Exploiting Partial Knowledge of Interference at the Transmitter
Pulkit Grover and Anant Sahai
Consider the cognitive radio framework. The aim is to reduce the interference caused by the primary's strong transmissions to the cognitive receiver. We attempt to understand limitations imposed by lack of complete knowledge of the channel connecting the primary transmitter and the cognitive receiver. We investigate the case when the cognitive transmitter knows the interference vector, but doesn't know the phase shift of the primary's transmissions at the cognitive receiver (for example, when the geographical locations are known only approximately). We show that in some cases, there is little advantage in exploiting the knowledge of primary's transmissions: the rates achieved by ignoring this knowledge are quite close to those achieved by any other "smart" technique.
We further extend the results to the case when the primary's signal undergoes a Rayleigh fade and the fade amplitude and phase are unknown at the transmitter. We demonstrate the necessity of outage formulation in this situation. The work has been presented in part at DySpAN '07 and ISIT '07.