Adaptive spatial modulation for spectrally-efficient MIMO spectrum sharing systems

We have recently introduced adaptive spatial modulation (ASM) [1], which comprises both adaptive modulation (AM) and spatial modulation (SM), with the aim of enhancing the average spectral efficiency (ASE) of multiple antenna systems. This technique was shown to offer high energy efficiency and low system complexity thanks to the use of SM while achieving high data rates thanks to the use of AM. Motivated by this technique and the need of such performance in a cognitive radio (CR) scenario, we extend in this paper the concept of ASM to a spectrum sharing system. In this context, we propose the ASM-CR scheme as an energy-efficient, spectrally-efficient, and low-complexity scheme for CR systems. Compared to selected existing spectrum sharing schemes, ASM-CR is shown to offer a considerable ASE improvement while experiencing a slight degradation in the average bit error rate (ABER) performance. In order to address this, a hybrid scheme compromising between ASE and ABER is proposed. The performance of both proposed schemes is analyzed in terms of ASE and ABER and confirmed with selected numerical results using Monte-Carlo simulations.