Browse Prior Art Database

Tone Alarm Control

IP.com Disclosure Number: IPCOM000038666D
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Tu, N: AUTHOR [+2]

Abstract

A Tone Alarm Control function is provided in a baseband modem without any loss of information on the transmit spectrum. The principle which has been chosen to perform the Tone Alarm Control function on a baseband coded signal is to transmit a low frequency tone and to detect it remotely. This tone is sent: when a power down is detected. - to initiate a remote self, or - to give a self test failure indication to the control modem. The tone chosen has been defined at 225 Hz which is the lowest frequency which can be transmitted on a baseband modem using DPSK (Differential Phase Shift Keying) coding, taking into account the usual line characteristics and the modem behavior at low frequencies.

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Tone Alarm Control

A Tone Alarm Control function is provided in a baseband modem without any loss of information on the transmit spectrum. The principle which has been chosen to perform the Tone Alarm Control function on a baseband coded signal is to transmit a low frequency tone and to detect it remotely. This tone is sent: when a power down is detected. - to initiate a remote self, or

- to give a self test failure indication to the control modem.

The tone chosen has been defined at 225 Hz which is the lowest frequency which can be transmitted on a baseband modem using DPSK (Differential Phase Shift Keying) coding, taking into account the usual line characteristics and the modem behavior at low frequencies. To be detected, the tone energy must be greater than the noise provided by the local modem in the bandwidth of the bandpass receive tone filter. A method to secure this tone detection would be to remove the 225 Hz energy on the transmit spectrum. This is possible without reducing the modem performance invoking the Nyquist criterion saying that the minimum bandwidth required to transmit a binary signal is 2 bits/sec/Hz. In a DPSK baseband, the transmission is made at O.5 bit/sec/Hz, so a high redundancy level is available and the removed information at 225 Hz can be recovered by analyzing the rest of the spectrum. The removal of this frequency is made by a simple notch filter with a 10 dB depth allowing 100% reliability in the tested modems.

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