WO2011089403A2

WO2011089403A2 - Method and system to reduce feedback between handsets in a communication system

Info

Publication number: WO2011089403A2
Application number: PCT/GB2011/000093
Authority: WO
Inventors: Anthony Michael Knowles; Christopher John Davies
Original assignee: Iml Limited
Priority date: 2010-01-25
Filing date: 2011-01-25
Publication date: 2011-07-28
Also published as: GB2477156A; WO2011089403A3; GB201001190D0

Abstract

A method and system for controlling a plurality of handsets in a mobile communication system in a region is described in which each handset has a loudspeaker, microphone, and a communication interface for receiving signals for the loudspeaker and transmitting signals received from the microphone. Adjacent handsets likely to cause feedback between the loudspeakers and the microphones of the adjacent handsets are identified. A microphone in a handset for a speaker is activated, and an acoustic output of the loudspeaker of at least one other adjacent handset is muted or reduced.

Description

METHOD AND SYSTEM TO REDUCE FEEDBACK BETWEEN HANDSETS IN A

COMMUNICATION SYSTEM

Field of the Invention

The present invention generally relates to a method and system to reduce feedback between handsets in a mobile communications system.

Background of the Invention

In meetings of people it is often desirable to provide a public address system so that listeners can hear speakers. In some meetings many people may want to speak and traditionally a 'roving' microphone is provided. However it takes time for the microphone to reach the speaker delaying the proceedings and if a speaker is sitting near a loudspeaker, annoying feedback is likely.

In large meetings where tiers of loudspeakers are used, differing time delays are introduced in the signals to the different tears of loudspeakers so that as the sound propagates from the stage to the back of the hall it remains in phase and avoids multiple echoes. Whilst this works for the presenter on stage any audience member asking a question using a portable microphone will notice a significant and distracting echo.

Using loudspeakers to drive the whole acoustic space results in the natural acoustic of the room influencing which frequency components of the amplified speech become unstable and result in feedback howl.

Where individual loudspeakers are provided for each member of the audience the output levels of each loudspeaker are much reduced and as audio is distributed via radio signals rather than audio waves no discernable echoes will be produced. This reduces the influence of the room acoustics. Consequently the sound is less dependent on the room and has a high proportion of direct sound to reflected sound echoes. However the potential for feedback between an audience speaker and their neighbour is a possibility. For meetings that require feedback from attendees, such as votes or selections of chosen responses, the attendees can be provided with a handset. In WO2004/017662, the content of which is hereby incorporated in its entirety by reference, such a system is disclosed. The voting handset is also provided with a loudspeaker and microphone to enable the handset to be used as a communication device enabling communication from the principle speaker and any speaker to all listeners. The handset uses wireless communication channels and hence enables listeners to move during a meeting whilst still benefiting from their own personal loudspeaker output to hear the proceedings. Thus mobile communications handsets are used in a communications system for the purpose of acting like a public address (PA) system. Holders of handsets can be given permission by a chairman in a meeting to speak. Their microphone can be enabled to enable them to become a speaker in the proceedings whereby their audio input is wirelessly transmitted to all participants.

To avoid the listener having to hold the handset close to their ear or inconveniently wear headphones, the acoustic output of the loudspeaker could be increased. This would enable a user to, for example place the handset on the table in front of them. However, the inventors have identified that this benefit brings with it the undesirable likelihood of a handset adjacent to the handset of a person speaking causing feedback i.e. the output of the loudspeaker of a handset in close proximity to the microphone of the handset of the speaker being picked up by the microphone and amplified in a feedback manner. It is difficult to avoid this since the very benefit brought about by allowing users to be mobile with their handsets increases the likelihood of handsets becoming interferingly adjacent to cause the feedback problem.

It is an object of the present invention to provide a method and system to reduce feedback between handsets in a mobile communications system. Summary of the Invention

One aspect of the present invention provides a method of controlling a plurality of handsets in a mobile communication system in a region, each handset having a loudspeaker and a microphone and a communication interface for receiving signals for the loudspeaker and transmitting signals received from the microphone, the method comprising identifying adjacent handsets likely to cause feedback between the loudspeakers and the microphones of the adjacent handsets; activating a microphone in a said handset for a speaker; and muting or reducing an acoustic output of the loudspeaker of at least one other adjacent handset.

Thus in accordance with this aspect of the present invention, the adjacency of handsets is determined so that when one of the handsets is used as a speaker handset, adjacent handsets have their acoustic output muted or reduced to avoid potential feedback.

In one embodiment, the communication interface of each handset transmits signals on a separate channel and combines signals received on each channel, and the acoustic output of said loudspeaker is reduced by muting or reducing an acoustic output for signals received on a channel from at least one other adjacent handset. Thus in this embodiment not all of the acoustic output from a loudspeaker of an adjacent handset need be muted. This recognises that if there is acoustic feedback it is likely that the user adjacent to the speaker will be able to hear the speaker directly and also be able to listen to other remote speakers, such as a chairman, presenter or moderator in a meeting, using the acoustic output of the loudspeaker of their handset since these acoustic outputs are not part of a feedback loop with the speaker's microphone. The use of different channels for the signals from handsets enables this discrimination.

In one embodiment, an adjacent handset is identified by a user of said adjacent handset as being adjacent to said handset for a speaker when the user can hear the speaker directly and the user mutes or reduces the acoustic output of the loudspeaker of said adjacent handset. This embodiment enables for manual intervention to avoid or reduce feedback. The handset users are instructed to only enable their loudspeakers when they cannot hear the speaker directly i.e. when the speaker is to far away from them to be heard clearly and hence the likelihood of feedback is low.

In one embodiment, a control unit controls the muting or reduction of the acoustic output of the loudspeaker of said at least one adjacent handset. This provides for separate control from the handsets and reduces the processing requirements for the handsets. In an alternative embodiment, said handset for said speaker controls the muting or reduction of the acoustic output of the loudspeaker of said at least one adjacent handset. In yet another embodiment, said at least one adjacent handset controls the muting or reduction of the acoustic output of a respective said loudspeaker.

In one embodiment the method includes including storing data identifying said at least one adjacent handset. The data can be stored in the control unit or in each said handset.

In one embodiment said identifying and storing are periodically repeated to update said data. This is useful where users are mobile and the proximity of the handsets is likely to vary.

In one embodiment said identifying is performed based on location data. The location data can be input by each said handset user or determined by determining the location of each said handset, such as by triangulation using multiple communication receiving antennae, by detecting an identity of a cradle into which the handset is placed. Alternatively the location data can be input at said control unit.

In one embodiment the identifying step comprises, for each handset, adding a training signal to a signal to the loudspeaker or modifying the signal to the loudspeaker, the acoustic output for each handset being unique in time and/or frequency; comparing a signal from the microphone with the training signal or modification; and identifying whether said handset is an adjacent handset using the result of the comparison. Thus in this embodiment, the loudspeaker of each handset can output a distinctive acoustic output which can be detected at microphones of adjacent handsets. In one embodiment said identifying comprises, for each handset, receiving a signal from a microphone of each other handset, comparing the signal with a signal from the microphone of the handset, and identifying whether said handset is an adjacent handset using the result of the comparison. This 'listening' method detects the inverse of the acoustic path from the loudspeaker of a handset to the microphone of an adjacent handset and operates on the basis of acoustic reciprocity. In one embodiment said identifying comprises, for each handset, receiving a signal from a microphone of each other handset, determining the signal strength or time delay of each signal, and identifying whether said handset is an adjacent handset using the result of the determination.

Another aspect of the present invention provides a mobile communication system comprising a plurality of handsets for use in a region, each handset having a loudspeaker and a microphone; activating means for activating a microphone in a said handset; and muting means for muting or reducing an acoustic output of the loudspeaker of at least one other adjacent handset.

In one embodiment the system includes identifying means for identifying adjacent handsets likely to cause feedback between the loudspeakers and the microphones of the adjacent handsets.

One aspect of the present invention provides a handset for use in a communication system by a user wishing to be a speaker, the handset comprising a loudspeaker for outputting an acoustic output from speakers using other said handsets; a microphone for receiving an acoustic input from the user when the user is a speaker; a communication interface for receiving signals for the loudspeaker and transmitting signals received from the microphone; and a processor programmed to activate the microphone when the user is a speaker; and to mute or reduce an acoustic output of the loudspeaker when at least one other user of a said handset is at least one speaker using at least one handset identified to be at least one adjacent handset.

In one embodiment, said processor is programmed to identify any adjacent handsets likely to cause feedback between the loudspeakers and the microphones of the adjacent handsets.

In one embodiment, when said user is a speaker, said processor is programmed to transmit a control signal to any said identified adjacent handsets to mute or reduce an acoustic output of the loudspeaker thereof. In one embodiment, said communication interface is adapted to receive a control signal, and said processor is programmed to mute or reduce an acoustic output of the loudspeaker in response to said control signal. Another aspect of the present invention provides a method of operating a handset in a communication system for a user wishing to be a speaker, the handset comprising a loudspeaker for outputting an acoustic output from speakers using other said handsets, a microphone for receiving an acoustic input from the user when the user is a speaker, and a communication interface for receiving signals for the loudspeaker and transmitting signals received from the microphone, the method comprising activating the microphone when the user is a speaker; and muting or reducing an acoustic output of the loudspeaker when at least one other user of a said handset is at least one speaker using at least one handset identified to be at least one adjacent handset. Another aspect of the present invention provides program code for controlling the processor in a handset to operate the handset. The code can be provided on any suitable carrier medium such as a storage medium (e.g. a hard disk, a solid state memory device, optical memory, or magnetic memory), or a transient medium such as a signal (e.g. an electrical signal, a magnetic signal, an optical signal, an acoustic signal, an RF signal or an electromagnetic signal such as a TCP IP signal over a computer network).

Brief Description of the Drawings Figure 1 is a schematic diagram of a mobile handset in accordance with one embodiment of the present invention,

Figure 2 is a schematic diagram of components of the mobile handset in accordance with one embodiment of the present invention,

Figure 3 is a schematic diagram of a mobile communications system in use in a meeting in accordance with one embodiment of the present invention,

Figure 4 is a schematic diagram of a mobile communications system showing the communications paths in accordance with one embodiment of the present invention, 11 000093

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Figure 5 is a schematic diagram of a control unit of the embodiment of figure 3 in accordance with one embodiment of the present invention, Figure 6 is a flow diagram illustrating a process implemented by the control unit to control the loudspeakers of the handsets in accordance with one embodiment of the present invention,

Figure 7 is a diagram illustrating the communication network using multiple channels in which an adjacent handset mutes only the audio received on a channel from an adjacent handset in accordance with one embodiment of the present invention,

Figure 8 is a flow diagram illustrating a process implemented by a handset adjacent to a handset used by a speaker to control the loudspeaker of the adjacent handset in accordance with one embodiment of the present invention,

Figure 9 is a flow diagram illustrating a process implemented by a speaker's handset adjacent to adjacent handsets to control the loudspeakers in the adjacent handsets in accordance with one embodiment of the present invention,

Figure 10 is a schematic diagram of two adjacent handsets in an active learning mode to identify whether the handsets are adjacent in accordance with one embodiment of the present invention, Figure 11 is a schematic diagram of two adjacent handsets in a passive or listening learning mode to identify whether the handsets are adjacent in accordance with another embodiment of the present invention,

Figure 12 is a schematic diagram of multiple adjacent handsets using multiple channels in a passive or listening learning mode to identify whether the handsets are adjacent in accordance with another embodiment of the present invention, and

Figure 13 is a schematic diagram illustrating a triangulation method to determine the location of handsets for use in the determination as to whether handsets are adjacent in accordance with an embodiment of the present invention. 011 000093

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Detailed Description of Embodiments of the Invention

Figure 1 illustrates a handset 1 in accordance with one embodiment of the present invention for use in a mobile communication session to enable one or more speakers to be heard by listeners using the handsets. The speakers may or may not be using a handset. For example, a speaker may use a microphone e.g. a chairman of a meeting sitting at a table, or a presenter. The handset 1 is capable of transmitting RF signals using an antenna 2 for mobile communications. A loudspeaker 4 is provided which is capable of generating an audio output that a user can hear from a distance e.g. 1 to 2 metres so that the handset 1 need not be held close to the ear of the user during use thus providing a more convenient arrangement.

A handset is also provided with a microphone 3 to enable the user to use the handset when the user wishes to speak so that other users can hear using their handsets. Also a keypad 5 is provided to enable a user to enter inputs. Although the keypad shown in Figure 1 is a numeric keypad, it can alternatively include alphameric keys or alphanumeric keys. The type of keypad will depend upon the input that is require to be input by the user. For example, the input can comprise configuration parameters for the handset which can include location information as will be described in more detail hereinafter. The keypad can be used for entering inputs in response to meeting parameters e.g. a voting input as for example described in WO 2004/017662 and for entering a request to speak.

In this embodiment the handset 1 is also provided with a smart card 6 which can be input into a slot in the handset 1 to enable data or code stored on the smart card 6 to be read by the handset 1. The code contained on the smart card 6 can be used to re- configure the functionality of the handset 1 and data on the smart card can be used to update parameters stored within the handset 1. Thus the smart card 6 can be used as a method of user input. For example, each user may be given a smart card which includes their own personal identification information and this can be taken with them and used to be inserted into any handset. This enables the smart card 6 to be more mobile than the handset 1. The handset 1 can be left lying around and used by any users who can simply insert their smart card 6 into the handset 1 to configure the handset as a unique handset for the user.

Figure 2 illustrates the components of handset 1 in more detail. An antenna 40 transmits RF signals to and from an RF logic circuit 41. The RF logic circuit 41 is connected to a digital signal processor (DSP) 42 providing audio processor functionality and hence the RF logic circuit 41 provides for up and down conversion of the signals from the DSP 42. A microphone 46 is provided for receiving acoustic input from a user to generate signals which are amplified by an amplifier 45 for input into the DSP 42. A loudspeaker 44 is provided for generating an acoustic output based on signals provided to it from an amplifier 43 which in turn receives signals from the DSP 42 to drive the loudspeaker 44.

A control processor 47 is provided to control the DSP 42 and the RF logic circuit 41. The function of the control processor 47 will be described in more detail as hereinafter.

The control processor 47 can read data from and write data to the data memory 48.

Programme memory 49 is provided for storing control code for controlling the operation of the control processor 47. In this way the code in the programme memory 49 can be updated and modified to change the control operations performed by the control processor 47. A smart card reader 51 is provided to read a smart card 6 when inserted into the handset 1. The control processor 47 controls the smart card reader 51 to read data from the smart card and to write data to the smart card.

The handset 1 is also provided with a power supply 50 in the form of a battery power supply with the ability to connect to a main supply when necessary.

Figure 3 illustrates a communication system and method implemented in a meeting in accordance with one embodiment of the present invention. In this meeting a speaker 10 uses a microphone device 10a to communication with a control unit 11. In this embodiment the microphone device 10a comprises a radio microphone for radio transmission to the control unit 11. Thus in this embodiment there is one principle speaker who is addressing an audience of listeners e.g. in a meeting or presentation format. A plurality of users 12a, 12b, 12c, 12d and 12e listen to the speaker 10 using respective handsets 13a, 13b, 13c, 13d and 13e. In this embodiment each handset 13a, 3b, 13c, 13d and 3e is docked in or connected to a cradle 14a, 14b, 14c, 14d and 14e respectively. The cradles 14a, 14b, 14c, 14d and 14e are fixed to locations e.g. chairs or tables at which users can be located. Each cradle 14a, 14b, 14c, 14d and 14e contains information which can be used to uniquely identify the location of the cradle 14a, 14b, 14c, 14d and 14e. Each handset 13a, 13b, 13c, 13d and 13e can be removed from its cradle 14a, 14b, 14c, 14d and 14e to allow the user 12a, 12b, 12c, 12d and 12e to move to another location. However, the user can only use their handset 13a, 13b, 13c, 13d and 13e once it has been placed in the cradle so that the location of the handset and hence the user can be known by the control unit 11. The location information stored in the cradle 14a, 14b, 14c, 14d and 14e can be transmitted by the handset 13a, 13b, 13c, 13d and 13e to the control unit 1. The location information stored in the cradle 14a, 14b, 14c, 14d and 14e can simply be a unit identifier and the control unit 1 can include data mapping of the unique identifier to a physical location in the region in which the users are located, or it can include more precise location information e.g. co-ordinates or seat number.

Each handset 13a, 13b, 13c, 13d and I3e can be used by a user 12a, 12b, 12c, 12d and 12e to request to speak and to then address other users using the microphone on the handset. In this arrangement any number of users can be given permission to speak. If there is only one audio channel, only one user or presenter can speak at a time. However, if the communication system is provided with multiple audio channels and the handsets are provided with audio mixers, it is possible for multiple speakers to speak and for the audio to be mixed and output through the loudspeakers on the handsets.

As can be seen in Figure 3, users 12a, 12b, 12c, 12d and 2e can thus conveniently sit comfortably with their handsets 13a, 13b, 13c, 13d and 13e sitting next to them to listen to the audio output from the handsets without having to hold the handset to their ear. This has the benefit of providing a more comfortable listening environment but does pose the risk of the loudspeaker from one handset interfering with the microphone input of another handset when the two handsets are adjacent i.e. when one handset is used by a speaker and another handset is being used by a listener and they are in close proximity. In the embodiment of Figure 3 the communication between handsets is controlled and moderated by the control unit 11. Each handset transmits to the control unit 1 and receives from the control unit 11. Figure 4 illustrates an alternative communication arrangement in which the handsets 20, 21 , 22, 23 and 24 are able to communicate with any other handset as well as with the control unit 25. In this embodiment when any one handset is given permission to transmit audio i.e. when the user can become a speaker, if there is only one audio channel, the microphones of all other handsets must be disabled to prevent a conflict of audio signals. The control unit 25 provides for the control to enable microphones in answer to requests to speak and to disable other microphones by the transmission of control signals over the network.

In an alternative embodiment, multiple communication channels can be used under the control of the control unit 25. The control unit 25 can assign communication channels to handsets so that each handset uses a unique channel. This enables multiple microphones to be enabled at the same time and hence multiple speakers since each handset is provided with an audio mixer to mix the audio from multiple speakers i.e. microphones of the handsets for output on the handset's loudspeaker. The control unit 25 can thus provide for communication control and can provide for assignment of communication channels.

In yet another alternative embodiment, no control unit is required. Each handset is assigned a fixed communication channel and any number of microphones can be enabled at any one time to enable the speakers to speak and these are mixed for output at each loudspeaker by a mixer in each handset.

Figure 5 is a schematic diagram of a control unit comprising a control processor 33 for implementing the main control functions. A programme memory 31 is provided for storing code for controlling the control processor 33. This enables the operation of the control processor 33 to be updated by storage and implementation of new code. A controller user interface 30 is provided connected to the control processor 33 to enable a user acting as a controller to enter parameters to control the communication system. A memory 32 stores a request to speak queue comprising a list of identified users who have entered a request to speak. Thus the control processor 33 controls the microphones of the handsets to activate only those handsets associated with users who have been given permission to speak in accordance with an algorithm implemented by code loaded into the control processor 33.. The control processor 33 will process the data and control the microphones by the generation of control signals in accordance with data entered by the controller user interface 30 and the queue data stored in memory 32.

The control of microphones is important since only certain microphones in the handsets are activated in the communication system at any one time. This reduces the complexity of controlling feedback between handsets. It also reduces the likelihood of feedback between handsets in an environment where only a limited number of users should be allowed to speak at any one time. For example, in a meeting, a presenter may ask if there are any questions and a participant may ask the question and enter into in a dialogue with the presenter. There are thus two principle speakers.

In this embodiment, a database of handset location data 35 is also provided in the control unit and is accessible for processing by the control processor 33. The database of handset location data can include absolute location data of the handset or it can provide look-up data such as handset identifiers together with position information such as seat number. Using this information the control processor 33 is able to calculate which handsets are near or adjacent to other handsets and hence are likely to experience feedback. This nearest neighbour data is stored in a nearest neighbour data memory 38. A digital signal processor (DSP) 34 is provided for audio processing and this is under the control of the control processor 33. The DSP 34 is connected to RF logic unit 36 which is provided with an antenna 37 for communication with the handsets. Thus in this embodiment the control unit is capable of receiving and transmitting audio communications as for example illustrated in Figure 3.

The RF logic unit 36 is also coupled directly to the control processor 33 for receiving and transmitting control signals such as control signals to enable and disable microphones on the handsets or to control the communication channels assigned to the handsets. Also, data can be transmitted and received by the control processor 33 using the RF logic unit 36. Such data can for example comprise the nearest neighbour data for use in each handset. Thus in this embodiment, the central processor 33 can process data in the database of handset location data to determine the nearest neighbour which can then be transmitted to the handsets for use in local control of feedback in each handset as an alternative to using central control in the control unit. Thus in alternative embodiments, nearest neighbour data can be stored in the control unit or in the handsets or both.

In the embodiment of Figure 4, when no control unit is present, each handset can carry out the nearest neighbour determination process and store the nearest neighbour data in the data memory 48.

A method for the control of handsets in order to reduce or avoid feedback between handsets will now be described with reference to Figure 6. In this embodiment the control of the process is performed at the control unit.

In step S50 a request to speak is received at a user's handset and this is transmitted to the control unit. The control unit identifies the handset in step S51 based on unique identification information transmitted from the handset e.g. a handset ID. The request to speak is stored in the request to speak queue memory 32. In step S52 the control processor 33 will determine whether the request has now reached a point in the queue where the user is permitted to speak. The process for a handset will wait until its turn to speak is arrived at.

When it is determined in step S52 that the user is permitted to speak, in step S53 the control unit looks up the nearest neighbours in the nearest neighbour data memory 38. The nearest neighbour data memory includes handset identifiers identifying each handset which is considered to be in the proximity of each other handset. Thus a set of zero or more handsets are identified as being nearest neighbours and hence in close enough proximity to the handset for the user requesting to speak that may result in feedback. The control unit thus broadcasts the identities of handsets to be muted and the identity of any handsets previously muted in step S54 the attention of the transmitted signal is to mute or reduce the volume output from certain handsets which may feedback to the speaker's handset and to re-enable loudspeakers which were previously muted or reduced in output volume for a previous speaker. When the nearest neighbour handsets identify themselves from the broadcast message the control processor 37 controls the DSP 42 in the handset to mute or reduce the audio output of the loudspeaker 44. In step S56 any handsets that were previously muted are identified from the broadcast signal and they re-enable their loudspeakers. The control unit transmits a microphone enable signal to be used as handset and a mike disable signal to the previous speaker's handset in step S57. As a result in step S58 the user's handset enables the microphone in receipt of the signal and a previous speaker's handset disables their microphone. Thus in this way there is a handover from one speaker to another and a change in the group of disabled loudspeakers based upon the newly appointed speaker.

In step S59 the process then awaits a new input of a request to speak on a handset.

Thus this embodiment of the present invention provides for control by a control unit transmitting control signals over the communications network to the handsets. These control signals can be transmitted independently of the audio communications channels e.g. using the communication methodologies of Figure 3 or Figure 4.

In the process of one embodiment of the present invention described with reference to Figure 6 where only a single communication channel is provided, only one speaker can speak at a time and hence only one microphone is enabled at a time. In such an embodiment the output of a loudspeaker can be completely muted or reduced to a low level to avoid the acoustic output reaching the microphone of an adjacent handset used by a speaker. In an alternative embodiment, multiple communication channels can be used. In such an embodiment each handset can be assigned a single communication channel for transmission of audio. Alternatively the control unit can control the dynamic allocation of an audio transmission channel for each handset, in this way multiple speakers can generate an audio output for transmission to other handsets wherein an audio mixer that each handset mixes the received audio for output as a combined audio output at the loudspeaker of each handset. Thus the process can allow more than one request to speak to occur at the same time. Using this arrangement, it is not necessary to completely mute or completely reduce the output sound from the loudspeaker of a handset. Instead the audio output from a loudspeaker can be selectively muted or reduced. This process will be described in more detail with reference to Figure 7. Figure 7 illustrates a multi-channel communication system which allows for one or more speakers and avoids the need to completely mute or broadly reduce the output audio from a loudspeaker which is adjacent to the handset of a speaker.

As can be seen in Figure 7, handset 60 is used by a first speaker and thus the microphone of the handset 60 is active. Two other handsets 61 and 62 are provided in the communication system. Handset 62 is also being used by a second speaker. Handset 61 is a nearest neighbour to the handset 60 of the first speaker since the output of the loudspeaker of handset 61 can be picked up by the microphone of the handset 60 of the first speaker thus introducing a feedback loop. The handset 60 of the first speaker transmits its audio output on channel 1 to the nearest neighbour listening handset 61 and to the second speaker's handset 62. The second speaker's handset 62 transmits its audio on channel 2 to the listener's handset 61 and to the first speaker's handset 60. In order to avoid feedback, the audio output received on channel 1 is muted or reduced in volume but the audio received on channel 2 is output at normal volume since it will not create a feedback loop when picked up by the microphone of the handset 60 of the first speaker. Thus the digital signal processing performed under the control of the control processor 47 in the handset will conditionally mute or reduce audio to be output on certain channels depending upon whether or not that channel is broadcast by a nearest neighbour.

To avoid feedback between the microphone and loudspeaker of a handset, whenever a speaker is given permission and a microphone is activated, for a single channel communication system, the output of the loudspeaker is muted. In this multi-channel embodiment, the two speakers using handsets 60 and 61 are still able to listen to an audio output from their loudspeakers for audio from a different handset. In other words, only audio received from the microphone of a handset that would be transmitted by the handset is muted and not output from a loudspeaker and audio received on other channels from other handsets is output at the loudspeaker. For example, handset 60 receives audio on channel 2 from the second speaker's handset 62 and this is output at the loudspeaker of handset 60. Similarly, the handset 62 of the second speaker receives audio on channel 1 from the handset 60 of the first speaker and this is output on the loudspeaker of the handset 62 of the second speaker. This arrangement of using multiple channels and only muting certain channels relating to the handset of the speaker and to nearest neighbours avoids feedback whilst allowing the handsets of the speaker and the nearest neighbours to receive audio from non-interfering handsets. The speaker and the users of the nearest neighbour handsets are able to listen to the audio from the speaker directly without requiring it to be transmitted over the communication system and output via the loudspeaker. In this way the users which are close to speakers can listen to the speaker directly and receive audio from other speakers that are remote via their handset loudspeakers. An alternative method of controlling the muting of the loudspeakers of handsets will now be described with reference to the flow diagram of Figure 8.

In this embodiment the handsets need to be configured and configuration starts in step S70. The nearest neighbour data is received in step S71 and stored. The nearest neighbour data can be received from the control unit or determined within the handset using a nearest neighbour data determination process as will be described in more detail hereinafter.

This embodiment of the present invention is based on a handset that determines that it is a nearest neighbour to a handset for a speaker performing its own muting determination and control. Thus in step S72 when a request to speak is received at a nearest neighbour handset i.e. speaking handset which is within interference range of this listing handset, in step S73 when an audio signal is received from the nearest neighbour handset the control processor 47 in the handset looks up the nearest neighbour data in the data memory 48 to determine whether the audio signal is from a nearest neighbour (step S75) if the audio signal is not from a nearest neighbour, there is no danger of feedback and thus the process ends in step S79. If the audio signal is determined to come from a nearest neighbour, in step S76 the audio is muted or reduced in its entirety in a single channel system or in a multi-channel system the audio channel from the nearest neighbour is muted or reduced (step S76). This continues until no more audio is received from the nearest neighbour (step S77). When it is determined e.g. from a period of silence that the audio from the nearest neighbour has finished, in step S78 the loudspeaker is re-enabled for full audio or the channel is re- enabled and the process terminates in step S79. Thus in this embodiment of the present invention, each handset is programmed to detect audio from neighbours to determine whether the output of the loudspeaker of the handset needs to be muted or reduced to avoid potential feedback. Figure 9 illustrates an alternative embodiment of the present invention in which the speaker's handset controls the muting of its nearest neighbours.

The process begins with the configuration in step S80 of the handsets. In step S81 nearest neighbour data is received either by downloading from the control unit, inputting manually, or a nearest neighbour detection process performed by the handset. In step S82 permission to speak is received at the user's handset. This can take the form of a simple request to speak where received no control of the speaking order takes place and anybody can speak at any time, or where a control unit controls who can speak e.g. a conference moderator can select speakers, the handset will receive control data permitting the speaker to speak.

In step S83 the nearest neighbours are looked up using the data stored in the data memory 48 and if no nearest neighbours are determined in step S84 the process ends in step S92. If it is determined that there are nearest neighbours likely to cause feedback in step S84 the speaker's handset will transmit a control signal to mute the nearest neighbours in step S85. This control signal can cause the muting of all audio from the loudspeaker of the nearest neighbour's handset, or just the output of audio for a single channel i.e. the channel on which the speaker's handset is transmitting. In step S86 the microphone of the speaker's handset is then activated and at the nearest neighbour the control signal is used to mute the audio in total or just the channel in step S87. This continues until no more audio is output from the speaker's handset in step S88. When there is no more audio transmitted from the speaker's handset, the microphone is de-activated in step S89 and a control signal is transmitted to the nearest neighbours to turn off the muting control in step S90. The nearest neighbours then receive and act upon the signal to disable the mute function in step S91 and the process terminates in step S90.

Thus in this embodiment of the present invention the speaker's handset provides a control function and no control unit is required. Thus the control methods described with reference to the flow diagrams require knowledge of nearest neighbours. As described with reference to Figure 3, this location data can take the form of handset position information determined from the physical location of the handset e.g. by fixing a cradle at a known location and recognising this at a control unit. Alternatively, the location of a handset can be input by inputting a seat location using the keypad. The identity of the handset and the position information can then be transmitted to the control unit and the control unit can include a map of the seat locations against which it can map the handset identities and thereby carry out proximity determination to determine distances between handsets and therefore the likelihood of interference. The calculation can be based on a threshold distance. If a handset is within a defined threshold distance of another handset it is considered to be a nearest neighbour of that handset. It will be apparent that nearest neighbours inherently pair up in that if a first handset is the nearest neighbour to a second handset, the second handset is also the nearest neighbour to the first handset. In this way, groups of nearest neighbours can be determined which comprise overlapping sets of handsets.

Thus the setting up of the location data can be performed when the handsets are relatively static in a meeting environment i.e. where the users sit at fixed locations during a meeting. It may be necessary to update this data periodically e.g. during meeting breaks. For example, in the embodiment of Figure 3, users may depart from the meeting area or move within the meeting area taking their handsets with them and then return to different locations. Once the handsets are placed in their cradles, the new positions of the users and hence handsets can be identified and thus the nearest neighbour data for the handsets can be updated and stored.

In alternative embodiments of the present invention, the nearest neighbour data can be determined dynamically by either detecting the location of the handsets or by detecting adjacency of handsets. There are three general methods of determining adjacency. A signal can be output from the loudspeaker of a handset which is added to or modified in a particular way which is detected by microphones of any adjacent handsets and transmitted back to the acoustic transmitting handset for comparison. This can be considered an active method. A passive method can be employed in which microphones of potentially adjacent handsets listen to the audio from a speaker and compare the detected signals to determine whether they can both hear the speaker. A third method can be employed in which handsets detect the signal strength of other handsets and base their determination of whether or not the handset is adjacent for a signal dependent upon the threshold signal strength of the signal received from the handset.

Figure 10 illustrates an active method in accordance with an embodiment of the present invention. A first handset 101 includes a signal insertion or modification device 106 for either generating a unique signal for generating a unique acoustic training output which can be overlaid over the normal acoustic output e.g. speech, or the acoustic output of a loudspeaker 107 is modified e.g. modulated in a particular way e.g. amplitude or frequency modulated so as to impart upon it a recognisable pattern.

The microphone 108 of the first handset 101 is disabled. Comparison logic 105 is provided in the first handset for comparing the signal that is inserted or the modification made to the acoustic output with a signal received from a second handset 100. The result of the comparison by the comparison logic 105 is input into control logic 104 for use in controlling the output of the loudspeaker 107 in the first handset 101 . The second handset 100 is provided with a microphone 102 and a RF logic circuit (not shown) for generating an RF signal depended upon the acoustic input detected. The loudspeaker 103 of the second handset is disabled.

Thus when the acoustic training output is output from the loudspeaker 107 of the first handset 101 and detected by the microphone 102 of the second handset 100 an RF signal is transmitted over the audio transmission channel that can be compared in the comparison logic. The comparison logic can compare the two signals using known signal comparison techniques such as correlation and if the comparison indicates that the signals are similar above a threshold this indicates that the second handset 100 is within acoustic proximity of the first handset 101 and thus the control logic 104 will operate to mute or reduce the output of the loudspeaker 107.

The logical units described with reference to Figure 10 are implemented by the digital signal processor 42 and the control processor 47 as described with reference to Figure 2. Thus the functionalities provided by a suitably programmed handset and 104, 105, and 106 can be provided as individual code modules or a combination of code.

The output of the acoustic training output can be performed during an initial training phase during which each handset outputs a signal which is unique in frequency or time i.e. the unique frequency output or a output which is temporary distinct e.g. a separate pulse for each handset. Thus each handset can learn its nearest neighbours and instead of controlling the microphones at this point since control is only required when the microphone of the nearest neighbour is activated for speaking, the handsets can store this information for use during an active session. Thus during a training phase, the microphones of certain handsets can be controlled to be switched on to listen for certain adjacent handsets. This can be controlled by a control unit, or where handsets are assigned unique communication channels, this can be performed on a channel by channel basis i.e. one handset on e.g. channel 1 switches its loudspeaker on and all the other handsets listen, then the next handset on channel 2 switches its loudspeaker on and all the other handsets listen and so on. This can be used to generate nearest neighbour data which is stored during the learning phase and can be updated periodically e.g. during breaks during the meeting. In an alternative embodiment, the process can be carried out more periodically. For example, when a user requests to speak and thus requests that their microphone becomes active, at the point of pressing the button to activate the microphone, a pulse of sound e.g. a beep or click can be output and thus the process shown in Figure 10 can take place in a short period just before a speaker speaks. This has the benefit of dynamically determining nearest neighbours at the point at which a speaker starts to speak. The acoustic pulse output can also act as an acoustic confirmation to the speaker that they have indeed pressed the microphone button and the microphone is thus now active for them to speak. It also informs listeners that the speaker is about to speak. This although it would appear that the output of a pulse of sound may be undesirable, it can be turned into a desirable effect for such speaker confirmation.

A passive process for determining nearest neighbours will now be described with reference to Figure 11. In this embodiment a first handset 110 is a handset to be used by speaker. Audio input from the speaker is detected by a microphone 112 in the first handset 110 and transmitted as an RF signal to a second handset 111. The output of a loudspeaker 113 in the first handset 110 is disabled.

In the second handset 111 , the microphone 117 is also enabled to detect any audio from the speaker. Comparison logic 114 compares the radio frequency signal transmitted over the channel from the first handset 110 with the audio from the microphone 117 to the second handset 111. The result of the comparison by the comparison logic 114 is input to control logic 115 which is used to control the loudspeaker 116 in the second handset 111.

Thus in this embodiment of the present invention, control of the loudspeaker and the identification of nearest neighbours is performed based on the concept of acoustic reciprocity i.e. if the second handset 111 is close enough to receive the acoustic output from the speaker then the acoustic output of the loudspeaker 116 of the second handset 111 is likely to be detectable by the microphone 112 of the first handset 110.

The comparison logic 114 can compare the RF signal and the signal output from the microphone 117 using any known signal comparison techniques such as correlation. If the comparison indicates the similarity above a threshold, it indicates that the handsets are adjacent and the control logic 15 will either store date identifying the handsets as adjacent and/or control the loudspeaker 1 16 accordingly to mute or reduce the acoustic output.

The method of Figure 11 has the benefit of not requiring an acoustic output to be generated which can be annoying to listeners. However, it does require an acoustic input at each handset in turn in order to learn the nearest neighbours. Thus an acoustic input could be applied to each handset during a learning phase to identify the nearest neighbours during this learning phase or whenever a speaker speaks, during an initial phase, the other handsets can listen and determine whether they are the nearest neighbours and if so switch off their loudspeakers i.e. mute or reduce the output of the loudspeakers either in total or just for the speakers channel to avoid feedback. This requires a rapid algorithm of adaption to cut out any potential feedback quickly. It does not however require data on there as neighbours to be stored. Thus the embodiments of Figures 10 and 11 can be used fully dynamically without requiring a learning phase and the storing of nearest neighbour data. The nearest neighbours can be detected and determined each time a speaker speaks either by outputting a training pulse just before the speaker speaks or using the speaker's audio input in the embodiment of Figure 11. Figure 12 illustrates an alternative embodiment of the present invention which is similar to the embodiment of Figure 11 except that it operates for multiple channels. In this embodiment of the present invention a first handset receives audio input 1 , a second handset 123 receives audio input 2 and a third handset 126 receives audio input 3. Each handset has a respective microphone 121 , 124 and 127 receiving the audio and generating a signal on a corresponding audio channel. Each handset 120, 123 and 126 also has a loudspeaker 122, 125 and 128 which is disabled.

A fourth handset 129 includes a microphone 123 which is enabled to listen for the three audio inputs. Comparison logic 123 is provided for comparing each channel of the audio received from the handsets with the output of the microphone 130. The result of the comparison is input into control logic 132. The input of the communication channels are also received by a mixer 133 to mix the audio for output to the loudspeaker 134 of the fourth handset 29. The control logic 132 thus controls the mixer to mute or reduce any of the audio channels dependent upon the comparison performed by the comparison logic 131.

Thus in this way any number of the channels can be muted or reduced dependent upon whether the handset 120, 123 or 126 is determined to be a nearest neighbour. The comparison performed in the method of Figure 11 or Figure 12 can include a comparison of the time delay for the signal received. Thus the comparison becomes a phase comparison which can be more sensitive than an amplitude comparison.

Figure 13 illustrates an alternative embodiment of the present invention for identifying nearest neighbours. In this embodiment of the present invention three RF antennae 140, 141 and 1 2 are provided for RF communications. These antennae are fixed and provide a means by which the location of handsets 143 can be determined by well known triangulation techniques. This method can be used by a control unit to monitor and update location information for handsets to be used to determine nearest neighbours and to update nearest neighbours whenever handsets move. This data can then be stored at the control unit or downloaded to the handsets. In one embodiment of the present invention, the muting of the loudspeaker and handset can be performed manually. Users of handsets can be instructed to turn off their loudspeakers whenever they can hear the speaker directly to avoid feedback. This method provides a simple control process but is reliant upon users remembering to perform the muting control function.

Although the present invention has been described with reference to specific embodiments, the present invention is not limited to these embodiments and it will be apparent to a skilled person in the art that modifications lie within the spirit and scope of the present invention.

The information identifying nearest neighbours can be predetermined and stored or nearest neighbours can be detected dynamically without requiring the storing of information identifying nearest neighbours.

The present invention is applicable to any form of wireless communication technology.

Claims

CLAIMS:

1. A method of controlling a plurality of handsets in a mobile communication system in a region, each handset having a loudspeaker and a microphone and a communication interface for receiving signals for the loudspeaker and transmitting signals received from the microphone, the method comprising:

identifying any adjacent handsets likely to cause feedback between the loudspeakers and the microphones of the adjacent handsets;

activating a microphone in a said handset for a speaker; and

muting or reducing an acoustic output of the loudspeaker of at least one other adjacent handset.

2. A method according to claim 1 , wherein the communication interface of each handset transmits signals on a separate channel and combines signals received on each channel, and the acoustic output of said loudspeaker is reduced by muting or reducing an acoustic output for signals received on a channel from at least one other adjacent handset.

3. A method according to claim 1 or claim 2, wherein a said adjacent handset is identified by a user of said adjacent handset as being adjacent to said handset for a speaker when the user can hear the speaker directly, and the user mutes or reduces the acoustic output of the loudspeaker of said adjacent handset.

4. A method according to claim 1 or claim 2, wherein a control unit controls the muting or reduction of the acoustic output of the loudspeaker of said at least one adjacent handset.

5. A method according to claim 1 or claim 2, wherein said handset for said speaker controls the muting or reduction of the acoustic output of the loudspeaker of said at least one adjacent handset.

6. A method according to claim 1 or claim 2, wherein said at least one adjacent handset controls the muting or reduction of the acoustic output of a respective said loudspeaker.

7. A method according to any one of claims, 1 , 2, 4, 5 or 6, including storing data identifying said at least one adjacent handset.

8. A method according to claim 4, including storing data identifying said at least one adjacent handset in said control unit.

9. A method according to claim 5 or claim 6, including storing data identifying said at least one adjacent handset in each said handset.

10. A method according to any one of claims 7 to 9, wherein said identifying and storing are periodically repeated to update said data.

11. A method according to any one of claims 1 , 2, or 4 to 10, wherein said identifying is performed based on location data.

12. A method according to claim 11 , wherein said location data is input by each said handset user.

13. A method according to claim 11 , wherein said location data is determined by determining the location of each said handset.

14. A method according to claim 13, wherein the location of each handset is determined by triangulation using multiple communication receiving antennae.

15. A method according to claim 13, wherein said location of each handset is determined by detecting an identity of a cradle into which the handset is placed.

16. A method according to claim 4, wherein said identifying is performed based on location data, and said location data is input at said control unit.

17. A method according to any one of claims 1 , 2, or 4 to 10, wherein said identifying comprises, for each handset, adding a training signal to a signal to the loudspeaker or modifying the signal to the loudspeaker, the acoustic output for each handset being unique in time and/or frequency; comparing a signal from the microphone with the training signal or modification; and identifying whether said handset is an adjacent handset using the result of the comparison.

18. A method according to any one of claims 1 , 2, or 4 to 10, wherein said identifying comprises, for each handset, receiving a signal from a microphone of each other handset, comparing the signal with a signal from the microphone of the handset, and identifying whether said handset is an adjacent handset using the result of the comparison.

19. A method according to any one of claims 1 , 2, or 4 to 10, wherein said identifying comprises, for each handset, receiving a signal from a microphone of each other handset, determining the signal strength or time delay of each signal, and identifying whether said handset is an adjacent handset using the result of the determination.

20. A mobile communication system comprising:

a plurality of handsets for use in a region, each handset having a loudspeaker and a microphone;

activating means for activating a microphone in a said handset; and

muting means for muting or reducing an acoustic output of the loudspeaker of at least one other adjacent handset.

21. A mobile communication system according to claim 20, including identifying means for identifying any adjacent handsets likely to cause feedback between the loudspeakers and the microphones of the adjacent handsets.

22. A mobile communication system according to claim 21 , wherein the communication interface of each handset is adapted to transmit signals on a separate channel and to combine signals received on each channel, and said muting means is adapted to reduce or mute the acoustic output of said loudspeaker by muting or reducing an acoustic output for signals received on a channel from at least one other adjacent handset.

23. A mobile communication system according to claim 21 or claim 22, said muting means including a control unit for controlling the muting or reduction of the acoustic output of the loudspeaker of said at least one adjacent handset.

24. A mobile communication system according to claim 21 or claim 22, wherein said muting means comprises a controller in said handset for said speaker for controlling the muting or reduction of the acoustic output of the loudspeaker of said at least one adjacent handset.

25. A mobile communication system according to claim 21 or claim 22, wherein said muting means comprises a controller in said at least one adjacent handset for controlling the muting or reduction of the acoustic output of a respective loudspeaker.

26. A mobile communication system according to any one of claims 21 to 25, including storage means for storing data identifying said at least one adjacent handset.

27. A mobile communication system according to claim 23, wherein said control unit includes a storage device for storing data identifying said at least one adjacent handset.

28. A mobile communication system according to claim 24 or claim 25, including a storage device for storing data identifying said at least one adjacent handset in each said handset.

29. A mobile communication system according to any one of claims 21 to 28, wherein said identifying means is adapted to perform the identifying based on location data.

30. A mobile communication system according to claim 29, wherein said handsets include input means for inputting said location data by each said handset user.

31. A mobile communication system according to claim 29, including location determining means for determining said location data by determining the location of each said handset.

32. A mobile communication system according to claim 31 , wherein said location means is adapted to determine the location of each handset by triangulation using multiple communication receiving antennae.

33. A mobile communication system according to claim 31 , including a plurality of cradles for receiving said handsets, each cradle having a unique identity and a know location, wherein said location determining means is adapted to determine said location of each handset by detecting an identity of a cradle into which the handset is placed.

34. A mobile communication system according to claim 23, wherein said control unit includes location determining means for determining said location data by determining the location of each said handset based on location data, said control unit includes user input means for inputting said location data at said control unit.

35. A mobile communication system according to any one of claims 21 to 28, wherein each handset includes a signal processor for adding a training signal to a signal to the loudspeaker or modifying the signal to the loudspeaker to make the acoustic output for each handset unique in time and/or frequency; and for comparing a signal from the microphone with the training signal or modification; and said identifying means is adapted to identify whether said handset is an adjacent handset using the result of the comparison.

36. A mobile communication system according to any one of claims 21 to 28 wherein each handset includes a signal processor for receiving a signal from a microphone of each other handset, and comparing the signal with a signal from the microphone of the handset; and said identifying means is adapted to identify whether said handset is an adjacent handset using the result of the comparison.

37. A mobile communication system according to any one of claims 21 to 28 wherein each handset includes a signal processor for receiving a signal from a microphone of each other handset, and for determining the signal strength or time delay of each signal; and said identifying means is adapted to identify whether said handset is an adjacent handset using the result of the determination.

38. A handset for use in a communication system by a user wishing to be a speaker, the handset comprising:

a loudspeaker for outputting an acoustic output from speakers using other said handsets;

a microphone for receiving an acoustic input from the user when the user is a speaker;

a communication interface for receiving signals for the loudspeaker and transmitting signals received from the microphone; and

a processor programmed to activate the microphone when the user is a speaker; and to mute or reduce an acoustic output of the loudspeaker when at least one other user of a said handset is at least one speaker using at least one handset identified to be at least one adjacent handset.

39. A handset according to claim 38, wherein said processor is programmed to identify any adjacent handsets likely to cause feedback between the loudspeakers and the microphones of the adjacent handsets.

40. A handset according to claim 39, wherein, when said user is a speaker, said processor is programmed to transmit a control signal to any said identified adjacent handsets to mute or reduce an acoustic output of the loudspeaker thereof.

41. A handset according to claim 38, wherein said communication interface is adapted to receive a control signal, and said processor is programmed to mute or reduce an acoustic output of the loudspeaker in response to said control signal.

42. A method of operating a handset in a communication system for a user wishing to be a speaker, the handset comprising a loudspeaker for outputting an acoustic output from speakers using other said handsets, a microphone for receiving an acoustic input from the user when the user is a speaker, and a communication interface for receiving signals for the loudspeaker and transmitting signals received from the microphone, the method comprising:

activating the microphone when the user is a speaker; and

muting or reducing an acoustic output of the loudspeaker when at least one other user of a said handset is at least one speaker using at least one handset identified to be at least one adjacent handset.

43. A method according to claim 42, including identifying any adjacent handsets likely to cause feedback between the loudspeakers and the microphones of the adjacent handsets.

44. A method according to claim 43, including, when said user is a speaker, transmitting a control signal to any said identified adjacent handsets to mute or reduce an acoustic output of the loudspeaker thereof.

45. A handset according to claim 32, including receiving a control signal, wherein the acoustic output of the loudspeaker is muted or reduced in response to said control signal.