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Li Fei 1 and Yi Chen 1 and Qiang Gao 1 and Xiao-Hong Peng 2 and Qiong Li 3
Academic Editor:Bulent Tavli
1, School of Electronic and Information Engineering, Beihang University, Beijing 100191, China
2, School of Engineering and Applied Science, Aston University, Birmingham B4 7ET, UK
3, Datang Wireless Mobile Innovation Center, Beijing 100191, China
Received 15 July 2014; Accepted 1 October 2014; 22 February 2015
This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1. Introduction
Extending the lifetime of wireless sensor networks (WSNs) is critical due to the limited energy supply of sensor nodes. Much research effort has been devoted to addressing this challenge through improving energy efficiency. Recently, the energy hole problem has been regarded as another key factor that seriously confines the network lifetime [1-3]. The cause of energy hole lies in the intrinsic many-to-one traffic pattern of WSNs. Nodes nearer to the sink carry heavier traffic loads, leading to more energy consumption. This unbalanced energy consumption phenomenon results in an energy hole around the sink. When the energy hole appears, no more data can be delivered to the sink. The network lifetime ends prematurely while a large amount of energy is unused. Experimental results in [4] show that up to 90 percent of the energy of a network would be left unused when the network lifetime is over.
Several approaches have been proposed to mitigate the energy hole problem in WSNs. Works in [5-7] deploy more nodes in heavy-loaded areas, which is known as the nonuniform deployment scheme. Another form of this scheme is to equip nodes closer to the sink with more initial energy [8]. Topology control strategies are proposed in [9-13], in which nodes collaboratively adjust their transmission power and form a proper network topology to balance energy consumption. In all above approaches, the data are transmitted through the single-input single-output (SISO) method.
Recently, cooperative communication has been applied to WSNs to enhance network performance, such as reliability, throughput, and coverage [14-16]. Energy efficiency can also be improved through this technique by exploiting the spatial diversity gain generated [17-20]. Moreover, since it allows the distributed nodes...