A novel approach to channel coding without bandwidth expansion

This paper introduces a new block coding technique without bandwidth expansion. The proposed technique derives from the multiple access concept recently introduced to increase the number of users on a multiple access channel. The basic principle consists of time spreading the parity-check symbols to the block length using Walsh-Hadamard (WH) sequences and superimposing the resulting signals to the block of information symbols. The interference between the two groups of symbols is handled using an iterative detection/decoding technique whose operation resembles that of turbo decoders. Several code constructions are presented using very simple block codes. Performance of the proposed coding technique is evaluated by means of computer simulations. After observing that correlation of the intermediate decision errors in this iterative detection/decoding process limits the achievable performance, a block interleaver is introduced and is shown to substantially reduce the performance degradation due to interference between the serially transmitted symbols and the WH-spread symbols.