MS MAX Re-trans

MS MAX Re-trans Value range: 1,  2,  4,  7

Unit:  Times

Content: One of the parameters of random access control information.  i.e. MS MAX. Re-trans Times. It is the upper limit of times that MS is allowed to send “Channel Request” in one immediate assignment procedure.

Recommendation: Set to 7:For areas with low traffic (suburban or rural area) and the cell radius more than 3 km.Set to  4: For areas with ordinary traffic (non-busy area in the city) and the cell radius  less than 3km. Set to 2: For micro-cellular Set to 1: For micro-cellular with heavy traffic or with obvious congestion.  And 4 or more is recommended to set for satellite transmission BTS.

 

After initiating immediate assignment process, MS keeps monitoring messages on BCCH and CCCH group it belongs to. If the network does not send Immediate Assignment or Immediate Assignment Extend message, MS will resend the channel request message at a certain time interval. The larger this value, the higher the call setup success rate, but the heavier the loads of RACH and SDCCH.

When MS initiates immediate assignment, it will send the “channel request” message to the network via RACH. As RACH is an ALOHA channel, the network is incapable of controlling the access time of MS. Thus in heavy traffic spot, it is unavoidable that several MS may simultaneously make an access request and cause collision which will lead to two results: one is when one request signal level is obviously higher than those of other access signals, the access request with higher level will be handled; the other is the network can recognize none of them due to mutual-interference. As the traffic increasing, access request loss due to collision will increase too. To make sure that the system can correctly receive the access request and increase the access success rate, the network allows MS to send several channel requests before receiving an immediate assignment message so as to have a higher access probability. MS will return to idle mode if it fails to receive an immediate assignment command after the max. retrans times. After MS sends channel request, it will start timer T3120 and wait on the downlink CCCH and BCCH. When timer is timeout while RACH resend times is not more than “MAX re-trans.”, MS will resend channel request message (contains one new random reference), and restart T3120 with a random value. When timer is timeout and “MAX re-trans” is reached, MS will start T3126. If MS still fails to receive a response from the network after T3126 is timeout, it will give up the access. If MS receives the access rejection, it will stop T3120 and start T3122. Within T3122, no new access attempt will be allowed.