Channel Research And Outdoor Measurements For Massive MIMO

With 4G going into large-scale commercial stage, next-generation wireless data network or called Fifth Generation 5G mobile communication technology research and development is being carried out in full swing. Massive MIMO technology, as a key technology in 5G,has caught attention from relevant institutions, and become a research hotspot. So-called Massive MIMO refers to a situation where dozens or hundreds of antennas are configured at the transmitter and receiver side simultaneously serving dozens of users’ communication,and a single antenna is used at UE side. Research shows that Massive MIMO technology can improve the performance of wireless communication system significantly, such as improving the system capacity and energy efficiency greatly, reduce intra-cell interference and system construction cost effectively. Taking Massive MIMO technology as the topic,Massive MIMO channels become focus in this paper.Radio channel is transmission medium of mobile communication, which is the basis of wireless system design and research. In order to obtain channel characteristics of Massive MIMO effectively, it is necessary to study radio channels by actual channel measurements.Based on the measurement data, channel parameters can be extracted. These channel parameters can reflect channel characteristics of Massive MIMO, and provide effective help to establish theoretical channel models of Massive MIMO. Also, it can be a tool to verify the accuracy and reasonableness of the channel model.Main work of this paper is to measure Massive MIMO channel in practical environment,process and analysis the obtained data. Firstly, an outdoor measurement scheme is built from aspect of channel characteristics, and relevant instruments, such as oscilloscopes,signal sources, etc., are bought for the measurement platform construction. According to the classification of general channel scenes, eight test sites are selected at Xidian University campus, including four LOS sites and four NLOS sites. In this scheme, transmitter is distributed at the eight test sites. Secondly, a virtual linear antenna array of 128 elements is used at the receiver side for channel measurement. During this process, pseudo-random sequences are sent at the transmitter side, and with the help of spread-spectrum channel sliding correlation measurements, the received signal are stored into a computer to process.This process is described in detail. Finally, get four channel parameters from the data processing, including Rice K factor, angle power spectrum, channel correlation coefficients between users, and distribution of eigen values. By actual measurements, we find that as the number of antennas increases, K factor changes dramatically with the element position,and correlation between user channels reduces. At the same time, the channel gain stay stable, and birth and death of multipath happens. All these findings can notonly indicate the non-stationary characteristic of Massive MIMO channels and advantages brought by Massive MIMO, but also provide reference for the establishment of theoretical Massive MIMO model. In addition, change of birth and death rate of Massive MIMO multipath channel is studied in this paper, and relationship between birth-death rates of multipath and channel impulse response is deduced based on actual measured data.