Spreading-Hopping Tradeoff in Wideband Ad-hoc Communications

We explore the tradeoff between hopping and spreading in a wideband spread spectrum transmitter-receiver link in an ad-hoc network with multi-user interference. The receiver is assumed to track the user´s channel, spreading signature and the overall SINR. Using expressions for the ergodic capacity of the link, we determine the amount of spreading required that maximizes the link capacity. As a comparison we also discuss optimal spreads in centralized architectures where the receiver has interference knowledge. While we find that in general a combination of spreading and hopping may achieve higher throughputs than either pure spreading or pure hopping, we prove that pure hopping and pure spreading are optimal strategies for ad-hoc networks at low SINR and for centralized networks at all SINR, respectively. Numerical results suggest that in an ad-hoc network, spreading is beneficial at high SNR.