Parallel Spread Spectrum Signal Acquisition System
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Solution Overview
Problem
In spread spectrum communication systems, detecting messages with unknown code phase, code frequency offset, and carrier frequency offset is challenging, especially in systems with high processing gain and low-cost transmitters, where traditional sequential searching methods are ineffective for short message transmissions and oscillators provide low accuracy.
Innovation Solution
A system comprising a receiver, multiple searchers, and an estimator that perform parallel searches for code phase, code frequency offset, and carrier frequency offset hypotheses to produce correlation results, allowing for simultaneous estimation of these unknown parameters and enabling faster acquisition and detection of spread spectrum encoded messages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional sequential searching methods are used to detect spread spectrum signals, then the detection process is simpler to implement, but the detection speed is slow and ineffective for short message transmissions
Solution Approach 1:
The detection process is segmented into three independent searchers, each responsible for searching one specific parameter (code phase, code frequency offset, or carrier frequency offset). This segmentation allows parallel processing of multiple parameters simultaneously, dramatically improving detection speed while keeping each individual searcher relatively simple in structure.
Solution Approach 2:
The invention transforms the traditional one-dimensional sequential search into a three-dimensional parallel search space by independently searching code phase, code frequency offset, and carrier frequency offset simultaneously. This dimensional expansion enables comprehensive parameter search without increasing the complexity of individual search components.
2Reliability
If high processing gain is used to spread transmitter power over large bandwidth, then the probability of detection by unauthorized users decreases, but the acquisition difficulty for authorized receivers increases
Solution Approach 1:
The acquisition process is divided into three separate searchers that independently search for code phase, code frequency offset, and carrier frequency offset. This segmentation reduces the complexity of acquiring signals with high processing gain by breaking down the difficult three-dimensional search into manageable independent components that can be processed in parallel.
Solution Approach 2:
The invention changes the search parameters from traditional sequential scanning to parallel searching across three distinct parameter dimensions (code phase, code frequency offset, carrier frequency offset). This parameter transformation enables efficient acquisition of high processing gain signals by simultaneously exploring the entire parameter space rather than sequentially.
3Productivity
If very short preambles are used to limit power consumption and enhance low probability of detection, then the transmission efficiency improves, but the time available for detection is reduced
Solution Approach 1:
The parallel searcher structure enables continuous and simultaneous searching of all three parameters (code phase, code frequency offset, carrier frequency offset) throughout the preamble duration. This continuous parallel processing maximizes the utilization of the short preamble time, ensuring that detection proceeds efficiently without wasting any of the limited available time.
Solution Approach 2:
By segmenting the detection task into three parallel searchers, the system can process multiple hypotheses simultaneously during the short preamble period. This segmentation allows the full detection capability to be applied continuously throughout the limited preamble time, rather than sequentially wasting time on one parameter at a time.
4Ease of manufacture
If low-cost transmitters with low-accuracy oscillators are used, then the manufacturing cost decreases, but the carrier frequency offset and code frequency offset accuracy deteriorate
Solution Approach 1:
The system uses itself to correct frequency offsets by searching for and identifying the actual carrier frequency offset and code frequency offset through the parallel searcher structure. Rather than relying on high-precision oscillators, the receiver autonomously determines the frequency parameters by processing the received signal through multiple hypothesis searchers, effectively compensating for the low accuracy of inexpensive oscillators.
Data Source
AI summary
A system and method for detecting a spread spectrum encoded message within a received signal is described. The spread spectrum encoded message has an unknown code phase, unknown code frequency offset, and unknown carrier frequency offset. A plurality of code phase hypotheses, code frequency offset hypotheses, and carrier frequency offset hypotheses are searched in parallel. The unknown code phase, unknown code frequency offset, and unknown carrier frequency offset may also be estimated.