As more and more mobile multimedia services are produced, end users are increasingly demanding access to high-speed, low-latency mobile communication networks. Among them, device-to-device (D2D) communication does not need the data to be forwarded through the base station relay but allows the two mobile devices adjacent to each other to establish a direct local link under control of the base station. This flexible communication method reduces the processing bottlenecks and blind spots of the base station and can be widely used in dense user communication scenarios such as transportation systems. Aiming at the problem of high energy consumption and improved quality of service demands by the D2D users, this paper proposes a new scheme to effectively improve the user fairness and satisfaction based on the user grouping into clusters. The main idea is to create the interference graph between the D2D users which is based on the graph coloring theory and constructs the color lists of the D2D users while cellular users’ requirements are guaranteed. Finally, those D2D users who can share the same channel are grouped in the same cluster. Simulation results show that the proposed scheme outperforms the existing schemes and effectively improve system performance.

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Multi Carrier Code Division Multiple Access (MC-CDMA) is a suitable modulation method for high data rates. In this modulation system, using of combining methods are inevitable for restoring orthogonality between diverse user signals. In this paper, the combining techniques of a MC-CDMA based on lifting discrete wavelet transform strategy (LDWT) are studied. Is presented to keep up the symmetry against the multipath Flat Fading Channels (FFC). Show of MC-CDMA under many channels similar the AWGN channel and FFC, is examined and BER versus SNR graphs are plotted and their presentation is deliberate.