Weighted Sum Rate Maximization for Downlink OFDMA With Subcarrier-Pair Based Opportunistic DF Relaying

This paper addresses a weighted sum rate (WSR) maximization problem for downlink OFDMA aided by a decode-and-forward (DF) relay under a total power constraint. A novel subcarrier-pair based opportunistic DF relaying protocol is proposed. Specifically, user message bits are transmitted in two time sl...

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Bibliographic Details
Published in:	IEEE transactions on signal processing Vol. 61; no. 10; pp. 2512 - 2524
Main Authors:	Tao Wang, Glineur, Francois, Louveaux, Jeme, Vandendorpe, Luc
Format:	Journal Article
Language:	English
Published:	New York, NY IEEE 01-05-2013 Institute of Electrical and Electronics Engineers The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subjects:	Algorithms Applied sciences Array signal processing Benchmark testing Convex optimization decode and forward Detection, estimation, filtering, equalization, prediction Exact sciences and technology Information, signal and communications theory Mathematical analysis Mathematical models Maximization Multiplexing OFDM Optimization orthogonal frequency division multiple access Protocol Protocols Relay Relaying Relays resource allocation Resource management Signal and communications theory Signal processing algorithms Signal, noise Studies subcarrier pairing Subcarriers Telecommunications and information theory transmit beamforming Performance evaluation Relaying Relay Resource allocation Frequency division multiple access Downlink Polynomial method Subcarrier Convex programming Beam forming Implementation Optimization Convex optimization Relaxation method Routing protocols decode and forward subcarrier pairing orthogonal frequency division multiple access Transmission protocol Algorithm transmit beamforming Orthogonal frequency division multiplexing Signal processing Transmission mode Resource management
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Summary:	This paper addresses a weighted sum rate (WSR) maximization problem for downlink OFDMA aided by a decode-and-forward (DF) relay under a total power constraint. A novel subcarrier-pair based opportunistic DF relaying protocol is proposed. Specifically, user message bits are transmitted in two time slots. A subcarrier in the first slot can be paired with a subcarrier in the second slot for the DF relay-aided transmission to a user. In particular, the source and the relay can transmit simultaneously to implement beamforming at the subcarrier in the second slot. Each unpaired subcarrier in either the first or second slot is used for the source's direct transmission to a user. A benchmark protocol, same as the proposed one except that the transmit beamforming is not used for the relay-aided transmission, is also considered. For each protocol, a polynomial-complexity algorithm is developed to find at least an approximately optimum resource allocation (RA), by using continuous relaxation, the dual method, and Hungarian algorithm. Instrumental to the algorithm design is an elegant definition of optimization variables, motivated by the idea of regarding the unpaired subcarriers as virtual subcarrier pairs in the direct transmission mode. The effectiveness of the RA algorithm and the impact of relay position and total power on the protocols' performance are illustrated by numerical experiments. It is shown that for each protocol, it is more likely to pair subcarriers for relay-aided transmission when the total power is low and the relay lies in the middle between the source and user region. The proposed protocol always leads to a maximum WSR equal to or greater than that for the benchmark one, and the performance gain of using the proposed one is significant especially when the relay is in close proximity to the source and the total power is low. Theoretical analysis is presented to interpret these observations.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	1053-587X 1941-0476
DOI:	10.1109/TSP.2013.2245326