Introduction
A key. feature of IMT-2020 systems are beamforming array antennas which use phase shifting to an array of individually fed antenna elements to dynamically steer a beam towards a specific user in order to maximise throughput.
The main beamforming antenna as specified in SEAMCAT is the Beamforming (Composite) antenna, which is in-line with the specifications outlined in section 5 of Rec. ITU-R M.2101. An implementation of 3GPP TR 37.840 is also available – the differences between these implementations are explained below.
Beamforming antenna arrays in SEAMCAT are specified at two levels – first the individual element antenna is specified as a regular antenna plugin, which is then used to form the larger array specified in a separate plugin. These are described in the following sections
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The beamforming element antenna is specified as a standard equation based antenna plugin in SEAMCAT.
Figure 3: Beamforming element antenna parameters
The input parameters and the corresponding notation as used in the following equations are:
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The total gain AEθ,φ is calculated as follows:
AEθ,φ=GE,max-min-AE,Hθ+AE,Vφ,Am |
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AE,Hθ=-min12θθ3dB2,Am | (3) |
AE,Vφ=-min12φ-90φ3dB2,SLAv | (4) |
Note that the notation for azimuth and elevation planes in these sections is the opposite of that used in M.2101 – this is for consistency with the wider SEAMCAT conventions, where φ=elevation and θ=azimuth.
This implementation is equivalent to the 3GPP TR 36.814 antenna pattern (
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Note that it is possible to use the element antenna in isolation (i.e. not as part of a beamforming array), however in this case any tilt settings will not be handled correctly. For this case it is recommended to instead use the 3GPP TR 36.814 antenna plugin directly.
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Once the element antenna has been specified, it can be applied to the composite array plugin which specifies the dimensions of the array:
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The element antenna can be modified by selecting Edit next to Element antenna. The other input parameters and the corresponding notation as used in the following equations are as follows
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The antenna peak gain is pre-calculated and shown for the input parameters (e.g. 23.1 dBi in Figure 4 above). This is provided for validation purposes.
Tilting of antennas is handled as for other antennas (see section x.y.z).
The beamforming gain Gθ,φ is calculated as follows:
Gθ,φ=AEθ,φ+10log10m=1NHn=1NVcosZn,m2+m=1NHn=1NVsinZn,m2NHNV
Zn,m=2πn-1dVλcosφ+sinφi,etilt+m-1dHλsinθsinφ-cosφi,etiltsinθi,escan
where
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- Pointing reference: towards the horizon
- Additional offset: Uniform distribution from -90° to +90°
Figure 5: Mobile station pointing settings
This is intended to reflect random user behaviour with the implementation of a UE with 2 antenna arrays pointing in opposite directions, where only the array which points towards the serving base station is active.
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Both of these options are illustrated below:
Figure 6: Beamforming antenna plot using "Gain envelope" mode
Figure 7: Beamforming antenna plot using "Full pattern" mode, with azimuth beamsteering angle set to 40 degrees
It is also possible to see the beamforming pattern on the individual event results – this can be useful to verify the gain values in a specific direction, as illustrated below:
Figure 8: Example of beamforming plots for interference between 2 IMT-2020 networks - ILT BS (red) to VLR UE (blue) - on the Event Results layout