Device-to-Device communication in CDMA-based cellular systems — Uplink capacity analysis

We study the uplink capacity gain when Device-to-Device (D2D) links are enabled in a FDD CDMA-based cellular system. In such a system, a direct link for data traffic is established if a communication pair is closely located, and better link quality is expected due to the short D2D transmission distance. We consider a single cell scenario, and assume uplink resource is utilized by D2D communications. We assume the D2D transmitter transmits at a power level no more than it transmits in a cellular mode; in this case no extra interference would be introduced into the CDMA system. Optimal transmit power for benefited D2D links is derived to improve system performance in terms of uplink capacity. Extensive simulations are conducted, which demonstrate that a significant capacity gain is obtained from D2D links. Subsequently, we discuss the performance gain and its affecting factors and try to derive some insights on practical implementation.