Facsimile Tone Detection Counter for CNG Misrecognition
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Solution Overview
Problem
Facsimile apparatuses misrecognize noise generated by pulse-dialing as a calling signal (CNG) during FAX/telephone answering automatic switching, especially when an outgoing message (OGM) is output onto the telephone line, impairing CNG detection performance.
Innovation Solution
A facsimile apparatus with a tone detecting unit, a counting unit, a controlling unit, and a hook detecting unit that detects and counts tone signals, and resets the count when the hook state changes, ensuring accurate CNG detection and preventing misrecognition by requiring multiple detections of the CNG pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If the facsimile apparatus monitors the telephone line to detect CNG for automatic FAX reception, then FAX reception can be automatically started when a FAX incoming call is detected, but noise generated by pulse-dialing is misrecognized as CNG causing erroneous automatic FAX reception
Solution Approach 1:
The patent applies dynamics by making the CNG detection threshold adaptive rather than fixed. The threshold is dynamically adjusted based on the detected tone frequency and its characteristics. When a tone matching CNG frequency (1100 Hz) is detected, the system verifies additional parameters (duration, interval patterns) before confirming CNG, allowing the detection criteria to adapt to different signal conditions and prevent misrecognition of pulse-dialing noise.
Solution Approach 2:
The patent changes multiple parameters for CNG verification beyond just frequency detection. It incorporates duration parameter (tone must persist for minimum time), interval parameter (specific time gaps between tones), and amplitude parameter (signal strength thresholds). By requiring multiple parameter matches simultaneously, the system distinguishes genuine CNG signals from pulse-dialing noise which may share the same frequency but differ in other characteristics.
2Measurement precision
If the facsimile apparatus uses frequency checking to prevent misrecognition of speech as CNG, then speech can be distinguished from CNG, but CNG detectability is considerably impaired when OGM is output onto the telephone line
Solution Approach 1:
The patent utilizes periodic action by detecting the characteristic rhythmic pattern of CNG signals. CNG is transmitted as periodic tone bursts with specific intervals (typically on for 0.5 seconds, off for 3 seconds). The system counts the number of periodic tone detections within a time window and requires a minimum count to confirm CNG, leveraging the periodic nature of genuine FAX calling signals versus the aperiodic noise of speech or OGM.
Solution Approach 2:
The system implements feedback by continuously monitoring the telephone line and using detected signal characteristics to adjust detection sensitivity. When tones are detected, the system feeds back additional verification checks (duration, interval timing, repetition count) before confirming CNG. This feedback mechanism allows the system to maintain high speech discrimination while preserving CNG detectability even during OGM output by requiring multiple confirming parameters.
3Adaptability or versatility
If the facsimile apparatus detects CNG superposed on OGM during FAX/telephone answering automatic switching, then FAX reception can be detected even when OGM is output, but the CNG misrecognition prevention method impairs CNG detectability
Solution Approach 1:
The patent transitions from single-dimension frequency detection to multi-dimensional signal analysis. Instead of relying solely on frequency (1100 Hz), it adds temporal dimensions (duration of tone, intervals between tones, total time window), amplitude dimension (signal strength thresholds), and pattern dimension (required number of periodic occurrences). This dimensional expansion allows discrimination of CNG from OGM noise by identifying the unique temporal pattern of periodic tone bursts superposed on the continuous OGM.
Solution Approach 2:
The system performs preliminary verification actions before confirming CNG detection. When a tone at CNG frequency is detected during OGM output, the system does not immediately trigger FAX reception but first verifies additional parameters (minimum duration, required number of periodic occurrences, proper interval timing). This preliminary multi-parameter verification prevents false detection of noise while maintaining ability to detect genuine CNG superposed on OGM.
Data Source
AI summary
After a telephone captures a line, a facsimile apparatus detects a tone signal on the captured line. The facsimile apparatus counts a number of the detected tone signals. When the counted number reaches a predetermined number, the facsimile apparatus controls to start a facsimile reception. The facsimile apparatus detects a change of a hook state of the telephone. When the change of the hook state of the telephone is detected, the facsimile apparatus resets the counted number.