ACHIEVEMENT DESCRIPTION Optimal ARQ Protocol For Multihop MIMO Relay Networks Yao Xie, Deniz Gunduz, Andrea Goldsmith IMPACT NEXT-PHASE GOALS ACHIEVEMENT DESCRIPTION STATUS QUO NEW INSIGHTS MAIN RESULTS 3D DMDT Surfaces for Various ARQ protocols ((4,1,3) system) ASSUMPTIONS AND LIMITATIONS: Long-term/short-term static channel Total number of ARQ rounds is L Decode-and-forward relaying strategy Channel state information at Rx, Rayleigh fading Closed form solution for special cases and DMDT as a solution of a convex optimization problem in general Found optimal ARQ protocol in multihop MIMO relay networks. Characterized DMDT surfaces provide insights for practical optimal ARQ protocols design. diversity What is the rate-reliability-delay tradeoff in multihop MIMO relay networks? Fractional variable L = 1 There are Diversity-multiplexing tradeoff (DMT) analysis for relay channel •Diversity-multiplexing-delay tradeoff (DMDT) for point-to-point MIMO with ARQ Block variable multiplexing Block Variable ARQ Fractional Variable ARQ L = 10 (2,2,2) system Long-term We characterize the diversity-multiplexing-delay tradeoff (DMDT) surface for various ARQ protocols •Theorem: the fractional variable ARQ protocol achieves optimal DMDT “Relay should talk ASAP” ARQ 1 ARQ 2 diversity H1 H2 How it works: ARQ protocols in the MIMO relay networks Short-term Optimal Operational Point What technical challenge is being undertaken on behalf of the project We characterized the 3D diversity-multiplexing-delay tradeoff (DMDT) surfaces for a multihop MIMO relay network. We also found the optimal ARQ protocol that achieves the optimal DMDT. 2. Why is it hard and what are the open problems We don’t know what is the optimal ARQ protocol for the relay network. Moreover, DMDT analysis for this type of channel is an open problem, especially for the short-term static channel assumption. 3. How has this problem been addressed in the past The diversity-multiplexing tradeoff (DMT) analysis for point-to-point MIMO and relay MIMO channel have been addressed; the diversity-multiplexing-delay tradeoff (DMDT) analysis only been done for the point-to-point MIMO and relay with single antenna case. DMDT for multi-hop MIMO relay channel case has not been done. 4. What new intellectual tools are being brought to bear on the problem Large deviation techniques in formulating a problem to find the DMDT surface. Convex optimization in solving the problem. 5. What is the main intermediate achievement We characterized the DMDT for this system both in the long-term and short-term static channel. Based on this, we proved the optimal ARQ protocol is the fractional variable ARQ. 6. How and when does this achievement align with the project roadmap (end-of-phase or end-of-project goal) These achievements marks an end-of-phase. 7. What are the even long-term objectives and consequences? Ultimately, we would look at the effects of power control in the ARQ protocol. We would also extend the DMDT result to joint source-channel coding for the MIMO multihop relay channel. 8. Which thrusts and SOW tasks does this contribution fit under and why? This fits into the second thrust: layerless dynamic networks. ARQ is an network protocol, whereas a DMT is previously a performance metric for physical layer. This work helps with combining network and physical layer design. Draft of this paper can be downloaded at: www.stanford.edu/~yaoxie/MH_DMDT_021909_v1.pdf rate Optimal ARQ protocol for general relay networks Effects of power control Joint source-channel coding in MIMO relay networks ARQ protocol provides one more dimension of tradeoff in MIMO relay networks.