Multi-carrier CDMA for network assisted device-to-device communications for an integrated OFDMA cellular system

Device-to-Device communication (D2D) has been a hot research topic in recent years, especially concerning the integration of D2D and conventional cellular networks. In general, the integration improves the efficiency and flexibility of the overall system. Furthermore, D2D can provide partial solutions for some inherent problems of cellular systems, such as cell edge related problems. Currently, most of the D2D integration studies assume that D2D UEs and cellular UEs use identical multiple access (MA) technology for the convenience of integration and backward compatibility. In this paper, besides the conventional OFDMA based D2D, we investigate the use of multicarrier code division multiple access (MC-CDMA) as the MA scheme for D2D UEs. The idea is to use processing gains obtained by spreading against critical interference, especially from cellular UEs. The study is emphasized on interference related issues, including interference analysis of the integrated system, and overall performance enhancement, mainly for D2D UEs, by utilizing frequency domain spreading. Network simulations show the gain against critical interference from cellular UEs. Meanwhile, it is shown that intra-cell cross mode interference control/elimination is the key scheme to guarantee performance of the integrated system. Furthermore, we discuss the potential benefits and procedures of MC-CDMA D2D based cluster integration.