1. Z. Ghassemlooy Mobile Communication Systems Professor Z Ghassemlooy Scholl of Computing, Engineering and Information Sciences University of Northumbria U.K. http://soe.ac.uk/ocr Professor Z Ghassemlooy Scholl of Computing, Engineering and Information Sciences University of Northumbria U.K. http://soe.ac.uk/ocr Part 7- Multiplexing

2. Z. Ghassemlooy Contents  Multiple Access  Multiplexing –SDM –FDM –TDM –CDM  Wideband Schemes  Duplex Method

3. Z. Ghassemlooy Multiple Access  In today’s data communications systems there is a need for several users to share a common channel resource at the same time. –The resource could be: high speed optical fibre links between continents frequency spectrum in a cellular telephone system twisted pair ‘ethernet’ cable in the office

4. Z. Ghassemlooy Multiple Access  For multiple users to be able to share a common resource in a managed and effective way, it requires: –Some form of access protocol Defines how or when the sharing is to take place and the means for identifying individual messages. Process is known as multiplexing in wired networks and multiple access in wireless digital communications.

5. Z. Ghassemlooy Multiplexing/Multiple Access There four possible ways to divide the frequency spectrum among many channels:  Space-division multiplexing (SDM)  Frequency-division multiplexing (FDM) / Frequency Division Multiple Access (FDMA)  Time-division multiplexing (TDM) / Time Division Multiple Access (TDMA)  Code-division multiplexing (CDM) / Code Division Multiple Access (CDMA)

6. Z. Ghassemlooy SDM s2s2 s3s3 s1s1 f t c k2k2 k3k3 k4k4 k5k5 k6k6 k1k1 f t c f t c channels k i

7. Z. Ghassemlooy  Dividing the entire frequency spectrum into smaller bands  A frequency band is allocated per channel for the entire transmission time  FDM, used in 1st generation systems, wastes spectrum  Advantages: –lower channel bit rate (than TDM) means less susceptible to multi path ISI –Requires coordination –works also for analog signals k2k2 k3k3 k4k4 k5k5 k6k6 k1k1 f t code Frequency Multiplex I

8. Z. Ghassemlooy Frequency Multiplex II  Disadvantages: –In-efficient use of bandwidth if the traffic is distributed unevenly – Requires guard band between channels –Cannot readily support variable user data rates, fixed channel width means fixed bit rate

9. Z. Ghassemlooy  Entire spectrum is allocated for a channel some of the time  For 2nd generation  Advantages: –Only one carrier in the medium at any given time –High throughput even for many users –Common TX component design, only one power amplifier  Disadvantages: –precise synchronization necessary –requires terminal to support a much higher data rate than the user information rate Time multiplex I f t code k2k2 k3k3 k4k4 k5k5 k6k6 k1k1 Time slots

10. Z. Ghassemlooy Example TDMA System GSM is a good example of a TDMA system GSM handsets transmit data at a rate of 270 kbit/s in a 200 kHz channel using GMSK modulation. each frequency channel is assigned 8 users, each having a basic data rate of around 13 kbit/s

11. Z. Ghassemlooy TDMA Frame  TDMA used for the 3G air interface  A frame length: 4.615 ms and it consist of 64 1/64 time slots of length 72 16 1/16 time slots of length 288 DownlinkUplink 72  s 288  s Switching point between uplink and downlink

12. Z. Ghassemlooy Time and Frequency Multiplex I  Combination of both methods –A certain frequency band for a given amount of time is allocated per channel –Example: GSM  Advantages: –Improved protection against tapping and frequency selective interference –Higher data rates compared to code multiplex  Disadvantages: –Requires precise coordination f t code k2k2 k3k3 k4k4 k5k5 k6k6 k1k1

13. Z. Ghassemlooy Code Multiplex I  Each channel has a unique code.  All channels use the same spectrum at the same time.  Advantages: –bandwidth efficient and good power control –no need for coordination and synchronization –good protection against interference and tapping  Disadvantages: –lower user data rates –more complex signal regeneration  Implemented using spread spectrum technology k2k2 k3k3 k4k4 k5k5 k6k6 k1k1 f t coding

14. Z. Ghassemlooy CDMA Classification  CDMA : direct sequence (DS)  CDMA : frequency hopping (FH) –Carrier frequency changes periodically, after T secs –Hopping pattern determined by spread code  CDMA : time hopping (TH) –Data transmitted in rapid bursts –Time intervals determined by code Direct sequence Frequency hopping Time hopping Time Frequency

15. Z. Ghassemlooy Direct Sequence CDMA  Directly modulated, discrete time, discrete valued code signal  Analogue or Digital  Code bits are ‘chips’ (  1)  Rate of Code >> Rate of Data  PSK, BPSK, D-BPSK, QPSK or MPSK Spreading modulation Data modulator Data DS-SS Transmitter Code generator Carrier generator

16. Z. Ghassemlooy DS-SS Transmitter & Receiver X Wideband modulator Binary Data Code generator Carrier generator Despreading Data demodulator Binary Data Code generator Carrier generator Code Synchronisation/trac king

17. Z. Ghassemlooy CDMA Evolution  Early Stages  Narrowband  Wideband

18. Z. Ghassemlooy Wideband-CDMA T c = chip time = 1 / 3.84  s Framing structure

19. Z. Ghassemlooy High Speed Wireless Access  Mobile communication system  Up to 30 Mbps  Using the SHF and other band (3-60 GHz)  Used for mobile video telephone conversations

20. Z. Ghassemlooy Ultra High Speed Wireless LAN  Wireless LAN  Up to 156 Mbps  Using the millimeter wave radio band (30-300 GHz)  Used for high quality TV conferences.

21. Z. Ghassemlooy 5GHz Band Mobile Access  Two types –ATM type Wireless Access –Ethernet type Wireless LAN  Using 5GHz band  Each system can transmit at up to 20-25Mbps  Used for multimedia information

22. Z. Ghassemlooy High Data Rate Wireless LAN Evolution ATM Gigabit Ethernet （ 1G bit/s) Gigabit Ethernet （ 1G bit/s) Fast Ethernet （ 100M bit/s) Fast Ethernet （ 100M bit/s) Ethernet （ 10M bit/s) Ethernet （ 10M bit/s) Ethernet (10M bit/s) Conventional 2.4GHz Ethernet Wireless LAN Conventional 2.4GHz Ethernet Wireless LAN 5GHz Ethernet Wireless LAN (IEEE802.11) 5GHz Ethernet Wireless LAN (IEEE802.11) Future 5GHz ATM Wireless LAN Future 5GHz ATM Wireless LAN 25M bit/s IMT 2000 384kbit/s 〜 2Mbit/s IMT 2000 384kbit/s 〜 2Mbit/s 36Mbit/s 2M bit/s ARIB, Japan, 1999

23. Z. Ghassemlooy Wireless Home-Link  Wireless Home-Link  Up to 100Mbps  Using the SHF and other band(3-60GHz)  Between PCs and Audio Visual equipments  Multimedia information.

24. Z. Ghassemlooy Home Link Concept Satellite Tuner CATV DVD VTR Telephone line 5GHz 5 Personal Computer Display Personal Computer Display Personal Computer

25. Z. Ghassemlooy Duplex Methods  Separating the send and receive signals (remember full duplex). Two approaches: –Frequency Division Duplex (FDD) Uses a pair of frequency bands – one for uplink and another for downlink –used in all second generation cellular systems –requires good frequency separation filters - diplexer –Time Division Duplex (TDD) Uses a single frequency band for both uplink and downlink – sharing the transmission time –propagation delay limits cell size –very efficient for asymmetric traffic, e.g. internet download –used in cordless systems (DECT) and wireless LANs

26. Z. Ghassemlooy What is Universal Mobile Telecommunication System ? European name for third generation (3G) radio system (1G = analog, 2G = digital voice and low speed data (GSM))  Key features with respect to 2G: Integration of fixed and mobile networks Expanded range of services (Packet, Internet, Multimedia) Bit rates: Rural outdoor: 144 kb/s, 500 km/h Suburban outdoor: 384 kb/s, 120 km/h Indoor, low range outdoor: 2Mb/s, 10 km/h Flexibility: Variable bit rates Circuit switched and packet oriented bearers Negotiation of bearer service attributes (bearer type, bit rate, delay BER, up/down symmetry, protection) Adaptability to quality, traffic, network load & radio conditions

27. Z. Ghassemlooy Summary  Multiple Access - sharing resources –Frequency Division Multiple Access - FDMA –Time Division Multiple Access - TDMA [Code Division Multiple Access – CDMA]  Duplex Methods –Frequency Division Duplex - FDD –Time Division Duplex - TDD

28. Z. Ghassemlooy Questions and Answers  Tell me what you think about this lecture –fary@ieee.orgfary@ieee.org