In the traffic channels of GSM there are 8.25 bits reserved for guard PERIOD can someone tell me, how bits is in point (0.25)?? i mean when we say a 2 bit no, there are 4 possibilities(i.e. 2^n) like 00,01,10,11. But how will 8.25 have possibilities REPLY ASAP PLEASE
The key to your question is located in the question...i.e. Guard PERIOD (or time). GSM's Gaussian Minimum Shift Keying modulation has a data throughput of 270.833 kilobits/second (kb/s). This works out to be 3.69 microsec./bit. Thus 8.25 bits would take 30.44 microseconds. This is the Guard PERIOD. This period is referenced to bits when in the context of frames. This guard time is needed due to the unknown distance of the MS from the BTS (propogation time/delay).
Everywhere it is written that 8.25 are GUARD bits So how can BIT be rational,it has to be a natural NO like 1,2,3...etc
You are talking about the guard period i.e a period of time not a count of bits sent or received. The units of this time period happen to be bits which is defined as the time that it takes to transmit 1 bit and obviously a time period can be any length you like so it can be some fraction of a bit long.
So it means that in GSM 148 bits of ONE burst are bits send or received and rest 8.25bit is GUARD period NOT send or received bits that makes it TIME SLOT=148(one burst)+8.25= 156.25