Adaptive Modulation and Coding for IEEE 802.11n

We propose a link adaptation technique for IEEE 802.11n MIMO-OFDM systems with convolutional coding. The technique dynamically selects the best modulation and coding scheme (MCS) based on channel conditions and on the medium access control (MAC) layer performance (coded BER or PER) requested by applications. We show that the coded performance at decoder output can be modeled as a function of decoder-input uncoded BER and the code rate. For MIMO-OFDM systems with different modulation types for different spatial streams at each subcarrier, we propose a simple and accurate method for computing the BER for each spatial stream mixed from different subcarriers. We also discuss approaches for searching and selecting the MCS.