Hand-free telephone set

0001A hands-free telephone unit allows the user to conversing with a remote party without holding the handset phone in hand.

0002A handsfree set includes a microphone and a speaker incorporated in its case, of greater sensitivity than those of the handset. Thus, the user can use his post-hook, being in distant.

0003This increase in the scope for the job transmit path is located on the microphone and the receive path leading the speaker, however, induced technical problems because the signal Voice is restored from the corresponding high level speaker and undergoes reflection on the walls of the room where the position as well as location The housing of the post, before being partially captured back by the microphone. The captured spurious signal is returned in line, superposition with the voice signal of the local user, and is, for corresponding echo.

0004Moreover, as the telephone line transmits the signals in both directions, the station includes a duplexer circuit, line interface, connecting the line to the transmission channel and the position of the reception path. The duplexer allows injection line signals to transmit and receive the signals from the corresponding, but not receive signals injected locally to avoid a clash sound or howling. In Indeed, on the receive path, the duplexer can not avoid taking a signal composite representing all of the received and transmitted signals, but after sampling on the reception path, it subtracts the signal emitted by the microphone so not apply to the speaker that the signal received from corresponding. This subtraction or balancing, canceling the return of transmitted signals, however, is never perfect since the intended balance depends the line impedance, which may vary from one line to the other and over time. Of this fact, and in practice, part of the transmitted signal from the microphone is reflected at the level of the duplexer toward the speaker.

0005In short, the transmission and reception paths are Job a sound loop, comprising, on the one hand, the acoustic reflection of the local and, on the other side, the electrical reflection of the duplexer. However, in the case of post speakerphone, microphone sensitivity and speaker is such that the signal traversing the loop is amplified to saturation and circuits production of feedback.

0006To avoid feedback and echo effect mentioned above, it is known to operate the post-duplex, that is to say only emission or reception, cutting the Larsen hanging loop echo. Continuous measurement of the microphone signal and the received line to determine which of the two interlocutors who produced the strong vocal energy and activate accordingly in the station, the transmission or reception path.

0007Such a solution, however, has drawbacks as a talkative interlocutor and strong voice can long monologue without power be interrupted by another. In addition, if it is hands-free two positions are connected, they operate in alternating is not synchronized, so they may be in phase, that is to say both in transmission, without any reception, or reception, with zero emissions. This leads to a chopped conversation.

0008It can be expected to make anti-echo filtering, acoustic and electrical, by means of adaptive filters, that is to say amending gradually their filter settings by determining a model local or line for converging the energy of the echo to a minimum. Acoustic feedback may also be removed by a filter performing a shift frequency, in case of detection of acoustic coupling on one frequency, and thus reducing the loop gain for the latter.

0009However, the filter convergence time are relatively high and fail to adapt to rapid changes the environment, such as movement of a person or opening a door modifying local echoes.

0010The present invention aims to overcome the disadvantages mentioned above, to enable full-duplex operation.

0011To this end, the invention relates to a telephone hands-free, arranged to be connected to a telephone line carrying signals phonic and comprising a transmission channel and a reception channel, each channel comprising attenuation means and the adaptive filtering means of echoes of the other channel, station characterized in that it comprises means measuring an adaptation defect in the filtering means, the means measure being designed to enable the attenuation means at least a tract when the defect exceeds a predetermined threshold.

0012Thus, upon the occurrence of a defect exceeding a threshold, the activation Mitigation means passing the full-duplex operation, without mitigation, operation in alternating or gradient full-duplex, with mitigation. This stifles the effects of mismatch and thus allows filtering means for rehabilitation in good conditions, thus eliminating the defect and allow measuring means then restore the full-duplex operation when the new environment has been fully apprehended.

0013The invention will be better understood using the following description a preferred embodiment of the handsfree set of the invention, in reference to the appended drawing, in which:<ul><li>Figure 1 is a functional block Position of the invention, and</li><li>Figure 2 is a flowchart illustrating the sequencing of sound adjustment of the position.</li></ul>

0014The hands-free station shown includes a transmission channel 1 and a reception path 2 connected to a telephone line 10, and a unit Central 3 commander tracks 1 and 2. In general, the line telephone with sound signals is any connection to the transmission of a conversation, such as a radio link or a data transmission network.

0015Transmitting path 1 comprises, in the direction of transmission of sound signals, a microphone 11 hands-free, converter analog / digital converter (ADC) 12 connected to first inputs of a adder-subtracter 13 itself associated with an acoustic echo cancellation filter 14 mounted in loop between its output and its second inputs, a filter 15 anti-Larsen, a controlled attenuator 16 and a converter digital / analog (DAC) 17 connected to the output line 10 through a circuit Hybrid 20 passage 2 son (line 10) / 4 son (2 emission son, 2 son receipt).

0016The reception path 2 includes, from the circuit 20, an ADC 22 connected to first inputs of an adder-subtracter 23 itself conjunction with an anti-echo filter 24 mounted in line loop between its output and its second inputs, a controlled attenuator 26 and a DAC 27 Commanding a loudspeaker 28 of hands-free.

0017The filter 14 also receives the signal from the attenuator 26, while filter 24 receives one of the attenuator 16.

0018The CPU 30 includes a measurement circuit 31 energy injected signals on channels 1 and 2, connected by the output of the adders-subtracters 13 and 23. A circuit 32 for measuring mismatches, comprising a microprocessor, receives the measurement results above and as fault signals or mismatch, from the filters 14 and 24.

0019The control circuit 32, all represented by non-bond, circuits 13 to 16 and from 23 to 26 as explained later. It also ensures, of Conventionally, synchronization of ADC and DAC 12, 22 and 17, 27 per other circuits above 13-16 and 23-24, 26, all of which are digital.

0020While an analog processing of signals of the two channels is not be excluded, thus unnecessarily ADC and DAC, this is where one signal processing processor which digitally performs the functions circuits 13-16 and 23-24, 26, the ADC and DAC 12, 22 and 17, 27 can also be integrated into the processor. It could also have been a planned line digital.

0021The operation of the station will be explained next the chart of Figure 2.

0022Under the control of the measuring circuit 32, the tracks 1 and 2 pass by various states based on information from the monitored circuits by the circuit 32.

0023When establishing a telephone communication, a step 41, the circuit 32 initializes, that is to say set to zero, the coefficients of filter used in the filter 14 to model the local acoustically in which is the position shown. The control circuit 32 as the insertion an attenuation, here on the two channels 1 and 2 by means of the attenuators 16 and 26. The attenuation in at least one location of the loop constituted phonic by tracks 1 and 2, the circuit 20 and the walls of the room and prevents Larsen coupling. In addition, the attenuation of the transmission channel 1 avoids return of excessive acoustic echo to the line 10.

0024In step 42, the circuit 32 controls the filter 14 to freeze indices, that is to say freeze the acoustic model of the local after a certain period of adjustment, or, when detecting absence of mismatch, as explained below. It also controls the initialization or reset the coefficients of the line filter 24 and the activation of the adjustment thereof to model the line 10 and the hybrid circuit 20.

0025We then go to step 43 in which the circuit 32 monitors a mismatch of the line filter 24.

0026anti-echo filter is recalled that temporarily stores the signal generating echo and then subtract it to the other channel signal affected by this echo. The adaptation is to delay and weighting so appropriate, each frequency component of the signal generating the echo subtract the echo signal. If imperfect adaptation of the coefficients determinant of filter adjustment, the filter detects that there remains a residue of filtering, or remaining echo having a correlation with the signal generating echo and it develops its coefficients to try to cancel this echo by converging its model to the real model of the room. the residue filter represents a mismatch, which is transmitted to the circuit 32.

0027For details on the filters 14, 15, 24, reference is made to US-A-5099472, WO 89/05068, JP 5-14476 and JP 5-48707, cited here by reference.

0028The circuit 32 monitors here at a step 43, the amplitude of default above from the line 24 to filter, if it exceeds a predetermined threshold, back to step 42 and thus reset the line filter 24 to avoid possible divergence, delaying or even preventing an adaptation, or convergence, later. Similarly, a slow convergence is detected, that is to say, we also returns to step 42 if a predetermined threshold time non-adaptation is exceeded. A mismatch corresponds to exceeding an amplitude threshold of the mismatch signal or exceeding a threshold duration during which the fault signal adaptation exceeds a predetermined value.

0029At all stages, the circuit 31 ensures the detection of an effect Larsen and the circuit 32 then controls the filter 15 which then shifts slightly the signal frequency spectrum and reduces crossing and immediately the loop gain for Larsen coupling frequency.

0030Without returning to step 42, the circuit 31 detects, at a step 44, if the energy is present on a single channel, 1 or 2, and inform the circuit 32, which disables the attenuator 16 or 26 of the other channel, 2 or 1. In If the presence of power on the two channels 1 and 2, the circuit 32 disables the attenuator 16 or 26 of the channels 1 and 2 which carries the signal of more low energy.

0031At step 45, the adaptation is continued the line model in the filter 24 when the circuit 31 detects a transmission channel energy signal 1. further continues comparing the energies of the two channels 1 and 2 for the circuit 32 switches the attenuation of the channels carrying the signal more low energy. It thus operates as a pseudo-duplex, maintaining low level transmission on the way "off."

0032In a following step 46, the line model adaptation in the filter 24 has continued, to achieve a satisfactory level of cancellation Echo Online. If the receive channel 2 receives a voice signal from a remote party and the local echo is predominant in the way Issue 1 on the user's signal station, the control circuit 32 adapting the model of the space in the filter 14.

0033In a following step 47, step 43 counterpart, if one detects filter convergence time 14 or the amplitude of the fault signal adaptation exceeds a predetermined threshold and then returns to step 46 after resetting the filter coefficients 14.

0034In the absence of mismatch on each channel transmitting and receiving 1 and 2, it goes to a step 48 in which the circuit 32 disables the attenuator circuits 16, 26 that was active and well established a state of true full-duplex without mitigation.

0035It will be understood that by "without mitigation" means substantially conforms to the transmission amplitude template provided for transmission of sound signals through the telephone network, to provide or restore a sound signal of sufficient amplitude but without risking saturation circuits of the telephone network or the transceiver channels of the post. To set the channels as above as a template, it may be necessary to continuously provide therein a mitigation, which does not concern the variable attenuation of this invention.

0036In step 48, the adaptation is continued models of filters 14 and 24. In case of occurrence of a mismatch of the model (14) of local exceeding a low threshold, here below the threshold (high) in step 47, the circuit 32 applies (step 49) limited attenuation (16) on the path Issue 1. In other words, and in general, the circuit 32 activates attenuator 16 when the defect exceeds the low threshold and a control increase the attenuation when the upper threshold is exceeded. We return to Step 48 when the low threshold of step 49 is crossed descent.

0037If exceeded the fault predetermined high threshold adaptation of the filter 14, it returns to step 46, that is to say, the circuit 32 active one attenuators 16, 26, by the attenuator 16 of the transmission channel 1, to return to the intermediate operation between full-duplex and half-duplex. We go here by step 47 to reset the filter coefficients 14.

0038It could be provided to enable the two attenuators 16, 26, as in step 41.

0039In other words, in steps 41 to 48, the circuit 32 disables Here, in case of defect exceeding the threshold, the filters 14, 24 of the two channels 1 and 2 successively one after the other until there is no defect exceeding the threshold. This sets more accurately each filter 14, 24, in avoiding evolution of the other filter 24, 14. In particular, the filter 14 of the track Issue 1 is disabled (step 42) before the filter 24 of the receiving channel 2.