On Cooperative Broadcast in MANETs with Imperfect Clock Synchronization

This paper considers the evaluation of the characteristics of the channel that arises in the context of cooperative broadcast in mobile ad-hoc networks (MANETs) with practical radios, and tackles the problem of detection with affordable frequency domain receivers. When multiple nodes use cooperative signalling to transmit a signal to a destination, their clock offsets, oscillator drifts, and non-negligible propagation delays yield an equivalent doubly-selective channel seen from any destination node's point-of-view. For demanding applications with high data rate requirements, this equivalent cooperative channel needs to be mitigated with physical layer signal processing. In the first part of the paper, statistical characteristics of the power-delay profile of the equivalent cooperative transmission channel are modelled to gain a better understanding of its behaviour. This preliminary analysis points out that equalization is required to successfully carry out cooperative broadcast. Next, conventional linear frequency domain equalizer (FDE) and a recently proposed non-linear FDE based on Bayesian inference, are considered for the equalization of the aforementioned channels. The detection performance of these receivers is evaluated in some critical channels which can jeopardize the robustness of the cooperative links, identified with the preliminary statistical analysis. Numerical results indicate that, non-linear but low-complexity frequency domain receivers are attractive solutions for cooperative broadcast, especially within high-data rate applications.