RF Front-End Gain Control to Prevent ADC Saturation
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Solution Overview
Problem
Traditional automatic gain control (AGC) methods in RF front ends for wireless channels, such as LTE, can lead to radio link failures due to high-gain application during high resource block occupancy subframes following low resource block occupancy subframes, causing signal saturation in the analog-to-digital converter (ADC).
Innovation Solution
A method to dynamically reprogram the maximum gain of the AGC function based on estimates of total noise and interference or received signal strength to maintain the digital data at a signal-to-interference-plus-noise-ratio (SINR) sufficient for the specified modulation and coding scheme, thereby preventing signal saturation and improving throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional automatic gain control dynamically adjusts receive-path gain to maintain nominal ADC input level, then weak received RF signals are boosted above the noise floor, but high gain applied to high-RB occupancy subframes causes ADC saturation and block errors
Solution Approach 1:
The patent implements dynamic maximum gain adjustment where the AGC function's maximum gain parameter is reprogrammed based on real-time estimates of total noise and interference power. Instead of using a fixed maximum gain, the system continuously adapts the gain ceiling to current channel conditions, preventing ADC saturation during high-RB occupancy subframes while maintaining adequate gain for weak signals during low-occupancy periods
Solution Approach 2:
The system establishes a feedback loop where the AGC function monitors the actual signal level at the ADC input and compares it against the digital set point. Based on this feedback and the estimated noise/interference conditions, the system adjusts the maximum gain parameter to maintain optimal operation, creating a closed-loop control mechanism that prevents both saturation and excessive noise amplification
2Power
If high gain is applied to boost weak signals during low resource block occupancy, then signal power is increased for ADC conversion, but the gain persists into high resource block occupancy subframes causing signal saturation
Solution Approach 1:
The patent applies preliminary action by estimating the total noise and interference power before processing each subframe and pre-adjusting the maximum gain parameter accordingly. This allows the system to prepare the appropriate gain ceiling in advance, preventing both the excessive gain that causes saturation and the insufficient gain that leaves signals buried in noise
Solution Approach 2:
The system dynamically changes the maximum gain parameter of the AGC function based on estimated noise and interference conditions. By modifying this critical parameter in response to changing channel conditions, the system adapts its signal processing behavior to prevent ADC saturation during high-RB occupancy while maintaining adequate signal boosting during low-occupancy periods
Data Source
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.