Abstract
Currently, high gain antenna arrays are deployed in cellular radio systems to enhance wireless capacity. These advanced antenna systems increase the peak equivalent isotropic radiated powers (EIRPs), thereby potentially also increasing the size of the exclusion zones for radio frequency (RF) electro magnetic field (EMF) exposure that are applied to limit the presence of workers and the general public in the vicinity of the antennas. The exclusion zones are determined from the RF EMF exposure limits, typically expressed in terms of time-averaged incident power density values as provided by national authorities and regulatory bodies. To mitigate possible deployment challenges in some urban areas due to the overly conservative use of peak EIRP in determining exclusion zones, the possibility of basing the exclusion zone on a time averaged EIRP is discussed. To support this new approach, this paper presents an average power feedback controller that mathematically guarantees that the average power transmitted over a specified time window by a single radio base station stays below a determined value defining the exclusion zone. Such automation may be required by regulators to allow the use of time averaged quantities for RF EMF exposure assessment and exclusion zone determination. The developed average power controller uses a combination of controllers to regulate the rate of change of a momentary fractional frequency resource limit in the scheduler. This restricts the momentary total transmit power since the transmit power is proportional to the scheduled frequency resources. Simulation results, laboratory measurements and on-site measurements for a commercially available 5G MIMO transmitting base station are then reported, all of them verifying that the average power controller performs as intended. The average power control solution is applicable for any 4G or 5G base station, with or without MIMO transmission capability.
Highlights
W HEN radio equipment is to be deployed, electromagnetic field (EMF) exposure regulations need to be accounted for
When determining the radio frequency (RF) EMF exclusion zones for deployments of multi-input-multi-output (MIMO) transmitting 4G or 5G radios with advanced antenna systems (AASs) capable of active beam steering [2], it is important to observe that the maximum beamforming gain and equivalent isotropic radiated power (EIRP) may be significantly increased as compared to traditional antennas [3]- [6], since traditional antennas do not possess the active steering enabled by the arrays of AASs
LABORATORY MEASUREMENTS To verify that the average power controller works as intended when implemented in the real products, and that the resulting time-averaged RF EMF exposure can be controlled below a set threshold, tests were initially performed in the Vodafone 5G laboratory in Düsseldorf, Germany
Summary
W HEN radio equipment is to be deployed, electromagnetic field (EMF) exposure regulations need to be accounted for. Since the beam gain increases significantly when AASs are introduced, the size of the exclusion zone increases, assuming the same transmit power and that the actual time-averaged value has not been taken into account This is challenging in particular in the case of co-siting where the combined RF exposure from all antennas need to be considered to meet the EMF limits at a site. This selected threshold is denoted ε below, and it is expressed as a fraction of the maximum power of the regulated radio system. The average power is computed for each sampling time instance of the feedback loop
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