Receiver Window Shaping for OFDM Narrowband Interference Mitigation
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Solution Overview
Problem
Wideband and ultra-wideband communication systems face challenges in eliminating or reducing the effects of frequency domain spreading of narrowband interference (NBI), which affects a larger portion of the bandwidth spectrum beyond the original interfering tones due to sinc function side lobes.
Innovation Solution
A method for receiver window shaping is introduced, where a first receiver window is shaped to concentrate narrowband interference energy to the center frequency, potentially overlapping with previous windows, and designed to minimize energy capture and place stop bands on interference side lobes, reducing leakage to other sub-carriers. This involves shaping the window as a trapezoid, adding channel impulse responses, and applying it at the edges of zero-padded symbols to focus interference energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a square or rectangular window function is applied by the receiver in the time domain, then the symbol extraction is simplified, but the narrowband interference spreads in frequency domain like a sinc function with slow-decreasing side lobes, affecting a larger portion of the bandwidth spectrum
Solution Approach 1:
The patent changes the window function parameters from a simple rectangular shape to a customized shape with specific characteristics: the window starts before the symbol begins, includes a flat region in the time domain between symbol edges, and has controlled decay edges. This parameter modification transforms the frequency domain response to concentrate interference energy at the center frequency while reducing side lobe levels, thereby resolving the contradiction between extraction simplicity and interference spreading.
Solution Approach 2:
The patent applies different window characteristics to different portions of the received signal. The window function has a flat region aligned with the symbol edges to preserve signal integrity, while having decaying edges before and after the symbol to control interference. This localized quality differentiation allows the window to simultaneously maintain symbol accuracy and suppress interference spreading in the frequency domain.
2Object-affected harmful factors
If the receiver window is extended to overlap with previous windows, then narrowband interference energy is concentrated to the center frequency, but the window complexity and processing requirements increase
Solution Approach 1:
The patent implements preliminary action by pre-defining the customized window shape parameters and characteristics before signal processing. The window function with its specific properties (starting point before symbol, flat region, decaying edges) is prepared in advance, allowing the receiver to simply apply this predetermined window to concentrate interference energy without requiring complex real-time calculations, thus reducing processing complexity while achieving interference concentration.
3Loss of energy
If the first receiver window is shaped to minimize total energy capture, then interference leakage to other sub-carriers is reduced, but the window design complexity increases
Solution Approach 1:
The patent minimizes interference leakage by optimizing specific window parameters: the flat region duration, edge decay rates, and overall window position relative to symbol boundaries. These parameter optimizations are designed to minimize the integral of the window function's frequency response outside the desired frequency band, thereby reducing interference leakage to other sub-carriers while maintaining a relatively simple window structure that can be implemented with standard signal processing techniques.
Data Source
AI summary
A receiver window for symbol extraction is provided. A symbol is spread across a plurality of sub-carriers of a frequency band for transmission. If the frequency band is affected by narrowband interference, the receiver window concentrates the narrowband interference energy to minimize its effect on distant sub-carriers within the frequency band. The receiver window is shaped for extracting the symbol from the frequency band, wherein the receiver window has a starting point before the start of the symbol. The receiver window overlaps a previous receiver window for the previous adjacent symbol on the same frequency band. The receiver window is shaped by overlapping and adding a channel impulse response segment from a zero-padded portion of the symbol to the beginning of the symbol and overlapping and adding a second portion from the previous zero-padded symbol (from the same frequency band) to the end of the symbol.