Facsimile machine having a phase/amplitude fluctuation detector

A facsimile machine includes a phase/amplitude fluctuation detector for quantitatively detecting fluctuation of the phase and amplitude of data received at a modem and a reception speed determiner for determining if the reception is to be continued or not and at which communication speed the data is to be received if reception is to continue, based on the fluctuation values detected at the phase/amplitude fluctuation detection means. The facsimile machine quantitatively detects the fluctuation values of the phase and the amplitude of the signal being received. When the fluctuation values exceed a designated range, even if the bit-pattern of the received data is normal, the facsimile machine starts receiving video information via a one-step reduced communication speed and therefore can accurately receive the video information even if the telephone circuit condition is not good.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a facsimile machine being connected to a 
communication circuit and having T30 protocol. 
(2) Description of the Prior Art 
When a communication speed is determined at a facsimile machine, a 
preferred method has been one based on whether the bit-pattern of the 
received training TCF (Training Check Facilities) signal is "0" or not. A 
common configuration of this type is shown in FIG. 1. 
In FIG. 1, when a facsimile machine receives a call, an NSF (Non-Standard 
Facilities)/DIS (Digital Identification Signal) signal is produced at a 
T30 protocol controller 16 and the signal is written in a communication 
control memory 15. The signal is read at a transmission data controller 14 
and then is written and modulated at a modem 12. Thus, the NSF/DIS signal 
is transmitted to another facsimile machine at a remote site (call-out 
site). 
T30 protocol is used in G3 facsimile and is described in Protocol T series 
issued from ITU (International Telecommunication Union). 
A DCS (Digital Command Signal) signal transmitted from the facsimile 
machine at the remote site is demodulated at modem 12. The demodulated 
data is written in communication control memory 15 through a reception 
data controller 13 and the DCS signal is analyzed at T30 protocol 
controller 16. 
T30 protocol controller 16 reads communication speed information included 
in the DCS signal. Controller 16 then determines a communication speed for 
modem 12 to receive a training TCF signal transmitted from the facsimile 
machine at the remote site according to the contents of the DCS signal. 
The training TCF signal transmitted from the facsimile machine at the 
remote site is then demodulated at modem 12, and is written in 
communication control memory 15 through reception data controller 13. A 
bit pattern of the TCF data extracted from the TCF signal is analyzed at 
T30 protocol controller 16. If the analyzed result of the recognized 
bit-pattern is "00", it is judged that the TCF reception is normal and a 
CFR (Confirmation to Receive) signal is transmitted to the facsimile 
machine at the remote site and the facsimile machine at the local site 
starts receiving video information. 
In the above-explained configuration, however, even if the electrical 
characteristic of the telephone circuit deteriorates during TCF reception 
and the phase and amplitude of the signal fluctuate widely, because only 
the bit-pattern of the TCF data is checked, if the TCF data for 1.5 
seconds happens to be "0", it is judged to be able to communicate at the 
present communication speed. The CFR signal is thus transmitted and the 
facsimile machine starts receiving video information. Therefore, a problem 
that sometimes occurs is that a data error increases after a period of 
time and the printed picture is distorted. That is, it has a problem that 
satisfactory communication cannot be realized in a region where the 
telephone circuit condition is not good. 
SUMMARY OF THE INVENTION 
The present invention offers a facsimile machine in which a printed picture 
is less distorted even if used in a region where the telephone circuit 
condition is not good. 
A facsimile machine in accordance with an exemplary embodiment of the 
present invention includes 
modulation means for modulating data to be transmitted and for transmitting 
the modulated data to a telephone circuit; 
demodulation means for demodulating data from a signal transmitted through 
the telephone circuit; 
protocol control means for controlling protocol between the facsimile 
machine at the local site and a facsimile machine at a remote site; 
phase/amplitude fluctuation detection means for detecting fluctuation 
values of phase and amplitude of the received signal transmitted through 
the telephone circuit; 
communication speed determination means for determining if the 
communication speed should be changed or not, based on the fluctuation 
values detected at the phase/amplitude fluctuation detection means; and 
control means for transmitting a signal to change the communication speed 
to the facsimile machine at the remote site through the protocol control 
means, if the communication speed determination means determines to change 
the communication speed. 
The phase/amplitude fluctuation detector quantitatively detects the 
fluctuation of the phase and the amplitude of the training TCF signal 
transmitted through the telephone circuit. When the fluctuation values of 
the phase and the amplitude of the training TCF signal detected at the 
phase/amplitude fluctuation detector is judged to exceed the designated 
allowance, the reception speed determination apparatus determines that the 
communication at the speed is impossible and makes the facsimile machine 
at the call-out site (remote site) decrease its communication speed 
through the protocol controller and determines at which speed to receive 
the data.

DETAILED DESCRIPTION OF THE INVENTION 
A block diagram of a facsimile machine in accordance with an exemplary 
embodiment of the present invention is shown in FIG. 2. When a facsimile 
machine receives an incoming call, an NSF/DIS signal is produced at a T30 
protocol controller 11 and the signal is written in a communication 
control memory 10. The data written in communication control memory 10 is 
read at a transmission data controller 3 and then is written in a modem 1. 
An NSF/DIS signal is then transmitted to a facsimile machine at a remote 
site (call-out site). 
A DCS signal transmitted from the facsimile machine at the remote site 
comes to modem 1 and data demodulated at modem 1 is read at a reception 
data controller 2. This date is then written in communication control 
memory 10 and the DCS signal from communication control memory 10 is 
analyzed at T30 protocol controller 11. A communication speed data value 
is included in the DCS signal. 
T30 protocol controller 11 reads a communication speed data value included 
in the DCS signal and determines the reception speed against modem 1 to 
receive a training TCF signal transmitted from the facsimile machine at 
the call-out site. At the same time, the reception speed is determined so 
that the facsimile machine at the call-out site can detect the fluctuation 
of the phase and the amplitude. This is performed according to the 
communication speed designated with a DCS signal which is acted on by a 
synchronization adjusting circuit 5 in the phase/amplitude fluctuation 
detector 4. 
The training TCF signal transmitted from the facsimile machine at the 
call-out site is demodulated at modem 1 and is then written in 
communication control memory 10 through reception data controller 2. The 
bit-pattern of the TCF data is analyzed at T30 protocol controller 11. 
The training TCF signal is supplied both to phase/amplitude fluctuation 
detector 4 and to modem 1. At synchronization adjusting circuit 5, a 
synchronous signal is generated corresponding to the designated speed and 
the received signal is synchronized with the synchronous signal. The 
synchronized received signal is distributed to a phase fluctuation 
detection circuit 7 and an amplitude fluctuation detection circuit 6. 
Each detection circuit, phase fluctuation detection circuit 7 and amplitude 
fluctuation detection circuit 6, converts the received signal to digital 
signals, E and .PHI., respectively, and supplies those digital signals to 
a detection level read circuit 8. 
An example of a signal space diagram of a facsimile machine in accordance 
with an exemplary embodiment of the present invention at a V29 9,600 bps 
communication speed is shown in FIG. 3. The points in FIG. 3 indicate 
reference points of a modulated signal at 9,600 bps communication speed 
and the signal space diagram is ideally to be on these reference points. 
The amounts of phase and amplitude deviation from the reference points are 
detected at phase fluctuation detection circuit 7 and amplitude 
fluctuation detection circuit 6 and they are quantitatively read out at 
detection level read circuit 8. 
At detection level read circuit 8, a value in the range from 0 to FF(HEX) 
is read. The larger the value is, the more difficult it is to determine 
which one of the two adjacent reference points shown in FIG. 3 is to be 
taken. It can be estimated that the received signal or the electric 
characteristic of the telephone circuit has some problem. 
Chain lines .sctn. 1 and .sctn. 2 shown in FIG. 3 indicate fluctuation 
allowance of the phase. If the phase value read at detection level read 
circuit 8 is outside of the range between .sctn. 1 and .sctn. 2, 
communication speed determination apparatus 9 determines that the 
communication speed should be reduced. 
Broken lines e.sub.1 and e.sub.2 shown in FIG. 3 indicate fluctuation 
allowance of the amplitude. If the amplitude value read at detection level 
read circuit 8 is outside of the range between e.sub.1 and e.sub.2, 
communication speed determination apparatus 9 determine that the 
communication speed should be reduced. 
The above-mentioned determination is expressed in FIG. 4 as waveforms. The 
symbols E and .PHI. express phase and amplitude, respectively. The symbol 
.PHI..sub.0 is a length of time of the synchronous signal generated at 
synchronization adjusting circuit 5. In this example, the signal phase 
.PHI. is measured at the zero cross point making .PHI..sub.0 a reference 
phase. The symbols .DELTA..PHI. and .DELTA.E are allowable fluctuation 
values of amplitude and phase, respectively. 
FIG. 4(a) shows a waveform of a normal input signal and the phase .PHI. of 
the signal is in the range of allowable fluctuation value .DELTA..PHI. and 
the amplitude E of the signal also is in the range of allowable 
fluctuation value .DELTA.E. FIG. 4(b) shows a waveform of the input signal 
having a phase deviation and the signal phase .PHI., is out of the range 
of allowable fluctuation value .DELTA..PHI.. FIG. 4(c) shows a waveform of 
the input signal having a decreased amplitude and the signal amplitude E' 
is out of the range of allowable fluctuation value .DELTA.E. 
Because the amplitude and the phase of the signal differ from one system 
configuration to another system configuration of a facsimile machine, the 
apparatus is designed so that the allowable fluctuation values, 
.DELTA..PHI. and .DELTA.E, of the phase and the amplitude are 
appropriately adopted for each system configuration. Thus, the system is 
determined to be abnormal when the value of the system, which can be 
selected by a service mode (switch) in the facsimile machine, falls 
outside of the allowable range. In an exemplary embodiment of the present 
invention, default (the value initially set at shipment) of the allowable 
value is determined according to each reception speed as follows: 
The maximum allowable fluctuation value at 9,600 bps communication 
speed=40(HEX), the maximum allowable fluctuation value at 7,200 bps 
communication speed=50(HEX), the maximum allowable fluctuation value at 
4,800 bps communication speed=70(HEX), and the maximum allowable 
fluctuation value at 2,400 bps communication speed=A0(HEX). 
The signal is determined to be an abnormal signal when the values exceeding 
the maximum allowable fluctuation value appear for 1.5 seconds and exceed 
the received training signal by more than 20%. Because the appearance 
probability depends on the telephone circuit condition, it is designed 
such that the communication speed can be selected with the service mode 
switch. 
FIGS. 5-7 show a flow chart for determining a reception speed at 
phase/amplitude fluctuation detector 4, T30 protocol controller 11 and 
reception speed determination apparatus 9 of a facsimile machine in 
accordance with an exemplary embodiment of the present invention. When T30 
protocol controller 11 analyzes the bit-pattern of the TCF data extracted 
from the training TCF signal and determines that there is no problem, T30 
protocol controller 11 confirms whether or not the fluctuation values of 
the phase and the amplitude of the training TCF signal detected at 
phase/amplitude fluctuation detector 4 and compared by reception speed 
determination apparatus 9 exceeds the fluctuation value defined at the 
facsimile machine at the local site. When the fluctuation value exceeds 
the value defined at the facsimile machine at the local site, even if the 
bit-pattern of the TCF data has no problems (that is, when the training 
TCF signal of T30 protocol is received, all the TCF data transferred from 
modem 1 to communication control memory 10 is "0"), the reception of the 
training TCF signal is judged to be abnormal. That is, when the 
above-mentioned fluctuation value exceeds the value defined at the 
facsimile machine at the local site, the reception is judged to be 
abnormal and a FTT (Failure To Train) signal is produced and is written in 
communication control memory 10. Then transmission data controller 3 reads 
out the FTT signal from communication control memory 10 and writes in it 
modem 1. Thus, the FTT signal is transmitted to the facsimile machine at 
the call-out site (remote site). 
The facsimile machine at the call-out site which received the FTT signal 
transmits a training TCF signal with a one step reduced communication 
speed. By repeating such a fall back procedure, the communication speed 
reduces step-by-step from, for example, 9,600 bps, to 7,200 bps, to 4,800 
bps and finally to 2,400 bps. During this period, the bit-pattern of the 
TCF data and the phase and the amplitude of the training TCF signal are 
detected at T30 protocol controller 11 and phase/amplitude fluctuation 
detector 4 at the same time, respectively. Only when both detections have 
no problem, the facsimile machine at the call-out site transmits a CFR 
signal and the facsimile machine at the local site starts receiving video 
information. 
A facsimile machine in accordance with an exemplary embodiment of the 
present invention functions to determine a communication speed using 
phase/amplitude fluctuation detector and reception speed determination 
apparatus upon reception of a training TCF signal. Accordingly, it is 
possible to receive video information accurately even in a region where 
the telephone circuit condition is not good. 
The invention may be embodied in other specific forms without departing 
from the spirit or essential characteristics thereof. The present 
embodiment is therefore to be considered in all respects as illustrative 
and not restrictive, the scope of the invention being indicated by the 
appended claims rather than by the foregoing description and all changes 
which come within the meaning and range of equivalency of the claims are 
therefore intended to be embraced therein.