Basic Gsm Frame Structure 5v4o2r

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GSM frame structure is used to transmit the data. The GSM frame structure establishes schedules for the predetermined use of time slots. By the use of a frame structure, both the mobile and the base station are able to communicate.

By using GSM frame structure ➢

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The voice data and signaling information is ed. What types of information are being transmitted. The GSM frame structure provides the basis for the various physical channels used within GSM. It is at the heart of the overall system.

Basic GSM frame structure ➢

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The basic element in the GSM frame structure is the frame itself. Eight slots, each used for different s within the TDMA system. The slots for transmission and reception for a given mobile are offset in time so that the mobile does not transmit and receive at the same time.

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The BS transmits two types of channel. Traffic and Control. Traffic:-one for the traffic on the main traffic carrier frequency. Control:-The 2nd for the control on the beacon frequency.

Time Slot Structure ➢

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Time slots are the smallest division of a communication channel. It is assigned to particular s in a communication system. Time slots can be combined for a single to increase the total data transfer rate available to that . In some systems, time slots are assigned dynamically (GPRS).

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Slot structure is the division of a time slot into different fields (information)parts. Slot structure fields typically include :A preamble for synchronization. Control header (e.g. address information). data, and error detection.

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The no of data bits in a ts depending on the type of the data. The structure of the time slot can vary. If the ts is on the UL or DL radio channel ,Each normal time slot contains 148 bits of information. Some time slot data bits are used for data and other bits are dedicated for control.

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For voice communication, s have a fixed assignment of particular time slots. For packet data transmission (such as GPRS), time slots are dynamically assigned.

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Time slots include ramp up and ramp down periods to minimize rapid changes in radio transmitter power. The ramp up and ramp down time is used to reduce unwanted radio emissions that occur from rapidly changing signals. A single time slot transmission is called a radio burst. 5 types of radio bursts are defined in the GSM system,Such as FCB,SB,AB,DB,NB

GSM multi frame ➢

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The GSM frames are grouped together to form multi frames. There are two type GSM multi frame structures:Such as Traffic multi frame &Control multi frame

Traffic multi frame ➢

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The Traffic Channel frames are organized into multi frames consisting of 26 bursts. It taking 120 ms. In a traffic multi frame,24 bursts are used for traffic.

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These are numbered 0 to 11 & 13 to 24. One of the remaining bursts is then used to accommodate the SACCH. the remaining frame (25) is idle. The actual position used alternates between position 12 and 25.

Control multi frame ➢

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the Control Channel multi frame that comprises 51 bursts. It taking 235.4 ms. It always occurs on the beacon frequency in time slot zero. It may also occur within slots 2, 4 and 6 of the beacon frequency as well. This multi frame is subdivided into logical channels.

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The logical channels are following:Frequency correction burst. Synchronization burst. Broadcast channel (BCH). Paging and Access Grant Channel (PACCH) Stand Alone Dedicated Control Channel (SDCCH).

Super frame ➢

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A super frame is a multi frame sequence that combines the period of a 51multiframe with 26 multi frames. It taking 6.12 seconds. The use of the super frame time period allows all mobile devices to scan all the different time frame types at least once

Hyper frame ➢

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A hyper frame is a multi frame sequence that is composed of 2048 super-frames. It is the largest time interval in the GSM system. It taking 3 hours, 28 minutes, 53 seconds. The hyper frame allows to synchronize frequency hopping sequence & encryption processes for voice privacy of subscribers’ conversations.

The 51-frame Control Channel Multi frame (BCCH/CCCH) ➢

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The BCCH/CCCH 51-frame structure will apply at TS 0 for each TDMA frame on the ‘BCCH carrier. The RF carrier frequency to which BCCH is assigned on a per cell basis. one TDMA frame with the first repetition (numbered 0) at the bottom.

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UL (MS–BSS) all time slot 0s are allocated to RACH. Because RACH is the only control channel in the BCCH/CCCH group which works in the UL direction. DL (BSS–MS), the arrangement is more interesting. Starting at frame 0 of the 51-frame structure, the first time slot 0 is occupied by a frequency burst (FB). The second by a synchronizing burst (‘S’) and then the following four repetitions of time slot 0 by BCCH data (B) .

Beacon Frequency Channel ➢ ➢ ➢ ➢ ➢ ➢

It is at Slot # 0 channel (TDMA Channel 0). It is formatted as 51-multi frame. 1st (Slot # 0 of the multi frame) is FCCH. The next one is SCH. This pair (FCCH & SCH) repeats 5x in a multi frame. BCCH channel 4 slots long appears once per 51multi frame and it takes Slot # 2 to 4 (3rd,4th,5th& 6th slots).

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The remaining slots care common control channels or CCCH (PCH and AGCH) BCCH, CCCH, SDCCH, SACCH and FACCH, form a message of 4 slots long. The beacon is a down link channel. GSM always has a pair of frequencies (up and down links) per ARFCN. up link contains RACH channel.