55_UMTS-Overview-(FDD-TDD)

8/7/2019 55_UMTS-Overview-(FDD-TDD)

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3. UMTS

UMTS: Universal Mobile Telephone System

3G standard in Europe

Key requirements for UMTS: Small, low-cost pocket terminals

World-wide roaming

A single system for residential, office, cellular andsatellite environments

High-speed data(vehicular 144kbps, pedestrian 384kbps,indoor 2Mbps)


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UMTS addresses these requirements through:

New services, including mobile multimedia and avirtual home environment, so that consumersexperience the same services anywhere

More spectrum with a new air interface

Evolution from and interworking with 2G systems,which is a key need to allow current GSM operators toprotect their infrastructure investments during theupgrade of their networks to support UMTS

A new commercial model to increase competition andthe range of services available

Advanced networking capabilities with the PSTNs,packet-based and advanced internet-based networks


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3Fig 3.1: Evolving GSM into UMTS


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Fig 3.2: UMTS standard


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A guide to the acronyms:

BSC/RNC: Base station Controller/Radio Node controller a

unit which controls a number of base stations BTS: Base Transciever Station or base stations

CAMEL: a standard to provide IN services within GSM

networks

GGSN: Gateway GPRS Support Node the point of

interconnection between the GSM and external packet networks

HLR: Home Location Register

NMC: Network Management Center

PDN: Packet Data Network

PSTN: Public Switched Telephone Network

TIPHon: The standard for voice transmission over IP

VoIP: Voice over IP


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3.1 Services

More than only voice communication

The key to market growth:

enable third parties to provide information and services

to the users of the system Therefore, in UMTS, operator will provide a pipe

which subscribers can use to access a wide range ofinformation and services.

Fig 3.3 is an example of a personalized dailynewspaper delivered electronically to a userscommunication device.


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7Fig 3.3: The service provider role within UMTS

Subscriber

database

Service

provider

Subscriber

Network operator

Value addedservice provider

Content

provider

Subscription & service

profile management

billing

billing

User data

managementaccounting

Information

service e.g Reuters

usage

usage

content e.g

newspaper


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To enjoy the service, we can follow the steps below:

(1) the user access a specialized service provider, e.g, Reuters,responsible for assembling the user-specific content.

(2)Reuters passes the information required directly to thenetwork operator who forwards it to the users mobile, butpasses billing information to the primary service provider who

collates this information to issue the user with a single bill. (3)The primary service service provider maintains the users

database of attributes so that secondary providers can access itas appropriate to provide personalized services.

It is an enhancement of the current GSM model whereby

operators are often service providers and users can onlyaccess services if they have been made available by theoperator.


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Other examples:

Special interest group subscriptions

Brand and loyalty-based service provision, etc

Utility will be increased by the concept of a softterminal, allowing consumers to choose a handsetslook and feel, with specialized service providersoffering solutions extending the handsets operationand functionality.

This is similar to the IT service industry wheresimple functionality extensions, for example

integrated file compression tools, can be purchasedfrom the Internet to improve operations of a desktopcomputer.


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Significant service changes from GSM:

GSM: voice-centric with data a secondary consideration

UMTS: data-centric with multimedia applications being ofprimary importance

With the growth in electronic content and applications,the usage of a mobile as an integral part of daily life

will be commonplace. This in itself will create new opportunities for service

providers.

Consumers will purchase communication services from

a wide variety of sources, with affinity branding andloyalty schemes being commonplace.

e.g: a high street chain store may offer a loyalty card, e-commerce smart card and telecommunication services


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3.2 Technical issues

UMTS uses a wideband CDMA technology comparedto GSMs narrowband TDMA.

Fig 3.4 shows the comparison of the architectures of2G and 3G networks.

It is envisaged that future networks will look muchmore like the internet with no single switch at thecenter.

The broadband networks will consist of

interconnected packet switches and routers andinterfaces to the outside world and will probably bebased on the Internet IP protocol.

In Fig3.4, all devices connect to broadband network.


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switch

PSTN

Operations

center

BSC

BS BS

Operations

center

Circuit

gateway

UMTSserver

BSC broadbandnetwork

BS

Legacy

networks

BS

Fig 3.4: Evolution to broadband switching


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In UMTS, the functions required to control themobile network will be server based and the

switching functions will be performed by theunderlying broadband network.

The core platforms are built upon a commonhardware and software architecture allowing

functions to be distributed as required. The key benefits of the new architecture:

Reduced network capital costs (packet routers)

Reduced network running costs (compressed form)

Higher quality, especially for voice calls(tandem-freeoperation and transcoding only where required)

Greater flexibility to introduce new services and tohandle multimedia traffic


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Fig.3.5 shows the infrastructure for UMTS.

Some indications of the migration path to be followedby operators who wish to move from 2G to 3G

networks:

Adding a packet-switching network to the existing MSC.

Packet switching services(the GPRS) introduced in GSM Over time, the packet switching network will become the main

switching function.

The packet backbone can be compatible with 2G.

Circuit Gateway is located at the edge of the network and

is responsible for adapting the internal voice and dataformats of the UMTS system to the external circuit-

oriented PSTN.


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15Fig.3.5: The infrastructure for UMTS

NMC

Service

Provider

Corporate

HLR, SLR

GMSC

CAMEL server

SIM server

Application

server

BTS

In-building

system

Broadband

Network

Circuit

gateway

PSTN PDN TIPHon

GGSN packet

gateway

UMTS

server

BSC/RNC

server

UMTSBTS

Dual

mode

BTS

GSMBTS

Service

management


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GGSN Packet Gateway: acts as the way to external packet data networks.

Likely to become the interface to new packet-oriented fixed networks

for voice transport such as TIPHON, the emerging voice-over-IPstandard

UMTS server: incorporates the call progressing and mobility of the MSC and GPRS

switching system.

Support an intelligent network interface enabling supplementaryservices to be implemented externally

BSC/RNC server: provides similar functionality to 2G

incorporates the selector function required to manage the W-CDMAsoft handover process

HLR server: provides a platform for enhanced services supporting both IN functions

provided by the CAMEL standards and client/server techniques.

This platform will be a core element enabling the service provider role.


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3.3 Air interface

WCDMA and TD/CDMA:

Proposals for the UMTS air interface: W-CDMA,OFDMA(orthogonal frequency division multiple

access), wideband TDMA, TD/CDMA(TDMA withspreading), etc.

Combination of WCDMA and TD/CDMA could beused, WCDMA for paired spectrum bands andTD/CDMA for the unpaired spectrum

WCDMA will be the dominant air interface since thereis more paired spectrum than unpaired.


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Wideband:

Chip rate: 4.096Mbps enabling each carrier to fit withina 5MHz bandwidth.

Most operators will be awarded either 2*15MHz or2*20MHz, which enables 3 or 4 carriers in total.

The same frequency will be reused in each sector of each

cell.

However, in the case of microcells, separate carrierfrequencies will normally need to be used with one beingused for the microcells and a separate frequency used forthe macrocells due to the very different power levels thatwill be used in these two environments.

Soft handover will also be supported.


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Users will be able to access a number of different

channels depending on the data rate at which theywish to transmit.

Most transmissions will be narrowband, utilizing around10kbps although users have the possibility transmit atdata rates of up to 2Mbps.

In a typical mobile environment, the average capacity ofa single carrier will be around 600kbps, allowing 60 ormore simultaneous low data rate calls but very few higherdata rate calls.

Data rates of 2Mbps will result in high levels ofinterference transmitted to neighboring cells unless theytake place within in-building picocells.


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3.4 UTRA system architecture

The radio interface independent functions, essentiallycall control and mobility management are outside thescope of UTRA and handled by core network.

UTRA(UTRAN): UMTS Terrestrial Radio AccessNetwork, shown in Fig3.6

consists of one or more radio network subsystems (RNSs),which in turn consist of base stations(Node B) and RNCs:

A node B may serve one or multiple cells.

Mobile stations are termed user equipments (UEs)and inpractice are likely to be multimode to enable handoverbetween the FDD and TDD modes and, prior to completeUMTS geographical coverage, GSM as well


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Fig3.6 UTRAN system architecture


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The UTRA permits, under certain conditions, the use ofmultiple radio links across multiple cells in support of a

single UTRA-UE connection (termed soft handover). Fig 3.7 shows a simplified version of the protocols

running between a UE and the UTRA.

Transport channels carry control plane or user plane databetween the UE and RNC, mapping onto physical channelson the air(Uu) interface(allocated by the radio resourcecontrol (RRC) layer) and ATM AAL2 (ATM AdaptationLayer type 2) connections over the I

ubinterface.

An important point: on the network side the MAC layer andradio link control (RLC) layer reside in the RNC, which iswhere most of the UTRA intelligence is concentrated.

The Frame Protocol(FP) is responsible for the relaying oftransport channels between the UE and the RNC via theNode B.


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Fig 3.7: A simplified version of the protocols

running between a UE and the UTRA


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This protocol stack is common to both FDD and TDDmodes with only minor differences required, for

example, to support macrodiversity in the FDD modeand timing advance for the TDD mode.

Fig.3.8 show the radio resource control protocolswithin UTRA.

NBAP: Node B Application Part, runs over the Iub

interface,responsible for the allocation and control of radio resources,e.g. carrier frequencies and spreading codes (and timeslots inTDD mode), to Node Bs.

RNSAP: Radio Network Subsystem Application Part, over

the Iur interface, responsible for co-ordination of radioresources between Node Bs in neighboring RNCs, i.e. insupport of links across the I

urinterface during soft handover.

RANAP: Radio Access Network Application Part, over the Iu

interface to support signaling across the I interface.


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25Fig.3.8: The radio resource control protocols within UTRA.


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Original UTRA concepts:

Comprises an FDD and TDD component to supportefficiently the different UMTS needs for symmetricaland asymmetrical services;

Initially, the UTRA depends mainly on FDD.

The original TD/CDMA concept has been adapted toTDD including the harmonization of parametersbetween TDD and FDD with respect to thedevelopment of economically feasible terminals.

Key parameters of the UTRA concept are presented in

Table 3.1.


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Table 3.1 UTRAN key parameters

16No. of power control

groups/time slots

16Timeslots per frame

10msFrame length

Root raised cosine, roll-off=0.22Pulse shaping

QPSKModulation

1-164-256Spreading factor range

4.096McpsChip rate

5MHzCarrier spacing

TD-CDMAW-CDMAMultiple access

scheme

TDDFDD


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UTRA FDD

In both uplink and downlink spreading with a variable

spreading factor from 4 to 256 is applied depending on thedata rate and service

different frame structure in uplink and downlink.

In the uplink, data(DPDCH-dedicated physical data channel) and

control channels(DPCCH- dedicated physical control channel) are

I/Q multiplexed(QPSK modulated).

whereas in the downlink data and control channels(DPCH-dedicated

physical channel) are time multiplexed.

For e.g., handover measurements the super frame length is defined

as 720ms=6*120ms as an integer multiple of the corresponding GSM

super frame for backward compatibility reasons. The slots correspond to power control groups.


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29Fig 3.9 Frame structure for FDD uplink


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30Fig 3.10 Frame structure for FDD downlink


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The connection dedicated pilot symbols for channel estimation,

and allowing coherent detection in both links, give an important

advantage for the application of adaptive antennas in the downlink

compared to cell specific common pilot codes. These pilot symbols are provided with each user signal, and thus in

the same antenna beam as the user data.

In the uplink pilot symbols are used for coherent detection.

Different coding schemes are under investigation depending on the

BER and delay requirements for different services. Convolutional codes with rate 1/3 and and constraint length 9 are

applied for services with BER requirements in the order of 10 -3.

For services with higher BER requirements in the order of 10-6 and

less stringent delay requirements convolutional coding in

concatenation with outer RS coding plus outer interleaving is used.

Turbo codes are currently under investigation for higher data rateand high quality services.

To maintain sufficient flexibility, additional service specific coding

is foreseen.


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For each service, coding and interleaving is applied; the

resulting data stream is rate matched and multiplexed on the

carrier.

UTRA FDD supports intra-frequency handover, inter-

frequency handover and inter-system handover.

intra-frequency handover: dedicated circuit switched channels

use soft handover, dedicated packet data channels can use softor hard handover and the common channels use hard handover

inter-frequency handover: the mobile measurements on other

frequencies are performed in slotted mode downlink

transmission or with a dual receiver.

inter-system handover: needed between UTRA and at least

GSM. This is a hard handover procedure.


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UTRA TDD

based on TD/CDMA, combination of TDMA and CDMA Each time slot comprises several (in maximum 16)

orthogonal spreading codes. Different user bit rates are supported by code and/or time slot

pooling.

Up to eight users can share up to 16 spreading codes. Due to the small number of spreading codes per time slot, this

approach enables multiuser detection or join detection with todaystechnology to mitigate the intracell interference.

Therefore, the requirements on power control accuracy are relaxed.

Due to the TDMA component, interference avoidancealgorithms by means of DCA(dynamic channelallocation) can be applied for both coordinated operation.


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The basic structure of UTRA TDD is similar to FDD with

a frame length of 10ms and 16 time slots.

These time slots are used for an additional TDMA component in

the multiple access scheme.

Fig 3.11 shows the frame structure including the spreading codes

within each time slot. The super frame length is also chosen as

720ms.

For downlink signaling: up to two time slots are allocated.

They are also applied to power control and handover

measurements in the downlink.

For uplink: The common control channel is the Random Access

Channel(RACH).


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35Fig 3.11 TDD frame structure


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Between uplink and downlink:

the ratio of asymmetry traffic can be selected between

DL:UL=15/1 to 1/7. several switching points are supported to enable a higherpower control update rate than on frame basis.

Joint detection is facilitated by a special trainingsequence for joint channel estimation.

The midambles of different active users in the same timeslot are time-shifted versions of one single periodic basiccode.

Therefore, the joint channel estimation of the channelimpulse response of different users can be achieved by asingle cyclic correlator.

The different user specific channel impulse responses areobtained sequentially in time at the correlator output.


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For multiplexing and coding, similar to UTRA FDD for real time services FEC and for non real rime services a

combination of ARQ and FEC are used.

Data are QPSK modulated.

spread by orthogonal spreading codes with length between 1 and16 and the same modulation scheme as for FDD.

Raised cosine pulse shaping is applied

Frame-synchronized network due to the same carrier frequency in uplink and downlink

to control interference for coordinated operation.

Flexibility for asymmetrical switching points and theiralignment with adjacent cells depends on

the distribution of users in the coverage area the load in the network

the availability of time slots for DCA to escape from close mobileto mobile interference in the time domain.


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3.5 Operators position

It is the operators who are currently facing the mostdifficult decisions since they need to place a priceon the UMTS licenses about to be rewarded.

too high a price: -- >a significant loss of profit over thecoming years;

too low a price: -- >losing the license in what maybecome the primary mobile radio technology in thecoming 5 or 10 years.

Operators face a range of choices with UMTSdepending on whether they are existing GSMoperators or new operators deploying their firstnetwork.


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For existing operators, possible strategies could include:

Capacity enhancement only: only deployed in areas withinsufficient GSM (unlikely)

Islands of coverage: in the main cities and along the maincommuter routes, providing a similar sort of coverage to thatin the early years of cellular.

Complete coverage: equivalent coverage to GSM (costly) New operators:

Go it alone (a high risk strategy)

Team with a GSM operator

General expectation: most UMTS licenses will be awarded toexisting operators, probably in a consortium, including mediaand other interested companies


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With a range of assumptions, it is possible to build abusiness case:

Expenditure side: costs will fall over time witheconomies of scale and as components increase incapability

Revenue side: Services: packet data transmission, email, Internet access and

multimedia

Modeling for these services can be made and actual prices will notbe able to differ too much

Payback might extend over five to seven yearsdepending on the speed if new users and the usageand tariff actually experienced.

Once payback has been achieved, UMTS appears tooffer an excellent revenue stream.

Documents

55_UMTS-Overview-(FDD-TDD)