On the Benefits of Network-Level Cooperation in Millimeter-Wave Communications

Relaying techniques for millimeter-wave wireless networks represent a powerful solution for improving the transmission performance. In this paper, we quantify the benefits in terms of delay and throughput for a random-Access multi-user millimeter-wave wireless network, assisted by a full-duplex network cooperative relay. The relay is equipped with a queue for which we analyze the performance characteristics (e.g., arrival rate, service rate, average size, and stability condition). Moreover, we study two possible transmission schemes: Fully directional and broadcast. In the former, the source nodes transmit a packet either to the relay or to the destination by using narrow beams, whereas, in the latter, the nodes transmit both the destination and the relay in the same timeslot by using a wider beam but with lower beamforming gain. In our analysis, we also consider the beam alignment phase that occurs every time, a transmitter node changes the destination node. We show the duration of how the beam is aligned, as well as position and a number of transmitting nodes, significantly affect the network performance. In addition, we discuss the impact of beam alignment errors and imperfect self-interference cancellation technique at the relay for full-duplex communications. Moreover, we illustrate the optimal transmission scheme (i.e., broadcast or fully directional) for several system parameters and show that a fully directional transmission is not always beneficial, but in some scenarios, broadcasting and relaying can improve the performance in terms of throughput and delay.