Digital AGC for Multiband OFDM With Fast Per-Band Gain Adjustment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Designing an automatic gain control (AGC) system for the WiMedia standard's multiband orthogonal frequency division multiplexed (OFDM) system that requires accurate and rapid initial adjustments within the packet preamble to ensure optimal channel equalization and performance, while also accommodating variable signal energy across multiple antennas and frequency bands.
Innovation Solution
Implementing a digital AGC method that uses a single energy lookup table to adjust each frequency band separately, with only two adjustments per band, and integrating low-noise amplifier control, allowing for programmable gain codes and variable target gains, and utilizing a parallel/serial interface to efficiently transfer gain codes, ensuring timely and accurate adjustments across multiple antennas and frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional AGC methods are used with multiple adjustments per band, then gain accuracy can be improved, but the adjustment time increases and may exceed the preamble duration
Solution Approach 1:
The patent segments the frequency spectrum into multiple bands and applies separate AGC adjustments to each band. By using a single energy lookup table to adjust each frequency band separately with only two adjustments per band, the system achieves accurate gain control while minimizing adjustment time to fit within the packet preamble.
Solution Approach 2:
The AGC adjustments are performed in advance during the packet preamble before the actual data transmission. This preliminary action ensures that all gain adjustments are completed before channel equalization and other operations depend upon gain, optimizing performance without exceeding the preamble duration.
2Device complexity
If digital AGC computations are performed based on ADC output energy, then the analog design complexity is reduced, but the requirement for precise digital energy measurement increases
Solution Approach 1:
The patent replaces complex analog AGC design with digital AGC computations. By performing AGC computations in the digital portion of the system based on energy observed at the ADC output, and feeding back gain adjustments to analog amplifiers, the system simplifies analog design while maintaining measurement precision through digital processing.
3Measurement precision
If AGC adjustments are made frequently to track channel variations, then gain accuracy is maintained, but the settling time of analog amplifiers may be insufficient
Solution Approach 1:
The patent implements periodic AGC adjustments during the packet payload transmission. Adjacent AGC adjustments are designed to occur far enough apart so that analog amplifiers can settle before the next measurement, while still maintaining accurate gain control through periodic updates that track channel variations.
4Device complexity
If a parallel/serial interface is used to transfer gain codes for multiple antennas and bands, then the interface complexity is reduced, but the transfer time increases
Solution Approach 1:
The patent uses a universal parallel/serial interface that can transfer gain codes for multiple antennas and frequency bands through a single interface structure. This multi-functional interface reduces the number of separate connections needed while maintaining efficient data transfer for controlling multiple VGAs and LNAs across different channels and bands.
Data Source
AI summary
The invention enables automatic gain control in ultra wideband applications over multiple channels and frequency bands.