Radio Base Station Power Control for RF EMF Compliance
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Solution Overview
Problem
Advanced antenna systems in radio base stations increase maximum beamforming gain, leading to higher momentary power density, which can exceed regulatory RF EMF exposure limits, necessitating efficient control of total average transmission power to maintain compliance with safety margins.
Innovation Solution
A back-off power control loop mechanism is implemented in a control device to compute and limit the total average transmission power over a specified time window, ensuring it remains below regulatory thresholds by setting momentary transmission power to a minimum value when the average exceeds the power threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If advanced antenna systems with large number of antenna elements are deployed to achieve high directivity, then beamforming gain is increased, but radiated power concentration in directional beams increases EIRP beyond RF EMF exposure limits
Solution Approach 1:
The control device performs preliminary evaluation of future total average transmission power before actual transmission occurs. By assessing whether limiting momentary power to minimum value would cause the average to exceed threshold, the system proactively prevents harmful power density levels before they occur, rather than reacting after exceeding limits
Solution Approach 2:
The patent implements a feedback control mechanism where the control device continuously monitors momentary transmission power values, evaluates their impact on total average transmission power, and adjusts future momentary power levels accordingly. When evaluation shows that current or future power levels would cause average power to exceed the threshold, the system feeds back a control signal to limit power to minimum values
2Reliability
If momentary transmission power is controlled to prevent exceeding average power threshold, then RF EMF compliance is maintained, but transmission power utilization efficiency is reduced
Solution Approach 1:
The control device applies partial power limitation only when necessary to maintain compliance. Instead of continuously limiting power to minimum values, the system evaluates future average power and applies limiting actions only for the specific discrete time values needed to prevent threshold exceedance, thereby maintaining maximum power utilization during compliant operation periods
Solution Approach 2:
The patent implements dynamic power control where the momentary transmission power level is continuously adjusted based on real-time evaluation of the total average transmission power. The system transitions between full power operation and minimum power limitation dynamically, optimizing power utilization while ensuring compliance with RF EMF exposure limits
3Reliability
If evaluation of future total average transmission power is performed for all discrete time values, then power threshold compliance is ensured, but computational complexity increases
Solution Approach 1:
The control device segments the evaluation process by focusing on discrete time values and individual momentary power values rather than continuously analyzing all possible future scenarios. The system divides the time domain into discrete intervals and evaluates power limits at specific points, reducing computational burden while maintaining compliance assurance
Data Source
AI summary
There is provided mechanisms for controlling total average transmission power of a radio base station. A method is performed by a control device. The method comprises performing, for a current discrete time value t, control of total average transmission power {Ptot}(t) of the radio base station according to a back-off power control loop. The total average transmission power {Ptot}(t) is computed over an averaging time window T of the present value of momentary transmission power and the N−1 values of momentary transmission power preceding the present value of momentary transmission power. The method comprises evaluating, for a future discrete time value less than, or equal to, t+T, the total average transmission power, assuming that values of momentary transmission power for all discrete time values from t up to t+T, starting at the next discrete time value t+1, is limited to a minimum value of said momentary transmission power. The method comprises limiting the momentary transmission power to the minimum value for at least the next future discrete time value when the evaluated total average transmission power, for any of the future discrete time values, exceeds a power threshold value based on a regulatory limit.