Communications COMMS (CE )

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Faculty of Computing, Engineering & Technology

Communications

COMMS (CE700038-2)

Alison L Carrington C203 [email protected] www.fcet.staffs.ac.uk/alg1 2008/9

Multiplexing, (FDM, TDM, CDM)

& mobile communications

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COMMS (CE700038-2) 2008/9

Multiplexing, (FDM, TDM, CDM) and

mobile communications

2

Overview & Objectives

Introduction

Multiplexing Schemes

FDM, TDM & CDM

History/future of Mobile communication

systems

1G, 2G, 3G & 4G?

Mobile Multiple Access Schemes

Advantages and disadvantages

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Introduction (1)

Multiplexing: name given to techniques which

allow more than one message to be transferred

via the same communication channel.

Channel: could be a transmission line

Twisted pair Co-axial cable A radio system Fibre optic cable Etc..

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Introduction (2)

Channel will offer a specified bandwidth, which

is available for a time, t, where t->

∞

.

With reference to the channel there are 3

‘degrees of freedom’

Bandwidth or frequency Time Code

Channel

B

_L

B

_H

Bandwidth

freq

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Introduction (3)

Multiplexing are techniques which

allow k users to occupy a channel

for the duration in time, that the

channel is available

freq

time

code

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Multiplexing

It costs significant amounts to change a

telephone system, not least the cost of the

“construction”

Hence the more calls you can pump down a

cable the more profitable the cable becomes

Telco’s

(Telephone companies) have

developed elaborate multiplexing schemes

The schemes can be divided into three

Sharing a medium

Time division multiplexing brought digital

technology to mobile communications

Recall, “multiplexing describes how several

users can share the same medium with

minimum or no interference” [Schiller 2003]

In mobile communications multiplexing can be

applied in 4 dimensions

Space

Frequency Time

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Space Division Multiplexing (SDM)

Premise that if we have entities wishing to

communicate using a single channel, then as long as we space them far enough apart interference will not occur

To reduce further, the risk of interference place guard space between the frequency spaces

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Frequency Division Multiplexing (FDM)

Divides the available frequency into non-overlapping bands with guard spaces between to avoid overlapping (adjacent channel interference)

Receiver only has to know the frequency to tune in to Used in analogue systems

f Ch ann el f 1 Ch ann elf 2 Ch an nel f 3 Ch ann el f 4 Ch ann el f 5 Cha nn el f 6 t

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Time Division Multiplexing (TDM)

Allows access to entire frequency bandwidth but for a limited amount of time

All senders use same frequency in at different time If two transmissions overlap known as co-channel interference

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Combining FDM/TDM

By allowing a channel to use a certain frequency for a certain period of time more efficient use of resource is achieved

More robust against interference and tapping

This is the scheme used by GSM between the handset and base station

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Combining FDM/TDM

Requires coordination between the different

senders

Two senders will interfere if they select the

same frequency

To avoid this the senders hop between

frequencies:

if the hop is fast enough the period of interference may be so small that if the coding of the data signal is sufficient to allow the receiver to recover the data the interference is deemed acceptable

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Code Division Multiplexing (CDM)

All channels use the same frequency, however,

each channel is given its own unique code

Each code must be sufficiently

orthogonal

to

allow appropriate guard spaces

Large range of codes provides significant

expansion, security, etc

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Code Division Multiplexing (CDM)

Highly complex scheme

Receiver has to know the code & be able to

separate out other traffic on different codes

which appear as background noise

Receiver & transmitter must be synchronised to

provide correct decoding

All signals must reach the receiver with

relatively equal strength or the receiver will not

be able to distinguish between them

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Mobile Introduction

Public mobile radio services developed during

the 1950’s

With a limited coverage area

With a service available to a limited number of subscribers.

The rapid development of radio and electronic

technology made possible the development of

cellular systems during the 1980’s.

During the 1990’s, digital cellular radio was

introduced

During the 2000’s truly multimedia tether less

communications will be introduced

This section provides a review of these

developments

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Radio Band Classification

100-10km 3-30kHz

VLF Very Low frequency

10-1m 30-300MHz

VHF Very high frequency

1000 -10m 3-30MHz HF High frequency 1-0.1cm 30-300GHz EHF Extra high frequency

10-1cm 3-30GHz

SHF Super high frequency

100-10m 300-3000MHz

UHF Ultra high frequency

1000-100m 300-3000kHz MF Medium frequency 10-1km 30-300kHz LF Low frequency λ Range Freq Range ABB Classification

The frequency & corresponding wavelength may be

determined using c = f λ, with c = 3x108_{m/s, f = frequency in Hz} & λ = wavelength in metres.

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Worldwide cellular subscriber growth

0 200 400 600 800 1000 1200 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 S u b scr ib er s [ m il li o n ]

Note that the curve starts to flatten in 2000

Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/

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Cellular subscribers per region (June 2002)

Asia Pacific; 36,9 Europe; 36,4 Americas (incl. USA/Canada); 22 Africa; 3,1 Middle East; 1,6

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Medium Access Control (MAC)

Whilst SDM, FDM, TDM, CDM describe how the

medium is accessed at the physical layer, how

the selected multiplexing scheme is “regulated”

is called the Medium Access scheme

(equivalent to OSI Layer 2 the Data Link Layer)

In mobile this layer is divided between the

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Medium Access Control (MAC)

Why can we not simply use proven data MAC’s

such ac CSMA/CD used on ethernet?

On a fixed wire, the propagation etc, is a known factor, the sender is responsible for detecting

collisions, etc. If collision occurs everyone using the medium will be aware

In wireless networks attenuation, etc means signal decreases as it propagates out from the transmitter, therefore a collision may occur but will not be

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The role of the Access Scheme

Clearly conventional digital access

schemes cannot be transferred to mobile

Each access scheme has its own solution

Mobile networks use a combination of

the schemes to overcome the problems

Space Division Multiple Access

Frequency Division Multiple Access

Time Division Multiple Access

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Cellular Communication System

Cellular telephones are personally portable devices that may be used in motor vehicles or by pedestrians

communicating by radio-wave at 800-900-MHz band

they permit a significant degree of mobility within a defined serving region that may be hundreds of square kilometers in area.

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Cellular Coverage

The geographic area to be served by a cellular

radio system is broken up into smaller

geographic areas, or cells.

Uniform hexagons most frequently are

employed to represent these cells on maps and

diagrams;

In practice, though, radio-waves do not confine

themselves to hexagonal areas, so that the

actual cells have irregular shapes.

All communication with a mobile or portable

instrument within a given cell is made to the

base station that serves the cell.

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Cellular Migration Paths

First Major Migration Path

I Gen, 80’s, ETACS (C-450,NMT-450..), (FDMA), Analogue

II Gen 90’s - GSM,

II.5 Gen - GPRS, EDGE, (TDMA) Digital

III Gen, 00’s, W-CDMA , (CDMA), All Digital

Second Major Migration Path

I Gen, 80’s, AMPS, (FDMA), Analogue

II Gen, 90’s, IS-54 (TDMA), IS-95 (CDMA), Digital III Gen, 00’s, Cdma2000 (CDMA), All Digital

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Mobile Communication #1

Two aspects of mobility:

user mobility

: users communicate (wireless)

“anytime, anywhere, with anyone”

device portability

: devices can be connected

anytime, anywhere to the network

Example Wireless vs Mobile

Stationary PC

Laptop in a hotel

Wireless LAN in

historic building

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Mobile Communication #3

The demand for mobile communication creates

the need for integration of wireless networks

into existing fixed networks:

local area networks: standardization of IEEE 802.11,ETSI (HIPERLAN)

Internet: Mobile IP extension of the internet protocol IP

wide area networks: e.g., internetworking of GSM and ISDN

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Mobile Communication #4

Started with Mobile phones

Which were voice only Limited battery life

Limited roaming capability Limited quality

Unsecured

Advent of Digital phones

Allowed for better use of this phone technology Allowed the user to roam and receive calls

anywhere

Call were encrypted

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Mobile Communication #5

Roaming capability

Brought forward technology Dual/Tri Band phones

Satellite phones

Expensive about £1.20 a minute for a world phone call

This allowed the user to move from the office/home environment and still be connected.

Laptops

As computers got smaller it was now possible to carry it with you

As the computer is available the data was required for it

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Mobile Communication #6

Data Use

GSM phones allowed 9.6 Kbps data communications

Enough for email and simple file transfers

SMS messaging is the most popular data use

Voice calls are coming to the peak of the popularity

Additional avenues of revenue are required Increased data is a obvious choice

Charge the user for the packet received Charge for the services they are accessing i.e. Football results service

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Personal Communication Services (PCS)

We will soon have the ability for anyone to access digital information like the Internet.

Unlike the Internet, there will be value added service from day one

Video on Demand

Paying your credit card bill Ordering services

Value added services will be the primary goal of the PCS

This will be needed to pay for the infrastructure and licenses paid for

Each user will be able to view the information as they want it

Central control will not be put upon on the users

Differing levels of hardware capability will effect the end presentation

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Applications

Vehicles

transmission of news, road condition, weather, music via DAB personal communication using GSM

position via GPS

local ad-hoc network with vehicles close-by to prevent accidents, guidance system, redundancy

vehicle data (e.g., from busses, high-speed trains) can be transmitted in advance for maintenance

Emergencies

early transmission of patient data to the hospital, current status, first diagnosis

replacement of a fixed infrastructure in case of earthquakes, hurricanes, fire etc.

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Mobile & Wireless Services: Best Connected

GSM 53 kbit/s Bluetooth 500 kbit/s

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Evolution path of cellular communication

1G

2G

2.5G

3G

4G

Analogue Digital Multimedia

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Tutorial - For Each Generation 1-4G define:

Strengths Weaknesses Technical Specification Reasons to Upgrade ?G

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Solution: 1G Technology #1

Strengths

Fairly High Range – Up to 50 miles from BS Uses FDMA to increase potential users

Cell based network allows for the same frequency to be reused within different cells

Weaknesses

High Power Usage – Required large battery

Finite amount of possible phone numbers provided by the service

No counteraction for noise, or scanning due to being an analogue signal

Interference with radio

Limited capacity due to available spectrum

Calls disconnected due to handover – no priority Voice only traffic

Roaming was impossible due to different standards Expansion difficult – frequency planning

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Solution: 1G Technology #2

Technical Specifications Range of 50 km

AMPS (advanced mobile phone system) base Uses a hexagonal cell based network

AMPS Operates on a signal range of 800 MHz Analogue AMPS, TACS, NMT, FDMA

TACS uses 900 MHz, 25 kHz channels, 1000 channels

Reasons to Upgrade

High power usage

The amount of phones trying to be used exceeded the possible usage

Analogue Technology prone to scanning or noise (security) Increased demand

Smaller devices Tracking of device

Interference limited also improved error checking Ability to expand the network

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Solution: 2G Technology #1

Strengths

Voice data can be compressed allowing greater throughput Less power intensive – longer battery life, small batteries Digital error checking removes noise

Introduction of SMS and email availability on mobile handsets (digital data services)

Harder to intercept digital signals and reduced scanning

Less signal power needed on handset so cells can be made smaller

Clearer voice data

GSM allows signal roaming

Standards based allows roaming Provides security

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Solution: 2G Technology #2

Weaknesses

Digital signals can produce dropouts rather than a static noise

Smaller cells cause some phones to struggle to receive a reasonable signal strength

Loss of tone on voice

Limited data on control channel Designed for voice

Still not one standard throughout the globe

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Solution: 2G Technology #3

Technical Specifications

GSM (European standard)

Operates in 4 different signal ranges (900 MHz or 1800 MHz for European and 850 MHZ or 1900 MHZ on the American Continent.

25 MHz bandwidth is divided into 124 carrier frequency channels, each spaced 200 kHz apart. Uses TDMA (Time Division Multiplexing) to give 8 full rate or 16 half rate speech channels per radio frequency channel.

Transmission power of 2 watt in 850/900 and 1 watt in 1800/ 1900.

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Solution: 2G Technology #4

Uses a GMSK (Gaussian minimum-shift keying) a modulation which is a continuous phase frequency shift keying which reduces interference from cross channel

Introduced the SIM (Subscriber Identity module) to contain the users subscription information and

phone book.

Reasons to Upgrade

Support more users, higher data rates are required Use of more data centric applications

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Solution: 2.5G Technology #1

Strengths

Frees up control channel

Higher data rate then 2G and 1G due to dedicated channels GPRS

Added the application of WAP

Enabled to work within the GSM technology framework with little in the way of change

Data is sent in packets thus lowering the resource requirements Capable of switching between voice and data communications and also providing simultaneous data and voice transfer

Packet and voice roaming possible

EDGE

Improved air interface technology QOS supported

Builds on GPRS technology 3 times faster than GPRS

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Solution: 2.5G Technology #2

Weaknesses

To use GPRS you need a GSM device Still not a global standard

Due to backward compatibility system not designed optimally

Because channels dedicated to packets there are less voice channel available

No 2.5G evolution in USA

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Solution: 2.5G Technology #3

Technical Specifications

FDM, FDMA and TDMA

Users can access more than 1 channel at a time hence the higher data rates. Data channels are shared.

GPRS

QPSK modulation

171 kbps theoretical maximum data rate, actual 30 – 40 Kbps

EDGE

384 kbps theoretical, 80 – 100 actual. Increases down to change in coding schemes

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Solution: 2.5G Technology #4

Reasons to Upgrade

Still not fully compatible globally

Voice and data still treated separately – require a standard so multimedia can be transmitted and received

Higher data rates and increased capacity

Higher security measures (CDMA is more difficult to intercept therefore more secure)

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Solution: 3G Technology #1

W-CDMA replaced TDMA to increase the amount of users and allow higher speeds

Strengths

3 different data rates based on distance. 2Mbps for fixed in building services (Pico cell), 384 kbps in urban environments (micro cell) and 144 in wide area mobile environments (macro cell) in FDD mode with a modulation of QPSK

UMTS Incorporates the developments made for the GPRS and EDGE networks

Without the chipping code the data is essentially useless so a moderate level of security (scrambling codes can be used)

Ability to extend network easily by adding cells or sectoring existing cells

Capacity not limited by bandwidth but other user interference Higher data rate then previously and also is flexible and variable depends on cell size, user mobility and requirements.

Dynamic allocation of bandwidth, i.e. direction of flow (TDD) Power control can save battery

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Solution: 3G Technology #2

Weaknesses

Still not one single global standard i.e. frequencies, duplex, multiple access technique, nodes in infrastructure – due to backward compatibility issues

Expensive licences – pass cost to user. Not fair competition i.e. not many providers (operators) difficult for new operators

Lack of coverage – too new hence migration to standard systems

Always on = drain of battery

Power control – requires signalling therefore a drain on resources

Technical Specifications

Uses 3 main technical implications - UMTS (Europe), CDMA2000(America) and TD-SCDMA (China)

UMTS uses ATM (Asynchronous Transfer Method) which allows circuit switched transfer of data using packets

UMTS using ATM also allows a high speed of data transfer up to 10Gbps and provides a QOS for the duration of packet

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Solution: 3G Technology #3

Technical Spec continued….

UMTS uses Wideband code division multiple access (W-CDMA) which uses 10x the current processing power of 2G to encode the signal and is done with QPSK

W-CDMA supports two modes of operation TDD (time division duplex) and FDD (frequency division duplex)

W-CDMA allows multiple users to communicate at the same time over the same frequency. Utilising “Chipping Codes” which is supplied by the base station to the device. The

chipping code is used to identify the signals from the device and it can also be used to adjust the frequency of data

transferred during the transfer.

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Solution: 3G Technology #4

Reasons to upgrade

1 standard required

1 device should connect to fixed network best/fast/lowest error rate

Reconfigure itself dynamically Software radio

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Solution: Reasons for Future G???? #1

Higher data rates, more secure and more reliable Single Standard

OFDM (Orthogonal Frequency division modulation) QAM (Quadrature amplitude modulation)

MIMO (Multiple input, multiple output) antenna arrays Killer app – What will be the new application that is a must for phone technology

Single device that can reconfigure itself dependant on access method

I.e. pda phone/laptop, personal organiser in one! Mp3 player

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Solution: Reasons for Future G???? #2

Beheshti, B.

“

Study of the technology migration path

of the cellular wireless industry from 3G

to 3.5G and beyond”

;

Long Island Systems, Applications and

Technology, 2005. IEEE Conference

6 May, 2005 Page(s):15 - 28

o 3 . 5 G a n d b e y o n d B e h e s h t i , B . ; L o n g I s l a n d S y s t e m s , A p p l

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Solution: Development of 4G - Future

Voice Packet Switched M3 Circuit Switched Fixed Network: ATM, IPv4/6, Diff Serv, MPLS PSTN, ISDN xDSL Wireless Personal Area Net (WPAN) Mobile Access Network (UTRAN) Hierarchical Cell Structure M3 Satellite Access Network

Bluetooth, WI-FI, WLAN, Cellular, Satellite Ad-Hoc

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Overlay Networks - the global goal

regional metropolitan area campus-based in-house vertical handover horizontal handover integration of heterogeneous fixed and

mobile networks with varying transmission characteristics

Communications COMMS (CE )

Communications

COMMS (CE700038-2)

Multiplexing, (FDM, TDM, CDM)

& mobile communications

Overview & Objectives

Introduction

Multiplexing Schemes

History/future of Mobile communication

systems

Mobile Multiple Access Schemes

Introduction (1)

Multiplexing: name given to techniques which

allow more than one message to be transferred

via the same communication channel.

Channel: could be a transmission line

Introduction (2)

Channel will offer a specified bandwidth, which

is available for a time, t, where t->

∞

.

With reference to the channel there are 3

‘degrees of freedom’

Channel

B

B

Bandwidth

freq

Introduction (3)

Multiplexing are techniques which

allow k users to occupy a channel

for the duration in time, that the

channel is available

freq

time

code

Multiplexing

It costs significant amounts to change a

telephone system, not least the cost of the

“construction”

Hence the more calls you can pump down a

cable the more profitable the cable becomes

Telco’s

(Telephone companies) have

developed elaborate multiplexing schemes

The schemes can be divided into three

categories

Sharing a medium

Time division multiplexing brought digital

technology to mobile communications

Recall, “multiplexing describes how several

users can share the same medium with

minimum or no interference” [Schiller 2003]

In mobile communications multiplexing can be

applied in 4 dimensions

Space Division Multiplexing (SDM)

Frequency Division Multiplexing (FDM)

Time Division Multiplexing (TDM)

Combining FDM/TDM

Combining FDM/TDM

Requires coordination between the different

senders

Two senders will interfere if they select the

same frequency

To avoid this the senders hop between

frequencies:

Code Division Multiplexing (CDM)

All channels use the same frequency, however,

each channel is given its own unique code

Each code must be sufficiently

orthogonal

to

allow appropriate guard spaces

Large range of codes provides significant

expansion, security, etc

Code Division Multiplexing (CDM)

Highly complex scheme

Receiver has to know the code & be able to

separate out other traffic on different codes

which appear as background noise