Abstract:
A multiplexing device allowing audio conferencing via a network with simplified circuit structure is disclosed. After combining received signals from all the participants to produce a combined signal, a signal of each of the participants is subtracted from the combined signal to produce a conference signal for a corresponding participant.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to multiplexing techniques for teleconferencing, and in particular to multiplexing method and device suitable for an audio conference system via a communication network.  
           [0003]    2. Description of the Related Art  
           [0004]    In audio teleconferencing, a voice multiplexing function is needed to transmit a speech from any participant to all the other participants and receive a speech from any of the other participants. In general, the audio conferencing has been provided by a conference function in a PBX (private branch exchange) or by the telephone companies.  
           [0005]    Recently, there have been proposes several digital cordless telephone systems allowing audio conferencing among three or more handset telephone terminals as well as a party on the other end of telephone line.  
           [0006]    For example, Japanese Patent Application Unexamined Publication No. 6-326779 discloses such a digital cordless telephone system composed of a base station connected to a telephone line and a plurality of handset telephone terminals connected to the base station by radio TDMA-TDD channels. The base station is provided with a plurality of memories each corresponding to receive time slots for the handset telephone terminals. Similarly, each of the handset telephone terminals is also provided with a plurality of memories each corresponding to receive time slots for the other handset telephone terminals and the base station. In such a system configuration, the voice multiplexing for telephone line transmission is performed by the base station storing voice data received from each of the handset telephone terminals into a corresponding memory and then adding all the stored voice data to transmit the added data to the party on the other end of the telephone line.  
           [0007]    However, this conventional voice multiplexing technique needs memories as many as the number of receive time slots and further needs a pair of switching circuit and adding circuit for storing received voice data to one of the memories and adding the stored data to produce transmission data. Accordingly, when the number of terminals increases, the amount of hardware in the base station and the terminals is also increased.  
           [0008]    Further, since the memories and a pair of switching circuit and adding circuit are needed for each terminal, the voice multiplexing becomes very complicated and costly in the whole system.  
         SUMMARY OF THE INVENTION  
         [0009]    An object of the present invention is to provide multiplexing method and device allowing audio conferencing via a network with simplified circuit structure.  
           [0010]    According to the present invention, a device for producing a conference signal to be transmitted to each of participants of a conference, includes: a signal combiner for combining received signals from all the participants Lo produce a combined signal; and a signal subtracter for subtracting a signal of each of the participants from the combined signal to produce a conference signal for a corresponding participant.  
           [0011]    The participants may be geographically dispersed, and the device may further includes a communication controller for establishing a connection to each of the participants to receive the signals from the participants and transmit the conference signal to the corresponding participant.  
           [0012]    At least one of the participants may be connected through a communications network.  
           [0013]    According to another aspect of the present invention, a voice multiplexer for producing a multiplexed voice signal for an audio communications session, includes: a first interface to a plurality of terminals; a second interface to a communications network; a communication controller controlling the first and second interfaces to establish a connection to each of the terminals and a connection to at least one party through the communications network; a signal combiner for combining a terminal voice signal received from the terminals through the first interface and a party voice signal received from at least one party through the second interface to produce a combined voice signal; a first signal subtracter for subtracting the terminal voice signal from the combined voice signal to produce a first multiplexed voice signal for a corresponding terminal; and a second signal subtracter for subtracting the party voice signal from the combined voice signal to produce a second multiplexed voice signal for a corresponding party.  
           [0014]    The multiplexer may further include: a calling signal discriminator for discriminating a calling signal from terminal and party voice signals, wherein, when a calling signal is received from one of a terminal and a party that do not participate in the audio communications session yet, the communication controller establishes a connection to the one so as to participate in the audio communications session.  
           [0015]    The multiplexer may further include: a destination address memory for registering a calling address of each of the terminals and the at least one party, wherein the communication controller uses the destination address memory to establish a connection to each of the terminals and a connection to at least one party through the communications network.  
           [0016]    As described above, after combining received signals from all the participants to produce a combined signal, a signal of each of the participants is subtracted from the combined signal to produce a conference signal for a corresponding participant. Accordingly, the signal multiplexing for audio conferencing can be performed with simplified structure. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a schematic diagram showing the general configuration of an audio conference system according to the present invention;  
         [0018]    [0018]FIG. 2 is a block diagram showing an internal circuit of a voice multiplexer of FIG. 1;  
         [0019]    [0019]FIG. 3 is a block diagram showing a circuit of a multiplexing device according to an embodiment of the present invention;  
         [0020]    [0020]FIG. 4 is a diagram showing a sequence of audio teleconferencing in the embodiment; and  
         [0021]    [0021]FIG. 5 is a block diagram showing a generalized circuit of a multiplexing device according to the embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    As shown in FIG. 1, it is assumed for simplicity that a voice multiplexer  101  accommodates three conference participant terminals PS 1 -PS 3  and a party  103  on the other end of an established line through a mobile communications network  102 .  
         [0023]    Here, the conference participant terminals PS 1 -PS 3  are connected to the voice multiplexer  101  by radio according to a predetermined wireless connection scheme such as PHS (Personal Handy-phone System) or Bluetooth™, The mobile communications network  102  may employ any mobile communications scheme such as GSM (Global System for Mobile communications), PDC (Personal Digital cellular), or IMT- 2000  (International Mobile Telecommunications  2000 ).  
         [0024]    Referring to FIG. 2, the voice multiplexer  101  includes an interface  201  to the mobile communications network  102 , a multiplexing device  202 , and an interface  203  to the conference participant terminals PS 1 -PS 3 .  
         [0025]    The voice multiplexer  101  further includes a communication controller (not shown), which controls the interface  201  to establish a connection to the other party  103  through the mobile communications network  102  and controls the interface  203  to establish connections to respective ones of the conference participant terminals PS 1 -PS 3 .  
         [0026]    The interface  201 , when receiving data from the other end party  103  through the mobile communications network  102 , transfers the received voice signal S B  to the multiplexing device  202 . When receiving a multiplexed transmission signal S T  from the multiplexing device  202 , the interface  201  sends it to the other end party  103  through the mobile communications network  102 .  
         [0027]    The interface  203 , when receiving transmission data from the conference participant terminals PS 1 -PS 3 , transfers it to the multiplexing device  202 . When receiving voice data for respective ones of the conference participant terminals PS 1 -PS 3  from the multiplexing device  202 , the interface  203  sends them to respective ones of the conference participant terminals PS 1 -PS 3 .  
         [0028]    As described in detail hereafter, the multiplexing device  202  performs multiplexing of voice data for audio conferencing.  
       Multiplexing  
       [0029]    As shown in FIG. 3, the multiplexing device  202  includes a signal combiner  301  and voice subtracters  302 - 305 .  
         [0030]    The signal combiner  301  inputs voice signals PS T1 , PS T2 , and PS T3  from respective ones of the conference participant terminals PS 1 -PS 3  and a received voice signal S R  from the interface  201 . The signal combiner  301  combines them to produce a combined signal, which may be represented by (S R +PS T1 +PS T2 +PS T3 ).  
         [0031]    The voice subtracter  302  inputs the combined signal (S n +PS T1 +PS T2 +PS T3 ) and the received voice signal S R . The subtracter  302  subtracts the received voice signal S R  from the combined signal (S R +PS T1 +PS T2 +PS T3 ) to produce a multiplexed transmission signal (conference signal) S T , which is represented by (PS T1 +PS T2 +PS T3 ) . The multiplexed transmission signal S T =PS T1 +PS T2 +PS T3  is transmitted to the other party  103  through the mobile communications network  102 . In other words, the voice signals PS T1 , PS T2 , and PS T3  of the conference participant terminals PS 1 -PS 3  are multiplexed to be transmitted to the other party  103  through the established line.  
         [0032]    The combined signal (S R +PS T1 +PS T2 +PS T3 ) is also output to the voice subtracters  303 - 305 . The voice subtracters  303 - 305  are provided corresponding to respective ones of the conference participant terminals PS 1 -PS 3  and input the voice signals PS T1 , PS T2 , and PS T3  from corresponding ones of the conference participant terminals PS 1 -PS 3 , respectively.  
         [0033]    The voice subtracter  303  inputs the combined signal (S R +PS T1 +PS T2 +PS T3 ) and the voice signal PS T1 . The subtracter  303  subtracts the voice signals PS, from the combined signal (S R +PS T1 +PS T2 +PS T3 ) to output a multiplexed voice signal (conference signal) PS R1 , which may be represented by (S R +FS T2  +PS T1 ), to the conference participant terminals PS 1 . Accordingly, the conference participant terminal PS 1  receives voices from all the other participants.  
         [0034]    Similarly, the voice subtracter  304  inputs the combined signal (S R +PS T1 +PS T2 +PS T3 ) and the voice signal PS T2 . The subtracter  304  subtracts the voice signals PS T2  from the combined signal (S R +PS T1 +PS T2 +PS T3 ) to output a multiplexed voice signal (conference signal) PS R2 , which may be represented by (S R +PS T1 +PS T3 ), to the conference participant terminal PS 2 . The voice subtracter  305  inputs the combined signal (S R +PS T1 +PS T2 +PS T3 ) and the voice signal PS T3 . The subtracter  305  subtracts the voice signals PS T3  from the combined signal (S R +PS T1 +PS T2 +PS T3 ) to output a multiplexed voice signal (conference signal) PS R3 , which may be represented by (S R +PS T1 +PS T2 ), to the conference participant terminal PS 3 .  
         [0035]    In this manner, the multiplexing device  202  produces voice multiplexed signals (conference signals) allowing audio conferencing among the conference participant terminals PS 1 -PS 3  as well as the party  103  on the other end of the line. Only the signal combiner  301  and the voice subtracters  302 - 305  are needed to produce the voice multiplexed signals. Therefore, even if the number of conference participant terminals is increased, the multiplexing device  202  can be easily formed by only increasing the number of input terminals of the signal combiner and the number of subtracters. In other words, the multiplexing device  202  can be easily applied to the case of N (N is an integer greater than  3 ) conference participant terminals.  
         [0036]    It should be noted that the multiplexing device  202  composed of the signal combiner  301  and voice subtracters  302 - 305  may be inplemented by a program-controlled processor or a dedicated hardware circuit. In the case of the program-controlled processor, a program having the signal combining and subtracting functions as described above is executed on the processor.  
       Operation sequence  
       [0037]    Referring to FIG. 4, when receiving calls to the other party  103  originated by the conference participant terminals PS 1 -PS 3 , the voice multiplexer  101  originates a single call to the other party  103  through the mobile communications network  102 . When the other party  103  sends an acknowledge back to the voice multiplexer  101 , the voice multiplexer lot sends acknowledges to the conference participant terminals PS 1 -PS 3  and thereby a communication line between the conference participant terminals PS 1 -PS 3  and the other party  103  is established through the mobile communications network  102 . Similarly, when the other party  103  originates a call, the same communication line can be established.  
         [0038]    Thereafter, the multiplexing device  202  performs the multiplexing of voice signals for audio conferencing as described above.  
         [0039]    As described before, the present invention is not restricted to the case of three conference participant terminals. It is apparent that the present invention can be easily applied to the case of N (N is an integer greater than  3 ) conference participant terminals.  
         [0040]    More specifically, as shown in FIG. 5, the multiplexing device  202  includes a signal combiner  401 , a voice subtracter  402  in the network side, and voice subtracters  403 . 1  to  403 .N in terminal side. Since the basic operation of this embodiment is the same as that of the first embodiment of FIG. 3, the details are omitted.  
         [0041]    Preferably, a destination address memory like a phonebook may be provided in the above embodiments, allowing easy calling operation to the increased number of terminals and other parties.  
         [0042]    Furthermore, a calling signal discriminator may be provided to discriminate a calling signal from voice signals during conference in the above embodiments. In this case, by calling another terminal or party during conference, that terminal or party can easily participate in the conference.