Title: Cooperative Strategies for Multihop Wireless Communications
Authors: Madhavan Vajapeyam, Urbashi Mitra (Poster II, 14)

ABSTRACT

In resource limited, large scale sensor networks, cooperative communication will occur over multiple hops to save power. Intermediate nodes between source and destination will thus act as cooperative relays. Herein, protocols coupled with space-time coding strategies are proposed and analyzed for distributed cooperative communication. The general scenario consists of a source node communicating to a destination node over L hops (L=1 is the direct/single-hop case); at each hop two relays participate. Amplify-and-forward type protocols are considered. The Alamouti-based scheme proposed by Hua et al is generalized for L>2 and the scheme is shown to achieve diversity d_L=2-(L- 1)log_P log P, where P is the total power used for transmission. For L=2 this result coincides with the analysis by Jing & Hassibi. Thus, for large, but finite P, the diversity decreases with L. Performance improvement over multiple hops can be achieved by employing larger block codes. Two new strategies that offer higher diversity gain for finite power P re proposed, for the specific case of L=3 hops. These schemes are based on the structure of rate-half and square-matrix embedded codes and are shown to achieve diversity d=2-log_P log P. Therefore, the new schemes preserve the same diversity of the 2 hop scheme by Hua.