1982 : CEPT (Conférence Européenne des Administrations des Postes et Télécommunications) decides to establish a &quot;Groupe Spécial Mobile&quot; (the initial origin of the Term GSM) to develop a set of common standards for a future pan-European Cellular Mobile Network. 1984 : Establishment of three Working Parties to define and describe GSM features: the radio interface, transmission and signaling protocols, interfaces and network architecture. 1985, 1986 : Discussion and adoption of a list of recommendations to be generated by the Group Spécial Mobile. A so-called permanent nucleus is established to continuously coordinate the work, which is intensely supported by industry delegates. Much thought goes into developing a radio transmission prototype.
One important question was how far GSM should go in its specification work; that is, to what degree the system had to be specified so as to be identical in all countries, and how much could be left to the operators and suppliers to agree upon. Clearly, without identical air interfaces in all networks, the subscribers were not going to have free roaming between networks. This was considered to be the absolute minimum degree of standardization, and this solution was favored. It might have been seen to be advantageous to specify everything in the system, including the hardware and the mobile station and even other parts of the system. It was agreed however that there would be no attempt to specify the system in such detail. Basically, only the functional interfaces between the major buildings blocks would be specified. This approach had several advantages, perhaps the most important of which is that for each major building block, the principle of functional specifications offers each operator, and thus the customer, the opportunity to purchase whatever make of equipment he wants, thus setting the stage for maximum competition between manufacturers. For instance the fact that an operator has purchased an exchange from a certain supplier does not force him to go on buying equipment from the same supplier. Standardized electrical interfaces as well as protocols were provided for both the fixed network and subscriber equipment. These included standardized rate adaptations compatible with conventional ISDN (Integrated Services Digital Network) definitions.
GSM phase 2 We can currently use a data terminal attached to an MS to connect to any standard data service provided by the PSTN, ISDN or PDN networks as long as the network accepts a data rate of 9.6 kbps and the Inter-Working Function (IWF) is installed. This includes access to the Web, e-mail, fax etc.. Use of these facilities is generally limited due to the speed of the communication. Internet use is expensive and slow due to the limited data rate and the circuit switched nature of the GSM system. The BSS provides two modes: transparent data service, non transparent data service, using RLP protocol between the MS and the IWF. GSM phase 2+ A new service has been standardized in ETSI to reach 14.4 kbps user rate on one TS. This new data rate is the result of a new channel coding on the radio interface. This enhancement is a part of a global strategy aimed at offering higher data rates and called High Speed Circuit Switched Data (HSCSD). HSCSD allows 14.4 kbps in one TS and up to 56 kbps in the future, using multiple TSs. It is however, still a circuit switched system which will supply expensive connections unless the operators pricing schemes are imaginative. It will help those who use data over GSM today and encourage others to use the services but it does involve a capacity penalty for the network.
Today, GSM has the capability to handle messages via the Short Message Service SMS and a 14.4 kbps circuit switched data service for data/fax calls. This maximum speed of 14.4 kbps is relatively low compared to wireline modem speeds of 34.4 and even 56 kbps. To enhance the current data capabilities of GSM, operators and infrastructure providers have specified new extensions to GSM phase 2: High Speed Circuit Switched Data (HSCSD) by using several circuit channels. General Packet Radio Service (GPRS) to provide packet radio access to external Packet Data Networks (Internet or X.25 networks). Enhanced Data rate for Gsm Evolution (EDGE), using a new modulation scheme, to allow up to three times higher throughput (for HSCSD and GPRS). Universal Mobile Telecommunication System (UMTS) , a new wireless technology but utilizing new infrastructure deployment. These extensions enable: higher data throughput, better spectral efficiency, lower call setup times.
The typical internet data traffic is characterized by an ON/OFF model. The user spends a certain amount of time downloading web pages in quick succession followed by indefinite periods of inactivity. During this inactivity the end-user may read the information or think or do something else. The traffic is sporadic and can be characterized as data packets of average size 16 kbytes/s with average intervals of 7 seconds. If a circuit switch connection is used to access the Internet, the bandwidth dedicated for the entire duration of the session is under-utilized.
Development of the GSM Standard 1982: Groupe Spécial Mobile (GSM) created 1984: Description of GSM features 1985: List of recommendations settled 1987: Initial MoU (Memorandum of Understanding) aside the drafting of technical specifications was signed by network operators of 13 countries: 1988: Validation and trials, of the radio interface. 1991: First system trials are demonstrated at the Telecom 91 exhibition. 1992: Official commercial launch of GSM service in Europe. First Launch in Finland 1993: The GSM-MoU has 62 signatories in 39 countries worldwide. 1995: Specifications of GSM phase 2 are frozen. 1999: GSM MoU joins 3GPP (UMTS) GPRS Trials begins 2000: 480M GSM Network operators Worldwide First GPRS Networks roll out End 2002: 792M GSM Net work Operators Worldwide
GSM Specifications 12 SERIES OPERATION AND MAINTENANCE 01 SERIES GENERAL 02 SERIES SERVICE ASPECTS 03 SERIES NETWORK ASPECTS 04 SERIES MS-BSS INTERFACE AND PROTOCOLS 05 SERIES PHYSICAL LAYER ON THE RADIO PATH. 06 SERIES SPEECH CODING SPECIFICATIONS 07 SERIES TERMINAL ADAPTERS FOR MOBILE STATIONS 11 SERIES EQUIPMENT AND TYPE APPROVAL SPECIFICATIONS 10 SERIES SERVICE INTERWORKING 09 SERIES NETWORK INTERWORKING 08 SERIES BSS TO MSC INTERFACES
GPRS = G eneral P acket R adio S ervice HSCSD = H igh S peed C ircuit S witched D ata EDGE = E nhanced D ata rate for G SM E volution UMTS = U niversal M obile T elecommunication S ystem 10 sec 1 min 10 min 1 hour 0 UMTS E/GPRS ISDN PSTN GSM web e-mail photo web photo e-mail web photo video clip report photo web photo e-mail video clip report video clip report video clip report video clip report
Wireless Data Technology Options throughput kbps 10 k 100 k 64 k 1 M 2 M 1 k 1998 1999 2000 2001 2002 Time frame UMTS GPRS HSCSD 9.6 14.4 packet GPRS = G eneral P acket R adio S ervice HSCSD = H igh S peed C ircuit S witched D ata EDGE = E nhanced D ata rate for G SM E volution UMTS = U niversal M obile T elecommunication S ystem EDGE circuit
Circuit-Switched or Packet-Switched Circuit mode Packet mode A -> F D -> H C -> G C -> G C -> G C -> G C -> G D -> H D -> H A -> F D -> H D -> H A -> F A -> F A -> F A B C D E F G H
GSM - Network Structure AuC MS MS BTS BTS BTS BSC BSC MSC MSC VLR VLR GMSC HLR PSTN EIR Um Abis Abis A A OMC Server Um B E E X.25 C F H X.25
GSM Network OMC AUC HLR MSC EIR VLR BSC BTS MS External PSTN & PDN N/W SS BSS Switching System Base Station System MS Mobile Station BTS Base transceiver System BSC Base Station Controller MSC Mobile Switching Center HLR Home Location Register VLR Visitor Location Register EIR Equipment Identity Register AUC Authentication Center OMC Operation And Maintenance Center
GSM Architecture HLR VLR EIR AUC MSC B S C B S C SMSC PSTN VMSC Mobile Station GSM Air interface OMCR TRAU Base Station System Network and switching subsystem A interface SS7 / speech SS7 X.25 BTS BTS BTS BTS BTS BTS Abis interface A interface OMCS
Fundamentals GSM utilizes two bands of 25 MHz. 890-915 MHz band is used for uplink while the 935-960 MHz is used for downlink. The frequency bands are divided into 200 KHz wide channels called ARFCNs (Absolute Radio Frequency Channel Numbers) i.e. there are 125 ARFCNs out of which only 124 are used. Each ARFCN supports 8 users with each user transmitting / receiving on a particular time slot (TS). 960 MHz 959.8MHz 200KHz 935 MHz 935.2 Mhz 915 MHz 200KHz 45 MHz Downlink (TDMA frame) = 8 TS Uplink (TDMA frame) Delay TS: Time slot 914.8 MHz 890.2 MHz 890 MHz DOWNLINK UPLINK Therefore 1 TDMA frame = 156.25 x 8 = 1250 bits and has a duration of 576.92 s x 8 = 4.615 ms The technology 1 2 …… …… . 123 124 1 2 …… …… . 123 124 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 Data burst = 156.25 bit periods = 576.9 s
Channels : differentiating between Physical and Logical channels Physical channels : The combination of an ARFCN and a time slot defines a physical channel. Logical channels : These are channels specified by GSM which are mapped on physical channels.
Channel concept Physical channel : One timeslot of a TDMA-frame on one carrier is referred to as a physical channel. There are 8 physical channels per carrier in GSM,channel 0-7(timeslot 0-7) Logical channel: A great variety of information must be transmitted between BTS and the MS,for e.g. user data and control signaling.Depending on the kind of information transmitted we refer to different logical channels.These logical channels are mapped on physical channel.
Logical Channels on Air interface LOGICAL CHANNELS COMMON CHANNELS DEDICATED CHANNELS BROADCAST CHANNELS COMMON CONTROL CHANNELS DEDICATED CONTROL CHANNELS TRAFFIC CHANNELS FCCH BCCH SCH SDCCH SACCH FACCH PCH AGCH RACH TCH/F TCH/EFR TCH/H
Frequency plan and importance of BCCH B3 B2 B9 B6 B4 B1 Sectored antennas MS ( monitoring the broadcast radio B1 in ‘idle mode’ ) F0 F50 F2 F3 F4 F5 F10 F11 F1
F,S,B exist in time slot 0 of each frame
B7 B8 B5 B10 B11 B12 BPL frequency plan : Broadcast frequencies : 15 Broadcast channels = 48-62 15 Hopping channels = 32-46 … .. … .. S F I … .. B B B B S F
The MS is monitoring the BCCH and has all the decoded information stored on the SIM ( including the LAC)
As soon as the mobile is on a TCH it sends the signal strength indication on the corresponding SACCH
The BSC monitors the signal strengths and on analysis sends a ‘handoff request’ on FACCH. The handoff process is completed on the FACCH.
After the completion of call, the MS starts monitoring the BCCH again. On finding the LAC (stored on SIM) and that decoded from the BCCH to be different , the MS requests a ‘Location Update’ through SDCCH.
Used by Mobile Station for requesting for a channel. When the mobile realizes it is paged it answers by requesting a signaling channel (SDCCH) on RACH. RACH is also used by the MS if it wants to originate a call.
Initially MS doesn’t know the path delay (timing advance), hence uses a short burst (with a large guard period = 68.25 bits).
MS sends normal burst only after getting the timing advance info on the SACCH.
EX OR data with cipher block, which is generated by applying A5 Algorithm to the Ciphering Key(Kc)
Multiplexing - Done at BTS
Modulation - Done at BTS and MS
GMSK(Gaussian filtered Minimum Shift Keying)
Phase change of +90 for 0 and -90 for 1
Speech Coding BP A/D SPEECH ENCODER CHANNEL CODING LP D/A SPEECH DECODER CHANNEL DECODING BAND PASS 300 Hz - 3.4 kHZ Every 125 s value is sampled from analog signal and quantised by 13 bit word Data rate = 13/125*10 -6 = 104 kbps Every 20ms 160 samples taken Data rate = 160 * 13/20ms = 104 kbps Linear Predictive Coding & Regular Pulse Excitation Analysis 1. Generates 160 filter coeff 2. These blocks sorted in 4 sequence 1,5,9,…37 / 2,6,10----38/ 3,7,11…39/8,12,16…40 3. Selects the sequence with most energy So data rate = 104/4 = 26 kbps Long term prediction analysis 1. Previous sequences stored in memory 2. Find out the correlation between the present seq. And previous sequences 3. Select the highest correlation sequence 4. Find a value representing the difference between the two sequences. Reduces data rate = 26 kbps/2 = 13 kbps ie 260 bits in 20ms 50 132 78 1A 1B 2 1A = Filter Coeff block ampl, LTP params 1B = RPE pointers & pulses 2 = RPE pulse & filter params 50 3 132 4 3 crc bits Four 0 bits for codec 378 coded bits Conv coding rate = 1/2 delay = 4 78 456 bits in 20 ms = 22.8 kbps 57 x 8 = 456 To modulator
The information format transmitted during one timeslot in the TDMA frame is called a burst.
Different Types of Bursts
Random Access Burst
Frequency Correction Burst
Normal Burst T 3 Coded Data 57 S 1 T. Seq. 26 S 1 Coded Data 57 T 3 GP 8.25 Tail Bit(T) :Used as Guard Time Coded Data :It is the Data part associated with the burst Stealing Flag :This indicates whether the burst is carrying Signaling data (FACCH) or user info (TCH). Training Seq. :This is a fixed bit sequence known both to the BTS & the MS.This takes care of the signal deterioration. 156.25 bits 0.577 ms
T 3 Training Sequence 41 Coded Data 36 T 3 GP 68.25 Random Access Burst T 3 Fixed Bit Sequence 142 T 3 GP 8.25 T 3 Coded Data 39 Training Sequence 64 Coded Data 39 T 3 GP 8.25 Synchronization Burst 156.25 bits 0.577 ms 156.25 bits 0.577 ms 156.25 bits 0.577 ms Freq. Correc. Burst
Selected cell should be a cell of the selected PLMN
Signal strength should be above the threshold.
Cell should not be barred
Register with the network by means of location updation procedures.
MS Location Update (registration) MS BTS BSC (G)MSC VLR HLR Action Channel Request (RACH) Channel Assignment (AGCH) Authentication Request (SDCCH) Authentication Response (SDCCH) Comparison of Authentication params Accept LUP and allocTMSI (SDCCH) Ack of LUP and TMSI (SDCCH) Entry of new area and identity into VLR and HLR Channel Release (SDCCH) Location Update Request (SDCCH) TMSI + old LAI
MS MS BTS BTS BTS BSC BSC MSC VLR GMSC HLR PSTN EIR AuC Mobile Originated Call Req for dedicated channel for signaling (RACH) Give SDCCH Allocates SDCCH using the AGCH Sends call set-up request including dialled digits on SDCCH Call set-up forwarded to BSC Call set-up forwarded to MSC Authentication request (SDCCH) Authentication response (SDCCH) Authentication response (SDCCH) Assigns TCH Req Activate TCH TCH assigned Assn complete Release SDCCH SDCCH released ACM Ring tone over FACCH Ring alert Called Sub answers Connect message Ring tone ceases over FACCH Speech path enabled
Mobile Terminated Call Authentication and Ciphering procedure done as seen in Location Updation MS MS BTS BTS BTS BSC BSC MSC VLR GMSC HLR PSTN EIR AuC Land to Mobile call (MSISDN) Query for VLR info Reply (MSRN) Route to MSC Query VLR for LAC and TMSI Paging the area (+TMSI) TMSI Paged on PCH Paging Ch. REQ over RACH Allocate SDCCH over AGCH Page RESP on SDCCH ( TMSI + LAI) Page RES Page RES Assign. REQ Assignment CMD (= TCH) on SDCCH * MS tunes * Assgn CMP * Phone rings Connect traffic Ch.to trunk frees SDCCH Assgn CMP Network Alerting
Power Control BTS commands MS at different distances to use different power levels so that the power arriving at the BTS’s Rx is approximately the same for each TS - Reduce interference - Longer battery life
Periodic Measurement Reports (SACCH) Cell 1 Cell 2 BSC BTS 1 BTS 2 Intra BSC handover Periodic Measurement Reports (SACCH) Periodic Measurement Reports HO required Activate TCH(facch) with HoRef# if 1. Check for HO passed 2. Channel avail in new BTS Acknowledges and alloctes TCH (facch) HO cmd with HoRef# Receives new BTS data(FACCH) MS tunes into new frequency and TS and sends HO message to new BTS (facch) HO performed Release TCH
Frequency Hopping permits the dynamic switching of radio links from one carrier frequency to another.
Base Band Hopping
At the BTS each the timeslot is shifted to another transceiver, which is transmitting at the hop frequency. User will be connected to different Transceivers depending on hop sequence.
At the BTS transceiver changes the frequencies used. The user will be connected to only one transceiver.
Decreases the probability of interference
Suppresses the effect of Rayleigh fading
Wireless Data 98 99 2000 2001 GSM DATA HSCSD GPRS EDGE UMTS SIM Toolkit WAP Data Application Time Circuit Switched technology Packet Switched technology Technology for Applications SMS Data: 160 -numeric characters User Data Rate : 9.6kbps One time slot over the air interface High Speed Circuit Switched Data User Data Rate:14.5kbps Use multiple timeslots (max=8), hence max rate = 115.2kbps. Needs a duplexor in MS for simultaneous Tx and Rx
Add-on to GSM network :
PCU; Packet Segmentation/re-assembly and scheduling
Radio channel access control and management
Transmission error detection and retransmission.
SGSN: GPRS mobility
GGSN : Interface to the PDN, Internet
Max user data rate : 21.4 kbps
Dynamic rate adaptation to suit the radio conditions at
that time ( 9.05 kbps, 13.4 kbps, 15.6 kbps 21.4 kbps)
W@P Gateway W@P Service W @ P F o n e Internet Mobile Network
Surf the Internet while on the move
W@P Gateway :
Adaptation of the information to the mobile
Compression of the data
Buffering of the information
Enhanced Data rate for GSM Evolution
EDGE is an enhancement of GPRS and CSD technologies.
Based on the current GSM technology - same TDMA frame structure, same bandwidth (200 kHz).
Uses 8-PSK modulation instead of GMSK.
Requires good propagation conditions.
Allows upto 48 kbps (EGPRS) and upto 28.8 kbps (ECSD) on every radio channel
EDGE helps GSM-Only operators to compete with UMTS.
Universal Mobile Telecommunication Standards
Innovative Service Architecture : VHE Concept - providing the us
the same look and feel of its personalized services independent of network and terminal.
Global Convergence : Fixed/Mobile, Telecom/Datacom, public/private
Mobile Multimedia driven market.
Wideband bearers - 2GHz band ( 5 MHz per carrier), -max. 2Mbps
Location Updates Location Updates can be classified into two: Periodic Location Updates: This occurs as per the timer set by the network operator. If the MS does not perform this update the MSC marks the MS as ‘Detached’ on the VLR. Location Update on a handover: This occurs if during a handover the MS is moved into a new Location Area Code (LAC).