On Exploiting Diversity and Spatial Reuse in Relay-enabled Wireless Networks

Relay-enabled wireless networks (eg. WIMAX 802.16j) represent an emerging trend for the incorporation of multi-hop networking solutions for last-mile broadband access in next generation wireless networks. The adoption of more sophisticated access technologies such as OFDM (orthogonal frequency division multiplexing) coupled with the relay-induced two-hop nature, provides two key benefits to these networks in the form of diversity and spatial reuse gains. However, leveraging these benefits calls for more sophisticated solutions, among which, user scheduling forms a key component. We consider the specific problem of scheduling users with finite buffers on the multiple OFDMcarriers (channels) over the two hops of the relay-enabled network. We propose scheduling algorithms that help leverage diversity and spatial reuse gains from these networks. We show that even the scheduling problem to exploit diversity gains alone is NP-hard and provide both theoretically and practically efficient polynomial-time algorithms with approximation guarantees. Building on the diversity solutions, we also propose an efficient polynomial-time scheduling algorithm for exploiting both spatial reuse as well as diversity. The proposed solutions are evaluated to highlight the relative significance of diversity and spatial reuse gains with respect to varying network conditions.