Telephonic communications – Transmission line conditioning – Interference suppression
Reexamination Certificate
1999-08-30
2003-08-26
Tieu, Binh (Department: 2643)
Telephonic communications
Transmission line conditioning
Interference suppression
C379S418000, C379S420040
Reexamination Certificate
active
06611595
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to a method for generating measuring signals for measuring the transmission properties of handsfree telecommunications devices. Handsfree equipment in telephones are electrical message systems comprising specific transmission links for voice transmission wherein the transmission links are mutually influenced by crosstalk. The possibility of being able to “talk handsfree” with a telephone significantly enhances the operating comfort of a telephone and the quality of a telephone call. Handsfree devices enable call situations like those that occur in natural conversation between talking parties and allow a significantly greater freedom of movement and action of the person speaking handsfree. Voice-controlled signal processing mechanisms are utilized in order, on the one hand, to get control of the discussion and listening-in conditions that clearly deteriorate compared to ordinary handset-bound telecommunication and, on the other hand, to minimize the risk of occurring feedback. As is known, the voice-controlled signal processing in handsfree telephones ensues by
1) voice-dependently switched attenuations in the respective transmission and reception paths (attenuation control of the transmission and reception paths; principle of the level scale),
2) dynamic compression methods,
3) frequency-selective level scales,
4) decorrelation of the transmission and reception signals, and
5) adaptive compensation of acoustic echos.
Over and above this, the phenomenon of double talk is a critical feature of handsfree devices. The remote subscribers communicating with one another can thereby talk simultaneously. Of the aforementioned methods employed in handsfree devices for signal processing, adaptive compensation of acoustic echos (constructing adaptive echo compensators) in handsfree devices especially leads to a considerably reduced attenuation boost of the respectively employed level scale. Double talk only becomes possible as a result thereof because, transmission and reception paths are simultaneously active on principle. However, the utilization of echo compensators does not yet assure an unproblematical double talk mode because the adaption algorithms that are employed react more or less sensitively to changes in the room (place at which the handsfree telephone is put) and disturbances due to double talk phases. Moreover, the finite adaption speed may result in a disturbing increase or too slow a decrease of the echos under certain circumstances. It is precisely the double talk occurring in handsfree devices that is greatly deteriorated by the aforementioned signal processing mechanisms. So that true-to-life conversations (acquisition of the real double talk call situation) can be realized with the handsfree devices, the auditively relevant parameters must, on the one hand, be extracted, and the instrumentally measurable, technical parameters that describe the handsfree device must be acquired. Instrumentally measurable parameters for characterizing the conversation parameters of a handsfree device are not contained in measurement rules currently under discussion—such as, for example, the publication prI-ETS 300-245-3, Part 3; PCM A-Law, Loudspeaking and Handsfree Telephony, Stockholm, November 1994 (approval regulation). No measurements whatsoever are specified either for the double talk parameters or for the attenuation control of the two transmission paths (transmission and reception paths). In order to nonetheless be able to make statements at all with respect to the conversation parameters of handsfree devices, it is at least necessary that, first, the attenuation boost realized in a handsfree device designed in conformity with the indicated approval regulation and, second, the attenuation distribution on the two transmission paths of the handsfree device in the quiescent condition are known. Neither statements that characterize the behavior of the handsfree device during a double talk event nor farther-reaching analyses of the transmission quality during the double talk event are possible with these two parameters because other technical parameters such as, for example, the prioritization of voice direction, switching times, blocking times, etc., play a part therein. In order to acquire the behavior of voice-controlled devices quite generally dependent on the time and level conditions of the two input signals, the publication
Fortschritte der Akustik
—DAGA 1993, Bad Honnef, DPG GmbH, pages 932-935; F. Kettler, “Neue Messmethodik zur Bestimmung der Übertragungseigenschaften von Sprachechokompensatoren in Fernsprechnetz für Enzelmessungen und Tandemschaltungen” discloses that two “composite source” signals with different cycle durations be employed. A suitable simulation and analysis of a time segment is thereby possible, whereby the two signals are simultaneously fed in (true double talk). Whether one voice path is prioritized, whether both voice paths are attenuated in alternation or, for example, whether a fixed attenuation distribution of both paths during double talk is present can be determined from the transmitted sequence.
FIG. 1
shows a measuring arrangement MA constructed according to ITU (International Telecommunication Union) publication Volume V—RECOMMENDATION P.34, Melbourne, 1988, pages 64 through 71, particularly Ch. 6, for measuring the transmission properties of a handsfree device FSE or a handsfree telephone FST in the “double talk” call situation. To this end, the handsfree device FSE is connected to a handsfree loudspeaker FL in a transmission direction (transmission path) via a first amplifier V
1
. In a reception direction (reception path), a handsfree microphone FM is connected to the handsfree device FSE via a second amplifier V
2
. Given the illustrated measuring arrangement MA, the double talk call situation occurring during handsfree calling is achieved in that an “artificial ear” KO and an “artificial mouth” KM are allocated to the handsfree loudspeaker FL and to the handsfree microphone FM, respectively, for simulating the handsfree conditions. The measuring arrangement MA also contains a measuring system MS in order to be able to acquire transmission properties of the handsfree device FSE. For simulating the real handsfree conditions, this measuring system MS supplies the handsfree device FSE with, first, a “remote” first transmission signal (measured signal) SS
1
via a transmission/reception duplexer SEW preceding the handsfree device FSE that proceeds via the handsfree loudspeaker FL to the “artificial ear” KO and, second, supplies it with a “near” second transmission signal (measured signal) SS
2
via the “artificial mouth” KM and the handsfree microphone FM. In the present case, the signals SS
1
, SS
2
are preferably selected such that their properties correspond to those of a natural voice signal (for example, crest factor, envelope, spectral composition, etc.).
The measurement of the transmission properties of the handsfree device FSE is implemented in the measuring system MS. To that end, the signals SS
1
, SS
2
sent from the measuring system MS are compared to a first reception signal ES
1
received by the measuring system MS via the “artificial ear” KO and to a second reception signal ES
2
received by the measuring system MS via the transmission/reception duplexer SEW.
Analogous to the real handsfree conditions, the known crosstalk phenomenon occurs in the present measuring arrangement due to the infeed of the signals SS
1
, SS
2
. This crosstalk is expressed therein that a first crosstalk signal ÜS
1
related to the first transmission signal SS
1
(for example, due to measuring arrangement and signal propagation properties) proceeds into the handsfree microphone FM in addition to the second transmission signal SS
2
, and that a second crosstalk signal ÜS
2
related to the second transmission signal SS
2
(for example, due to measuring arrangement and signal propagation properties) proceeds into the “artificial ear” KO in addition to the first transmission signal SS
1
. How
Leckschat Dieter
Pflaum Karl-Heinz
Bell Boyd & Lloyd LLC
Siemens Aktiengesellschaft
Tieu Binh
LandOfFree
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