Link adaptation design for interfering cognitive radio with QoS constraints

In this paper, we consider a primary and a cognitive user transmitting over a wireless fading interference channel. Both primary and cognitive links are subject to delay-QoS constraints. The achievable throughput subject to a given delay-QoS constraint can be quantified as the effective capacity of a link. We consider a system in which the primary user transmits with a constant power and utilizes an adaptive modulation and coding (AMC) scheme subject to its required bit error rate (BER). A link (power and rate) adaptation scheme is proposed for the interfering cognitive radio to maximize its effective capacity, while a minimum required effective capacity for the primary user is provisioned. A BER performance requirement and a power constraint are also considered for the cognitive radio. The resulting problem is then cast as a nonlinear discrete optimization problem for which a fast and efficient suboptimum solution is presented. Comparisons with the scheduled (non-interfering) adaptive cognitive transmission demonstrate the efficiency of the proposed interfering transmission scheme.