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Cooperative communication aims to achieve spatial diversity gain via the cooperation of user terminals in transmission without requiring multiple transceiver antennas on the same node. It employs one or more terminals as relays in the neighbourhood of the transmitter and the receiver, which collaborate in the transmission and serve as a virtual MIMO antenna array. Allowing cooperation in wireless communication engenders new problems related to resource allocation and relay selection. Optimal relay selection is vital for reaping the performance benefit of cooperative communication. It is a challenging task to share channel information in timely and distributed manner and at the same time make optimal selection of relay in a time varying radio environment. This paper presents a comprehensive survey of distributed relay selection schemes for cooperative communication that have been proposed in the literature. We discuss various classifications of relay selection schemes and describe their characteristics and functionality. We then present a qualitative comparison of their performance against a set of representative metrics. Finally, we discuss some of their shortcomings and suggest some research directions.

Cellular networks, e.g. UMTS, provide voice and data services to mobile users. In hot spots where users need high speed data services operators can deploy low-cost high-speed WLANs, e.g. 802.11, to cover hot-spots. This paper proposes a possible architecture of integrating UMTS and 802.11 WLAN. The architecture allows a mobile node to maintain data (PS) connection through WLAN and voice (CS) connection through UMTS in parallel. This is especially attractive because WLAN is currently used primarily for high-speed best-effort data service only.

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