White Space Modem Co-Channel Interference Mitigation
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Solution Overview
Problem
White space modems experience significant performance degradation due to co-channel interference from narrow multiband signals, leading to synchronization failures, estimation errors, and reduced data rates, particularly in TV spectrum bands occupied by undesired licensed or unlicensed signals.
Innovation Solution
A system and method that includes an interference detection module, a dynamic notch filter module, an interference aware signal to noise ratio (SNR) estimation module, and an interference aware de-mapper module in both base-station and customer premises equipment (CPE) to detect and mitigate co-channel interference by identifying central interference carriers and suppressing their power, thereby maintaining frame detection capability and achieving optimal de-mapping and bit error rate (BER) in OFDM signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If white space modems operate in TV spectrum bands, then data connectivity is enabled in unused broadcasting frequencies, but co-channel interference from narrow multiband signals severely degrades performance
Solution Approach 1:
The system segments the OFDM signal into multiple carriers and identifies specific interference-affected carriers. By processing each carrier individually through interference detection and selective filtering, the system can mitigate interference in specific frequency portions while maintaining operation in other carriers, thus preserving overall spectrum utilization while improving reliability.
Solution Approach 2:
The system extracts and removes interference components from the received signal by detecting interference carriers and applying notch filtering. This extraction process separates the desired signal from the harmful narrow multiband interference, enabling the modem to maintain reliable communication in the TV spectrum bands.
2Reliability
If dynamic notch filtering is applied to suppress interference carriers, then co-channel interference is mitigated, but frame detection capability may be affected
Solution Approach 1:
The system performs preliminary interference detection and identifies interference carriers before applying notch filtering. By detecting the interference pattern in advance and preparing the filtering operation, the system can suppress interference while preserving the integrity of frame detection signals, thus maintaining both interference mitigation and detection accuracy.
Solution Approach 2:
The system applies notch filtering selectively only to identified interference carriers rather than across the entire spectrum. This localized approach ensures that frame detection capability is preserved in non-interfered carriers while interference is suppressed in affected carriers, maintaining measurement precision while achieving reliability.
3Reliability
If interference-affected carriers are rejected from data allocation, then bit error rate is minimized, but data transmission capacity is reduced
Solution Approach 1:
The system segments the available spectrum into interference-free carriers and interference-affected carriers. By allocating data only to clean carriers and excluding affected carriers from data transmission, the system minimizes bit errors in transmitted data while maximizing utilization of available interference-free frequency resources, thus balancing reliability and productivity.
Data Source
AI summary
Disclosed is a system for mitigating co-channel interference (CCI) in white space (WS) modems. The system includes a base-station that includes a base-station transmitter and a base-station receiver. The base-station receiver receives an OFDM signal from one or more CPE transmitters. An interference detection module detects presence of co-channel interference in carriers of the OFDM signal and determines co-channel interference affected carriers. A dynamic notch filter module (i) receives central interference carriers from interference detection module and (ii) mitigates the co-channel interference of co-channel interference affected carriers without affecting frame detection capability of the system. An interference aware signal to noise ratio (SNR) estimation module determines an average signal to noise ratio (SNR) of (i) interference unaffected carriers and (ii) co-channel interference affected carriers. An interference aware de-mapper module processes average signal to noise ratio of (i) interference unaffected carriers and (ii) co-channel interference affected carriers.