Near-far Effect Study In D2D Communication

Mobile communication technology has experienced the first generation frequency division multiple access communication, the second generation time division multiplexing communication, the third generation code division multiple access communication, now has entered into the fourth generation LTE (Long Term Evolution) mobile communication. Mobile communication has brought people’s life great convenience, but it also faces many problems, such as a lot of users with limited system capacity, base station overloaded, radio spectrum resources becoming less and less and other issues. With the development of all kinds of mobile applications, the power consumption of the mobile terminal is also gradually increasing. Just in this case, D2D (Device-to-Device) communication appears. D2D communication is a kind of technology which can make one device transmits message to another directly without through base station in short distance. It reduces the load of the base station and the transmitting power of the terminal, increases the spectrum efficiency. D2D communication has many advantages, but the near-far effect affects the quality of D2D communication seriously.This paper studies the phenomenon of new-far effect under D2D communication mode, analyses the factors which affect new-far effect and the simulation results under different conditions. Since the D2D communication technology belongs to the category of LTE communication system, first this paper introduces the LTE communication needs, technical characteristics, protocol architecture and the use of advanced technology and other related knowledge. Then focus on the architecture of D2D communication, D2D communication process and the interference between D2D and cellular communication. Since the existence of multiple access interference in CDMA system, near-far effect phenomenon has seriously affected the performance of the CDMA (Code Division Multiple Access) system. D2D communication mode for LTE systems will also be affected. The LTE system uses OFDM (Orthogonal Frequency Division Multiplexing) multi-carrier modulation. Since D2D communication is based on the function of LTE process, the near-far effect phenomenon in D2D communication mode will be different. There are some methods to suppress the near-far effect, such as power control, multi-user detection, adaptive interference cancellation and frequency hopping. This paper introduces the radio wave propagation model and wireless channel model, selects urban micro channel model as the simulation channel model, and sets up the D2D communication simulation system. Through different conditions such as different received power, different time offset, different frequency offset, different resource blocks intervals to analyze D2D near-far effect and come to a conclusion. Finally, the K-means clustering algorithm is used to study D2D near-far effect. According to the different number of clusters and different number of users who send signal simultaneously in each cluster to make simulation analysis and come to a conclusion.