Achievable Transmission Capacity of Relay-Assisted Device-to-Device (D2D) Communication Underlay Cellular Networks

Device-to-Device (D2D) communication is considered to be a promising resource reuse technology for local users, which can support high-speed and power- saving services. However, when D2D users are far away from each other or the quality of D2D channel is not good enough for direct communication, transmission via a direct link is not a good choice. In this paper, we focus on the performance of relay assisted D2D network. Unlike the previous works that mainly study practical relay selection algorithm, we analyze the achievable transmission capacity of multi-hop D2D system over Rayleigh fading channels. First, by using stochastic geometry, the probability distribution of end-to-end signal-to-interference- plus-noise ratio (SINR) in the spectrum sharing network is formulated. Then the achievable transmission capacity is modeled as an optimization problem with constraints that guarantee the outage probability of both cellular and D2D systems. Finally the optimal design of D2D spatial density and transmit power is analyzed and the achievable transmission capacity of multi-hop D2D system is given in closed-form expression. Numerical results show the performance of the D2D network can be effectively enhanced by relay-assisted transmission. We also verify the optimal design of D2D parameters and evaluate the influence of the number of relay hops on the system capacity and power efficiency.