LPWA Object Location via Phase Difference Hyperbolic Trilateration
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Solution Overview
Problem
Existing methods for accurately locating objects in LPWA networks face challenges due to high energy consumption, incompatibility with indoor environments, low time resolution of narrowband signals, and the need for synchronisation and multiple packet transmissions, which degrade network performance.
Innovation Solution
A method that involves a connected object transmitting an RF signal across multiple frequency channels, with base stations performing translations and phase corrections to estimate phase and frequency offsets, allowing for accurate phase difference calculations without a reference node, using a server to calculate phase differences and construct composite transfer functions for hyperbolic trilateration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If narrowband signals are used for long-distance propagation in LPWA networks, then the transmission distance is improved, but the time of arrival resolution deteriorates
Solution Approach 1:
The patent transforms the problem from the time domain to the frequency domain by using phase difference measurements across multiple frequency channels. Instead of attempting to measure time of arrival directly with narrowband signals, the system measures phase differences at multiple frequencies and uses these to calculate distance, effectively changing the measurement dimension from temporal to spectral.
Solution Approach 2:
The patent changes the measurement parameter from time of arrival to phase difference. By measuring phase differences at multiple frequency channels and using the relationship between phase and frequency, the system achieves distance measurement precision that would otherwise require broadband signals. The phase difference φ(f) is measured at each frequency f, and these measurements are used to compute the time delay τ = -dφ/df.
2Measurement precision
If multiple packets are transmitted for PoF measurement, then the distance measurement accuracy is improved, but the network performance deteriorates
Solution Approach 1:
The patent uses partial action by measuring phase differences at a limited number of discrete frequency channels rather than continuously sweeping through the entire bandwidth. This partial frequency sampling is sufficient to achieve accurate distance measurement through the phase-vs-frequency relationship, while avoiding the excessive packet transmissions required by full bandwidth scanning methods.
Solution Approach 2:
The system uses periodic frequency hopping across a set of predefined channels to gather phase difference measurements. By periodically switching between these channels and accumulating phase measurements, the system achieves accurate distance estimation without requiring continuous transmission or excessive packets, thus maintaining network performance.
3Measurement precision
If hyperbolic trilateration based on ToA is used, then the locating accuracy is improved, but the need for broadband signals increases energy consumption
Solution Approach 1:
The patent changes the signal characteristic from broadband to narrowband by using phase difference measurements instead of time of arrival measurements. This parameter change allows the use of energy-efficient narrowband signals while still achieving accurate locating through hyperbolic trilateration, because phase differences can be measured precisely with narrowband signals and then converted to time delays.
Data Source
AI summary
A method for locating a connected object within an LPWA network using a plurality of base stations. The connected object transmits packets in RF frequency channels forming a virtual band being scanned once in the uplink direction and once in the downlink direction in a symmetrical manner. The base stations receiving the signal perform an RF to intermediate frequency translation and then a baseband translation in digital mode. The phase differences of arrival for each pair of base stations and the attenuation coefficients of each transmission channel between the connected object and each base station enable a composite transfer function to be constructed for each pair of base stations. The peaks of highest amplitude are detected in the corresponding impulse responses and the distance differences between the connected object and the different base stations are derived therefrom. The position of the object is then estimated by hyperbolic trilateration.