JPS59219058A - Exchange for loudspeaker telephone set - Google Patents

Abstract

PURPOSE:To save the number of echo cancellors by providing an echo cancellor in an exchange so as to use the echo canceller in common. CONSTITUTION:The exchange connecting lines between plural telephone sets including a loudspeaker telephone set is provided with the echo canceller, a loudspeaker talking detection circuit 608 and a control circuit 606. The circuit 606 detects whether or not a telephone set in line connecting state conducts loudspeaker talking and the circuit 606 inserts the echo canceller to the line at the loudspeaker talking depending on the output of the circuit 608 and controls the system so as to eliminate the acoustic coupling between the speaker and microphone of the loudspeaker telephone set 609. Thus the echo canceller is used in common and the required number is saved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in an exchange equipped with a loudspeaker telephone capable of making calls using a speaker.

[Technical background of the invention and its problems 1 There is an increasing demand for high-performance telephones that provide various new services as next-generation telephones.

Among these, it is desired that loudspeaker telephones, which allow telephone calls to be made without having to hold a handset, have improved call quality. This is because most of the current loudspeaker telephones use a voice switch system, which causes problems such as truncated speech and difficulty in simultaneous two-way conversation.

A voice switch is required in a public address telephone for the following reasons. Since the public address telephone ' uses a speaker, the degree of acoustic coupling caused by the sound emitted from the speaker entering the microphone is greater than that of a general telephone.

Therefore, when the loudspeaker telephone is connected to a two-line line, the sequence is as follows: microphone → transmitting amplifier, everyone on the side of the hybrid coil → receiving amplifier → speaker → acoustic coupling → microphone.

When a G4 loop is formed and the loop gain becomes 1 or more, there is a high possibility that howling will occur. Also, in a call between A and B's loudspeaker telephones, the microphone to A's transmitting amplifier →
Line → Receiving amplifier of B → Speaker of B → Acoustic coupling of B →
B's microphone → B's transmitting amplifier → Line → A's receiving amplifier →
A signal loop is created from A's speaker → A's acoustic coupling → A's microphone, and the impedance of the hybrid coil has a good matching of PE and howling is likely to occur even when there is little sidetone or when using a 4-wire line. Become. Furthermore, even if howling does not occur, if the other party's telephone is a loudspeaker telephone, the user's own voice will be greatly reflected due to the acoustic coupling on the other party's side, which will interfere with communication. This will become a major problem in the future when a switching system such as a packet switching system that may have a large signal delay is introduced, or when a transmission line itself has a large delay such as a satellite communication line.

In order to prevent the above-mentioned problems, the voice switch method introduces a loss on the receiving side when sending a call, and a loss on the sending side when receiving a call.
Although this method removes acoustic coupling and sidetone coupling, it takes time to detect transmission/reception determination, resulting in truncations at the beginning of words, and when two-way simultaneous calls are made, there is always a loss on one side, resulting in audio cut-off on one side. There are problems. There is an echo canceller type that solves this voice switch problem.

Figure 1 shows an echo canceller for removing acoustic coupling.
This will be explained below.

The reception signal xfi't) to the loudspeaker telephone is transmitted to the receiving amplifier (
101) and input to a speaker (106). The output of this speaker is reflected from walls and human traps, and α
Reverberation signal y(t) due to acoustic coupling with dB attenuation
h and input into the microphone (107).

Here, if an echo canceller or voice switch is not used, this signal y(r) will be transmitted directly to the transmitting amplifier (10
(However, in the case of a two-wire line, the signal is sent out after being converted from four wires to two wires by an hybrid coil.) This causes various problems as described above.

Here, the echo canceller (103) uses a control signal from the double talk detector (105) to turn the received signal X([) into an echo signal y(t) when there is no transmitted signal x(t). The characteristic characteristic of the echo path is X([) and y
(t), and synthesizes a filter having pseudo echo path characteristics, which is an approximation of the echo path characteristics, within its own circuit. Then, the output 'Tht) of this filter is sent to a subtracter (104).
By subtracting from the transmitted signal y(t) + n(t) including the echo signal, a narrow transmitted signal n(L) is extracted.

Therefore, the echo canceller uses the echo signal y(t)
This makes it possible to reduce the total acoustics without causing problems like the voice switch method.

Note that the double talk detector (105) is, for example,
Compare the powers of X(() and y(t)In(+), and obtain (X
(t) power) -ct In1n ()'(t)In
(t) power (however, αmin is the worst value of acoustic coupling)
When this happens, it is determined that there is double talk and the estimated operation of the echo canceller is stopped.

Although the echo canceller is a very effective method as described above, it has the problem that it requires more complicated digital signal processing than the voice switch method, resulting in higher costs. Furthermore, especially when used for removing acoustic coupling, compared to canceling the echo signal generated by a no-brid coil.

Since the amount of delay of the reverberant signal to be handled is large, the amount of .

In the conventional system, one such high-cost echo canceller is always required for each loudspeaker telephone set, so when m loudspeaker telephones are connected to one exchange as shown in Figure 2, m echo cancellers are also required, making the entire system extremely expensive.

[Object of the Invention] The present invention has been made in view of the problems of conventional exchanges for public address telephones, and it is an object of the present invention to provide an exchange for public address telephones that requires fewer echo cancellers and is inexpensive as a whole system. shall be.

The present invention is to move the echo canceller that was in the 7-phone loudspeaker machine to the switchboard, and to share one echo canceller with a plurality of loudspeaker telephones.

[Effects of the Invention] According to the present invention, by having an echo canceller in the exchange and sharing it, it is possible to significantly reduce the overall cost. , m echo cancellers are required for m loudspeaker telephones, which increases the cost.

Furthermore, not all of the ln, 11, and 11 are in use at all times, and only a portion of the loudspeaker telephones are in use.

Furthermore, even if you are using a loudspeaker telephone, there are people who are still talking using a receiver. Therefore, among the rn echo cancellers, the one producing nτL1,
Only a few of them9. It is extremely uneconomical.

As shown in Figure 3, the present invention reduces the number of echo cancellers in the telephone system by moving expensive echo cancellers into the exchange and sharing them among multiple loudspeaker telephones, thereby lowering the overall system cost. .

In FIG. 3, a switch using the present invention is shown within the broken line.

In the figure, a case where a public telephone (301) connected to this exchange and a general telephone (302) make a call will be explained with reference to FIG.
hooks off and dials, the scanning circuit (306
) detects this and transmits this information to the control circuit (307). At this time, if the loudspeaker telephone (301) is set to the loudspeaker call button, for example, a control signal sent after the dial signal will notify the loudspeaker detection device (305) that it is a loudspeaker call. The detection device (305) detects this and transmits it to the control circuit (307). Control circuit (3
07) is (a) in the diagram for calls between ordinary telephones.
The call path is set up in the same way as in a conventional exchange, but in the case of a loudspeaker call as in this example, the call path is set up via the echo canceller unit (304) as shown in (b) in the figure. Ru. Echo canceller unit (304)
Since the f'i loudspeaker telephone has a function of removing the echo signal generated by the echo canceller using an echo canceller, even if the loudspeaker telephone (301) does not have an echo canceller,
Here, echo signal removal becomes possible.

FIG. 4 explains this by focusing on the route from the loudspeaker telephone (301) to the telephone.

In addition, in Fig. 4, for the sake of simplicity, the matching with the high print coil is close to ideal (for example, in the case of private exchange 4).
．． When the path is short (as in If the sidetone cannot be ignored, such as on a public line, an echo canceller for sidetone removal may be used. This echo canceller handles a smaller amount of delay than one for acoustic coupling, so the cost is relatively low. The exchange will still be a 4-wire exchange.

In the figure, the transmission signal of the general telephone is transmitted through the hybrid coil (408), the line, and the hybrid coil (407).
), switchboard, hybrid coil (404), line,
The signal is input to the speaker (411) via the hybrid coil (403) and the receiving amplifier of the loudspeaker telephone. Then, the sound output from the speaker (411) is input to the microphone (410) through acoustic coupling, follows the reverse route, and is transmitted to the telephone (3).
03) into the handset. At this time, if the echo signal is not removed, the echo coupling of the loudspeaker telephone will be large, and the speaker's own voice will be reflected to a large extent, causing discomfort to the speaker.

According to the present invention, an echo canceller (405
) and a subtractor (406') to cancel the echo signal.
The above-mentioned problems can be improved.

In the case of calls between loudspeaker telephones, two echo canceller units (
501) and (502).

The configuration of the first embodiment of the present invention is shown in FIG. 6 and will be described.

The exchange shown in FIG. 6 is a small scale digital private branch exchange using a time division system.

In the figure, the digital input/output terminals Di and Dci of the codecs (601) to (603) are commonly connected to the data bus, and are connected to control signals such as hook-on, hook-off, and dial signals detected by the scanning circuit (607). Based on
The control circuit (606) performs the exchange by controlling the digital input/output timing of each codec using the output timing signal ST and the input timing signal RT, which is a common method in conventional time division exchange. .

The present invention is characterized in that the exchange has a loudspeaker detection circuit and an echo canceller unit in front of each of the above circuits.

In the following, a description will be given of how to cancel the echo signal of the loudspeaker telephone in this embodiment.

In this switch, time-division switching divides the time of one audio sample into 16 time slots, and separates the input and output time slots of each codec, as shown in Figure 7(a) (C). Replacement shall be performed by switching.

FIG. 7(R) is an example of connection between general telephones, and the scanning circuit (607) shown in FIG.
10) and a dial signal, the control circuit (606) searches for 16 free time slots and makes a call. COL>ECB (602) and C0D.
The data output timing of the ECN (603) is specified by the sending timing signal 8T. At the same time, the reception timings R and T of both CODECs are designated at opposite timings. As a result, the telephone set (610) and the telephone set (612) are connected via both CODEC', and a telephone conversation becomes possible.

Next, FIG. 7(b) shows the timing in the case of a loudspeaker telephone and a general telephone. In this case, the loudspeaker detection circuit (6
When 08) detects that the telephone (609) has turned on the loudspeaker switch, the control circuit (606) uses a control signal.
tell to. At this time, the control circuit (606) checks whether the EC units and time slots in the own exchange are empty, searches for one that is not in use, and if any of them is in use, the control circuit (606) sends a control signal BUSY to the loudspeaker call detection circuit. (608
), and the same circuit notifies the public address telephone (609) of this fact. At this point, the loudspeaker telephone (609) decides whether to prohibit the loudspeaker call or, if it has a voice switch function, activates the voice switch.

Next, if there is a vacant EC unit and time slot, connect the reception timing signal XT to the output timing of the COL)EC connected to the general telephone, and connect the Y reception timing signal YT to the public address telephone. C doing
These signals are input to the EC unit via the data bus in accordance with the output timing of 0DEC.Then, the E sending timing control signal ET is input to the empty time slot.
is used to output the signal after cancellation.

Further, the reception timing RT of the general telephone is made to match the E output timing of the EC unit, and the cancellation residual signal of the EC unit is given to the reception side of the general telephone in place of the transmission signal of the amplification telephone.

By the above timing operation, an echo canceller will be inserted into the communication path as in Figure 4. Furthermore, the timing in the case of loudspeaker telephones is as shown in Figure 7 (C).
become that way. In this case, two EC units and two time slots for outputting this residual signal are required to cancel the echo signals of both loudspeaker telephones.For example, EC unit 1 sets the X reception timing to the output of C0DBCA. Adjust the Y reception timing to the C0DBCC output timing and perform EC.
Unit 2 does the opposite. Also, the reception timing of C0DBCA and C is changed to the residual signal E of EC units 1 and 2.
By matching the transmission timing, instead of the output signal containing the echo signal of the loudspeaker telephone connected to C0DECA, the residual signal from which this echo signal has been removed is used as the output signal containing the echo signal of the loudspeaker telephone connected to C0DECC. Alternatively, a residual signal from which this echo signal has been removed can be used.

By performing the above-mentioned timing operations, two echo cancellers are inserted into the communication path as in FIG. 5.

The main circuits in this embodiment will be explained.

FIG. 8 shows an example of the configuration of a loudspeaker telephone.

In the figure, if the speaker wishes to make a loudspeaker call, he/she flips the switch (817) f to the IA side. At this time, the monostable 7 multivibrator (812) outputs a single pulse of a fixed time at the rise of this switch output. Oscillator (814
) receives this signal and maintains a constant frequency f during the period of this pulse.
A sine wave of 1 is output, and an adder (818), (808
) to the line. This signal becomes a signal for starting a loudspeaker call in the loudspeaker detection circuit of the exchange.

When the exchange receives this signal, it checks whether the Be unit is empty and, if it is empty, sends a +2 sine wave to the loudspeaker telephone, indicating that loudspeaker communication is possible.

When the detection circuit (810) receives the +2 signal of
Set the flip-flop, which causes F/F (8
16) becomes High, the switch circuits (806) and (807) turn the switch connected to the handset to the loudspeaker side, enabling a loudspeaker call.

The next time the speaker wants to end the loudspeaker call, the speaker must switch (
817) to the B side.

At this time, the monostable multivibrator (813) U outputs a single pulse of a certain period according to the fall of the output signal of this switch. And this pulse is 8 F/F
(816) reset terminal ((input, φ(816)
The switch circuit (806
), (807) selects the handset, thereby ending the loudspeaker call. Furthermore, the oscillator (815) sends a loudspeaker end signal, which is a sine wave with a single pulse section frequency f3, to the line, thereby notifying the exchange that the loudspeaker call has ended.

The OR circuit (811) and the switch (815) are circuits for preventing the transmission signal from being mixed in while the control sine wave is being sent out.

Next, FIG. 9 shows an example of the configuration of the loudspeaker detection circuit. In the same figure, a detection circuit (901) is a circuit that detects a sine wave at the frequency [1] at which the loudspeaker call starts, which is sent out from the loudspeaker telephone.
/F (904) is set and control signal LTBL is H4g
h, it is transmitted to the control circuit. The control circuit is
Upon receiving this signal, if the E C unit and time slot) K are empty, the oscillator (90
3) transmits a single sine wave of frequency f3 to enable loudspeaker communication. Conversely, if there is no vacancy in at least one of the EC unit and the time slot, the control signal BUSY
This resets the RSF/FC904). Furthermore, at the end of the loudspeaker call, the detection circuit (902) detects a single sine wave of frequency f2, and the R8F/F (904)
to notify the control circuit of the end of the loudspeaker call state.

The EC unit, which is the main circuit of this embodiment, can be constructed as shown in FIG. The echo path input signal X is loaded into the input buffer (root) with the ilJ control signal XT, and the echo path output signal Y is loaded into the input buffer (100
3).

Since these data are C0DEC output signals, a Δ-linear conversion circuit (
1002) and (1004), and X is added to the data input of the echo canceller (100B). Further, Y is added to the reference signal input of the echo canceller (1008), and is also added to the subtracter (100) in order to subtract the pseudo echo signal generated by the echo canceller.
9), and after the echo signal is removed, it is converted into data of a +7 near μ conversion circuit p-7low, and then loaded into an output buffer (1005). Output buffer (1
005) has a high impedance except for a predetermined time slot due to the control signal BT, and at the sending timing, the cancellation residual signal in the buffer is output.

The double talk detection circuit (1007) detects double talk by detecting the X and Y powers, and prohibits the echo canceller from estimating the echo path.

A second embodiment of the present invention is shown in FIG. 11 and will be described.

This embodiment differs from the first embodiment in that the loudspeaker call is detected using a table.

That is, whether the telephone connected to the exchange is a public address telephone or not is registered in the table (1101) in advance, and when the telephone number detected by the scanning circuit is used at the time of starting line connection, the table is checked and it is determined that the telephone is a public address telephone. , an echo canceller is inserted into the communication path as in the first embodiment. Therefore, with this device, even if a handset call is being made on a loudspeaker telephone, an echo canceller will be inserted.However, since it has the advantage of simplifying the loudspeaker call detection circuit, small-scale replacement Valid in the system.

The above are examples of the present invention.

Although the above embodiment of the present invention has been explained using a one-time division switch, it is effective in all switching systems from crossbar to the latest packet switching.

Furthermore, the network configuration can be either an analog network or a digital network. Particularly in the latter digital network, the structure of the loudspeaker detection unit can be simplified by adding data for detecting whether or not a loudspeaker call is being made to the digital data from the telephone.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a configuration example of a conventional loudspeaker telephone with an echo canceller for removing acoustic coupling, FIG. 2 is a configuration diagram of a conventional switching system having a loudspeaker telephone, and FIG. 3 is a configuration example of a switching system of the present invention. FIG. 4 is a diagram for explaining a call route between a loudspeaker telephone and a general telephone, FIG. 5 is a diagram showing a route between loudspeaker calls, and FIG. 6 is an embodiment of the present invention (exchange)
, FIG. 7 is a diagram for explaining the time division exchange timing in the present invention, FIG. 8 is a diagram for explaining the configuration of a loudspeaker telephone in an embodiment of the present invention, and FIG. 9 is a diagram for explaining the time division switching timing in the present invention. A block diagram of a loudspeaker detection circuit, FIG. 10 is a block diagram of an echo canceller unit in an embodiment of the present invention,
FIG. 11 is a block diagram of another embodiment of the present invention, 501, 502 are echo cancellers, 503, 5
04 is a subtracter, 801 is a microphone, 802 is a speaker, 803, 80
4 is an amplifier, and 819 is a handset. Agent Patent Attorney Noriyuki Chika (and 1 other person) Figure 1 Figure 2 Figure 3 @ Figure 4 Figure 5 Figure 6 Figure 7 (0-) (b) Figure 7 (C)

Claims (1)

[Claims] (1) An echo canceller, which is a switchboard that connects lines between multiple telephones, including loudspeaker telephones, and removes acoustic coupling between the speaker and microphone of the loudspeaker telephone, and a telephone that is connected to the line, performs a loudspeaker call. There is a loudspeaker detection circuit that detects whether there is a loudspeaker or not, and the output of this detection circuit generates an echo on the line when a telephone connected to the line is making a loudspeaker call.
Canceller (2) A switchboard that connects lines between multiple telephones, including loudspeaker telephones, and other exchanges, and includes an echo canceller that removes acoustic coupling between the speaker and microphone of the loudspeaker telephone, and a switch that is prepared in advance. A loudspeaker determination circuit that determines whether or not a telephone connected to the line is a public address telephone according to the contents of a table; Ni engineering