Abstract:
This invention provides a conferencing arrangement for use with two or more wireless terminals. According to the invention, the conferencing arrangement receives signals from a plurality of input communication paths of which at least two are from wireless terminals. In one embodiment of the invention, the wireless terminals will receive either a low bit rate (LBR) signal which has undergone conversion from a pulse code modulated (PCM) signal, or an LBR signal forwarded from an input terminal without any conversion. Advantageously, the ability to forward an original LBR signal from a wireless terminal to one or more output terminals reduces unnecessary tandem encoding. In another embodiment, only LBR signals required for conference summing are decoded and encoded, thereby resulting in hardware savings.

Description:
FIELD OF THE INVENTION 
     This invention relates to a technique for conferencing arrangements and, in particular, to a technique for a conferencing arrangement for use with two or more wireless terminals. 
     BACKGROUND OF THE INVENTION 
     Conferencing is the ability to couple information signals among three or more users in a communication system. The conferencing arrangement may involve voice or non-voice signals, including data, video, and facsimile signals. 
     In the case of audio teleconferencing, there may be one or more wireless users involved in the communication. Typically, in digital wireless systems speech is transmitted over the air interface as packets or frames. Accordingly, the incoming speech at a subscriber terminal is collected, organized into frames and low bit rate encoded. The speech is then transcoded to pulse code modulated speech (PCM) before entering the mobile switching center (MSC). Then generally, in the case where a voice conferencing bridge is involved, the signal power of the conferees is measured, compared, and each conferee receives a weighted sum of perhaps the two loudest talkers other than him/herself. For conference calls involving two or more wireless participants, the signals received by the wireless terminals will be transcoded to linear PCM, a weighted sum will be taken and then reencoding will take place, even when only a single participant in the conference is speaking. Such a tandem-encoded signal will demonstrate degraded quality of voice. 
     There was an attempt made in the prior art by D. Nahumi in U.S. Pat. No. 5,390,177 to improve the voice quality in a conference bridge. In the Nahumi patent, the conferencing bridging technique is for use with compressed information signals only. The technique involves first measuring the signal energy transmitted by each conferee. When there is only one conferee speaking, the summing circuit and the speech decoding/coding apparatus is bypassed, and the talking conferee&#39;s signal is broadcast to all conferees. When there is more than one conferee speaking at a given time, then only the speaking conferees&#39; signals are routed to an associated speech decoder wherein those conferees&#39; compressed signals are decompressed. The summing circuit then combines these decompressed signals and the sum is recompressed and broadcast to all conferees. The invention disclosed in the Nahumi patent does not have the capability to provide more than one output signal, as the conference bridge has only a single speech encoder in the output direction. Thus, the same compressed signal is broadcast to all users. 
     There exists therefore a need for a telephone conferencing arrangement in the situation where there are two or more wireless users, and there may or may not be PSTN users whose signals may or may not be compressed, which would provide clearer communication than that associated with prior conferencing arrangements and in which there is the capability to provide more than one output signal. There is a need for a system in which the conference bridge would result in superior signal addition and performance. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved telephone conferencing arrangement for use with two or more wireless terminals, and any or no PSTN terminals. 
     In accordance with an aspect of the present invention, there is provided a conferencing apparatus comprising means for receiving signals at a conference bridge from a plurality of input communication paths of which at least two are associated with low bit rate voice signals, means for estimating the signal energy in each of said input communication paths to give a signal energy estimation, means for comparing each of said signal energy estimations against a predetermined threshold, and means responsive to said signal energy estimating and comparing means for forwarding the low bit rate voice signal from one of said input communication paths to a second output communication path also associated with an incoming low bit rate voice signal, when said signal energy estimation provides a first result. 
     In accordance with another aspect of the present invention, there is provided a conferencing apparatus comprising means for receiving signals at a conference bridge from a plurality of input communication paths of which at least two are associated with low bit rate voice signals, means for estimating the signal energy in each of said input communication paths to give a signal energy estimation, means for comparing each of said signal energy estimations against a predetermined threshold, and means responsive to said signal energy estimating and comparing means for forwarding the low bit rate voice signal from one of said input communication paths to one or more output communication paths, each associated with an incoming low bit rate voice signal, if the signal energy estimation of only said one of said input communication paths is above said predetermined threshold. 
     In accordance with a further aspect of the present invention, there is provided a conferencing apparatus comprising means for receiving signals at a conference bridge from a plurality of input communication paths of which at least two are associated with low bit rate voice signals, means for estimating the signal energy in each of said input communication paths to give a signal energy estimation, means for comparing each of said signal energy estimations against a predetermined threshold, and means responsive to said signal energy estimating and comparing means for forwarding a first low bit rate voce signal and a second low bit rate voice signal from each of two input communication paths to output communication paths associated with said two input communication paths, wherein said first low bit rate voice signal is forwarded to the output communication path associated with the second low bit rate voice signal and vice versa, when said signal energy estimating and comparing means provides a second result. 
     In a still further aspect of the invention, there is provided a conferencing apparatus comprising means for receiving signals at a conference bridge from a plurality of input communication paths of which at least two are associated with low bit rate voice signals, means for estimating the signal energy in each of said input communication paths to give a signal energy estimation, means for comparing each of said signal energy estimations against a predetermined threshold, and means responsive to said signal energy estimating and comparing means for decoding only each of said low bit rate voice signals that is required by said conferencing apparatus. 
     In a yet further aspect of the invention, there is provided a method of providing a conference communication comprising the steps of receiving signals at a conference bridge from a plurality of input communication paths of which at least two are associated with low bit rate voice signals, estimating the signal energy in each of said input communication paths to obtain a signal energy estimation, comparing each of said signal energy estimations against a predetermined threshold to obtain a signal energy comparison, and in response to said signal energy estimations and comparisons, forwarding the low bit rate voice signal from one of said input communication paths to a second output communication path also associated with an incoming low bit rate voice signal, when said signal energy estimation provides a first result. 
     In another aspect of the invention, there is provided a method of providing a conference communication comprising the steps of receiving signals at a conference bridge from a plurality of input communication paths of which at least two are associated with low bit rate voice signals, estimating the signal energy in each of said input communication paths to obtain a signal energy estimation, comparing each of said signal energy estimations against a predetermined threshold to obtain a signal energy comparison, and in response to said signal energy estimations and comparisons, forwarding the low bit rate voice signal from one of said input communication paths to one or more output communication paths, each associated with an incoming low bit rate voice signal, if the signal energy estimation of only said one of said input communication paths is above said predetermined threshold. 
     In a still further aspect of the invention, there is provided a method of providing a conference communication comprising the steps of receiving signals at a conference bridge from a plurality of input communication paths of which at least two are associated with low bit rate voice signals, estimating the signal energy in each of said input communication paths to obtain a signal energy estimation, comparing each of said signal energy estimations against a predetermined threshold to obtain a signal energy comparison, and in response to said signal energy estimations and comparisons, forwarding a first low bit rate voce signal and a second low bit rate voice signal from each of two input communication paths to output communication paths associated with said two input communication paths, wherein said first low bit rate voice signal is forwarded to the output communication path associated with the second low bit rate voice signal and vice versa, when said signal energy estimation and comparison provides a second result. 
     In a yet further aspect of the invention, there is provided a method of providing a conference communication comprising the steps of receiving signals at a conference bridge from a plurality of input communication paths of which at least two are associated with low bit rate voice signals, estimating the signal energy in each of said input communication paths to obtain a signal energy estimation, comparing each of said signal energy estimations against a predetermined threshold to obtain a signal energy comparison, and in response to said signal energy estimations and comparisons, decoding only each of said low bit rate voice signals that is required for said conference communication. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an illustrative block diagram of the steps involved in a conventional conference call involving two mobile users; 
     FIG. 2 is an illustrative block diagram of the steps involved in an improved conference call involving two mobile users according to a first embodiment of the present invention; 
     FIG. 3 is a block diagram providing an overview of the mobile switching center in FIG. 2; 
     FIG. 4 is a block diagram providing an overview of the conference server in FIG. 3; 
     FIG. 5 is an illustrative block diagram of the steps involved in a conference call according to a second embodiment of the present invention; and 
     FIG. 6 is a block diagram providing a detailed overview of a conference unit according to the second embodiment. 
    
    
     Similar references are used in different figures to denote similar components. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In order to lighten the following description, the following acronyms will be used: 
     DEMUX: Demultiplexer 
     LBR: Low Bit Rate 
     MSC: Mobile Switching Center 
     MUX: Multiplexer 
     PCM: Pulse Code Modulation 
     PSTN: Public Switching Telephone Network 
     RF: Radio Frequency. 
     Typically in wireless systems, speech is transmitted over the air interface as packets or frames. The incoming speech at a subscriber terminal is collected, organized into frames and LBR encoded. The speech is transcoded into PCM before entering the MSC. 
     Referring to FIG. 1, there is illustrated the signal flow for a conventional three party conference call. In this example, two of the participants are using mobile or portable terminals  2 ,  4  and the third participant is using a PSTN terminal  6 . The mobile users communicate via RF channels  8 ,  10  to base stations, each of which is comprised of a base station transceiver  12 ,  14  and a base station controller  16 ,  18 . The signals  20 ,  22  represent LBR encoded speech and the signals  24 ,  26  represent companded PCM, the result of signals  20 ,  22  having passed through the respective transcoders  28 ,  30 . Companded PCM signals  24 ,  26  are then forwarded to the respective MSCs  32 ,  34 . The speech from the PSTN terminal  6  enters the MSC  32  as PCM signal  27 . 
     Then, typically in a voice conferencing bridge the signal power from the participants is measured and compared and each participant receives a weighted sum of the  2  loudest talkers other than him/herself. For conference calls involving two or more wireless participants, as is the case described in FIG. 1, the signals received by the wireless terminals are tandem encoded. This means that for the signals that were transcoded to linear PCM as outlined above, a weighted sum is taken, and then there will be reencoding. This tandem encoding will occur even when there is only a single participant in the conference call who is speaking. Unfortunately, tandem encoding results in degradation in the quality of the voice. 
     Referring now to FIG. 2, there is shown an improved conference arrangement. As was the case in the scenario illustrated in FIG. 1, two of the participants are using mobile or portable terminals  102 ,  104  and the third participant is using a PSTN terminal  106 . The mobile users communicate via RF channels  108 ,  110  to base stations, each of which is comprised of a base station transceiver  112 ,  114  and a base station controller  116 ,  118 . The transcoders  128 ,  130  within base station controllers  116 ,  118  convert the LBR speech  120 ,  122  to PCM, as was the case in the description of the prior art above. In this case, however, in contrast to the prior art, the PCM and the LBR speech frames are both delivered to the respective MSC  132 ,  134  in the form of a composite signal  124 ,  126 . The speech from the PSTN terminal  106  enters the MSC  132  as PCM signal  127 . 
     FIG. 3 shows a more detailed view of the signals received by the base station transceivers  212 ,  214  as they are transferred to the MSCs  232 ,  234 . Each of the base station transceivers  212 ,  214  forwards the LBR signal  220 ,  222  to the base station controller  216 ,  218 , including the respective transcoder  228 ,  230 . As was discussed with respect to FIG. 2, the transcoders  228 ,  230  convert the LBR speech to PCM, and then send a composite multiplexed signal  224 ,  226  to the MSCs  232 ,  234 . In this case, MSC  234  is simply serving as a pipeline through which signal  226  must pass before reaching MSC  232  in which the conference server  236  is located. The PCM and the LBR speech which comprise composite signals  224 ,  226 , are received via the base station controller interface or mobile switching center interface  238 ,  240  at MSC  232 . Each composite signal  224 ,  226 , along with the PCM signal  227  from the PSTN, is then routed to conference server  236 , more clearly described below with reference to FIG.  4 . 
     The internal switching arrangement of a MSC could be based on circuit switching, packet switching or hybrid arrangements, and a composite signal can be transported in a number of different formats depending on the internal switching arrangement of the MSC. Some examples of internal switching arrangements include Time Division Multiplexing (TDM), Frame Relay and Asynchronous Transfer Mode (ATM). 
     FIG. 4 provides a more detailed representation of the conference server. Again FIG. 4 is directed to the scenario involving a three port bridge, but is extendable to where there are greater than three ports. The conference server is generally comprised of a PCM conference bridge circuit  342  and a selector circuit  344 , as well as a plurality of DEMUXs  345 ,  347 ,  349  and MUXs  370 ,  372 ,  374 . Each input to the conference server, originating from conference participants  302 ,  304 ,  306 , first passes through a DEMUX  345 ,  347 ,  349  in order to separate the incoming signal into PCM speech frames and LBR speech frames. Then, the PCM speech frames  346 ,  348 ,  350  are routed to PCM conference bridge circuit  342  and the LBR speech frames  352 ,  354  are routed to selector circuit  344 . There are no LBR speech frames from the PSTN terminal  306  as is indicated by the broken connection from DEMUX  349  to selector circuit  344 . 
     In selector circuit  344 , LBR speech frames  352 ,  354  are aligned in time. Timing information  356  is sent to PCM conference bridge circuit  342 , which circuit can be of a conventional design with decisions on the output signals  358 ,  360 ,  362  synchronized with the speech frame boundaries. 
     In PCM conference bridge circuit  342 , a control signal  364  is generated and sent to selector circuit  344 . It is this control signal  364  which contains information about the identity of the dominant speaker(s), if any, whose LBR signal(s), if available, should be forwarded to the output MUX connected to the appropriate mobile terminal(s) with a control signal indicating that the LBR signal is valid and is to be forwarded to the terminal. The LBR signal and the control signal together forwarded by selector circuit  344  are indicated by reference  366 ,  368 . Specific scenarios illustrating when an LBR signal is the valid signal will be detailed below. The PCM conference bridge circuit  342  also outputs the appropriate PCM signal  358 ,  360 ,  362  to each output MUX  370 ,  372 ,  374 . Again, exactly what the appropriate PCM signal is will be illustrated in the examples detailed below. 
     Each of the output MUXs  370 ,  372  multiplexes the PCM and the LBR speech- frames that it receives and forwards these signals together with an indication of which signal is valid on output  380 ,  382 . This output  380 ,  382  is forwarded to the transcoder of the base station controller of the appropriate mobile terminal  302 ,  304 . The transcoder encodes the PCM. If the LBR signal is valid, the LBR signal is forwarded to the mobile terminal, whereas if the PCM signal is valid, then the output of the transcoder is sent to the mobile terminal. Output MUX  374 , however, receives only PCM signal  362 , which it forwards as output  384  to the PSTN user  306 . 
     With respect to the above description, it should be noted that for bandwidth savings, it is not necessary to send both the PCM and the LBR signals on the output paths  380 ,  382 . Only the valid signal could be forwarded at that point. 
     The following scenarios further illustrate the above details. 
     In the situation where there is only a single dominant mobile speaker  302 , transcoding of the speech to PCM is not required for the recipient mobile participant  304 . Control signal  364  will contain the information on the identity of the dominant speaker, namely mobile terminal  302 . In response, selector circuit  344  will send signal  368 , which includes the LBR speech frames  352 , from mobile terminal  302 , as well as a control indicating that the LBR signal is valid and is to be forwarded to mobile terminal  304 . 
     In the situation where there is only a single PSTN speaker  306 , since the speech is not LBR based, the issue of forwarding an LBR signal does not arise. 
     Turning to the scenario where there is more than one speaker at a particular time, if one of the speakers is from PSTN terminal  306 , then transcoding of a mobile participant&#39;s speech to linear PCM, taking a weighted sum and reencoding is required. This represents a tandem coding with its attendant degradation. This will, however, be partially masked by the mixing of the voices of more than one speaker. 
     Now if there are two simultaneous speakers and both are mobile users  302 ,  304 , then the situation is somewhat different. Selector circuit  344  would indicate that the LBR speech frames from mobile terminal  302  are the valid output for mobile terminal  304  and that the LBR speech frames from mobile terminal  304  are the valid output for mobile terminal  302 . Each of these would be a much clearer signal as compared to a signal that resulted from steps involving conversion to PCM. The PSTN terminal  306 , however, receives a PCM signal  384 , which results from a combination of, and is likely a weighted sum of, the PCM signals  358 ,  360  of the two mobile users  302 ,  304 . It should also be noted that where users of mobile terminals  302 ,  304  are simultaneously talking, if terminal  306  were also a mobile terminal but silent, as opposed to a PSTN terminal, the selector circuit  344  would forward a control indicating that the PCM signal is the valid output, and accordingly it should be forwarded to the transcoder and the terminal  306 . 
     The above discussion assumes a standard conferencing arrangement in which a participant hears the two loudest speakers other than the participant him/herself. It can be seen from the above description that with the present invention, conference calls involving two or more wireless participants will achieve a higher quality of sound in a number of circumstances. The conferencing arrangement is suitable whether there are or are not PSTN users involved. Further, there is the ability to provide more than one output signal. 
     The invention described herein for the situation in which there are two mobile users simultaneously speaking is equally applicable where there are more than two speakers speaking simultaneously, whether mobile or PSTN users, but where the conferencing arrangement must select only the two loudest, or “dominant”, speakers (as opposed to the two loudest speakers other the listener him/herself) for the purposes of the conference call and those are mobile terminals. 
     In another embodiment of the invention, as will be described below, in addition to the advantages described above, there is the opportunity for significant hardware savings in the way of limiting the number of decoders and encoders necessary. 
     Referring to FIG. 5, there is shown a general arrangement of the second embodiment. Again, two of the participants are using mobile or portable terminals  402 ,  404  and the third participant is using a PSTN terminal  406 . The mobile users communicate via RF channels  408 ,  410  to base stations, each of which is comprised of a base station transceiver  412 ,  414  and a base station controller  416 ,  418 . It can be seen that the main difference between this embodiment and the one described previously is that the conference unit  436  is located external to both MSCs  432 ,  434 . Further the transcoding function is no longer automatically taking place within the base station controller for all mobile speakers, and thus the transcoders  428 ,  430  within base station controllers  416 ,  418  may or may not exist. Instead the decoding and encoding are performed by the conference unit  436  as in indicated by the LBR signals between the base station controllers  416 ,  418  and the conference unit  436 , and the PCM signals between the conference unit and the MSCs  432 ,  434  (with more details to be illustrated in FIG.  6 ). Furthermore, decoding is only performed when needed, and only for particular conference participant(s), also to be outlined in more detail with reference to FIG.  6 . 
     It should be noted that if bandwidth savings are a concern, then the transcoders  428 ,  430  within base station controllers  416 ,  418  could be utilized to convert the PCM signals from the PSTN to LBR before sending them to the conference unit  436 . It should also be noted that although transcoders are logically located within base station controllers, typically they are co-located with the MSCs. 
     FIG. 6 provides a detailed overview of a conference unit according to the second embodiment. The flow of the speech signals from mobile conference participants  502 ,  503 ,  504  as well as from PSTN participants  505 ,  506 ,  507  are illustrated. The LBR speech  521 ,  522 ,  523  from mobile participants  502 ,  503 ,  504  is forwarded both to a power estimation circuit  538  as well as to a selector input circuit  540  for mobile users. The PCM speech  524 ,  525 ,  526  of the PSTN participants  505 ,  506 ,  507  is forwarded both to the power estimation circuit  538  as well as to a selector input circuit  542  for PSTN users. In the power estimation circuit  538 , the power or signal energy of each participant&#39;s speech is determined from either the LBR frames in the case of mobile users or the PCM frames in the case of PSTN users. Then the signal energy values  543 ,  544 ,  545 ,  546 ,  547 ,  548  of the speech signals are forwarded to the conference algorithm circuit  550 . In the conference algorithm circuit  550 , it is decided which speakers are the dominant speakers, according to its particular conference algorithm, and this information will be forwarded to the relevant selector input circuits  540 ,  542  in the form of control signals  556 ,  558 . There are also control signals  560 ,  562 ,  568  which are forwarded to the selector output circuits  552 ,  554  and the conference summing circuit  572  respectively which will be discussed in further detail below. 
     In accordance with control signal  556 , selector input circuit  540  will then forward any dominant mobile speakers&#39; LBR speech frames to the decoder circuit  564  as well as to the selector output circuit  552 . Decoding of the LBR speech will take place in the decoder circuit  564  unless conference algorithm circuit  550  has forwarded a control signal  566  to the decoder indicating that there is a single dominant speaker and that conversion to PCM is not necessary as there are no PSTN users, or that there are no dominant speakers art all. This control line is optional and is indicated by a dotted line in FIG.  6 . Similarly there is optional control line  570  to encoder  574 . 
     Next, the output of the decoder circuit  564 , namely the PCM speech, is forwarded to the conference summing circuit  572 . In accordance with control signal  558 , selector input circuit  542  forwards any dominant PSTN speakers&#39; PCM frames directly to the conference summing circuit  572 . The conference summing circuit  572  then performs the summing function as per the particular conference arrangement&#39;s specifications and instructions from the conference algorithm circuit  550  via control line  568 . Control line  568  may also be used to indicate that summing is not necessary at all to inhibit the function of the conference summing circuit  572  to save processing. Certain PCM signals are then sent from the conference summing circuit  572  to the encoder circuit  574  for encoding, while certain PCM signals are sent to selector output circuit  554 . 
     At each selector output circuit  552 ,  554 , it should be noted that there is control line  560 ,  562  from the conference algorithm circuit  550 . Each control line indicates which output goes to which participant. Finally, the selector output circuits  552 ,  554  forward to the conference participants  502 ,  503 ,  504 ,  505 ,  506 ,  507  the appropriate outputs  581 ,  582 ,  583 ,  584 ,  585 ,  586 . 
     It should be noted that the embodiment of FIG. 6 could be modified to omit any direct forwarding of LBR speech frames to the selector output circuit  552 . While this means that the ability to forward an incoming LBR signal to an output path without any conversion at all is lost, the potential hardware savings, as will be now discussed in detail, still exist. 
     For the common conferencing arrangement in which the two loudest speakers other than the participant him/herself is considered, the potential hardware savings is great. For this arrangement, a maximum of three decoders and three encoders are required. The three decoders are required for the three speakers that could be considered by the conferencing arrangement, and the three encoders are required for the three potential outputs, namely the loudest two speakers for all participants except for the two loudest speakers themselves, the second and third loudest speakers for the loudest speaker, and the first and third loudest speakers for the second loudest speaker. For a conferencing arrangement in which more than the two dominant speakers other than oneself are considered, n speakers for example, then accordingly (n+1) decoders and (n+1) encoders are necessary. 
     Now considering the conferencing arrangement in which two loudest speakers are considered for the purposes of the conference call, there is even greater hardware savings. A maximum of two decoders and three encoders are required. The two decoders are needed for the maximum two speakers that will be considered by the conferencing arrangement, and the three encoders are needed for the maximum number of potential outputs, namely the loudest speaker alone, the second loudest speaker alone, and the two loudest speakers together. For a conferencing arrangement in which n dominant speakers are considered, then accordingly (n) decoders and (n+1) encoders are necessary. 
     Variations of the embodiment described with reference to FIG. 6 are also possible. For example, there could be only one selector input circuit and only one selector output circuit, for both the mobile terminals and the PSTN terminals to share with a multiplexing ability. 
     In the embodiments described herein, each time reference is made to either a single dominant speaker or multiple dominant speakers, it is assumed that each speaker has a voice energy that is above a minimum threshold energy of the conferencing arrangement, which threshold represents the energy in the voice of a typical person. 
     Also, in the embodiments described herein, the speech of the mobile speakers has been LBR encoded and it is assumed that the output port uses the same transcoder algorithms. In the event that different algorithms are being used, conversion between formats can be performed. An example of this type of conversion is described in applicant&#39;s co-pending U.S. patent application, Ser. No. 08/883,353, now U.S. Pat. No. 5,795,923 which is incorporated herein by reference. 
     With respect to the issue of echo control, currently there are two network control arrangements used in wireless systems. In one arrangement, the echo control is colocated with the transcoder on the “wireless side” of the MSC. For the arrangement described in this specification, this type of echo control function should be disabled for conference calls. That is because a conference bridge presents a time varying channel to the echo canceler and performance could be compromised. Accordingly the conference bridge should provide echo control on all ports connected to the PSTN. In the second type of network control arrangement, however, the network echo control function is provided on the interface from the MSC to the PSTN. This is the preferred arrangement. In this arrangement, network error control is not required of the conference service. 
     Further, the arrangements described herein are for illustrative purposes only. Other arrangements are possible to achieve the desired functionality. Such a system is not limited to just mobile or wireless users, but can be equally applicable to other LBR based systems, including a corporate network utilizing LBR voice or Voice over Internet Protocol (VoIP).