Spectral Efficiency and Outage Performance for Device-to-Device Cooperation in Uplink Cellular Communication

We propose a time-division uplink transmission scheme that is applicable to Long Term Evolution Advanced (LTE-A) systems and utilizes device-to-device (D2D) cooperation. We analyze its spectral efficiency and outage performance and show that compared to existing frequency-division schemes, the proposed scheme achieves the same or better spectral efficiency and outage performance while having simpler signaling and shorter decoding delay. Using time-division, the proposed scheme divides each transmission frame into three phases with variable durations. The two user equipments (UEs) partially exchange their information in the first two phases, then cooperatively transmit to the base station (BS) in the third phase. We further formulate its common and individual outage probabilities, taking into account outages at both UEs and the BS. We analyze this outage performance in Rayleigh fading environment assuming full channel state information (CSI) at the receivers and limited CSI at the transmitters. Results show that comparing to non-cooperative transmission, the proposed D2D cooperation always improves the instantaneous achievable rate region even under half-duplex transmission. Moreover, as the received signal-to-noise ratio increases, this uplink D2D cooperation significantly reduces overall outage probabilities and achieves the full diversity order of 2 in spite of additional outages at the UEs. These characteristics of the proposed uplink D2D cooperation make it appealing for deployment in future cellular networks.