Ant Colony Optimization approach to interference minimizing code assignment in cognitive CDMA networks

In this paper we focus on the problem of code assignment to cognitive users in a synchronous underlay network using Code Division Multiple Access (CDMA) scheme. No knowledge of the spreading codes used by the primary CDMA network is available to the cooperative secondary users a priori, other than the spreading factor. An evolutionary algorithm of relatively low complexity order is proposed based on Ant Colony Optimization (ACO) for assigning spreading codes to secondary users such that the mutual interference between existing secondary and primary users is minimized. This is accomplished at the secondary fusion center by minimizing the mean square cross-correlation between the candidate codes and the matrix which includes all independently received signals by the cooperative secondary users. Simulation results show that performance of the ACO-based method can converge to the optimal interference minimizing code assignment method while the complexity order is significantly reduced.