We consider relay selection technique in a cooperative cellular network where
user terminals act as mobile relays to help the communications between base
station (BS) and mobile station (MS). A novel relay selection scheme, called
Joint Uplink and Downlink Relay Selection (JUDRS), is proposed in this paper.
Specifically, we generalize JUDRS in two key aspects: (i) relay is selected
jointly for uplink and downlink, so that the relay selection overhead can be
reduced, and (ii) we consider to minimize the weighted total energy consumption
of MS, relay and BS by taking into account channel quality and traffic load
condition of uplink and downlink. Information theoretic analysis of the
diversity-multiplexing tradeoff demonstrates that the proposed scheme achieves
full spatial diversity in the quantity of cooperating terminals in this
network. And numerical results are provided to further confirm a significant
energy efficiency gain of the proposed algorithm comparing to the previous best
worse channel selection and best harmonic mean selection algorithms.