System capacity and coverage of a cellular network with D2D mobile relays

It has been predicted that the recent explosive growth in wireless data traffic will continue for the foreseeable future. To date, attempts to address this explosive growth have included increasing base station density through smaller cells, and to a lesser extent, by improving spectral efficiency using close-to-capacity channel coding and MIMO techniques. Providing further capacity and coverage improvements through ever shrinking cells could lead to large infrastructure costs and operating expenses. In this paper we propose a far less expensive alternate solution using a topology which employs mobile User Equipment (UE) nodes as virtual infrastructure to enhance the cellular capacity while also improving network coverage. The improvements in capacity and coverage are achieved by enabling cellular controlled direct Device to Device (D2D) links to carry relayed traffic. Each terminal UE (T-UE) with an active connection could potentially be assigned a Helper UE (H-UE), depending on the network conditions and traffic requirements to improve the system capacity. In addition, T-UEs which are out of coverage can also be assigned a H-UE, which would extend the typical coverage of a base station and lead to improved network coverage. In this paper, we present both coverage enhancement and system capacity results using Monte Carlo simulation techniques for both uplink and downlink communications. Our results indicate that cell edge percent throughput capacity improvements as well as percent throughput coverage improvements of more than 150% may be realized using idle UEs in the system as mobile relays.