(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2006/0147063 A1
`Chen
`(43) Pub. Date:
`Jul. 6, 2006
`
`US 2006O147063A1
`
`(54) ECHO CANCELLATION IN TELEPHONES
`WITH MULTIPLE MCROPHONES
`(75) Inventor: Juin-Hwey Chen, Irvine, CA (US)
`Correspondence Address:
`STERNE, KESSLER, GOLDSTEIN & FOX
`PLLC
`1100 NEW YORK AVENUE, N.W.
`WASHINGTON, DC 20005 (US)
`(73) Assignee: Broadcom Corporation, Irvine, CA
`(21) Appl. No.:
`11/239,351
`(22) Filed:
`Sep. 30, 2005
`
`Related U.S. Application Data
`(63) Continuation-in-part of application No. 1 1/215.304,
`filed on Aug. 31, 2005, which is a continuation-in
`part of application No. 11/135,491, filed on May 24,
`2005, which is a continuation-in-part of application
`
`No. 11/065,131, filed on Feb. 24, 2005, which is a
`continuation-in-part of application No. 11/018,921,
`filed on Dec. 22, 2004.
`
`Publication Classification
`
`(51) Int. Cl.
`(2006.01)
`H04B I/00
`(2006.01)
`H04M 9/08
`(52) U.S. Cl. ....................................... 381/119; 379/406.01
`(57)
`ABSTRACT
`The present invention is directed to a telephone equipped
`with multiple microphones that provides improved perfor
`mance during operation of the telephone in a speaker-phone
`mode. For example, the multiple microphones can be used
`to improve voice activity detection, which in turn, can
`improve echo cancellation. In addition, the multiple micro
`phones can be configured as an adaptive microphone array
`and used to reduce the effects of (i) room reverberation,
`when a near-end user is speaking, and/or (ii) acoustic echo,
`when a far-end user is speaking.
`
`te
`
`
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`Page 1
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`IPR PETITION
`US RE48,371
`Amazon Ex. 1010
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`SO
`A
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`50
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`Outputs firstudio signal from the first
`microghans, the first audio signal
`comprisings voice component and a
`background Roise component
`
`second microphors
`
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`
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`arease aratio ofths voice component
`to the poise component of histadio
`signal based on the content of at leastone
`of the first audio signal and the second
`audio signal to produce a third audio
`signal
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`S38
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`A
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`70
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`Output afirst audio signal from the first
`microphone, the first audio signal
`comprising avoice component and a
`background noise component
`
`second microphone
`
`Cance at least sportion ofthe
`background noise component of the first
`Budio signal based or the content of the
`second audio signal to produce a third
`adio signal
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`730
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`1100
`M
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`20
`
`30
`
`Output afirst audio signalfion the first
`miorophone, the first audio signal
`comprising avoice componentanda
`background moist component
`
`Second microphone
`
`Suppress at tastaportion of the
`background noise component of the first
`audio signal based on the contentofthe
`first audio signal and the second audio
`signal to produce a third Budio signal
`
`
`
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`
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`F.C. 1
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`Page 13
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`400 M
`
`40
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`430
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`Outputs first audio signalfion the first
`microphone, the firstadio signal
`comprising a voice component and a
`background noise component
`
`second microphont
`
`Detect time intervals in which the voico
`componentis presentin the first audio
`signal based on the conteatofthe first
`
`
`
`
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`
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`
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`
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`FC 14
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`Page 17
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`Page 18
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`Jul. 6, 2006 Sheet 18 of 30
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`0014
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`Page 19
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`Patent Application Publication
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`Jul. 6, 2006 Sheet 19 of 30
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`000Z
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`Page 20
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`Patent Application Publication Jul. 6, 2006 Sheet 20 of 30
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`Page 21
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`Patent Application Publication Jul. 6, 2006 Sheet 21 of 30
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`US 2006/0147063 A1
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`
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`FG.22A
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`FG.22B
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`FG.22C
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`FIG.22E
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`Page 22
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`Patent Application Publication Jul. 6, 2006 Sheet 22 of 30
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`US 2006/0147063 A1
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`Page 23
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`Patent Application Publication
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`Jul. 6, 2006 Sheet 23 of 30
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`US 2006/0147063 A1
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`Patent Application Publication Jul. 6, 2006 Sheet 24 of 30
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`US 2006/0147063 A1
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`Patent Application Publication
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`Jul. 6, 2006 Sheet 25 of 30
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`US 2006/0147063 A1
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`Patent Application Publication Jul. 6, 2006 Sheet 26 of 30
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`US 2006/0147063 A1
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`Patent Application Publication
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`Jul. 6, 2006 Sheet 28 of 30
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`US 2006/0147063 A1
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`Patent Application Publication Jul. 6, 2006 Sheet 29 of 30
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`US 2006/0147063 A1
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`3000
`
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`Output a first
`audio signal
`
`300
`
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`3030
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`3040
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`Output a second
`audio signal
`
`ProceSS the two
`audio signals in a
`voice activity
`detector (VAD)
`
`Cancel an echo in
`the first audio
`signal resulting in a
`third audio signal
`
`Transmit the third
`audio signal
`
`3050
`
`FIG. 30
`
`Page 30
`
`

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`Patent Application Publication
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`Jul. 6, 2006 Sheet 30 of 30
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`US 2006/0147063 A1
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`3100
`
`N
`
`Output audio signals
`from each microphone in
`a microphone array
`
`31.10
`
`Detect direction of arrival
`(DOA) of a room
`reverberation
`
`31.20
`
`Adaptively combine the
`audio signals based on the
`DOA
`
`3130
`
`FIG 31A
`
`
`
`
`
`3150
`
`Output audio signals
`from each microphone in
`a microphone array
`
`3160
`
`Detect direction of arrival
`(DOA) of sound waves
`corresponding to a far-end
`user's voice
`
`31.70
`
`Adaptively combine the
`audio signals based on the
`DOA
`
`318O
`
`FIG 31B
`
`Page 31
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`

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`US 2006/O 147063 A1
`
`Jul. 6, 2006
`
`ECHO CANCELLATION IN TELEPHONES WITH
`MULTIPLE MCROPHONES
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`0001. This application is a continuation-in-part of U.S.
`patent application Ser. No. 1 1/215.304 to Chen et al.,
`entitled “Wireless Telephone with Multiple Microphones
`and Multiple Description Transmission' and filed Aug. 31,
`2005, which is a continuation-in-part of U.S. patent appli
`cation Ser. No. 1 1/135,491 to Chen, entitled “Wireless
`Telephone with Adaptive Microphone Array' and filed May
`24, 2005, which is a continuation-in-part of U.S. patent
`application Ser. No. 11/065,131 to Chen, entitled “Wireless
`Telephone With Uni-Directional and Omni-Directional
`Microphones' and filed Feb.24, 2005, which is a continua
`tion-in-part of U.S. patent application Ser. No. 11/018,921 to
`Chen et al., entitled “Wireless Telephone Having Multiple
`Microphones' and filed Dec. 22, 2004. The entirety of each
`of these applications is hereby incorporated by reference as
`if fully set forth herein.
`
`BACKGROUND
`
`0002)
`1. Field
`0003. The present invention relates generally to tele
`phones. More specifically, the present invention relates to
`improving the performance of telephones when used in a
`Speaker-phone mode.
`0004 2. Background
`0005. Many telephones may be used in a speaker-phone
`mode. However, using a telephone in a speaker-phone mode
`may lead to adverse effects that degrade the performance of
`the telephone. These adverse effects may depend on who is
`talking-i.e., whether the user of a far-end telephone is talking
`or the user of a near-end telephone is talking.
`0006 For a near-end telephone used in speaker-phone
`mode, acoustic echo may be an issue when a far-end user is
`talking. An "acoustic echo can occur, for example, when
`the voice signal of a far-end user output by the loudspeaker
`of the near-end telephone is picked up by the microphone on
`the near-end telephone. When this occurs, an acoustic echo
`is sent back to the far-end user via the near-end telephone.
`0007 For a near-end telephone used in speaker-phone
`mode, room reverberation may be an issue when a near-end
`user is talking. The “room reverberation” effect occurs when
`a near-end user's voice reflects off the walls of a room. The
`reflection of the near-end user's voice can then be picked-up
`by the microphone on the near-end telephone. The reflected
`Sound waves picked-up by the near-end telephone make the
`near-end user's voice sound distant and unnatural to a
`far-end user.
`0008 What is needed then, are improvements to control
`acoustic echo and/or room reverberation when a telephone is
`used in a speaker phone mode.
`
`BRIEF SUMMARY
`0009. The present invention is directed to a telephone
`equipped with multiple microphones that provides improved
`performance during operation of the telephone in a speaker
`phone mode.
`
`0010. In a first embodiment of the present invention, the
`telephone includes a receiver, a loudspeaker, a first and
`second microphone, a voice activity detector (VAD), an
`echo canceller, and a transmitter. The first and second
`microphones are used to improve voice activity detection,
`which in turn, can improve echo cancellation. For example,
`the receiver receives a far-end audio signal including a voice
`component of a far-end user. The loudspeaker converts the
`far-end audio signal into Sound waves. The first microphone
`picks up the Sound waves and outputs a first audio signal.
`The first audio signal includes a first voice component
`associated with the Voice of a near-end user and a second
`voice component associated with the voice of the far-end
`user. The second microphone outputs a second audio signal.
`The VAD processes the first audio signal, the second audio
`signal and the far-end audio signal to generate output
`relating to at least one of (i) time intervals in which the first
`Voice component is present in the first audio signal and (ii)
`time intervals in which the second Voice component is
`present in the first audio signal. The echo canceller cancels
`the second Voice component included in the first audio
`signal based on the output from the VAD, thereby producing
`a third audio signal. The transmitter transmits the third audio
`signal.
`0011. In a second embodiment of the present invention,
`the telephone includes an array of microphones and a digital
`signal processor (DSP). Each microphone in the microphone
`array is configured to receive Sound waves emanating from
`the Surrounding environment and to generate an audio signal
`corresponding thereto. The DSP receives the audio signals
`from the microphone array and is configured to adaptively
`combine the audio signals to produce a first audio output
`signal. In this embodiment, the microphone array and DSP
`are configured to reduce the adverse effects of (i) room
`reverberation, when a near-end user is speaking, and/or (ii)
`acoustic echo, when a far-end user is speaking.
`0012 To reduce room reverberation in accordance with a
`first example, the DSP is configured to detect a direction of
`arrival (DOA) of sound waves emanating from the mouth of
`a near-end user based on the audio signals and to adaptively
`combine the audio signals based on the DOA to produce the
`first audio output signal. The DSP adaptively combines the
`audio signals based on the DOA to effectively steer a
`maximum sensitivity angle of the microphone array So that
`the mouth of the near-end user is within the maximum
`sensitivity angle. The maximum sensitivity angle is defined
`as an angle within which a sensitivity of the microphone
`array is above a threshold. This first example can be effective
`at reducing room reverberation when the reverberated sound
`waves are reflected from objects in the surrounding envi
`ronment in a Substantially isotropic manner.
`0013 To reduce room reverberation in accordance with a
`second example, the DSP is configured to detect a direction
`of arrival (DOA) of sound waves corresponding to a rever
`beration of a Voice of a near-end user and to adaptively
`combine the audio signals based on the DOA to produce the
`first audio output signal. The DSP combines the audio
`signals based on the DOA to effectively steer a minimum
`sensitivity angle of the microphone array so that a source of
`the reverberation of the voice of the near-end user is within
`the minimum sensitivity angle. The minimum sensitivity
`angle is defined as an angle within which a sensitivity of the
`microphone array is below a threshold.
`
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`US 2006/O 147063 A1
`
`Jul. 6, 2006
`
`0014. This second example can effectively reduce room
`reverberation when the reverberated sound waves are
`reflected from objects in the Surrounding environment in a
`highly directional manner.
`0.015 To reduce acoustic echo when a far-end user is
`speaking, the DSP is configured to perform two functions.
`First, the DSP is configured to detect a DOA of sound waves
`corresponding to the voice signal (echo) of the far-end user.
`Second, the DSP is configured to adaptively combine the
`audio signals based on the DOA to effectively steer a
`minimum sensitivity angle of the microphone array so that
`a source of the Sound waves corresponding to the far-end
`user's voice is within the minimum sensitivity angle. The
`Source of these sound waves can be, for example, a loud
`speaker of the telephone or an object that reflects sound
`waves (e.g., a wall or the like). The minimum sensitivity
`angle is defined as an angle within which a sensitivity of the
`microphone array is below a threshold.
`0016 Further embodiments and features of the present
`invention, as well as the structure and operation of the
`various embodiments of the present invention, are described
`in detail below with reference to the accompanying draw
`1ngS.
`
`BRIEF DESCRIPTION OF THE
`DRAWINGSFFIGURES
`0017. The accompanying drawings, which are incorpo
`rated herein and form a part of the specification, illustrate the
`present invention and, together with the description, further
`serve to explain the principles of the invention and to enable
`a person skilled in the pertinent art to make and use the
`invention.
`0018 FIG. 1A is a functional block diagram of the
`transmit path of a conventional wireless telephone.
`0019 FIG. 1B is a functional block diagram of the
`receive path of a conventional wireless telephone.
`0020 FIG. 2 is a schematic representation of the front
`portion of a wireless telephone in accordance with an
`embodiment of the present invention.
`0021
`FIG. 3 is a schematic representation of the back
`portion of a wireless telephone in accordance with an
`embodiment of the present invention.
`0022 FIG. 4 is a functional block diagram of a transmit
`path of a wireless telephone in accordance with an embodi
`ment of the present invention.
`0023 FIG. 5 illustrates a flowchart of a method for
`processing audio signals in a wireless telephone having a
`first microphone and a second microphone in accordance
`with an embodiment of the present invention.
`0024 FIG. 6 is a functional block diagram of a signal
`processor in accordance with an embodiment of the present
`invention.
`0025 FIG. 7 illustrates a flowchart of a method for
`processing audio signals in a wireless telephone having a
`first microphone and a second microphone in accordance
`with an embodiment of the present invention.
`0026 FIG. 8 illustrates voice and noise components
`output from first and second microphones, in an embodi
`ment of the present invention.
`
`0027 FIG. 9 is a functional block diagram of a back
`ground noise cancellation module in accordance with an
`embodiment of the present invention.
`0028 FIG. 10 is a functional block diagram of a signal
`processor in accordance with an embodiment of the present
`invention.
`0029 FIG. 11 illustrates a flowchart of a method for
`processing audio signals in a wireless telephone having a
`first microphone and a second microphone in accordance
`with an embodiment of the present invention.
`0030 FIG. 12A illustrates an exemplary frequency spec
`trum of a voice component and a background noise com
`ponent of a first audio signal output by a first microphone,
`in an embodiment of the present invention.
`0031
`FIG. 12B illustrates an exemplary frequency spec
`trum of an audio signal upon which noise Suppression has
`been performed, in accordance with an embodiment of the
`present invention.
`0032 FIG. 13 is a functional block diagram of a transmit
`path of a wireless telephone in accordance with an embodi
`ment of the present invention.
`0033 FIG. 14 is a flowchart depicting a method for
`processing audio signals in a wireless telephone having a
`first microphone and a second microphone in accordance
`with an embodiment of the present invention.
`0034 FIG. 15 shows exemplary plots depicting a voice
`component and a background noise component output by
`first and second microphones of a wireless telephone, in
`accordance with an embodiment of the present invention.
`0035 FIG. 16 shows an exemplary polar pattern of an
`omni-directional microphone.
`0036 FIG. 17 shows an exemplary polar pattern of a
`Subcardioid microphone.
`0037 FIG. 18 shows an exemplary polar pattern of a
`cardioid microphone.
`0038 FIG. 19 shows an exemplary polar pattern of a
`hypercardioid microphone.
`0039 FIG. 20 shows an exemplary polar pattern of a line
`microphone.
`0040 FIG. 21 shows an exemplary microphone array, in
`accordance with an embodiment of the present invention.
`0041
`FIGS. 22A-D show exemplary polar patterns of a
`microphone array.
`0042 FIG. 22E shows exemplary directivity patterns of
`a far-field and a near-field response.
`0043 FIG. 23 shows exemplary steered and unsteered
`directivity patterns.
`0044 FIG. 24 is a functional block diagram of a transmit
`path of a wireless telephone in accordance with an embodi
`ment of the present invention.
`0045 FIG. 25 illustrates a multiple description transmis
`sion system in accordance with an embodiment of the
`present invention.
`0046 FIG. 26 is a functional block diagram of a transmit
`path of a wireless telephone that can be used in a multiple
`
`Page 33
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`
`Jul. 6, 2006
`
`description transmission system in accordance with an
`embodiment of the present invention.
`0047 FIG. 27 illustrates multiple versions of a voice
`signal transmitted by a first wireless telephone in accordance
`with an embodiment of the present invention.
`0.048
`FIG. 28 is a functional block diagram of a tele
`phone that provides improved acoustic echo cancellation by
`using multiple microphones in accordance with an embodi
`ment of the present invention.
`0049 FIG. 29 is a functional block diagram of a transmit
`path and a receive path of a telephone that may be used to
`reduce room reverberation and/or acoustic echo, when the
`telephone is used in a speaker-phone mode, in accordance
`with an embodiment of the present invention.
`0050 FIG. 30 is a flowchart depicting a method for
`improved echo cancellation in a telephone having a first
`microphone and a second microphone in accordance with an
`embodiment of the present invention.
`0051 FIGS. 31A and 31B are flowcharts depicting
`methods for reducing the effects of room reverberation and
`acoustic echo, respectively, in a telephone used in a speaker
`phone mode and having an adaptive microphone array.
`0.052 The present invention will now be described with
`reference to the accompanying drawings. In the drawings,
`like reference numbers may indicate identical or function
`ally similar elements. Additionally, the left-most digit(s) of
`a reference number may identify the drawing in which the
`reference number first appears.
`
`DETAILED DESCRIPTION
`0053. The present invention is directed to a telephone
`implemented with multiple microphones and configured to
`provide improved echo cancellation. In addition, as will be
`described in more detail herein, the multiple microphones
`can be configured as an adaptive microphone array and may
`be used to reduce the room reverberation effect and/or
`acoustic echo, when the telephone is operated in a speaker
`phone mode.
`0054 The detailed description of the invention is divided
`into eleven subsections. In subsection I, an overview of the
`workings of a conventional wireless telephone is discussed.
`This discussion facilitates the description of embodiments of
`the present invention. In subsection II, an overview of a
`wireless telephone implemented with a first microphone and
`second microphone is presented. In Subsection III, an
`embodiment is described in which the output of the second
`microphone is used to cancel a background noise component
`output by the first microphone. In subsection IV, another
`embodiment is described in which the output of the second
`microphone is used to Suppress a background noise com
`ponent output by the first microphone. In Subsection V, a
`further embodiment is discussed in which the output of the
`second microphone is used to improve VAD technology
`incorporated in the wireless telephone. In subsection VI,
`alternative arrangements of the present invention are dis
`cussed. In Subsection VII, example uni-directional micro
`phones are discussed. In Subsection VIII, example micro
`phone arrays are discussed. In Subsection IX, a wireless
`telephone implemented with at least one microphone array
`is described. In Subsection X, a multiple description trans
`
`mission system in accordance with embodiments of the
`present invention is described. In subsection XI, embodi
`ments that use multiple microphones to improve the perfor
`mance of a telephone used in speaker-phone mode are
`described.
`I. Overview of Signal Processing within Conventional Wire
`less Telephones
`0055 Conventional wireless telephones use what is com
`monly referred to as encoder/decoder technology. The trans
`mit path of a wireless telephone encodes an audio signal
`picked up by a microphone onboard the wireless telephone.
`The encoded audio signal is then transmitted to another
`telephone. The receive path of a wireless telephone receives
`signals transmitted from other wireless telephones. The
`received signals are then decoded into a format that an end
`user can understand.
`0056 FIG. 1A is a functional block diagram of a typical
`transmit path 100 of a conventional digital wireless tele
`phone. Transmit path 100 includes a microphone 109, an
`analog-to-digital (A/D) converter 101, a noise Suppressor
`102, a voice activity detector (VAD) 103, a speech encoder
`104, a channel encoder 105, a modulator 106, a radio
`frequency (RF) module 107, and an antenna 108.
`0057 Microphone 109 receives a near-end user's voice
`and outputs a corresponding audio signal, which typically
`includes both a voice component and a background noise
`component. The A/D converter 101 converts the audio signal
`from an analog to a digital form. The audio signal is next
`processed through noise Suppressor 102. Noise Suppressor
`102 uses various algorithms, known to persons skilled in the
`pertinent art, to suppress the level of embedded background
`noise that is present in the audio signal.
`0058 Speech encoder 104 converts the output of noise
`suppressor 102 into a channel index. The particular format
`that speech encoder 104 uses to encode the signal is depen
`dent upon the type of technology being used. For example,
`the signal may be encoded in formats that comply with GSM
`(Global Standard for Mobile Communication), CDMA
`(Code Division Multiple Access), or other technologies
`commonly used for telecommunication. These different
`encoding formats are known to persons skilled in the rel
`evant art and for the sake of brevity are not discussed in
`further detail.
`0059) As shown in FIG. 1A, VAD 103 also receives the
`output of noise suppressor 102. VAD 103 uses algorithms
`known to persons skilled in the pertinent art to analyze the
`audio signal output by noise Suppressor 102 and determine
`when the user is speaking. VAD 103 typically operates on a
`frame-by-frame basis to generate a signal that indicates
`whether or not a frame includes Voice content. This signal is
`provided to speech encoder 104, which uses the signal to
`determine how best to process the frame. For example, if
`VAD 103 indicates that a frame does not include voice
`content, speech encoder 103 may skip the encoding of the
`frame entirely.
`0060 Channel encoder 105 is employed to reduce bit
`errors that can occur after the signal is processed through the
`speech encoder 104. That is, channel encoder 105 makes the
`signal more robust by adding redundant bits to the signal.
`For example, in a wireless phone implementing the original
`GSM technology, a typical bit rate at the output of the speech
`
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`US 2006/O 147063 A1
`
`Jul. 6, 2006
`
`encoder might be about 13 kilobits (kb) per second, whereas,
`a typical bit rate at the output of the channel encoder might
`be about 22 kb/sec. The extra bits that are present in the
`signal after channel encoding do not carry information about
`the speech; they just make the signal more robust, which
`helps reduce the bit errors.
`0061 The modulator 106 combines the digital signals
`from the channel encoder into symbols, which become an
`analog wave form. Finally, RF module 107 translates the
`analog wave forms into radio frequencies, and then trans
`mits the RF signal via antenna 108 to another telephone.
`0062 FIG. 1B is a functional block diagram of a typical
`receive path 120 of a conventional wireless telephone.
`Receive path 120 processes an incoming signal in almost
`exactly the reverse fashion as compared to transmit path
`100. As shown in FIG. 1B, receive path 120 includes an
`antenna 128, an RF module 127, a channel decoder 125, a
`speech decoder 124, a digital to analog (D/A) converter 122,
`and a speaker 129.
`0063. During operation, an analog input signal is
`received by antenna 128 and RF module 127 translates the
`radio frequencies into baseband frequencies. Demodulator
`126 converts the analog waveforms back into a digital
`signal. Channel decoder 125 decodes the digital signal back
`into the channel index, which speech decoder 124 converts
`back into digitized speech. D/A converter 122 converts the
`digitized speech into analog speech. Lastly, speaker 129
`converts the analog speech signal into a sound pressure
`wave so that it can be heard by an end user.
`II. Overview of a Wireless Telephone Having Two Micro
`phones in Accordance with The Present Invention
`0064. A wireless telephone in accordance With an
`embodiment of the present invention includes a first micro
`phone and a second microphone. As mentioned above and as
`will be described in more detail herein, an audio signal
`output by the second microphone can be used to improve the
`quality of an audio signal output by the first microphone or
`to support improved VAD technology.
`0065 FIGS. 2 and 3 illustrate front and back portions,
`respectively, of a wireless telephone 200 in accordance with
`an embodiment of the present invention. As shown in FIG.
`2, the front portion of wireless telephone 200 includes a first
`microphone 201 and a loudspeaker 203 located thereon.
`First microphone 201 is located so as to be close to a user's
`mouth during regular use of wireless telephone 200. Speaker
`203 is located so as to be close to a user's ear during regular
`use of wireless telephone 200.
`0.066 As shown in FIG. 3, second microphone 202 is
`located on the back portion of wireless telephone 200.
`Second microphone 202 is located so as to be further away
`from a user's mouth during regular use than first microphone
`201, and preferably is located to be as far away from the
`user's mouth during regular use as possible.
`0067 By mounting first microphone 201 so that it is
`closer to a user's mouth than second microphone 202 during
`regular use, the amplitude of the user's voice as picked up
`by the first microphone 201 will likely be greater than the
`amplitude of the user's voice as picked up by second
`microphone 202. Similarly, by so mounting first microphone
`201 and second microphone 202, the amplitude of any
`
`background noise picked up by second microphone 202 will
`likely be greater than the amplitude of the background noise
`picked up by first microphone 201. The manner in which the
`signals generated by first microphone 201 and second micro
`phone 202 are utilized by wireless telephone 200 will be
`described in more detail below.
`0068 FIGS. 2 and 3 show an embodiment in which first
`and second microphones 201 and 202 are mounted on the
`front and back portion of a wireless telephone, respectively.
`However, the invention is not limited to this embodiment
`and the first and second microphones may be located in other
`locations on a wireless telephone and still be within the
`Scope of the present invention. For performance reasons,
`however, it is preferable that the first and second microphone
`be mounted so that the first microphone is closer to the
`mouth of a user than the second microphone during regular
`use of the wireless telephone.
`0069 FIG. 4 is a functional block diagram of a transmit
`path 400 of a wireless telephone that is implemented with a
`first microphone and a second microphone in accordance
`with an embodiment of the present invention. Transmit path
`400 includes a first microphone 201 and a second micro
`phone 202, and a first A/D converter 410 and a second A/D
`converter 412. In addition, transmit path 400 includes a
`signal processor 420, a speech encoder 404, a channel
`encoder 405, a modulator 406, an RF module 407, and an
`antenna 408. Speech encoder 404, channel encoder 405,
`modulator 406, RF module 407, and antenna 408 are respec
`tively analogous to speech encoder 104, channel encoder
`105, modulator 106, RF module 107, and antenna 108
`discussed with reference to transmit path 100 of FIG. 1A
`and thus their operation will not be discussed in detail below.
`0070 The method by which audio signals are processed
`along transmit path 400 of the wireless telephone depicted in
`FIG. 4 will now be described with reference to the flowchart
`500 of FIG.5. The present invention, however, is not limited
`to the description provided by the flowchart 500. Rather, it
`will be apparent to persons skilled in the relevant art(s) from
`the teachings provided herein that other functional flows are
`within the scope and spirit of the present invention.
`0.071) The method of flowchart 500 begins at step 510, in
`which first microphone 201 outputs a first audio signal,
`which includes a voice component and a background noise
`component. A/D converter 410 receives the first audio signal
`and converts it from an analog to digital format before
`providing it to signal processor 420.
`0072 At step 520, second microphone 202 outputs a
`second audio signal, which also includes a voice component
`and a background noise component. A/D converter 412
`receives the second audio signal and converts it from an
`anal