Resource allocation schemes with subcarriers grouping approach over an orthogonal frequency division multiplexing-based cognitive radio system considering the channel uncertainty

Abstract

Dynamic resource allocation in an orthogonal frequency division multiplexing (OFDM) based cognitive radio (CR) system is an important challenge since several parameters (i.e. primary users (PUs) activity, the interference and main channel gain) are involved in this. This problem is more significant in a cognitive radio scenario when perfect channel state information (CSI) is not available at secondary users (SU)’s transmitters. Channel estimation error and feedback channel propagation delay are two source that provide the channel uncertainty. In this paper, resource allocation problem considering hybrid sharing scheme with uncertainty assumptions for the interference channel gain is investigated. First, sensitivity of optimal solution is evaluated under the interference channel uncertainty. It is found that the determination of the Lagrangian variables in a multiuser network acquires a complex iterative method since the number of constraints is increased by the size of PU’s network linearly. Moreover, an idle subcarrier grouping approach is proposed to deal with such a complex iteration problem. The resource allocation with imperfect CSI of the interference channel is discussed and a suboptimal solution is proposed. The numerical results show that the SU’s capacity is improved for two proposed schemes compared with the conventional algorithms. Indeed, the interference power level is unchanged by increasing the transmit power for the proposed algorithms.