Adaptive modulation using orthogonal STBC in MIMO Nakagami fading channels

Orthogonal space-time block coding (STBC) provides a full diversity gain over the MIMO fading channel while allowing simple linear decoding at the receiver. We consider adaptive modulation (AM) using STBC in the presence of Nakagami fading. For this type of fading channel, we first derive the outage and Shannon (ergodic) capacities of the STBC diversity scheme. We then assess the performance of AM using M-ary quadrature amplitude modulation (M-QAM) in terms of three metrics, namely, the outage probability, the average bit error rate (BER), and the average spectral efficiency. As a reference point, we also derive the average BER for nonadaptive binary phase shift keying (BPSK) used in conjunction with STBC. It is shown that AM allows the Shannon capacity of STBC to be approached and yields a significant performance enhancement compared to fixed modulation schemes.