JPS59139731A - Transmission control system - Google Patents

Abstract

PURPOSE:To satisfy the using standard and at the same time to ensure the proper pre-equalization of a transmission line by detecting at a called station an additional signal which is added to the 1st modulated signal and transmitted from a calling station, and controlling the equalizing characteristic of a fixed equalizer in response to said detected level. CONSTITUTION:A calling station 100 is connected to a called station 200 via a transmission line 300, and these stations serve as terminal devices which transmit the facsimile, etc. via the using control means of the stations 100 and 200. A system control circuit 108 of the station 100 transmits the 1st modulated signal added with the additional signals set at both outer sides of the occupied band of the 1st modulated signal. These modulated and added signals are received at the station 200, and each level of these signals is detected by a pilot signal level detector 206. This detected level is applied to a system control circuit 208 and to a compromising equalizer 210. Then the equalizing characteristic of the equalizer 210 is controlled by the circuit 208. In such a way, satisfies the standard of the using control procedure is satisfied and at the same time the proper pre- equalization of the line 300 is ensured.

Description

[Detailed Description of the Invention] The present invention relates to a transmission control system, particularly a modem device (MODE).
This relates to a transmission control method for transmitting signals such as images and digital data between transmitting and receiving stations via an analog transmission line via M).

[In the United States and Japan, modem equipment generally has an automatic equalization function to compensate for variations in transmission line characteristics.

Of course, the better the transmission characteristics of the line, the more quickly the parameters of the automatic equalizer converge. On the other hand, if the line characteristics are poor,
There are limits to having the automatic equalizer bear all the compensation for these characteristics.

See, for example, the International Telegraph and Telephone Consultative Committee (CCITT) Recommendation V, 21. V, 28bis, V, 27bis, V
, 27ter, V, 29, etc., various training sequences are defined for adapting automatic equalizers. However, as mentioned above, in poor line conditions, the parameters may not converge during the training period specified, and there is a limit to the degree of compensation.

Therefore, it is necessary to insert a fixed equalizer such as a combromized divider to pre-equalize the transmission characteristics. However, if such an equalizer is permanently inserted, if it happens to be connected to a line with good transmission characteristics, over-correction will occur, causing problems such as failure of modulator/demodulator parameters to converge.

In a modem having only a fixed equalizer with an automatic equalizer, a specific test signal is sent in advance to adjust the number of fixed equalizer stages inserted. However, such test signals do not comply with predetermined protocols such as the recommendations mentioned above.

--1 It is an object of the present invention to provide a transmission control system that can eliminate the drawbacks of the prior art, satisfy existing standards, and can satisfactorily equalize line characteristics.

Note that in this specification, the term "data" is interpreted in a broad sense to include not only digital data handled by a computer in a narrow sense, but also signals obtained by encoding analog signals such as audio or images.

BEST MODE FOR CARRYING OUT THE INVENTION The configuration of the present invention will be described below based on one embodiment.

FIG. 1 shows an embodiment of a transmission control system to which a transmission control method according to the present invention is applied.
and a called station 200 are connected via a transmission line 300. The calling station 100 and the called station 200 are, for example, CCr.
It can be thought of as a terminal device such as a facsimile machine, that is, a home device that follows a transmission control procedure such as TT Recommendation 1.30. In reality, the calling station 100 and the called station 200 may have the same configuration, but in order to avoid complicating the diagram, only the parts related to the present invention are shown. In addition, in order to avoid confusion, only the functions necessary for transmitting data from the calling station 100 to the called station 200 are shown in this figure. From calling station 10
This includes a function to return the data to 0.

The transmission line 300 is, for example, an analog transmission line such as a telephone line, and it does not matter whether it is a public network or a private network, but the problem in the present invention is when this is a switched line network where the connection route is not constant. It is. In this example, the telephone band (200
~35001(z) is a switched line including unloaded cables and transport links.

The calling station 100 has a low speed transmitter 102 . High speed transmitter 104. It has a pilot signal generator 10B and a system control circuit 108. The low-speed transmitter +02 has a modulator (not shown) for modulating a data transmission rate of 300 bits/s as specified in Recommendation V, 21, for example, and the signal outputted to its output 110 is Solid line 4 in figure 3
As shown by 00, the frequency band that decreases by 3 dB is approximately 150.
Eliminate the frequency spectrum from 0 to 2000Hz.

In this embodiment, the high-speed transmitter 104 has, for example, 2400~
It has a modulator (not shown) for modulating a data transmission rate of 8800 bits/second. This data transmission rate is selected by control via control line 112 from system control circuit IO8. Even 1-2 facsimile.

Image data such as images are transmitted as messages by this high-speed transmitter 104.The output 110 of the low-speed transmitter 102 is connected to one input of a mixer 114, and the other input 114 is connected to a pilot signal generator. The output of 10B is combined with 115 power supply and delay.

The pilot signal generator 10B is an oscillator that generates pilot signals 402° and 404 as shown in FIG.
900) has a frequency of 1z. These pilot signals 402 and 404 are not limited to the frequencies mentioned above.
/) is basically the communication signal band 500 of the transmission line 300.
~3100 Hz and outside the modulation signal band 400 of the low-speed transmitter 104 is a possibility.

Note that even if it is outside the communication band of the transmission line 300, a specific other frequency signal may be used as long as it is within the radio frequency band. You can also do %.

The output 11B of the mixer 114 is connected to the output 120 of the high-speed transmitter 104 and, alternatively, to the transmission output +22 of the originating station 100 via a contact 118, and is sent to the transmission line 300. Contact 118 symbolically represents a switching circuit that alternatively connects signal lines 116 and 120 to transmit output 122 .

System control circuit 108 controls these circuits 102, 104 and 10B by control line 112, and also controls switching of contact +18, as shown symbolically by dotted line 124, according to a predetermined transmission control procedure as described below. Performs system control of the entire calling station.

The called station 200 has a low speed receiver 202 . High speed receiver 204.
Pilot signal level detector 206. It has a system control circuit 208, a combromized equalizer 21O1, and band pass filters (BPF) 212 and 214.

Receive power 222 from the transmission line is alternatively connected to input 22B of BPF 214 and input 220 of combromized equalizer 210 via switching contact 21B similar to contact 118. Also, this reception input is BPF212
is also connected to the input.

The low-speed receiver 202 corresponds to the low-speed transmitter 102 and has a demodulator (not shown) that demodulates the signal transmitted from the low-speed receiver 202 into a baseband signal and outputs the baseband signal. BPF 214 has a frequency band that passes low speed signal 400 (FIG. 3) and blocks other signals, including, for example, pilot signals 402 and 404, and provides only this signal to low speed receiver 202.

The high-speed receiver 204 corresponds to the high-speed transmitter 104 and has a demodulator (not shown) that demodulates the signal transmitted therefrom into a baseband signal and outputs it as, for example, a facsimile signal. This demodulator may include an automatic equalizer that operates adaptively according to a predetermined training sequence, for example as defined in Recommendation V, 27ter, etc.

The combromized equalizer 210 is a fixed equalizer that pre-equalizes the transmission characteristics of the transmission line 300, and its activation and deactivation and adjustment of the equalization characteristics are controlled by the system control circuit 208.

Therefore, if the equalization amount of the combromized equalizer 210 is controlled according to the loss of the unloaded cable and the carrier link included in the transmission path 300 estimated as described below, the transmission path characteristics can be appropriately compensated. be able to.

Note that this combromized equalizer 210 may be configured with an LC or RC circuit, or may be realized by digital signal processing operations together with, for example, a system control circuit.

Another bandpass filter 212 receives the two pilot signals 40 transmitted from the pilot signal generator 1.08.
2 and 402 and blocks other signals, and its output 216 is connected to the pilot signal level detector 208.

The pilot signal level detector 208 is a BPF 212
This is a detection circuit that detects the energy level of the pilot signals 402 and 404 that have passed through the control line 228 and reports this detected level to the system control circuit 208 through the control line 228. Note that, similarly to the combromized equalizer 210, the pilot signal level detector 206 and the BPF
Circuits such as 212 and 214 may be constructed of LC or RC circuits, or may be realized by digital signal arithmetic processing.

By the way, the transmission characteristics of the transmission line 300 that are compensated by the combromized equalizer 210 are distortions caused by the unloaded cable and the transport link included therein. It is generally known that the distortion caused by an unloaded cable is approximately proportional to the square of the frequency, as shown in FIG. 4A. Additionally, the distortion caused by the carrier link is generally approximately symmetrical with respect to the center frequency of the transmission band, as shown in FIG. 4B. Both distortions are added to the signal received through the transmission path 300.

Therefore, the number of transport links included in the transmission path 300 can be estimated by comparing the received signal level at approximately the center of the transmission band of the transmission path 300 and the received signal level in the lower band. Further, by comparing the received signal level in the high frequency range and the received signal level in the low frequency range, the length of the unloaded cable included in the transmission path 300 can be estimated.

In this embodiment, a facsimile signal is transmitted or a call is made in accordance with the transmission control procedure specified in Recommendation T.30 mentioned above. As shown in FIG. 2, when the calling station 100 makes a call and transmits a facsimile signal to the called station 200, the system control circuit 10B of the calling station first contacts the switching contact 118.
Connect to the signal line 118 side as shown in the figure, and connect the low-speed transmitter 1
02 to generate a DC3 signal (digital command signal) at 300 bits/sec, and pilot signal generator lOθ to generate pilot signals 402 and 40.
4 is superimposed on this through the mixer +14, and the transmission line 300
have it sent to

Since the system control circuit 208 of the called station 200 connects the switching contact 218 to the signal line 22B side at this time,
The DO9 signal and pilot signals 402, 404 transmitted through the transmission line 300 are sent to the BPFs 214 and 212, extracted, respectively, and received by the low speed receiver and pilot signal level detector 206. Low speed receiver 2
02 is approximately the center of the band of the received DOS signal (therefore, this is also approximately the center of the band of the transmission path 300).
The system control circuit 2 detects the energy level of the signal.
Report this to 08. Pilot signal level detector 206 also detects received pilot signals 402 and 40.
4 energy level and reports this to the system control circuit 2084.

System control circuit 208 compares these three energy levels as described above and estimates the length of unloaded cable and number of carrying links included in transmission line 300.

Therefore, the system control circuit 208 controls the combromized equalizer 210 to provide an equalization amount according to this estimation result, that is, the unloaded cable length and the number of transport links. As a result, the combromized equalizer 21
0 is a state in which the transmission characteristics of the transmission path 300 can be pre-equalized. Therefore, the system control circuit 208 switches the contact 218 to the signal line 220 side.

The system control circuit 108 of the calling station 100
After sending the signal, connect the contact 118 to the signal line! 20 side and drives the high speed transmitter 104 to send the training check field (TCP) (FIG. 2) at high speed, e.g.
It is transmitted through the transmission line 300 at 800 bits/second.

The system control circuit 208 of the called station 200 connects the contact 218
is switched to the signal line 220 side, the TGF is received by the combromized equalizer 210 and the high-speed receiver 204, the demodulator in the high-speed receiver 204 is trained, and various parameters of the automatic equalizer included therein are converged. let When convergence fails, the called station 200 reports this to the calling station 100, and the system control circuit 108 of the calling station 100 controls the high-speed transmitter 104 to transmit data at the same data transmission rate or at a lower rate. The TCF may be retransmitted at a transmission rate of, for example, 4800 bits/second.

If the training is successful, the system control circuit 208 of the called station 200 transmits a CFR signal (reception readiness confirmation signal) to the calling station 100, and in response, the system control circuit 108 of the calling station 100 transmits a high-speed transmitter. 104 to transmit a message, eg, a facsimile signal, to the called station 200 at the same data transmission rate at which the training was successful.

In this way, the called station 200 receives the low-speed 6 OC8 signal and pre-equalizes it with the combromized equalizer 210 before receiving the high-speed data δ, thereby reducing the amplitude distortion caused by the transmission line 300. Once the phase distortion is corrected to some extent by the combromized equalizer 210, the automatic equalizer of the high-speed receiver 204 can easily perform subsequent automatic equalization operations. In addition, by receiving the low-speed DC8 signal, the received signal level can be predicted to some extent, and the automatic gain control (A
GO) circuitry (not shown) can be operated adaptively. That is, before receiving a high-speed data signal, some preparatory operations are performed for the two adaptive operations necessary for training the demodulator included in the high-speed receiver 204, namely the AGC operation and the automatic equalization operation. be able to.

Circle--1 As described above, according to the present invention, it is possible to appropriately pre-equalize a transmission line while maintaining compatibility with current standards. Therefore, there are very few training failures of the modem, and from the viewpoint of using a communication device such as a facsimile, the communication rate increases, that is, the hang-up rate decreases. In addition, the time required for training is also reduced, and, for example, the conventional 8800 bit/
Transmission speeds that used to be transmitted in seconds can now be transmitted at 14.4 bits per second, making even faster transmission possible.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a transmission control system to which the transmission control method according to the present invention is applied, FIG. 2 is a flow diagram showing an example of the transmission control procedure of the system shown in FIG. 1, and FIG. A frequency spectrum diagram showing an example of a signal used in the system. FIGS. 4A and 4B are graphs used to explain an example of transmission path characteristics. 102, low-speed transmitter 104, high-speed transmitter 10B, pilot signal generator 108.20
8. , system control circuit 114, , , mixer 118.218. , switching contact 202, , , low-speed receiver 204, , , high-speed receiver 201 (, , pilot signal level detector 210,
, , , Combromized Equalizer 212.214
．． , bandpass filter patent applicant Ricoh Co., Ltd. Figure 2 Figure 3 Figure 4A Figure 4B Comparison Figure 4B

Claims (1)

[Claims] Data is transmitted between calling and receiving stations via an analog transmission line via a modem, and the calling station transmits data in a relatively middle range of the transmission band of the transmission line before transmitting information. After the first modulated signal used, a second modulated signal using a relatively entire transmission band is transmitted to the transmission path, and the called station uses a fixed equalizer to adjust the transmission characteristics of the transmission path. Transmission control system for pre-equalization The fixed equalizer can control its equalization characteristics, and the calling station adds additional signals of frequencies located on both sides of the occupied band of the first modulated signal. the called station receives the first modulated signal and the additional signal, detects the levels of these signals, and adjusts the fixed equalization according to the detected level. A transmission control method characterized by controlling the equalization characteristics of the transmitter.