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US5426696A
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Method of improving receiver sensitivity and speech immunity with DTMF-reception
Assignee: Telefonaktiebolaget LM Ericsson AB
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Filing: 1993-07-01
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Granted: 1995-06-20
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Expires: 2013-07-01
Abstract
Abstract A method of improving the sensitivity and speech immunity of a receiver in conjunction with DTMF-reception is disclosed. The number of zero-crossings of the input signal are counted during one of a number of measuring intervals in real time at frequencies which occur in the low frequency group and the high frequency group of a DTMF-signal. At the end of each of the measuring intervals, the number of zero-crossings in a current measuring interval is compared for each frequency group, with a corresponding number of zero crossing in a number of nearest preceding measuring intervals, and the magnitude of any difference is established. The input signal is treated as a DTMF-signal when the difference is at most equal to a permitted limit value.
Inventors
- 👤 Slaven Zimbrek
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 23:07
CPC Classifications
H; H04; H04Q; H04Q1/00; H04Q1/18; H04Q1/30; H04Q1/44; H04Q1/444; H04Q1/46
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
208 words
A method of improving the sensitivity and speech immunity of a receiver in conjunction with DTMF-reception, comprising the steps of: measuring in real time in a low frequency group band and a high frequency group band during each of a number of measuring intervals an energy parameter which is representative of the tone energy of an input signal; determining the average value of said measuring parameters over the measuring intervals from the beginning of the signal concerned during the end of each measuring interval; determining the difference between each of the relevant energy parameters in the two bands and the average value established parameter; determining at least three threshold values for said difference, wherein said three threshold values are a normal value beneath which a DTMF-signal is considered to exist, at least one greater-than-normal value, and at least one smaller-than-normal value; determining whether the difference in one of the bands lies above the normal value; determining whether the difference in questions also lies above the greater-than-normal value when it is determined that the difference lies above the normal value; and comparing the difference in the second band with the smaller-than-normal value in order to establish whether the difference lies beneath said value, which indicates that a DTMF-signal exists.
Claim 2
Independent Claim
208 words
A method of improving the sensitivity and speech immunity of a receiver in conjunction with DTMF-reception, comprising the steps of: measuring in real time in a low frequency group band and a high frequency group band during each of a number of measuring intervals an energy parameter which is representative of the tone energy of an input signal; determining the average value of said measuring parameters over the measuring intervals from the beginning of the signal concerned during the end of each measuring interval; determining the difference between each of the relevant energy parameters in the two bands and the average value established parameter; determining at least three threshold values for said difference, wherein said three threshold values are a normal value beneath which a DTMF-signal is considered to exist, at least one greater-than-normal value, and at least one smaller-than-normal value; determining whether the difference in one of the bands lies above the normal value; determining whether the difference in questions also lies above the greater-than-normal value when it is determined that the difference lies above the normal value; and comparing the difference in the second band with the smaller-than-normal value in order to establish whether the difference lies beneath said value, which indicates that a DTMF-signal exists.
Claim 3
Dependent Claim
148 words
A method according to claim 1, wherein two greater-than-normal values are used, and a DTMF-signal is considered to exist when one of the following conditions is fulfilled, (a) the current energy of the two bands lies beneath the smaller-than-normal value or the normal value; (b) the current energy of a band exceeds the normal value but not the lower of the greater-then-normal values, and the current energy of the other band is lower than the smaller-than-normal value or the normal value; and (c) the current energy of a band exceeds the lower but not the higher of the greater-than-normal values, the current energy of the other band is lower than the smaller-than-normal value and earlier energy of said other band has not exceeded the lower greater-than-normal value, said earlier energy being counted from the 6 ms interval in which the DTMF-signal concerned is detected for the first time.
Claim 4
Independent Claim
57 words
A method of improving the sensitivity and speech immunity of a receiver in conjunction with DTMF-reception, comprising the steps of: determining the first occurrence of an interference frequency during one of a plurality of measuring intervals when decoding a DTMF-signal; and tolerating this interference frequency when the same interference frequency is encountered in a following measuring interval.
Claim 5
Independent Claim
57 words
A method of improving the sensitivity and speech immunity of a receiver in conjunction with DTMF-reception, comprising the steps of: determining the first occurrence of an interference frequency during one of a plurality of measuring intervals when decoding a DTMF-signal; and tolerating this interference frequency when the same interference frequency is encountered in a following measuring interval.
Claim 6
Dependent Claim
140 words
A method for improving the sensitivity and speech immunity of a receiver in conjunction with DTMF-reception according to claim 3, further comprising the steps of: counting during each of a number of measuring intervals, said measuring intervals lasting at least a plurality of wavelengths of an input signal, in real time the number of zero-crossings of the input signal at frequencies which occur in a low frequency group and a high frequency group of a DTMF-signal; comparing at the end of each of the measuring intervals the number of zero-crossings for each frequency group in a current measuring interval with the number of zero-crossings in a number of immediately preceding measuring intervals, and establishing the magnitude of any difference therebetween; and treating the input signal as a DTMF-signal when the difference is at most equal to a permitted limit value.
Claim 7
Dependent Claim
12 words
A method according to claim 4, wherein the limit value is 1.
Claim 8
Dependent Claim
25 words
A method according to claim 4, wherein said comparison of said number of zero-crossings is carried out during at least two mutually sequential measuring intervals.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1998-06-19 | 1998-12-19 | 1999-06-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2002-06-19 | 2002-12-19 | 2003-06-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2006-06-19 | 2006-12-19 | 2007-06-20 | $7700.00 | Window Closed / Lapsed |