Per-Symbol Receiver Scaling for Rapid OFDM Channel Changes
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Solution Overview
Problem
High-speed movement of receivers or transmitters in OFDM systems leads to rapid changes in channel conditions, making existing Automatic Gain Control (AGC) and digital AGC processes insufficient for maintaining signal amplitude within a suitable range, thereby deteriorating receiver performance.
Innovation Solution
A per-symbol scaling apparatus with a calculating unit and a scaling unit that estimates signal strength and generates a scaling factor to adjust the amplitude of symbols in a symbol-by-symbol manner, eliminating the need for digital AGC and reducing hardware costs by using a feed-forward control scheme.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional feedback-based AGC and digital AGC processes are used, then signal amplitude can be controlled under stable channel conditions, but receiver performance deteriorates under rapidly changing channel conditions caused by high-speed movement
Solution Approach 1:
The patent applies preliminary action by estimating the signal strength of the current received symbol and generating a scaling factor before the symbol undergoes digital signal processing. This feed-forward approach pre-determines the scaling factor based on current channel conditions, eliminating the delay inherent in feedback-based AGC systems. The scaling factor is calculated using the formula: scaling factor = threshold / (sqrt(sum of squared magnitudes of pilot subcarriers)), allowing immediate adaptation to channel changes without waiting for feedback loops.
Solution Approach 2:
The patent segments the gain control process by applying scaling factors on a per-symbol basis rather than using continuous feedback control. Each symbol receives an independent scaling factor calculated from its own signal strength estimation, enabling granular adaptation to rapid channel variations. This segmentation allows the system to handle each symbol independently according to its specific channel conditions, significantly improving responsiveness to high-speed movement-induced fading.
2Object-affected harmful factors
If filter is used to remove adjacent frequency band interference, then interference is reduced, but the desired signal amplitude becomes smaller requiring additional digital AGC
Solution Approach 1:
The patent merges the interference filtering function with the gain control function into a single integrated process. The scaling apparatus is positioned after the filter that removes adjacent frequency band interference, and the scaling factor calculation inherently compensates for the signal attenuation caused by filtering. By combining these functions, the system eliminates the need for separate digital AGC stages while maintaining both interference rejection and proper signal amplitude levels throughout the digital signal processing chain.
3Ease of operation
If feedback-based AGC control is implemented, then signal amplitude can be adjusted, but the control response is too slow for high-speed movement scenarios
Solution Approach 1:
The patent inverts the traditional feedback control architecture by implementing a feed-forward control scheme. Instead of measuring the output signal and adjusting the gain based on feedback (which introduces delay), the system estimates the input signal strength and applies the scaling factor proactively before digital signal processing. This inversion of the control flow eliminates the feedback loop delay, achieving immediate response to channel conditions changes caused by high-speed movement while maintaining ease of amplitude control through systematic scaling factor calculation.
Data Source
AI summary
A scaling apparatus set in a receiver is disclosed. The receiver includes a symbol-processing unit. The scaling apparatus includes a calculating unit and a scaling unit. The calculating unit estimates the signal strength of an input symbol and generates a scaling factor accordingly. The scaling unit scales an output symbol outputted from the symbol-processing unit according to the scaling factor. The output symbol is generated from the symbol-processing unit through processing the input symbol.