Sunday, April 29, 2012


Tx-integer Value range: 3~12,  14,  16,  20,  25,  32,  50
Unit: Number of RACH timeslots (equivalent to one timeslot, 0.577ms)
Content: Extended Transmission Timeslots(T), used to calculate the number of timeslots in the interval between two channel requests sent by MS.
Recommendation: 25 (If the cell immediate assignment success rate is low, set the S with a larger value. Select 32 for satellite transmission, so as to reduce satellite transmission delay).
It is set to reduce the collisions on RACH. It mainly affects the execution efficiency of the immediate assignment process. The value of this parameter is related to CCCH configuration mode, both work together to determine parameter S. The number of timeslots (excluding the timeslot from where the message is sent) from MS starts the immediate assignment process to the first channel request message sent is a random value in the set {0, 1, …, MAX(T, 8)--1}. And the number of timeslots between any two adjacent channel request messages is a random value in the set {S, S+1, …, S+T-1}.
Generally, parameter S should be as small as possible (in order to shorten the access time of MS) when parameter T is fixed, but AGCH and SDCCH must not be overloaded. During the operation, a random value can be selected for parameter T for the cell with unknown traffic to ensure the minimum value of S. If AGCH or SDCCH of the cell is overloaded, then parameter T can be changed to make parameter S larger, until AGCH or SDCCH of the cell is not overloaded.
The range of value T can be specified according to the above principles (multiple values can be selected for parameter T corresponding to various values of parameter S). When the RACH collisions is serious, value T should be large. When the number of RACH collisions is small, value T should be as small as possible.

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