Bluetooth Channel Sounding with Interference Cancellation for Indoor Ranging
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Solution Overview
Problem
Existing phase-based ranging solutions using narrow-band radios like Bluetooth Low Energy (BLE) struggle to achieve centimeter accuracy in indoor environments due to dynamic changes in signal propagation paths, reflections, diffractions, and multipath interference, as well as interference from other wireless devices.
Innovation Solution
A Bluetooth Low Energy channel sounding (BLE CS) processing pipeline that includes a scene identifier module, feature selection module, and interference cancellation modules to adaptively filter and process phase measurements, transforming data from the frequency to the time domain using minimum variance distortion-less response (MVDR) algorithms and Kalman filters to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase-based ranging solutions using unmodulated pulses are used to achieve sub-meter accuracy, then ranging precision is improved, but measurement accuracy deteriorates in cluttered indoor environments due to multipath interference and signal reflections
Solution Approach 1:
The patent applies successive interference cancellation to convert harmful multipath interference into beneficial information by identifying and removing interference peaks from the channel impulse response. The system detects peak locations in the frequency domain, transforms them to time domain, and iteratively cancels the strongest interference components, allowing the direct path signal to be extracted with centimeter-level accuracy even in highly reflective indoor environments
Solution Approach 2:
The patent performs preliminary frequency domain transformation and peak detection before time domain analysis. By first transforming the channel sounding data to the frequency domain, identifying peak locations, and preparing interference cancellation parameters in advance, the system optimizes the subsequent time domain processing and range estimation accuracy
2Reliability
If multiple frequency measurements are performed to mitigate multi-path fading, then signal reliability is improved, but measurement time increases
Solution Approach 1:
The patent implements continuous channel sounding across multiple frequencies without interruption, maintaining uninterrupted signal exchange between devices. The system continuously measures phase shifts at multiple frequency points and processes them through the interference cancellation pipeline, ensuring that the useful measurement action continues without gaps while gathering sufficient data for accurate ranging
Solution Approach 2:
The patent segments the multi-frequency measurement process into independent frequency point measurements that can be processed parallel to each other. Each frequency point is measured and transformed independently, allowing the system to efficiently process multiple frequencies without sequential delays, thereby reducing overall measurement time while maintaining signal reliability
3Measurement precision
If interference cancellation processing is applied to remove multipath signals, then range estimation accuracy is improved, but computational complexity increases
Solution Approach 1:
The patent extracts only the essential interference components by identifying and removing the strongest peaks from the channel impulse response. Instead of processing the entire signal, the system focuses computational resources on extracting and canceling the most significant interference peaks, thereby reducing the overall computational burden while maintaining accuracy
Solution Approach 2:
The patent applies partial interference cancellation by limiting the number of peaks removed to the most significant ones rather than attempting to cancel all multipath components. This partial action approach achieves sufficient accuracy improvement without the excessive computational cost of complete interference removal, balancing complexity and performance
Data Source
AI summary
Disclosed are techniques for successively cancelling interference in time-domain representation of I/Q phase measurement data based on detecting frequency peaks with maximum intensity or frequency peaks with maximum energy in frequency-domain for phase-based ranging (PBR). In one aspect, the frequency peaks may contain the maximum energy in least squares sense. An initiator of the PBR operating in a cluttered environment may identify at least an intensity or an index of a peak in a frequency-domain representation or a time-domain representation of the phase measurement data obtained between the initiator and a reflector. The initiator may remove the peak from a time-domain representation of the phase measurement data based on at least the intensity or the index of the peak to generate a residual time-domain representation. The initiator may estimate a range to the reflector based on the index of the peak or another peak derived from the residual time-domain representation.