1. (Selective feedback) The downlink of IS-856 has K users each experi- encing i.i.d. Rayleigh fading with average SNR of 0 dB. Each user selectively feeds back the requested rate only if its channel is greater than a threshold y. Suppose y is chosen such that the probability that no one sends a requested rate is E. Find the expected number of users that sends in a requested rate. Plot this number for K = 2, 4, 8, 16, 32, 64 and for E = 0 1 and E = 0 01. Is selective feedback effective?
2. About channel measurement, prediction and feedback are based on an FDD system. Discuss the analogous issues for a TDD system, both in the uplink and in the downlink.