Joint adaptive spatial modulation and power adaptation for spectrum sharing systems with limited feedback

We have recently proposed adaptive spatial modulation (ASM) for multiple antenna systems with the aim of improving the energy efficiency through spatial modulation (SM) and improving the average spectral efficiency (ASE) through adaptive modulation. In this paper, we extend ASM to spectrum sharing systems in an effort to improve the secondary system's performance in terms of energy efficiency and ASE. Based on a limited feedback from the primary user (PU), the secondary transmitter (ST) uses power adaptation in order to maximize its ASE while respecting a peak interference constraint to the PU. When compared to the recently-proposed fixed power scheme (FPS), the adaptive power scheme (APS) proposed in this paper offers lower transmission delays, higher effective throughput, and comparable error performance. In this work, we analyze the performance of APS in terms of ASE, effective throughput, and average bit error rate (ABER). We also provide several simulations through which we corroborate these analytical results.