Timing Offset Compensation in Spread Spectrum Systems
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Solution Overview
Problem
Spread spectrum systems are sensitive to clock timing offsets, leading to inter-chip interference and degradation, with existing methods like early-late gate and Mueller-Muller algorithms being computationally intensive or sensitive to carrier offsets, respectively.
Innovation Solution
An apparatus and method that oversamples symbols to obtain multiple samples, calculates chip and system clock timing offsets using peak value sample indices, and compensates for these offsets through downsampling, reducing computational complexity and improving estimation precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If early-late gate algorithm is used to estimate timing offset, then timing estimation can be performed, but computational complexity increases significantly in high data rate systems
Solution Approach 1:
The patent extracts only the necessary information (peak sample indices from despread sequences) needed for timing offset estimation, avoiding the need to process and compare multiple sample points around ideal positions as in early-late gate algorithm. This extraction approach maintains estimation capability while significantly reducing computational burden.
Solution Approach 2:
The patent uses oversampling to create multiple copies of the signal at different time positions, then processes these copies through despreading and peak detection. This copying approach allows accurate timing estimation without requiring complex comparisons at multiple points, as the oversampled copies provide sufficient information for precise offset calculation.
2Device complexity
If Mueller-Muller algorithm is used to estimate timing offset, then computational complexity is reduced, but sensitivity to carrier offset increases and timing estimation performance degrades
Solution Approach 1:
The patent segments the received signal into multiple oversampled sequences and processes each segment through despreading with unique codes. By dividing the signal processing into segments and using peak detection on despread sequences, the method achieves accurate timing estimation without the carrier offset sensitivity issues of Mueller-Muller algorithm.
Solution Approach 2:
The patent introduces despreading with unique codes as an intermediary process between signal reception and timing offset estimation. This intermediary step transforms the signal into a form where peak detection provides accurate timing information, avoiding the direct carrier offset sensitivity problem of Mueller-Muller algorithm while maintaining low computational complexity.
3Speed
If downsampling is performed without timing offset compensation, then processing rate is reduced, but timing errors increase when timing error fluctuates within symbol unit
Solution Approach 1:
The patent performs timing offset estimation using oversampled sequences before downsampling. By calculating the timing offsets (both chip clock and system clock offsets) in advance while the signal is still oversampled, the method ensures accurate timing compensation is applied before the signal rate is reduced, preventing timing errors that would otherwise increase during downsampling.
Data Source
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AI summary
Provided are an apparatus and method for compensating for a timing offset in a spread spectrum system which perform an oversampling of respective symbols to obtain a plurality of samples, estimate a chip clock timing offset and a symbol clock timing offset from the plurality of samples, and compensate for the chip clock timing offset and the symbol clock timing offset. The apparatus includes an oversampling unit (10) that oversamples, by a multiple P, data whose each of N symbols is spread over and received by C chips, an oversampled chip collection unit (20) that collects C, which is a number of chips, samples at positions apart from each of all the oversampled samples by the multiple P, which is the oversampling multiple, a despreading unit (30) that despreads each of collected oversampled chips using a unique code of the corresponding symbol, a peak value detection/storage unit (40) that detects an oversampled chip having a largest correlation value among despread oversampled chips in every predetermined section and then stores sample indices of the detected oversampled chips as peak value sample indices, a timing offset calculation unit (50) configured to calculate a chip clock timing offset Oct and a system clock timing offset Ost using the respective peak value sample indices, and a downsampling unit (60) that downsamples the oversampled samples while compensating for the chip clock timing offset and the system clock timing offset.