Abstract
This paper presents an analysis of the effect that the radiation pattern of the antenna element that makes up the base station array has on the structure of multi-user multiple-input multiple-output (MU-MIMO) channels. In this paper, the analysis focuses on the uplink. It is well known that the antennas are an inseparable part of the radio channel. The use of more or less directional antennas as elements of the base station array of a MIMO system influences the channel in two fundamental parameters that affect the performance of MU-MIMO systems: on the one hand, the coherence bandwidth, which determines the necessary overhead in the channel estimation; and, on the other hand, the orthogonality of the subchannels between the multiple users and the base station, which influences the degree with which the condition of “favorable propagation” is fulfilled. Based on an experimental analysis using both omnidirectional and directional antennas, conclusions are drawn about how these two parameters are affected and their influence on the spectral efficiency obtainable. The measurement campaign was carried out in an indoor environment in the 3 to 4 GHz band.
Highlights
The development of the fifth generation of mobile communications systems (5G) requires the availability of more spectrum to meet both the 5G usage scenarios and to enable the key capabilities of IMT-2020 [1], and the optimum use of the radio channel, enhancing the spectral efficiencies
This paper investigates the influence on the MU-multiple input and multiple output (MIMO) channel of the directivity of the type of antenna element considered for the base station (BS) array, using to quantify these differences the following fundamental parameters: the coherence bandwidth, the condition number of the channel matrix and the achievable up-link sum capacity of the system when using both omnidirectional and directional antennas
RESULTS the omnidirectional channels (OCh) and directive channels (DCh) channels are compared based on the statistical distribution of the most relevant channel parameters, i.e., BC, inverse of the condition number (ICN), and sum capacity (C)
Summary
The development of the fifth generation of mobile communications systems (5G) requires the availability of more spectrum to meet both the 5G usage scenarios and to enable the key capabilities of IMT-2020 [1], and the optimum use of the radio channel, enhancing the spectral efficiencies. The results presented in this paper correspond with new measurement campaigns carried out in two propagation environments that complement those already carried out in the same scenarios in the 3 to 4 GHz band [21], [22], using a directional ultra-wideband antenna as the main element of the BS antenna array, instead of the omnidirectional one, and including some new UT locations in the study. This paper investigates the influence on the MU-MIMO channel of the directivity of the type of antenna element considered for the BS array, using to quantify these differences the following fundamental parameters: the coherence bandwidth, the condition number of the channel matrix and the achievable up-link sum capacity of the system when using both omnidirectional and directional antennas.
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