Exploiting Multi-User Diversity and Multi-Hop Diversity in Dual-Hop Broadcast Channels

Ammar Zafar, Mohammad Shaqfeh, Mohamed-Slim Alouini, Hussein Alnuweiri
2013 IEEE Transactions on Wireless Communications  
We propose joint user-and-hop scheduling over dual-hop block-fading broadcast channels in order to exploit multi-user diversity gains and multi-hop diversity gains all together. To achieve this objective, the first and second hops are scheduled opportunistically based on the channel state information. The joint scheduling problem is formulated as maximizing the weighted sum of the long term achievable rates of the users under a stability constraint, which means that in the long term the rate
more » ... eived by the relay should equal the rate transmitted by it, in addition to power constraints. We show that this problem is equivalent to a single-hop broadcast channel by treating the source as a virtual user with an optimal weight that maintains the stability constraint. We show how to obtain the source weight either off-line based on channel statistics or on real-time based on channel measurements. Furthermore, we consider special cases including the maximum sum-rate scheduler and the proportional fair scheduler. We also show how to extend the scheme into one that allows multiple user scheduling via superposition coding with successive decoding. Numerical results demonstrate that our proposed joint scheduling scheme enlarges the rate region as compared to scheduling schemes that exploit the diversity gains partially. Index Terms-Broadcast channels, dual-hop, block-fading, multi-hop diversity, multi-user diversity, joint scheduling, optimal resource allocation. Ammar Zafar (S'12) received his B.E. and M.Sc. degrees in electrical engineering from National University of Sciences and Technology (NUST), Pakistan, in 2007 and 2009, respectively. He joined the Department of Electrical Engineering at King Abdullah University of Science and Technology (KAUST) in August 2010, where he is currently a Ph.D student. His research interests include wireless communication theory, cognitive radio networks, cooperative networks and multiuser scheduling. Mohammad Obaidah Shaqfeh (S'07-M'09) received the B.Sc. degree in electrical engineering (communications stream) from United Arab Emirates University in 2003 and the M.Sc. degree in communications technology from Ulm University, Germany in 2005. He received the Ph.D. degree from
doi:10.1109/tw.2013.060413.121136 fatcat:hzeevof4ijg5nfjwrrahxdbvwa