Abstract
This paper presents an analysis of the massive multiple input and multiple output (MIMO) channel in an indoor picocell with a high number of active user terminals and a base station consisting of a virtual array with up to one hundred elements. The analysis is based on the results of a measurement campaign carried out in the 3.2 to 4 GHz band in a scenario of reduced size and with a symmetrical geometry, in which users are also placed in an orderly manner. The channel meets the condition of favorable propagation depending on several factors, one of the most important being the spatial distribution of users. Results concerning the inverse condition number as well as the channel sum capacity are included. Another factor that determines the performance of massive MIMO systems when operated in an orthogonal frequency division multiplexing (OFDM) framework is the frequency selectivity of the channel that limits the size of the coherence block (ChB). Focusing on the most significant results achieved, it can be concluded that the channel reaches a capacity of 89% with respect to an i.i.d. Rayleigh channel. Concerning the cumulative distribution function (CDF) of the sum capacity, it can also be observed that the tails are not very pronounced, which indicates that a homogeneous service can be given to all users. Regarding the number of samples that make up the ChB, although it is high in all cases (of the order of tens of thousands), it strongly depends on the degree of correlation used to calculate the coherence bandwidth.
Highlights
The evolution and subsequent deployment of the fifth generation of mobile communications systems (5G), as well as the development of the generation (6G) will require the optimum use of the radio channel, enhancing the spectral efficiencies
As outlined in the previous section, channel parameters such as the mean delay and the root mean square (RMS) delay spread can be directly obtained from the power delay profile (PDP), and the coherence bandwidth at different levels of correlation, which quantifies the frequency selectivity of the channel, depends on the PDP
The dispersion of the NC values shows the convenience of having more experimental data, of BC values, and of TC
Summary
The evolution and subsequent deployment of the fifth generation of mobile communications systems (5G), as well as the development of the generation (6G) will require the optimum use of the radio channel, enhancing the spectral efficiencies. In order to carry out such an analysis, massive MIMO channels must be measured in different environments, frequency bands and system configurations, i.e. for arrays with different numbers and types of antennas, as well as for different spatial distributions of the UTs. From the initial experimental research [15]–[18] to the present, a great deal of work has been performed to empirically characterize massive MIMO channels in different environments and frequency bands. From the initial experimental research [15]–[18] to the present, a great deal of work has been performed to empirically characterize massive MIMO channels in different environments and frequency bands From the correlation function the coherence bandwidths (BC ) for different correlation levels can be obtained [29]
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