Pulse or digital communications – Repeaters – Testing
Patent
1990-02-14
1994-10-04
Bocure, Tesfaldet
Pulse or digital communications
Repeaters
Testing
370 321, 379411, H03H 730
Patent
active
053533054
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transmitter and receiver apparatus (transceiver) and in particular relates to an initial training apparatus for use in an echo canceler transmission apparatus for correcting an echo signal in the best way by using an adaptive gain of an automatic equalizer.
2. Description of the Related Art
Equipment for transmitting and receiving signals is used to take advantage of the recently introduced bidirectional digital transmission method.
FIG. 1 shows a system structure based on digital subscriber line transmission. In FIG. 1, 1 designates a terminal apparatus provided within a subscriber's premises and 2 a transmission apparatus (transmitter). The subscriber's premises are connected to other transmission apparatuses in a station by a subscriber line 3, which is a two-wire metallic cable. This cable is used for bidirectional digital transmission, and provides a data capacity of 160 kb/s. A structural view of a transmission apparatus for a subscriber's premises is shown in FIGS. 2A and 2B. Generally, the transmission apparatus needs an automatic equalizer EQL to compensate for a waveform distortion on a transmission line.
Further, some transmission apparatuses include an echo canceler for suppressing echo leaking from a transmitted signal, and some do not. FIG. 2A shows a structural view of a transmitting apparatus based on a ping-pong transmission method, which does not use an echo canceler, and FIG. 2B shows a structural view of a transmission apparatus based on an echo cancelling transmission method, which does use an echo canceler. At present, a ping-pong transmission system is used in Japan and an echo cancelling transmission system is used in Europe and North America.
In the ping-pong transmission system, as illustrated in FIG. 2A, the data capacity for transmission is 160 kb/s, but as bidirectional transmission is used in a time divisional manner, the data capacity on subscriber line 3 is doubled, to 320 kb/s. Transmitting or receiving is switched by a transmitting and receiving switch SW. Transmission data is coded by a coding circuit, (coder) COD, and are driven by a line driver DRV. At this time a transmission switch SW selects a transmission site to transmit a signal on a subscriber line 3. On the other hand, a received signal transmitted from subscriber line 3 is selected by a transmitting and receiving switch SW, and then enters line equalizer EQL. Line equalizer EQL includes .sqroot.F AGC (automatic gain control) and automatically controls gain lost in a transmission line of a subscriber to automatically correct a gain matched with a frequency. The output of line equalizer EQL is applied to decoder DEC, thereby providing received data. In this case, timing reproducing circuit TIM reproduces a clock signal, namely, a synchronizing signal from a received signal and decodes the received data by using the clock. This ping-pong transmission method uses bidirectional signals on a transmission line in a time divisional manner. Thus, when transmission data are transmitted outwardly, they do not leak into the receiving side. Therefore, this system does not need an echo canceler. On the other hand, the data capacity of the transmission line becomes double the demanded data capacity of 160 kb/s, namely 320 kb/s. Therefore, a smaller hardware is required, but the transmission rate is lowered, so that there is a trade-off relationship.
FIG. 2B shows the structure of an echo canceler transmission system. Transmission data are coded by a coding circuit COD and are transmitted on subscriber line 3 through line driver DRV. In an echo canceler transmission system, data capacity of a transmission on subscriber line 3 is 160 kb/s and it does not perform bidirectional time divisional multiplexing. Then, transmitted and received signals are multiplexed in an analog manner. A received signal is inputted to hybrid circuit HYB i.e. a 2-wire/4-wire conversion circuit, from subscriber line 3. Where a transmission signal is transmitted on
REFERENCES:
patent: 4535206 (1985-08-01), Falconer
patent: 4799214 (1989-01-01), Kaku
patent: 4868874 (1989-09-01), Takafori et al.
patent: 4924492 (1990-05-01), Gitlin et al.
Awata Yutaka
Fukuda Misao
Kawada Kinji
Maruyama Kazuyoshi
Miyoshi Seiji
Bocure Tesfaldet
Fujitsu Limited
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