Downlink Interference Cancelation In Multiple Antennas System

The popularity of smart cellphone greatly stimulated people’s expectation for higher communication speed and better communication quality, and promoted the rapid development of wireless communication simultaneously. The segmentation of cells, the increasing of antennas numbers and the application of heterogeneous network technology lead to more overlapping areas among different cells,which severely restricts the communication quality and the system capacity of wireless communication.The conventional methods to combat the downlink interference are pre-coding techniques. As we know, the based station is unable to acquire the downlink channel state information. The common measure to solve this problem is sending some pilot signals related to the channel information to the base station through the uplink channel, and then estimating the channel information or computing the corresponding pre-coding matrix based on the pilot signals. Therefore, the quality of pre-coding does not only depends on the accuracy of channel estimation, but also impacts of the feedback amount. Inspired by this issue, some researchers proposed the receiver interference cancelation schemes.In addition, the system capacity of nonlinear pre-coding schemes is much more close to the theoretical limit of wireless systems than linear pre-coding schemes. The computation amount of nonlinear pre-coding algorithm made it difficult to realize in practical. However, in some special scenarios, such as forward channel communication, having a large number of receivers with high complexity is much less promising than having one transmitter that employs high complexity encoding.This paper mainly focuses on two interference cancelation schemes: receiver interference cancelation scheme which mainly utilizes the joint iterative decoding technique, and transmitter interference cancelation scheme which employs the expand constellation dirty paper coding technique.Firstly, this paper introduced the basic idea of joint iterative decoding in detail. Its main idea is assume the interference as additive white Gaussian noise and recover the desired and interference signals at the same time. The transmitters of joint iterative decoding system doesn’t need the channel information, so its performance is independent of channel feedback information and much better than some linear pre-coding schemes. Furthermore, a closed form of the relationship between the channel estimation error and the signal interference noise ratio is provided in this paper, which can be a performance indicator for joint iterative decoding in practical.Secondly, this paper introduced the main process of expand constellation dirty paper coding technique, whose main idea is expanding the original signals on two-dimensional plane, finding the point which is most close to the interference, and using the difference between the interference and the closet point as the coding signal. The processing of expand constellation dirty paper coding can not only reduce the average and peak power of the transmit signals, but also avoid some capacity lose caused by symmetric modulo. Furthermore, this paper introduced a user selection method which can increase the system decoding capacity compared by common dirty coding technique.