Wide Area Positioning System Hybrid Multiplexing Signal Separation
Solution Overview
Problem
Conventional positioning systems, such as GPS, experience degraded performance in poor signal conditions due to cross-interference and the need to distinguish multiple concurrent transmissions from geographically spread beacons, particularly in urban and wide area environments, where signal blockage and attenuation are significant, leading to challenges in accurate position measurement.
Innovation Solution
A wide area positioning system (WAPS) that employs a hybrid multiplexing method combining time division multiplexing (TDMA), code division multiplexing (CDMA), and frequency offset multiplexing (FOM) to distinguish transmissions from multiple beacons, using pseudorandom ranging signals with Gold codes and frequency offsets to reduce cross-interference and improve signal separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional positioning systems (GPS) are used in poor signal conditions, then the system can operate in wide area environments, but performance degrades due to cross-interference and signal blockage
Solution Approach 1:
The system segments the positioning infrastructure into multiple geographically distributed beacons that transmit positioning signals. Each beacon operates semi-autonomously, and the receiver processes signals from multiple beacons to determine position. This segmentation reduces the impact of signal blockage from any single beacon and distributes the cross-interference problem across multiple independent signal sources with distinct characteristics.
Solution Approach 2:
The patent introduces pseudorandom ranging signals with Gold codes as intermediaries between the beacons and the receiver. These coded signals act as unique identifiers for each beacon and enable the receiver to distinguish between concurrent transmissions from different beacons through code correlation, effectively mediating the separation of mixed signals in poor signal conditions.
2Adaptability or versatility
If multiple concurrent transmissions from geographically spread beacons are used to improve wide area coverage, then positioning availability increases, but cross-interference and difficulty in distinguishing transmissions increase
Solution Approach 1:
Each beacon is assigned unique local qualities in the form of pseudorandom Gold codes and frequency offsets. These local distinctions enable the receiver to identify and process signals from different beacons even when they transmit concurrently. The unique code properties (autocorrelation and cross-correlation characteristics) provide the necessary discrimination capability for signal separation in wide area environments.
Solution Approach 2:
The system adds additional dimensions for signal differentiation beyond simple time division. By incorporating code division (Gold codes) and frequency offset dimensions, the system creates a multi-dimensional signal space that allows concurrent transmissions from multiple beacons to be distinguished. This dimensional expansion enables wide area coverage with multiple simultaneous transmissions without proportionally increasing interference complexity.
3Measurement precision
If hybrid multiplexing method (TDMA, CDMA, FOM) is used to distinguish multiple beacon transmissions, then signal separation improves, but system complexity increases
Solution Approach 1:
The patent merges three multiplexing approaches (TDMA, CDMA, and FOM) into a unified hybrid system where time slots, Gold codes, and frequency offsets work together to distinguish beacon transmissions. This combination allows the system to achieve superior signal separation by exploiting multiple orthogonal dimensions simultaneously, with each dimension providing redundant discrimination capability that reinforces the others.
Solution Approach 2:
The hybrid multiplexing system is designed with universal applicability across wide area positioning scenarios. The same framework of combining TDMA, CDMA, and FOM can accommodate varying numbers of beacons, different geographic distributions, and diverse signal conditions. The Gold codes serve multiple functions including beacon identification, signal separation, and ranging measurement, reducing the need for separate mechanisms.
4Measurement precision
If pseudorandom ranging signals with Gold codes and frequency offsets are used to reduce cross-interference, then position measurement accuracy improves, but processing requirements increase
Solution Approach 1:
The receiver performs preliminary acquisition and tracking of pseudorandom ranging signals before final position calculation. By pre-processing the incoming signals to identify and correlate with expected Gold codes from multiple beacons, the receiver reduces the computational burden of subsequent position determination. The frequency offsets are used early in the processing chain to separate signals, enabling more efficient correlation operations.
Data Source
AI summary
A position location system comprises transmitters that broadcast positioning signals. Each broadcasted positioning signal comprises a pseudorandom ranging signal. The position location system includes a remote receiver that acquires and measures the time of arrival of the positioning signals received at the remote receiver. During an interval of time, at least two positioning signals are transmitted concurrently by the transmitters and received concurrently at the remote receiver. The two positioning signals have carrier frequencies offset from one another by an offset that is less than approximately twenty-five percent of the bandwidth of each positioning signal of the two positioning signals. Cross-interference between the positioning signals is reduced by tuning the remote receiver to a frequency of a selected signal of the two positioning signals and correlating the selected signal with a reference pseudorandom ranging signal matched to a transmitted pseudorandom ranging signal of the selected signal.