Question

A metropolitan area is to be given wireless digital telephone service. Throughout this area there is approximately uniform service demand. Assume that the frequency is allocated in two blocks of 4 MHz with a separation of 50 MHz, one block for the uplink and the other for the downlink, which constitutes a frequency-division duplex (FDD) operation. The system uses the hybrid frequency-division/time-division multiple access (FD/TDMA) scheme as follows: The frequency band is divided into 500 kHz “channels” (which is the frequency division part), and on each of those “channels” a total 40 high-quality digital voice circuits are multiplexed in a TDMA manner.

a) Draw the time-frequency plane and partition that plane appropriately for this FDD FD/TDMA system.

b) The modulation scheme used is 8-QAM which is implemented with the square-root- raised cosine pulses with a roll-off factor, α of 0.25. Find the bit rate for each user.

Hint: ?_? = ^?⁄_{1 + ?} , where ?_? is the rate and w is the bandwidth.