Overhearing Gain Analysis in Low-Traffic CDMA Wireless Sensor Networks

There have been trends in using spread spectrum channel accessing techniques in wireless sensor networks to mitigate the effect of potential collisions in concurrent transmissions and to increase the throughput as well as countering jamming-like noises. Overhearing of the data has been previously analyzed in cellular CDMA networks as this technique was first introduced for mobile communications with multiple transmitting users sending their data to a single base station which controls their transmission power. But sensor (and ad hoc) networks are usually devoid of any coordinating devices and the transmission is usually done toward different local destinations using distributed power controlling methods. This paper provides a systematic analysis of overhearing performance in low-traffic sensor networks especially when the sensing point is located somewhere at the middle of the network which is not necessarily near the sink. The distributed code assignment which is a key issue in infrastructureless CDMA networks has been taken into account in the development of a theoretical model. The result of this analysis shows that the higher the number of used codes, the higher is the gain of overhearing. Thus using this parameter, the network designer has statistical control over the amount of potential overheard data. We have also developed simulations of the proposed model and the results support the predictions of the theoretical model.