GSM Global System for Mobiles
GS CHANNELS GSM C S
By: Mrs. Shweta Shah 1
Multiple access schemes With GSM The h radio d transmission in GSM networks k is based on digital technology. Digital transmission in GSM is implemented using two methods known as Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA).
Concept of TDMA and FDMA used in GSM along with SDMA using cellular structure
Frequency Division Multiple Access (FDMA) refers to the fact that each Base Transceiver Station is allocated different radio frequency channels. Mobile p phones in adjacent j cells ((or in the same cell) can operate at the same time, but are separated according to frequency.
Time Division Multiple Access (TDMA) divides one radio frequency channel into consecutive periods of time, each one called a "TDMA frame". Each TDMA frame contains eight g shorter p periods of time known as "timeslots".
Time is divided into discrete periods called “timeslots”. The timeslots are arranged in sequence and are conventionally numbered 0 to 7. 7 Each repetition of this sequence is called a “TDMA frame”. The information carried in one timeslot is called a “burst”. “b t” Each MS telephone call occupies one timeslot ((0–7)) within the frame until the call is terminated, or a handover occurs. For such a system to work correctly, synchronization and timing has to be maintain correctly.
GSM 900 calculations: GSM-900 l l ti -Forward link (BS to mobile)-- 960 MHz – 935 MHz = 25 MHz -Reverse link (Mobile to BS)- 915 MHz – 890 MHz = 25 MHz
Total available bandwidth 25MHz -Total number of channels = = = 125 200 kHz Per channel bandwidth - ARFCN = 0 to 124 -Per channel 8 time slots assigned and -channel data rate is 270.833 kbps -effective channel transmission rate =270.833/8 =270 833/8 = 33 33.854 854 kbps -In GSM with overhead user data is actually sent at 24.7 kbps instead of 33.854 kbps -Signaling Signaling bit duration = 1/270.833 1/270 833 =3.692 3 692 µs s 8
Transmission through air interface The principle of air interface can be understand by an example of an army which has to moved from one place to another and a group of vehicles is set aside to do the job. j Each vehicle has eight seats and therefore only eight people can be carried in each vehicle. One officer and seven soldiers are allocated to each vehicle. There are different types of people in army, soldiers and officers. This could be referred to as g differences as their functions are “logical” different.
To move them form one place to another, a “physical” connection is employed, p y , that is,, the vehicle and seats. The physical channel is the medium over which the information is carried, in the case of a terrestrial te est ial interface inte face this would o ld be a cable. The logical channels consist of the information carried over the physical channel.
Physical and Logical Channels The TDMA frame can be compared p to the vehicle in our example. Each TDMA frame contains eight shorter periods of time k known as "timeslots". " i l " These Th timeslots i l can be b compared d to the seats in the vehicle. The TDMA timeslots Th ti l t are called ll d "physical " h i l channels", h l " as they are used to physically move information from one place to another. The radio carrier signal between the mobile station and the BTS is divided into a continuous stream of timeslots, which in turn are transmitted in a continuous stream of TDMA frames - like a long line of vehicles with eight seats in each.
The contents of the physical channels - that is, the soldiers and officers traveling in the eight seats of the vehicle, hi l according di t their to th i roles, l are called ll d "logical "l i l channels". For such Fo s ch a system s stem to work o k correctly, co ectl the timing of the transmissions to and from the mobiles is critical. The MS or Base Station must transmit the information related to one call at exactly y the right g moment,, or the timeslot will be missed. The information carried in one timeslot is called a “burst”. In the h example l off the h army, the h soldiers ld are one type off logical channel and the officers are other types of logical channels, and they exercise some kind of control depending on their responsibilities. In GSM, the logical channels can be divided into two types: dedicated channels common channels.
Hierarchy of Logical channels
Logical channels There are 12 different types of logical channels, which are mapped into physical channels in the radio path. Logical channels comprise dedicated channels.
of
common
channels
and
Common channels are those that are used for broadcasting different information to MS and for setting up signalling channels between the MSC/VLR and the mobile station. t ti Over the radio path, different types of signalling channels are used between the MS and the BTS, BSC and the MSC/VLR. All these signalling channels are called dedicated control channels. Traffic channels are also dedicated channels,, as each channel is dedicated to only one user to carry speech or data.
LOGICAL CHANNELS
TRAFFIC
FULL RATE Bm 22.8 Kb/S
SIGNALLING
HALF RATE Lm 11.4 Kb/S BROADCAST
FCCH
SCH
COMMON CONTROL
DEDICATED CONTROL
BCCH PCH
FCCH -- FREQUENCY CORRECTION CHANNEL SCH -- SYNCHRONISATION CHANNEL BCCH -- BROADCAST CONTROL CHANNEL PCH -- PAGING CHANNEL RACH -- RANDOM ACCESS CHANNEL AGCH -- ACCESS GRANTED CHANNEL SDCCH -- STAND ALONE DEDICATED CONTROL CHANNEL SACCH -- SLOW ASSOCIATED CONTROL CHANNEL FACCH -- FAST ASSOCIATED CONTROL CHANNEL
RACH
AGCH
SDCCH
SACCH
FACCH
DOWN LINK ONLY UPLINK ONLY
BOTH UP & DOWNLINKS
TDMA frames with common and dedicated channels
Different logical channels are placed in different timeslots depending on whether they are common channels used by several MS (blue above) or if they are dedicated to a certain MS in connection with a call (yellow above). The common and dedicated channels are grouped in different multiframes. The common channels are grouped in a 51 TDMA frame order, and The dedicated channels are a e grouped g o ped in a 26 TDMA frame f ame order. By multiplying 51 with 26, we can conclude that any TDMA y in both multiframes frame number will occur simultaneously every 1326 TDMA frames (which corresponds to 6.12 seconds). Such cycles are called superframes.
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Relationship of All Time Segments
Control Channel Multiframe
Control Channel Multiframe composed of 51 TDMA frames duration = 235.4 ms
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Traffic Channel Multiframe composed of 26 TDMA frames d duration ti = 120 ms
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Traffic Channel and Control Channel Multiframes
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Superframe A Superframe is composed of multiple Multiframes. Again, there is a superframe for Control Channels and one for Traffic Channels. Control Channel Superframe composed of 26 Control Channel (CCH) multiframes (each CCH multiframe has 51 TDMA frames) d duration i =6 6.12 12 seconds d Traffic Channel Superframe composed of 51 Traffic Channel (TCH) multiframes (each TCH) multiframe has 26 TDMA frames) duration = 6.12 seconds Each superframe, whether it is a CCH or TCH frame, consists of 1326 TDMA frames (51 * 26) *Note: The CCH and TCH frame sequences q will synchronize y every superframe. 25
Hyperframe A hyperframe is composed of 2048 superframes. superframes duration = 3h 28m 53s 76ms (12,533.76 seconds) consists of 2,715,548 TDMA frames
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GSM burst The GSM burst, burst or transmission can fulfil a variety of functions. Some GSM bursts are used for carrying data while others are used for control information. information As a result of this a number of different types of GSM burst are defined.
Normal burst uplink and downlink Synchronisation burst downlink Frequency correction burst downlink Random Access (Shortened Burst) uplink 27
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GSM normal burst This GSM burst is used for the standard communications between the base station and the mobile, and typically transfers the digitised voice data. The structure of the normal GSM burst is exactly defined and follows a common format. format It contains data that provides a number of different functions:
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3 tail bits: These tail bits at the start of the GSM burst give time for the transmitter to ramp up its power 57 data bits: used to carry information (contains the digitised voice data) although on occasions it may be replaced with signalling information in the form of the Fast Associated Control CHannel (FACCH). The type of data is indicated by the flag that follows the data field
1 bit flag: This bit within the GSM burst indicates the type of data in the previous field. 26 bits training sequence: used as a timing reference and for equalisation. There is a total of eight different bit sequences that may be used, each 26 bits long. long The same sequence is used in each GSM slot, but nearby base stations using the same radio frequency channels will use different ones, and this enables the mobile to differentiate between the various cells using th same frequency. the f 30
1 bit flag Again this flag indicates the type of data in the data field. 57 data bits Again, this block of data within the GSM burst is used for carrying data. data 3 tail bits These final bits within the GSM burst are used to enable the transmitter power to ramp down. They are often called final tail bits, bits or just tail bits. bits 8.25 bits guard time At the end of the GSM burst there is a guard period. This is introduced to prevent transmitted bursts from different mobiles overlapping. overlapping As a result of their differing distances from the base station.
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GSM synchronisation burst The purpose of this form of GSM burst is to provide synchronisation for the mobiles on the network. 3 tail bits: Again, these tail bits at the start of the GSM burst give time for the transmitter to ramp g p up p its p power 39 bits of information: 64 bits of a Long Training Sequence: 39 bits Information: 3 tail bits Again these are to enable the transmitter power to ramp down. 8.25 bits guard time: to act as a guard interval.
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GSM frequency correction burst With the information in the burst all set to zeros, zeros the burst essentially consists of a constant frequency carrier with no phase alteration. 3 tail bits: Again, Again these tail bits at the start of the GSM burst give time for the transmitter to ramp up its power. 142 bits all set to zero: 3 tail t il bits bit Again A i these th are to t enable bl the th transmitter t itt power to ramp down. 8.25 bits guard time: to act as a guard interval.
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GSM random access burst This form of GSM burst used when accessing the network and it is shortened in terms of the data carried, having a much longer guard period. This GSM burst structure is used to ensure that it fits in the time slot regardless of any severe timing problems that may exist. Once the mobile has accessed the network and timing has been aligned, then there is no requirement for the long guard period. 34
7 tail bits: The increased number of tail bits is included to provide additional margin when accessing the network. 41 training bits: 36 data bits: 3 tail bits Again these are to enable the transmitter power to t ramp down. d 69.25 bits guard time: The additional guard time, filling the remaining time of the GSM burst provides for la ge timing differences. large diffe en es
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The normal burst contains a training sequence and an SB (Stealing Bit). The training g sequence q is known,, which makes it possible to correct bit errors by applying Viterbi Equalisation. There are eight different sequence patterns, patterns and the one to be used is determined at the time of call set-up. The stealing bits indicate if the burst contains FACCH (handover) information. 36
Traffic Channels (TCH) The traffic channel carries speech or data information. information The different types of traffic channel are listed below: Full rate TCH/FS: Speech (13 kbit/s net, 22.8 kbit/s gross) TCH/EFR: Speech (12.2 kbit/s net, 22.8 kbit/s gross) TCH/F9.6: 9.6 kbit/s – data TCH/F4.8: 4.8 kbit/s – data TCH/F2.4 2.4 kbit/s – data
Half rate TCH/HS: speech (6.5 kbit/s net, 11.4 kbit/s gross) TCH/H4.8 4.8 kbit/s – data TCH/H2.4 2.4 kbit/s – data 37
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TCH Full Rate/Half Rate User data U d t is i contained t i d within ithi one TS per frame H lf R Half Rate t :S Sampled l d att a rate t half h lf than Full Rate,Mapped onto the same time slot but it sent into alternate frames TCH/FS TCH/F 9.6, TCH/FS, 9 6 TCH/F 4.8, 4 8 TCH/F 2.4 S Speech h channel h l Digitized Di iti d 13 KBPS After channel coding 22.8 KBPS
Traffic Channel (TCH) Traffic channels are logical channels that transfer user speech or data, which can be either in the form of half rate traffic (5.6 Kbits/s) or full rate traffic (13 Kbits/s) Another form of traffic channel is the Kbits/s). Enhanced Full Rate (EFR) traffic channel. The speech coding in EFR is still done at 13 Kbits/s, but the coding mechanism is different than that used for normal full rate traffic. od g g gives b better speech p quality qua y a at the same a bit b EFR coding rate than normal full rate. Traffic channels can transmit both speech and data and are bi-directional channels. channels 40
In the air interface, interface TDMA is used where one frequency is shared by, at the most, eight users. Consider the example of a 2 Mbit/s PCM signal that can carry 30 speech h channels, h l with h each h channel h l occupying 64 Kbits/s. p signals g from the mobile stations must be The speech placed into a 2 Mbit/s signal that connects the BTS and the BSC. It is very important that all the mobile stations in the same cell send the digital information at the correct time to enable the BTS to place this information into the correct position in the 2 Mbit/s signal. signal 41
In the air interface, interface a TDMA timeslot is a time interval of approximately 576.9 µs (~ 0.577 ms), which corresponds to the duration of 156.25 bit times. times All bursts occupy this period of time, but the actual arrangement of bits in the burst depends on the burst type.
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Control channels
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Broadcast group Base stations can use several TXs, TXs but there is always only one TX that can carry common channels. They are downlink point-to-multipoint channels. They contain general information about the network and the broadcasting cell. There are three types of broadcast channels: 1. Broadcast Control Channel (BCCH) 2. Frequency Correction Channel (FCCH) 3 Synchronisation Channel (SCH) 3.
Broadcast Control Channel (BCCH) Broadcast information for, for the network, e.g. for describing the current control channel structure. a MSs present cell and The surrounding cells.
It is transmitted continuously as its signal strength is measured by all MSs on surrounding cells. cells The information carried on the BCCH is monitored by the MS periodically (at least every 30 secs), when it is switched on and not in a call. call The BCCH is a point-to-multipoint channel (BS-to-MS). It also broadcasts a list of channels that are currently in use within the cell. cell
The BCCH is transmitted at constant power at all times, times and its signal strength is measured by all MS which may seek to use it. “Dummy” bursts are transmitted to ensure continuity when there is no BCCH carrier traffic. traffic Broadcast Control Channel (BCCH) – Carries the following information: 1. 1 2. 3. 4 4. 5. 6. 7 7. 8.
Location Area Identity (LAI). (LAI) List of neighboring cells which should be monitored by the MS. List of frequencies used in the cell. Cell identity. identity Power control indicator. DTX permitted. Access control (for example, example emergency calls, calls call barring). barring) CBCH description.
Frequency Correction Channel (FCCH) This is transmitted frequently on the BCCH timeslot and allows the mobile to synchronize its own frequency to that of the transmitting base site. The FCCH may only be sent during timeslot 0 on the BCCH carrier frequency and therefore it acts as a flag to the mobile to identify Timeslot 0. The MS scans for this signal after it has been switched on, since it has no information as to which frequency to use. use
Synchronisation Channel (SCH) The SCH carries the information to enable the MS to synchronize to the TDMA frame structure and know the timing of the individual timeslots. The following parameters are sent: – Frame number. – Base Site Identity Code (BSIC). The BSIC is needed to identify y that the frequency q y strength being measured by the mobile station is coming from a particular base station. The MS will monitor BCCH information from surrounding cells and store the information from the best six cells. The SCH information on these cells is also stored so that the MS may quickly qu c y resynchronize esy c o e when e itt e enters te s a new e ce cell.
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Common control channels (CCCH) group Common control channels comprise the second set of logical channels. They are used to set up a point to point connection. Th CCCHs The CCCH are off two t main i types: t The forward common channels are used for paging to inform a mobile of an incoming call, responding to channel requests, and broadcasting g bulletin board information. The return common channel is a random access channel used by the mobile to request channel resources before timing information is conveyed by the BSs.
The Common Control Channel is responsible for transferring control information between all mobiles and the BTS. This is necessary for the implementation of “call origination” and “call call paging” paging functions functions. 52
There are three types of common control channels: 1. 2. 3. 4.
Paging Channel (PCH) Random Access Channel (RACH) Access Grant Channel (AGCH) Cell Broadcast Channel (CBCH) ( )
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Paging Channel (PCH) downlink channel broadcast by all the BTSs of a location area in the case of a mobile terminated call.
The h PCH transmits IMSI off the h target subscriber b b which is with a request for acknowledgement form the mobile on RACH. used for “cell broadcast” (ASCII text messages to all MSs in form of SMS)
Used by the BTS to page MS, MS (paging can be performed by an IMSI, TMSI or IMEI).
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Random Access Channel (RACH) only uplink and the first point to point channel in the common control channels. It is used by the mobile station in order to initiate a transaction, or as a response to a PCH. RACH is used by MSs to gain access to the system.
Main functions are access requests, requests response to call announcement, location update, etc. It is used by subscriber unit to acknowledge a page form the PCH and also to originate a call by mobile. 55
Access Grant Channel (AGCH) The AGCH is the answer to the RACH. RACH It is used to assign a mobile Stand-alone Dedicated Control Channel (SDCCH). It is a downlink, point to point channel. It is the final CCCH message sent by the BS before a subscriber is moved off the control channel and will move to the dedicated channel in order to proceed with either a call setup, response to a paging message, Location Area Update or Short Message Service. Service The PCH and AGCH are never used at the same time.
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Cell Broadcast Channel (CBCH) This channel Thi h l is i used d to t t transmit it messages to be broadcast to all MSs within a cell. cell The CBCH uses a dedicated Th d di d controll channel to send its messages, however it is considered a common channel because the messages can be received by all mobiles in the cell. cell 57
Active A ti MS mustt frequently MSs f tl monitor it both BCCH and CCCH. The CCCH will be transmitted on the RF carrier with the BCCH.
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Dedicated control channels (DCCH) The dedicated channels are of two main types: those used for signaling, and those used for traffic. The signaling channels are used for maintenance of the call and for enabling call set up, providing facilities such as handover when the call is in progress, and finally terminating the call.
The traffic channels handle the actual payload.
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Dedicated control channels (DCCH) Dedicated control channels compose the third group of logical channels. The dedicated channels are: 1. Stand Alone Dedicated Control Channel (SDCCH) 2. Associated Control Channel (ACCH) 1. 2.
Slow Associated Control Channel (SACCH) Fast Associated Control Channel (FACCH)
They are The a e used sed for fo call set-up, set p sending measurement meas ement reports and handover. They are all bi-directional and point to point channels. 61
Stand-alone Dedicated Control Channel (SDCCH) It is used for signaling exchanges, exchanges e.g. e g during call setup, setup registration / location updates. The SDCCH carries signaling data following the connection of MS with the BS and just before a TCH assignment is issued by the BS. It ensures that the mobile and BS remain connected while the base station and MSC verify the subscriber unit and then it allocates resources for the mobile. It can be considered as an intermediate temporary channel accepting a newly completed call from the BCH. BCH It holds the traffic while waiting for the base station to allocate a TCH channel. The SDCCH is used to send authentication and alert messages. messages 62
Slow Associated Control Channel (SACCH) An SACCH is associated with each SDCCH and TCH. TCH It transmits measurement reports and is also used for power control, time alignment and in some cases for transmitting short messages. messages On the forward link, SACCH is used to send slow but regularly changing control information to the mobile e.g. transmit power level instructions, instructions specific timing advance instructions for each user on the ARFCN. On the reverse link, SACCH carries information about the received signal strength and quality of the TCH and also the BCH measurement resulting from neighboring cells. The SACCH is transmitted in 13th frame (also in 26th frame when half rate traffic is used) of every speech /dedicated control channel multiframe. 63
Fast Associated Control Channel (FACCH) The FACCH is transmitted instead of a TCH. TCH The FACCH ‘‘steals” the TCH burst and inserts its own information. The FACCH is used to carry out user authentication, handovers and immediate assignment. assignment
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Power On
Select the channel with highest RF level among the control channels
Scan Channels, monitor RF levels
Scan the channel for the FCCH NO
Select the channel with ith next highest Rf level from the control list.
Is FCCH detected? YES Scan channel for SCH NO Is SCH detected? d d? YES Read data from BCCH and determine is it BCCH?
From the channel data update the control channel list
NO
Is the current BCCH channel included? Camp on BCCH and start decoding
YES
Example: Incoming Call Setup MS MS MS MS MS MS MS MS MS MS MS MS MS S MS MS MS
↓ BSS/MSC / -----↑ BSS/MSC-----↓ BSS/MSC -----↑ BSS/MSC -----↓ BSS/MSC -----↑ BSS/MSC -----↓ BSS/MSC -----↑ BSS/MSC -----↓ BSS/MSC -----↑ BSS/MSC -----↓ BSS/MSC -----↑ BSS/MSC -----↑ BSS/MSC -----↑ BSS/MSC SS/ SC -----↓ BSS/MSC -----⌦BSS/MSC
Paging g g request q ((PCH)) Channel request (RACH) Immediate Assignment (AGCH) Paging Response (SDCCH) Authentication Request (SDCCH) Authentication Response (SDCCH) Cipher Mode Command (SDCCH) Ci h Mode Cipher M d Compl. C l (SDCCH) Setup (SDCCH) Call Confirmation (SDCCH) Assignment Command (SDCCH) Assignment Compl. (FACCH) Alert (FACCH) Connect Co ect ((FACCH) CC ) Connect Acknowledge (FACCH) ------ Data (TCH)
Channel combinations The different logical channel types mentioned are grouped into what are called channel combinations. Full Rate Traffic Channel Combination – TCH/FACCH + SACCH Broadcast Channel Combination – BCCH + CCCH Dedicated Channel Combination – SDCCH + SACCH Combined Channel Combination BCCH+CCCH+SDCCH+SACCH
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1 Hyper frame = 2048 Super frames =2715648 TDMA frames 3h ( 28 min 53 sec 760 ms)
0
1
2
3
2045
2046 2047
1 Super frame = 1326 TDMA frames (6.12s) = 51(26 frames) Multi frame
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0 12 3 1 Super frame = 1326 TDMA frames (6.12s) = 26(51 frames) Multi frame
0
1
2
23 24
3
1(51 frames) Multi frame = 51 TDMA frames (3060/13 ms)
1(26 frames) Multi frame = 26 TDMA frames (120 ms)
T0
T1
T2
T12 (SACCH)
T23
0 1
I
49 50
2 3
1 TDMA frame = 8 time slots (120/26 or 4.615ms)
0
1
2
25
3 4
5
6
7
1 time slot = 156.25 bit duration (15/26 or 0.577 ms) (1 bit duration = 48/13 or 3.69 s)
A practical approach: Suppose a subscriber switches on his mobile phone and receives a call. This simple act of switching on the phone involves the following steps: 1. The mobile scans all the radio frequencies and d measures them. th 2. It selects the frequency with the best quality and tunes to it. 3. With the help of a synchronization signal in a TDMA frame, the mobile synchronizes itself to the network.
The synchronization s nch oni ation information info mation required eq i ed by b this process p ocess is broadcast by the network and analyzed by the mobile. Registration and authentication are the next steps and they consist of the following operations: 1. A point to point connection must be set up. The mobile station makes a request for a channel to establish the connection. 2. The network acknowledges the request and allocates a channel The mobile receives and reads this information. channel. information 3. The mobile then moves to the allocated (dedicated) channel for further transactions with the network. The next steps are registration and authentication.
Initiation of a call
Once the subscriber is registered in the network and the authentication is successful, calls can be set up. In the case of a mobile terminated call, the subscriber has to be paged. This process is like this: 1. The network sends a paging message to all the BTS within the Location Area (LA) where the subscriber is registered. registered 2. The mobile station answers the paging message by sending a service/channel request. 3. The network acknowledges g this request q and again g an authentication is needed. 4. A dedicated signalling channel is assigned in order to transmit the data related to the call. A traffic channel is assigned for the conversation. conversation
During the conversation, conversation the mobile measures the signal strength of adjacent carriers and sends measurement reports to the Base Station Controller ( (BSC). ) A channel must be dedicated also for this function. p description p of the p process,, but it This is a simplified conveys the idea that there are many functions involved in the air interface to enable a mobile user to have conversation. Each one of these functions requires a separate "logical channel", as the data contents are different. Some of them are uplink, others are downlink and some are bi-directional. bi-directional
Mobile to Land Sequence Steps
Land to Mobile Sequence
MS Initiated Call Clearing Se e e Sequence
Call completion from the called side
Mobility Management Messages Message name AUTHENTICATION REQUEST AUTHENTICATION RESPONSE AUTHENTICATION REJECT IDENTITY REQUEST IDENTITY RESPONSE TSMI REALLOCATION COMMAND LOCATION UPDATING REQUET LOCATION UPDATING ACCEPT LOCATION UPDATING REJECT IMSI DETACH REQUEST CM SERVICE REQUEST CM RE-ESTABLISHMENT REQUEST MM-STATUS
Transmitted by Base Mobile Base Base Mobile Base Mobile Base Base Mobile Mobile Mobile bil Mobile/Base
Call management g messages g Message name
Transmitted by Starting a call
SETUP Mobile/base EMERGENCY SETUP mobile CALL PROCEEDING base PROGRESS base CALL CONFIRMED mobile ALERTING mobile/base CONNECT mobile/base During a call START DTMF Mobile STOP DTMF mobile MODIFY mobile/base USER INFORMATION mobile/base Ending a call DISCONNECT Mobile/base RELEASE mobile/base RELEASE COMPLET mobile/base Abnormal conditions STATUS Mobile/base STATUS ENQUIRY mobile/base CONGESTION CONROL mobile/base
Radio Resources Management Messages Message name
Logical channel Transmitted by
SYNC CHANNEL INFORMATION SYSTEM INFORMATION (TYPE 1,2,3,4,5) SYSTEM INFORMATION (TYPE 6) CHANNEL REQUEST PAGING REQUEST (TYPE 11,2.3) 2 3) IMMEDIATE ASSIGNMENT IMMEDIATE ASSIGNMENT EXTENDED IMMEDIATE ASSIGNMENT REJECT ASSIGNMENT COMMAND ADDITIONAL ASSIGNMENT PAGING RESPONSE MERSUREMENT REPORT HANDOVER COMMAND HANDOVER ACCESS PHYSICAL INFORMATION HANDOVER COMPLETE CIPHERING MODE CHANNEL RELEASE PARTIAL RELEASE FREQUENCY REDEFINITION
SCH BCCH SACCH RACH PCH AGCH AGCH AGCH FACCH FACCH SDCCH SACCH FACCH TCH FACCH FACCH FACCH FACCH FACCH SACCH FACCH SACCH FACCH FACCH FACCH SACCH
CLASSMARK CHANGE CHANNEL MODE MODIFY RR STATUS
Base Base Base Mobile B Base Base Base Base Base Base Mobile Mobile Base Mobile Base Mobile Base Base Base Base Mobile Base Mobile/base
Message sequence and system operations for registration of a te o terminal a in a visited s ted service se ce a area ea Prior MSC
Prior VLR
HLR
Serving VLR
Serving MSC
Serving Base
Registration info
Store info REGISTRATION NOTIFICATION INVOKE Store info REGISTRATION NOTIFICATION INVOKE Change g info REGISTRATION NOTIFICATION RESULT REGISTRATION NOTIFICATION RESULT REGISTRATION CANCELLATION INVOKE remove info REGISTRATION CANCELLATION RESULT
REGISTRATION CANCELLATION INVOKE QUALIFICATION REQUEST INVOKE remove info REGISTRATION CANCELLATION RESULT QUALIFICATION REQUEST RESULT PROFILE REQUEST INVOKE PROFILE REQUEST RESULT Store info
Location-Updating g Procedure Mobile station
Base station
Category
Carrier sine wave
Logical Channel FCCH
SYNC CHANNEL INFORMATION
RRM
SCH
SYSTEM INFORMATION TYPE3
RRM
BCCH
RRM RRM
RACH AGCH
MM MM MM
SDCCH SDCCH SDCCH SDCCH SDCCH
CHANNEL REQUEST IMMEDIATE ASSIGNMENT LOCATION UPDATING REQUEST AUTHENTICATION REQUEST AUTHENTICATION RESPONSE CIPHERING MODE COMMAND CIPHERING MODE ACK LOCATION UPDATING ACCEPT TMSI ALLOCATION COMPLETE CHANNEL RELEASE
RRM RRM MM MM RRM
SDCCH SDCCH SDCCH
Call Deliver to MH Mobile station
Base station Carrier sine wave SYNC CHANNEL INFORMATION SYSTEM INFORMATION PAGING REQUEST CHANNEL REQUEST IMMEDIATE ASSIGNMENT PAGING RESPONSE AUTHENTICATION REQUEST AUTHENTICATION RESPONSE CIPHERING MODE CIPHERING MODE ACK SETUP CALL CONFIRMED ALERTING CONNECT ASSIGNMENT COMMAND ASSIGNMENT ACK CONNECT ACK conversation conversation conversation DISCONNECT RELEASE RELEASE COMPLETE CHANNEL RELEASE
Category
RRM RRM RRM RRM RRM RRM MM MM RRM RRM CMCM CM CM RRM RRM CM
CM CM CM RRM
Logical Channel FCCH SCH BCCH PCH RACH AGCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH FACCH TCH TCH FACCH FACCH FACCH FACCH
Location-Updating g Procedure Mobile station
Base station
Category
Carrier sine wave
Logical Channel FCCH
SYNC CHANNEL INFORMATION
RRM
SCH
SYSTEM INFORMATION TYPE3
RRM
BCCH
RRM RRM
RACH AGCH
MM MM MM
SDCCH SDCCH SDCCH SDCCH SDCCH
CHANNEL REQUEST IMMEDIATE ASSIGNMENT LOCATION UPDATING REQUEST AUTHENTICATION REQUEST AUTHENTICATION RESPONSE CIPHERING MODE COMMAND CIPHERING MODE ACK LOCATION UPDATING ACCEPT TMSI ALLOCATION COMPLETE CHANNEL RELEASE
RRM RRM MM MM RRM
SDCCH SDCCH SDCCH
Call Deliver to MH Mobile station
Base station Carrier sine wave SYNC CHANNEL INFORMATION SYSTEM INFORMATION PAGING REQUEST CHANNEL REQUEST IMMEDIATE ASSIGNMENT PAGING RESPONSE AUTHENTICATION REQUEST AUTHENTICATION RESPONSE CIPHERING MODE CIPHERING MODE ACK SETUP CALL CONFIRMED ALERTING CONNECT ASSIGNMENT COMMAND ASSIGNMENT ACK CONNECT ACK conversation conversation conversation DISCONNECT RELEASE RELEASE COMPLETE CHANNEL RELEASE
Category
RRM RRM RRM RRM RRM RRM MM MM RRM RRM CMCM CM CM RRM RRM CM
CM CM CM RRM
Logical Channel FCCH SCH BCCH PCH RACH AGCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH FACCH TCH TCH FACCH FACCH FACCH FACCH
Mobile-Assisted Handover Mobile station
Base station
conversation conversation MEASUREMENT REPORT conversation conversation conversation MEASUREMENT REPORT conversation HANDOVER COMMAND HANDOVER ACCESS HANDOVER ACCESS HANDOVER ACCESS PHYSICAL INFORMATION HANDOVER COMPLETE conversation conversation ti MEASUREMENT REPORT conversation conversation conversation MEASUREMENT REPORT conversation
Logical Channel TCH TCH SACCH TCH TCH TCH SACCH TCH FACCH new TCH TCH TCH TCH FACCH TCH TCH SACCH TCH TCH TCH SACCH TCH
Mobile-Assisted Handover Mobile station
Base station
conversation conversation MEASUREMENT REPORT conversation conversation conversation MEASUREMENT REPORT conversation HANDOVER COMMAND HANDOVER ACCESS HANDOVER ACCESS HANDOVER ACCESS PHYSICAL INFORMATION HANDOVER COMPLETE conversation conversation ti MEASUREMENT REPORT conversation conversation conversation MEASUREMENT REPORT conversation
Logical Channel TCH TCH SACCH TCH TCH TCH SACCH TCH FACCH new TCH TCH TCH TCH FACCH TCH TCH SACCH TCH TCH TCH SACCH TCH
B t and Bursts dF Frames 1 TDMA frame = 8 timeslots
Normal Burst (NB)
TB 3
0
1
2
3
4
5
Fixed bits
TB 3
Access burst (AB)
TB Synchronization sequence Encrypted bits 36 TB 3 41 3
Encrypted bits 39 Synchronization sequence 64
Mixed bits 58
TB 3
142
Synchronization burst (SB)
TB 3
7
1 timeslot = 156.25 bit durations (15/26 =~ 0.577 ms) (1 bit duration 48/13 =~ 3.69 micro sec) flag Training sequence 26flag Encrypted bits 57 TB GP Encrypted bits 57 1 3 8.25 1
Frequency correction TB burst (FB) 3
Dummy burst (DB)
6
Training sequence 26
GP 8.25
Encrypted bits 39 TB GP 3 8.25 GP 68 68.25 25
Mixed bits 58
TB GP 3 8.25
TB: Tail bits GP: Guard period
GSM terrestrial interfaces By: Mrs. Shweta Shah
• • • • •
Each GSM component is designed to communicate over an interface specified by the GSM standards. This provides flexibility and enables a system operator to adopt system components from different manufacturers. F For example l Motorola M t l BSS equipment i t may be coupled with a Nokia NSS. Each interface within the GSM system has a specified f d name associated d with h it. This table illustrates the names of all the interfaces specified p by y GSM.
•
It comprise p all the connections between the GSM system entities, while the Um, or air – interface is not included since it belongs to radio interface
This diagram Thi di shows h th GSM system the t with the 2Mbps interfaces, which are highlighted. highlighted These interfaces carry traffic from the PSTN to the MSC, MSC between MSCs, MSCs from an MSC to a BSC and from a BSC to remotely sited BTSs. BTSs These links are also used between the MSC and IWF. IWF
