Department of Electronic Engineer Department of Electronic Engineer ELE 52PMC Personal Mobile Communication GSM Public Land Mobile GSM Public Land Mobile Network (PLMN) Network (PLMN) Michael Feramez [email protected]www.ee.latrobe.edu.au/~mf Lecture 4
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Department of Electronic EngineeringDepartment of Electronic EngineeringELE 52PMC
Personal Mobile Communication
GSM Public Land Mobile Network GSM Public Land Mobile Network (PLMN)(PLMN)
Transmission rate: (1/T) = 270 kbps Baseband: B = 270 x 0.3 = 81 kHz The GSM RF channel is 200 kHz which means the
bandwidth efficiency is 270 kbps / 200kHz = 1.35 b/s/Hz
27
GMSK Modulation
coscos
sinsin
GaussianFilter
GaussianFilter
dt dt
-sin t
cos t
cos [t + (t, n)]cos [(t, n)]
sin [(t, n)]
(t, n)
Phase pulse shaping
28
GSM Channels
Physical channels– Full rate
– Half rate
– One-eighth rate
Logical channels– Downlink common channels
– Uplink common channel
– Signalling channels
29
Physical Channels
Physical channel in a TDMA system is defined as a timeslot with a timeslot number TN in a sequence of TDMA frames.
GSM employs TDMA combined with FH and hence the physical channel is partitioned in both time and frequency.
FH is known to be very efficient in combating channel fading.
30
TCH (Traffic Channels)
TCH/F 22.8 kbps (Full Rate)– TCH/F9.6
– TCH/F4.8
– TECH/F2.4
TCH/H 11.4 kbps (Half Rate)– TCH/H4.8
– TCH/H2.4
TCH/8 (One-eighth Rate)
31
Downlink Common Channels
FCCH - Frequency Correction Channel SCH - Synchronisation Channel BCCH - Broadcast CCH PAGCH - Paging and Access Grant Channel CBCH - Call Broadcast Channel
32
0 1 2 3 4 5 6 7
1 TDMA Frame = 8 Timeslots
1 Timeslot = 156.25 Bit Duration
Tail Bits3
Encrypted Bits58
Training Sequence26
Encrypted Bits58
Tail Bits3
Guard Period8.25
Normal Burst (NB)
Tail Bits3
Fixed Bits142
Tail Bits3
Guard Period8.25
Frequency Correction Burst (FCB)
Tail Bits3
Encrypted Sync Bits39
Extended TrainingSequence 64
Encrypted Sync Bits39
Tail Bits3
Guard Period8.25
Synchronisation Burst (SB)
Tail Bits8
SynchronisationSequence 41
Encrypted Bits36
Tail Bits3
Guard Period68.25
Access Burst (AB)
33
Uplink Common Channel
RACH - Random Access Channel is used by MS to access a call.
RACH/F - Full rate, one timeslot every 8 BP. RACH/H - Half rate, using 23 timeslots in the 51 x 8
BP cycle. The frame is 8 BP (Burst Periods) of 4.615 ms duration.
34
Signalling Channels
CCCH - Common Control Channel ACCH - Associated CCH SACCH - Slow Associated CCH FACCH - Fast Associated CCH SDCCH - Stand-alone Dedicated CCH
35
Multiple-Access Scheme
A combination of FDMA and TDMA A total of 124 FDMA channels of 200 kHz bandwidth
each. The Uplink frequency band 935 - 960 MHz (25 MHz)
and Downlink 890 - 915 MHz (25 MHz). The duplex separation is 40 MHz. TDMA employs 8 timeslots forming a frame of 4.16
ms, 0.577 ms per timeslot.
36
TDMA/FDMA
F1 F’1F0
Cell Rx Cell Tx
F2 F’2
45 MHz
Amplitude
Frequency
37
GSM FDMA/TDMA
ch #1 ch #2 ch #3 ch #4 ch #5 ch #6 ch #8ch #7
ch #1 ch #2 ch #3 ch #4 ch #5 ch #6 ch #8ch #7
ch #1 ch #2 ch #3 ch #4 ch #5 ch #6 ch #8ch #7
Frequency 1
Frequency 2
Frequency 124
Fre
quen
cy D
omai
n
Time Domain
TS0 TS3 TS4 TS5 TS6 TS7TS1 TS2
38
Frequency Hopping
GSM employs a slow frequency hopping rate defined in bits per hop.
The regular rate is 217 hops/s, with 270 kbps transmission rate, the result is 1200 bits/hop.
It is worth mentioning that FH improves the propagation performance when considering the effect of frequency selective fading.
39
Radio Resource Management
Radio channels (resources) are allocated for call setup, handover, and release on a call basis.
Management involves three functions: location, handover, and roaming.
Three link protocols are used for RR functions:– Radio Link Protocol (LAPDm)
– Link Access protocol (LAPD)
– Message Transfer Protocol (MTP)
40
Mobile-Originating Call
Mobile StationMobile Station Base StationBase Station
Random Access
Immediate Assignment
Exchange of Call Setup Information
Traffic Channel Assignment
Data Flow
41
Mobile-Assisted Handoff (MAHO)
MAHO algorithm is carried out within the MS. MS scans for another RF carrier under direction from a
BS. BS requests MS to measure the signal strength of a
specific RF carrier. Upon request, MS forwards the result to BS. BS initiates handover on the basis of:
– Signal strength at MS from the candidate BTS– Signal strength at the candidate BTS from MS
42
Mobility Management
Location updates, handovers, and roaming Cell selection Authentication:
– PIN checked locally by SIM– GSM network RAND and SRES
Encryption User identity protection - Security management, SIM
(MS side) and AUC (network side).
43
Cell Selection
C1 = A - max(B, 0)C1 = A - max(B, 0)A = received level average - p1A = received level average - p1B = p2 - maximum RF power of the MSB = p2 - maximum RF power of the MSp1 = a value between -110 and -48 dBmp1 = a value between -110 and -48 dBmp2 = a value between 13 and 43 dBmp2 = a value between 13 and 43 dBmMS maximum power = 29 to 43 dBmMS maximum power = 29 to 43 dBm
MS chooses the best cell depending on:MS chooses the best cell depending on:1. The level of the signal received by MS,1. The level of the signal received by MS,2. The maximum transmission power of MS2. The maximum transmission power of MS3. Two parameters p1 and p2 specified by the cell3. Two parameters p1 and p2 specified by the cell
Both values of p1 and p2 are broadcast from the cell.Both values of p1 and p2 are broadcast from the cell.
44
Authentication
Authentication protects the network against unauthorised access.
Phase One - PIN is checked locally by the SIM. Phase Two - A 128-bit RAND is sent from the network
to MS.– RAND mixes with MS’ secret parameter Ki in A3 process
algorithm producing a 32-bit SRES.
– SRES (signed result) is sent from MS to network for verification.
45
Authentication Computation
Ki RAND
A3
SRES
Ki RAND
A3
SRES
RAND
Equal?
MS Network
46
User Identity Protection
SIM (MS side) and AUC (network side) are the repositories of the subscriber’s key Ki.
The key Ki never transmits over the air. Both sides perform A3 and A8 computations.
47
Communication Management
CM layer provides telecommunication services (speech, fax, and data) via RR and MM layers.
The management functions of CM layer are:– Call Control
To provide the subscriber with a wide range of services and facilities, both voice and nonvoice, that are compatible with those offered by existing networks (e.g. PSTN, ISDN)
To introduce a mobile RS that is compatible with ISDN To provide certain services and facilities exclusive to
mobile situations To give compatibility of access to the GSM network for
a mobile subscriber in a country that operates the GSM system
50
Objectives of GSM PLMN - cont.
To provide facilities for automatic roaming, locating, and updating of mobile subscribers
To provide services to a wide range of mobile stations, including vehicle mounted stations, portable stations, and handheld stations
To provide for the efficient use of the frequency spectrum
To allow for low-cost infrastructure, terminal, and service cost
51
GSM PLMN Services
A telecommunication service supported by the GSM PLMN is defined as a group of communication capabilities that the service provider offers to the subscribers
Associated control channelAssociated control channel Extra frameExtra frame
TimeslotTimeslot 0.577 ms0.577 ms
56
MSMS Mobile Station Mobile StationTETE Terminal Equipment Terminal EquipmentMTMT Mobile Terminal Mobile TerminalBSBS Base Station Base StationBTSBTS Base Transceiver Station Base Transceiver StationBSCBSC Base Station Controller Base Station ControllerMSCMSC Mobile Switching Centre Mobile Switching CentreHLRHLR Home Location Register Home Location RegisterVLRVLR Visitor Location Register Visitor Location RegisterNMCNMC Network Management Centre Network Management CentreOMCOMC Operation and maintenance Centre Operation and maintenance CentreADCADC Administration Centre Administration CentreAUCAUC Authentication Centre Authentication CentreEIREIR Equipment Identifier Register Equipment Identifier Register
57
MAHO Mobile Assisted HandoffMAHO Mobile Assisted HandoffGMSCGMSC Gateway MSC Gateway MSCRPERPE Regular Pulse Excitation Regular Pulse ExcitationLPCLPC Linear Prediction Coding Linear Prediction CodingBPBP Burst Period Burst PeriodRSRS Radio Service Radio Service
58
References
[1] Garg, Vijay K and Wilkes Joseph E, “Wireless and Personal Communication Systems”. Prentice Hall PTR
[2] Parsons J D and Gardiner J G, Mobile Communication Systems, Blackie USA Halsted Press
[3] Lee, William C. Y., Mobile Cellular Telecommunications Systems, McGraw-Hill, Inc.
[4] Gibson, D. Jerry, The Communications Handbook, 1997 CRC Press, Inc.
[5] GSM World from GSM Association: www.gsmworld.com