OTFS Receiver Design for CFO Compensation in Doppler Channels
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Solution Overview
Problem
Existing OTFS communication systems face challenges in maintaining spectral efficiency and reliability due to carrier frequency offset (CFO) and Doppler spread, particularly in high-mobility scenarios, leading to increased pilot overhead and computational complexity.
Innovation Solution
A dual-rate data communication frame is introduced, utilizing first-type blocks with low-rate data and superimposed pilots for initial OFO estimation, followed by GCE-BEM-based channel estimation and compensation, allowing for efficient OFO estimation and compensation without additional pilots, thereby optimizing spectral efficiency and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional OFDM is used for wireless communication, then spectral efficiency and robustness against frequency selective fading are improved, but performance deteriorates under high-mobility conditions with Doppler spread and time-varying channels
Solution Approach 1:
The patent transforms the communication approach by changing the domain parameters from time-frequency (OFDM) to delay-Doppler (OTFS). This parameter transformation allows the system to maintain reliability under high-mobility conditions by representing signals in a domain where Doppler spread and time-varying effects are naturally handled, thus resolving the contradiction between OFDM's spectral efficiency and adaptability to high-mobility channels.
Solution Approach 2:
The patent introduces a dimensional transformation by moving from 1D time-domain or 2D time-frequency domain (OFDM) to a 2D delay-Doppler domain (OTFS). This dimensional change enables the system to capture and exploit the structure of doubly selective fading channels, achieving both reliability and adaptability to high-mobility scenarios simultaneously.
2Reliability
If OTFS modulation is used to cope with doubly selective fading, then robustness against Doppler spread is improved, but computational complexity increases
Solution Approach 1:
The patent applies preliminary action by performing channel estimation and equalization in the delay-Doppler domain before signal detection. By pre-processing the received signal to estimate channel characteristics and compensate for Doppler spread effects beforehand, the system reduces the computational burden during the actual detection phase, thus resolving the contradiction between robustness and computational complexity.
Solution Approach 2:
The patent substitutes complex time-domain equalization and Doppler compensation operations with simpler delay-Doppler domain processing. By transforming the problem into a domain where channel effects are diagonalized or simplified, the system replaces computationally intensive operations with more efficient algorithms, maintaining robustness while reducing complexity.
3Measurement precision
If pilots are increased to estimate and compensate OFO in OTFS systems, then estimation accuracy is improved, but spectral efficiency deteriorates
Solution Approach 1:
The patent applies multi-functionality by designing communication frames where data symbols serve dual purposes: both as information carriers and as pilots for OFO estimation. This allows the system to achieve accurate OFO estimation without dedicating separate pilot resources, thus resolving the contradiction between estimation accuracy and spectral efficiency by making the data symbols universally functional.
Solution Approach 2:
The patent implements self-service by enabling the data symbols to automatically serve as their own pilots for OFO estimation. Instead of requiring external dedicated pilot signals, the system uses the inherent structure and properties of the transmitted data symbols to perform self-estimation and self-compensation of frequency offsets, maintaining both accuracy and spectral efficiency.
Data Source
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Figure 3
Figure 4a~4c
AI summary
A communication frame for an OTFS transmission system includes at least one first-type and at least one second-type block. At least the first-type block comprises data signals two-dimensionally arranged along the delay domain and the Doppler domain of which at least one has a superimposed pilot signal. The second-type block comprises data signals two-dimensionally arranged along the delay domain and the Doppler domain which may or may not have superimposed pilot signals. At least one second-type block is preceded and followed, in the delay-domain, by first-type blocks, the first-type blocks preceding and following a second-type block having at least one identical data symbol and associated superimposed identical pilot symbol at an identical location in the two-dimensional arrangement. An OTFS transmitter generates and transmits the communication frame, and a receiver uses its properties for compensating oscillator frequency offset and channel estimation.