Interference-Aware and Coverage Analysis Scheme for 5G NB-IoT D2D Relaying Strategy for Cell Edge QoS Improvement

In an interference-limited 5G narrowband Internet of Things (NB-IoT) heterogeneous networks (HetNets), device-to-device (D2D) relaying technology can provide coverage expansion and increase network throughput for cell-edge NB-IoT users (NUE). However, as D2D relaying improves the network’s spectral efficiency, it makes interference management and resource allocation more difficult. To improve cell-edge user quality of service (QoS), we propose an interference-aware and coverage analysis scheme for 5G NB-IoT D2D relaying. We divide the optimization problem into three subproblems to reduce the algorithm complexity. First, we use the max-max signal-to-noise-plus-interference ratio (Max-SINR) to select an optimal D2D relay with the highest channel-to-interference-plus-noise ratio (CINR) to relay the source NUE information to the NB-IoT base station (NBS). Second, we optimize the transmit power (TP) of the cell-edge NUE to the relay under the peak interference power constraints using a Lagrange dual approach to ensure the user’s service life. We fixed the TP between the D2D relay and the NBS and then transformed the D2D relay’s coverage problem that maximizes the network uplink data rate into a 0–1 integer programming problem. Then, we propose a heuristic algorithm to obtain the system performance. Due to the high-channel gain between the two communicating devices, the simulation results show that the Max-SINR selection scheme outperforms the other relay selection schemes except for the D2D communication scheme in efficiency, data rate and SINR.