RF Front-End Gain Control for ADC Saturation Prevention
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Solution Overview
Problem
The existing automatic gain control (AGC) systems in RF front ends, particularly in LTE wireless systems, face challenges in dynamically adjusting gain to prevent signal saturation during transitions from low to high resource block occupancy sub-frames, leading to increased radio link failures due to latency and saturation of analog-to-digital converters.
Innovation Solution
A gain control function dynamically reprograms the maximum gain of the AGC by estimating the total noise and interference power or using received signal strength indications to maintain the digital data at a nominal level, ensuring the amplified signal does not saturate the ADC, thereby preventing radio link failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional AGC dynamically adjusts receive-path gain to maintain nominal ADC input level, then weak signals are boosted above noise floor, but latency causes high gain to be applied to high-RB occupancy sub-frames resulting in ADC saturation
Solution Approach 1:
The patent applies preliminary action by predicting the resource block occupancy of upcoming sub-frames before they occur. The base station uses scheduling information to anticipate whether the next sub-frame will have high or low RB occupancy, and pre-adjusts the AGC gain accordingly. This eliminates the latency problem because the gain adjustment is made in advance based on predicted conditions rather than reacting to past measurements.
Solution Approach 2:
The patent implements dynamics by making the AGC gain adjustment dependent on the predicted RB occupancy state. The system dynamically switches between different gain levels based on whether high-RB or low-RB occupancy is predicted, rather than using a fixed or purely reactive gain adjustment mechanism. This allows the system to adapt quickly to changing signal conditions.
2Measurement precision
If AGC applies high gain to boost weak signals above noise floor, then weak signal detection is improved, but the same high gain causes strong signals to saturate the ADC
Solution Approach 1:
The patent applies local quality by tailoring the AGC gain setting to the specific characteristics of each upcoming sub-frame. Instead of using a uniform gain adjustment, the system applies different gain levels localized to each sub-frame based on its predicted RB occupancy. This ensures that each sub-frame receives the appropriate gain treatment - high gain for low-RB occupancy sub-frames and low gain for high-RB occupancy sub-frames.
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting the AGC gain parameter based on predicted RB occupancy. The system changes the gain parameter from a fixed value to a variable that adapts to different sub-frame conditions. This allows the gain parameter to be optimized for each specific signal condition, preventing both weak signal loss and ADC saturation.
3Ease of operation
If AGC uses time-domain average power measurement for gain control, then simple implementation is achieved, but inaccurate power measurement during low-RB occupancy leads to incorrect gain adjustment
Solution Approach 1:
The patent applies preliminary action by using scheduling information to predict RB occupancy before sub-frames occur. This prediction mechanism prevents inaccurate power measurements by anticipating when low-RB occupancy will occur and adjusting gain accordingly, rather than relying on post-measurement analysis that is too late to prevent saturation.
Data Source
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AI summary
One embodiment is directed to controlling a gain for a receive signal path for receiving wireless signals. The following are repeatedly performed: determining an estimate of the total noise and interference in a received signal and determining a gain value for the receive signal path based on the estimate of the total noise and interference in order to maintain the digital data at a digital set point for a signal-to-interference-plus-noise-ratio (SINR) decoded with a highest modulation and coding scheme specified for the wireless channel. Another embodiment is directed to determining a received signal strength of the signals received at the receive signal path and determining a gain value for the receive signal path based on the received signal strength that maintains the digital data at a digital set point for a SINR sufficient to decode the MCS specified for the wireless channel.