Carrier sensing not working

I am using “carrier_sensed()” to detect the signal from other USRP.
However,carrier sensing always return false irrespective of signal from
other usrp device.
I tried by increasing the gain(8 to 15),threshold (from 10 to 30) still
carrier sensing is not working .
I also tested ,sensing in the same script also not working.
previously ping was not working by using so I added the sleep
10 ms and ping starts working(this issue was discussed in forum and I
this 10ms magic number from forum ).
And also I changed the distance between USRP’s also (from 10cm to 1m).
So can anybody provide me some pointers regarding the same that why
sensing is not working and what will be reason for this.
I am using
USRP2 : USRPN210 with daughterboard : XCVR2450