OFDM Receiver FFT Window Adjustment for Preceding Wave Interference
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Solution Overview
Problem
In OFDM receivers, significant inter-symbol interference occurs when a preceding wave is present, leading to deterioration in reception quality due to multipath delays exceeding the guard interval, especially when the time difference between the main wave and the preceding wave is larger than the guard interval.
Innovation Solution
The OFDM receiver adjusts the FFT window's start position by shifting it forward by an amount corresponding to the guard interval when a time difference larger than the guard interval is detected between the main wave and the preceding wave, and employs band filtering to pass both the main and preceding waves, thereby minimizing inter-symbol interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a guard interval is introduced to improve reception performance under multipath environment, then inter-symbol interference is reduced for delay waves, but significant inter-symbol interference occurs when preceding waves are present with time difference larger than guard interval
Solution Approach 1:
The FFT window position is dynamically adjusted based on the detected time difference between main wave and preceding wave. When the time difference exceeds the guard interval, the FFT window position is shifted forward by the guard interval duration, allowing the system to adapt to varying multipath conditions and eliminate inter-symbol interference from preceding waves
Solution Approach 2:
The system changes the FFT window position parameter based on detected multipath conditions. By shifting the FFT window position forward when a preceding wave is detected with time difference larger than guard interval, the system modifies its operational parameters to maintain reception quality under varying environmental conditions
2Device complexity
If FFT window position is fixed at symbol start position, then simple processing is maintained, but inter-symbol interference occurs when multipath delay exceeds guard interval
Solution Approach 1:
The FFT window position transitions from a fixed configuration to a dynamic one that adjusts based on detected multipath conditions. The system detects the time difference between main wave and preceding wave, and only shifts the FFT window position when necessary (when time difference exceeds guard interval), maintaining simplicity while improving reliability
3Reliability
If band filtering is applied to pass both main and preceding waves, then inter-symbol interference is minimized, but additional processing steps are required
Solution Approach 1:
The system performs preliminary detection of the time difference between main wave and preceding wave using delay profile generation. Based on this detection, it preliminarily determines whether FFT window position adjustment is needed, performing the filtering action only when necessary to minimize unnecessary processing while maintaining reception quality
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly improves reception quality by reducing inter-symbol interference even when multipath delays exceed the guard interval, maintaining good reception quality until the time difference between the main and preceding waves exceeds 260μ seconds.
Implementation Method 1
an FFT unit generating a frequency domain signal from an OFDM signal by Fourier transform
Implementation Method 2
a delay profile generation unit generating a delay profile of the OFDM signal using the frequency domain signal
Data Source
AI summary
An FFT unit generates a frequency domain signal by converting an OFDM signal using Fourier transform. A delay amount calculation unit generates a delay profile of the OFDM signal. The control determination unit detects a main wave and an interference wave using the delay profile. When the time difference between the main wave and a preceding wave is larger than a guard interval of the OFDM signal, an FFT window control unit sets the start position of the FFT window at a position shifted forward from the symbol start position of the main wave by an amount corresponding to the guard interval.