Mobile Communication Systems 2 MSc Data Comm

1. Mobile Communication Systems 2 MSc Data Comm Rolando A Carrasco Professor in Mobile Communications BSc(Hons), PhD, CEng, FIEE r.carrasco@ncl.ac.uk School of Electrical, Electronic and Computing Engineering University of Newcastle upon tyne

2. PSTN, ISDN BISDN,... Fixed Networks A B Handoffs • If a mobile moves into another cell whilst a transfer is in progress • the RNC transfers the packets to a channel belonging to the new BS • Requires identifying a new BS & data & control signals are allocated to channels at the new BS MSC

3. Hard Handoff Communication is suspended when MS moves from one BS to another Soft Handoff The same signal is sent from both BSs to MS, except for the power control commands Macro Diversity combining in the uplink Downlink BS1 Uplink RNC2 BS2 Fixed Networks Different Types of Handoff RNC1 BS1 BS2 A B

4. Handoff or Handover • Processing handoffs is an important task in any cellular radio system • Some handoff strategies • prioritise handoff requests over call initiation request when allocating unused channels in a cell site. • Handoffs must be • successful, infrequent and imperceptible to the users • System designers specify a signal level at which a handoff is initiated • a slightly stronger signal level is used as a threshold at which a handoff is made • difference in the levels, such that no unnecessary handoffs take place • A drop in the signal level must not be mistaken for a momentary fade. • BS monitors signal level for a certain period of time

5. Handoff in First Generation • In first generation analogue cellular systems, signal strength measurements are made by the base stations and supervised by the MSC. • Each base station constantly monitors the signal of all mobiles to determine their relative location. • The MSC decides if a handoff is necessary or not.

6. Handoff in Second Generation • In second generation systems that use digital technology, handoff decisions are mobile assisted • Mobile Assisted Handoff Operation (MAHO) • every mobile measures the received power from surrounding BSs • continually reports the results to the serving BS • A handoff is initiated when the power received from another BS begins to exceed the power received from the current base station by a certain level or for a certain period of time. • The MSC no longer has to monitor the complete process

7. Handoff in Third Generation • Roam the entire globe • Soft handover – connect to >1 BS at a time • Mobile Assisted Handoff Operation (MAHO) • Power control – very important

8. Multimedia applications Voice web browsing e-mail, voice video conferencing file transfer database access NOKIATM concept 3G terminals

9. Standardisation Bodies • ITU • Internet Engineering Task Force, • Request for Comments • http://www.faqs.org/rfcs/

10. Radio Access Techniques Frequency Division Multiple Access (FDMA) Time Division Multiple Access (TDMA) Code Division Multiple Access (CDMA)

11. Code Frequency Channel 1 Channel 2 Channel 3 ChannelN Time Frequency Division Multiple Access (FDMA)

12. Code Channel N Channel 3 Time Slots Channel 2 Channel 1 Frequency Time Time Division Multiple Access (TDMA)

16. TDMA • Several TDMA schemes have been studied for the third generation air interface • The frame length is 4.615 ms and it can consist of • 64 1/64 time slots of length 72 • 16 1/16 time slots of length 288 Downlink Uplink Switching point between uplink and downlink 288ms 72ms

17. Capacity and Interference for FDMA and TDMA • The Capacity to Interference for FDMA and TDMA is defined by where Eb is the energy per bit, I0 is the interference power per Hertz, Bc is the radio channel bandwidth in Hertz and Rb is the bit rate. • In FDMA and TDMA Rb is equal or very similar to Bc.

18. Capacity and Interference for FDMA and TDMA • at the base station is always greater than 1 • Radio capacity, m, can be expressed as • where M is the total number of channels and is given by

19. Power Control Code Channel 1 Channel 2 Channel 3 Frequency Channel N Time Code Division Multiple Access (CDMA) MAI Cancellation Macrodiversity

24. Capacity and Interference in CDMA • where M is the number of Traffic channels per cell, R is the radius of the cell and  is a constant • factor related to the transmission. • If power control is applied then the interference to adjacent cells is reduced

25. CDMA Classification • CDMA : direct sequence (DS) • CDMA : frequency hopping (FH) • CDMA : time hopping (TH) Frequency Direct sequence Frequency hopping Time hopping Time

26. CDMA Evolution • Pioneer Era • Narrowband Era • Wideband Era

27. Multiple access capability Protection against multipath interference Privacy, interference rejection Anti-jamming capability Low probability of interception Basic principles of CDMA

28. Data modulator Spreading modulation DS-SS Transmitter Data Carrier generator Code generator 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

29. DS-SS Transmitter & Receiver Binary Data Binary Data Wideband modulator Despreading Data demodulator X Code generator Carrier generator Code Synchronisation/tracking Code generator Carrier generator

30. Generation of BPSK modulated signal Data Signal Code Signal Data Signal x Code Signal BPSK-modulated signal time

31. Frequency Hopped CDMA • Carrier frequency changes periodically, after T secs • Hopping pattern determined by spread code • hop-set of frequencies frequency frequency time time FH DS

32. Down converter Data demodulator Baseband modulator Up converter Data Data Synchr. tracking Code generator Frequency synthesiser Frequency synthesiser Code generator FH-SS Transmitter & Receiver

33. frequency time Time Hopped CDMA • Data transmitted in rapid bursts • Time intervals determined by code • Time axis divided into frames of M slots • Uses the whole spectrum as in WCDMA, for short time periods

34. Data demodulator Data Data modulator Carrier generator Code generator Code generator Carrier generator TH-SS Transmitter & Receiver Buffer Data fast in slow in slow out fast out

35. Cell Splitting Centralised DCA Distributed DCA Power Control MAI Cancellation Macrodiversity Improvements Vs Drawbacks Increase number of handoffs High processing overhead (bottlenecks) Carrier frequency usage in adjacent cells No control of out cell interference Codes use in interfering cells Additional resources

36. Asynchronous TransferMode (ATM) • Different types of services at different traffic rates using the same unique Universal Network • Common Network Layer for all types of traffic • Intelligent Network that assures QoS • UMTS and Wireless ATM (Mobile) • connection based, • fixed size cells • Service dependent, QoS traffic contracts • IP over ATM ATM Protocol Reference Model

37. Access Transmission Speeds

38. 2G Digital Systems

39. Global System for Mobile, GSM • Allocation of a common European frequency band in 1978 • Two 25 MHz bands around 900 MHz for mobile • In 1990 it was decided that GSM frequency should be 1800MHz. • GSM radio interface GSM Phase 2+ • 8 channels per carrier Adaptive multirate coder • 200 – KHz carrier bandwidth 14.4 Kbp data service • Slow frequency hopping General packet radio service • Enhanced data rates using • optimised modulation (EDGE)

40. GSM Development Time Schedule • 1982 Groupe Special Mobile established within CEPT • 1984 Several proposals for GSM multiple access : wideband TDMA, narrowband TDMA, DS-CDMA, hybrid CDMA/FDMA, narrowband FDMA • 1986 Eight prototype systems tested in CNET laboratories in France • Permanent nucleus is set up • 1987 Basic transmission principles selected : 8-slot TDMA, 200-kHz carrier spacing, frequency hopping • 1987 MoU signed • 1988 GSM becomes an ETSI technical committee • 1990 GSM phase 1 specifications frozen (drafted 1987 – 1990) • GSM1800 standardisation begins • 1991 GSM1800 specifications are frozen • 1992 GSM900 commercial operation starts • 1992 GSM phase 2+ development starts

41. GSM Development Time Schedule cnt.. • 1995 GSM submitted as a PCS technology candidate to the United States • 1995 PCS1900 standard adopted in the United States • 1996 Enhanced full rate (EFR) speech codec standard ready • 1996 14.4-Kbps standard ready • GSM1900 commercial operation starts • 1997 HSCSD standard ready • GSM cordless system (home base station) standardisation started • EDGE standardisation started • 1998 GPRS standard ready • WCDMA selected as the third generation air interface 1 GSM1800 was originally termed DCS1800 (Digital Cellular System 1800).

42. 3G Air Interface • Wideband CDMA • CDMA has a bandwidth of 5 MHz or more • Data rates of 144 and 384 Kbps • Even 2-Mbps peak rate • Provision of multi-rate services • Packet data and complex spreading • A coherent uplink using a user dedicated pilot • Additional pilot channel in the downlink for beamforming • Seamless inter frequency handover • Fast power control in the downlink • Optional multi-user detection

43. Features of Wideband CDMA

44. 136 HS and GSM EDGE parameters