channels introduced for HSDPA.

New Modulation and Coding Schemes

While Rel.99 only supported one type of modulation (QPSK), in HSDPA three different Modulation

schemes have been defined: QPSK, 16QAM and 64QAM. Typical devices today support QPSK and

16QAM, and at least five parallel codes. With five codes allocated to HSDPA, QPSK can provide 1.8

Mbps peak rate and 16QAM can reach 3.6 Mbps.

Modified Protocol Architecture

Rel5 introduced a modification of the radio protocol architecture. The MAC layer was split in two sub

layers, each of them located in a different network element: MAC-d, located in the RNC and MAC-hs,


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located in the Node-B. The data to be transmitted on the HS-DSCH channel is transferred from Mac-d

to Mac-hs via the Iub interface. A Mac-hs entity has four major functionality components:

Flow control, which manages the data flow control between Mac-d and Mac-hs.

Scheduler, which manages the HSDPA resources in the sector.

HARQ entity.

Transport Format and Resource Combination selection entity.

Adaptive Modulation and Coding (AMC)

Adaptive modulation and coding (AMC) provides an alternative to the conventional CDMA fast power

control for link adaptation. With AMC, the coding rate and modulation scheme for each user is

dynamically adjusted based on the average channel condition of the radio link. In general, the channel

power is constant over an interval defined by the system. The link adaptation is achieved by assigning

a different modulation scheme or coding rate to each user based on the channel condition reported by

the terminal device. The channel quality index (CQI) has been defined in the standard to report the

channel condition measured by the mobile to the HSDPA scheduler .However, the calculation of the

CQI value is not clearly defined in the standard, and hence variations among handset vendors in CQI

reporting can be expected.

HARQ (Hybrid Automatic Repeat Request)

HARQ improves throughput by combining failed transmission attempts with the re-transmissions,

effectively creating a more powerful error correction scheme. Hybrid ARQ can be combined withAdaptive Modulation and Coding (AMC), making the initial selection of Modulation and code rate

more tolerant to errors. HSDPA defines two different Hybrid ARQ methods: Chase Combining and

Incremental Redundancy (IR), that will be selected based on the UE category and network

configuration. With Chase Combining, the re-transmitted data is identical to the original transmission.

HSDPA UE categories

The different HSDPA UE categories are outlined in the table below. From this it can be sent that the

overall raw data rate and hence the category is determined by a number of elements including the

maximum number of HS-DSCH codes, TTI, block size, etc.


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UE Category Codes Inter-TTI

Interval

MAX TB Size IR Buffer Size Peak Rate

Category 1 5 3 7298 19200 1.2 Mbps

Category 2 5 3 7298 28800 1.2 Mbps

Category 3 5 2 7298 2800 1.8 Mbps

Category 4 5 2 7298 38400 1.8 Mbps

Category 5 5 1 7298 57600 3.6 Mbps

Category 6 5 1 7298 67200 3.6 Mbps

Category 7 10 1 14411 115200 7.2 Mbps

Category 8 10 1 14411 134400 7.2 Mbps

Category 9 15 1 20251 172800 10.1 Mbps

Category 10 15 1 27952 172800 14 Mbps

Category 11 5 2 3630 14400 0.9 Mbps

Category 12 5 1 3630 28800 1.8 Mbps

Table 1.5: UE categories.

1.5.2 HSUPA (High Speed Uplink Packet Access):

It has been generally accepted that internet traffic has an asymmetric nature, that is, users are more

likely to download content from the internet than to upload their own information. Such a trend was

determined by the wide utilization of applications such as web browsing, content downloading (music,

documents, etc.) and audio or video broadcasting which predominantly generate traffic on the

downlink. However, with the emergence of more social networking applications such as YouTube and

MySpace, the demand on uplink capacity has been steadily increasing. Users will upload information,

typically multimedia, from their own PC or other consumer electronic devices to the internet on a

regular basis and share them with other members of the virtual community they belong to.

Main HSUPA Features:

In 3GPP release 6, enhanced uplink performance, also known as HSUPA, was proposed to improve the

uplink dedicated transport channel performance for data services. The goal was to provide significant

enhancements in terms of user experience with increased throughput, and higher capacity.

HSUPA enhanced uplink includes a set of new features, very similar to the ones introduced Previously

by HSDPA in the downlink direction. The impact of these changes on the existing Protocols and

network structure was not significant:


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This table resumes the Differences between HSDPA and HSUPA

Features HSDPA HSUPA

Maximum throughput 14.4M bps 5.76 Mbps

NodeB based

scheduling

Yes Yes

TTI 2 ms 2 or 10ms

Modulation 16QAM and QPSK QPSK

HARQ Yes Yes

Transpor t channel Shared HS-DSCH Dedicated E-DCH

Scheduling scheme Rate control Power control

AMC Yes No

Handover Cell change Soft handover but serving cell follows HSDPA

Table 1.6: Differences between HSDPA and HSUPA.

1.6 Summary

In this chapter, we have provided an overview of a UMTS networks components and Capabilities. We

focused on the data capabilities of UMTS, namely HSDPA on the downlink and HSUPA on the

uplink; we provided an overview of the channel structures, In a nutshell, these are the main benefits

of the HSPA technology as compared to the legacy ofRel.99 channels:

Higher peak rates (14.4 Mbps in downlink, 5.76 Mbps in uplink).

Faster network dynamics and reduced latency (90 ms with HSDPA, 50 ms with HSPA).

New link adaptation and hybrid ARQ processes very efficient thanks to the shorter radio

frames.

The combined effect of all the improvements will result in higher spectral efficiency too.

HSPA RF planning requires a special treatment as compared to regular UMTS traffic.

The link budget analyses for HSDPA and HSUPA indicate that it is possible to achieve very

good bitrates (around 1 Mbps) at large separation distance from the site (over two miles).


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3G+ radio access network design

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2.1 Introduction

Radio Network design is a simplified analysis for radio network; it provides the first and most rapid

evaluation of the network element number as well as the associated capacity of those elements. The

target of dimensioning phase is to estimate the required site density and site configurations for the area

of interest. Design activities include radio link budget and coverage analysis, capacity evaluation and

final estimation of the amount of NodeB hardware and E1, cell average throughput and cell edge

throughput.

2.2 Dimensioning

2.2.1Coverage dimensioning

In the coverage dimensioning, radio link is estimated according to elements such as planned area,

network capacity and equipment performance in order to obtain the allowed maximum path loss. The

maximum cell radius is obtained according to the radio propagation model and allowed maximum path

loss. Then, the site coverage area is calculated. Finally, the site quantity result will be defined. Of

course, the site quality is only for the ideal cell status, and some additional sites will be needed in

actual terrain environment.

R99 Uplink Budget

Path Loss= UE Tx Power + Antenna Gain + SHO Gain -Margins Loss -Node B sensitivity.

Antenna gain=UE Antenna Gain + Node B Antenna Gain.SHO Gain=SHO Gain against Slow Fading+SHO Gain against Fast Fading.

Margins=Slow Fading Margin Fast Fading Margin Interference Margin.

Interference Margin( noise rise) = 10log(1 )[dB].is the uplink cell load.Loss=Body Loss + Cable Loss + Penetration Loss.

Node B sensitivity (dBm)= -174(dBm/Hz)+1.6(dB)+Eb/No-PG.

Eb/No:required Eb/No to maintain service quality.

PG:Processing Gain.

R99 Downlink Budget

Path Loss= Node B Tx Power + Antenna Gain + SHO Gain -Margins Loss- UE sensitivity.

Antenna gain=UE Antenna Gain + Node B Antenna Gain.

SHO Gain=SHO Gain against Slow Fading+SHO Gain against Fast Fading.

Margins=Slow Fading Margin Fast Fading Margin Interference Margin.


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Interference Margin=Noise Rise= I/ P. Where Iis the total interference and Pis the receiver

noise.

Loss=Body Loss + Cable Loss + Penetration Loss.

HSPA Link Budget Principle

The HSDPA link budget is usually based on the R99 link budget to get the cell edge throughput in

downlink. there is a parameter specific for HSDPA that is used alongside Ec/No to get the cell edge

throughput, the so called coupling loss.

DL_Coupling Loss= PL_DL + Lf_BS - Ga_antenna +Lb+SFM+ Lp.

PL_DL:Downlink path loss.

Lf_BS:cable loss of NodeB.

Ga_antenna: Gain of UE antenna and NodeB antenna.

Lb:Body loss.

SFM: Slow fading margin without soft handover.

Lp:Penetration loss

Cell edge Ec/No

Ec/ No = 10 log( ()

)

PHS-DSCH : total power of HS-DSCH channel

: non- orthogonality factor.

f: neighbor cell interference factor

: downlink load factor including R99 and HSDPA servicePmax:max transmission power of downlink

Nt:thermal noise power spectral density , typical value is -108.16dB

NF :receiver noise figure of UE, typical value is 7dB


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Figure 2. 1 HSDPA Link Budget Principles.

Propagation Model

In our radio network planning, COST231-HATA (modified by Huawei technologies) is chosen

as adequat propagation model according to Algeria topography, frequency band and the technology

used. The formula for path loss is: Lu (dB) =46.3 + 33.9*log (f) - 13.82*log (Hb) - a (Hm) + [44.9 -

6.55*log (Hb)]*log (d) + Cm. where: a (Hm) = [1.1*log (f) - 0.7]*Hm - [1.56*log (f) - 0.8] .

2.2.2 Capacity dimensioning

The second phase of dimensioning is estimating the amount of supported traffic per base station site

based on given traffic model.When the frequency reuse of a WCDMA system is 1, the system is typically interference-limited and

the amount of interference and delivered cell capacity must thus be estimated.

Traffic model

We need to set up an expected traffic model of the customer so that we can plan the network properly

.Traffic model is one user profile in one hour, it must be measured in busy hours , because only in busy

Scenario Cm

Dense urban 3

Urban 0

Suburban -8

Rural and road -15

Table 2.1: CM values.


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hours the traffic will reach to each maximum value and we need to know our network support

maximum traffic in busy hours or not .

Service Value

UL DL

AMR12.2 (Erl) 0.02 0.02

CS64 (Erl) 0.0001 0.0001

PS64 (kbit) 504 0

PS128 (kbit) 0 1008

PS384 (kbit) 0 1008

HSPA (kbit) 4536 18144

Table 1.2 Example of Traffic Model in busy hour per user.

Uplink Interference Analysis

The uplink load per cell is the total received power coming from all terminals divided by the total

received power. The uplink load factor of one connection is given by:

=

Where Pis the received power from the user j and Iis the the total received wideband powerincluding thermal noise power in the base station.

The uplink load factor for the cell can be written as:

= ( +)

= ( + )

+

where W is the chip rate,

is the activity factor of user j, N is the number of simultaneously connected

users in the cell, Ris the bit rate of user j, and f is the ratio of other cell to own cell interference.

When the uplink load factor is 1, Iis infinite, and the corresponding capacity is

called threshold capacity.

From the equations we can calculate the number of uplink simultaneously connected users in the cell


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=

Downlink Interference Analysis

The downlink load factor for the user j can be written as:

=

=

(/ ) ( + +

)

/

Where Pis the transmission power of Node B for User j, Pthe downlink maximum power of one

cell , P is the actual transmission power of Node B,is non-orthogonality factor in the downlink and

CL is Downlink Coupling Loss. We Define the downlink load factor for the cell as:

=

So the number of downlink simultaneously connected users can be calculated as total

transmission power used by traffic channels in a cell divided by the power used by single user

as shown in the equation below:

=

=

Actual Load Calculating

The purpose of capacity dimensioning is to determine the actual total load factor for each cell.

According to the previous calculation we can obtain the actual total cell load in two senses by the two

formulas:

Uplink: _ = ,+ +

Downlink:

_ + = ,+ +

Calculation of average CS Cell Load

Uplink:


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=

Downlink:

= (

+

)

(

+

)

Where Ris the ration of SHO.

Calculation of average PS Cell Load

=

Where Nthe number of equivalent is is is channels for service i and is given by the formula:

= ()() Where:

ThroughputPerUser: is the Throughput per user for the service i.

R : is the ratio of data retransmission for service I because of block error.

R : is the traffic ratio burrstone.

1.2.5HSPA capacity dimensioning :

The purpose of HSPA capacity dimensioning is to obtain the required HSPA power to satisfy the cell

average throughput.

During the HSDPA capacity dimensioning procedure, we know the Cell Coverage Radius (obtained

from the coverage planning) and Cell Average Throughput (obtained from the traffic model), and we

want to get the HSDPA Power Allocation based on simulation.

For the HSUPA capacity dimensioning procedure, we know the Cell Coverage Radius (obtained from

the coverage dimensioning) and Cell Average Throughput (Obtained from the traffic model),

then we can calculate the needed load in uplink.


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Figure 2. 2: HSDPA capacity dimensioning procedure.

In our project our target in the uplink and downlink load factor for R99&HSPA is :

Every time we find the actual total cell load factor higher than the target we increase the number of site

in this area because if we increase the load factor the noise rise increases too.

UL Cell Load Factor 50%

DL Cell Load Factor 75%

HSDPA Cell Load Factor 90%

HSUPA Cell Load Factor 75%

Table 2.2 :Total target cell load.

CE Dimensioning

Each user signal is extracted and processed by an individual electronic circuit; this circuit is called

Channel Element CE. There is two types of channel elements, Uplink and Downlink CE.

HSDPA channels dont occupy R99 CE resource, but we should calculate the A-DCH CE witch its

consumption depends on its bearing rate.

=

=

= ,+ +


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Bearer Up Link Down Link

CE Number CE Number

AMR 12.2kbps 1 1

PS 64Kbp 3 2

PS 64Kbps 3 2

PS 128Kbps 5 4

PS 384Kbps 10 8

Table 2.3 :CE mapping for R99 bearer.

Traffic Up Link Down Link

HSDPA Traffic --- 0 CE

HS-DPCCH 0 CE ---

A-DCH(DPCCH) 3 CE 1 CE

Table 2.4: HSDPA CE elements consumption.

2.3 Planning study:

Based on the network dimensioning, site information, geography and traffic distribution, we used U-

NET and digital map to do our planning. Initially we located site, then we implemented parameters

such as antenna type, azimuth, tilt, and altitude, after that we introduced the cell parameter such as

transmission power of traffic channel and common channel, orthogonal factor, primary scrambling

code Analysis is made to check whether the coverage and interference of the system meet the

requirements or not. Finally, the system capacity is analyzed to check whether it meets the

requirement.

2.3.1 Preparations for Necessary Input Data

Coordinate system

One general requirement for radio network planning tool digital maps are the ability to support various

projections, ellipsoids and coordinate systems. Examples include the Universal Transverse Mercator

projection and the WGS-84 ellipsoid. The necessary coordinate systems depend not only on the

internal needs of the RNP tool, but also on the external software the RNP tool is interfacing.


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Digital Map

The most important basic preparatory requirement for any RNP tool is a geographical map of the

planning area. The map is needed for coverage (link loss) predictions and subsequently the link loss

data is utilised in the detailed calculation phase and for analysis purposes. For network planning

purposes, a digital map should include at least topographic data (terrain height), morphographic data

(terrain type, clutter type) and building location and height data , in the form of raster maps.

Importing Sites

When planning third-generation networks, a typical scenario is that an operator may wish to utilize

existing second-generation networks as much as possible. Therefore it is important for an RNP tool to

provide support for importing 2G site locations and basic antenna data into a new plan, especially

when making a combined network plan for both 2G and 3G networks. Site import functionality

automatically brings site and antenna information into an RNP tool plan. Naturally, such automatic

importing of data saves network planners time. The imported information may include site location,

site ground height, number of cells and antenna directions

Antenna Editor

In RNP tools, 'antenna' is a logical concept that includes antenna radiation pattern and parameters such

as antenna gain and frequency band. Once antenna is defined, it can then be assigned and used for

selected cells and coverage predictions.

Transmitters

A transmitter is the source or generator of any signal on a transmission medium. A transmitter is a

piece of equipment composed of some antennas located on a site.

Cells

Each carrier on a transmitter defines a WCDMA cell; cell table gives the carrier characteristics on a

transmitter.

User Profil

Depending on the interests and abilities of each individual category, we defined two types of

users: Business user and standard user . For each profile, we defined the services that will be

used, the number and communications duration.


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Terminals parameters

The following table presents the performance for R99 and HSPA terminals, which will be used in the

radio network design.

Figure 2. 3: Terminals Parameters.

Mobility parameters

We define for each type of speed a type of mobility. Each type of mobility is characterized

by a minimum value of Ec/Io achievement for a cell so that it can access to the Active Set.

The simulations have given a value of -15 dB for all environments and all speeds.

Planning Neighbors

We can allocate neighors for each cell manually or automatically. We can define two types of

neighboring. The following neighbor types in a UMTS network:

Intra-technology neighbors: Intra-technology neighbors are cells defined as neighbors that

also use UMTS. Intra-technology Neighbors can be divided into:

Intra-carrier neighbors: Cells defined as neighbors which perform handover using the

same carrier.

Inter-carrier neighbors: Cells defined as neighbors which perform handover using a

different carrier.

Inter-technology neighbors: Inter-technology neighbors are cells defined as neighbors that

use a technology other than UMTS.

In our case we choose the automatically intra technology neighbor allocation and exactly intra-

carrier neighbors. For that we fixed the following parameter to decide which cell can be

considered as a neighbor: Max. Inter-site Distance (maximum distance between the reference cell and a possible

neighbor) = 1000 m.

Max. Number of Neighbors (maximum number of intra-carrier neighbors that can be

allocated to a cell) = 16.

Coverage Conditions: The coverage conditions must be respected for a cell to be


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considered as a neighbor :

Signal Level (Pilot) > -95 dBm

Ec/Io > -12 dB

Ec/Io Margin (dB) (difference of EcI0 between reference cell A and possible neighbor

cell B in the overlapping area.): 5 dB

% Min. Covered Area (The minimum, in percentage, that a possible neighbor cells

coverage area must overlap the reference cells coverage area) = 10%.

Carriers: The carriers on which we run the allocation.

After analyzing the Log file collected by Drive Test we did some modification in the neighbor list to

optimize the network parameters.

2.4 Summary :

In this chapter we have explained the design process of of 3G+ radio access network including

dimensioning and planning, dimensioning process consist to determine the number of sites required to

cover an area and estimating the amount of supported traffic per base Station site based on given traffic

model.

After dimensioning planning and simulation comes comes the stage of site integration, this is the last

step before launching the network .


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3G+ radio access network redesign and optimization

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3.1 Introduction

the Radio Network redesign and Optimization , is to reasonably adjust the communication network

planning and design as per certain criteria so as to enable the network operation more reliable

and economical, improve the network service quality and Resource utilization, which is of great

importance to network carriers.

While questing for reasonable utilization of network resource and improving the Service quality

to the greatest extent, the network optimization solution can provide Evidences and principle for

future network expansion. The network optimization can supplement and correct the network

planning that was well implemented but has some aspects not considered, adjust and correct to

network when the conditions (Such as transmission environment and traffic) change. Therefore, in

the whole Solution, the network optimization plays a key role.

The optimization process goes through several steps: single site verification, RF optimization and

service optimization.

3.2 Single Site Verification

The purpose of single site verification is by using Scanner + UE to: Verify coverage (RSCP & Ec/Io),

verify scrambling codes, and verify no installation faults and Verify the base function.

3.3 RF Optimization

Any RF issues at edge of cluster must be resolved in coordination with the adjacent cluster as soon aspossible. The purpose of RF optimization is by using Scanner + UE to optimize CPICH and service

coverage and cell dominance , minimize interference , minimize pilot pollution ,optimize neighbor list

, resolve any RF-related drop call and improve connected ratio, delayed time connected .

3.3.1 Redesign Recommendation and Implementation

Changes will mainly include:

Engineering parameter adjustment and neighbor list change.

Engineering Parameter AdjustmentMost of the problems of coverage or interference can be solved by adjusting the Engineering

parameter. The purpose is to enhance the coverage to eliminate the blind Area or conversely to control

coverage and interference. To be specifically, to use the Combination of ways below:


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power control

Access parameters

Other related parameters.

The influence caused by the cell parameters adjustment should be analyzed carefully by optimization

engineer.

The parameters adjustment to a live network should be performed when traffic is low (for example: at

midnight). It is essential to do the service functional test after Adjustment.

Figure 3.1 : optimization work flow.

3.5 Performance indicators

Key Performance Indicators (KPIs) are a minimum set of metrics for tracking system progress toward

a performance target. During network deployment and optimization, several sets of KPIs can be

dened.


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2) Coverage probability (DT) (CPICH Ec/Io dB & the UL transmit power of planned

whole coverage services< dB & the total test miles of reverse forward RSCPdBm/ total

miles of test route*100%.

3) SHO ratio(DT) (A2 A3)/ ( A1 +A2+A3), In DT A1 indicates that the quantity of cell

in active set is 1, A2 indicates that the quantity of cell in active set is 2, A3 indicates that

the quantity of cell in active set is 3

4) Pilot pollution ratio (DT) The point of the number of the CPICH which can enter the

Active set more than 4 /total number of drive test data*100%

5) UL interference cell ratio (Stat.) The number of cells which RTWP in half an hour is

higher than -98dBm / total cell number*100%

Accessibility

1) Radio paging success ratio(Stat.) The successful time of CN paging UE / total paging

times of CN*100%

2) RRC setup success ratio (Stat.) RRC connection setup success time / RRC connection

request time received by RNC*100%

3) RAB setup success ratio (Stat.) The number of 'RAB setup complete' in CS domain or

in PS domain received from UE/ Receive number of CS or PS RAB setup request which

is sent by CN*100%

4) PDP activation success ratio (DT&CQT) PDP activation success time/PDP activation

request time*100%

Retain ability

1) CS drop call ratio (DT&CQT) Service drop call time/Service access time*100%

2) PS drop call ratio (DT&CQT) PS service drop call time/PDP success activation time

Service Integrity

1) UL/DL BLER worsening ratio(DT&CQT) The number of point which UL/DL BLER is

higher than threshold value / UL/DL total test point *100%

2) MOS (Mean Opinion Score) (DT&CQT) Using equipment to test the score of MOS

3) UL/DL average throughput(DT&CQT) Average throughput statistic from application layer.


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3.5.1 RF optimisation Target:

Target Item Reference Value

Coverage Probability 95% (CPICH Ec/Io -12dB & RSCP -95dBm)

CPICH Ec/Io -12dB 95%

CPICH RSCP -95dBm 95%

SHO Percentage 30% - 40%

Pilot pollution Percentage 5%

Table 3.2: RF Optimization Target.

3.6 Category of optimization problems:

3.6.1CoverageOptimization

a- Classifying and Defining Coverage Problem

1. Signal Dead Zone

Definition:

A signal dead zone generally refers to the area where the pilot signal is less than the Lowest access

threshold (such as RSCP threshold is -115dBM, Ec/lo threshold is -18dB), and the area can be a

concave area, hill rear, elevator shaft, tunnel, Underground garage or basement, and internal part

in a tall building.

Reasons: Lack of NodeBs

Incorrectly configured sectors

NodeB shutdown due to power amplifier fault .

The over great indoor penetration loss causes weak coverage.

Steps for Resolving signal dead zones :

Adjust antenna for increasing coverage .

Use RRU , repeater or leakage cable

Construct a new node B

Use indoor distributed coverage system

Adjust radio parameters .


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Figure 3.2: Coverage dead zones.

2. Coverage Hole :

Definition

A coverage hole refers to the coverage area where the pilot signal is lower than the lowest value

required by full-coverage services such as voice, VP and PS 64K Service, but higher than the

lowest access threshold of mobile phones.

Reasons:

- Practically some as dead zone problem.

Steps for Resolving coverage hole

Adjust antenna for increasing coverage

Use RRU , repeater or mini site

Adjust the max radio link power for the service

Figure 3.3: coverage hole.

3. TransRegional Coverage (overshooting):

Definition:

The trans-regional coverage usually refers to the coverage of some base stations exceeds the planned

scope. The trans-regional coverage can cause discontinuous dominant areas in the coverage of other


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base stations if the strength of trans-regional signal meets the requirement for the full-coverage

services. The trans-regional coverage is called also overshooting, when a call is accessed to the

Island area which is far from a nearby base station and the nearby cells are not set as adjacent cells

to Island the during setting the cell handover parameters, the call drop will happen as soon as the

mobile phone leaves the "Island.

Reasons :

Cell has too high altitude

Small down tilt, 0 degree.

close cells have overshooting as well .

Steps for Resolving TransRegional coverage:

Change site location.

Adjust mechanical tilt angle of the cell .

Adjust the pilot power can be adjusted or the electric tilt angle antenna can be used so as to

remove the "Island effect by reducing the coverage.

Figure 3.4: overshooting.

4- Pilot Pollution

Definition:

The pilot pollution means that too many pilots are received on a point, in which there

has not a dominant pilot.

the following method is used to judge the existent of the pilot pollution:


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- the number of the pilots that meet the condition CPICH _ RSCP > -95dBm is more than 3 with

(1st _ CPICH RSCP - 4 th _ CPICH RSCP dB) < 5 db.

The reason of adding the judgment to the absolute threshold of pilot RSCP is to distinguish coverage

hole from no dominant call in the edge of the target coverage area. No matter it is the coverage of a

micro cell or a macro cell, if the pilot pollution happens, the available signals will be influenced, which

leads to the increased lo, decreased Ec/lo and increased BLER and causes the ping pong handover and

call drop.

Reasons :

In general, the possible reasons for pilot pollution may be the unreasonable site distribution.

too high the location of the base station .

too high antenna unreasonable directional angle of the antenna, and the influence caused by the

back radiation of the antenna,

Unreasonable setting of pilot power and the influence of around environments.

the influence of around environment can be the obstacle of tall building or mountain, signal

transmission extended along streets or water area or signal reflection caused by the glass curtain

wall on the tall building.

Steps for resolving pilot pollution problem:

Adjust the position of the site or adjust the antenna.

Reduce the poser of the CPICH channel

Figure 3.5 :pilot pollution.


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5-Unbalanced Uplink/Downlink

Definition:

The unbalanced uplink/downlink refers to the restricted uplink coverage (for example, the transmitting

power of UE cannot meet the uplink BLER requirement although it reaches the maximum) or the

restricted downlink coverage (for example: the transmitting power of the dedicated downlink channel

code cannot satisfy the downlink BLER requirement although it reaches the maximum) in the target

area.

Reasons :

Uplink interferences

Downlink interferences.

Steps for resolving cross-cell problem :

checking the antenna feeder installation and adding the RF configuration.

for the problem happens on the antenna shared by 3G and 2G system, it can be solved by adding a

band-pass filter

For the uplink coverage restriction on the cell edge, it can be solved by improving the base station

sensitivity with the tower amplifier, subject to due downlink capacity loss

For the unbalanced up/downlink due to the restricted up/downlink power It can be solved using

by sector splitting or adding carrier frequency, or by establishing the new micro cell

6- Cross-cell coverage:

Definition:

Cross-cell coverage refers to the fact that the coverage range of some NodeBs is beyond the planned

range and discontinuous primary pilot coverage areas form in coverage areas of other NodeBs.

Reasons

Bad installation of feeders .

Steps for resolving cross-cell problem

Adjust the mechanical tilt angle and azimuth of the antenna

Adjust pilot power , and reduce coverage area of node B


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Figure 3.6 : cross-cell.

b- Coverage Problem Analysis

I. Planning Analysis :the precondition for analyzing pilot coverage and reference service coverage

is to work out the planning solution for the target area, including site distribution, base station

configuration, antenna feeder configuration, pilot coverage predication and service loading

distribution.

II. Drive Test Data Analysis

1) Downlink coverage

a) Pilot strength analysis In general, the strongest downlink receiving RSCP of each site in the

coverage area should be higher than -85dBm.

b) Dominant cells analysis:

Figure 3.7 : dominant cell .


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c) Coverage comparison and analysis between UE and Scanner:

Cells shown by UE are decided by neighbor cell configuration. If missing neighbor cell occurs, the

cells shown by UE and Scanner are different.

Figure 3. 8 : Comparing and analyzing UE and Scanner Coverage Scanner shows the real coverage.

d) Downlink code transmitting power distribution analysis: The downlink code transmitting power of

the most sites should almost be the same when the UE downlink power control is normal and the

network coverage is good. Only little areas will a little higher, as shown in Figure 18.

Figure 3.9 : Downlink code transmitting power of voice with the downlink 50% loading Recorded by RNC.

e) Soft handover rate analysis: According to the drive test data collected by the Scanner, the rate of

the soft handover area can be obtained, which is defined as:

Soft Handover area rate = ( Number of points meeting the handover condition and collected by

theScanner in drive test/total number of points collected by the scanner in drive test )


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Note that the Number of Point which is used to calculate SHO Ratio is recorded by Scanner., Usually

the SHO Ratio is 30%40% if there is no load, SHO Ratio would be affected by modifying the SHO

parameters.

2) Uplink coverage

a) Uplink interference analysis:the uplink RTWP data of each cell can be recorded in RNC. As shown

in Figure 3.10, the antenna of this cell receives signals through space diversity.

Figure 3. 10 : UL RTWP abnormity recorded by Node B.

b) Distribution of UE uplink transmitting power:

Figure 3.11 : UE transmitting power distribution (micro cell).


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Configuration Parameters adjustment related to coverage problems:

The following content lists the radio configuration parameters that may be adjusted for solving the

coverage problem: CPICH TX Power, MaxFACHPower, Sintrasearch, Sintersearch and Ssearchrat,

PreambleRetransMax, Intra-FILTERCOEF, Intra-CellIndividualOffset, RLMaxDLPwr and

RLMaxDLPwr (service-oriented).

3.6.2AccessOptimization

Definition

The data analyzed tool Assistant defines access failure as the rule that any situation where one of the

following conditions is met after the original UE issues the RRC Connection Request:

1) UE receives the RRC Connection Reject message;

2) After having received the RRC Connection setup message, UE receives or sends the RRCConnection Release message.

3) During the Call setup process, UE receives the BCCH message.

4) Timer times out, that is, within 3 seconds (T300) after UE has sent the RRC Connection Request

message, UE fails to receive the RRC Connection Setup message.

To sum up, any of the signaling failures before conversation will cause access failure.

KPI Items Reference value

RRC Conncetion Setup Success Rate(service) >=95%

RRC Conncetion Setup Success Rate(other) >=95%

AMR RAB Assignment Success Rate >=95%

Video call RAB Assignment Success Rate >=95%

PS RAB Assignment Success Rate >=95%

Table 3.3: accessibility optimization target.

General methods for access problems analysis:


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Figure 3.12 : methods for access problem analysis.

RRC Connection Setup Failure Analysis:

The RRC connection setup failure can be detected by the UE signaling process and RNC single-user

trace. RRC connection is established via the following steps: UE sends the RRC Connection

Request message via RACH, RNC sends the RRC Connection Setup message via FACH, then

UE establishes the downlink dedicated channel, synchronizes it, and now sends the RRC Connection

Setup CMP message via the uplink dedicated channel.

Reasons:

Errors or faults in uplink RACH.( limited power for preamble transmission ,node B VSWRproblem , improper access radius settings )

Downlink FACH power distribution.

cell parameter reselection.

low downlink initial transmitting power.

Uplink initial power control.

Congestion, abnormal equipment.

The RRC Connection Request message sent by UE is not received by RNC. If Ec/Io of thedownlink CPICH is not too low (say, about -12dB), then normally RACH fails due to incorrect

power control estimation for the uplink open loop, or insufficient power escalation of Preamble, or

lower-than-required output power of UE.


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Steps for resolving access problems:

RNC, after having received the RRC connection request sent by UE, sends the RRC connection

Setup message but UE fails to receive it. Now check the CPICH Ec/Io. If it is blow -12dB and

there is no better cell in the monitored set, then it must be failure of coverage, in which case,increase the FACH power. If there is a better cell in the monitored set, it might be caused by cell

reselection, in which case, adjust the cell reselection parameters to speed up the reselection.

Figure 3.13 : Signaling process of the calling UE.

Access-related Parameter Configuration :

FACH Transmitting Power , PCH Transmitting Power , PICH Transmitting Power , Cell Reselection

ParameterQhyst2s , Cell Reselection ParameterTreselections , Cell Reselection Parameter

Sintrasearch , Cell Reselection ParameterQoffset2 , AICH Transmitting Power , PRACH parameters

3.6.3CallDropOptimization

Definition

a- Definition of Call Drop in Drive Test: From the air message recorded on the UE during the

conversation, that is, in the connection mode if any one of the following three conditions is met,

that will be considered as a call drop:

Receive BCH message, that is, the system message.


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Receive RRC release message and the cause value for releasing as Not Normal.

receive any message of CC disconnect, CC release complete and CC release, the cause value

for release as Not Normal Clearing, Not Normal or Unspecified.

b- Definition of Call Drop in Statistics: The related indicators on UTRAN refer to the number of thereleased service RABs triggered by RNC, including two aspects:

1) RNC sends the RAB RELEASE REQUEST message to CN after the service is established.

2) RNC sends the IU RELEASE REQUEST message to CN, and then receives the IU

RELEASE COMMAND from CN after the service is established. At present, the two aspects use one

statistics indicator, RNC_RAB_REL_TRIG_BY_RNC. The statistics can be classified according to

actual services. Meanwhile, the statistics also counts the reasons for releasing various service RABs

triggered by RNC. The formula for calculating the call drop rate:

CS_CDR= (CSRABrelTriggedByRNC/CSRRABSetupSuccess)*100%

PS_CDR= (PSRABrelTriggedByRNC/PSRRABSetupSuccess)*100%

RNC KPIs(Average Value during Ndays)

Al l Service

CDR

CS AMR call Drop Rate0.48%

VP AMR call Drop Rate 0.92%

PS Service Drop Rate 0.34%

HSDPA CDR HSDPA Drop Rate 0.27%

HSUPA CDR HSUPA Drop Rate 0.29 %

Table 3.4: optimization target for call drop rate.

Reasons:

Call Drop due to Poor Coverage :

Usually, for voice, when CPICH Ec/lo is more than -14dB and RSCP more than -100dBm

(with the Scanner measurement value), the call drop is impossible to happen due to the poor

coverage. The so called poor coverage refers to the poor RSCP. Whether it is the poor uplink coverageor the poor downlink coverage that causes the call drop can be determined through the dedicated

channel power of uplink or downlink before the call drop.

Call Drop due to absent neighbor cell or Missing Configuration of neighbor Cell :

In general, most call drops happening during the early period in the network optimization

is caused by the missing adjacent cell.


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Call Drop due to Handover :

The reasons for call drop due to soft handover or intra-frequency hard handover can be classified into

two kinds, non-timely handover or Ping-Pong handover. From the signaling flow, the symptom is that

the mobile phone cannot receive the command for updating the active set in the CS service

(physical channel reassignment upon inter-frequency hard handover), while that of the PS service is

the command for updating the active set is not received or the TRB reset happens prior to the

handover.

From the signal, the main phenomena for non-timely handover are:

1) Corner effect: Ec/lo of the source cell plummet, while that of the target cell escalates (rising

to the very large value suddenly)

Figure 3.14:corner effect.

2) Needlepoint effect: Ec/lo of the source cell rises after plummeting for a period, and the target

cell escalates for a short period of time.

Figure 3.15 :Needlepoint effect.

From the signaling flow, before the call drop the mobile phone usually reports the 1a or 1c

measurement report of the adjacent cell, and RNC receives the measurement report and delivers the

message for updating the active set, but UE cannot receive the message.

The Ping-Pong handover has the following phenomena:


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1) Quick change of the dominant cell: two or more cells become the dominant cell alternatively, and

the dominant cell has the good RSCP and Ec/lo, but the time for each cell being the dominant cell is

very short.

2) No dominant cell: there are multiple cells existing, but the RSCP and Ec/Io are poor and there is

almost no variance between them. From the signaling flow, after a cell is deleted, it will request to

access again at once. Now, the command for updating the active set issued by RNC cannot be

received, which will lead to the failure.

Solution to corner and needlepoint effect

1) Configuring the 1a event parameter for the cell (decrease time to trigger , decrease the threshold ),

to enable the handover to be Triggered easier. For example, the trigger time can be decreased to

200ms, reduce the hysteresis.

2) Configuring the CIO to 5 dB between the two cells where the corner effect happens to facilitate

the target cells join.

3) Adjusting the antenna to make the antenna coverage of the target cell over the corner, enabling

that the handover happens before the corner.

IV. Call Drop due to Interference

Strong downlink interference (CPICH RSCP is not low, but Ec/Io is low)

Strong uplink interference. On the basis of the RSSI scanning result or analysis of the SIB7,

there is uplink interference.

V. Call Drop due to Equipment Abnormity

After all the above reasons are excluded, the reason for other call drop may be the equipment problem,

which can be analyzed by viewing the equipment log and alarm.

For example, the abnormal NodeB leads to the synchronization failure, enabling the transmit link to be

added and deleted continuously. For example, the call drop happens because the mobile phone does

not report the 1a measurement report.

Steps for resolving call drop problems :

The call drop due to non-timely handover can be solved by adjusting the antennas to enlarge the

handover area, or configuring the handover parameters of the 1a event to make the handover easier

to happen, or configuring CIO to make the target cell to perform the handover in advance.


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the call drop due to the Ping-Pong handover can be solved by adjusting the antenna to make the

coverage area form the dominant cell, or configuring the handover parameters of the 1b event to

prevent the Ping-Pong handover from happening. For the inter-frequency or inter-system

handover, the compressed mode ( needed when making measurements on another frequency (inter-

frequency) or on a different radio technology (inter-RAT) ) . should be started for the handover to

perform the inter-frequency or inter-system measurement. If the compressed mode is started too

late, the mobile phone will have no time to measure the signal in the target cell, so the call drop

happens, or the mobile phone finishes the measurement, but it cannot receive the inter-frequency or

inter-system handover request, leading to the call drop.

Parameter Configuration adjustment Related to Call Drop :

Cell Individual Offset (CIO) , Delayed Trigger Time Related to Soft Handover , Intra- frequency

Measurement FilterCoef , Threshold for Starting/Stopping Compressed Mode , Trigger Time of Inter-

system Handover (Confirming the Delayed Trigger Time) , Maximum Retransmission Times of

Signaling and Service , Inter-frequency Cell Hard Handover Threshold Represented by RSCP ,

GsmRSSICSThd and GsmRSSIPSThd , Timers and Counters Related to Call Drop .

Figure 3.16 : Flow chart for analyzing call drop.


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3.6.4InterferenceOptimization

Definition

The interference of WCDMA system includes to parts, one part is self- interference of system, the

other part is some abnormal interference. Usually, abnormal interference can not be predicted, in some

cases, it will cause some problems.

Reasons for variance of the uplink main diversity RTWP :

in Figure 27, the main diversity RTWP has obvious variance. By analysis, the causes may be:

Intensity of the interferences on the main diversity has much variance.

Some cells such as the indoor base stations use only one receiving channel.

NodeB has never performed the radio frequency channel calibrating.

Figure 3.17 : Variance of the uplink main diversity RTWP.

Reason for the RTWP Abnormality :

I. Uplink Inter-modulation Interference:

When several systems are installed in same area, different frequencies of these systems maybe cause

Inter-modulation.

Solution to inter-modulation interference

Check the roof if there exists any metal article around the antenna or the antenna

is too close to the antennas of other carriers;

Check the DCS bearer characteristics to find the 2G frequencies that combine with the 3G

frequencies, and mark out the BCCH branch.

Example :

Multiple-frequency inter-modulation caused by load


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The cell in this case is an indoor system, with combined output of 2G signals of two carriers. RTWP is

abnormal in the cell. The field study finds that it is caused by loose load connection. A slight touch on

the load will trigger violent RTWP fluctuation, which disappears after the load is replaced.

Figure 3.18 : RTWP 24-hour measurementinter-modulation caused by load.

II. Uplink External Interference

1) Classification of frequently seen external interference

First type: these interference come from antenna interaction Especially, when the antennas belong to

different system had been installed face to face, because isolation is smaller, so spurious emission will

affect the site, When environment is complex, and there are so many metal, so there are so many

interactive result

Second type: these interference come from some microwave equipment Some interference is

periodical, just appears in special time , Some interference just appears in narrow band

2) Solution to the external interference:

Adjust antenna: change the position, the direction of antenna, make main beam of antenna fall

away from interference

Use some method to decrease interference, e.g. we can check 2G antenna has been added filter or

not, antenna and feeder system is OK or not. We also can modify the frequencies If the

interference come from microwave equipment, we should find the transmitter, We can use Yagi

antenna, and observe in which direction the signal is strongest, then we can find the transmitter.


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3.6.5Inter-systemRoamingHandoverOptimization

Common Inter-system Handover Strategies:

I. Handover Based on Coverage

To ensure continuous coverage of the GSM/WCDMA users in areas where there is no 3G system

coverage, the coverage-based handover or cell reselection is required for continuity of service.

II. Handover Based on Load

Load-based handover or cell reselection is applied for load sharing between GSM and WCDMA

systems. The trigger for such a handover is the measured cell load of GSM or the WCDMA network.

III. Handover Based on Service

Service-based handover is applied to guide the traffic of the GSM or WCDMA network. Even when

there is no load in the source cell, the service-based handover can also proceed. During the load-based

handover/cell reselection or call setup period, the service-based handover can be utilized. With this

function, carriers can guide the voice service to GSM and all VP and packet data to WCDMA to

reduce investment on the 3G circuit network and 2G packet switched network.

Applied Inter-system Roaming Handover Strategies

I. Difficult to Perform Reselection and Handover

In areas where the 3G coverage is better than that of 2G, the mobile phone should be kept in the 3G

network as much as possible, which can be realized by configuring parameters as shown below:

When the mobile phone is in idle and the 2G signal level is better than 3G Delta dB, reselect the 2G

network. Delta dB depends on the value of Qoffset1sn which is the key parameter for adjustment

and is suitable for both the network and configuration. You may increase the value of Qoffset1sn

(the range is -50~50dB with the default value as 0), say, 50dB, and make it hard for the mobile phone

to be reselected to 2G.

When the mobile phone is in the Connect status, you may increase the value of CellIndividualOffset

(the range is -50~50dB with the default value as 0), say, -50dB, to make it impossible for the mobile

phone to switch to the 2G network.

II. 2G Easy to Perform Reselection and Handover

In some places the 2G coverage is better than 3G. For example, inside the building, 2G coverage has

DAS, and 3G has no coverage. When the mobile phone moves from the 3G coverage area to that of the

2G and is in conversation, the handover to 2G should ensure no call drop. When the mobile phone


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is in idle and is to be reselected to 2G, the handover should ensure no disconnection from the

network.

When the mobile phone is in idle, Qoffset1 can be set to 0. When the mobile phone is in the Connect

status, you may increase the compression mode start and stop threshold, launch at an earlier time the

compression mode to measure the 2G signal (say, -90/-85dBm) and set CellIndividualOffset to

0. The purpose is to increase the overlapping area of 3G and 2G, especially to ensure the mobile

phone to switch to 2G when the 3G signal quality plummets from the outside to inside.

Example :

Inter-system ping-pong reselection

1) Description of the case

In some area inside a building of a commercial office, when the mobile phone is in idle, the UMTS-

GSM dual-mode mobile phone will frequently switch between WCDMA Radio the 3G and 2G

networks. The monitors of the Siemens U15 and MotoA835 mobile phones frequently and

alternatively display 3G and 2G, and the Qualcomm test mobile phone monitor frequently and

alternatively display WCP and GCP. Reselection from 3G to 2G takes on average 1 minute, and

from 2G to 3G 1-2 minutes, with the mobile phone location and the environment remain unchanged.

2) Analysis of the case

Reselection from 3G to 2G is as follows:

When the value of the pilot signal quality Ec/Io of the 3G service cell minus Qqualmin is

smaller than the inter-system measurement threshold SsearchRAT, measurement of the

adjacent 2G cells launches;

When the signal quality of the adjacent 2G cell reaches the cell reselection criteria and keeps on

for a period of time Treselection, UE will select to reside in the 2G cell.

The value of the 3G RSCP at the 3G network edge is basically below -90dBm while the 2G signal

quality is very good, mostly around -60~-70Bm. Therefore, once UE launches measurement of the

signals in the adjacent 2G cell and there is no improvement in the local cell signal withinTreselection , UE will reselect to reside in the 2G cell. Therefore, the key parameter in reselection

from 3G to 2G is SsearchRAT, while proper configuration of the reselection delay parameter

Treselection is also beneficial for solving the Ping-Pong handover.

Reselection from 2G to 3G is as follows:


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1) When the strength of the cell signal of a 2G service cell is right for the inter-system measurement

threshold Qsearch_I, measurement of the adjacent 3G cell signals will launch; With a view to first

selecting 3G, the current configuration of the parameter is 7 (permanently launch).

2) When the intensity of the 3G cell signal minus the current value of RLAC (the average intensity of

the 2G service cell and the non-service cell) is larger than FDD_Qoffset and it keeps on for 5 seconds,

then the 3G cell is taken as a candidate cell for reselection; At present, FDD_Qoffset is set to 7 (always

reselecting the 3G cell).

3) When the signal quality Ec/Io of the 3G cell is larger than or equal to the threshold FDD_Qmin,

then the 3G cell can be taken as a candidate cell for reselection.

4) Among all 3G cells that meet the above criteria, UE selects the best one as the reselection target

cell. Therefore, the key parameter for reselection from 2G to 3G is FDD_Qmin, with the default value

as -12dB.

5) Solution to the case

In practical network optimization, the following measures can be taken

Increase the interval between SsearchRAT and FDD_Qmin. By default, if the 3G CPICH Ec/Io

is larger than -12dB, UE will reselect from 2G to 3G, and if CPICH Ec/Io


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HSDPA throughput factors :

Ue categories

Maximum available HS-PDSCH code in the cell

Retransmission rate

Number of HSPA users in the cell

Channel quality indicator CQI The reported CQI value determines the maximum rate on the air

interface available to the UE.

CQI Mapping table for UE categories 7 and 8

CQI

Value

Transport

Block Size

Number of HS-PDSCH Modulation Reference power

adjustment

0 N/A out of range

1 137 1 QPSK 0

2 173 1 QPSK 0

3 233 1 QPSK 0

28 14411 10 16-QAM -3

29 14411 10 16-QAM -4

30 14411 10 16-QAM -5

Table 3.5: CQI Mapping Table.

Reasons :

Limitation on radio resources ( codes, power ,,,,)

Improper Parameter setting such as MBR

Incorrect throughput limitation through the AT command ( configuration for user )

Limitation on CE resources .Steps for resolving HSPA throughput problem :

Checking signaling process to obtain : ( Ue categories , max bit rate assigned by CN, whether

the service is established on HSPA ) .


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Figure 3.19 : indication of type of UE.

The information in the figure indicates that the UE is of HSDPA category 8 and supports a throughput of 7.2

Mbit/s.

Figure 3.20 : max bite rate assignd by CN in the RANAP_RAB_ASSIGNEMENT_REQ message.

Checking the quality on the air interface to obtain the channel quality indicator CQI

Figure 3.21 : CQI reported by UE during the HSPA data transmission .


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Checking the radio resources to obtain ( available HS-PDSCH code and power in the cell ,

WCDMA user number in the cell , whether 16QAM is enabled in the cell ,IUb transmission in

the cell )

Checking the UE TX power

Checking the UPLINK power load to obtain whether the uplink load of the cell already reaches

the threshold

Checking the uplink bandwidth allocated by RNC to obtain whether the Uplink bandwidth

allocated by RNC is insufficient

3.7 Summery

In This chapter we explained the redesign an made during our project after this phase we have

moved to the optimization of the services parameters to improve KPIs of the network. In general,

drive test, statistics and users subjective sense are used as optimization Evidences, while signaling

tracing and analysis play a crucial role in troubleshooting. The basic method for network

optimization is to analyze an adjust engineering Parameters and cell parameter according to

OMC statistics result and drive test result so as to optimize the network finally.


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The Practical part

58

apter 4

Chapter 4: the practicalpart

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