Noise Distribution Shaping for CDMA Signal Acquisition
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Solution Overview
Problem
CDMA signal reception is impaired by impulsed noise in environments like those near ignition systems or power lines, leading to reduced signal-to-noise ratio due to conventional blankers setting thermal noise signals to zero, which affects synchronization and detection during signal acquisition.
Innovation Solution
A method and device for noise distribution shaping in CDMA signal acquisition, where the blanking thresholds are dynamically adjusted based on estimated signal power, thermal noise, and interference, using a test signal with a spreading sequence and carrier modulation to optimize correlation and detection, allowing for adaptive blanking and improved receiver operating characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional blanker with fixed thresholds is used to suppress impulsive interference, then interference rejection is improved, but signal-to-noise ratio deteriorates due to blanking of thermal noise signals
Solution Approach 1:
The blanking thresholds are made dynamic by continuously adapting them based on the estimated signal power and noise characteristics. The thresholds track the signal level through correlation with a known spreading sequence, allowing the blanker to distinguish between high-power interference and legitimate signal peaks, thereby suppressing interference while preserving thermal noise signals.
Solution Approach 2:
The blanking thresholds are changed from fixed symmetric values to adaptive values that depend on the estimated signal power and noise standard deviation. The thresholds are scaled by the square root of estimated signal power and adjusted by noise statistics, enabling them to adapt to varying signal and interference conditions while maintaining optimal detection performance.
2Device complexity
If fixed symmetric thresholds are used for blanking, then implementation simplicity is improved, but detection precision deteriorates in acquisition phase
Solution Approach 1:
The blanking threshold adaptation employs feedback from the correlation output between the received signal and the known spreading sequence. The estimated signal power is derived from this correlation, which then feeds back to adjust the thresholds. This feedback mechanism enables precise detection by continuously optimizing thresholds based on actual signal conditions without requiring complex manual tuning.
3Object-affected harmful factors
If blanking thresholds are offset from signal peaks, then interference blanking is improved, but correlation accuracy deteriorates due to misalignment with chip transitions
Solution Approach 1:
The method performs preliminary correlation between the received signal and the known spreading sequence to estimate signal power and timing characteristics before setting the blanking thresholds. This preliminary action allows the thresholds to be pre-aligned with the expected signal structure, ensuring that subsequent blanking operations do not misalign with chip transitions and maintain correlation accuracy.
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 enhances the signal acquisition process by reducing false alarms and missed detections, improving the signal-to-noise ratio and detection performance, even in noisy environments, by synchronizing blanking thresholds with the actual CDMA signal characteristics.
Implementation Method 1
demodulating the CDMA signal by multiplying with a carrier signal modulated with an estimated Doppler frequency
Implementation Method 2
modifying the noise distribution of the CDMA signal to generate a modified CDMA signal by blanking samples of the CDMA signal, when the samples of the CDMA signal exceed an upper or lower blanking threshold
Implementation Method 3
acquiring the CDMA signal, when a correlation between the modified CDMA signal and the generated test signal is above a predefined detection threshold
Data Source
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AI summary
The present invention provides a method of noise distribution shaping for signal acquisition of a Code Division Multiple Access signal. The method comprises demodulating the CDMA signal by multiplying with a carrier signal modulated with an estimated Doppler frequency. The carrier of the carrier signal is the CDMA signal carrier. The method further comprises generating a test signal having a spreading sequence according to the CDMA signal. The test signal is shifted by an estimated code delay. The method comprises modifying the noise distribution of the CDMA signal to generate a modified CDMA signal by blanking samples of the CDMA signal, when the samples of the CDMA signal exceed an upper or lower blanking threshold. The upper and lower blanking thresholds are offset by a square root of an estimated power, Pest, of the CDMA signal multiplied by a chip value polarity of the generated test signal and a predefined scaling factor, α. α is positive, negative, constant, time dependent, or changing its sign over time as function of the generated test signal. The method comprises acquiring the CDMA signal, when a correlation between the modified CDMA signal and the generated test signal is above a predefined detection threshold.