![]() If the wanted signal contains a number of beams, and/or considering that the phase impact of intermodulations will vary in a frequency-specific manner, the pattern of emissions arising from such transmitter distortions is likely to be beamformed, but potentially with a different pattern to that of the wanted signal (See Fig. Other components are related to distortions of the wanted signal, such as intermodulations. These components will not experience coherent beamforming and will be radiated according to the pattern of the element groups driven by each transmitter. Some unwanted emissions components are generated by random noise-like processes, which are uncorrelated between different transmitters. The radiation pattern of unwanted emissions from an AAS base station depends on several factors. For any conformance requirements that need to consider the radiation pattern of the base station, the requirements need to be placed on the AAS BS as a whole such that the impacts of all beamforming mechanisms in addition to transceiver performance are captured. The radiated beam pattern is the composite result of all digital and analog beam steering, antenna and subarray radiation patterns, and transceiver properties. The beamforming functionality of the base station is in general distributed between so-called analog beamforming, which takes place within the antenna element groups driven by each individual transmitter or receiver and digital beamforming, which takes place in the digital domain prior to conversion to analog transmission (as described in Section 7.3). However, OTA testing alone is not the only challenge to consider in setting regulatory requirements for AAS base stations. OTA testing of base stations is a major paradigm shift for base station testing that has resulted in significant work in standardization and regulatory fora. Thus, for AAS base stations, it is necessary to specify requirements and corresponding relevant metrics and perform conformance testing (as well as other forms of testing such as research and development testing and manufacturing testing) over the air, that is, by means of analyzing signals radiated from the base station and/or exposing the base station to radiated signals in a controlled environment. Even for systems for which connectors can be provided, since beamforming is a key component of the base station function it is desirable to set some requirements that encompass the antenna array as well as the radio/transceiver. For large arrays and in particular for millimetric-wave systems, provision of test connectors becomes unfeasible. Chapter 14, considers in more detail the application scenarios and benefits/drawbacks of each architecture option.Ī first and very significant challenge for an AAS is that when there is a large number of radio transmitters and receivers, the feasibility of building antenna connectors for each individual radio transmitter together with a testing setup that enables testing of the combined response of individual radios is severely compromised. AAS base stations may be built around a number of different architecture concepts, ranging from fully digital, in which each individual antenna element is driven by an individual radio transmitter to hybrid, in which groups of elements (e.g., columns) are driven by a transmitter. The ability to dynamically adjust the radiation pattern contrasts with the systems described in Section 11.4.1, in which the radiation pattern is fixed. In 3GPP RAN4 it is assumed that an AAS base station comprises a system in which active radio/transceivers and antenna components are integrated, which is capable of dynamically varying the radiation pattern in a controlled manner. Erik Larsson, in Advanced Antenna Systems for 5G Network Deployments, 2020 11.4.2 Challenges Introduced by Advanced Antenna System Radio Performance Requirements and Regulation
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