Related Works on Cooperative Wireless Networks

In this chapter, we introduce the background information and the related works on cooperative wireless networks. Cooperative communications at the physical layer enable single-antenna devices to reap the benefits of MIMO systems by sharing their antennas with each other to create a virtual MIMO system. Through cooperation at the physical layer, the channel reliability can be improved via spatial diversity. However, when multiple relay nodes are available, they access the wireless medium at the same time, which leads to packet corruption. Besides, wireless networks may also suffer from some other problems, such as time varying channel, mobility and limited power of the hosts, and hidden terminal problem caused by location-dependent carrier sensing. In order to overcome these problems and achieve good performance in wireless networks, the MAC layer should properly schedule the cooperative entities to achieve the cooperation gain. A cooperative MAC protocol may focus on either a non-diversity scenario or a diversity scenario. For the contention-based solutions, we classify the well-known proposals according to how they address two fundamental questions for user cooperation, i.e., when to cooperate and whom to cooperate with. According to how the entities (the source or the helper nodes) handle the above two questions, we classify the mainstream cooperative MAC protocols into three categories. In addition, we point out several challenging issues on MAC-layer cooperation that needs to be addressed properly.