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time slot allocation on gsm radio

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  • #36134 Reply
    frededrick mbogo
    Guest

    how will I assign time slot for a given radio and what are the basics should one need to know regarding this issue?

    #36135 Reply
    Nguyen
    Guest

    Sorry but your question was not so clearly for me. Please describe more concrete, so that other can help you.

    Brgds

    #36136 Reply
    frededrick
    Guest

    would you tell me all issues regarding timeslot in gsm radios to your knowledge and capacity to keep pace in this growing telecom indusrty.

    help me in whichever way your think gonna make it.

    #36137 Reply
    Nguyen
    Guest

    OK, the TDMA and FDMA are implemented in the GSM. By using FDMA we have 124 carriers.

    Each of these carrier frequencies is divided in 8 timeslots, using a TDMA scheme.

    The fundamental unit of time in this TDMA scheme is called a burst
    period and it lasts approx 0.577 ms. 8 burst periods are grouped
    into a TDMA frame (approx 4.615 ms), which forms the basic unit for
    the definition of logical channels.
    One physical channel is one burst
    period per TDMA frame.

    Channels for speech and data traffic (TCH) use 26-frame multiframe. Other control channels (such as BCCH, RACH, PCH,…) use 51-frame multiframe.

    Pls adv if you have other question.

    Brgds

    #36138 Reply
    Mohd. Muzammil
    Guest

    Fredrick,

    The following link on GSM overview explains brusts and burst formats. Hope this helps you.

    http://ccnga.uwaterloo.ca/~jscouria/GSM/gsmreport.html

    regds.

    #36139 Reply
    MOSES
    Guest

    Once a time slot is assigned to a user means, whether the same time slot will be associated with the user till he ends his call or any possibilities for change in time slot??

    #36140 Reply
    Wallis Dudhnath
    Guest

    Hi Moses,

    This GSM burst is used for the standard communications between the basestation and the mobile, and typically transfers the digitised voice data.

    GSM uses a combination of both TDMA and FDMA techniques. The FDMA element involves the division by frequency of the (maximum) 25 MHz bandwidth into 124 carrier frequencies spaced 200 kHz apart as already described.

    The carriers are then divided in time, using a TDMA scheme. This enables the different users of the single radio frequency channel to be allocated different times slots. They are then able to use the same RF channel without mutual interference. The slot is then the time that is allocated to the particular user, and the GSM burst is the transmission that is made in this time.

    Each GSM slot, and hence each GSM burst lasts for 0.577 mS (15/26 mS). Eight of these burst periods are grouped into what is known as a TDMA frame. This lasts for approximately 4.615 ms (i.e.120/26 ms) and it forms the basic unit for the definition of logical channels. One physical channel is one burst period allocated in each TDMA frame.

    VBR/ Wallis Dudhnath

    #36141 Reply
    Pix
    Guest

    Hi MOSES

    “Once a time slot is assigned to a user means, whether the same time slot will be associated with the user till he ends his call or any possibilities for change in time slot??

    The timeslot can be changed, and will most probably be changed during the average 2mn lifetime of a call.
    1/ user is mobile and needs the call to be handed over to a neighbour cell : the TCH will be allocated to another cell, and this is managed by the BSC.

    2/ traffic condition is the cell requires the call rate to be modified, from Full Rate to Half Rate (or vice versa). In this case the call will most likely be allocated to another physical timeslot.

    3/ quality is poor and the BSC thinks it is caused by frequency interference. In this case the BSC moves the call to a timeslot located on another TRX, with a different frequency.

    Those are 3 basic scenarios in which the timeslot on which the call is set is modified during the call. There are some other scenarios as well.

    Cheers
    Pix

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