Pulse or digital communications – Repeaters – Testing
Patent
1986-03-18
1987-06-09
Safourek, Benedict V.
Pulse or digital communications
Repeaters
Testing
375 12, 375 14, 375 15, H04B 304
Patent
active
046726306
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
TECHNICAL FIELD
This invention relates to a training method for making ready the data transmission and reception by training a modulator/demodulator (hereinafter referred to as modem) connected through the transmission line with a training signal, and particularly to a training method of data receiving equipment which facilitates the training within the optimum time for the transmission line by utilizing a training signal corresponding to line characteristic of the line employing the modulation system such as orthogonal phase modulation.
BACKGROUND ART
In such a communication system which realizes communications between modems connected through transmission lines, it is generally known that the modems in communication are synchronized at least during data transmission and reception between the sending terminal and receiving terminal connected to the respective modems and the modem in the receiving side is capable of equalizing the line characteristic.
In view of meeting such conditions, a training signal of a predetermined constant pattern containing at least a binary random data signal is transmitted from the modem in the sending side just before actual data transfer from, for example, the terminal in order to train the modem in the receiving side and thereby the receiving modem is placed in a condition matching said respective conditions just before transmission and reception of data between terminals.
However, such a conventional training method has a disadvantage in that the length of training signal is fixed and such a length must be sufficiently long so that the modem in the receiving side can be trained perfectly even, in case line characteristics are different.
Meanwhile, it has been proposed to realize communication between a modem in the center and a plurality of modems by connecting such a modem and the modems provided in a plurality of terminals.
In such a communication system the distance from the center modem to each terminal is different. Therefore, the conventional training method explained above requires longer training times before the start of data transmission from the terminals; and such times have not been employed for such a communication system because the time is determined in accordance with the transmission line having the worst line characteristic.
On the other hand, as a training method which assures very high speed training, the method disclosed in the specification of U.S. Pat. No. 3,962,637 is known.
FIGS. 1(a) and (b) show the conventional training method explained above. FIG. 1(a) indicates the block diagram of a modem, while FIG. 1(b) indicates the pattern of a training signal.
In FIG. 1(a), numeral 1 indicates an automatic gain controller (AGC), while 2 indicates a demodulating circuit, 3 indicates a roll-off filter, 4 denotes an equalizer, 5 indicates a phase controller, 6 indicates a discriminator, 7 deontes a code converter, 40 indicates a high speed pull-in circuit, 8 indicates a timing generator, and 9 indicates a carrier detector.
In FIG. 1(b), "tone" means a tone signal, "tim" means a timing signal, "imp" means an impulse, "dat" means a data and T0.about.T7 respectively indicate times.
A training means will be explained hereunder.
First, a training signal shown in FIG. 1(b) is sent from the sending side (now shown).
The modem in the receiving side causes, at first, the AGC 1 and pulling of phase of signal using the tone signal starting from the time T0 and obtains a detecting output CD from the detector 9.
The phase of the carrier signal is adjusted by the timing signal "tim" starting from the time T1 and the send timing is pulled by timing generator 8.
The impulse signal "imp" appearing between the time T3 and T6 of the training signal contains impulses i1 and i2 which are synchronized with the timing of data and provided with no-signal period in both sides.
This signal is supplied to the high speed pull-in circuit 40 from the phase controller 5. The high speed pull-in circuit 40 discriminates line characteristics by operating on components of
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Fujitsu Limited
Safourek Benedict V.
Seidenglanz Elissa
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