Performance improvement of transmission links in overlay cognitive radio through interference alignment

Abstract

In this paper we propose a method to enhance the performance of both the primary and secondary links through interference alignment (IA) in an overlay cognitive scheme. We consider a cognitive network in which multiple multi-input multi-output (MIMO) secondary users (SUs) seek to overlay their signals with an existing MIMO primary user (PU). Since in overlay scheme, the cognitive transmitters have knowledge of the primary message, they can improve or maintain the communication of the PU. IA enables the SUs to enhance their performance without causing/receiving any interference to/from the PU while also improve the rate of the primary link. We try to enhance the performance of the users in two different scenarios. In the first one, the SUs assign part of their power to assist the primary transmission to reach its target rate and the remaining power for their own communication. In the second one, the SUs allocate part of their power for their own transmissions to reach their target sum rate and the remainder to assist the primary transmission. In addition, we employ power allocation method as an important issue to further improve the performance of the cognitive users. The analytical results are confirmed through simulations.