WAPS Hybrid Multiplexing for Cross-Interference Reduction
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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 result in a high dynamic range of received power levels.
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 noise (PN) codes and frequency offsets to reduce cross-interference and improve signal separation, allowing for accurate ranging measurements in multipath environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional positioning systems (GPS) are used in urban environments, then positioning capability is provided, but cross-interference from multiple concurrent transmissions degrades performance
Solution Approach 1:
The patent segments the transmission medium by assigning different time slots (TDMA), code sequences (CDMA), and frequency offsets (FOM) to different beacons. This segmentation allows multiple beacons to transmit concurrently without interference, as each beacon occupies a unique combination of time, code, and frequency resources. The receiver can separately process signals from different beacons by correlating with the assigned codes and filtering at assigned frequencies, thereby eliminating cross-interference in urban environments.
Solution Approach 2:
The patent introduces an additional dimension for signal separation by combining three multiplexing dimensions: time (TDMA), code (CDMA), and frequency (FOM). Instead of relying on a single dimension, the system uses a three-dimensional resource allocation space where each beacon is assigned a unique triplet of (time slot, code sequence, frequency offset). This multi-dimensional approach provides sufficient separation even when beacons are geographically spread and transmit concurrently, resolving the cross-interference problem.
2Measurement precision
If multiple concurrent transmissions from geographically spread beacons are distinguished, then positioning accuracy is improved, but signal blockage and attenuation in urban environments create high dynamic range of received power levels
Solution Approach 1:
The patent applies preliminary signal processing at the receiver by pre-correlating received signals with stored pseudorandom codes assigned to each beacon. This preliminary correlation action occurs before full signal processing, allowing the receiver to identify and isolate desired signals from concurrent transmissions. By performing this correlation-based separation in advance, the system can accurately measure signal arrival times even in the presence of blockage and attenuation, maintaining positioning accuracy in urban environments.
Solution Approach 2:
The patent uses pseudorandom noise codes as an intermediary mechanism to separate desired signals from interfering signals. The receiver correlates incoming signals with stored PN codes, and only signals matching the assigned code produce strong correlation peaks. This intermediary correlation process acts as a filter that passes desired signals while rejecting blocked or attenuated signals from other beacons, enabling accurate ranging measurements despite high dynamic range variations caused by urban blockage and attenuation.
3Reliability
If hybrid multiplexing method (TDMA, CDMA, FOM) is employed to reduce cross-interference, then signal separation is improved, but system complexity increases
Solution Approach 1:
The patent merges three multiplexing techniques (TDMA, CDMA, FOM) into a unified hybrid system where they work together rather than independently. By combining these methods, the system achieves signal separation with moderate complexity in each domain. The time-division aspect reduces the number of concurrent signals at any moment, the code-division aspect provides correlation-based separation, and the frequency-offset aspect adds spectral separation. This merged approach distributes the complexity across three simpler dimensions rather than requiring one complex separation mechanism.
Solution Approach 2:
The patent implements dynamic resource allocation where the hybrid multiplexing parameters (time slots, codes, frequency offsets) can be flexibly assigned to different beacons based on their geographic locations and transmission characteristics. This dynamic assignment allows the system to optimize signal separation for each specific deployment scenario, reducing the effective complexity by adapting to actual operating conditions rather than requiring fixed, overly complex separation mechanisms for all possible scenarios.
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.