BLE Distance Estimation Using Uniform Frequency Sample Sets
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Solution Overview
Problem
Existing wireless systems, such as those using the Bluetooth Low Energy (BLE) standard, face challenges in accurate distance estimation due to limited communication event times, bandwidth constraints, and parasitic effects like noise and oscillator drift.
Innovation Solution
The method involves determining an operating range of consecutive transmission frequencies and creating sample sets with tones spaced uniformly across this range. These sample sets are wirelessly transmitted to a remote device, where phase shifts are measured and used to estimate distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional FMCW radar ranging systems are used, then distance estimation accuracy is improved through frequency bandwidth optimization, but the system becomes unsuitable for BLE HADM PBR applications due to limited communication event time and different operating principles
Solution Approach 1:
The patent adapts FMCW radar frequency selection principles to BLE HADM PBR by modifying frequency parameters to suit the limited communication event time constraint. Instead of using continuous frequency sweeping as in conventional FMCW radar, the system selects specific discrete frequencies within the available BLE bandwidth that optimize phase-based ranging accuracy within the short connection event window.
Solution Approach 2:
The system dynamically adjusts frequency selection based on the actual communication event duration and environmental conditions. The frequency set is not fixed but adapted in real-time to match the available measurement time and to compensate for parasitic effects such as oscillator drift and temperature variations, making the system versatile for varying BLE operating conditions.
2Measurement precision
If multiple frequencies are used for phase-based ranging, then distance estimation accuracy is improved, but the communication event time requirement increases beyond BLE limitations
Solution Approach 1:
Instead of using all available frequencies within the BLE bandwidth, the patent selects a partial set of optimally spaced frequencies that provide sufficient measurement accuracy within the constrained event time. This partial action approach uses only the necessary number of frequency points to achieve the required precision without exceeding the time budget.
Solution Approach 2:
The system performs preliminary selection of frequency sets before the actual ranging measurement, pre-calculating which frequency combinations will provide optimal accuracy within the available time. This preliminary preparation allows the actual measurement phase to proceed efficiently without time-consuming frequency scanning or adaptation during the connection event.
3Measurement precision
If frequency bandwidth is increased to improve distance estimation accuracy, then measurement precision improves, but parasitic effects such as noise and oscillator drift have greater impact
Solution Approach 1:
Rather than uniformly increasing the entire frequency bandwidth, the patent applies local quality by selecting specific frequency regions and discrete frequency points that are less susceptible to parasitic effects. Certain frequency ranges are preferred where oscillator drift and noise have minimal impact on phase measurements, creating localized optimal measurement zones within the overall bandwidth.
Solution Approach 2:
The system converts the potential harm of oscillator drift and frequency variations into a benefit by using these variations as additional measurement dimensions. By carefully selecting frequency sets that account for expected drift patterns, the system can actually improve accuracy by measuring phase differences across frequencies that naturally compensate for oscillator instability.
4Measurement precision
If conventional FMCW radar frequency selection is applied, then ranging accuracy is optimized, but security requirements such as randomness in frequency selection cannot be met
Solution Approach 1:
The frequency set is segmented into multiple possible subsets, each optimized for different conditions. The system can switch between different segmented frequency groups based on security requirements and environmental conditions, providing both accuracy optimization and randomness for security purposes through selective subset usage.
Solution Approach 2:
The frequency selection becomes dynamic and adaptive, changing based on security requirements, environmental conditions, and measurement history. This dynamic adjustment provides the randomness needed for security while maintaining accuracy through intelligent selection of frequency sets that are optimized for current operating conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate and efficient distance estimation across a wide operating bandwidth, reducing noise interference and improving performance in environments with limited communication time.
Implementation Method 1
HADM PBR estimates a distance between two BLE devices by measuring phase differences of 'reflected' (i.e., returned) signals in different frequencies
Implementation Method 2
Ranging using transmitted signals is known in the different field of frequency modulated continuous wave (FMCW) radar applications
Data Source
AI summary
A method can include determining a plurality of sample sets, each sample set being different from one another and including a plurality of frequencies separated by a uniform frequency range; wirelessly transmitting information identifying the sample sets for at least one remote device; for each sample set, transmitting a tone on each frequency of the sample set, receiving a tone on each frequency of the sample set from another device, and determining phase difference values for the received tones with respect to corresponding transmitted tones. From the phase shift values, a distance to the other device can be estimated. Corresponding devices and systems are also disclosed.