Uplink cell capacity of cognitive radio networks with peak interference power constraints

A cognitive radio (secondary) network can reuse the under-utilized spectrum licensed to a primary network on a non-interruptive basis. In this paper, we study the uplink capacity of a secondary network where a secondary base station (BS) is located at the center while multiple secondary users are uniformly distributed within a circular cell of radius R. Primary users are assumed to be distributed in the same plane according to a Poisson point process with a density parameter lambda_p. To protect primary services, secondary users can only transmit under a peak interference power constraint which guarantees that the instantaneous interference power perceived by any primary user is not larger than a certain threshold. In addition, we assume an opportunistic scheduler at the BS which exploits multi-user diversity among M secondary users and stochastically maximize the cell capacity.We first study the capacity with a simple channel model considering only the path loss and derive the closed-form cumulative distribution function (CDF) of the capacity. We then study the capacity with realistic fading channel models using a semi-analytical approach. The impacts of the parameters R, lambda_p, and M on the capacity are quantified and discussed. Moreover, we find that shadowing and fading only have limited impacts on the distribution of the capacity.