Differentiated assignment of extrinsic information based on code weights of single parity check product code

Constant amplitude multi-code CDMA (CAMC) removes the amplitude fluctuation in multi-code CDMA, by which the large power consumption of a power amplifier with a strict linearity can be avoided. The nature of CAMC is a recursive single parity check product code (SPCPC). CAMC for N = 4^k is equivalent to k-dim SPCPC. As a top-level CAMC codeword is recursively constructed from lower-level codewords, log likelihood ratio (LLR), a priori information (API) and extrinsic information (El) of upper-level codewords are obtained as a function lower-level codewords. The codewords of CAMC were found to have fixed code weights, (N ± √ N)/2. In this paper, we show that differentiated assignment of El in the iterated decoding can boost the BER performance. If any of the lower-level codewords have weights other than the fixed value, the El associated with these erroneous lower-level codewords has lower confidence. El from a wrong codeword is given lower weights in the computation of LLR, API and El of the upper-level codeword. With differentiated assignment of El, the BER performance improved by 0.1~0.3 dB.