Bit manipulation techniques for LDPC coding in OFDM

This work considers a wireless OFDM system employing a short-length, regular, low density parity check code (LDPC) when only limited feedback is available between receiver and transmitter. Methods are discussed for combining the advantages of LDPC codes with adaptive techniques, when the transmitter is subject to a restricting spectral mask. 0.5 dB gain is demonstrated when combining a regular, rate-half, LDPC code with adaptive bit-permutation using a constant modulation scheme over all subchannels. Gains of up to 1.5 dB are reported when combining this code with a BER-optimized adaptive bit-loading technique.