University of Cyprus

Dr Panayiotis Kolios

Department of Computer Science

University of Cyprus

Thematic Areas Digital transmission model

Wireless access techniques

Wireless network standards

2

Digital Transmission Diagram

3

Wireless Access Techniques Various methods envisioned to allow share of the radio

spectrum between different users Different techniques strive to achieve an increase in

utilization Either maximize spectrum efficiency

Improve fairness in radio access

Increase flexibility in radio resource utilization

Five basic Multiple-Access Strategies (MASs) introduced: FDMA – spectrum divided in frequency channels TDMA – access to the whole bandwidth made in turns CDMA – chip codes used but interference limits # of users SDMA – spectrum is reused by users at disperse locations CSMA – transmission occurs only when medium appears free

4

Comparison of MASs FDMA TDMA CDMA SDMA CSMA

Modulation -relies on bandwidth efficient modulation

-relies on bandwidth efficient modulation

-simple modulation

-transparent

-relies on bandwidth efficient modulation

Forward error correction

-increases power efficiency at the expense of bandwidth efficiency

-increases power efficiency at the expense of bandwidth efficiency

-can be implemented without affecting bandwidth efficiency

-transparent

-increases power efficiency at the expense of bandwidth efficiency and other user QoS degradation

5

Comparison of MASs FDMA TDMA CDMA SDMA CSMA

Source coding

-improves efficiency

-improves efficiency

-improves efficiency -improves other user QoS

-transparent

-improves efficiency -improves other user QoS

Diversity -requires multiple transmitters or receivers

-requires multiple transmitters or receivers

-includes frequency diversity when implemented with special (RAKE) receivers

-single antenna reduces space diversity -orthogonal coding improves diversity with multiple antenna elements

-transparent

6

Comparison of MASs FDMA TDMA CDMA SDMA CSMA

User terminal complexity

-simple -medium complexity

-more complex

-requires smart antennas

-simple

Cellular Handover

-hard -hard

-soft -hard

-transparent

System complexity

-large number of simple components

-reduced number of channel units

-large number of complex interacting components

-signal processing complexity associated with antennas

-relatively low complexity which is related to supported channels

Multiple-access interference

-limited by system planning

-limited by system planning

-dynamic power control

-limited by resolution of antennas

-dynamic utilization of channel

7

Comparison of MASs FDMA TDMA CDMA SDMA CSMA

Fading -flat-fading -no diversity -simple to track

-maybe frequency selective -may need equalizer

-frequency-selective diversity possible

-reduced multipath

-maybe frequency selective

Bandwidth efficiency

-hard limits -based on modulation and channel spacing

-hard limits -based on modulation and channel spacing

-soft -large number of complex interacting components

-depends on antenna resolution

-hard limits -based on modulation and channel spacing

Synchronization

-low resolution

-medium resolution

-high resolution

-requires terminal location estimates

-none

8

Comparison of MASs FDMA TDMA CDMA SDMA CSMA

Flexibility -fixed data rate

-data rate variable in discrete steps

-variety of data rates

-transparent

-variety of data rates -depends on congestions

Voice and data integration

-possible but may require system revisions

-straight forward using multiple slots

-multicode transmission which may decrease efficiency

-transparent

-straight forward using successive access to channel

Expandability

-bandwidth to fit application

-requires medium initial bandwidth

-requires large initial bandwidth

-flexible -can add extra antennas as needed

-very flexible

9

Wireless Network Standards

10

Comparison between strategies followed by different standards

Physical layer characteristics

Modulation characteristics

Access strategies

Reachability

Utilization

Wireless Network Standards

11

IEEE 802.11x family of standards

IS-95

(TDMA)

(CDMA)

(CDMA)

(OFMA)

(CSMA/CA, FDMA)

(TDMA) (WCDMA)

UMTS (WCDMA)

Telephone Network Standards DECT GSM IS-95 WCDMA LTE

Frequency band

1880-1900 MHz

935-960MHz 890-915MHz

869-894MHz 824-849MHz

1920-1980MHz 2110-2117MHz various for TDD

Variable (including spectrum refarming) 1800MHz, 2100MHz, etc

Channel Bandwidth

1.728MHz 200KHz 1.25MHz 5MHz 1.4MHz, 3MHz, 5MHz, 15MHz and 20 MHz

Modulation GMSK GMSK BPSK QPSK BPSK, QAM

Data rate 1.152Mbps 270Kbps

1200, 2400, 4800, 9600 bps

up to 2Mbps

Variable, up to 300 Mbps standardized

12

Telephone Network Standards DECT GSM IS-95 WCDMA LTE

Cell size <300m <35Km <35Km <35Km >100Km

Access strategy

FDMA/TDMA/TDD

FDMA/TMDA/FH

FDMA/CDMA

FDMA/CDMA/FDD(TDD)

SC-TDMA, OFDMA

Forward error correction

None (16-bit CRC)

Variable Variable Variable Variable

Frame size 10ms 4.61ms 20ms 10ms 10ms

Traffic channels/ RF channels

12 8 Up to 63 in theory

Depends upon data rate

Variable

13

Data Network Standards GPRS LTE IEEE

802.11b Bluetooth IEEE 802.11a

Frequency band

935MHz-960MHz

Variable (including spectrum refarming)

2.4GHz 2.4-2.4385GHz

5.2GHz

Channel Bandwidth

200KHz 1.4MHz, 3MHz, 5MHz, 15MHz and 20 MHz

50MHz 80MHz 20MHz

Modulation GMSK BPSK, QAM

BPSK/QPSK FH/DS

GMSK/FH BPSK/QAM OFDM

Data rate Up to 116Kbps

Variable, up to 300Mbps

Up to 11Mbps

<1Mbps Up to 54Mbps

14

Data Network Standards GPRS LTE IEEE

802.11b Bluetooth IEEE 802.11a

Cell size Up to 35Km >100Km 1-20m 1-10m 1-100m

Access strategy

FDMA/TDMA

SC-TDMA, OFDMA

CSMA/CA FH/TDD FDMA/CSMA

Forward error correction

variable variable specified Variable repetition

Specified

Frame size 4.61ms 10ms Up to 20ms 625μs x n n=1,…,5

24μs to 5ms

Network topology

cellular/ point-to-multipoint

cellular/ point-to-multipoint

point to multipoint

point-to-point connection and connectionless

point to multipoint

15