Abstract:
A wireless conference phone system has a base station to couple at least one conference unit to a telephone network, such as the public switched telephone network (PSTN) or a digital telephone network such as a voice over internet protocol (VoIP) network. Each conference unit performs echo cancellation of the audio signal received from a remote location allowing a simplified base station implementation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Patent Application 60/669,008 filed Apr. 7, 2005. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to conference telephones. More particularly, the present invention relates to a wireless handsfree conference phone system. 
     BACKGROUND OF THE INVENTION 
     Conference phones are commonly used in a number of environments, such as meeting rooms, conference rooms, boardrooms and the like, to allow a group of people at a single location to participate in a phone call. 
     Many standard telephone sets can provide rudimentary conference abilities through a handsfree mode that uses a speaker and a microphone to communicate audio larger distances from the handset. To avoid echo, many such telephone sets employ half duplex switching so that the microphone and speaker are not active simultaneously. While half duplex switching allows a number of people to sit at a single location and participate in a call, there are a number of short comings to such a rudimentary conferencing capability. For instance, any noises in the room will cut off the far-end audio. Thus speaking, coughing, or paper shuffling will all prevent any inbound audio from being heard. This soon results in halting discussion patterns over the telephone link to the point where even a request to repeat a missing point may not be heard. 
     A conference phone is typically defined by having two features. The first feature is the ability to provide a speaker supporting full duplex audio capability that permits simultaneous transmission and reception of audio, and the second feature is a multi-line capability which provides the ability to use more than one phone line to serve as a rudimentary conference bridge. The availability of third party dial in conference bridges has made the multi-line capability feature of these phones redundant to a certain degree, but the feature is still considered to be a standard conference phone offering. 
     In large environments, a simple telephone handset in a speakerphone mode is unsuitable as a conference room phone. In large rooms, the audio quality provided by standard speakerphone implementations is not sufficient. To address this problem, dedicated conference phones are provided. 
     Dedicated conference phones, such as those offered by Polycom, Inc., ClearOne etc. provide only a handsfree experience. The conventional handsfree conference phone provides a dial pad and display to allow the user to dial and create a conference session. The phone typically has a plurality of microphones, and a single speaker. By using a plurality of microphones, the system can switch between active and passive microphones based on the position of a person speaking. 
     One common problem with conference phones is echo. When a remote participant in the call speaks, the voice is reproduced through the speaker of the unit. This sound is then received by the microphones as input, and is provided back to the remote participant with a slight delay. This causes an apparent echo that is often found to be distracting. To address this matter early solutions employed a half-duplex design, so that the microphones and the speaker do not operate simultaneously. A more sophisticated full duplex solution is presently found in dedicated conference phones. The full duplex solution makes use of echo-canceling circuitry to analyze the received signal and subtract that signal from the signal generated by the microphones allowing the speaker and microphones to operate simultaneously. 
     To address the needs of larger boardrooms, many conference phone systems make use of slaved microphone units that allow corded satellite units to connect to a central unit. The echo cancellation then factors in the sounds received at all the microphones, including those from the satellite units. 
     Recently wireless conference phones have been introduced to allow the phone to be moved between conference rooms or to be easily repositioned in a conference room. These wireless units are virtually identical to their wired analogs, but replace the cord between the phone and a wall jack with a wireless link to a base station connected to the telephone wall jack. These wireless units do not typically offer satellites, and when they do, the satellites are connected to the phone with wires, thus limiting the high degree of mobility and flexibility offered by the wireless phone unit. These wireless units cannot serve large meeting rooms without the ability to attach satellite units. 
     Outside of conference phones, simply using a plurality of telephone handsets connected to a single base station is known. This has not been implemented for conference phones due to the great complexity of dealing with echo cancellation across a plurality of different phones each connected to the base station but not to each other. 
     It is, therefore, desirable to provide a wireless conference phone system with the ability to support larger conference rooms. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to obviate or mitigate at least one disadvantage of previous wireless conference phones. 
     Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
     Generally, the present invention provides a method and system for connecting a plurality of wireless conference units to an outside world telephone network. 
     Whereas previous conference phone systems employed sophisticated switching and echo cancellation in the phone for both a main or master conference phone and each satellite or slave unit, this technique is not optimal for wireless systems. A preferred configuration has wireless conference phone units that do not talk directly to each other, but rather communicate with a base station. The wireless conference phone units, also referred to as PODs, relay information to a base station, which connects the PODs to the outside world telephone network. The outside world telephone network carries call signaling and audio communications between a near-end location and a far-end location. There are many forms of telephone networks that can advantageously be used, for instance, the public switched telephone network (PSTN), a Voice over Internet Protocol (VoIP) telephone network service over the Internet, a cellular telephone network and the like. 
     Whereas previous conference phone systems have employed sophisticated switching and echo cancellation incorporated into the base phone and each satellite phone, this technique is not always optimal or suitable for wireless conference phone systems. 
     In accordance with the invention, wireless conference phone units, or PODs are in communication with a base unit connected to a telephone network. The PODs exchange call signaling and audio communications with a base unit that connects them to the outside world telephone network. In a presently preferred embodiment, each POD operates independently. This allows the POD to be used alone and extra PODs are added as needed to allow coverage of larger conference rooms. As a result, the PODs are not designed to communicate with each other in a master-slave configuration or with a central POD relaying echo cancellation information to the other PODs. However, building complex circuitry in the base station for multi-POD echo cancellation drives up the cost of the base station when the base station will often be used to support only a single POD unit. 
     In accordance with the invention a telephone network interface is provided in a base station connected to an outside world telephone network. The audio signal received at the base from the telephone network is transmitted to each POD over a wireless channel. Each POD reproduces the received audio signal on its loudspeaker. Thus far-end audio is reproduced for the near-end conference participants on the speakers of the PODs. The POD microphones pick up near-end audio, which is processed in the POD to remove the loudspeaker audio cross-talk also picked up by the POD microphones. The processed near-end audio signal from each respective POD is transmitted to the base station over a unique wireless channel. The base station receives near-end audio signalling from each POD and sums them all together and delivers the result to the outside world telephone network for transport to the far-end participants. Because the PODs are all located in the same conference room, there is no need to have each POD receive and play the audio generated by other POD units in the room. This simplifies the implementation of the base station and allows for a plurality of independent PODs to connect to the same base station and provide complete coverage in a large conference room environment. The base unit has a processor providing a signal processing capability to perform more complex processing of the received near-end audio signals beyond simply adding them together. For example, a weighted addition process is used, or such other processing as may be desirable, to provide a suitable near-end audio signal for transmission over the telephone network to the outside world. However, the signal processing in the base ensures that the audio signal received from one POD is not delivered to another POD. That is no side-tone is provided to any POD by the signal processing at the base station. The near-end audio signal is delivered only to the telephone network and not to any of the PODs. 
     In one of its aspects the invention provides a conference phone system comprising a base station having a telephone line interface, a POD interface and a base control processor coupled to the telephone line interface and the POD interface operable to exchange call control and audio communications signalling between the telephone line interface and the POD interface. The conference phone system has at least one POD unit, each such POD unit having a microphone system, a loudspeaker, a base interface and a POD control processor interconnecting the microphone system, loudspeaker and base interface to exchange communications signalling with the base station via the POD interface and base interface and operable to filter out audio signalling received over the base interface from the signal produced by the microphone system supplied to the base interface. 
     In another of its aspects the invention provides a method for conducting a conference call using a base station with a call control processor controlling a telephone line interface connected to a telephone network and a POD interface operable to exchange call control and audio communications signalling between the telephone network and the POD interface and at least one POD control processor unit controlling a microphone system, a loudspeaker and a base interface to exchange communications signalling with the base station POD interface. The method comprises the steps of producing audio output on each POD loudspeaker corresponding to audio signalling received from the telephone network; then performing echo cancellation processing at the POD control processor on the audio signalling produced by the microphone system to remove the audio output received from the telephone network and delivering the echo cancellation output produced by each POD to the base station call control processor for summing and delivery into the telephone network. 
     Embodiments of the present invention will now be described, by way of example only, with reference to the attached figures, wherein: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram of an exemplary embodiment of the invention having two wireless POD conference units and a base unit; 
         FIG. 2  is a functional block diagram of a base unit providing a PSTN line interface; 
         FIG. 3  is a functional block diagram of a wireless POD conference unit; and 
         FIG. 4  is a schematic of an RF interface provided in the POD and the base units. 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion provides an exemplary embodiment of the present invention. Those skilled in the art will realize that although this discussion is made with reference to specific embodiments, the specific embodiments are not intended as being limiting, but rather are intended solely to provide examples of embodiments of the invention. 
     As shown in  FIG. 1 , a basic setup of an exemplary conference telephone system comprises a base station unit  100  and two wireless POD units  102 . The base station and POD units communicate over radio frequency (RF) wireless channels, such as in the 2.4 GHz standard ISM RF band. The base station  100  is connected to the outside world telephone network  110  and to the wireless PODs  102 . Each POD has a respective microphone system  112  and a loudspeaker  114 . Preferably the POD microphone system  112  has 3 microphones to pick up audio in all directions around the POD. The wireless PODs are placed within a conference room to position the POD microphones system  112  as close as practicable to each of the conference call participants. During a phone conversation, near-end speech is picked up dynamically by one or more of the POD microphones and far-end speech is reproduced on each respective POD loudspeaker  114 . 
     A POD has a keypad  116  providing a user input mechanism to control calling on the system. The keypad has a plurality of switches typically including an on/off switch, an offhook/onhook switch, a volume control, a mute switch and a telephone dialing keypad group of switches, that is, a plurality of key switches labeled to include the numbers 0 to 9, asterisk (*) and octothorp (#). 
     The keypad switches are manipulated by a user to answer or place a call over the telephone network. When both PODs are powered up, pressing offhook on one POD preferably activates the other POD as well so that both PODs are in communication with the base station and telephone network. Dialing, muting and going onhook/offhook is done using the keypad of either POD. The PODs have a display  118  to provide call and status information to the users, for example, caller ID, dialed number, transient display of volume levels when the volume controls are manipulated etc. 
     A telephone network line interface  104  couples the base to an outside world telephone network  110  and supports call supervisory signalling and audio communication over the telephone network. The audio received from the telephone network is provided as the RxL signal on line  148  which is split at  108  into separate Rx(i) signals for each POD. Thus for the example embodiment employing two PODs, two signals Rx 1  and Rx 2  are produced and sent from the base via RF to each POD simultaneously. The return audio transmitted from each POD, Tx 1  and Tx 2 , is sent via RF to the base unit  100  where each is summed as depicted by summer  106 . The summed audio signal is then provided as the TxL signal on line  146  to the telephone network line interface  102  for supply to the outside world telephone network  110 . In the base, no side-tone or reflection of the transmitted audio received from a POD, i.e. Tx(i), that is, Tx 1  and Tx 2  in the two POD embodiment depicted in the figure, appears on the Rx audio signal that the base sends back to another POD. 
     In accordance with the invention, each POD performs Rs own acoustic echo cancellation so that echo and howling coming from a POD is virtually eliminated. Near-end speech picked up by a POD is sent out to the outside world telephone network  110  by the base unit  100  and is not echoed back to itself or to another POD. 
     With the ability of the base to block near-end audio of one POD from appearing at another POD, the above arrangement is suitable to allow multiple PODs to be used. The number of PODs that can be used advantageously to communicate audio simultaneously with the base is not limited to the two PODs depicted in the exemplary configuration of  FIG. 1 . Three or more PODs can be deployed where the maximum number of PODs will depend on the number of available radio channels and time slots provided in the system wireless design. Thus, in accordance with the invention, near-end audio echo cancellation is performed in the PODs, and consequently a simple base station implementation is achieved that does not greatly increase either the complexity or cost of producing the base station unit. 
       FIG. 2  is a functional block diagram of a preferred embodiment of the base station unit  100 . The base has a processor  120  which controls the operation of the elements of the base system. A suitable processor in this regard is a DECT baseband processor produced by National Semiconductor in the SC144xx part family. The base processor  120  runs program code stored in memory  122 , for example an internal flash memory, and any variables and operating parameters are kept in memory  124 , which, in the preferred embodiment, is a 16 kbit external EEPROM serial memory device. 
     The processor  120  also provides the necessary RF control signals to the RF module  126  over RF interface  130 , which is described in more detail in the discussion relating to  FIG. 4 . The base RF module  126  transmits and receives digital information with each POD using a suitable radio antenna  128 , for example, one configured for use in the 2.4 GHz ISM band. 
     For a user interface, the base processor  120  drives an in-use indicator  132 , for example light emitting diode (LED), to indicate when a connection with the outside world telephone network is active. Where the outside world telephone network is the PSTN as depicted in the embodiment of  FIG. 2 , the in-use indicator  132  will indicate that the data access arrangement (DM) line interface  136  has gone off-hook, for example, to dial an outgoing call or to carry on a conversation over the telephone network. Preferably the base includes a page key  133  to page the PODs. In the preferred embodiment, the base has a page key  133 , such as a push button switch, that is polled by the base processor and when the page key is pressed, the base signals the PODs causing them to emit an audible signal to enable a user to locate any POD units registered to the base. 
     Preferably the base provides a test and update connector  134 , such a connector to a Universal Asynchronous Receiver Transmitter (UART) interface, to enable firmware download and testing functions to be performed. 
     A suitable outside world telephone network line interface is provided in the base to support call supervisory signalling with the telephone network and to facilitate audio communication over the telephone network. In the exemplary embodiment, the outside world telephone network is the PSTN and consequently the telephone network interface is configured to connect to the PSTN. A PSTN interface is implemented using a digital access arrangement device, depicted as DAA line interface  136  and protection elements  140 . The DAA line interface  136  provides PSTN data terminal equipment/customer premise equipment functionality to terminate the connection to the PSTN  110 . A suitable DM line interface device is manufactured by Clare, Inc. in their Lite Link (trade-mark) product family parts numbered as CPC5620x. The protection elements  140  include fuses, capacitors and sideactors suitably configured for overcurrent and overvoltage protection to provide the necessary electrical isolation between the outside world telephone network  110  and the rest of the base unit circuitry. For other outside world telephone networks, such as VoIP, the devices provided for the telephone network line interface  104  (of  FIG. 1 ) will be selected for operation with the media link characteristics and protocols of such other networks. 
     The base processor  120  has connections or lines for communication with and control of the other devices in the base unit. For instance, to provide call supervisory signaling to the outside world telephone network, an onhook control line  142  controls the on-hook/off-hook operation of the DM line interface  136  to allow the base to initiate, receive or terminate a call over the telephone network  110 . The DAA line interface produces an audio signal converted from the far-end audio received over the telephone network into the RxL signal  148 . The digital near-end audio received from each of the PODs via antenna  128  is processed and summed by the base processor  120  and the result is supplied as the TxL signal  146  to the DAA line interface  136  for conversion to a suitable analogue form signal for delivery into the outside world telephone network  110 . 
     The DM interface  136  also has an on-hook ring detect line  144  to signal processor  120  of an incoming call. The incoming call is reported to each POD which responds by causing ring signaling to be produced on the POD, for example over the POD loudspeakers  114 , and any available caller ID details are displayed on the POD display  118 . In the preferred embodiment, the base includes a record jack  152  to facilitate telephone conversation recording. To provide this capability, an analogue version of the TxL and RxL transmit and receive audio signals is supplied to an amplifier  150  which provides an amplified output that is then available to a recording device connected to recording jack  152 . 
       FIG. 3  is a functional block diagram of elements in a preferred embodiment of a POD unit constructed in accordance with the principles of the invention. The POD  102  has a control processor  200  such as a DECT baseband processor produced by National Semiconductor in the SC144xx part family. The POD further includes an RF module  202 , an RF interface  204 , keypad  116  and status indicators  228 . A Digital Signal Processor (DSP)  206 , such as a DSP manufactured by Freescale Semiconductor in the DSP563xx part family, carries out speech signal processing tasks. The POD also has related circuitry for the microphones, loudspeakers, ADC/DAC operations and battery charging function. 
     The POD is in wireless communication with the base over a radio channel and each POD has an antenna  201  to transmit and receive radio frequency signaling over the channel. Rx(i) signalling from the base to the POD is received on the POD antenna  201  and supplied to the POD RF module  202  for conversion and recovery of the data contained in the radio signalling. The recovered data is supplied to the POD processor  200  over RF interface  204 . RF interface  204  supports bi-directional communication between the POD processor  200  and the RF module  202 . Consequently, data from the POD to be delivered over the radio channel to the base is supplied to the RF module  202  by the POD processor over RF interface  204 . The RF module  202  in turn converts and encodes the received data onto a radio signal, Tx(i), that is delivered into the radio channel by antenna  201 . 
     When digital speech audio information sent by the base is received by the POD control processor  200  from the POD RF module  202 , the POD control processor  200  converts the digital speech into analog form and then transmits it to the DSP unit via a differential interface RX_AUDIO  208 . This analog audio is amplified and converted again into a digital data stream at OPAMP  210  and ADC  212  respectively for supply to the DSP  206 . As a consequence, the DSP is provided with input representative of the received audio. The DSP then performs signal processing of the signal and the resultant digital audio output is converted to analog form at DAC  213 . An OPAMP  214  and power AMP  216  amplify this audio signal and drive the POD loudspeaker  218  thus reproducing far-end audio at the POD. 
     For the near-end audio, the user speech is picked up by the microphone system  112 . Preferably the microphone system  112  has three microphones, shown as MIC[ 1  . . .  3 ] in the drawings, arranged to pick up audio from all directions surrounding the POD. The microphone signals are amplified at corresponding OPAMPs  222  and supplied to an analogue to digital converter ADC  212  which converts them to digital for signal processing steps performed by the POD DSP  206 . The POD DSP  206  performs the speech processing, for example, removing from the Tx(i) signal sent to base processor  120  any cross talk or local feedback of the Rx output picked up by the microphones. The resultant digital data is sent to a digital to analogue converter DAC  214 , where the output data is converted to analogue and supplied to an OPAMP  224  which outputs a differential analog signal TX_AUDIO carried on line  226  to the POD control processor  200 . The POD control processor  200  receives this signal and converts it into digital data and transmits it to the base via the RF module  202  as the POD&#39;s Tx(i) signal, two examples of which are shown as the Tx 1  and Tx 2  signals in the two POD configuration of  FIG. 1 . 
     The POD processor  200  and the DSP  206  also communicate via a bus interface,  205 . Bus interface  205  is coupled to display  118  to enable processor  200  to provide status information, such as number dialed, caller ID and the like on the display  118 . A memory  230 , such as an electrically erasable programmable read only memory is coupled to bus interface  205  to store operating program instructions. The DSP reads and executes a program stored in memory  207 , which preferably is a flash memory module. 
     Status indicators  228 , preferably LED&#39;s, provide a visual indication of the POD status. In the preferred embodiment, green LED&#39;s indicate the unit is powered on and red LED&#39;s flash to indicate the POD microphones are muted. Preferably the POD includes a battery  209  to permit the wireless unit to be relocated to any convenient location. The batteries may be replaceable consumables, but to reduce spent battery waste, rechargeable batteries are preferred. A line powered recharge adaptor  211  produces recharge current that is supplied to the battery by a charge circuit  213  that controls battery recharging and prevents overcharging of the batteries. If desired, the green LED&#39;s may be flashed in various ways to provide a visual indication that the batteries are being recharged and/or are fully charged, or the charge status of the batteries may periodically be indicated on the POD display  118 . 
       FIG. 4  shows a schematic diagram of a preferred embodiment of an RF interface used in both the base  130 , and in each POD  204  for signaling paths to facilitate exchange of data and control of the RF modules  126  and  202  in the base and PODs by the corresponding processor  120 ,  200 . In the RF interface, inputs supplied to the respective RF module include SYS_CLOCK which provides the basic clock for the RF module and is gated on and off when needed. The PLL_ENABLE, PLL_DATA, and PLL_CLOCK input signals are used to adjust and multiply the carrier frequency, for example to allow frequency hopping or channel selection to occur. The transmit inputs supplied to the respective RF modules include a TDO signal, which provides the transmit data output that will be encoded onto the wireless communications channel using a suitable modulation scheme, for example, GMSK modulation. The PWR_ON input is used to turn the RF power amplifier on and off. The PWR_SEL input is used to select a low or a high transmit power level. Preferably frequency hopping is used. On the receive side, the outputs from the respective RF modules include a received data in (RDI) signal corresponding to the data input received at the RF module and the RXDSG and RSSI signals are used to indicate the received signal strength. 
     The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.