Non-binary Spreading Codes for Multipath Mitigation in Positioning Systems
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Solution Overview
Problem
Conventional positioning systems, such as GPS, experience degraded performance in poor signal conditions due to multipath issues, where mobile receivers receive multiple signals from direct and reflected paths, leading to inaccurate time-of-arrival measurements and location determination.
Innovation Solution
The use of wide area positioning systems (WAPS) with non-binary spreading codes, such as quaternary codes, that provide improved autocorrelation and cross-correlation properties, allowing for better multipath mitigation and higher data rates, along with a network of synchronized beacons and a server for position computation, enhancing the accuracy of location determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional positioning systems (GPS) are used, then the system is simple and widely available, but performance degrades in poor signal conditions due to multipath issues
Solution Approach 1:
The patent changes the parameter of spreading codes from conventional binary codes to non-binary codes (such as quaternary codes with symbols from a larger alphabet). This parameter change improves autocorrelation and cross-correlation properties, enabling better multipath mitigation and maintaining positioning accuracy in poor signal conditions while supporting higher data rates
2Reliability
If non-binary spreading codes are used, then multipath mitigation and data rates improve, but system complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-planning and pre-synchronizing the non-binary spreading codes at both transmitter and receiver ends. The codes are designed with specific autocorrelation and cross-correlation properties beforehand, allowing the receiver to efficiently process signals and mitigate multipath effects without requiring complex real-time computations
3Productivity
If non-binary spreading codes are used, then data rates increase, but signal processing complexity increases
Solution Approach 1:
The patent changes the parameter of code alphabet size from binary (2 symbols) to non-binary (e.g., quaternary with 4 symbols or larger). This enables more bits to be transmitted per chip, increasing data rate. The specific code design maintains good correlation properties to manage signal processing complexity while achieving higher throughput
Data Source
AI summary
Embodiments describe determining position by selecting a set of digital pseudorandom sequences. The magnitudes of the cross-correlation between any two sequences of the chosen set are below a specified threshold. A subset of digital pseudorandom sequences are selected from the set such that the magnitudes of the autocorrelation function of each member of the subset, within a specified region adjacent to the peak of the autocorrelation function, are equal to or less than a prescribed value. Each transmitter transmits a positioning signal, and at least a portion of the positioning signal is modulated with at least one member of the subset. At least two transmitters of the plurality of transmitters modulate respective positioning signals with different members of the subset of digital pseudorandom sequences.