A source coding and modulation method for power saving and interference reduction in DS-CDMA sensor network systems

A source coding and modulation technique for reducing multiple access interference (MAI) as well as for reducing power consumption in DS-CDMA wireless sensor network systems is presented. Source symbols are represented by a special coding, termed minimum energy coding (ME coding), which exploits redundant bits for saving power when transmitted via RF links with on-off-keying. Since energy is consumed mostly when high bits are transmitted, the ME coding represents source symbols with the least number of high bits, given an extended word length. When each channel uses the ME coding combined with a spreading code and OOK, fewer high bits are transmitted. It is shown that signal-to-noise ratio is significantly increased and that the error probability is lowered as well. First, the communication system architecture of this low MAI DS-CDMA is described, followed by the principle of interference reduction. Second, a signal model is obtained for the new source coding and transmission process. Third, guidelines for designing the length of codeword, the number of communication channels, and power efficiency are obtained. A RF sensor network system is designed.