Spectral Efficiency and Outage Performance for Hybrid D2D-Infrastructure Uplink Cooperation

We propose a time-division uplink transmission scheme that is applicable to future-generation cellular systems by introducing hybrid device-to-device (D2D) and infrastructure cooperation. Compared with existing frequency-division schemes, the proposed time-division scheme achieves the same or better spectral efficiency and outage performance with simpler signals and shorter decoding delay. These advantages come from sending a different message in each transmission block without block Markovity as in existing schemes. Using time-division, the proposed scheme divides each transmission frame into three phases with variable duration. The two user equipment units (UEs) partially exchange their information in the first two phases and then cooperatively transmit to the base station (BS) in the third phase. We further formulate the end-to-end outage probabilities, considering outages at both UEs and the BS. We analyze this outage performance in Rayleigh fading environment assuming full channel state information (CSI) at receivers and limited CSI at transmitters. Results show that user cooperation improves the achievable rate region even under half-duplex transmission. Moreover, as the received SNR increases, this uplink cooperation significantly reduces outage probabilities and achieves the full diversity order despite additional outages at the UEs. These characteristics make the proposed scheme appealing for deployment in future cellular networks.