Mobile communication networks

Master for international studentsPolitecnico di TorinoYear 2013

Enrico BuracchiniBruno Melis

2Enrico Buracchini received, with full marks, the degree in Electronic Engineering from the University of Bologna in October 1994. In December 1994, he was employed in the Mobile Services Division of CSELT (R&D labs of Telecom Italia Group), now TILab, as a Research Engineer. His activity concerns the study of multiple access methods (TDMA, CDMA, OFDMA) for mobile communications systems. He was part of Italian Delegation to ITU R TG8/1 group dedicated to IMT 2000 standardisation and he is currently 3GPP RAN1 delegate.He managed, in 2000-2003 period, several consultancy projects for international Telecom Italia activities in Austria, Greece and Spain on UMTS planning.He was involved in several European research programs (COST, ACTS, IST) dedicated to 3G and future mobile systems. He published several papers on third and future generation mobile systems, smart antennas, SWradios and Cognitive Radios. Since 2003, he has managed the R&D projects dedicated to Systems beyond 3G including TILab E2R I & II and E3 activities.He did several lectures @ Telecom Italia School (SSGRR) on GSM, UMTS, HSDPA, SDMA and SDR, several lectures in Universities (Bologna, Catania, UPRC, UOA) on Evolution of mobile systems and several tutorials in conferences on SDR.

3Bruno Melis received, with full marks, the degree in Electronic Engineering from Politecnico di Torino in 1995. In the same year, he was employed in CSELT (today TILAB) Mobile Division. His activity concerns the study of multiple access methods (TDMA, CDMA, OFDMA) for mobile communications systems. . He matured a significant experience in analysis and dimensioning of digital radio systems such as GSM, UMTS, HSPA, LTE and WIFI by numerical simulation techniques. He is autor of several papers and IPRs related to digital signal processing and MIMO techniques.

4Mobile Communications the course

1. Basic concepts

2. GSM/GPRS radio access

3. GSM/GPRS architecture and protocols

4. Universal Mobile Telecommunications System radio access

5. UMTS radio resource management

6. UMTS architecture and protocols

7. High Speed Down Link Packet Access and Long Term Evolution

8 LTE

9. LTE ADVANCED

10. Mobile Network Engineering

5Mobile Communications

1.1 Basic concepts of mobile communications

1. Basic Concepts

61. Basic concepts

1.1 Basic concepts of mobile Communications

channel modelsradio coveragefrequency re-usestatic and dynamic frequency allocation

extensions:

propagation modelse1.2

e1.3 interference behavior

e1.4 digital transmissione1.1 channel models

7Some wireless history hints

8Some wireless history hints 1947 Bell Laboratories introduced the idea of cellular communications

with the police car technology. The basic concept of cellular phones began, when researchers looked at crude

mobile (car) phones and realized that by using small cells (range of service area) with frequency reuse they could increase the traffic capacity of mobile phones substantially. However at that time, the technology to do so was nonexistent.

AT&T proposed that the FCC allocate a large number of radio-spectrum frequencies so that widespread mobile telephone service would become feasible.

The FCC decided to limit the amount of frequencies available, the limits made only twenty-three phone conversations possible simultaneously in the same service area.

1968 AT&T and Bell Labs proposed a cellular system to the FCC of many small, low-powered, broadcast towers, each covering a 'cell' a few miles in radius and collectively covering a larger area. Each tower would use only a few of the total frequencies allocated to the system. As the phones traveled across the area, calls would be passed from tower to tower.

FCC reconsidered its position by stating "if the technology to build a better mobile service works, we will increase the frequencies allocation, freeing the airwaves for more mobile phones."

1973 (April)The first call on a portable cell phone is Made by Dr Martin Cooper, a former general manager for the systems division at Motorola, who is also considered the inventor of the first modern portable handset.

1977 AT&T and Bell Labs had constructed a prototype cellular system. A year later, public trials of the new system were started in Chicago with over 2000 trial customers.

9Some wireless history hints 1979 The first commercial cellular telephone system began operation in

Tokyo. 1980 Analog cellular telephone systems were experiencing rapid growth

in Europe, particularly in Scandinavia, United Kingdom, France and Germany. Each country developed its own system, which was incompatible with everyone else's in equipment and operation

1981 Motorola and American Radio telephone started a second U.S. cellular radio-telephone system test in the Washington/Baltimore area.

1982 FCC authorizes commercial cellular service for the USA. 1982 The Conference of European Posts and Telegraphs (CEPT) formed

a study group called the Groupe Special Mobile (GSM) to study and develop a pan-European public land mobile system. 1983The first American commercial analog cellular service or AMPS (Advanced Mobile Phone Service) was made available in Chicago by Ameritech.

1987 Cellular telephone subscribers exceeded one million and the airways were crowded.

1989 GSM responsibility was transferred to the European Telecommunication Standards Institute (ETSI)

1990 Phase I of the GSM specifications were published. 1991 Commercial launch of cellular service based on GSM standard in

Finland. 2000 Pre-commercial UMTS network in Tokyo, JAPAN October 1, 2001 NTT DoCoMo launched the first commercial WCDMA 3G

mobile network.

10

Some wireless history hints

LINKS for History FANs

- http://www.coai.com/history.php- http://www.umtsworld.com/umts/history.htm

11

A wireless mobile system

PSTN / ISDNOther Networks

IN

MSC (Switching & MM)

Control ofRadio Stations (BSC/RNC)

RadioCoverage

(BTS,Node B)

RadioAccess

Web, Internet

12

ACCESS TECHNIQUES FORMOBILE COMMUNICATIONS

P - PowerT - TimeF - Frequency

P

T

P

T

F

P

T

F

FDMA (TACS)

TDMA (GSM)

CDMA (UMTS)

F

13

OFDM: Orthogonal Frequency Division Modulation

OFDM as modulation Spectrum is divided in several sub-carriers orthogonal: f=1/Ts Information flow is divided over the sub-carriers Mo-demodulation by FFT/iFFT

OFDM as mulitple access (OFDMA) A group of sub-carriers can be allocated to different users inside the available

bandwidth

ffsingle-carrier mod.

fconventional multi-carrier modulation

O FDM

14

OFDM: Characteristics

Sub-carriersFFT

Time

Symbols

N subcarriers in W Bandwidth

Guard Intervals

Frequency

f=1/Ts

15

Positioning of different systems wrt user mobility and maximum user data rate

16

An overall view of the mobile service needs

Service area

homogeneous area:

QoS constraints traffic density propagation characteristics % of coverage

homogeneous area efficiency

service dependent

BRMefficiency

required bit rate

potential users

bandwidth available

17

Need for orthogonal channels

channel

RxnTxn

Tx2

Tx1

Rx2

Rx1 distinction on the basis of orthogonal functions constructed over:

time, frequency, code

the receiver has to use some correlation function

TDMA, FDMA

CDMA

filteringtime synchronisation

correlation

limits: adjacent channel overlapping (FDMA)time dispersion (TDMA)non-adequate correlation (CDMA)

18

Three kinds of efficiency pursued

N: # of orthogonal functionsB: bandwidthB0: B/N bandwidth needed for each active userM: potential users (active and non-active)MN: potential users related to N

N

N

MM

NM

BR

BRMefficiency

0

frequency [bit/s/Hz] time [users/Hz] space [users/users]

modulation synchronisation re-use

19

The communication system

Basic issues: how to transmit a signal between two point of the space how to deal with the modifications induced by the channel on the signal how to recognise the transmitted signal on the receiving side

Noise characterisation

Signal to Noise Ratio (powers)

)()()( tntAstr received transmitted

channel amplification

noise + .. thermal addictive co-(adjacent) channels fading non-linearity

source transmitter transmissionchannel receiver user

Bt t

average power of s(t) (amplified)average noise power

20

Communication system roles and issues

Source: generator of the original signals to be transmitted how to represent the signal how to reduce the amount of data to be transmitted by maintaining the

information content (source coding):

Transmission channel : thermal addictive + co-(adjacent) interference + fading + non-linearity

Transmitter: transforms the source-generated signal in the signal to be sent over the channel (modulation)

frequency content in relation to the channel bandwidth channel coding (redundancy)

Receiver: extracts from the received signal the one transmitted by the source (demodulation)

how to reduce the error probability

source transmitter transmissionchannel receiver user

21

The channel model time and frequency selectivity

Time and frequency selective (continuous time)

)()();()( tndtxthty

)()()()( tndtxhty Time invariant and frequency selective channel

Time invariant and non frequency selective channel

)()()( tnthxty

);( thchannel response at time t to a unit impulse transmitted at t-

)( time selectivity: channel dependency

on time frequency selectivity: input-output

relation dependent on the convolution between x(t) and the impulse response

22

Cellular System - Frequency Reuse

Theoretical Cluster

12

34

56

7 12

3

4

56

7

12

34

56

7

1 2 3 4 5 6 7

bandwidth

23

Cluster & channel grouping

A B C D A B D

1 2 3 4 5 6 N

A = { 1, 5, 9, ....}

24

Frequency reuse concept

B

A

B

A

B

B

A

B

A

BA

A

B

A

B

D

C

D

C

D

C

D

C

D

C

D

C

D

C

D

25

Choosing The Cluster Size

CS

CAPA CI T Y

Q UA L

I TY

26

Choosing The Cell Size

CS = CONSTANT

R

CAPA CI T Y

COS T

27

Cell Size

a) b)

C C

B B

B

B

C

C

C

C C

C

C C

A A A

A A A

A A

B B

B B

B B B

A A

A

28

The cluster topology

12

34

56

7

1

The axes may definethe reuse distance (the distance between co-channel cells)

i

j

Number of cells belonging to the cluster

ijjiM 22

29

Carrier to Interference ratio evaluation

1

1

1dr

2

4)()()(

)(

rBGmGCPCP mTR

2

4)()()(

)(

dBGmGBPIP iiTiR

rd

IPCPIC

i iR

R

61

)()(/ uniform conditions and selection of the (6)

closest co-channel stations

1

min

63

ICM

rd(C/I)min used to evaluate the cluster

dimension M

30

Antenna solutions for cellular coverage

a) b)

31

Planning the cell size and layouta matter of channel/Km2 requirements (traffic constraint)

tuning the cell sizeover a single layer

adopting overlapping coverage solutions (umbrella cells)

32

Microcellular environmentnew conditions for propagation