Terrestrial Positioning Timing System Using CDMA
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Solution Overview
Problem
Current terrestrial positioning and timing systems, such as DME and VOR, have limitations in providing accurate position, velocity, and time (PVT) services, especially when GPS is unavailable, due to their pulsed modulation formats, substantial ground facility requirements, and multipath signal errors.
Innovation Solution
A Terrestrial Positioning and Timing System (TPTS) using CDMA signal format and pseudo-random noise codes, integrated with existing DME infrastructure, providing differential corrections and multiple signal components for range and bearing determination, enabling PVT solutions through a network of synchronized TPTS stations and user antennas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pulsed modulation format is used in DME system, then range measurement capability is provided, but timing accuracy and range accuracy deteriorate due to pulse timing derivation limitations
Solution Approach 1:
The patent changes the modulation parameter from pulsed format to continuous wave (CW) format with code division multiple access (CDMA) spreading codes. This parameter change enables precise range measurement through correlation processing of the continuous signal, replacing the pulse timing derivation method and achieving better range accuracy without the limitations of pulsed modulation.
Solution Approach 2:
The patent substitutes the mechanical pulse timing measurement system with an electronic correlation processing system. Instead of measuring range by deriving timing from broadcast pulses, the system uses correlation of CDMA spreading codes with the transmitted signal to achieve precise range measurement, replacing the mechanical timing derivation approach with electronic signal processing.
2Ease of operation
If VOR system is used for bearing information, then bearing capability is provided, but ground facility requirements and multipath errors increase substantially
Solution Approach 1:
The patent merges the range measurement function and bearing capability into a single integrated system. By using a network of TPTS stations with CDMA signaling, the system provides both range and bearing information from the same infrastructure, eliminating the need for separate VOR ground facilities and reducing multipath errors through the robustness of CDMA signal processing.
Solution Approach 2:
The patent introduces CDMA spreading codes as an intermediary mechanism to enable bearing determination. The unique spreading codes assigned to each TPTS station allow the user receiver to identify and process signals from specific stations, enabling bearing calculation through signal arrival direction and timing without requiring the substantial ground facilities of traditional VOR systems.
3Measurement precision
If GPS satellite-based positioning is used, then position accuracy is provided, but service availability deteriorates when GPS is unavailable
Solution Approach 1:
The patent creates a terrestrial copy of the GPS positioning function. By implementing a ground-based TPTS network that mimics the satellite-based GPS architecture using CDMA signaling and pseudorandom noise codes, the system provides equivalent position, velocity, and timing (PVT) services terrestrially, ensuring service availability when GPS is unavailable while maintaining comparable accuracy.
Solution Approach 2:
The patent establishes a terrestrial positioning infrastructure in advance that can serve as a backup or alternative to GPS. By deploying TPTS stations with CDMA signaling before GPS failure occurs, the system provides a pre-positioned alternative that ensures continuous PVT service availability, cushioning against the risk of GPS unavailability.
4Reliability
If TPTS station network is deployed for PVT services, then service continuity is improved when GPS is unavailable, but device complexity increases
Solution Approach 1:
The patent designs TPTS stations with multi-functionality to reduce overall system complexity. Each station is capable of providing range measurement, bearing information, and timing services simultaneously through CDMA signaling. This universal functionality eliminates the need for separate specialized facilities for each function, reducing infrastructure complexity while maintaining service continuity.
Solution Approach 2:
The patent employs periodic transmission of CDMA spread spectrum signals by TPTS stations. The periodic nature of the signaling allows user receivers to accumulate signal energy over multiple periods through correlation processing, improving measurement accuracy and reliability without requiring excessive transmission power or complex station infrastructure.
Data Source
AI summary
A terrestrial positioning and timing system (TPTS) comprising a ground segment and user segment is disclosed that is comprised of a spread-spectrum based range and bearing reference signal, with respect to a reference time, transmitted by an antenna over a broad region of space; and a spread-spectrum based bearing variable signal with bearing specific modulation referenced to a reference time, transmitted using a scanning antenna over a spatial region of space that is more narrow than the spread-spectrum based range and bearing reference signal transmission spatial area. Various embodiments enable the TPTS station and user to support various position, velocity or time services. Most notably, an embodiment with a single TPTS station, active interrogation/transponder reply, and data delivery subsystem can provide a position, velocity, and time solution for the user. Additional embodiments disclosed provide varying levels of user solutions to include bearing, position, velocity, or time.