Measurement-Based Characterizations of Indoor Massive MIMO Channels at 2 GHz, 4 GHz, and 6 GHz Frequency Bands

Massive MIMO has been chosen as one of the candidate technologies of the fifth-generation mobile communication system (5G), and channel modeling of massive MIMO is of great importance. The most direct and effective approach to investigate the propagation characteristics of massive MIMO channels is channel measurements. However, there are only few measurements of massive MIMO channels, and there still lacks deep investigations of massive MIMO channel characteristics. In this paper, we present a measurement campaign of indoor massive MIMO channels, by using a linear large-scale array with 64 elements. The measurements are conducted at 2 GHz, 4 GHz, and 6 GHz, respectively, with a bandwidth of 200 MHz. Both LOS and NLOS propagation scenarios are considered in the measurements. The basic channel parameters are extracted, including path loss, delay spread, and coherence bandwidth. The non-stationarity of radio channels, which is reflected by the variations of delay spread and coherence bandwidth over different array locations, is discussed. The impact of carrier frequency on the above channel parameters is further discussed. The results would be useful for the design of massive MIMO system in the indoor environments.

I. Introduction

Massive MIMO is considered to be one of the most important technologies of the next generation wireless communication systems [1], where base station of massive MIMO is equipped with a large number of antennas (tens to hundreds, in general) to achieve extra system gain. The channel vectors become pairwise orthogonal as the number of antennas at base station increases to infinity [2], therefore massive MIMO can greatly improve the spectrum efficiency by using the same frequency resource at the same time and also improve the power efficiency with diversity gain and array gain [3]. Current research of the massive MIMO is mostly based on the theoretical independent and identically distributed (i.i.d.) complex Gaussian channels. However, deep investigations on the channel behaviors are required, as the system performance is determined by the radio channels. As a result, channel measurements are needed, especially in different typical scenarios, such as indoor hall, railway station, and high-speed railway [4]–[5] and so on. Fig. 1.

Measurement system of massive MIMO