Abstract: An analytical model for performance evaluation of unslotted spread spectrum ad hoc networks is presented by introducing a queuing system and a Markov chain. The model is used to derive packet success probability and expressions for calculating throughput and delay. Based on the derived expressions, the impacts of received SNR, packet length, and spreading gain are discussed in terms of throughput and delay. Numerical results show that a significant improvement in throughput and delay can be obtained by raising SNR at low SNR. However, raising SNR does not improve performance further when SNR>30 dB. Nonetheless, throughput and delay can be improved by reducing the packet length. In addition, improvement of delay performance is acquired when the spreading gain increases. There is an optimal value of spreading gain to maximize the normalized throughput due to the fact that spread spectrum transmission occupies an additional bandwidth.

Key words: spread spectrum ad hoc, throughput, transmission delay, Markov chain