Research On Single-frequency Full-duplex MIMO System And Multi-user System

With the development of radio technology, a large number of radio devices are invented and are demanded in all walks of life. The shortage of spectrum resources will be the bottleneck of wireless communication’s application and sustainable development. Therefore, it is an effective way to solve the shortage of spectrum resources to promote the efficiency of utilize the spectrum resources. In this paper, we propose single frequency full-duplex communication and smart antenna technology to promote the spectrum efficiency.Theoretically, single frequency full-duplex communication can double the spectrum efficiency. Time division duplex and frequency division duplex are traditional duplex communication methods. The former is half-duplex. The latter is full-duplex, but nodes transmit bidirectional signals synchronously in different frequencies in this mean. In the paper, we propose a single frequency full-duplex communication system. In this system, the nodes can transmit and receive signals simultaneously in the same frequency. How to eliminate the local strong self-interference is the key to realize single frequency full-duplex communication. We describe the interference cancellation methods in the system, which are Antenna Separation, Analog Cancellation and Digital Cancellation. Through the simulation, we found that the performance of Analog Cancelation have an effect on Digital Cancelation. The amount of one cancellation’s loss is another’s gain. When the amount of Analog Cancelation reaches a certain critical point, the sum of the amount of Analog Cancelation and Digital Cancelation is the most.It is another way to improve the spectrum efficiency to take advantage of smart antenna technology. We can divide the space into different regions, and transmit signals in different directions in same frequency, which can multiply improve spectrum utilization. In this paper, we propose a multi-user system based on smart antenna. In the system, multiple users transmit their signals in different directions in the transmitter. In the receiver, signals are received by array antenna. We can obtain the number of users and each user’s direction of arrival in direction of arrival estimation method. Then we obtain every user’s signal by using adaptive beamforming technology. So multiple users can communicate synchronously. Through simulation, we found that the performance of the system get better and better with the increase of SNR. We also found the system get the best performance when using multiple signal classification direction of arrive estimation and Maximum Signal to Interference Ratio or Minimum Mean Square Error criterion.