Adaptive Threshold Estimation for Variable Rate MQAM in Full-Duplex Systems With Imperfect CSI

The adaptive threshold estimation algorithm for discrete variable rate M-ary quadrature amplitude modulation (VR-MQAM) is investigated in full-duplex (FD) systems with imperfect channel state information (CSI). First, detailed FD system modeling is carried out, taking into account the differences from the half-duplex systems on rate adaptations. Then, in this model, we obtain the closed-form expression of the VR-MQAM spectral efficiency by deriving the distribution of the received signal to interference and noise ratio (SINR). Finally, we propose an adaptive threshold estimation scheme for VR-MQAM, which can adapt to the variation of imperfect CSI as well as residual self-interference (SI). Numerical results reveal that both residual SI and CSI imperfection depress the performance of VR-MQAM. Comparing to the existing variable threshold scheme, our adaptive scheme improves the spectral efficiency without any extra complexity.