AoA Carrier Frequency Offset Correction Using Phase Oversampling
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Solution Overview
Problem
Existing Angle of Arrival and Angle of Departure algorithms are affected by carrier frequency offset (CFO) inaccuracies, leading to less accurate angle calculations due to frequency inaccuracy in network devices, which is common given the tolerance of crystals used in generating carrier frequencies.
Innovation Solution
A system and method for detecting and compensating for CFO by oversampling incoming signals, calculating the phase, and determining the carrier frequency offset using the time derivative of the phase, allowing for adjustment of received signals to improve the accuracy of angle calculations in AoX algorithms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If carrier frequency is generated using standard crystals with ±20 ppm tolerance, then device manufacturing cost and ease of operation are maintained, but angle of arrival calculation accuracy deteriorates due to carrier frequency offset
Solution Approach 1:
The patent changes the frequency parameter from a fixed crystal-generated value to a dynamically measured and compensated value. By measuring the actual carrier frequency at both transmitting and receiving ends and calculating the offset, the system adapts the frequency parameter to real-world variations, thereby improving angle of arrival accuracy without requiring higher-precision crystals.
Solution Approach 2:
The patent implements a feedback mechanism where the measured carrier frequency offset is used to adjust and compensate the angle of arrival calculation. The system continuously monitors the frequency deviation and applies corrective calculations, creating a closed-loop system that maintains accuracy despite crystal tolerance variations.
2Measurement precision
If carrier frequency offset compensation is implemented, then angle of arrival accuracy is improved, but device complexity and computational requirements increase
Solution Approach 1:
The patent performs preliminary frequency measurement and offset calculation before the main angle of arrival computation. By pre-determining the carrier frequency offset using the constant tone extension, the system prepares the correction factor in advance, simplifying the subsequent processing and reducing real-time computational burden.
Solution Approach 2:
The patent uses the constant tone extension as an intermediary element to measure and determine the carrier frequency offset. This intermediary signal serves as a reference that facilitates the frequency measurement process, enabling accurate offset calculation without directly processing the main data signal, thereby reducing overall processing complexity.
3Measurement precision
If constant tone extension is used for frequency measurement, then carrier frequency offset detection accuracy is improved, but packet structure complexity and transmission time increase
Solution Approach 1:
The patent applies partial action by using only a specific portion of the constant tone extension (the guard period and reference period) for frequency offset measurement, while other portions serve different purposes. This selective usage optimizes the balance between measurement accuracy and transmission efficiency, avoiding the need to extend the entire packet duration.
Solution Approach 2:
The constant tone extension serves multiple functions: it provides a reference for carrier frequency offset measurement, maintains synchronization, and structures the packet format. By making this element multi-functional, the patent avoids adding separate dedicated measurement signals that would increase transmission time, thereby optimizing the trade-off between accuracy and efficiency.
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
The proposed solution significantly improves the accuracy of AoX algorithms by compensating for CFO, reducing errors in angle calculations and enhancing the precision of determining the angle of arrival or departure, as demonstrated by tests showing a reduction in calculation errors from 8 degrees to 4 degrees.
Implementation Method 1
calculate a phase of each sample, wherein the phase is defined as arctan(I/Q)
Data Source
AI summary
A system and method for detecting and compensating for carrier frequency offset is disclosed. This system compensates for CFO and calculates a corrected phase. This corrected phase may be used by, for example, an AoX algorithm, such as MUSIC, to more accurately determine the angle of arrival or angle of departure of a signal. In certain embodiments, the system oversamples the incoming signal to create a plurality of samples. The system then determines the phase of each of the plurality of samples and calculates the carrier frequency based on the time derivative of the phase. In certain embodiments, a particular portion of an incoming packet is used to determine the carrier frequency offset. In other embodiments, the system calculates the carrier frequency offset throughout an entirety of the incoming packet. Once the carrier frequency offset is determined, it can be used to adjust the received signals. These adjusted signals are then used to determine the angle of arrival or angle of departure.