Adaptive MCS Selection with Dynamic and Fixed Sub-channelling for Frequency-Coherent OFDM Channels

This paper presents two strategies for joint adaptive modulation and coding (AMC) techniques. The first strategy is based on the fixed sub-channel (FS)-AMC allocation, which exploits the coherence bandwidth of the wireless channel to divide the transmitted frame into independent sub-channels that correspond to the channel coherence bandwidth as well as selecting the optimal modulation and coding scheme (MCS) for each individually. The second strategy is based on dynamic sub-channel (DS)-AMC allocation, reduces the size of pilot sub-carriers for the stable sub-channel profiles; where the redundant pilots are replaced with additional data sub-carriers, which enhance the total system throughput. These strategies are implemented for orthogonal frequency division multiplexing (OFDM) systems with channel state information (CSI) feedback. Low density parity check (LDPC) codes are utilized for encoding by employing signal-to noise ratio (SNR) dependent coding rates, as well as distinct modulation schemes to achieve adaptivity to time-varying channel conditions. The performance of the proposed system was tested on Rayleigh fading channels that exhibit frequency coherent bands. Numerical results obtained via simulation demonstrate that the throughput and bit error rate (BER) performances of both proposed systems are better than previously suggested approaches. Additionally, there is a significant improvement in the throughput performance of the dynamic sub-channel allocation strategy over the fixed sub-channel allocation method.