Mobile Communication Systems Mobile Communication Systems 2 2 MSc Data Comm MSc Data Comm Rolando A Carrasco Professor in Mobile Communications BSc(Hons), PhD, CEng, FIEE [email protected]School of Electrical, Electronic and Computing Engineering University of Newcastle upon tyne
Mobile Communication Systems 2 MSc Data Comm. Rolando A Carrasco Professor in Mobile Communications BSc(Hons), PhD, CEng, FIEE [email protected] School of Electrical, Electronic and Computing Engineering University of Newcastle upon tyne. PSTN, ISDN BISDN,. Fixed Networks. A. B. - PowerPoint PPT Presentation
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Mobile Communication Systems 2Mobile Communication Systems 2 MSc Data Comm MSc Data Comm
Rolando A CarrascoProfessor in Mobile CommunicationsBSc(Hons), PhD, CEng, [email protected] of Electrical, Electronic and Computing EngineeringUniversity of Newcastle upon tyne
2
HandoffsHandoffs
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, ISDNBISDN,...
B
A
MSC
3
A
B
RNC1
BS1
BS2
FixedNetworks BS1
BS2
RNC2
Downlink
Uplink
Different Types of HandoffDifferent 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 HandoverHandoff 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 GenerationHandoff 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 GenerationHandoff 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 GenerationHandoff 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
Capacity and Interference in CDMACapacity and Interference in CDMA
13312.3
1
MI
C
S
4444
4
)633.2(6)2(321
RMRMMRRM
R
I
C
S
where M is the number of Traffic channels per cell, R is the radius of the cell and is a constantfactor related to the transmission.
• If power control is applied then the interference to adjacent cells is reduced
controlpower Perfect 1
1
)1( 4
4
MRM
R
I
C
S
25
CDMA ClassificationCDMA Classification
CDMA : direct sequence (DS) CDMA : frequency hopping (FH) CDMA : time hopping (TH)
Direct sequence
Frequency hopping
Time hopping
Time
Frequency
26
CDMA EvolutionCDMA Evolution
Pioneer Era
Narrowband Era
Wideband Era
1949 John Pierce : time hopping spread spectrum1949 Claude Shannon and Robert Pierce : basic ideas of CDMA1950 De Rosa-Rogoff : direct sequence spread spectrum1956 Price and Green : antimultipath “RAKE” patent1961 Magnuski : near-far problem1970s Several developments for military field and navigation systems
1978 Cooper and Nettleton : cellular application of spread spectrum1980s Investigation of narrowband CDMA techniques for cellular applications1986 Formulation of optimum multiuser detection by Verdu1993 IS-95 standard
1995 - Europe : FRAMES FMA2Japan : Core-AUSA : cdma2000Korea : TTA I, TTA II
2000s Commercialization of wideband CDMA systems
WCDMA
27
Basic principles of CDMABasic principles of CDMA
Multiple access capability Protection against multipath
interference
W id eb a nd N a rro w b a n d
D S
F a s tF re q u e n cyH o p p ing
S lo wF re q u e n cyH o p p ing
F H T H
P u re C D M A
D S /F HD S /T HF H /T HD S /F H /T H
T D M A /C D M A M C -C D M AM T -C D M A
H yb rid C D M A
C D M A
Privacy, interference rejection Anti-jamming capability Low probability of interception
28
Direct Sequence CDMADirect Sequence CDMA
Directly modulated, discrete time, discrete valued
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
Global System for Mobile, GSMGlobal 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 coder200 – KHz carrier bandwidth 14.4 Kbp data serviceSlow frequency hopping General packet radio service
Enhanced data rates using optimised modulation (EDGE)
40
GSM Development Time ScheduleGSM 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
41GSM Development Time Schedule GSM Development Time Schedule cnt..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 Interface3G 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 CDMAFeatures of Wideband CDMA
WCDMA Korea TTA II Korea TTA I CDMA2000Chip rate (1.024) / 4.096 /
Frame length 4.615 ms 4.615 msNumber of slots 8 64 (72 s )
16 (288 s )
Coding Convolutional 1/2, 1/4, 1/3, 1/1ARQ
Convolutional 1/2, 1/4, 1/3, 1/1Hybrid Type II ARQ
Frequency Hopping Optional OptionalDynamic Channel Allocation Optional OptionalNote: the modulation parameters are for the original EDGE and UWC-136 proposals (B-O-QAM and Q-O-QAM), In 1998, a new modulation scheme (8-PSK) replacing the original schemes has been adopted.