Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Reexamination Certificate
2000-05-11
2002-09-17
Chin, Vivian (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
C379S022010, C379S029060, C455S069000
Reexamination Certificate
active
06453153
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a method and system for employing customer premises equipment (CPE) as an agent in communication network maintenance; and, in a particular embodiment, for employing CPE to aid in measuring the effect of network loss on received sound quality so that such loss may be compensated and sound quality thereby improved.
BACKGROUND OF THE INVENTON
TrueVoice® is a telephone network sound enhancement technology invented by AT&T Corp. TrueVoice provides AT&T customers with “closer,” clearer sounding voice communications on telephone calls carried by the AT&T network. TrueVoice applies both a frequency independent gain (a constant gain across all frequencies in the telephone bandwidth) and a frequency selective gain (sometimes referred to as “pre-emphasis”) to telephone connections. Technical features of TrueVoice are described in U.S. Pat. Nos. 5,195,132; 5,333,195; and 5,206,902 (which are hereby incorporated by reference).
FIG. 1
is a diagram of a typical telephone network connection employing TrueVoice. It includes CPE
20
and
21
at two end points for a calling party and a called party, respectively, and analog and digital network components in between. CPE
20
,
21
is, e.g., a conventional telephone. CPE
20
,
21
is connected to a conventional hybrid converter
22
,
23
at telephone central offices via local loops
31
,
34
. Each hybrid
22
,
23
converts bidirectional signal transmission in a two-wire telephone line to two unidirectional signal paths (two wires each). The calling party's “transmit path” includes local loop
31
, network paths
35
and
36
and local loop
34
. This transmit path is also the called party's “receive path.” The called party's transmit path includes local loop
34
, network paths
38
and
37
, and local loop
31
. This transmit path is also the calling party's receive path. (Local loops
31
and
34
are common to both calling and called parties' transmit and receive paths.) The point of the network between paths
35
and
36
/
37
and
38
is said to be at 0 “TLP” (or transmission level point). This point may be conveniently used as a reference for gain or loss experienced at different points in the network.
Signals on the calling party transmit network path
35
are processed by a D/A-A/D converter
24
, which is conventional equipment located at the calling party's local central office. (For clarity of presentation of the invention, conventional switches associated with the local central offices are not shown.) A long-distance telephone network switch, e.g., a No. 4 Electronic Switching System
26
(4ESS) in the AT&T Network, is connected to the D/A-A/D
24
converter of the local central office. The 4ESS
26
is then connected to a special automatic volume control filter (AVC)
30
which, as shown in
FIG. 1
, includes, for example, TrueVoice® elements
32
and
33
. As a matter of general background, automatic volume control filters are conventional, for example, those described in U.S. Pat. Nos. 4,499,578 and 4,535,445, which are hereby incorporated by reference. TrueVoice element
33
applies the sound enhancement for speech signals spoken at CPE
20
for transmission to CPE
21
. Element
32
applies echo cancellation to diminish an echo of speech signals (originally spoken at CPE
21
) returning to CPE
21
. As shown in
FIG. 1
, similar connections are used in network path
36
to deliver speech from the calling party. This path includes a −6 dB attenuator
29
, intentionally inserted into the network, typically by the called party's Local Exchange Carrier (LEC), to further mitigate echo in a long distance connection (it is not needed in a local connection). The Figure further illustrates similar connections for network path
38
(which is like network path
35
) and network path
37
(which is like network path
36
). (Although much of the discussion which follows is presented from the point of view of the calling party's transmit path (which is the same as the called party's receive path), such discussion has applicability to the called party's transmit path/calling party's receive path, with for example, the roles of elements
32
and
33
reversed.)
The part of the network which is digital—that part between and including D/A-A/D converters
24
,
25
—exhibits no unintentional loss (there are −6 dB attenuators
28
,
29
, however, which are intentionally placed in the circuit). The analog part of the network—the balance of the network diagram of FIG.
1
—does suffer unintentional loss, however. This loss is variable depending on the length of the local loop
31
,
34
between the CPE
20
,
21
and the central office. In addition, the level of a speech signal presented to the analog part of the network is variable, depending on the CPE (telephone)
20
,
21
microphone efficiency, as well as how loudly a person is speaking into the microphone and how close the person's mouth is to the microphone. As shown in the Figure, the average loss on the analog portion of the calling party's transmit path—referred to as TOLR (telephone+local loop loss) is −46 dB.
As discussed in greater detail in the referenced patents, TrueVoice®
33
sound enhancement operates to mitigate the effect of signal loss in a telephone network connection for signals traveling from the calling party to the called party. TrueVoice
33
sits in the middle of the digital network and adds gain of a fixed amount (4 dB) to a computed input power of a transmitted speech signal.
FIG. 2
illustrates this. The power of the transmitted (input) signal is computed over a time interval. For example, the signal may have an average power over the interval of −21 dB. TrueVoice will amplify the signal such that the signal will have an average power of 4 dB better (or −17 dB). If the average power of the input signal is −17 dB, the output power will be raised to −14 dB. Through its combination of pre-emphasis (base boost) and the AVC, TrueVoice
33
compensates some or all of the network path
31
,
35
attenuation, as well as CPE
20
efficiency variation, to improve how speech carried over the telephone connection “sounds” to someone listening.
Although there is an optimal TrueVoice
33
output power level to which the network signal could be adjusted, TrueVoice employs a conservative boost of, e.g., a constant 4 dB, to compensate for attenuation suffered in the paths
31
and
35
of the network. Unfortunately, there are several variables related to the paths
34
and
36
of the network which affect the amount of signal loss a speech signal may suffer in transmission over a telephone circuit. For example, the attenuator
29
is not always present in a long distance connection. Network response variability is also caused by variation in local-loop
34
length carrying received signals and variability in the efficiency of CPE
21
's electric-to-acoustic transduction. This response variability can cause, among other things, variability of objective loudness as perceived by telephone customers. Moreover, because TrueVoice®
33
applies a conservative gain mapping (4 dB, for example) when administering active volume control, called parties connected on long loops or loops that cause great attenuation may not be able to perceive all the benefits of TrueVoice®
33
. Since TrueVoice
33
does not know what the loss will be on the paths
36
,
34
of the network, it does not compensate for such loss and, in fact, provides a relatively conservative maximum gain because of this.
SUMMARY OF THE INVENTION
The present invention is directed to the use of CPE as an agent of the network to assist in providing network maintenance. An illustrative embodiment of the invention is directed to improving network sound enhancement systems, such as TrueVoice. In this embodiment, the TrueVoice network element
41
(see
FIG. 3
) emits a first signal at the beginning of an ordinary telephone call (where the reference numeral
41
Bowker Duane Oliver
Daumer William Richard
Shelby Kevin Alan
Singer Howard M.
Appiah Charles N.
AT&T Corp.
Chin Vivian
Koba Wendy W.
LandOfFree
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