Cross‐layer design of T‐ARQ and adaptive modulation and coding in a spectrum sharing with cooperative relaying system

This study presents an analysis for a cross‐layer design of a combined adaptive modulation and coding (AMC) with a truncated automatic repeat request (T‐ARQ) scheme in an underlay spectrum sharing cognitive radio employing an amplify‐and‐forward cooperative relaying system. The considered AMC employs a coded M‐ary quadrature amplitude modulation scheme combined with a T‐ARQ to improve the performance of the secondary user (SU) system in the considered cognitive radio. To establish the performance analysis, the cumulative distribution function (CDF) of the end‐to‐end signal‐to‐noise‐ratio at the receiver side of the SU system is derived. Then, using the derived CDF, closed‐form expressions are derived for three important performance metrics: the average spectral efficiency, the average packet‐error‐rate, and the outage probability. To evaluate the performance of the considered system, numerical results obtained from the derived closed‐form formulas are presented and compared. In addition, to verify the validity of the analysis, Monte–Carlo simulation results are also provided.