Hi Zhenhua,
gr-gsm should be a good project for you and for the community. I wish you success.
You may want to look at the slow frequency hopping implementation of airprobe that is placed here: https://github.com/BogdanDIA/airprobe-hopping.
It uses PFB to split a 20mhz band received with USRP-N210 into GSM channels and then use all of them according to the hopping algorithm decoded on the Immediate Assignment message and SI 1. It is not a perfect implementation as airprobe is not perfect too, that is why I think this will be a good project.
The hopping patch has been done two years ago and has API for gnuradio3.6 era. I did not update it yet on 3.7. Here is small paper I wrote at the moment of creating a patch. It may be of help to you.
http://yo3iiu.ro/blog/wp-content/uploads/2012/04/Evaluating_GSM_hopping_V1.1.pdf
Bogdan
On Tuesday, March 11, 2014 5:40 AM, zhenhua han <address@hidden> wrote: