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Efficient, Accurate Measurement of Three-Second Average Energy

IP.com Disclosure Number: IPCOM000061231D
Original Publication Date: 1986-Jul-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 3 page(s) / 53K

Publishing Venue

IBM

Related People

West, LP: AUTHOR

Abstract

A method is described to squelch signals being supplied to telephone lines that would violate Federal Communications Commission (FCC) Regulation Part 68 which requires that the average energy transmitted to a telephone line not exceed certain energy bounds. One of these requirements is that any signal other than telephone dialing or live voice must produce a three-second average energy less than -9 dBm. The restriction for telephone dialing is that the three-second average must be less than 0 dBm. There is no restriction for live voice. Where there are a number of sources of signals to be transmitted to the telephone line, there is not a prior assurance that most of these will be pre-limited to meet the FCC requirement.

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Efficient, Accurate Measurement of Three-Second Average Energy

A method is described to squelch signals being supplied to telephone lines that would violate Federal Communications Commission (FCC) Regulation Part 68 which requires that the average energy transmitted to a telephone line not exceed certain energy bounds. One of these requirements is that any signal other than telephone dialing or live voice must produce a three-second average energy less than -9 dBm. The restriction for telephone dialing is that the three- second average must be less than 0 dBm. There is no restriction for live voice. Where there are a number of sources of signals to be transmitted to the telephone line, there is not a prior assurance that most of these will be pre-limited to meet the FCC requirement. A method is therefore provided within the signal processing code to squelch signals which would otherwise violate the energy restriction. An exact three-second average of energy may be obtained by storing a moving histogram of all samples transmitted for the previous three seconds, but the method suffers from a major drawback in that a very large sample buffer is required to store the three seconds' worth of samples. The method taught here involves use of a novel and accurate approximation to the three-second average, while requiring fewer than sixteen bytes of storage. A lossy integrator can provide a suitable three-second average if properly designed, provided that the energy is approximately sinusoidal and continuous. For non-continuous energy, however, the approximation can be remarkably poor. Fig. 1 shows the response of a lossy integrator to the onset of continuous energy at the required -9 dBm level. As may be seen, the estimate after three seconds is accurate. Fig. 2, however, shows the response of this integrator to a signal which is intermittent in nature. The energy in this case is ON for a period of 1.5 seconds, then OFF for a period of 1.5 seconds. The actual energy level is -9 dBm. As may be seen from Fig. 2, the lossy integrator reports that the allowable energy level has been exceeded in less than 240 milliseconds. At this point, the three-sec...