Abstract-This paper investigates the performance of different low-complexity combining schemes in the context of dual-hop amplify-and-forward relaying networks. It is assumed that the relay uses single transmit (receive) antenna due to space limitation and to reduce the processing complexity. On the other hand, the transmitter and the receiver use antenna arrays to improve the overall diversity gain. However, this gain is achieved at the expense of increased processing complexity and power consumption. To this end, some combining schemes aiming at reducing the processing complexity and decreasing the number of active receive channels are investigated. Through the analysis, new formulas for the end-to-end signal-to-noise ratio statistics in slowly varying and frequency flat Rayleigh fading channels are derived, which are then used to present some performance measures. Numerical and simulation results are presented to clarify the trade-off between the achieved diversity gain and the receive processing complexity.
I. INTRODUCTIONIt is well-known that relaying techniques can improve the spectral efficiency of wireless systems and mitigate the severe effect of large-scale fading. Moreover, the use of multiple antennas schemes in relaying networks have also shown further improvements in system capacity and communication reliability [1], [2]. Various diversity combining schemes have been studied in the context of multiple-antenna relaying systems [3]- [9]. However, an important aspect of employing diversity methods in such scenarios is to maintain as low processing complexity and power consumption as possible while satisfying a target performance level. This paper investigates different combining schemes with reduced processing complexity for dual-hop relaying networks employing the simple amplify-and-forward (AF) relaying protocol. The performance of this protocol can be improved when the channel state information (CSI) of the preceding hop is available to control the relaying gain, and it may be useful when simple relaying is required and/or when the transmitted data is time-sensitive [10], [11].For the dual-hop AF relaying system under consideration, the relaying station is assumed to use single antenna in each direction due to space limitation and processing power constraints. On the other hand, different low-complexity configurations are investigated assuming uncorrelated antenna arrays at the transmitter and the receiver. Specifically, the scheme proposed in [12] is adopted to considerably reduce the power drain from the battery while satisfying a target performance.