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

2 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 Fixed Networks PSTN, ISDN BISDN,... B A MSC

3 A B RNC 1 BS 1 BS 2 Fixed Networks BS 1 BS 2 RNC 2 Downlink Uplink Different Types of Handoff 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

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 N OKIA TM concept 3G terminals Multimedia applications –Voice –web browsing – , voice –video conferencing –file transfer –database access

9 Standardisation Bodies ITU Internet Engineering Task Force, –Request for Comments

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

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

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

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

17 Capacity and Interference for FDMA and TDMA The Capacity to Interference for FDMA and TDMA is defined by where E b is the energy per bit, I 0 is the interference power per Hertz, B c is the radio channel bandwidth in Hertz and R b is the bit rate. In FDMA and TDMA R b is equal or very similar to B c.

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

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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) Direct sequence Frequency hopping Time hopping Time Frequency

26 CDMA Evolution Pioneer Era Narrowband Era Wideband Era

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

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

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

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 time frequency FHDS

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

33 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 frequency time

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

35 Improvements Vs Drawbacks Cell Splitting Centralised DCA Distributed DCA Power Control MAI Cancellation Macrodiversity 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 ATM Protocol Reference Model Asynchronous Transfer Mode (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

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 interfaceGSM Phase 2+ 8 channels per carrierAdaptive multirate coder 200 – KHz carrier bandwidth14.4 Kbp data service Slow frequency hoppingGeneral packet radio service Enhanced data rates using optimised modulation (EDGE)

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

41 GSM Development Time Schedule cnt GSM submitted as a PCS technology candidate to the United States 1995PCS1900 standard adopted in the United States 1996Enhanced full rate (EFR) speech codec standard ready Kbps standard ready GSM1900 commercial operation starts 1997HSCSD standard ready GSM cordless system (home base station) standardisation started EDGE standardisation started 1998GPRS 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

HS and GSM EDGE parameters

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