Cooperative access for cognitive radios to guarantee QoS for cell edge primary users

Cognitive radio (CR) systems have been proposed for efficient usage of spare spectrum licensed to primary systems. This leads to the issue of providing as much spectrum to CR users as possible while not degrading the quality of service (QoS) of primary users of the spectrum. This paper proposes a novel cooperation scheme between primary and CR users to guarantee QoS of primary users up to the cell edge while making the licensed spectrum available for opportunistic access by the CR users. Thus the proposed method can provide a so called ¿win-win strategy¿ by benefiting both primary and CR users. The proposed scheme solves efficiently the Gaussian multiple access problem for power allocation of primary systems that cooperates with CR systems. We show that the Gaussian multiple access problem can be formulated as a standard semi-definite programming (SDP) problem. Numerical results show that the QoS of primary users at the cell edge is improved by the proposed cooperative access scheme.