Let us take a case when BCCH TRX is serving to a longer distance in comparison to the TCH TRX. In this case when MS initiates a call on BCCH TRX, a situation might occur when there is no TCH free on the BCCH TRX and the BSC allot a TCH on TCH TRX. But the MS is not in the coverage of TCH TRX so hhhhhhjkhsha will happen.
Now in case of 900/1800 cells where the BCCH is on 900 and TCH is on 1800 as well as 900.
I assume the coverage circle of 1800 will be less than the coverage circle of 900 BCCH as well as 900 TCH TRX’s.
Under this scenario,
if the MS who is actually in the coverage circle of 900 BCCH or 900 TCH gets allotted an TCH of 1800 by BSC
then the case i want to discuss will come into effect.
Now, before allotting the TCH of 1800 how can BSC know its RXLEVEL?
It will be only after the MS is allotted the TCH of 1800, the MS measures the RXLEVEL and send it back the BSC will come to know the RXLEVEL.