Fast Frame Timing Acquisition with Frequency Offset Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing communication modem technologies face challenges in synchronizing with signals that have significant frequency offsets, leading to degradation in detection performance and increased acquisition time, especially in satellite communications where frequency uncertainty can prevent detection of Unique Words (UW) and result in substantial loss of signal-to-noise ratio.
Innovation Solution
A method involving UW modulation elimination, partial coherent addition, and Fourier Transform processing, combined with a two-dimensional search for UW timing and frequency offset, is implemented to facilitate fast and accurate synchronization, utilizing a Field Programmable Gate Array (FPGA) for efficient processing and minimizing detection loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frequency scanning is used to locate UW in presence of frequency offset, then detection performance is improved, but acquisition time increases significantly
Solution Approach 1:
The patent applies preliminary action by performing coarse frequency offset estimation and compensation before UW detection. The receiver estimates frequency offset using pilot symbols or preamble sequences, compensates for it in advance, and then proceeds with UW detection. This prevents the need for time-consuming frequency scanning during acquisition, thus resolving the contradiction between detection reliability and acquisition time.
Solution Approach 2:
The patent segments the acquisition process into distinct stages: frequency offset estimation, frequency compensation, and UW detection. By dividing the acquisition process into manageable segments with specific functions, the system can efficiently handle frequency offset without requiring exhaustive frequency scanning, thereby reducing acquisition time while maintaining detection performance.
2Reliability
If frequency step size is reduced to Rs/2L to limit residual frequency error, then detection performance degradation is reduced, but number of frequency steps increases
Solution Approach 1:
The patent performs preliminary frequency offset estimation using available signal structures (pilots, preambles) before UW detection. By estimating and compensating for the frequency offset in advance, the system eliminates the need for fine frequency scanning with small step sizes, thus achieving both good detection performance and fast acquisition.
Solution Approach 2:
The patent changes the frequency offset parameter by estimating it from the received signal and applying compensation. This transforms the problem from one requiring exhaustive frequency search to one where the frequency offset is actively corrected, reducing acquisition time while maintaining detection performance.
3Ease of operation
If UW correlation is performed with unknown phase, then amplitude or power detection is used, but frequency offset causes incoherent addition and detection degradation
Solution Approach 1:
The patent applies preliminary phase and frequency compensation using pilot symbols or known preamble sequences before performing UW correlation. By correcting frequency offset and phase in advance, the correlation operation can proceed coherently, maintaining both detection simplicity and performance.
Solution Approach 2:
The patent introduces an intermediary frequency compensation stage between signal reception and UW detection. This intermediary process corrects frequency offset and phase errors, enabling coherent correlation and improving detection performance without complicating the overall operation.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Modern digital signals include framing. A known sequence of transmission symbols (Unique Word (UW)) included in the transmitted signal may be used by a receiver for framing synchronization. A receiver configured to receive such a signal may be configured to detect the UW even when the signal is received with some frequency uncertainty (e.g. offset or error). A method is presented for fast acquisition of symbol and/or frame timing of a signal, including in the presence of frequency uncertainty. In some embodiments, the presented method may be used for determining a frequency offset of the received signal and a location of a unique word (UW) within a frame of the received signal, wherein said determining is based on a two-dimensional search map.