Extrinsic information in iterated decoding of fixed weight codewords

Constant amplitude multi-code (CAMC) CDMA is generated by spreading of lower dimensional codewords concatenated with bit-by-bit parity vectors. CAMC has dual aspects of a spread spectrum signal and a product code. Error correcting methods for CAMC are based either on processing gain in spread spectrum, or on iterative decoding of product codes. The weights of CAMC codewords are fixed at two symmetrical values. In this paper, we present performance improvement of CAMC by the control of extrinsic information (EI) in the iterated decoding of CAMC. The control is based on whether the decomposed codewords have the correct weights, or not. Preferred assignment of EI on correct weight and as a predictor of despreading brings an improvement in BER performance of 0.1 ~ 0.3 dB.