Mobile Telecommunication

3G UMTS HSPA RADIO NETWORK OPTIMIZAION 1

Dept. of ECE (2013-2014)

1. MOBILE COMMUNICATION

1.1 Revolution in telecommunication

The telephone has long been important in modern living, but it use has been constrained

by connecting wires. The advent of mobile radio telephony and particularly the cellular radio has

removed this restriction and led to explosive growth in mobile throughout the world. The phone

is really on move now. With the phenomenal and unprecedented growth of more than forty fold

in just ten years a strong demand for mobile cellular services has created an industry which now

accounts for more than one third of all telephone lines.

1.2 Concept of mobile communication

The first wire line telephone system was introduced in the year 1877.Mobile

communication systems as early as 1934 were based on Amplitude Modulation (AM schemes

and only certain public organizations maintained such systems. The development of Frequency

Modulation (FM) technique by Edwin Armstrong, the mobile radio communication systems

began to witness many new changes. Mobile telephone was introduced in the year 1946.

However, during its initial three and a half decades it found very less market penetration owing

to high costs and numerous technological drawbacks. But with the development of the cellular

concept in the 1960s at the Bell Laboratories, mobile communications began to be a promising

field of expanse which could serve wider populations.

1.3 Mobile communication objectives

The important objectives of mobile communications are

Anytime anywhere communication

Mobility& Roaming

High capacity and subs density

Efficient use of radio spectrum


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Table 1.1: Different generations- Analog and Digital systems

1946-1960 1980 1990 2000

Appearance 1G 2G 3G

Analog Digital Digital

Multi Standard Multi Standard Unified Standard

Terrestrial Terrestrial Terrestrial &Satellite

The features and benefits expected in the new system

Superior speech quality

Low terminal, operational, and service costs

A high level of security

International Roaming

Support of low terminal hand portable terminals

A variety of new services and network facilities.

1.4 Constraints in Implementation

A host of services like teleservices supplementary services and value added services are being

promised by GSM Networks. There are certain impairments in realizing an effective mobile

communication system which has to meet the twin objectives of quality and capacity.

(a) Radio frequency reuse

High spectrum efficiency should be achieved at reasonable cost. The bandwidth on radio

interface i.e. between the user equipment and the radio transceiver is to be managed effectively


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to support ever increasing customer base with very limited number of radio carriers. For high

BW services e.g. MMS as the GSM evolves towards 3G, more spectrums is demanded.

(b) Multi path radio environment

The most significant problem in mobile radio systems is due to the channel itself. In mobile radio

systems, indeed, it is rare for there to exist one strong line of sight path between transmitter and

receiver. Usually several significant signals are received by reflection and scattering from

buildings etc. .And then they are Multiple paths from transmitter receiver.

Fig 1.1 Multipath radio environment

The signals on these paths are subject to different delays phase shifts and Doppler shifts

and at the receiver in random phase relation to one another. The interferences between these

signals give rise to a number of deleterious effects. The most important of these are Fading and

Dispersion.

Fading is due to the interference of multiple signals with random relative phase that causes

variations in the amplitude of the received signal. This will increase the error rate in digital

system since errors will occur when the signal-to noise ratio drops below certain threshold.

Dispersion is due to differences in the delay of the various paths, which disperses

transmitted pulses in time. If the variation of delay is comparable with the symbol period delayed


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signals from an earlier symbol may interface with the next symbol causing Inter- symbol

interference (ISI).

(c) Mobility management

Mobility management is concerned with how the network supports this function. When a call is

made to mobile customer the network must be able to locate the mobile customer. Network

attachment process which includes a location updating process is the answer for mobility

management. In the location update process , the network databases are updated dynamically so

that the mobile can be reached to offer the services if this process is not done efficiently it will

result in poor call management and network congestion.

(d) Services

International roaming shall be provided. Advanced PSTN services should be provided consistent

with ISDN services at limited bit rates only. Encryption should be used to improve security for

both the operators and the customers.

(f) Cost

The system parameters should be chosen to limit costs particularly mobiles and handsets .In a

competitive environment cost is the deciding factor for the survival of an operator.


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2. BANDWIDTH MANAGEMENT

2.1 INTRODUCTION

Radios move information from one place to another over channels and radio channel is an

extraordinarily hostile medium to establish and maintain reliable communications. The channel

is particularly messy and unruly between mobile radios. All the schemes and mechanisms we use

to make communications possible on the mobile radio channel with some measure of reliability

between a mobile and its base radio station are called physical layer or the layer1 procedures.

The mechanisms include modulation, power control, coding timing, and host of other details that

manage establishment and maintenance of the channel the radio channel has to be fully exploited

for maximum capacities and optimum quality of service. Band width is a scarce natural resource.

The bandwidth has to be managed for maximum capacity of the system and interference free

communications. The spectrum availability for an operator is very limited .The uplink or

downlink spectrum is only 25 MHz, out of this 25 MHz, 124 carriers of each 200 kHz are

generated. These carriers are to be shared amongst different operators. And as a result each

operator gets only a few tens of carriers making a spectrum management a challenging area.

2.2 Cellular structures and Frequency Reuse

Traditional mobile service was structured similar to television broadcasting:

One very powerful transmitter at the highest spot in area would broadcast in an area radius of up

to fifty kilometers. The scenario changes as the mobile density as well as coverage area grows.

The answer to tackle the growth is the extensions based on addition of new cells. The cellular

concept structured the mobile telephone network in a different way. Instead of using one

powerful transmitter many low-powered transmitter were placed throughout a coverage area. For

example, by dividing metropolitan region into one hundred different areas (cells) with low power

transmitters using twelve conversations (channels) each, the system capacity could theoretically

be increased from twelve to thousands of conversations using one hundred low power

transmitters while reusing the frequencies The cellular concept employs variable low power

levels, which allows cells to be sized according to subscriber density and demand of a given

area. As the populations grow, cells can be added to accommodate that growth. Frequencies used

in one cell cluster can be reused in other cells. Conversations can be handed over from cell to


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cell to maintain constant phone service as the user moves between cells.

Cells:

A cell is the basic geographic unit of cellular system. The term cellular comes from the

honeycomb areas into which a coverage region is divided. Cells are base stations transmitting

over small geographic areas that are represented as hexagons. Each cell size varies depending

upon landscape. Because of the constraint imposed by natural terrain and man-made structures,

the true shape of cell is not a perfect hexagon.

(a) Cellular System Characteristics

The distinguishing features of digital cellular systems compared to other mobile radio

systems are:

Small cells

A cellular system uses many base stations with relatively small coverage radii (on

the order of a 100 m to 30 km).

Clusters and Frequency reuse

The spectrum allocated for a cellular network is limited. As a result there is a limit to the

number of channels or frequencies that can be used. A group of cells is called a cluster. All the

frequencies are used in a cluster and no frequency is reused with in the cluster. And the total set

of frequencies is repeated in the adjacent cluster. Like that the total service area, i.e. may be a

country or a continent, can be served with a small group of frequencies. Frequency reuse is

possible because the signal fades over the distance and hence it can be reused .For this reason

each frequency is used simultaneously by multiple base-mobile pairs; located at geographically

distant cells. This frequency reuse allows a much higher subscriber density per MHz of

spectrum than other systems. System capacity can be further increased by reducing the cell size

(the coverage area of a single base station), down to radii as small as 200 m.

Small, battery-powered handsets

In addition to supporting much higher densities than previous systems, this approach


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enables the use of small, battery-powered handsets with a radio frequency that is lower than the

large mobile units used in earlier systems.

Performance of handovers

In cellular systems, continuous coverage is achieved by executing a "handover"

(the seamless transfer of the call from one base station to another) as the mobile unit crosses cell

boundaries. This requires the mobile to change frequencies under control of the cellular

network.

(b) Co channel cells and interference

Radio channels can be reused provided the separation between cells containing the same

channel set is far enough apart so that co-channel interference can be kept below acceptable levels

most of the time. Cells using the same channel set are called Co-channel cells. Co-channel cells

interfere with each other and quality is affected.

The following figure shows an example. Within the service area (PLMN), specific channel sets

are reused at a different location (another cell). In the example, there are 7 channel sets: A

through G. Neighboring cells are not allowed to use the same frequencies. For this reason all

channel sets are used in a cluster of neighboring cells. As there are 7 channel sets, the PLMN

can be divided into clusters of 7 cells each. The figure shows three clusters.

Co-channel interference

Frequencies can be reused throughout a service area because radio signals typically

attenuate with distance to the base station (or mobile station). When the distance between cells

using the same frequencies becomes too small, co-channel Interference might occur and lead to

service interruption or unacceptable quality of service.

As long as the ratio Frequency reuse distance = DNCell radius

Is greater than some specified value, the ratio

Received radio carrier power = C/I

Received interferer radio carrier power will be greater than some given amount for small as


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well as large cell sizes; when all signals are transmitted at the same power level. The average

attenuation of radio signals with distance in most cellular systems is a reduction to about 1/16

of the received power for every doubling of distance (1/10000 per decade). The frequency reuse

distance known as separation distance is also known as the signal-to-noise ratio. The figure on

the opposite page shows the situation. At the base station, both signals from subscribers within the

cell covered by this base station and signals from subscribers covered by other cells are received.

Interference is caused by cells using the same channel set. The ratio D/R needs to be large

enough in order for the base station to be able to cope with the interference. A co-channel

interference factor Q is defined As Q=D/R = v 3K where D is Frequency reuse distance, R is

the cell radius and K is the reuse factor or the number of cells in a cluster

K=reuse factor=No of cells in a cluster

Q=D/R = v 3K

Q is more Sys quality high

If K is more no of cells in a clutters is more

No of channels per cell less Traffic handling capacity

low

Fig 2.1: Frequency reuse


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3. 3G UMTS NETWORK ARCHITECTURE

3G has become an umbrella term to describe cellular data communications with a target

data rate of 2 M bits/sec. The ITU originally attempted to define 3G in its IMT-2000

(International Mobile Communications-2000) specification, which specified global wireless

frequency ranges, data rates, and availability dates. However, a global standard was difficult to

implement due to different frequency allocations around the world and conflicting input. So,

three operating modes were specified. In general, a 3G device will be a personal, mobile,

multimedia communications device that supports speech, color pictures, and video, and various

kinds of information content. There is some doubt that 3G systems will ever be able to deliver

the bandwidth to support these features because bandwidth is shared. However, 3G systems will

certainly support more phone calls per cell

3.1 Introduction to UMTS

The 3rd generation mobile communication system (3G) is put on agenda when the 2nd

generation (2G) digital mobile communication market was significantly evolving. The 2G

mobile communication systems have the following disadvantages: limited frequency spectrum

resources, low frequency spectrum utilization and weak support for mobile multimedia services

(providing only speech and low-speed data services). Also, there was incompatibility between

2G systems. The 2G mobile communication system has a low system capacity hardly meeting

the demand for high speed bandwidth services and impossible for the system to implement

global roaming. Therefore, the 3G communication technology is a natural result in the

advancement of 2G mobile communication technology.

As the internet data services are becoming increasingly popular nowadays, the 3G

communication technology opens the door to a brand new mobile communication world. In

addition to clear voice services, it allows users to conduct multimedia communications with their

personal mobile terminals, for example, internet browsing, multimedia database access, real time

stocks quotes query, videophone, mobile e-commerce, interactive games, wireless personal audio

player, video transmission, knowledge acquisition and entertainments. Some unique features

include location related services, which allows the users to know about their surroundings


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anytime, anywhere, for example, block map, locations of hotels, supermarkets and weather

forecasting. The 3G mobile phone has become a good assistant to peoples life and work.

3.2 History

Discussion of a potential successor system for GSM started in ETSI and other standard

developing organizations already in the late 1980, even before any second-generation system

was in commercial operation. The ETSI-term for the future system was Universal Mobile

Telecommunications System (UMTS). Simultaneously, the International Telecommunication

(ITU) also started discussions on a potential future mobile system initially referred to as Future

Public Land Mobile System (FPLMTS) and started to specify a set of system requirements. Due

to the huge world-wide success of GSM, the interest among European network operators and

manufacturers to consider a completely new system was rather low until to the mid-1990s. Only

after the ITU has taken the initiative to formulate a concrete roadmap towards a new mobile

system to be deployed in the early 2000s, the specification activities for UMTS in ETSI were

ramped up in 1995. The ITU term for the future 3G system was later changed to IMT-2000,

International Telecommunications System for the 2000s. As part of the roadmap, a deadline for

submission of proposals for IMT-2000 by the regional standardization development

organizations was agreed to be in July 1998.In January 1998 ETSI selected two radio

transmission technologies (from originally 4 different proposals) for UMTS terrestrial radio

access (UTRA), referred to as UTRA FDD and UTRA TDD, which were submitted to ITU as

candidates for IMT-2000.

The proposals included a number of different Wideband CDMA (WCDMA) based

Radio access technologies, from ETSI, TTC/ARIB (Japan), TTA (Korea), ANSI T1 (USA) and

TIA (USA), which can be grouped into two types. The one type of proposals requires

synchronized base stations and is building up on the IS-95 2G radio transmission technology.

The other group of concepts does not rely on base station synchronization.


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Table 3.1: Terrestrial radio transmission technologies proposed by ITU

By the end of 1998 two specification development projects were founded by the regional

Standardization organizations, 3GPP (3rd Generation Partnership Project) and 3GPP2. The goal

of both 3GPP and 3GPP2 was to merge a number of the W-CDMA based proposals into a single

one. 3GPP2 was concerned with the IS-95 based systems. The split of standardization activities

into two camps was partly caused by a dispute on Intellectual Property Rights (IPR) on W-

CDMA technology between various telecom manufacturers. After these IPR issues were

resolved in mid-1999, the members of 3GPP and 3GPP2 agreed on a harmonized global IMT-

2000 CDMA proposal. This agreement then paved the way for a harmonized overall concept of

an ITU IMT-2000 family of 3G systems.


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Fig 3.1: ITU EMT-2000 family of 3G system

The 3G mobile communication system, IMT-2000, is the general term for the next

generation communication system proposed by ITU in 1985, when it was actually referred to as

Future public Land Mobile Telecommunications System (FPLMTS). In 1996, it was officially

renamed to IMT-2000.The 3G mobile communication technologies enjoys the integrated

bandwidth network service as far as it can to the mobile environment, transmitting multimedia

information including high quality images at rates up to 10Mbps.

Comparing with the existing 2G system, the 3G system has the following characteristics as

summarized below:

1. Support for multimedia services, especially internet services

2. Easy transition and evolution

3. High frequency spectrum utilization

Currently, the three typical 3G mobile technology communication standards in the world are

CDMA2000, WCDMA and TD-SCDMA. CDMA2000 and WCDMA work in FDD mode

whereas TD-SCDMA works in TDD mode, where uplink and downlink of the system work in

different timeslots of the same frequency.


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The 3G mobile communication is designed to provide diversified services and high quality

multimedia services. To achieve these purposes, the wireless transmission technology must meet

the following requirements:

1. High speed transmission to support multimedia services

Indoor environment : > 2 Mbps

Outdoor walking environment : 384 kbps

Outdoor vehicle moving : 144 kbps

2. Allocation of transmission rates according to needs

3. Accommodation to asymmetrical needs on the uplink and downlink

In the concept evaluation of the 3G mobile communication specification proposals, the

WCDMA technology is adopted as one of the main stream 3G technologies due to its technical

advantages.

3.2.1 Frequency spectrum allocation:

The frequency bands allocated for initial operation of IMT-2000/UMTS systems is

shown in figure 1.4. In Europe there is one paired frequency band in the range 1920 1980 MHz

and 2110 2170 MHz to be used for UTRA FDD and there are two unpaired bands from 1900

1920 MHz and 2010 2025 MHz intended for operation of UTRA TDD.

In the USA 3G systems shall initially be operated in the PCS band which is already partly

used for 2G systems. MSS refers to spectrum reserved for 3G mobile satellite systems (1980 -

2010 MHz and 2170 2200 MHz). The PCS band in the USA was already divided into chunks

of 5 MHz and mostly sold in form of 25 MHz paired band to PSC network operators before any

3G systems were proposed. This situation in the USA has imposed the requirement that it must

be possible to operate a 3G system within a 2 5 MHz paired frequency band.

The UMTS band in Europe is therefore divided into twelve 5 MHz paired frequency

slots, suitable for UTRA FDD, and four plus three 5 MHz unpaired frequency slots suitable for

UTRA TDD mode.

In Germany the UMTS spectrum will be auctioned starting in July 2000. One operator is

allowed to acquire at least two, at most three paired bands. Therefore there will be initially

between 4 and 6 UMTS operators in Germany.


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In May 2000 further frequency bands for UMTS/IMT-2000 was identified by the ITU World

Radio Conference (WRC-2000). These bands (more than 160 MHz additional spectrum) shall

ensure future extension of UMTS.

Fig 3.2 spectrum assigned to operation of 3G system

3.2.2 UMTS (Release 99) Architecture:

Fig 3.3 UMTS (release99) architecture


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The Universal Mobile Telecommunication System (UMTS) is a 3G mobile communication

system adopting WCDMA air interface. Therefore, the UMTS is usually called a WCDMA

system.

In terms of functions, the network units comprise the radio access network (RAN) and core

network (CN). The RAN accomplishes all the functions related to radio communication. The CN

handles exchange and routing of all the calls and data connections within the UMTS with

external networks. The RAN, CN and the User equipment (UE) together constitute the whole

UMTS.

3.2.3 UE (USER EQUIPMENT):

The UE is equipment which can be vehicle installed or hand portable.

Through the Uu interface, the UE exchanges data with network equipment and

provides various CS and PS domain services, including common voice services, broadband voice

services, mobile multimedia services, and applications ( such as email, WWW browse and FTP).

3.2.4 UTRAN (UMTS Terrestrial Radio Access Network):

The UMTS terrestrial radio access network (UTRAN) comprises node B and radio network

Controller (RNC).

1.) Node B1.

At the base station(wireless transceiver) in the WCDMA system, the node B is composed

of the wireless transceiver and baseband processing part, connected with the RNC

through standard Iub interface, node B processes the Un interface physical layer

protocols. It provides the functions of spectrum spreading/decoding and mutual

conversation between baseband signals and radio signaling.

2.) RNC

The RNC manages various interfaces, establishes and releases connections, performs

handoff and macro diversity/combination and manages and controls radio resources. It

connects with the MSC and SGSN through lu interface. The protocol between UE and

UTRAN is terminated here.


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The RNC that controls Node B is called controlling RNC(CRNC).The CRNC

performs load control congestion control of the cells it serves and implements admission

control of cells it serves and implements admissions control and code word allocation for

the wireless connections to be established.

If the connection between a mobile subscriber and the UTRAN uses many RNS

resources, the related RNC has two independent logical functions:

Serving RNC (SRNC). The SRNC terminates the transmission of subscriber data and the

Iu connection and RANAP signaling to/from the CN. It also terminates the radio resource

controlling signaling (i.e. the signaling protocol between UE and UTRAN). In addition,

the SRNC performs L2 processing of the data sent to/from the radio interface and

implements some basic operations related to radio resources management.

Drift RNC (DRNC) - All other RNCs except SRNC are called as DRNCs. They

control the cells used by UEs.

3.3 CORE NETWORK (CN):

The CN is the in charge of connections with other networks as well as the management

and communication with UEs. The CN can be divided into CS domain and PS domain from the

aspect of logic.

The CS domain equipment refers to the entities that provide circuit connection or related

signaling connections for subscriber services. The specific entities in the CS domain include:

1. Mobile switching center (MSC)

2. Gateway mobile switching Centre (GMSC)

3. Visitor location register (VLR)

4. Interworking function (IWF)

The PS domain provides packet data services to subscribers.

The specific entities in the PS domain include:

5. Serving GPRS support node (SGSN)

6. Gateway GPRS support node (GGSN)

Other equipment such as the Home Location Register (HLR) or HSS, Authentication Centre

(AUC) and Equipment Identity Register (EIR) are shared by CS domain and PS domain.


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3.3.1 Functions of core network

1. MSC/VLR

As the functional node in the CS domain of the WCDMA core network, the

MSC/VLR connects with the UTRAN through Iu CS interface, with external

networks (PSTN, ISDN and other PLMNs) through PSTN/ISDN interface, with the

HLR/AUC through C/D interface, with the MSC/VLR, GMSC or SMC through E

interface, with the SCP through CAP interface and with the SGSN through Gs

interface.

The MSC/VLR accomplishes call connection, mobility management, authentication

and encryption in the CS domain.

2. GMSC

As the gateway node between the CS domain of WCDMA network and external

networks, the GMSC is an optional entity. It connects with the external networks

(PSTN, ISDN and other PLMNs) through PSTN/ISDN interface and with the SCP

through CAP interface.

The GMSC accomplishes the incoming and outgoing routing of the visited MSC

(VMSC).

3. SGSN

As the functional node in the PS domain of WCDMA core network, the SGSN

connects with the UTRAN through Iu_PS interface, with GGSN through Gn/Gp

interface, with the HLR/AUC through Gr interface, with the MSC/VLR through Gs

interface, with SCP through CAP interface, with the SMC through Gd interface, with

the CG through Ga interface and with SGSN Gn/Gp interface.

The SGSN accomplishes the routing forward, mobility management, session

management, authentication and encryption in PS domain.

4. GGSN

The GGSN connects with the SGSN through Gn interface and with the external data

networks (internet/intranet) through Gi interface. The GGSN provides routes to the

data packets between the WCDMA network and external data networks and

encapsulates these data packets. The major functions of the GGSN is to provide


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interface to the external IP packet-based network, thus the UEs can access the

gateway of the external packet based network. To the external networks, the GGSN

seems like the IP router that can be used to address all the mobile subscribers in the

WCDMA network. It exchanges routing information with external networks.

5. HLR

The HLR connects with the VMSC/VLR or GMSC through C interface, with the

SGSN through Gr interface, and with the GGSN through Gc interface. The HLR

stores subscriber subscription information, supports new services and provide

enhanced authentication.

3.3.2 Teleservices and supplementary services

A basic requirement defined for UMTS is that it needs to support all GSM teleservices, e.g.

speech, emergency call and short message service (SMS). Below, the most important teleservices

and supplementary services are listed and described briefly.

3.3.2.1 Telephony

Speech: Telephone speech service in UMTS is supported by employing the Adaptive Multi-Rate

(AMR) speech codec. This Codec is compatible with the speech codecs presently used in GSM

systems and it will also be introduced in GSM in the near future. It shall operate with no

discernible loss of speech on handover between the GSM access network and the UTRAN.

Emergency Call: UMTS Release 99 shall support an emergency call teleservice. This is just a

special case of normal speech service. It requires to work even without USIM included in the

UE.

Teleconferencing: Teleconferencing provides the ability for several parties to be engaged in a

speech communication. This service can be established with ordinary telephone service in

combination with supplementary service, allowing the user to establish multiparty calls.

Voice-band-data: Support of modems supporting user rates of 14.4 kbps or more.

3.3.2.2 Sound and Video telephony

Wideband-speech: Speech service or radio sound at 0 7 kHz bandwidth (future UMTS

release)

High-Quality Audio: Audio service with Compact Disk quality (future UMTS release)


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Video telephone: Ability for two-way speech and image communications.

Video Conference: Ability for multi-party speech and image communications.

Video Surveillance/Monitoring: Provides the transmission of image and sound in one direction.

3.3.2.3 Tele-action services:

Telemetric services: Services for e.g. remote control, remote terminal, credit authorization

requiring low bit rate per transaction but possibly fast response time.

3.3.2.4 Message handling services

Short Message Service: A means for sending messages of limited size to and from mobile

terminals which makes use of a Service Center which acts as store and forward center for short

messages (supported by GSM and UMTS release 99).

Voice Mail: Voice mail enables calling users to record a voice message against the called users

identity under a variety of conditions (e.g. called user busy, not answering, and not reachable).

Electronic mail: In their simplest form electronic mail service provide the ability to transfer

textual messages between users via a variety of intervening networks. Electronic mail systems

may also provide format conversion enabling text and data to be converted from one format into

another, including media conversion, e.g. mail send as text but received as voice.

3.3.2.5 Facsimile service

Store-and-Forward telefax: A service, where a file or message transfer program is used to

transfer text or images from a mobile terminal to a store and forward unit for subsequent delivery

to the facsimile machine in the PSTN/ISDN. The user (or the user's PC) may receive notification

of successful delivery of the fax. Fax messages from PSTN/ISDN to mobile terminals are stored

in a store-and-forward unit (service center). The user retrieves the fax message with a file or

message transfer program from the store-and-forward unit. The mobile terminal may be notified

that a fax message is available. Note that this service also belongs to the category of message

handling services (supported by GSM and UMTS release 99).

End-to-End telefax: A fax service using an end-to-end fax session between a PSTN/ISDN fax

machine and a mobile terminal. This service shall work end-to-end such that a sender on the

PSTN is aware of whether or not the fax has succeeded, and such that a mobile sender is aware

of whether or not the fax has succeeded. From the user perspective the end-to-end fax service

must look and feel like a T.30 based fax service. The end-to-end service may work with ordinary


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T.30 based fax machines at the mobile end using a mobile fax adapter with a modem that

terminates the analogue 2-wire connection from the fax machine (supported by GSM and UMTS

release 99).

3.3.2.6 Broadcast Services

(Message) Cell Broadcast Service (CBS): Provides transmission of a message to all users

within a specified geographic area which have a subscription to this service.

Multicast service: A data broadcast service for a specified group of users within a specified

geographic area.

3.3.2.7 Supplementary Services:

Supplementary services modify or supplement a basic telecommunication service.

Consequently, it cannot be offered to a customer as a standalone service. It must be offered

together with or in association with a basic telecommunication service. UMTS will support GSM

Release '99 supplementary services and many further extensions.

Below, some examples of supplementary services are listed:

call barring,

call forwarding,

call hold,

conference calling,

in call modification (dialing),

handling of closed user groups,

Credit card calling.

3.4 Multimedia Services

UMTS shall support multimedia services and provide the necessary capabilities.

Multimedia services combine two or more media components (e.g. voice, audio, data, video,

pictures) within one call. A multimedia service may involve several parties and connections

(different parties may provide different media components) and therefore flexibility is required

in order to add and delete both resources and parties.

Multimedia services are typically classified as interactive or distribution services.

Interactive services are typically subdivided into conversational, messaging and retrieval

services:


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Conversational services: These are real time (no store and forward), usually bi-directional

where low end to end delays (< 100 ms) and a high degree of synchronization between media

components (implying low delay variation) are required. Video telephony and video

conferencing are typical conversational services.

Messaging services: These offer user to user communication via store and forward units

(mailbox or message handling devices). Messaging services might typically provide combined

voice and text, audio and high resolution images.

Retrieval services: These enable a user to retrieve information stored in one or many

information center. The start at which an information sequence is sent by an information center

to the user is under control of the user. Each information center accessed may provide a different

media component, e.g. high resolution images, audio and general archival information.

3.4.1 Distributional services

Distribution services are typically subdivided into those providing user presentation control

and those without user presentation control.

Distribution services without user control: These are broadcast services where information is

supplied by a central source and where the user can access the flow of information without any

ability to control the start or order of presentation e.g. television or audio broadcast services.

Distribution services with user control: These are broadcast services where information is

broadcast as a repetitive sequence and the ability to access sequence numbering allocated to

frames of information enables the user (or the users terminal) to control the start and order of

presentation of information.

3GPP specifications shall support single media services (e.g. telephony) and multimedia services

(e.g. video telephony). All calls shall have potential to become multimedia calls and there shall

be no need to signal, in advance, any requirement for any number of multimedia components.

However, it shall be possible to reserve resources in advance to enable all required media

components to be available.


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3.4.2 Bearer services

Circuit switched data: Circuit switched data services and "real time" data services shall be

provided for interworking with the PSTN/ISDN so that the user is unaware of the access network

used (UMTS and GSM access network or handover between access networks). Both transparent

(constant delay) and non-transparent (zero error with flow control) services shall be supported.

These data services shall operate with minimum loss of data on handover between the GSM

access network and the UTRAN.

Packet switched data: Packet switched data services shall be provided for interworking with

packet networks such as IP-networks and LANs. The standard shall provide mechanisms which

ensure the continuity of packet based services upon handover e.g. between GSM and UMTS.

Fig 3.4 3G UMTS Generation


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4. HIGH SPEED PACKET ACCESS

4.1 Overview

The introduction of High-Speed Downlink Packet Access, (HSDPA), implies a major

extension of the WCDMA radio interface, enhancing the WCDMA downlink packet-data

performance and capabilities in terms of higher peak data rate, reduced latency and increased

capacity. This is achieved through the introduction of several of the techniques described in Part

II, including higher-order modulation, rate control, channel-dependent scheduling, and hybrid

ARQ with soft combining.

4.1.1Shared-channel transmission

A key characteristic of HSDPA is the use of Shared-Channel Transmission. Shared

channel transmission implies that a certain fraction of the total downlink radio resources

available within a cell, channelization codes and transmission power in case of WCDMA, is seen

as a common resource that is dynamically shared between users, primarily in the time domain.

The use of shared-channel transmission, in WCDMA implemented through the High-Speed

Downlink Shared Channel (HS-DSCH) as described below, enables the possibility to rapidly

allocate a large fraction of the downlink resources for transmission of data to a specific user.

This is suitable for packet-data applications which typically have burst characteristics and thus

rapidly varying resource requirements. The HS-DSCH code resource consists of a set of

channelization codes of spreading factor 16, where the number of codes available for HS-DSCH

transmission is configurable between 1 and 15. Codes not reserved for HS-DSCH transmission

are used for other purposes, for example related control signaling, MBMS services, or circuit-

switched services. The dynamic allocation of the HS-DSCH code resource for transmission to a

specific user is done on 2 ms TTI basis. The use of such a short TTI for HSDPA reduces the

overall delay and improves the tracking of fast channel variations exploited by the rate control

and the channel-dependent scheduling as discussed below. In addition to being allocated a part of

the overall code resource, a certain part of the total available cell power should also be allocated

for HS-DSCH transmission. Note that the HS-DSCH is not power controlled but rate controlled

as discussed below. This allows the remaining power, after serving other channels, to be used for


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HS-DSCH transmission and enables efficient exploitation of the overall available power

resource.

Fig 4.1 Channelization codes in HSDSCH Transmission

4.1.2 Channel-dependent scheduling

Scheduling controls to which user the shared-channel transmission is directed at a

Given time instant. The scheduler is a key element and to a large extent determines

The overall system performance, especially in a highly loaded network. In each

TTI, the scheduler decides to which user(s) the HS-DSCH should be transmitted and, in close

cooperation with the rate-control mechanism, at what data rate. Since the radio conditions for the

radio links to different UEs within a cell typically vary independently, at each point in

Time there is almost always a radio link whose channel quality is near its peak. As this radio link

is likely to have good channel quality, a high data rate can be used for this radio link. This

translates into a high system capacity. The gain obtained by transmitting to users with favorable

radio-link conditions is commonly known as multi-user diversity and the gains are larger, the

larger the channel variations and the larger the number of users in a cell. Thus, in contrast to the

traditional view that fast fading is an undesirable effect that has to be combated, with the


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possibility for channel-dependent scheduling fading is potentially beneficial and should be

exploited. In addition to the channel conditions, traffic conditions are also taken into account

By the scheduler. For example, there is obviously no purpose in scheduling a user with no data

awaiting transmission, regardless of whether the channel conditions are beneficial or not.

Furthermore, some services should preferably be given higher priority. As an example, streaming

services should be ensured a relatively constant long-term data rate while background services

such as file download have less stringent requirements on a constant long-term data rate.

Fig 4.2 channel dependent scheduling for HSDPA

4.1.3 Rate control and higher-order modulation

For HSDPA, rate control is implemented by dynamically adjusting the channel coding

rate as well as dynamically selecting between QPSK and 16QAM modulation. Higher-order

modulation such as 16QAM allows for higher bandwidth utilization than QPSK, but requires

higher received Eb/N0. Consequently, 16QAM is mainly useful in advantageous channel

conditions. The data rate is selected independently for each 2 ms TTI by the NodeB and the rate

control mechanism can therefore track rapid channel variations.

4.1.4 Hybrid ARQ with soft combining

Fast hybrid ARQ with soft combining allows the terminal to request retransmission of

erroneously received transport blocks, effectively fine-tuning the effective code rate and

compensating for errors made by the link-adaptation mechanism. The terminal attempts to

decode each transport block it receives and reports to the NodeB its success or failure 5 ms after

the reception of the transport block. This allows for rapid retransmissions of unsuccessfully


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received data and significantly reduces the delays associated with retransmissions compared to

Release 99. Soft combining implies that the terminal does not discard soft information in case

It cannot decode a transport block as in traditional hybrid-ARQ protocols, but combines soft

information from previous transmission attempts with the current retransmission to increase the

probability of successful decoding. Incremental redundancy, IR, is used as the basis for soft

combining in HSDPA that is the retransmissions may contain parity bits not included in the

original transmission. It is known that IR can provide significant gains when the code

Rate for the initial transmission attempts is high as the additional parity bits in the retransmission

results in a lower overall code rate. Thus, IR is mainly useful in bandwidth-limited situations, for

example, when the terminal is close to the base station and the amount of channelization codes,

and not the transmission power, limits the achievable data rate. The set of coded bits to use for

the retransmission is controlled by the NodeB, taking the available UE memory into account

4.1.5 Architecture

From the previous discussion it is clear that the basic HSDPA techniques rely on fast

adaptation to rapid variations in the radio conditions. Therefore, these techniques need to be

placed close to the radio interface on the network side at the same time, an important design

objective of HSDPA was to retain the Release 99 functional split between layers and nodes as far

as possible. Minimization of the architectural changes is desirable as it simplifies introduction of

HSDPA in already deployed networks and also secures operation in environments where not all

cells have been upgraded with HSDPA functionality. Therefore, HSDPA introduces a new MAC

sub-layer in the NodeB, the MAC-hs, responsible for scheduling, rate control and hybrid-ARQ

protocol operation. Hence, apart from the necessary enhancements to the RNC such as admission

control of HSDPA users, the introduction of HSDPA mainly affects the NodeB Each UE using

HSDPA will receive HS-DSCH transmission from one cell, the serving cell. The serving cell is

responsible for scheduling, rate control, hybrid ARQ, and all other MAC-hs functions used by

HSDPA. Uplink soft handover is supported, in which case the uplink data transmission will be

received in multiple cells. Mobility from a cell supporting HSDPA to a cell that is not supporting

HSDPA is easily handled. Uninterrupted service to the user can be provided, albeit at a lower

data rate, by using channel switching in the RNC and switch the user to a dedicated channel in


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the non-HSDPA cell. Similarly, a user equipped with an HSDPA-capable terminal may be

switched from a dedicated channel to HSDPA when the user enters a cell with HSDPA support.

Fig 4.3 HSDPA architecture

4.2 HSDPA vs. UMTS

Various methods for packet data transmission in WCDMA downlink already exist in

Release'99. The three different channels in Release'99/ Release 4 WCDMA specifications that

can be used for downlink packet data are:

Dedicated Channel (DCH)

Downlink-shared Channel (DSCH)

Forward Access Channel (FACH).

The basic requirements for HSDPA are to carry high data rate in the downlink. The HSDPA

technology will:


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Increase the UTRAN network capacity

Reduce the round trip delay

Increase the peak data rates up to 14 Mbps

In order to achieve this few architectural changes have been made in the R99 architecture. The

transport channel carrying the user data with HSDPA operation is denoted as the High-speed

Downlink-shared Channel (HS-DSCH) known as downlink "fat pipe".

As discussed above the primary motivation behind HSDPA was to achieve high data rates by not

disturbing to the current UMTS architecture too much. Thus it's clear that by implementing the

HSDPA the current UMTS architecture is maintained and some other features or functionalities

are added on top of the existing architecture. In HSDPA (Release 5) three new transport channels

are introduced. They are:

HS-DSCH (High Speed Down link Shared Channel)

To support the HS-DSCH Operation Two Control Channels are added

HS-SCCH (High Speed Shared Control Channel)

DL channel

HS- DPCCH (High Speed Dedicated Physical Control Channel)

UL Channel

With HSDPA two fundamental features of WCDMA are disabled which is:

Variable SF

Fast Power Control


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These two features are replaced by

Adaptive Modulation and Coding (AMC)

Fast retransmission strategy (HARQ)

Scheduling Algorithm

4.2.1 HS-DSCH:

The High-Speed Downlink Shared Channel (HS-DSCH), is the transport channel

Used to support shared-channel transmission and the other basic technologies in HSDPA,

namely channel-dependent scheduling, rate control (including higher order modulation), and

hybrid ARQ with soft combining. As discussed in the introduction and illustrated in Figure 9.1,

the HS-DSCH corresponds to a set of channelization codes, each with spreading factor 16. Each

such channelization code is also known as an HS-PDSCH High-Speed Physical Downlink

Shared Channel. In addition to HS-DSCH, there is a need for other channels as well, for example

for circuit-switched services and for control signaling. To allow for a trade-off between the

amount of code resources set aside for HS-DSCH and the amount of code resource used for other

purposes, the number of channelization codes available for HS-DSCH can be configured,

ranging from 1 to 15 codes. Codes not reserved for HS-DSCH transmission are used for other

purposes, for example related control signaling and circuit-switched services. The first node in

the code tree can never be used for HS-DSCH transmission as this node includes mandatory

physical channels such as the common pilot. Sharing of the HS-DSCH code resource should

primarily take place in the time domain. The reason is to fully exploit the advantages of channel-

dependent scheduling and rate control, since the quality at the terminal varies in the time

Domain, but is (almost) independent of the set of codes (physical channels) used for

transmission. However, sharing of the HS-DSCH code resource in the code domain is also

supported as illustrated in. With code-domain sharing, two or more UEs are scheduled

simultaneously by using different parts of the common code resource (different sets of physical

channels).reasons, not able to dispread the full set of codes, and efficient support of small

payloads when the transmitted data does not require the full set of allocated HSDSCH codes. In


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either of these cases, it is obviously a waste of resources to assign the full code resource to a

single terminal.

In addition to being allocated a part of the overall code resource, a certain part of the total

available cell power should also be used for HS-DSCH transmission. To maximize the utilization

of the power resource in the base station, the remaining power after serving other, power-

controlled channels, should preferably be used for HS-DSCH transmission as illustrated in

Figure 9.4. In principle, this results in a (more or less) constant transmission power in a cell.

Since the HS-DSCH is rate controlled as discussed below, the HS-DSCH data rate can be

selected to match the radio conditions and the amount of power instantaneously available for HS-

DSCH transmission. To obtain rapid allocation of the shared resources, and to obtain a small

enduser delay, the TTI should be selected as small as possible. At the same time, a too small TTI

would result in excessive overhead as control signaling is required for each transmission. For

HSDPA, this trade-off resulted in the selection of a 2 ms TTI.

Downlink control signaling is necessary for the operation of HS-DSCH in each TTI.

Obviously, the identity of the UE(s) currently being scheduled must be signaled as well as the

physical resource (the channelization codes) used for transmission to this UE. The UE also needs

to be informed about the transport format used for the transmission as well as hybrid-ARQ-

related information. The resource and transport-format information consists of the part of the

code tree used for data transmission, the modulation scheme used, and the transport-block size.

The downlink control signaling is carried on the High-Speed Shared Control Channel (HS-

SCCH), transmitted in parallel to the HS-DSCH using a separate channelization code. The HS-

SCCH is a shared channel, received by all UEs for which an HS-DSCH is configured to find out

whether the UE has been scheduled or not. Several HS-SCCHs can be configured in a cell, but as

the HS-DSCH is shared mainly in the time domain and only the currently scheduled terminal

needs to receive the HS-SCCH, there is typically only one or, if code-domain sharing is

supported in the cell, a few HS-SCCHs configured in each cell. However, each HS-DSCH-

capable terminal is required to be able to monitor up to four HS-SCCHs. Four HS-SCCH has

been found to provide sufficient flexibility in the scheduling of multiple UEs; if the number was

significantly smaller the scheduler would have been restricted in which UEs to schedule

simultaneously in case of code-domain sharing.


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HSDPA transmission also requires uplink control signaling as the hybrid-ARQ

mechanism must be able to inform the NodeB whether the downlink transmission was

successfully received or not. For each downlink TTI in which the UE has been scheduled, an

ACK or NAK will be sent on the uplink to indicate the result of the HS-DSCH decoding. This

information is carried on the uplink High-Speed

Dedicated Physical Control Channel (HS-DPCCH). One HS-DPCCH is set up for each UE with

an HS DSCH configured. In addition, the NodeB needs information about the instantaneous

downlink channel conditions at the UE for the purpose of channel-dependent scheduling and rate

control. Therefore, each UE also measures the instantaneous downlink channel conditions and

transmits a Channel-Quality Indicator (CQI), on the HS-DPCCH. In addition to HS-DSCH and

HS-SCCH, an HSDPA terminal need to receive power control commands for support of fast

closed-loop power control of the uplink in the same way as any WCDMA terminal. This can be

achieved by a downlink dedicated physical channel, DPCH, for each UE. In addition to power

control commands, this channel can also be used for user data not carried on the HS-DSCH, for

example circuit-switched services.

In Release 6, support for fractional DPCH, F-DPCH, is added to reduce the consumption

of downlink channelization codes. In principle, the only use for a dedicated channel in the

downlink is to carry power control commands to the UE in order to adjust the uplink

transmission. If all data transmissions, including higher-layer signaling radio bearers, are mapped

to the HS-DSCH, it is a waste of scarce code resources to use a dedicated channel with spreading

factor 256 per UE for power control only. The F-DPCH resolves this by allowing multiple UEs

to share a single downlink channelization code. To summarize, the overall channel structure with

HSDPA is illustrated in neither the HS-PDSCH, nor the HS-SCCH, are subject to downlink

macro diversity or soft handover. The basic reason is the location of the HS-DSCH scheduling in

the NodeB. Hence, it is not possible to simultaneously transmit the HS-DSCH to a single UE

from multiple NodeBs, which prohibits the use of inter-NodeB soft handover. Furthermore, it

should be noted that within each cell.


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4.3 Scheduler

The scheduler for HSDPA is referred to as being fast due to the fact that, compared with

Release 99 specifications; the scheduler is moved from RNC to node Bs to reduce delays so

faster scheduling decisions can be made. In addition to other functionalities, such as the choice

of redundancy version and modulation and coding scheme, a fundamental task of the scheduler

for HSDPA is to schedule the transmission for users. The data to be transmitted to users are

placed in different queues in a buffer and the scheduler needs to determine the sequential order in

which the data streams are sent. The scheduling algorithms are:

Round-robin method: This algorithm selects the user packets in a round robin fashion.

In this method, the number of time slots allocated to each user can be chosen to be

inversely proportional to the users data rates, so the same number of bits is transmitted

for every user in a cycle. Obviously, this method is the fairest in the sense that the

average delay and throughput would be the same for all users. However, there are two

disadvantages associated with the round-robin method. The first is that it disregards the

conditions of the radio channel for each user, so users in poor radio conditions may

experience low data rates, whereas users in good channel conditions may not even

receive any data until the channel conditions turn poor again. This is obviously against

the spirit of the HSDPA and it would lead to the lowest system throughput. The second

disadvantage of the round-robin scheduler is that there is no differentiation in the quality

of services for different classes of users.

Maximum C/I (carrier-to-interface) ratio method: In this method, the scheduler

attempts to take advantage of the variations in the radio channel conditions for different

users to the maximum, and always chooses to serve the user experiencing the best

channel condition, that is, the one with maximum carrier-to-interference ratio.

Apparently, the max C/I scheduler leads to the maximum system throughput but is the

most unfair, as users in poor radio conditions may never get served or suffer from

unacceptable delays.


Dept. of ECE (2013-2014)

Proportional fairness or R[n]/Rav Method: This method takes into account both the

short-term variation of the radio channel conditions and the long-term throughput of each

user. In this method, the user with the largest R[n]/Rav is served first, where R[n] is the

data rate in the current time slot n and Rav is the average data rate for the user in the past

average window. The size of the average window determines the maximum duration that

a user can be starved from data, and as such it reflects the compromise between the

maximum tolerable delay and the cell throughput. According to this scheduling scheme,

if a user is enjoying a very high average throughput, its R[n]/Rav will probably not be

the highest. Then it may give way to other users with poor average throughput and

therefore high R[n]/Rav in the next time slots, so the average throughput of the latter can

be improved. On the other hand, if the average throughput of a user is low, the R[n]/Rav

could be high and it might be granted the right of transmission even if its current channel

condition is not the best.

The figure below illustrates the performance of different scheduling algorithm

Fig. 4.4 performance of scheduling algorithms

Fast scheduling and AMC, in conjunction with HARQ, is a way of maximizing the instantaneous

use of the fading radio channel in order to realize maximum throughput. The HSDPA technology

enables higher-rate data transmission through a higher-modulation and coding rate and limited

retransmissions, while keeping the power allocated to HS-DSCH channel in a cell constant.


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Notwithstanding, the slow power control is still needed to adjust the power sharing among

terminals and between different channel types.

HSDPA Impact on Radio Access Network and UE Architecture

All Release99 transport channels presented earlier in this document are terminated at the

RNC. Hence, the retransmission procedure for the packet data is located in the serving RNC,

which also handles the connection for the particular user to the core network. With the

introduction of HS-DSCH, additional intelligence in the form of an HSDPA Medium Access

Control (MAC) layer is installed in the Node B. This way, retransmissions can be controlled

directly by the Node B, leading to faster retransmission and thus shorter delay with packet data

operation when retransmissions are needed. With HSDPA, the Iub interface between Node B and

RNC requires a flow control mechanism to ensure that Node B buffers are used properly and that

there is no data loss due to Node B buffer overflow.

Although there is a new MAC functionality added in the Node B, the RNC still retains

the Release99/Release 4 functionalities of the Radio Link Control (RLC), such as taking care of

the retransmission in case the HS-DSCH transmission from the Node N would fail after, for

instance, exceeding the maximum number of physical layer retransmissions.

The key functionality of the new Node B MAC functionality (MAC-hs) is to handle the

Automatic Repeat Request (ARQ) functionality and scheduling as well as priority handling.

Ciphering is done in any case in the RLC layer to ensure that the ciphering mask stays identical

for each retransmission to enable physical layer combining of retransmissions. Similar to Node B

a new MAC entity, MAC-hs is added in the UE architecture. The functionalityof the same as on

the Node B side.


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Fig. 4.5 node b protocol stack

Transport and Control Channel in HSDPA

Fig. 4.6 transport and control channel in HSDPA


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High Speed Downlink Shared Channel (HS-DSCH)

The HS-DSCH is allocated to users mainly on the basis of the transmission time interval

(TTI), in which users are allocated within different TTIs.

HS-DSCH has the following features:

TTI = 2ms (3 time slots): This is to achieve short round trip delay for the operation

between the terminal and the Node B for retransmissions. TTI in R99 is 10ms

Adding higher order modulation scheme, 16 QAM, as well as lower encoding

redundancy has increased the instantaneous peak data rate. In the code domain

perspective, the SF is fixed; it is always 16, and multi-code transmission as well as code

multiplexing of different users can take place.

The maximum number of codes that can be allocated is 15, but depending on the terminal (UE)

capability, individual terminals may receive a maximum of 5, 10 or 15 codes.

4.4 MOBILITY PROCEDURES

Once a terminal is in the so-called CELL_DCH state when dedicated channels have been

set up, it can be allocated with one or more HS-PDSCH(s), thus allowing it to receive data on the

HS-DSCH. For dedicated channels, it is advantageous to employ the so-called soft handover

technique, which is to transmit the same data from a number of Node Bs simultaneously to the

terminal, as this provides diversity gain. Owing to the nature of packet transmission, however,

synchronized transmission of the same packets from different cells is very difficult to achieve, so

only hard handover is employed for HS-PDSCH.

This is referred to HS-DSCH cell change, and the terminal can have only one serving HS-

DSCH cell at a time. A serving HS-DSCH cell change message facilitates the transfer of the role

of serving HS-DSCH radio link from one belonging to the source HS-DSCH cell to another


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belonging to the target HS-DSCH cell. In theory, the serving HS-DSCH cell change can be

decided either by the mobile terminal or by the network. In UTRAN Release 5, however, only

network-controlled serving HS-DSCH cell changes are supported and the decision can be based

on UE measurement reports and other information available to the RNC. A network-controlled

HS-DSCH cell change is performed based on the existing handover procedures in CELL_DCH

state.

Since the HSDPA radio channel is associated with dedicated physical channels in both

the downlink and uplink, there are two possible scenarios in changing a serving HS-DSCH cell:

(1) only changing the serving HS-DSCH cell and keeping the dedicated physical channel

configuration and the active set for handover intact; or (2) changing the serving HS-DSCH cell

in connection with an establishment, release, and/or reconfiguration of dedicated physical

channels and the active set.

Although an unsynchronized serving HS-DSCH cell change is permissible, a

synchronized one is obviously preferable for ease of traffic management. In that case, the start

and stop of the HS-DSCH transmission and reception are performed at a given time. This is

convenient especially when an intranode B serving HS-DSCH cell change is performed, in which

case both the source and target HS-DSCH cells are controlled by the same node B and the

change happens between either frequencies or sectors.

If an internode B serving HS-DSCH cell change is needed, the serving HS-DSCH Node

B relocation procedure needs to be performed in the UTRAN. During the serving HS-DSCH

node B relocation process, the HARQ entities located in the source HS-DSCH node B belonging

to the specific mobile terminal are deleted and new HARQ entities in the target HS-DSCH node

B are established. In this scenario, different controlling RNCs may control the source and target

HS-DSCH node Bs, respectively.


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Intranode B Serving HS-DSCH Cell Change

Figure below illustrates an intranode B serving HS-DSCH cell change while keeping the

dedicated physical channel configuration and the active set, using the physical channel

reconfiguration procedures. The transition from source to target HS-DSCH cells is performed in

a synchronized fashion, that is, at a given activation time. For clarity, only the layers directly

involved in the process are shown and the sequence of the events starts from the top and finishes

at the bottom.

Fig. 4.7 Intranode serving node b

In this scenario, the terminal transmits a measurement report message containing

intrafrequency measurement triggered by the event change of best cell. When the decision to

perform handover is made at the serving RNC (SRNC), the node B is prepared for the serving

HS-DSCH cell change at an activation time indicated by CPHY-RL-Commit-REQ primitive.

The serving RNC then sends a physical channel reconfiguration message, which indicates the

target HS-DSCH cell and the activation time to the UE. Since the same node B controls both the

source and target HS-DSCH cells, it is not necessary to reset the MAC-hs entities. Once the


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terminal has completed the serving HS-DSCH cell change, it transmits a physical channel

reconfiguration complete message to the network.

It should be pointed out that, in this particular case, it is assumed that HS-DSCH transport

channel and radio bearer parameters do not change. If transport channel or radio bearer

parameters are changed, the serving HS-DSCH cell change would need to be executed by a

transport channel reconfiguration procedure or a radio bearer reconfiguration procedure,

respectively.

Internode B Serving HS-DSCH Cell Change

For terminals on the move, what happens more often than the intra-node B serving HS-DSCH

cell change is the so-called internode B serving HS-DSCH cell change. For synchronized case,

the reconfiguration is performed in two steps within UTRAN.

To begin with, the terminal transmits a measurement report message containing measurement

triggered by the event change of best cell. The serving RNC determines the need for hard

handover based on received measurement report and/or load control algorithms. As the first step,

the serving RNC establishes a new radio link in the target node B. After this, the target Node B

starts transmission and reception on dedicated channels. In the second step, this newly created

radio link is prepared for a synchronized reconfiguration to be executed at a given activation

time indicated in the CPHY-RL-Commit-REQ primitive, at which the transmission of HS-DSCH

will be started in the target HSDSCH node B and stopped in the source HS-DSCH node B.

The serving RNC then sends a transport channel reconfiguration message on the old

configuration. This message indicates the configuration after handover, both for DCH and HS-

DSCH. The transport channel reconfiguration message includes a flag indicating that the MAC-

hs entity in the terminal should be reset. The message also includes an update of transport

channel-related parameters for the HS-DSCH in the target HS-DSCH cell.

After physical synchronization is established, the terminal sends a transport channel

reconfiguration complete message. The serving RNC then terminates reception and transmission


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on the old radio link for dedicated channels and releases all resources allocated to the UE. The

process of internode B handover for HS-DSCH is shown in Figure below.

Fig. 4.8 Intra Node B serving


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5. KEY PERFORMANCE INDICATORS (KPIS)

5.1 INTRODUCTION

For radio network optimization it is necessary to have key performance indicators. These

KPIs are parameters that are to be observed closely when the network monitoring process is

going on. Mainly, the term KPI is used for parameters related to voice and data channels, but

network performance can be broadly characterized into coverage, capacity and quality criteria

also that cover the speech and data aspects.

The performance of the radio network is measured in terms of KPIs related to voice

quality, based on statistics generated from the radio network. Drive tests and network

management systems are the best methods for generating these performance statistics.

5.2 NETWORK PERFORMANCE AND MONITORING

The whole process of network performance monitoring consists of two steps:

Monitoring the performance of the key parameters,

Assessment of the performance of these parameters with respect to capacity and coverage.

First the radio planners assimilate the information/parameters that they need to monitor.

The KPIs are collected along with field measurements such as drive tests. For the field

measurements, the tools used are ones that can analyze the traffic, capacity, and quality of the

calls, and the network as a whole. For drive testing, a test mobile is used. This test mobile keeps

on making calls in a moving vehicle that goes around in the various parts of the network. Based

on the DCR, CSR, HO, etc., parameters, the quality of the network can then be analyzed. Apart

from drive testing, the measurements can also be generated by the network management system

and finally, when 'faulty' parameters have been identified and correct values are determined, the

radio planner puts them in his network planning tool to analyze the change before these

parameters are actually changed or implemented in the field.


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5.3 DRIVE TESTING

The quality of the network is ultimately determined by the satisfaction of the users of the

network, the subscribers. Drive tests give the 'feel' of the designed network as it is experienced in

the field. The testing process starts with selection of the 'live' region of the network where the

tests need to be performed, and the drive testing path. Before starting the tests the engineer

should have the appropriate kits that include mobile equipment (usually three mobiles), drive

testing software (on a laptop), and a GPS (global positioning system) unit.

When the drive testing starts, two mobiles are used to generate calls with a gap of few

seconds (usually 15-20 s). The third mobile is usually used for testing the coverage. It makes one

continuous call, and if this call drops it will attempt another call. The purpose of this testing to

collect enough samples at a reasonable speed and in a reasonable time. If there are lots of

dropped calls, the problem is analyzed to find a solution for it and to propose changes.

5.4 KPIs IN 3G

The following are the key performance indicators in any 3G network.

1. Received Signal Code Power (RSCP)

2. Ec/Io

3. Handover status

4. Throughput

5. Eb/No


Dept. of ECE (2013-2014)

RSCP Plot

It is a coverage plot indicating the received code power for pilot channel.

Ec/Io Plot

This plot indicates the Ec/Io achieved on pilot channel.

Handover status

The plot indicates handover status for different areas in a given network.

Throughput

The plot indicates probable throughput in the network on WCDMA PS bearers. It should

be noted that the throughput plot is based on the allotment of different PS bearers and does not

indicate continuous user data transfer rate.

Eb/No Plot

In a mixed traffic scenario the plot indicates the Eb/No targets achieved for downlink.


Dept. of ECE (2013-2014)

6. Radio Network Optimization

6.1 Introduction to optimization

Every alive Network needs to be under continues control to maintain/improve the

performance. Optimization is basically the only way to keep track of the network by looking deep

into statistics and collecting/analyzing drive test data. It is keeping an eye on its growth and

modifying it for the future capacity enhancements. It also helps operation and maintenance for

troubleshooting purposes.

Successful Optimization requires:

Recognition and understanding of common reasons for call failure

Capture of RF and digital parameters of the call prior to drop

Analysis of call flow, checking messages on both forward and reverse links to establish what

happened, where, and why. Optimization will be more effective and successful if you are aware

of what you are doing. The point is that you should know where to start, what to do and how to

do.

Purpose and Scope of Optimization

The optimization is to intend providing the best network quality using available spectrum as

efficiently as possible. The scope will consist all below:

Finding and correcting any existing problems after site implementation and integration.

Meeting the network quality criteria agreed in the contract.

Optimization will be continuous and iterative process of improving overall network quality.

Optimization cannot reduce the performance of the rest of the network.

Area of interest is divided in smaller areas called clusters to make optimization and follow up

processes easier to handle.

6.2 Optimization Process

6.2.1Problem Analysis

Analyzing performance retrieve tool reports and statistics for the worst performing BSCs

and/or Sites

Viewing ARQ Reports for BSC/Site performance trends


Dept. of ECE (2013-2014)

Examining Planning tool Coverage predictions

Analyzing previous drive test data

Discussions with local engineers to prioritize problems

Checking Customer Complaints reported to local engineers

6.2.2 Checks Prior to Action

Cluster definitions by investigating BSC borders, main cities, freeways,

Major roads.

Investigating customer distribution, customer habits (voice/data usage)

Running specific traces on Network to categorize problems

Checking trouble ticket history for previous problems

Checking any fault reports to limit possible hardware problems prior to test.

6.2.3Drive Testing

Preparing Action Plan

Defining drive test routes

Collecting RSSI Log files

Scanning frequency spectrum for possible interference sources

Redriving questionable data

6.2.4Subjects to Investigate

Nonworking sites/sectors or TRXs

Inactive Radio network features like frequency hopping

Disabled GPRS

Overshooting sites coverage overlaps

Coverage holes

C/I, C/A analysis

High Interference Spots

Drop Calls

Capacity Problems

Other Interference Sources

Missing Neighbors

Oneway neighbors


Dept. of ECE (2013-2014)

PingPong Handovers

Not happening handovers

Accessibility and Retain ability of the Network

Equipment Performance

6.2.5After the Test

Post processing of data

Plotting RX Level and Quality Information for overall picture of the driven area

Initial Discussions on drive test with Local engineers

Reporting urgent problems for immediate action

Analyzing Network feature performance after new implementations

Transferring comments on parameter implementations after new changes


Dept. of ECE (2013-2014)

7. DRIVE TESTING

7.1 Introduction

The Indian telecommunication industry, with about 708.4 million mobile phone

connections as of Jan 2013, is the second largest telecommunication network in the world. The

Indian telecom industry is the fastest growing one in the world and it is projected that India will

have a 'billion plus' mobile users by 2014. The Indian telephone lines have increased from a

meagre 40 million (approx.) in the year 2000 to an astounding figure now. The main drivers for

this extraordinary growth are because of Governments Telecom reforms and the stupendous

success of GSM standard, which is the most popular standard for mobile telephony systems in

the world.

RF performance parameters such as the Received Signal Code Power, Ec/Io, Eb/No,

throughput etc., are defined for the efficient and effective functioning of the RF network. The

Drive Testing (DT) is performed in 3G UMTS network to ensure the availability, integrity, &

reliability of the network. How to optimize the BTS coverage area successfully is the real

challenge. As we move further ahead, the need for better technologies and reliability of services,

integration and cost effective solutions have become a necessity for service providers. If the

optimization is successfully performed, then the QOS, reliability and availability of RF Coverage

area will be highly improved resulting in more customers and more profits to the mobile telecom

service providers.


Dept. of ECE (2013-2014)

Figure 7.1 Integrated drive-test bench

7.2 What is drive test?

Drive testing is the most common and maybe the best way to analyze network

performance by means of coverage evaluation, system availability, network capacity, and

network, retain ability and call quality. Although it gives idea only on downlink side of the

process, it provides huge perspective to the service provider about what is happening with a

subscriber point of view.

The drive testing is basically collecting measurement data with a phone, but the main

concern is the analysis and evaluation part that is done after completion of the test. Remember

that you are always asked to perform a drive test for not only showing the problems, but also

explaining them and providing useful recommendations to correct them.

Drive Test, as already mentioned, is the procedure to perform a test while driving. The

vehicle does not really matter; you can do a drive test using a four-wheeler or a motorcycle or a

bicycle. What matters is the hardware and software used in the test.

A notebook - or other similar device (1)

With collecting Software installed (2),

A Security Key - Dongle - common to these types of software (3),

At least one Mobile Phone (4),

One GPS (5),


Dept. of ECE (2013-2014)

A Scanner optional (6).

Also there is a common use of adapters and / or hubs that allow the correct interconnection of all

equipment.

The following is a schematic of the standard connections.

Fig. 7.2 Schematic diagram of drive test.

The main goal is to collect test data, but they can be viewed / analyzed in real time (Live)

during the test, allowing a view of network performance on the field. Data from all units are

grouped by collection software and stored in one or more output files (1).

Fig. 7.3 Drive test output from various sources.


Dept. of ECE (2013-2014)

GPS: collecting the data of latitude and longitude of each point / measurement

data, time, speed, etc. It is also useful as a guide for following the correct routes.

MS: mobile data collection, such as signal strength, best server, etc ...

SCANNER: collecting data throughout the network, since the mobile radio is a

limited and does not handle all the necessary data for a more complete analysis.

The minimum required to conduct a drive test, simplifying, is a mobile device with

software to collect data and a GPS. Currently, there are already cell phones that do everything.

They have a GPS, as well as a collection of specific software. They are very practical, but are

still quite expensive.

7.3 Drive Test Routes

Drive Test routes are the first step to be set, and indicate where testing will occur. This

area is defined based on several factors, mainly related to the purpose of the test. The routes are

predefined in the office.

A program of a lot of help in this area is Google Earth. A good practice is to trace the

route on the same using the easy paths or polygons. The final image can then be brought to the

driver.

Figure 7.4 Drive test route map


Dept. of ECE (2013-2014)

Some software allows the image to be loaded as the software background (geo-

referenced). This makes it much easier to direct routes to be followed.

It is advisable to check traffic conditions by tracing out the exact pathways through which

the driver must pass. It is clear that the movement of vehicles is always subject to unforeseen

events, such as congestion, interdicted roads, etc. Therefore, one should always have on hand -

know - alternate routes to be taken on these occasions.

Avoid running the same roads multiple times during a Drive Test (use the Pause if

needed). A route with several passages in the same way is more difficult to interpret.

7.4 Drive Test Schedule

Again depending on the purpose, the test can be performed at different times - day or

night. A Drive Test during the day shows the actual condition of the network - especially in

relation to loading aspect of it. Moreover, a drive test conducted at night allows you to make, for

example, tests on transmitters without affecting most users.

Typically takes place nightly Drive Test in activit

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