On the Universality of Sequential Slotted Amplify and Forward Strategy in Cooperative Communications

While cooperative communication has many benefits and is expected to play an important role in future wireless networks, many challenges are still unsolved. Previous research has developed different relaying strategies for cooperative multiple access channels (CMA), cooperative multiple relay channels (CMR) and cooperative broadcast channels (CBC). However, there lacks a unifying strategy that is universally optimal for these three classical channel models. Sequential slotted amplify and forward (SSAF) strategy was previously proposed to achieve the optimal diversity and multiplexing tradeoff (DMT) for CMR. In this paper, the use of SSAF strategy is extended to CBC and CMA, and its optimality for both of them is shown. For CBC, a CBC-SSAF strategy is proposed which can asymptotically achieve the DMT upper bound when the number of cooperative users is large. For CMA, a CMA-SSAF strategy is proposed which even can exactly achieve the DMT upper bound with any number of cooperative users. In this way, SSAF strategy is shown to be universally optimal for all these three classical channel models and has great potential to provide universal optimality for wireless cooperative networks. Index Terms Cooperative networks, transmission strategy, sequential slotted amplify and forward (SSAF), diversity and multiplexing tradeoff, relay. This work was published in part in the IEEE International Conference on Communications 2009 (ICC 2009), Dresden, Germany, June 2009. The authors are with Department of Electrical and Electronic Engineering, Imperial College London, London SW7 2AZ, UK (e-mail: [email protected]; [email protected]; [email protected]).