Cross-layer adaptive modulation and coding design for space-time block coded MIMO–OFDM systems

This paper developed a cross-layer adaptive modulation and coding (AMC) design for space-time block coded (STBC) MIMO–OFDM systems, which combines the AMC at the physical layer with an automatic repeat request (ARQ) protocol at the data link layer, in order to maximize spectral efficiency under specified delay and packet error ratio (PER) constraints. The transmission mode for each subcarrier is updated frame-by-frame to match the time-varying channel conditions, in order to take full advantage of the OFDM systems. The proposed cross-layer AMC design is also incorporated with STBC to further improve the system performance. Numerical results have demonstrated that retransmission at the data link layer alleviate rigorous error-control requirements at the physical layer and thereby allows higher data rate transmission. It is shown that this cross-layer design has achieved considerable spectral efficiency gain in comparison with traditional AMC without cross-layer design. Note that increasing the maximum number of retransmissions beyond one has little effect on spectrum efficiency and will cause longer system delay. This suggests that a desirable trade-off between spectral efficiency and delay in the STBC MIMO–OFDM system is achieved by a small number of retransmission.