Angular dispersion is the effect of a multi-path propagation observed in received signals. An assessment of this phenomenon is particularly important from the viewpoint of emerging fifth generation (5G) communication systems. In these systems, using the beam-forming and massive multiple-input multiple-output antenna arrays are planned. This phenomenon also has a negative impact on direction finding and older generation communication systems used in an urban environment. In this paper, we present the angular dispersion evaluation for various propagation environments based on simulation studies. This analysis is carried out for different environment types defined in the 3GPP standard model for a selected frequency. In this case, the angular spread is determinated based on the power angular spectrum. This parameter is the basis for the influence evaluation of the propagation environment on the received signal angular dispersion.
A common feature of the EHF and THF ranges is the use of geometric optics principles [10] in propagation phenomena modeling. The wave propagation modeling for the THF and optical frequency ranges is relatively simple, as it mainly concerns LOS conditions. For the EHF, the millimeter wave propagation can also occur under non-LOS (NLOS) conditions. In this case, the additional problem is a multipath propagation phenomenon. This is associated with dispersions in time and angle domains that can be observe in a received signal. For modeling these phenomena, geometry-based propagation models are used, e.g., [11]. Geometric optics is the basis of these models.
The evaluation of the angular dispersion of the received signals consists in determining a distribution of angle of arrival angle (AOA) at surroundings of a receiver (Rx). In this case, the analysis reduces to the evaluation of propagation path trajectories in the presence of scatterers. Appropriate geometric structures are used to map scatterer positions on the plane (2D) or in space (3D). Shapes of scattering areas, their location in relation to the Tx and Rx positions, and a density distribution of the scatterers are the criteria that differentiate individual models.
Currently, 3D models are more popular, e.g., [11]. They provide to evaluate the angular dispersion in the azimuth and elevation planes. However, results presented in a literature, e.g., [12] [13], show unequivocally that the phenomenon of the angular dispersion is more visible in the azimuth plane. In the elevation plane, a parameter defining this dispersion, i.e., rms angle spread (AS), is usually equal to a few degrees. For this reason, the assessment of the angular dispersion presented in this paper focuses only on the azimuth plane.
The previous wireless systems were based mainly on omnidirectional or sectorial antenna systems. Diversification of radio resources also in the field of space has forced the use of spatial multiplexing techniques such as multiple-input multiple-output (MIMO) [14]. In the emerging 5G systems, more complex antenna techniques are planned to use [3], e.g., wideband beamforming [15], massive-MIMO [16], active phased array antenna (APAA), and massive APAA [17]. In practical terms, a single beam can be modeled as a narrowbeam directional antenna. In the future communication systems, in addition to antenna arrays, the millimeter waves also enforces the use of singular directional antennas, which are characterized by low half power beamwidths (HPBWs) and high gains [5]. Jan M. Kelner The purpose of this paper is to evaluate the angular dispersion for different environment types. This analysis is carried out for 38-39 GHz, which is planned to use in the upcoming 5G systems. In the assessment based on simulation studies, we use the multi-elliptical propagation model (MPM) [18]. The choice of this model results from two premises. Firstly, MPM is characterized by the best approximation of measurement data available in a literature [19]. Secondly, MDM is one of few models that considers the transmitting and receiving antenna patterns. As mentioned above, considering the antenna patterns in the analysis is very important in modeling the emerging 5G communication systems.
The remainder of this paper is organized as follows. Section II describes the method of modeling the angular dispersion. Assumptions for simulation studies and AS assessment for various propagation environments are presented in Sections III and IV, respectively. In section V, the summary is shown.
The basis of MPM is the multi-elliptical structure, which defines potential locations of the scatterers. In this case, the Tx and Rx are located in the ellipse foci. This approach was first proposed by Parsons and Bajwa [20]. A cluster structure of empirical power delay profiles (PDPs) or spectrum (PDSs) is the premise for this. Therefore, the basic input data for MPM is PDP/PDS. The dimensions of the confocal ellipses results from the delays of the analyzed PDP. The MPM geometry is shown in Fig. 1. Delayed scattering components associated with the multielliptical structure are the core of this geometry. In MPM, we assume additionally the occurrence possibility of a direct path and local scattering around the receiving antenna. In this case, the von Mises distribution [21] is used for the local scattering components. However, for LOS conditions, the Rice factor determines the power division between the direct path component and local scattering.
In [19], MPM for omnidirectional antennas is described. Consideration of the transmitting and receiving antenna patterns was first presented for the 3D model, called the multiellipsoid model, in [22] and [23], respectively. Its simplification to the azimuth plane shown in [24] [18] is the basis for evaluating the angular dispersion in this paper.
The angular dispersion can be analyzed in surroundings of the Rx or at the output of the receiving antenna. In the first c
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