OFDM AGC Gain Tracking During Cyclic Prefix Intervals
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Solution Overview
Problem
In wireless communication systems using orthogonal frequency division multiplexing (OFDM), existing automatic gain control (AGC) systems face challenges in dynamically adjusting gain during the cyclic prefix (CP) period to account for varying signal strength and channel conditions, leading to potential data loss and increased complexity in channel estimation and ADC design.
Innovation Solution
A system incorporating a variable gain amplifier (VGA) with an AGC module that selectively adjusts gain during the CP period, accompanied by a channel estimation module that generates independent channel estimates, allowing for dynamic gain adjustment based on signal strength and using a digital gain adjuster to compensate for VGA gain changes, thereby reducing the need for large dynamic range and channel fading margin in the ADC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing AGC systems adjust gain during the cyclic prefix period in OFDM systems, then signal strength variations can be compensated, but data loss may occur and channel estimation complexity increases
Solution Approach 1:
The patent segments the OFDM symbol into two distinct parts: the cyclic prefix (CP) period and the useful symbol period. The AGC gain adjustment is applied exclusively during the CP period, while the useful symbol period maintains a fixed gain setting. This segmentation allows the system to exploit the redundant nature of the CP for gain tracking without affecting the integrity of the data-carrying useful symbols, thereby preventing data loss while still compensating for signal strength variations.
Solution Approach 2:
The patent implements preliminary gain adjustment during the cyclic prefix period before the useful symbol transmission begins. By completing the AGC gain tracking and stabilization during the CP period, the system ensures that the gain is properly set before actual data transmission starts in the useful symbol period, preventing data loss while achieving signal strength compensation.
2Reliability
If existing AGC systems dynamically adjust gain during transmission, then signal strength variations are compensated, but system complexity increases
Solution Approach 1:
The patent divides the transmission period into distinct segments with different AGC control strategies: the CP period allows dynamic gain adjustment for tracking signal strength variations, while the useful symbol period uses a fixed gain setting to simplify processing. This temporal segmentation reduces overall system complexity by limiting dynamic adjustments to only the necessary period.
Solution Approach 2:
The patent implements periodic AGC gain adjustment that occurs only during the cyclic prefix period of each OFDM symbol, rather than continuously throughout the entire symbol duration. This periodic action synchronized with the OFDM structure allows the system to compensate for signal strength variations while maintaining simplicity during the data-carrying useful symbol period.
3Measurement precision
If existing AGC systems use long settling time for gain adjustment, then accurate gain tracking is achieved, but the cyclic prefix period may be insufficient
Solution Approach 1:
The patent employs a dynamic AGC system that adapts its settling time requirements by utilizing the cyclic prefix period specifically for gain tracking. The system design ensures that the VGA's settling time is accommodated within the CP duration, and once settled, the gain remains stable throughout the useful symbol period. This dynamic approach allows accurate gain tracking to be achieved within the constrained CP duration.
Solution Approach 2:
The patent performs the gain adjustment and settling process preliminarily during the cyclic prefix period before the useful symbol transmission begins. By completing all necessary gain tracking and stabilization actions during the CP period, the system ensures that the full settling time requirement is met within the available CP duration, while the subsequent useful symbol period operates with stable, predetermined gain settings.
Data Source
AI summary
A system including a variable gain amplifier, an automatic gain control module, and a channel estimation module. The variable gain amplifier is configured to amplify an input signal in accordance with a gain. The input signal includes a plurality of orthogonal frequency domain multiplexing symbols. Each of the plurality of orthogonal frequency domain multiplexing symbols is preceded by a respective cyclic prefix. The automatic gain control module is configured to adjust, based on a signal strength of the input signal, the gain of the variable gain amplifier during the respective cyclic prefix preceding each of the plurality of orthogonal frequency domain multiplexing symbols. The channel estimation module is configured to generate a channel estimate for each of the plurality of orthogonal frequency domain multiplexing symbols, and to update the channel estimate in response to the gain of the variable gain amplifier being adjusted.