Supervisory audio tone detection in a radio channel

US4698769A · kind A · utility

Assignees

• American Telephone and Telegraph, Co. · US
• Bell Telephone Laboratories, Inc. · US

Inventors

• Ross McPherson · Denville, US
• Kenneth Frank Smolik · Naperville, US
• David Thomson · Southampton, GB

Key dates

• Filing date: Feb 4, 1985
• Grant date: Oct 6, 1987
• Expiry date: Feb 4, 2005

Classification

• Technology area (CPC H): Electricity
• CPC primary: H04Q1/442
• WIPO field: Telecommunications
• WIPO sector: Electrical engineering

Abstract

Supervisory audio tones received from a mobile telephone unit are converted from analog to digital form. The tone is then converted to a complex number by bifurcating the tone path and multiplying one path by a sine function and the other path by a cosine function. The complex numbers are accumulated and the frequencies where significant power exists is found using the discrete Fourier transform. If the power at an assigned frequency exceeds a threshold, the corresponding supervisory audio tone is declared to have been detected.