Asymptotic Performance Analysis of Generalized User Selection for Interference-Limited Multiuser Secondary Networks

We analyze the asymptotic performance of a generalized multiuser diversity scheme for an interference-limited secondary multiuser network of underlay cognitive radio systems. Assuming a large number of secondary users (SUs) and that the noise at each SU's receiver is negligible compared to the interference from the primary transmitter, the secondary transmitter (ST) transmits information to the kth best SU, namely, the one with the kth highest signal-to-interference ratio (SIR). We use extreme value theory to show that the kth highest SIR converges uniformly in distribution to an inverse gamma random variable for a fixed k and large number of SUs. We use this result to derive asymptotic expressions for the average throughput, effective throughput, average bit error rate and outage probability of the kth best SU under continuous power adaptation at the ST, which ensures satisfaction of the instantaneous interference constraint at the primary receiver caused by the ST. Numerical simulations show that our derived asymptotic expressions are accurate for different values of system parameters.