Uplink cell capacity of cognitive radio networks with interference outage constraints

Cognitive radio (secondary) networks have been proposed as a means to improve the spectrum utilization. Existing works study the capacity of cognitive radio networks as a random variable given certain peak/average interference power constraints. Such cognitive radio networks with random capacities, however, are limited in their applications since the quality of service (QoS) cannot be guaranteed. In this paper we investigate the maximum stable capacity that can be provided by a cognitive radio network with interference power outage constraints. We consider a scenario 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. We assume that secondary users transmit on a time-division-multiple-access (TDMA) basis and dynamically adjust their transmit power to maintain the received signal power at the BS as P₀. We first study the interference raised by such a secondary network as a random variable. Its cumulative distribution function (CDF) is derived under both simple and realistic channel models. We further assume that in order to protect primary services, the probability that the interference power perceived at a primary receiver exceeding a threshold I₀ should not be larger than an outage probability limit chi. Such an interference outage constraint imposes a limit on P₀ and allows us to express the capacity as a function of I₀ and chi. Moreover, the impacts of the parameters R, shadowing, and fading on the capacity are investigated.