Adaptive Puncturing for Coded OFDMA Systems

A scheme is proposed for adaptively changing the code rate of coded OFDMA systems via changing the puncturing rate within a single codeword (SCW). In the proposed structure, the data is encoded with the lowest available code rate then it is divided among different resource blocks (tiles) where it is punctured adaptively based on some measure of the channel quality for each tile. The proposed scheme is compared against using multiple codewords (MCWs) where the transmitter divides the data over tiles and encodes them separately. We investigate two different adaptive modulation and coding (AMC) selection methods. The first is a recursive scheme that operates directly on the SNR whereas the second operates on the effective SNR value that is obtained using Mutual Information Effective SNR Mapping (MIESM). We then compare our scheme to Per-Frame Adaptation (PFA) where we fix the modulation and coding scheme (MCS) over a given frame. We show via simulations that when using the recursive rate selection method the SCW scheme significantly outperforms the MCWs and the PFA. It is also shown that applying the MIESM rate selection method, the PFA improves significantly, yet the SCW scheme is the best performer. We also introduce a novel interleaving method prior to puncturing that improves the performance for certain restricted adaptation mechanisms.