Q: RACH & TA

[peanut]

Dears,

Is it possible to calculate the TA (2G technology) from RACH message so we can stop RACH messages exeeding some TA threshold

Kind Regards,

[fantominox]

well,
there is no possibility to estimate TA basing on RACH message - you can limit access at most by received signal level on RACH at BTS.


BR
Fantominox

[firstmaxim]

To put it in another way, RACH burst size is made small, with a big guard period, so that the bursts from mobiles at a distance of 35 km can arrive within the first time slot, so as not to cause an overlap with the user of the second timeslot, avoiding Inter Symbol Interference.

[maahsan]

TA is calculated from RACH message. There is no way to stop a mobile from sending RACH message so the access is controlled by not sending Immediate Assignment command on AGCH if the TA calculated based on RACH was greater than MAXTA.

[firstmaxim]

We are considering BTS deriving the initial timing advance information from the RACH. Thanks for the insight maahsan!

[peanut]

Thanks Maahsan,

I understand from you post that the BTS has the ability to calculate TA from the RACH burst, do you know how?

regards,

[maahsan]

For a detailed discussion please visit this link

http://gsmfordummies.com/timing/timing.shtml