Adaptive Guard Interval Combining for OFDM Signal Reception
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Solution Overview
Problem
Conventional communication systems face challenges in accurately receiving RF signals due to interference and noise, particularly in multipath environments where Doppler frequency shifts and inter-carrier interference (ICI) occur, leading to errors in Bit-Error-Rate (BER) and Packet-Error-Rate (PER).
Innovation Solution
The implementation of adaptive guard interval (GI) combining, where a portion of the guard interval is combined with the corresponding portion of the OFDM symbol to reduce noise and ICI, utilizing a 1-tap infinite impulse response low-pass filter to determine the delay spread and adjust the GI combining based on channel conditions, thereby mitigating the effects of Doppler shifts and time-variation in the channel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If guard interval combining is applied to reduce noise and ICI, then signal reception quality improves, but system complexity increases due to additional processing requirements
Solution Approach 1:
The patent implements adaptive guard interval combining where the processing is dynamically adjusted based on channel conditions. The system selectively applies GI combining only when delay spread conditions are favorable, making the processing complexity variable rather than fixed, thus improving reception quality only when beneficial while managing overall system complexity.
Solution Approach 2:
The system changes the processing parameter (whether to apply GI combining) based on measured channel characteristics, specifically delay spread. By monitoring channel parameters and adjusting processing accordingly, the system optimizes the trade-off between reception quality and processing complexity in real-time.
2Reliability
If adaptive GI combining is implemented to mitigate Doppler shifts and time-variation, then communication performance improves, but computational requirements increase
Solution Approach 1:
The patent employs dynamic adaptive processing where computational effort is adjusted based on channel conditions. When delay spread is small and channel conditions are stable, the system applies full adaptive GI combining. When conditions deteriorate or are unfavorable, the processing is reduced or bypassed, optimizing power consumption relative to performance gains.
Solution Approach 2:
The system applies different processing strategies to different portions of the signal based on local channel characteristics. By analyzing delay spread and applying GI combining selectively to appropriate signal portions rather than uniformly processing all data, the system reduces unnecessary computational power consumption while maintaining performance where beneficial.
3Measurement precision
If delay spread filtering is performed to determine channel conditions, then accuracy of GI combining improves, but processing time increases
Solution Approach 1:
The patent implements a filtering mechanism that processes delay spread measurements with appropriate smoothing to reduce noise and improve accuracy. The filter operates at an optimized level - not overly aggressive that would cause excessive delay, but sufficient to provide accurate channel condition assessment for GI combining decisions, balancing measurement precision with processing time constraints.
Data Source
AI summary
Methods and systems are provided for adaptive guard interval (GI) combining. A signal carrying a symbol that is preceded by a guard interval (GI) that includes a portion of the symbol may be received, and a portion of the GI that is free from inter-symbol interference (ISI) may be determined. Only a part of the ISI-free portion of the GI may be selected. The selected part of the ISI-free portion of the GI may be less than a whole of the ISI-free portion. The selection may be configured based on a parameter that is applied to a function used in extracting the symbol. The parameter may be a timing adjustment, relative to a start of the symbol, applied to the function when extracting the symbol. Only the part of the ISI-free portion of the GI may then be extracted and combined with a corresponding portion of the symbol.