OFDM Multi-Carrier Phase Tracking With Nested Dual-Domain PLLs
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Solution Overview
Problem
The traditional carrier phase tracking method in OFDM multi-carrier systems is affected by frequency errors due to crystal oscillator frequency deviation and Doppler offset, leading to phase offset accumulation and reduced positioning accuracy.
Innovation Solution
A carrier phase tracking method using a double-loop structure with nested frequency and time domain phase locked loops (PLLs) to track phase changes in both domains, involving frequency domain tracking, inter-symbol phase average offset determination, and adaptive loop filter adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional carrier phase tracking method is applied to OFDM multi-carrier system, then positioning accuracy is improved, but phase offset accumulation occurs due to frequency error between received and transmitted signals
Solution Approach 1:
The patent segments the phase tracking process into two independent domains: frequency domain tracking for inter-subcarrier phase correction and time domain tracking for inter-symbol phase correction. This segmentation allows each domain to be optimized independently, preventing the phase offset accumulation that occurs when a single tracking method is applied to the entire OFDM signal.
Solution Approach 2:
The patent introduces a dual-domain approach by adding the frequency domain dimension to the traditional time domain tracking. Frequency domain tracking addresses the inter-subcarrier phase offset caused by frequency errors, while time domain tracking handles inter-symbol phase offset, together providing comprehensive phase correction across multiple dimensions.
2Measurement precision
If frequency error occurs between OFDM received signal and transmitted signal, then phase offset accumulates with increase of subcarrier number, but traditional single-domain tracking cannot correct this accumulation
Solution Approach 1:
The patent implements a nested dual-loop PLL structure where the frequency domain PLL and time domain PLL are nested within each other. The frequency domain tracking corrects phase offsets for each subcarrier, and the time domain tracking further refines the carrier phase estimation across symbols. This nested structure enables comprehensive phase correction without requiring a completely separate tracking system.
Solution Approach 2:
The patent introduces an inter-symbol phase average offset as an intermediary parameter that bridges the frequency domain and time domain tracking processes. This intermediary allows the two domains to work together coherently, enabling the time domain tracker to use information from the frequency domain tracker to improve overall phase estimation accuracy.
3Measurement precision
If double-loop structure with nested frequency and time domain PLLs is used, then tracking precision is improved, but system complexity increases
Solution Approach 1:
The patent designs the dual-loop PLL structure to perform multiple functions: the frequency domain PLL corrects inter-subcarrier phase offsets and provides frequency error compensation, while the time domain PLL corrects inter-symbol phase offsets and provides fine carrier phase tracking. This multi-functionality justifies the increased structural complexity by delivering comprehensive phase correction that a single-loop system cannot achieve.
Data Source
AI summary
Provided in the embodiments of the present disclosure are a carrier phase tracking method and device for an orthogonal frequency division multiplexing (OFDM) multi-carrier system. The method includes: performing frequency domain tracking on a received current OFDM symbol and determining a phase of each subcarrier; analyzing a phase curve of all subcarriers and determining an inter-symbol phase average offset, and the inter-symbol phase average offset is used to characterize an estimated value of a difference obtained by subtracting a second value from a first value, the first value is a carrier phase value of the current OFDM symbol, and the second value is an estimated value of a carrier phase of a previous OFDM symbol; and performing time domain tracking by using the inter-symbol phase average offset as an input phase and determining an estimated value of a carrier phase of the current OFDM symbol.