Bidirectional regenerative half-duplex relaying using relay selection

We consider the problem of relay selection in a network with N relay nodes. A half-duplex relay node enables bidirectional communication between two nodes with a spectrally efficient two-phase protocol. In the first phase both nodes transmit their messages to a relay node, which decodes the messages and broadcasts a composition using superposition encoding in the succeeding phase. The probability that the achievable rate region of one relay node contains all other rate regions decreases with the number of relay nodes N. Therefore, we propose a relay selection criterion that decides according to the weighted rate sum for any bidirectional rate pair on the boundary of the achievable rate region individually. If we allow time-sharing between the usage of different relay nodes, we can enlarge the achievable rate region. In an iid Rayleigh fading scenario relay selection realizes multi-user diversity so that the sum-rate of any rate pair on the boundary of the ergodic rate region asymptotically grows with Theta(log(log(/V))).