JPS5836053A - Data transmission system - Google Patents

Abstract

PURPOSE:To perform loop-back transmission by fixing the gain of an opposite station reception part by transmitting and receiving a specific patten, varying the level of a carrier signal, and detecting that on the opposite station side. CONSTITUTION:For the loop-back transmission of the transmission system in the figure, a specific pattern from a pattern generator 7 is inputted to a modulator 3 through a DA converter 1 and an LPF2. The modulator 3 modulates said pattern by a carrier from a carrier generator 4 and transmits the modulated pattern to an opposite station through a filter 6. At the reception part of the opposite station, when said pattern is detected through a filter 11, a variable gain amplifier 12, a demodulator 13, a filter 14, an equalizer 15, an AD converter 16, and a pattern detector 18, the gain of the amplifier 12 is fixed. The transmitting station varies the level of the succeeding carrier signal of the carrier generator 4, and the receiving station when detecting variation in carrier level by a detector 17A loops the digital signal output back to the transmission part of the station.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a data transmission system that can perform loopback (1) between opposing modems without using a pilot signal for loopback.

As a modem service function, it has a general game loopback function that receives the signal from the transmitting station (returns it to the i station and transmits it).This loopback function is used in tests to isolate the modem and transmission line, etc. This is necessary when carrying out.

Conventionally, game loopback in modems is a method in which a pilot signal for loopback is combined with a transmission signal on the transmitting side and sent out, and when the level of this pilot signal is detected by a level detector on the receiving side, loopback is performed. was used.

FIG. 1 shows the configuration of a conventional data transmission system when loopback is performed. In the figure, 1 is a digital-to-analog (D/A) converter that converts an input digital signal into a baseband signal consisting of an analog signal;
3 is a converter that converts the baseband signal into a carrier signal; 4 is a carrier generator that generates a carrier for modulation; and 5 is a pilot signal for loopback. 6 is a transmitting bandpass filter (BPFS) that limits the band of the transmitting carrier signal.1
．． 11 is a reception bandpass filter (BPFR) that limits the entire band of the reception carrier signal, and 12 is the reception carrier wave 'i AQ.
The AGC amplifier 13 amplifies the received carrier wave and controls the amplitude. 14 is a low-pass filter (LPF) that limits the entire band of the received baseband signal; 15 is an automatic equalizer (AEQ) that equalizes the amplitude and delay of the received baseband signal; 1
6 is an analog-to-digital (A/D) converter that converts the received baseband signal into a digital signal; 17 is a level detector (IT) that detects the level of the loopback monthly pilot signal; The components indicated by the numbers 11 to 17 indicate the transmitting section, and the components indicated by the numbers 11 to 17 indicate the receiving section.

In FIG. 1, a digital signal is input to a VA converter 1.
It is converted to a baseband signal consisting of a multi-level analog signal via the LPF 2'i, further converted to a carrier band analog signal via the modulator 3, and output together with a carrier pilot via the IIPIi'5(3)6.

In a game, the carrier band analog signal input sound 111
After band-limiting by 'FRII and AGC amplification by carrier pilot consisting of residual carrier in AGC amplifier 12, demodulator 13 and LPF'1
4, regenerates the entire baseband signal, and transfers it to AEQ15.
After equalizing the amplitude and delay distortion, the A/D converter 16
The digital signal is reproduced and output.

The signal from the opposing station is also transmitted as an analog signal through a transmitting section having a similar configuration, and is configured to reproduce the original signal through a receiving section having a similar configuration at the own station.

When attempting to perform a game loopback in such a transmission system, a pilot signal for loopback is generated from the pilot signal generator 6 in the transmitter, combined with an analog signal, and transmitted. In a game, this pilot signal is detected from the received analog signal by DET 17, and if the level is less than a certain value, AEQ 15
Loopback can be performed by looping back the baseband signal or the output of the A/1) converter 16 to the LPF 2 or D/A converter 1 input of the own station (4).

FIG. 2 shows an example of the spectral distribution of analog signals in the data transmission system shown in FIG. In the figure, A indicates the entire spectrum of the data signal, B indicates a gear rear pilot signal formed by residual modulation carrier, and C indicates a loopback pilot signal. In this way, the carrier pilot signal is inserted at a constant level at the end of the data signal spectrum band, and the loopback pilot signal is inserted at a constant level outside the band.

Therefore, in conventional data transmission systems, as a result of inserting a pilot signal outside the band to perform loopback,
Not only must the band be widened, but the receiving side must also consider the filter characteristics to suppress this pilot signal, and if the filter characteristics are steep, this may cause distortion in the data signal. there were.

The present invention attempts to eliminate these drawbacks of the prior art, and its purpose is to provide a system that can perform loopback between loopback dems.

° When attempting to perform loopback, the data transmission method of the present invention first sends out a specific pattern from the transmitting side, detects this on the receiving side, stops AGC operation, and fixes the amplifier gain for the received signal. Make it. Next, by changing the level of the carrier pilot signal on the transmitting side, when the receiving side detects all of the carrier pilot signals, loopback is performed by returning the received output to the transmitting input of the own station.

Hereinafter, the present invention will be described in detail with reference to Examples.

FIG. 3 shows the structure of one embodiment of the data transmission system of the present invention. In the same figure, the same parts as in FIG. 1 are indicated by the same numbers, 7 is a pattern generator that generates a specific digital pattern, and 17A is a level detector (DET) that detects the entire level of the carrier pilot signal.
, 1.8 is a pattern detector that detects all specific digital patterns.

In FIG. 3, the operations of the transmitter and receiver when transmitting and receiving data signals are the same as in FIG. 1.

In the transmission system shown in FIG. 3, when a complete loopback is to be performed, a specific pattern is first input from the pattern generator 7 in transmission [11tl. This pattern is converted into a baseband signal in the l)/A converter 1, and further converted into an analog signal and transmitted to the opposing station. In the game, analog key signal input all baseband 4
g, and further converted into digital 46 by the A/D converter 16. The pattern detector 18 detects the same specific pattern as on the transmitting side and detects the AGC fixed point 1 (
A signal is generated and input to the AGC amplifier 12. When the AGC amplifier 12 receives this signal, the level adjustment is completely stopped and the gain becomes fixed.

Next, on the transmitting side, the level of the carrier pilot signal is increased or decreased by a certain value.

In a game, the DET installed at the output of the AGC amplifier 12
17A to monitor the carrier pilot level,
When a level change is detected, (7) the baseband signal output or digital signal output is looped back to the transmitter of the own station.

In this way, in the data transmission system of the present invention, after the gain of the receiver on the opposing side is fixed by transmitting and receiving a specific pattern,
By changing the level of the gear rear pilot, the opposing side can detect this level change and perform a loopback.

FIG. 4 shows an example of the spectral distribution of an analog signal in the data transmission system of the present invention.

In the figure, A shows the entire spectrum of the data signal, B shows the carrier pilot in the normal state, and B' shows the carrier pilot in the loopback state.

As is clear from the above explanation, according to the data transmission method of the present invention, there is no need to insert the entire pilot signal outside the band in order to perform loopback, and therefore the filter characteristics are not suitable for suppressing this pilot signal. This method is extremely effective because it does not cause distortion of the data signal spectrum based on the data signal.

[Brief explanation of drawings]

(8) Figure 1 is a block diagram showing the configuration of a conventional data transmission system, Figure 2 is a diagram showing the spectral distribution of analog signals in the conventional data transmission system, and Figure 3 is one of the data transmission systems of the present invention. FIG. 4 is a block diagram showing the configuration of the embodiment. FIG. 4 is a diagram showing an example of the spectral distribution of an analog signal in the data transmission system of the present invention. 1...Digital analog (D/A) converter, 2...
...Low pass filter (LPF), 3...Modulator, 4
... Carrier generator, 5... Pilot signal generator, 6... Transmission band pass filter (BPIi'S),
? ... Pattern generator, 11... Reception band pass filter (BPFR), i2... Human GC amplifier, 13
... Demodulator, 14 ... Low pass filter (LPF)
, 15... Automatic equivalent equipment (AEQ), 16... Analog-to-digital (A/D) converter, 17.17A...
Level detector (OET), 18... pattern detector. Patent Applicant: Fujitsu Ltd. Representative Patent Attorney: Hisashi Tamamushi (3 others) (e)
a3

Claims (1)

[Claims] In a data transmission system for communication between modems, a pattern generator for generating a specific pattern and a means for changing the level of a carrier pilot signal consisting of a residual carrier for modulation are provided on the transmitting side, and a pattern for detecting all of the specific patterns. a detector, a means for fixing an amplifier gain for a received signal by detecting the pattern;
A level detector for detecting the level of the carrier pilot signal in No. 6 is provided on all receiving sides, and upon detection of a level change in the level detector, the receiving side loops back the received output to the transmitting input of its own station, thereby creating a loopback. A data transmission method characterized by: