Opportunistic Communications with Distorted CSIT

The effects of distorted channel state information at the transmitter (CSIT) on opportunistic schemes are investigated for the symmetric broadcast channels. Opportunistic schemes are defined in the presence of distorted CSIT, by specification of scheduling schemes and rate-adaptation schemes. Then, two types of CSIT distortion - either from noisy feedback channel or from delay - are considered, and the diversity- multiplexing tradeoff (DMT) as well as the throughput achieved by the opportunistic schemes are observed. With noisy CSIT, the opportunistic schemes exploit multiuser diversity so that both the throughput and the DMT improves either as the number of users increases or as the quality of the feedback channel improves. With delayed CSIT, however, the opportunistic schemes do not achieve improved DMT, while the throughput gain is still observed.