Cross-layer design for cognitive radios with joint AMC and ARQ under delay QoS constraint

In order to guarantee dual quality-of-service (QoS) measures, namely, packet error rate (PER) and delay constraint, in a spectrum-sharing channel, we propose a cross-layer resource allocation approach in this paper. In particular, we assume an underlay cognitive radio scenario, in which, a secondary user (SU) is granted access to the spectrum as long as its average interference power, imposed on the primary-user (PU) receiver is below a predefined threshold. The SU employs adaptive modulation and coding (AMC) at the physical layer and automatic repeat request (ARQ) at the link-layer. An adaptive power and rate allocation scheme is proposed for the SU transmitter to meet both the PER requirement and the statistical delay constraints. To this end, we use the effective capacity concept and obtain closed-form expressions for the power allocation and capacity of the SU´s link in Nakagami-m fading channels.