Hierarchical Delay Tree for CDMA Path Search
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Solution Overview
Problem
Conventional wireless receivers face challenges in efficiently identifying and managing candidate delays for RAKE fingers due to changing channel parameters and the need to prevent unnecessary reassignment, which affects signal-to-noise ratio and path discovery in CDMA systems.
Innovation Solution
A new path search and verification method using a hierarchical delay tree and state machine to identify surviving delay nodes, where a tree generator builds the delay tree and a tree searcher identifies candidate delays, and a controller promotes or demotes delays based on subsequent searches, optimizing the selection of candidate delays for RAKE fingers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional path searchers use peak detection or grid overlay methods to identify candidate delays, then candidate delays can be identified, but the computational complexity increases and unnecessary reassignment of RAKE fingers occurs
Solution Approach 1:
The search space is segmented into hierarchical levels (coarse search at higher levels, fine search at lower levels). The delay search is divided into multiple stages: first searching at a coarse resolution to identify potential candidate regions, then refining the search in those regions at finer resolutions. This segmentation reduces the total number of computations required compared to a uniform fine-grained search across the entire range.
Solution Approach 2:
The verification function performs preliminary actions by evaluating candidate delays against multiple criteria (signal energy threshold, persistence over time, consistency across multiple measurements) before committing to RAKE finger reassignment. This preliminary verification filters out false candidates early, preventing unnecessary reassignments and reducing the computational burden of subsequent processing.
2Reliability
If the path searcher continuously monitors the received signal to track current RAKE finger delays and search for new candidate delays, then current delays are tracked accurately, but unnecessary reassignment of RAKE fingers occurs
Solution Approach 1:
The verification function implements feedback mechanisms by continuously monitoring candidate delays and comparing them against established criteria. When a candidate delay fails verification (e.g., signal energy drops below threshold, or the delay proves unstable across measurements), the system provides feedback to reject that candidate and maintain the current RAKE finger assignment. This feedback loop prevents premature or erroneous reassignments while maintaining accurate tracking of legitimate delay changes.
3Adaptability or versatility
If RAKE fingers are reassigned to new candidate delays, then the receiver adapts to changing channel conditions, but the reassigned RAKE finger must be disabled for a period of time causing service interruption
Solution Approach 1:
The verification function performs preliminary validation of candidate delays using multiple criteria (signal energy thresholds, persistence over multiple measurement intervals, consistency checks) before triggering RAKE finger reassignment. By thoroughly verifying candidates in advance, the system reduces the likelihood of erroneous reassignments, thereby reducing the frequency with which RAKE fingers need to be disabled and reassign ed, thus minimizing total service interruption time.
Data Source
AI summary
The present application describes a new path search and verification method and apparatus for identifying and selecting one or more delays for a receiver. A front-end receiver receives a signal having one or more signal images, where each signal image has a corresponding signal delay. A tree generator builds a hierarchical delay tree from a plurality of delay nodes, each corresponding to one of the signal delays. A tree searcher searches through the delay tree to identify one or more surviving delay nodes, where each surviving delay node corresponds to a candidate delay for the receiver. The receiver may also include a state machine comprising a plurality of ordered states for providing candidate delays for the receiver. The state machine stores the candidate delays and shifts the candidate delays between states within the state machine based on the latest results from the tree searcher.