A simple low rate turbo-like code design for spread spectrum systems

In this paper, we introduce a simple method to construct very low rate recursive systematic convolutional codes from a standard rate-1/2 convolutional code. These codes in turn are used in parallel concatenation to obtain very low rate turbo like codes. The resulting codes are rate compatible and require low complexity decoders. Simulations results show that an additional coding gain of 0.9 dB in additive white Gaussian noise (AWGN) channel and 2 dB in Rayleigh fading channel is possible compared to rate-1/3 turbo code. The low rate coding scheme increases the capacity by more than 25% when applied to multiple access environments such as code division multiple access (CDMA).