WCDMA Receiver Gain Control for Adjacent Channel Clipping
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Solution Overview
Problem
Wideband Code Division Multiple Access (WCDMA) receivers face issues with adjacent channel interferences due to limited selectivity of radio units, leading to signal clipping at the sigma delta analog to digital converter (SD-ADC) input, as existing architectures require high dynamic range SD-ADCs and leave the desired signal susceptible to impairments.
Innovation Solution
The implementation of a power measurement unit that adjusts the gain of amplifiers and filters to set a predetermined input power for the SD-ADC, using a low dynamic range converter and a bandwidth selector to attenuate adjacent channel interferences, ensuring the desired signal is within the optimal range and reducing clipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the dynamic range of SD-ADC is expanded to handle adjacent channel interferences, then signal clipping is prevented, but the complexity and cost of the ADC increases
Solution Approach 1:
The patent segments the interference handling function from the desired signal processing path by introducing a separate measurement path. The power measurement unit measures total input power including interferences, while the matched filter processes only the desired signal. This segmentation allows the ADC to operate with lower dynamic range while still capturing the desired signal accurately.
Solution Approach 2:
The patent introduces an intermediary measurement path with a power measurement unit that measures the total input signal power including adjacent channel interferences. This measurement serves as an intermediary indicator that feeds back to the AGC, enabling gain adjustment without requiring the main signal path to handle the full dynamic range of interferences.
2Object-affected harmful factors
If headroom is left at the upper part of SD-ADC dynamic range for adjacent channel interferences, then clipping is avoided, but the desired signal is pushed to a lower part of the range where it is more susceptible to implementation impairments
Solution Approach 1:
The patent implements a feedback mechanism where the power measurement unit continuously monitors the total input power and feeds this information back to the AGC. The AGC adjusts the amplifier gain based on this feedback to maintain the desired signal at an optimal level in the upper part of the ADC dynamic range, preventing both clipping and susceptibility to impairments.
Solution Approach 2:
The patent dynamically changes the gain parameter of the amplifiers based on the measured power level of adjacent channel interferences. By adjusting the gain according to the actual interference conditions, the system optimizes the positioning of the desired signal within the ADC dynamic range, ensuring it remains in the optimal region regardless of interference levels.
3Measurement precision
If the gain of amplifiers is adjusted based on assigned channel power measurement, then the desired signal level is optimized, but adjacent channel interferences cause clipping at the ADC input
Solution Approach 1:
The patent extracts the interference measurement function from the desired signal processing path. The power measurement unit is configured to measure the total input power including interferences, while the matched filter extracts only the desired signal. This extraction allows the system to account for interferences in gain control without letting them contaminate the desired signal measurement.
Data Source
AI summary
Briefly, a radio receiver architecture and a method of measuring a power of a received signal to provide a first measurement, measuring a power of an assigned channel signal to provide a second measurement and adjusting a power of an input signal of an analog to digital converter according to a difference between the first and second power measurements.