Title: Cooperative Coding for Wireless Networks: Cluster Behavior via a Geometric Distance Profile
Authors: Ruoheng Liu, Predrag Spasojevic, Emina Soljanin (Poster I, 13)

ABSTRACT

We study an incremental redundancy (IR) cooperative coding scheme for wireless networks. Our scheme enhances the network performance by embedding IR cooperative coding into an existing noncooperative route. To exploit the spatial diversity benefit we, based on a quasi-static Rayleigh fading channel model which also incorporates the geometric distance profile of the network, propose a cluster-based collaborating strategy as follows. For each of the noncooperative hops, we form a collaborating cluster of M nodes consisting of the (hop) sender and its M-1 neighbors. The transmitted message is encoded using a mother code and partitioned into M blocks corresponding to each of M slots. In the first slot, the (hop) sender broadcasts its information by transmitting the first block with its neighbors attempting to decode this message. In the remaining slots, each of the leftover M-1 blocks is sent either through a neighbor which has decoded the message or directly by the (hop) sender where a dynamic schedule is based on the ACK-based feedback within the cluster. By employing the so called good codes (e.g., turbo, LDPC, and raptor codes) whose performance is characterized by a threshold behavior, our approach improves the reliability of multi-hop routing through not only cooperation diversity benefit but also a coding advantage.

The study of the diversity and the coding gain of the proposed scheme is based on a frame-error rate (FER) performance analysis. A maximum-likelihood decoding FER upper bound and its asymptotic (in SNR) version are derived as a function of channel SNRs and the mother code noise threshold. These bounds exhibit a full cooperation diversity gain in the high SNR regime and, furthermore, guide a geometric distance based cluster design which achieves the spatial diversity benefit.