Receiver Frequency Offset Correction After False Signal Lock
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Solution Overview
Problem
Modems in broadband communication systems often lock onto frequencies that are not the actual transmission frequency, leading to suboptimal data reception with high error rates and reduced communication speeds, especially noticeable in voice communications and file downloads.
Innovation Solution
A receiver system comprising a tuner, controller, and comparator that adjusts the frequency by determining and correcting the frequency offset between the locked frequency and the intended transmission frequency, ensuring accurate tuning and reducing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the modem scans the downstream frequency spectrum to detect a data signal, then the modem can find and lock onto a frequency, but the modem may lock onto a frequency that is not the actual transmission frequency
Solution Approach 1:
The patent implements a feedback mechanism where the modem continuously monitors the frequency offset between the locked frequency and the actual transmission frequency. The comparator compares these frequencies and provides feedback to the controller, which then adjusts the tuner to eliminate the offset, ensuring the modem locks onto the correct transmission frequency.
Solution Approach 2:
The patent replaces manual frequency scanning and locking mechanisms with an automated electronic frequency offset correction system. The comparator and controller work together to automatically detect and correct frequency offsets, substituting the need for manual intervention or complex mechanical tuning systems.
2Productivity
If the modem uses a channel map to instruct which frequencies to scan, then the scanning process is more efficient, but the modem may still lock onto a frequency that is not the actual transmission frequency due to lock range encompassing multiple channels
Solution Approach 1:
The feedback mechanism continuously monitors the frequency offset and provides real-time corrections, ensuring that even when using a channel map for efficient scanning, the modem ultimately locks onto the precise transmission frequency rather than just any frequency within the lock range.
Solution Approach 2:
The channel map provides preliminary guidance on which frequencies to scan, and the frequency offset correction mechanism then performs preliminary adjustments to ensure the final locked frequency is accurate. This two-stage approach combines the efficiency of pre-planned scanning with the precision of automated correction.
3Reliability
If the modem locks onto a frequency that is not the actual transmission frequency, then data can be received, but the communication speed and quality are greatly reduced
Solution Approach 1:
The feedback mechanism detects frequency offsets that would otherwise cause degraded communication performance. By continuously monitoring and correcting the frequency alignment, the system maintains optimal communication speed and quality while ensuring reliable data reception.
Data Source
AI summary
A receiver is tuned to a transmission frequency of a data signal after the receiver has already locked onto a frequency carrying the data signal. A frequency offset between a locked frequency of a tuner on the receiver and the actual transmission frequency is determined by a comparator. If the frequency offset is greater than a threshold value, then the tuner is stepped to another frequency and the frequency offset is determined again. The direction of the tuning step can be determined by comparing multiple frequency offsets. An average value of multiple frequency offset measurements may also be used to determine if the tuner should retune to another frequency by comparison with the threshold value.