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DESIGN AND ANALYSIS OF MULTISTAGE COOPERATIVE BROADCAST WITH AMPLIFY AND FORWARD RELAYS by Bhargava Yammanuru Cooperative communication achieves spatial diversity by having the transceivers in an ad-hoc network pool their resources at the physical layer and cooperatively transmit their information. For this to be possible without adding a large overhead, we need low overhead-distributed protocols. This thesis proposes one such distributed scheme for wireless ad-hoc networks. In this work, we study the propagation of the signal in a cooperative network where a single source message is retransmitted by multiple stages (levels) of relays. Relays are assumed to have limited computational abilities and hence adopt the amplify-and-forward scheme. At each node, cooperative diversity is obtained by combining the signals from the multiple levels of relays (in different time slots) using a matched filter. The network is distributed in the sense that the levels are not predetermined and are formed based on the decisions made independently at each node. The retransmission criterion is based on the signal-to-noise ratio (SNR) of the signal after the matched filtering operation. If the received SNR is greater than the SNR threshold then the signal is retransmitted. The parameter SNR threshold plays a critical role in determining the broadcast rate. We provide the expressions for the received signal at each node as the message is forwarded in the network. We study the channel and noise statistics for a specific realization of a network. We also recursively characterize the effective channel, and accumulated noise. We study the effects of noise accumulation, the number of levels used in the signal combination and the decoding and retransmission threshold on the number of nodes that successfully receive the message.

Design and analysis of multistage cooperative broadcast with amplify and forward relays