Green Resource Allocation in OFDMA Networks with Opportunistic Beamforming-Based DF Relaying

Tao WANG  Mingfang WANG  Yating WU  Yanzan SUN  

Publication
IEICE TRANSACTIONS on Communications   Vol.E102-B   No.8   pp.1715-1727
Publication Date: 2019/08/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.2018EBP3169
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
Keyword: 
energy efficiency,  OFDMA,  beamforming,  subcarrier pair,  cooperative communication,  

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Summary: 
This paper proposes an energy efficiency (EE) maximized resource allocation (RA) algorithm in orthogonal frequency division multiple access (OFDMA) downlink networks with multiple relays, where a novel opportunistic subcarrier pair based decode-and-forward (DF) protocol with beamforming is used. Specifically, every data transmission is carried out in two consecutive time slots. During every transmission, multiple parallel paths, including relayed paths and direct paths, are established by the proposed RA algorithm. As for the protocol, each subcarrier in the 1st slot can be paired with any subcarrier in 2nd slot to best utilize subcarrier resources. Furthermore, for each relayed path, multiple (not just single or all) relays can be chosen to apply beamforming at the subcarrier in the 2nd slot. Each direct path is constructed by an unpaired subcarrier in either the 1st or 2nd slot. In order to guarantee an acceptable spectrum efficiency, we also introduce a minimum rate constraint. The EE-maximized problem is a highly nonlinear optimization problem, which contains both continuous, discrete variables and has a fractional structure. To solve the problem, the best relay set and resource allocation for a relayed path are derived first, then we design an iterative algorithm to find the optimal RA for the network. Finally, numerical experiments are taken to demonstrate the effectiveness of the proposed algorithm, and show the impact of minimum rate requirement, user number and circuit power on the network EE.