E00c032.PDF

GENERAL INTEREST

Telephone Service (1)

Part 1: From System 1 to UMTS

By G. Kleine

The frequency allocation sell

off for the next generation of

mobile phones caused a stir

this April when the U.K. gov-

ernment scooped £22.48 bil-

lion. More recently the Ger-

man government netted a

staggering £31.8 billion in its

licence sell off. What new

features can we expect from

this next generation of

mobile phone?

The ETSI or European Telecommunications

Standards Institute has defined a technology

standard for the third generation of mobile

phones called IMT-2000 or International

Mobile Telecommunications 2000 These pro-

posals have been approved by the

ITU and also go by the name UMTS

or Universal Mobile Telecommuni-

cations System. The main aim of

this standard is to ensure global

harmonisation of broadband mobile

communications for 3G or Third

Generation phones including fre-

quency allocation and data transfer

protocols. This will ensure that

Elektor Electronics

12/2000

Universal Mobile

GENERAL INTEREST

UMTS handsets will be compatible

in whatever country adopts the net-

work. One of the main goals of the

standard is this so called global

roaming. You should be able to

make calls using a UMTS/IMT2000

mobile phone whether you’re in

Bratislava or Bridlington. This

means that when you sign up for a

UMTS phone and are assigned a

phone number, it will be a global

number. No need to prefix with

country codes — you can always be

reached on this number.

The theoretical maximum data

rate of UMTS is 2 Mbit/s but this can

only be achieved under optimum

propagation conditions for example

if the mobile is operating in a city

and is not moving (immobile?). If the

mobile is moving relatively slowly

(i.e. walking pace) then transmission

rates of up to 384 kbit/s are possible.

In any case the minimum guaran-

teed data rate is 128 kbit/s even

with the mobile travelling at vehicu-

lar speeds.

New UMTS features

Tomorrow’s globally roaming UMTS mobile

phone will offer many more features than we

see on current handsets. Along with SMS and

WAP there will be a multitude of multimedia

facilities available. At last you should see the

introduction of true video phones and video

conferencing over a UMTS radio link. High

quality music tracks will be downloaded in

an instant and short video postcards may be

sent to friends. Interactive games with other

phone users will be introduced and shopping

methods will also be transformed, your UMTS

handset will deal with authorisation and pay-

ment of purchases. Company reps and ser-

vice personnel will find that while on the

move they have a direct link to the company’s

intranet. As a UMTS handset moves, its

approximate location will also be logged so

that when you request information on local

restaurants for example or ask for a street

map if you are lost you will receive informa-

tion relevant to your current location. Anyone

dealing with Fleet management or deploy-

ment of emergency services and those who

need to know the whereabouts of the mobile

will ﬁnd this feature useful.

Predicting how a UMTS handset will look

is difficult but anyone who has sent an email

using a WAP phone will realise that it will

need to be equipped with a more convenient

method of data entry and will probably

evolve along the lines of a portable PC or

palmtop.

Abbreviations

Second Generation (Mobile System)

Third Generation (Mobile System)

AMPS

Advanced Mobile Phone System (US analogue cell network)

ANSI

American National Standards Institute (USA)

ARIB/TTC

Association of Radio Industry and Business (Japan)

Bandwidth

CDMA

Code Division Multiple Access

DCS

Digital Cellular System (DCS1800)

DECT

Digital European Cordless Telephone

EDGE

Enhanced Data Rate for GSM Evolution

ETSI

European Telecommunications Standardisation Institute

FDD

Frequency Division Duplexing

FDMA

Frequency Division Multiple Access

FPLMTS

Future Public Land Mobile Telephone System

GMSK

Gaussian Minimum Shift Keying

GSM

Global System for Mobile Communications

(originally called: Groupe Speciale Mobile)

GPO

General Post Office (State run predecessor to BT)

GPRS

General Packet Radio Service

A glimpse back into the past

HSCSD

High Speed Circuit Switched Data

IMT

International Mobile Telecommunications

Commercial mobile communications systems

in the U.K. really began with System 1 oper-

ated by the G.P.O. (see table 1 ). The system

had very poor coverage and was not cellular.

Each radiophone requires one frequency for

sending and one for receiving i.e. four chan-

nels in total for a call between two radio-

phones. With a voice channel bandwidth of

100kHz each call needed 400kHz of the entire

network bandwidth. System 2 was developed

but never implemented. System 3 was later

introduced with a reduced voice bandwidth

of 25 kHz. Despite the increased capacity it

could never keep up with the demand for this

system.

The big breakthrough came with the intro-

duction of the first cellular networks.

Although the fundamentals of the cellular

network had been theorised, it was in 1947

that D.H. Ring of Bell Labs in the USA for-

malised the cellular concept in a paper. The

basic idea is that instead of using powerful

transmitters to cover a large area, the area is

divided up rather like the hexagonal panels

ITU

International Telecommunications Union

LNA

Low Noise Ampliﬁer

Local Oscillator

MSS

Mobile Satellite Service

NMT

Nordic Mobile Telephone (Scandinavian analogue cellular net)

NTT

Nippon Telecom & Telegraph Corp. (Japanese analogue cellular net)

Power Ampliﬁer

PCS

Personal Communications System

QPSK

Quaternary Phase Shift Keying

8PSK

8 Phase Shift Keying

SIM

Subscriber Identity Module

SMS

Short Message Service

TACS

Total Access Communication System (U.K.)

TCP/IP

Transport Control Protocol / Internet Protocol

TD/CDMA

Time Division CDMA

TDD

Time Division Duplexing

TDMA

Time Division Multiple Access

TTA

Telecommunications Technologies Association (South Korea)

UMTS

Universal Mobile Telephone Service

UTRA

UMTS Terrestrial Radio Access

WAP

Wireless Access Protocol

W-CDMA

Wideband Code Division Multiple Access, Wideband-CDMA

WRC

World Radiocommunication Conference

12/2000

Elektor Electronics

GENERAL INTEREST

of a patchwork quilt. Low power base sta-

tions are placed at the centre of each panel or

‘cell’. Base stations in adjacent cells are not

allowed to use the same frequencies, but

these frequencies can be re-used in other

non-adjacent cells. The beauty of the system

is that if the number of subscribers in a par-

ticular area is large, for example in central

London, the number of cells can be increased

by reducing the cell size and using more,

lower powered base stations, thereby

increasing the network capacity.

The U.S. company Bell made trials of the

first cellular system in 1978 in Chicago but

did not start deployment of their AMPS

(Advanced Mobile Phone System) until about

1983. Meanwhile the Scandinavian countries

had installed the ﬁrst commercial cellular net-

work in 1981. Working at 450 MHz, this first

generation analogue mobile phone system

was known as NMT (Nordic Mobile Tele-

phone) and offered roaming. It was later

superseded by a 900 MHz version. In the

early 80’s the U.K. introduced TACS (Total

Access Communication System). This is

based on the American AMPS but is, need-

less to say, not compatible with it.

The UK government took an unusual step

by deciding that the network licences should

be awarded to commercial companies rather

than a state owned monopoly like the G.P.O.

Cellnet and Racal Vodafone were the suc-

cessful bidders.

TACS operates in the 900 MHz band and

uses analogue FM. The frequency bands are

divided up using FDMA upper and lower

bands at 935-960 MHz and 890-915 MHz

allow 1000 channels per band with a nominal

channel spacing of 25 kHz. The channels are

employed as duplex pairs so that if a mobile

is receiving a signal in channel 3 of the upper

band, it will be transmitting on channel 3 of

the lower band. The send and receive signals

will therefore always be separated by

45 MHz. Dedicated control channel pairs are

included to enable the network to handle

mobile registration, ‘handover’ as the mobile

passes from one cell boundary to another,

output power adjustment, call tariff logging

and more.

A typical cell size has a 1 km radius in

urban and 15 km radius in rural environ-

ments. Maximum base station power is

100 W and mobiles are restricted to 10 W out-

put power. To handle the ever increasing sub-

scriber base, extra frequencies were later

introduced to boost the network capacity.

This system became known as ETACS. At the

time of writing, Cellnet have marked the dis-

continuation of its analogue network and

Vodafone plans to follow suit in the summer

of 2001.

WWW Information sources

Organisations:

UMTS-Forum http://www.umts-forum.org

UMTS-Licence information http://www.umts-forum.org/licensing.htm

International Telecommunication Union http://www.itu.int/imt

European Telecommunications Standards Institute http://www.etsi.org/umts

UK Regulatory authority http://www.spectrumauctions.gov.uk

Universal Wireless Communications Consortium

http://www.uwcc.com

Third Generation Partnership Project

http://www.3gpp.org

Manufacturers and network operators:

BTCellnet

http://www.btcellnet.ne t

Ericsson

http://www.ericsson.co.uk

Nokia

http://www.nokia.com

Alcatel

http://www.alcatel.co.uk

Motorola

http://www.motorola.co.uk

Nortel

http://www.nortelnetworks.com

Nippon Telecom & Telegraph Corporation

http://www.nttdocomo.com

Orange

http://www.orange.co.uk

Philips

http://www.pcc.philips.com

Sagem

http://www.Sagem.com

Vodafone

http://www.vodafone-retail.co.uk

During 1990 the GSM Phase 1

specification appeared after its 11

year incubation period with the

ETSI. This was the beginning of the

2G or second generation mobile

phones and uses digitised speech.

One year later Vodafone launched

the first U.K. GSM network, and by

1992 coverage was beginning to

extend from the large cities and air-

ports into rural areas. The frequency

bands used are identical to the

TACS system (400 TACS channels

were deliberately reserved for the

introduction of GSM). In 1993 and

1994 One2one and Orange respec-

2000

UMTS

Kbit/s

384

EDGE

115

GPRS

57.8

HSCSD

GSM +

14.4

GSM

9.6

1992

2000 2001 2003

000183 - 1 - 11

Figure 1. Evolution of GSM to UMTS.

Elektor Electronics

12/2000

GENERAL INTEREST

tively launched their GSM system,

this time using GSM1800 (other-

wise known as PCN or DCS1800)

operating in the 1.8 GHz band. 1994

also saw the introduction of the BT

Cellnet GSM network in the

900 MHz band. Most current

mobiles offer dual-band operation

and are therefore compatible with

both. This dual-band capability is

useful if you intend using the

mobile overseas in one of the 110

countries that have adopted GSM,

or if your network provider decides

in the future to use both bands to

solve capacity problems.

In North and South America and

in Canada things are a little differ-

ent. Here GSM1900 operates at

1.9 GHz (also known as PCS1900).

Some dual-band mobiles work at

GSM900 and GSM1900. Alternatively

a tri-band mobile will cover every

eventuality. Like TACS, GSM 900

uses FDMA to divide the frequency

bands. This time however each of

the two bands is divided into 125

channels with a bandwidth of

200 kHz per channel. The 45 MHz

duplex spacing is maintained.

GSM1800 has 374 channels with a

duplex spacing of 95 MHz. In addi-

tion to using FDMA to divide up the

frequency band into channels,

TDMA is used to chop up each chan-

nel into contiguous time frames of

4.615 ms. Each frame is further

divided into 8 time slots of 0.577 ms.

When a mobile is making a call it

will be allocated one slot in each

frame for sending its digitised voice.

Likewise one slot in the receive band

is claimed for receiving digitised

voice. Mobiles in stand-by mode will

only need to listen to certain frames

in a paging channel.

Modern GSM mobiles comprise of

two to four highly integrated

chipsets. A fully integrated base

band chip is under development and

coupling this with an HF stage and

a few components will allow hand-

sets to shrink in size even further. A

relatively new concept is the Dual-

mode mobile. This is a GSM mobile

phone that can automatically switch

into a DECT cordless phone when

you are in range of a home base unit

(or in the office through the company

PABX), thereby making cheaper calls

through your cordless phone base

unit over a land line. Phones offering

this feature have been introduced by

Sagem and BT Cellnet.

The success of GSM has been

much greater than ﬁrst anticipated,

current estimates indicate approxi-

mately 400 million GSM subscribers world-

wide. Forecasts for the year 2010 indicate

1.8 billion subscribers, the greatest growth

expected in Asia. In Europe in the coming

years the increasing use of multimedia fea-

tures means that the relatively low data rate

of GSM will not be sufficient. We shall look at

some of the interim solutions that have been

developed to increase the GSM data rate. Its

eventual replacement by UMTS will of course

allow a maximum data rate of 2 Mbit/s.

One characteristic of multimedia applica-

tions is that the volume of data ﬂowing to and

from a subscriber is not symmetrical. Unlike

speech communication, browsing the Inter-

net will produce far more information passing

from the base station to the subscriber

(downlink direction) than in the uplink direc-

tion. Also unlike speech, the transfer of the

data is not real-time critical, it can be sent in

Table 1. Mobile radio networks in the U.K.

Generation

Network

Operating

Frequency range

Channel

Duplex

Modulation

pairs

spacing

System 1

1965

163 MHz

100kHz

FM, analogue

System 3

c.1970

163 MHz

25 kHz

FM, analogue

1 G

TACS

1985-2000

890 - 960 MHz

1000

25 kHz

45 MHz

FM, analogue

2 G

GSM

1991

880 - 960 MHz

173

45 MHz

GMSK, digital

PCN(GSM1800)

1993

1710 - 1880 MHz

374

200 kHz

95 MHz

GMSK, digital

3 G

UMTS

2002 ?

1885 - 2025 MHz,

5 MHz

190 MHz

WCDMA, digital

2110 - 2200 MHz

12/2000

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GENERAL INTEREST

packets which do not necessarily need to be

transferred in the correct order. The capacity

of the uplink and downlink can be adjusted

according to needs.

7 min.

85 sec.

From GSM to UMTS

70 sec.

The thirst for increased data capacity

becomes more apparent year by year. WAP

phones are the current fashion but they do

not offer any increase in data capacity over

the standard 9.6 kb/s. Network providers are

implementing various techniques to increase

data capacity and bridge the gap between

the 9.6 kb/s offered by the 2G GSM phones

and the 2Mb/s offered by future 3G phones

(see Figure 1 ). Handsets that can use these

techniques are known as 2.5G phones. Each

of these methods is compatible with the GSM

network and does not cause problems with

existing handsets.

A standard GSM channel achieves a data

rate of 9.6 kb/s with just one time slot in the

frequency channel containing 8 timeslots.

Altering timeslot allocation is just one

method that can be used to increase data

capacity. Using a technique called HSCSD or

High Speed Circuit Switched Data , is the sim-

plest and cheapest method for the network

operator to increase capacity. It requires only

a software update at the base stations. Firstly

a more efficient data coding method is used

to increase the data rate of each GSM chan-

nel from 9.6 kb/s to 14.4 kb/s (so called

GSM+ ). Next, four of the eight TDMA times-

lots are allocated to one subscriber. This

gives a data rate of 57.6 kbit/s. For the user

with an HSCSD compliant mobile however

this technique has a few disadvantages.

Firstly, it takes about one minute to set up the

HSCSD call. Secondly, once the connection is

established, it acts as a quasi fixed-line in

that the four channels are allocated to the

subscriber for the duration of the call. The call

tariff takes this into account and this method

turns out to be expensive for the subscriber.

This technique has not been widely deployed

in the U.K. but Orange are currently using this

method on some of its services.

Another 2.5G system is the GPRS or Gen-

eral Packet Radio Service . This is a speciﬁca-

tion produced by the ETSI to provide packet

data transfer in a GSM network. This tech-

nique can provide a maximum data rate of

171.2 kb/s i.e., three times faster than current

modems using a land line! The increased

speed is achieved by utilising all 8 slots in a

GSM TDMA frame. These would normally be

assigned to eight different subscribers. GPRS

is actually a universal packet switched data

service which overlays the GSM system. It is

responsible for packetising data, spreading it

31 sec.

28 sec.

14 sec.

10 sec.

6 sec. 5 sec.

2 sec.

0000183 - 1 - 12

out over free time slots and reassem-

bling it all again at the other end i.e.,

in the mobile.

A novel feature of this system is

its totally different approach to

phone use and call billing. The

phone is typically switched on in the

morning to log on to the network

and remains connected for the whole

day. Call charges are based on the

volume of data sent rather than the

connect time. This ‘always-on’ fea-

ture allows almost instantaneous

email and web browsing.

BT Cellnet launched their GPRS

network in June 2000. Offering a

data rate of 28 kb/s, this should be

up to 96 kb/s by the new year.

Nation-wide coverage was antici-

pated by September 2000. Orange

and Vodafone plan to begin their ser-

vice before the year end and many

European countries have announced

similar timescales so GPRS roaming

in Europe will be possible. Detrac-

tors of the system have pointed out

that the claimed data rate of this

method is overly optimistic. What

happens to all those other 7 sub-

scribers whose timeslots you stole?

Well, it seems as though multimedia

data ﬂow is typically not continuous

but ‘bursty’. A screenful of data or a

ﬁle for example will be downloaded

in a burst of activity and then …

silence as we scratch our head and

decide which option to select. The

silences are used to service other

subscribers.

Further enhancement to GSM can

also be achieved by using a more

efficient method of signal modula-

tion. GSM uses GMSK or Gaussian

Minimum Shift Keying, changing this

to 8-PSK or eight times Phase Shift

Keying increases the capacity of

each channel from 9.6 kb/s to

48 kb/s. This technique is used for

EDGE , or Enhanced Data rates over

GSM Evolution. Peak data rates of

384 kb/s can be achieved with this

system because like GPRS it will use

all 8 time slots to send data.

GSM/EDGE transceivers will be able

to switch between the two modula-

tion modes dynamically to ensure

backward compatibility for existing

handsets. EDGE provides an evolu-

tionary path from GPRS to UMTS by

combining the packet data transfer

of GPRS with the modulation method

that will be used in the future with

UMTS. Integration of this system will

be less costly than building the com-

pletely new network necessary for

UMTS. This system will be offering

high speed data links for GSM users

before and after the introduction of

UMTS and we can be sure to see

dual band/dual mode handsets oper-

ating between GSM and UMTS in

the near future.

(000183-1)

In the second and final part of this

article we look at the frequency allo-

cation, licensing and technical back-

ground to UMTS.

Elektor Electronics

12/2000

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