Aperiodic DSSS Detector Using Cascaded Correlators
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Solution Overview
Problem
The matched filter technique is not applicable to aperiodic DSSS systems due to unpredictable sign modulation of the PN sequence, making it impossible to discriminate between correctly and incorrectly aligned PN sequences.
Innovation Solution
A detector system using partial adapted correlators with coefficients chosen from different segments of the PN sequence, cascaded with a square module block to remove sign dependence, allowing for effective synchronization in aperiodic DSSS systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the matched filter technique is used for PN sequence acquisition, then acquisition speed and performance under low signal-to-noise ratio conditions are improved, but the technique becomes inapplicable to aperiodic DSSS systems due to unpredictable sign modulation
Solution Approach 1:
The patent divides the PN sequence into multiple segments and uses separate correlators for each segment. By processing segments independently and combining results, the system can handle unpredictable sign modulations in aperiodic DSSS while maintaining acquisition performance.
Solution Approach 2:
Instead of trying to match the entire PN sequence directly (which fails due to sign modulation), the patent inverts the approach by using correlators with coefficients that are exact replicas of PN sequence segments, then combining the squared outputs to achieve reliable detection regardless of sign changes.
2Adaptability or versatility
If serial search or sequential search techniques are used for PN sequence acquisition, then adaptability to aperiodic DSSS systems is maintained, but acquisition speed and performance under low signal-to-noise ratio conditions deteriorate
Solution Approach 1:
The patent creates a multi-functional acquisition system that can operate effectively in both periodic and aperiodic DSSS modes. The correlator structure with segment-based processing and squared output combination provides universal applicability across different DSSS system types while maintaining high acquisition performance.
3Measurement precision
If the entire PN sequence is used in each correlator, then complete correlation capability is achieved, but computational complexity and resource requirements increase significantly
Solution Approach 1:
The patent segments the PN sequence and assigns different segments to different correlators. This segmentation reduces the computational burden on each individual correlator while maintaining overall correlation accuracy through the combination of multiple correlator outputs.
Solution Approach 2:
Instead of requiring each correlator to process the entire PN sequence, the patent uses partial actions where each correlator processes only a segment. The combination of multiple partial correlations achieves the equivalent of full sequence correlation with reduced individual complexity.
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
Enables accurate synchronization and despreads the received signal by generating correlation peaks, overcoming the limitations of the matched filter technique in aperiodic DSSS systems.
Implementation Method 1
the received information signal is sequentially fed to a correlator whose coefficients are an exact replica of the PN sequence (i.e., a matched filter). The matched filter generates an output signal that is maximum when the PN sequence contained in the received signal is aligned (in phase) with the correlator coefficients.
Implementation Method 2
cascaded with a square module block to remove sign dependence
Data Source
Figure 1a~2
Figure 3~4
Figure 5~6c
AI summary
A DSSS detector (19) for detecting a synchronization between an aperiodic spread spectrum signal (r(nTc)) having a plurality of chips (r(n) ) and a spreading sequence (PN) having a plurality of chips (pi). The DSSS detector (19) has at least one branch (16) adapted to receive the spread spectrum signal, and the branch is formed by a plurality of correlators (1) cascade connected to each other and separated one another by a branch delay block (20). Each correlator (1) has a multiplier (12) for correlating chips (pi) of the spreading sequence (PN) with chips (r(n) ) of the spread spectrum signal (r(nTc)) and generating each an own correlation value (y(n)). The DSSS detector (19) further has a matching detector (22, 23, 27) receiving the correlation values (y(n) ) and detecting when all the correlation values (y(n)) are maximum.