Generalized Self Spread-Spectrum Communications with Turbo Soft Despreading and Decoding

Abstract: Self-spreading (SSP) is a spread spectrum technique where the spreading sequence is generated from data bits. Al-though SSP allows communications with low probability of inter-ception by unintended receivers, despreading by the intended re-ceiver is prone to error propagation. In this paper, we propose both a new transmitter and a new receiver based on SSP with the aim to a) reduce error propagation and b) increase the conceal-ment of the transmission. We first describe a new technique for the generation of SSP spreading sequence, which generalizes SSPs of existing literature. We include also coding at the transmitter, in order to further reduce the effects of error propagation at the re-ceiver. For the receiver, we propose a turbo architecture based on the exchange of information between a soft despreader and a soft-input soft-output decoder. We design the despreader in order to fully exploit the information provided by the decoder. Lastly, we propose a chip decoder that extracts the information on data bits contained in the spreading sequence from the received signal. The performance of the proposed scheme is evaluated and compared with existing spread-spectrum systems. Index Terms: Low probability of interception, self spread spec-trum, turbo despreader. I