The development of science and technology carries more and more convenience to human’s life. One of these improvements is the Internet. General life is getting stricter connection with the Internet. People now, do not only do surfing the Internet, but do shopping, learning, chatting, searching. It is true that the Internet gets connected to each corner of the common live. However, with the increase of using the Internet, it also comes many problems. People may get annoyed not only if they cannot get used to the Internet, for example as to online game, live show, online finical transaction or chat view. Or, in some special cases, people cannot get enough speed to transmit data by using the Internet. Especially, when people is watching a football game in a stadium, it is highly probable that since too many people in the same stadium is using the Internet at the same time, each one cannot share their video or their comment on online SNS at once. In fact, there are more than these two cases that would affect the user experience. So, to solve these problems, some new technology is needed to promote the development of the Internet in the future.
Actually, the easiest way is to expand the frequency spectrum. However, because the frequency spectrum is a limited source, this method is not an optimal solution. So, our group tries to develop a MIMO (multiple input multiple output) full-duplex method to replace the half duplex method which is being used now in tele communication system to improve the efficiency of data transmission.
The core concept of MIMO full duplex method is that transmitting and receiving data at the same time by using multiple antenna. By using this method, the data transmission efficiency will get a huge improvement in theory. But, since multiple antenna is used and data receiving and transmission is done at the same time, signal interference is expected to be extremely large. Then, this so much and so large signal interference will affect the detection and decoding of the real received signal. So, to make this technology available, our group is trying many ways to cancel the signal interference part.
Research results and evaluation results
To cancel interference signal, the common method includes analog cancellation method and digital cancellation method. While, our group focus more on the digital cancellation. As to the digital cancellation, it can be divided into linear cancellation and non-linear cancellation. Many other groups focus on linear cancellation, while our group focus more on non-linear cancellation. We use two RLS (recursive linear square) algorithms. One is used to do linear cancellation and the other is used to realize non-linear cancellation. When the transmitter keeps transmitting signal, which is seen as interference signal, the RLS algorithm will keep updating and design a pre-calibration filter to decrease the effect caused by power amplifier, which causes the non-linear interference part. From the simulation, it can be seen that full duplex method has a superiority to half duplex and this shows that full duplex communication is a potential solution to improve data transmission efficiency.
By now, we have two versions. One includes a RF chain and one does not use RF chain. Though the version with RF chain converges faster, since there is a RF chain, it will cause some difficulties on the design of circuit. So, we develop version two. Version two has similar performance but it converges a little bit longer than version 1. To make the simulation be more similar to the real situation, we plan to add speed to simulate interference cancellation with antenna mobility. This is because in real live, people usually walk while use mobile phones. So, the situation considering antenna mobility is of great value to focus on.