Adaptive eigenmodes beamforming and interference alignment in underlay and overlay cognitive networks

Abstract

This paper considers a cognitive network that comprises one multi-input multi-output (MIMO) primary link and one MEMO secondary link for the underlay and overlay modes. In the underlay mode, instead of using water-filling algorithm to maximize the primary rate selfishly, we propose adaptive number of eigenmodes beamforming (ANEB) algorithm for the primary user (PU), which can adjust the number of PU's eigenmodes to meet its rate requirement The secondary user (SU) coexists with the PU using interference alignment (IA) scheme. In the overlay mode, the secondary transmitter has non-causal knowledge of the primary message and helps with the primary transmission. We combine IA algorithm with power allocation scheme to maximize the SU's rate as well as meet the PU's rate requirement Finally, numerical simulation results show that our scheme is win-win for both the PU and SU.