GSM Bursts Frames

download GSM Bursts Frames

of 15

Transcript of GSM Bursts Frames

  • 8/7/2019 GSM Bursts Frames

    1/15

    GSM Bursts & Frames

  • 8/7/2019 GSM Bursts Frames

    2/15

  • 8/7/2019 GSM Bursts Frames

    3/15

  • 8/7/2019 GSM Bursts Frames

    4/15

  • 8/7/2019 GSM Bursts Frames

    5/15

    Bursts and time slots in the Air

    Interface ... ...

    Bursts from Mobile Stations

    BTS

    2Mbit/s to BS

    TDMA Time Slot

    TDMA Frame

  • 8/7/2019 GSM Bursts Frames

    6/15

    Burst:

    It is defined as the information presentin a particular time slot

    Each GSM RF carrier supports eighttimeslots and the data are transmitted

    in the form of bursts that are designedto fit within these slots.

  • 8/7/2019 GSM Bursts Frames

    7/15

    GSM burst types

    tailbits

    3

    fixed bits ("0")142

    tailbits

    3

    guardperiod

    8,25 bits

    FREQUENCY CORRECTION BURST

    tailbits

    3

    encrypted bits57

    SB1

    trainingsequence

    26

    SB1

    encrypted bits57

    tailbits

    3

    guardperiod

    8,25 bits

    NORMAL BURST

    TDMA FRAME ~ 4.615 ms

    576.9 s

  • 8/7/2019 GSM Bursts Frames

    8/15

    GSM burst types (2)

    ext. tailbits

    8

    synchronisationsequence

    41

    encrypted bits36

    tailbits

    3

    extended guard period68,25 bits

    ACCESS BURST

    tailbits

    3

    encrypted bits39

    extended trainingsequence

    64

    encrypted bits39

    tailbits

    3

    guardperiod8,25bits

    SYNCHRONISATION BURST

    tailbits

    3

    mixed bits142

    tailbits

    3

    guardperiod

    8,25 bits

    DUMMY BURST

  • 8/7/2019 GSM Bursts Frames

    9/15

    Burst types

    The information contained in one time slot is a burst. 5 types of bursts are available

    Norm al bu rs tUsed to send all other logical channel information.

    Freq uen cy correc ti on burs tUsed to transmit the FCCH channel.

    Syn chr oni sation burstUsed to transmit synchronisation information.

    Acces s burstUsed to send RACH information.

    It has a long guard period to allow the BTS to calculate the MS distancefrom the BTS and to provide timing advance information to the MS.

    Dum my b urs tUsed to fill up unused timeslots, which transmits the BCCH channel.

    No real information.

  • 8/7/2019 GSM Bursts Frames

    10/15

    Normal Burst

    T3 Coded Data

    57

    Training

    Sequence 26

    Coded

    Data 57

    GP

    8.25

    S1 S1 T3

    148 bits = 0.54612 msec

    This burst is used to carry information on TCH and on the control channels

    BCCH, PCH, AGCH, SACCH and FACCH.

    Note: GP (Guard Period)

  • 8/7/2019 GSM Bursts Frames

    11/15

    Normal burst The tail bi ts (T) are a group of 3 bits set to zero and placed at

    the beginning an d the end of a burst. The coded data bi ts corresponds to two groups, of57 bits

    each, containing signaling or user data. The stea l ing fl ag s(S) indicate, to the receiver, whether block

    contains data or is "stolen" The train ing sequence has a length of26 bits . It is used to

    adapt parameters of receiver to the current path propagationcharacteristics. It synchronizes the receiver, thus masking outmultipath propagation effects. Strongest signal selected in case of multipath propagation

    The guard peri od (GP), with a length of8.2 5 bits , is used toavoid a possible overlap of two mobiles information.

  • 8/7/2019 GSM Bursts Frames

    12/15

  • 8/7/2019 GSM Bursts Frames

    13/15

    Synchronization Burst The synchronization burst is used to transmit

    synchronization channel information (SCH).

    As its name suggests, this burst carriesdetails of the GSM frame structure and allowsan MS to fully synchronize with the BTS.

    The synchronization burst is the first burst

    that the MS has to demodulate and, for thisreason, the training sequence is extended to64 bits. It also allows larger multipath delayspreads to be resolved.

  • 8/7/2019 GSM Bursts Frames

    14/15

    Access Burst In contrast to the bursts described so far, the access

    burst comes in a rather unique format because of itsspecial tasks.

    A mobile station uses the access burst only for theinitial access to a BTS. MS does not know the current distance to the BTS it

    generally is uncertain if the access burst arrives within specified time frame and there exists chances of

    overlapping with other bursts. To ensure that an access burst arrives at the BTSduring the proper time period the number of bits forthe access burst was set to only 88 bits along withincreased guard band bits of 68.25.

  • 8/7/2019 GSM Bursts Frames

    15/15

    The purpose of this extra free space isto measure the distance between MS

    and BTS at the beginning of aconnection.