Cooperative Wireless Networking Beyond Store-and-Forward

In future wireless networks devices may cooperate to form logical links. Each of these links may consist of several independent physical channels which are shared by the cooperating partners. Even without multiple antennas this cooperation provides diversity in time and space. This so-called cooperation diversity increases the robustness of the link vs. fading and interference. After surveying approaches in cooperation diversity we focus on optimizing its performance by combining several cooperation schemes and by integrating cooperation into space-time coding. For multiple scenarios, we further discuss the factors and benefits introduced by user cooperation and how cooperation-aware resource allocation can be employed to further increase the performance of cooperative networks. When it comes to implementation, the question arises how cooperation can be integrated efficiently into existing wireless networks. A case study for 802.11-based WLANs reveals the issues that need to be solved in order to deploy cooperative techniques. We provide an overview of the state of the art in implementing cooperation approaches, analyze how appropriate these approaches solve the issues, and, where appropriate, point out their deficiencies. We conclude with a road map for future research necessary to tackle these deficiencies for the practical implementation of cooperation in next generation mesh, WLAN, WMAN, and cellular standards.