Reseach On Appling Device-to-device Communication In Cellular Networks

Nowadays, smart phones, tablets and other mobile terminals have become the necessities of people’s life, and as a result the mobile user data traffic increases rapidly. However the bandwidth available for mobile networks is limited. In order to solve the contradiction between the increment of data traffic and limited spectrum resource, new mobile communication technologies need to be developed. One Promising method is applying Device-to-Device(D2D) communication in cellular networks, i.e. two geographically nearby devices are allowed to communicate with each other directly, instead of following the traditional "Equipment- Base Station- Equipment" cellular communication mode.This paper mainly researches the technology of applying D2 D communication in cellular networks and proposes an orthogonal D2 D resource allocation mechanism based on graph coloring. Cellular networks allocate a resource pool for D2 D communication which is orthogonal to cellular communication. The resource pool is divided into several sub-bands and each sub-band could be reused by multiple D2 D pairs. Graph coloring is used to finish reuse selection. On the basis of graph coloring, this paper proposes a specific resource allocation method based on utility. In this method, the bandwidth allocated to each sub-band is proportional to the number of D2 D pairs that use the same sub-band. Considering that one of the most important features is reducing power consumption, power control is performed after resource allocation.Under the proposed mechanism, there are three possible realization schemes according to different forming graph methods:Received-power-based scheme: A received power threshold Pr xG is predefined by Base Station(BS). The adjacency of two nodes in graph G is judged by following procedure: D2 Di transmits prob signal firstly; if the received power of D2 Dj is larger than Pr xG, BS believes that D2 Di and D2 Dj is adjacent; otherwise, BS believes that D2 Di and D2 Dj is not adjacent.SIR-based scheme: BS defines a SIR threshold SIRG and assumes that all D2 D pairs reuse the same frequncy resources firstly. For a certan D2 Di, other D2 D pairs is in turn eliminated according to the order of interference from strong to weak until()SIRSIR i 3 G. The eliminated D2 D pairs are adjacent to D2 Di ingraph G.Utility-based scheme is an ergodic scheme: The max available color number is N, i.e. the color number range from 1 to N, all together N kinds of coloring schemes. In each round, BS formulates a new graph, performs vertex coloring, allocates resources and calculates sum utility. At last, check out the optimum scheme which produces maximum sum utility.Among those three schemes, Received-power-based scheme is the best scheme through the comparison of performance of Matlab simulation and the algorithm complexity.At last, the effectiveness of proposed orthogonal resource allocation mechanism is validated by comparison between orthogonal mode scheme and reuse mode scheme. The result shows that the mechanism proposed in this paper has good performance in the following aspects: spectrum efficiency, system energy efficiency, quality of communications, signaling overhead and the effect on cellular networks bring about by D2 D communication.