Telephonic communications – Transmission line conditioning – Interference suppression
Reexamination Certificate
1998-09-23
2001-09-04
Matar, Ahmad (Department: 2642)
Telephonic communications
Transmission line conditioning
Interference suppression
C379S028000, C379S399010, C379S406010, C379S416000
Reexamination Certificate
active
06285755
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transmission system including a plurality of transmission apparatuses which use a single channel commonly, and to the transmission apparatuses used in the transmission system.
2. Description of the Related Art
Recently, in the field of data transmission, it is a trend that a single monitoring system integrally monitors different transmission systems such as PDH (Plesiochronous Digital Hierarchy), SDH (Synchronous Digital Hierarchy) and so forth. Thereby, a scale of the monitoring system becomes larger.
As shown in
FIG. 1
, respective transmission apparatuses
1
through
6
are connected therebetween by not only user information transmission lines
7
but also order-wire transmission lines (OW transmission lines or meeting transmission lines)
8
for transmitting a monitoring signal and for transmitting an order-wire signal, which is a telephone-conversation signal, between the transmission apparatuses. Recently, as the scale of an information transmission system becomes larger, the scale of a network of the order-wire transmission lines becomes larger.
FIG. 2
shows an example of an arrangement of the transmission apparatus B
2
, transmission apparatus C
3
, and transmission apparatus E
5
. In this example, the transmission apparatus C
3
and transmission apparatus E
5
are branched off from an analog separation and combining portion
13
of the transmission apparatus B
2
. A digital audio signal from the transmission apparatus A
1
is transmitted through an optical/radio transmission path
20
, is input to an optical/radio transmission portion
10
(for transmitting and receiving optical/radio signals) of the transmission apparatus B
2
, then, is demultiplexed from another signal(s) through a multiplexing/demultiplexing portion
11
(for multiplexing and demultiplexing signals), and is input to a two-wire telephone
16
via an order-wire transmission portion
19
. Thereby, a voice from the transmission apparatus A
1
can be heard in the transmission apparatus B
2
. An analog signal from the telephone
16
of the transmission apparatus B
2
is transmitted to the transmission apparatus A
1
through a route reverse to the above-mentioned route. That is, an audio signal output from the telephone
16
of the transmission apparatus B
2
is transmitted to, via the order-wire transmission portion
19
, the multiplexing/demultiplexing portion
11
which then multiplexes the audio signal with another signal(s), and, then, the thus-multiplexed signal is transmitted from the optical/radio transmission portion
10
through the optical/radio transmission path
20
. Thus, the digital audio signal is transmitted to the transmission apparatus A
1
.
The order-wire transmission portion
19
includes a codec portion
12
which performs coding and decoding, an analog separation and combining portion
13
which performs separation and combining of analog signals, a 2W/4W converter
14
which performs conversion between a 2-wire signal and a 4-wire signal, and a terminal DTMF (Dual Tone Multi-Frequency) sending/detecting portion
15
. The analog separation and combining portion
13
has a function such that each port outputs a signal of the sum of the signals input from all the other ports, and, a signal input through each port does not return to this port. The terminal DTMF sending/detecting portion
15
performs sending and detecting of a DTMF signal for signaling. In a case of calling, the terminal DTMF sending/detecting portion
15
sends a calling signal. In a case where a calling signal is received by this transmission apparatus, the terminal DTMF sending/detecting portion
15
sends a call detection signal to a terminal (transmission apparatus) which has sent the calling signal. Thereby, a telephone conversation is performed in the order-wire system by using a single channel, it is possible to select/change a transmission apparatus with which a telephone conversation will be performed, and it is possible that a telephone conversation is performed between arbitrary terminals (transmission apparatuses). In the example shown in
FIG. 2
, the terminal DTMF sending/detecting portion
15
is provided inside the order-wire transmission portion
19
. However, it is also possible that the terminal DTMF sending/detecting portion
15
is provided outside the order-wire transmission portion
19
.
Operation of the order-wire transmission portion
19
will now be described. In a case of signal reception, a received digital signal is converted into an analog signal through the codec portion
12
, and is then combined through the analog separation and combining portion
13
with the signals transmitted from the transmission apparatuses C
3
and E
5
in an analog state. The thus-combined signal is input to the two-wire telephone
16
via the 2W/4W converter
14
. In a case of signal transmission, an analog signal output by the telephone
16
is input to the analog separating and combining portion
13
via the 2W/4W converter
14
. The analog separation and combining portion
13
combines the thus-input analog signal with signals from the transmission apparatuses C
3
and E
5
in the analog state. The combined signal is converted into a digital signal through the codec portion
12
, and is input to the optical/radio transmission portion
20
in a digital signal form.
In the related art, the following influences occur when the scale of the network increases:
(1) Problem of Plurality of Telephone Conversations
There is only a single order-wire channel, and a frequency of using of the order-wire channel increases when the scale of the network increases. As a result, in many cases, multiple telephone conversations are performed through the single order-wire channel. Thereby, crosstalk occurs.
(2) Noise Generation Due to Analog Coupling between Transmission Apparatuses
FIG. 3
illustrates generation of noise due to analog coupling between transmission apparatuses in the related art. In this example, the transmission apparatuses
32
and
34
are branched off from an analog coupler
44
of the transmission apparatus
31
.
FIG. 3
shows a situation where noise is generated when a telephone conversation is performed from the transmission apparatus
30
to the transmission apparatus
33
. An analog signal ‘a’ from the transmission apparatus
30
is transmitted via an analog-to-digital converter
40
, a transmission path
35
, a digital-to-analog converter
41
, the analog coupler
44
, an analog coupler
45
, an analog-to-digital converter
42
, a transmission path
37
and a digital-to-analog converter
43
.
In this case, because a digital circuit does not connect (
36
) between the transmission apparatuses
31
and
32
, the digital-to-analog converter
41
and the analog-to-digital converter
42
are needed. Further, through a transmission path between the analog couplers
44
and
45
, noise &agr; (external noise, internal noise of an electronic circuit and so forth) is picked up. This analog noise &agr; is converted through the analog-to-digital converter
42
. Accordingly, from the transmission apparatus
32
, in addition to the signal received at the transmission apparatus
31
, the noise &agr; and quantization noise of the noise &agr; are transmitted. As a result, the output of the digital-to-analog converter
43
includes, other than the signal ‘a’, quantization of the signal ‘a’, noise &agr;, and quantization noise of the noise &agr;. In
FIG. 3
, f(a) represents a digital signal obtained when the analog signal ‘a’ is quantized, and Nq(a) represents a quantization error generated at this time. Similarly, Nq(&agr;) represents a quantization error generated when the noise &agr; is quantized.
SUMMARY OF THE INVENTION
The present invention is directed to eliminating the above-described problems, and, an object of the present invention is to eliminate crosstalk and prevent noise generation due to analog coupling in a transmission system such as an order-wire transmission system.
A transmission system according to the pres
Bui Bing
Fujitsu Limited
Helfgott & Karas P.C.
Matar Ahmad
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