(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2008/0076489 A1
`(43) Pub. Date:
`Mar. 27, 2008
`Rosener et al.
`
`US 2008.0076489A1
`
`(54) PHYSICALLY AND
`ELECTRICALLY-SEPARATED,
`DATA-SYNCHRONIZED DATA SINKS FOR
`WIRELESS SYSTEMS
`
`(75) Inventors:
`
`Douglas K. Rosener, Santa Cruz,
`CA (US); Jay Wilson, Portola
`Valley, CA (US); Scott Walsh,
`Foxham (GB); David Huddart,
`Westbury-on-Trym (GB); Andrew
`Knowles, Southampton (GB)
`
`Correspondence Address:
`PLANTRONICS, INC.
`345 ENCINAL STREET, P.O. BOX 635
`SANTA CRUZ, CA 95060-0635
`
`(73) Assignee:
`
`PLANTRONICS, INC.
`
`(21) Appl. No.:
`
`11/500,571
`
`(22) Filed:
`
`Aug. 7, 2006
`
`
`
`Publication Classification
`
`(51) Int. Cl.
`(2006.01)
`H04M I/00
`(52) U.S. Cl. .................................................... 455/575.2
`(57)
`ABSTRACT
`Wireless systems having a plurality of physically and elec
`trically-separated data sinks. An exemplary wireless system
`includes first and second data sinks having no physical or
`electrical connection therebetween. The first and second
`data sinks each include a wireless communication device,
`e.g., a radio frequency (RF) receiver or transceiver config
`ured to receive data signals over one or more single-access
`wireless links or over a multi-access wireless link. The first
`and second data sinks in exemplary embodiments may
`comprise audio data sinks, e.g., Stereo speakers, left-ear and
`right-ear earphones (e.g., earbuds or canalphones), left-ear
`and right-ear circum-aural over-the-ear headphones, etc. At
`least one of the first and second data sinks may also be
`coupled to a wireless transmitter and accompanying data
`Source (e.g., a microphone or sensor), so as to provide, for
`example, two-way communications between a user and an
`external data device (e.g., a cellular telephone).
`
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`Patent Application Publication Mar. 27, 2008 Sheet 1 of 13
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`US 2008/0076489 A1
`
`Mar. 27, 2008
`
`PHYSICALLY AND
`ELECTRICALLY-SEPARATED,
`DATA-SYNCHRONIZED DATA SINKS FOR
`WIRELESS SYSTEMS
`
`FIELD OF THE INVENTION
`0001. The present invention relates to wireless systems.
`More particularly, the present invention relates to wireless
`communication between a data source and two or more and
`physically and electrically-separated wireless data sinks
`Such as, for example, wireless earphones.
`
`BACKGROUND OF THE INVENTION
`0002 Headphones have come into widespread use ever
`since they were invented in the late 1930s. Today, head
`phones are used in numerous industrial settings, for listening
`to music and radio broadcasts, and for receiving voice
`communications from mobile telephones. A conventional
`pair of headphones comprises a pair of Sound transducers
`(i.e., speakers), which are configured to receive electrical
`signals from an audio source (e.g., compact disk (CD)
`player, digital audio player (MP3 player), cellular telephone,
`personal digital assistant (PDA), or personal computer) and
`provide Sound to a user's ears.
`0003 FIGS. 1A and 1B are illustrations of a user 100
`wearing two different types of early-model headsets The
`headset in FIG. 1A comprises a pair of headphones 102,104,
`a headband 106 and a pair of electrical cables 108, 110,
`which connect the headphones 102, 104 to an external audio
`source. The headband 106 is worn over the top of the user's
`100 head, and physically connects the pair of headphones
`102, 104. A cable clip 112 may be used to secure the
`electrical cables 108, 110 so that they do not interfere with
`the movement of the user 100 and to prevent tangling of the
`electrical cables 108, 110. The headset in FIG. 1B is similar
`to the headset in FIG. 1A, except that only a single electrical
`cable 114 is connected between one of the headphones 102,
`104 and the audio source. Because cabling is provided only
`to a single headphone 102, electrical wiring is routed
`through the headband 106 to electrically connect the head
`phones 102, 104. The headsets in FIGS. 1A and 1B are often
`referred to in the art as “binaural headsets since they each
`comprise a headset having a pair of headphones 102,104 for
`each of the user's 100 ears.
`0004 Recent advances in wireless technology have
`allowed the design and manufacture of wireless headsets.
`For example, the recent introduction of the Bluetooth indus
`trial specification (also known as the IEEE 802.15.1 stan
`dard) allows a user to establish a short range wireless
`personal area network (PAN) in which various electronic
`devices (e.g., cell phones, PDAs, MP3 players, personal
`computers, printers, etc.) can communicate with each other
`over wireless links. Because the PAN is a radio communi
`cation system using low gain antennas, the Bluetooth
`enabled devices do not have to be in line of sight of each
`other. Furthermore, because the PAN is completely wireless,
`the clutter and obstruction of electrical cables can be
`avoided.
`0005 FIG. 2 is an illustration of a user 200 wearing a
`binaural Bluetooth enabled headset. Similar to the wired
`headsets in FIGS. 1A and 1B, the Bluetooth enabled headset
`in FIG. 2 comprises a pair of headphones 202, 204 and a
`headband 206, which physically connects the pair of head
`
`phones and provides Support for positioning the headset over
`the user's 200 head. Electrical wiring within the headband
`206 electrically connects the pair of headphones 202, 204.
`Rather than using electrical cabling between the headphones
`202, 204 and the external audio source, as is done in the
`conventional wired headsets in FIGS. 1A and 1B, one of the
`headphones 202, 204 of the Bluetooth enabled headset
`includes a Bluetooth transceiver that wirelessly communi
`cates with a Bluetooth enabled external audio source 208
`over a wireless link 210.
`0006. The binaural wireless headset in FIG. 2 does afford
`the benefits of wireless operation. However, similar to the
`traditional wired headsets shown in FIGS. 1A and 1B, the
`headphones 202, 204 are physically connected by a head
`band 206. Some users find wearing a headband to be
`uncomfortable and/or disruptive to their headdress or coif.
`fure.
`0007. One way to avoid the drawbacks associated with
`use of a headband is to use a pair of conventional wired
`earbuds. An earbud is a small headphone that fits into the
`concha of the pinna of the user's ear. FIG. 3 shows a user
`300 wearing a pair of wired earbuds 302, 304. A pair of
`electrical cables 306, 308 connects transducers within the
`earbuds 302, 304 to an external audio source. A cable clip
`310 may also be used to secure the electrical cables 306, 308
`so that they do not interfere with the movement of the user
`300 and to prevent tangling of the electrical cables 308, 310.
`While use of earbuds does avoid the drawbacks of having to
`wear a headband, their use still requires cabling (i.e. wires)
`between the earbuds and the external audio device.
`0008 Another type of headset that avoids the use of a
`headband is the Bluetooth enabled over-the-ear wireless
`headset. This type of headset is known in the art as a
`“monaural headset, since it operates with only one of the
`user's two ears. FIG. 4 is an illustration of a user 400
`wearing a Bluetooth enabled over-the-ear wireless headset.
`The headset includes a headphone 402 and an earloop 404
`that is configured to fit around the outer ear of the user 400.
`The headphone 402 includes a single audio transceiver for
`placement near the ear and a voice tube 406 for directing
`sound from the user's voice to a microphone within the
`headphone housing. The single audio transceiver commu
`nicates with an external wireless audio device 408 (e.g., a
`cellular telephone) over a wireless link 410.
`0009. Because the Bluetooth enabled over-the-ear wire
`less headset is monaural, it is incapable of providing high
`fidelity stereo audio to the user 400. For this reason, such
`devices are used primarily for enabling hands-free operation
`of a mobile telephone and not for listening to music.
`00.10 Each of the various types of prior art headsets
`described above has its own unique benefits and drawbacks.
`For example, a benefit of the conventional wired binaural
`headsets in FIGS. 1A and 1B are that they are relatively
`inexpensive to manufacture and acquire. A benefit of the
`binaural Bluetooth enabled headset in FIG. 2 is that it is
`wireless and provides stereo audio. Unfortunately, each of
`these three types of headsets requires the use of a headband
`and/or an electrical connection (i.e., electrical wiring)
`between the two headphones of the headset. The earbud type
`headset is beneficial in that it obviates the need for a
`headband. However, the earbuds are also wired, i.e., require
`cabling to electrically connect the transducers in the earbuds
`to an external audio device. Finally, whereas the Bluetooth
`enabled over-the-ear wireless headset avoids both the need
`
`15
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`

`US 2008/0076489 A1
`
`Mar. 27, 2008
`
`for a headband and the need for cabling to connect to an
`external audio device, it is, unfortunately, monaural. Con
`sequently, it is incapable of providing high-quality stereo
`Sound to a user.
`
`BRIEF SUMMARY OF THE INVENTION
`Wireless systems having a plurality of physically
`0011
`and electrically-separated data sinks are disclosed. An exem
`plary wireless system includes first and second data sinks
`having no physical or electrical connection therebetween.
`The first and second data sinks each include a wireless
`communication device, e.g., a radio frequency (RF) receiver
`or transceiver configured to receive data signals over one or
`more single-access wireless links or over a multi-access
`wireless link. The first and second data sinks in exemplary
`embodiments described herein comprise audio data sinks,
`e.g., left-ear and right-ear earphones (e.g., earbuds or canal
`phones), left-ear and right-ear circum-aural over-the-ear
`headphones, Stereo speakers, speakers for a Surround Sound
`system, etc. At least one of the first and second data sinks
`may also be coupled to a wireless transmitter and accom
`panying data source (e.g., a microphone or sensor), so as to
`provide, for example, two-way communications between a
`user and an external data device (e.g., a cellular telephone).
`Those of ordinary skill in the art will readily appreciate and
`understand that the inventions defined by the claims attached
`hereto are not be limited to or by the summary of the
`exemplary embodiments provided here or to or by the
`detailed description of the exemplary embodiment set forth
`below.
`0012. Further features and advantages of the present
`invention, as well as the structure and operation of the
`various exemplary embodiments of the present invention,
`are described in detail below with respect to accompanying
`drawings, in which like reference numbers are used to
`indicate identical or functionally similar elements.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0013 FIG. 1A is an illustration of a user wearing a prior
`art headset comprising a pair of headphones connected by a
`headband, where both headphones are connected to a pair of
`cables leading to an external audio Source;
`0014 FIG. 1B is an illustration of a user wearing a prior
`art headset comprising a pair of headphones connected by a
`headband, where only one of the pair of headphones is
`connected to a cable leading to an external audio source, and
`where the headphones are electrically coupled by wiring
`within the headband of the headset:
`0015 FIG. 2 is an illustration of a user wearing a prior art
`binaural Bluetooth enabled headset having a headband that
`physically connects the two headphones of the headset:
`0016 FIG. 3 is an illustration of a user wearing a pair of
`prior art wired earbuds;
`0017 FIG. 4 is an illustration of a user wearing a prior art
`Bluetooth enabled over-the-ear monaural wireless headset:
`0018 FIG. 5 is an illustration of a user wearing a wireless
`headset comprising first and second wireless earphone, in
`accordance with an embodiment of the present invention;
`0019 FIG. 6 is a diagram showing a wireless system that
`may be used to wirelessly transmit data signals to two or
`more data sinks, in accordance with an embodiment of the
`present invention;
`
`0020 FIG. 7A is a diagram of a two-stage transmitter that
`may be used to implement each of the first and second
`transmitters in the wireless system shown in FIG. 6, in
`accordance with embodiments of the present invention;
`0021
`FIG. 7B is a diagram of a direct conversion trans
`mitter that may be used to implement each of the first and
`second transmitters in the wireless system shown in FIG. 6,
`in accordance with embodiments of the present invention;
`0022 FIG. 8A is a diagram of a superheterodyne receiver
`that may be used to implement each of the first and second
`receivers in the wireless system shown in FIG. 6, in accor
`dance with embodiments of the present invention;
`0023 FIG. 8B is a diagram of a direct conversion
`receiver that may be used to implement each of the first and
`second receivers in the wireless system shown in FIG. 6, in
`accordance with embodiments of the present invention;
`0024 FIG. 9 is a diagram of an RF transceiver that may
`be used in place of one or more of the RF transmitters and
`receivers of the various disclosed embodiments, in accor
`dance with embodiments of the present invention;
`0025 FIG. 10 is a diagram showing a wireless system
`that may be used to wirelessly transmit data signals to two
`or more data sinks, in accordance with an embodiment of the
`present invention;
`0026 FIG. 11 is a diagram showing a wireless system
`that may be used to wirelessly transmit data signals to two
`or more data sinks, in accordance with an embodiment of the
`present invention;
`0027 FIG. 12 is a diagram showing a wireless system
`that may be used to wirelessly transmit data signals to two
`or more data sinks, in accordance with an embodiment of the
`present invention;
`0028 FIG. 13 is a diagram showing a wireless system
`that may be used to wirelessly transmit data signals to two
`or more data sinks, in accordance with an embodiment of the
`present invention; and
`0029 FIG. 14 is a diagram showing a wireless system
`that may be used to wirelessly transmit data signals to two
`or more data sinks, in accordance with an embodiment of the
`present invention.
`
`DETAILED DESCRIPTION
`0030 FIG. 5 is an illustration of a user 500 wearing a
`wireless headset comprising first and second wireless ear
`phones 502,504, in accordance with an embodiment of the
`present invention. Each of the first and second wireless
`earphones 502, 504 comprises a housing containing a
`speaker, an RF receiver or transceiver and a battery. The
`speaker may comprise, for example, a magnetic element
`attached to a voice-coil-actuated diaphragm, an electrostati
`cally charged diaphragm, a balanced armature driver, or a
`combination of one or more of these transducer elements. As
`explained in detail below, the receiver or transceiver of each
`of the first and second earphones 502, 504 is operable to
`communicate with one or more external data or audio data
`devices (e.g., a cellular telephone, PDA, MP3 player, CD
`player, radio, personal computer, game console, etc.) over
`one or more wireless links. Each of the first and second
`earphones 502, 504 may be in the form of an earbud
`designed to fit into the concha of the pinna of the user's ear;
`a canalphone, which can be fitted within the ear canal of the
`user's ear; an over-the-ear circum-aural type headphone; or
`any other Suitable configuration that may be attached to,
`worn on, or fitted within the user's ear. Each of the first and
`
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`
`second earphone 502, 504 may further include a clip,
`earloop, or other Suitable securing mechanism to help main
`tain the earphone 502 or 504 on the ear of the user. Either
`or both of the first and second earphones 502, 504 may
`further be coupled to a second data or audio data source Such
`as, for example, a sensor or a microphone for capturing
`sound waves generated by the user's 500 voice.
`0031
`FIG. 6 is a diagram showing a wireless system 600
`that may be used to wirelessly transmit data signals to first
`and second data sinks 602, 606, in accordance with an
`embodiment of the present invention. According to this and
`other exemplary embodiments of the invention, the data
`signals may comprise audio data signals, and the first and
`second data sinks 602, 606 may correspond to the first and
`second earphones 502,504 in FIG. 5. The first data sink 602
`is electrically coupled to a first radio frequency (RF)
`receiver 604 and the second data sink 606 is electrically
`coupled to a second RF receiver 608. The first and second
`RF receivers 604, 608 may be analog or digital receivers.
`0032. A first RF transmitter 610 is adapted to be wire
`lessly coupled to the first RF receiver 604 over a first
`single-access wireless link 612, and a second RF transmitter
`614 is adapted to be wirelessly coupled to the second RF
`receiver 608 over a second single-access wireless link 616.
`The first and second RF transmitters 610, 614 may be analog
`or digital transmitters. Further, in an alternative embodi
`ment, one or more of the first and second RF receivers 604,
`608 and first and second RF transmitters 610, 614 may
`comprise one or more RF transceivers, which allow com
`munication in both directions of the first and second single
`access wireless links 612, 616.
`0033. The first and second RF transmitters 610, 614 are
`adapted to receive data signals from a data source 618. The
`data Source 618 may comprise a digital data source or an
`analog data source. For example, the data source 618 may be
`provided from a digital audio data output of an MP3 player,
`CD player, PC, PDA, mobile telephone, game console,
`component of an entertainment system, etc. If the data
`Source 618 is an analog data source, and the RF transmitters
`610, 614 are digital transmitters, an analog-to-digital con
`verter (A/D converter) may be provided, either as part of the
`processing circuitry of the RF transmitter 610 or external to
`the RF transmitter 610, to convert the analog data signals to
`digital data signals.
`0034. In the wireless system 600 shown in FIG. 6, the
`data source 618 is electrically coupled to both the first and
`second transmitters 610, 614, as indicated by the “CH1 and
`“CH 2 labels in the drawing. According to an exemplary
`embodiment, the data provided by the data source 618
`comprises first and second digital data streams having data
`packets formatted in compliance with any one of various
`wireless technologies. For example, Gaussian Frequency
`Shift Keying (GFSK) or Frequency-Shift Keying (FSK) are
`two exemplary modulation schemes that may be used to.
`The baseband portions of the first and second RF transmit
`ters 610, 614 may also be configured to operate on the data
`packets to provide error correction, source encoding and/or
`channel encoding for error minimization, compression and/
`or data redundancy purposes.
`0035. According to an aspect of the invention, the base
`band portion of the first and second RF transmitters 610,614
`in the embodiment of the invention shown in FIG. 4, as well
`as in other embodiments in this disclosure, process and
`configure the incoming data from the data source 618 into
`
`data packets compliant with the Bluetooth radio standard.
`Details concerning the Bluetooth radio standard may be
`found in “Bluetooth End-to-End' by Dee Bakker, Diane
`McMichael Gilster and Ron Gilster, Hungry Minds, Inc.,
`2002 (ISBN: 0-7645-4887-5), which is incorporated into
`this disclosure by reference. Those of ordinary skill in the art
`will readily appreciate and understand that, whereas the
`Bluetooth radio standard may be used, that other low power
`radio standards and communication protocols may alterna
`tively be used.
`0036. As shown in FIG. 6, the data signals from the data
`Source 618 are separated into first and second data streams.
`The first and second data streams are modulated onto RF
`carriers by the first and second RF transmitters 610, 614 and
`wirelessly transmitted to the first and second RF receivers
`604, 608, via the first and second single-access wireless
`links 612, 616. Upon receiving the first and second data
`streams, the first and second RF receivers 604, 608 down
`convert the modulated RF carriers and electrically couple
`the demodulated first and second data streams to the first and
`second data sinks 602, 606. The baseband portions of the
`first and second RF receivers 604, 608 may also contain, if
`necessary, a digital-to-analog (D/A) converter and/or other
`or additional processing circuitry to facilitate the electrical
`coupling of the first and second RF receivers 604, 608 to the
`first and second data sinks 602, 606. Alternatively, such
`components may be included as part of the data sinks 602,
`606 themselves. These additional conversion and signal
`processing aspects may also be applied to other embodi
`ments of the invention disclosed herein.
`0037. If the first and second RF transmitters 610, 614 and
`first and second RF receivers 604, 608 are implemented as
`digital transmitters and receivers, the first and second RF
`transmitters 610, 614 and first and second RF receivers 604,
`608 may include data buffers to compensate data packet
`losses. To compensate for data packet losses, which may be
`caused by, for example, radio interference, data buffers may
`be included in each of the first and second RF transmitters
`610, 614. Accordingly, if a data packet is lost or for some
`reason not received by an intended one of the first and
`second RF receivers 604, 608, the receiver not receiving the
`data packet may request a resend (ARQ). So long as the
`communication rate between the requesting receiver and the
`corresponding transmitter is faster than the data consump
`tion rate of the receivers, the resending of the data packet
`results in no loss of information to the corresponding data
`sink 602 or 604.
`0038 Timing differences between the first and second
`data streams may also be of concern, particularly in appli
`cations where the data packets comprise audio data. Audio
`data can be monophonic or stereophonic. In either case, a
`listener does not perceive delay differences (differential
`latency) between the left and right speakers (i.e., left and
`right data sinks 602, 604), so long as the audio data packets
`in the first and second data streams arrive at the first and
`second data sinks 602, 606 within about 100 us of each
`other. Nevertheless, in some circumstances either or both of
`the analog-to-digital (A/D) converters of the first and second
`RF receivers 604, 608 may consume data faster or slower
`than the data provided by the first and second RF transmit
`ters 610, 614. If either one of the A/D converters is too slow,
`data sent by the corresponding one of the first and second RF
`transmitters 610, 614 will be lost at the sending end since the
`data has no place to go. On the other hand, the A/D converter
`
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`
`will stall if it operates too fast, since it will run out of data
`faster than data is provided to it.
`0039. There are a number of ways to compensate for
`differential latencies between the first and second data
`streams. One way is to include data buffers in each of the
`first and second RF receivers 604, 608 and control the
`buffers so that they maintain a predetermined constant
`occupancy. So, for example, if the data occupancy of a data
`buffer of one of the first and second RF receivers 604, 608
`becomes too low (e.g., due to a fast A/D converter), inter
`polated or repeated data samples may be inserted into the
`data buffer to increase the data occupancy of the buffer,
`thereby forcing the buffer to maintain the intended prede
`termined data occupancy. Conversely, if the data occupancy
`of the data buffer becomes too high (e.g., due to a slow A/D
`converter) data samples may be removed from the buffer to
`reduce the data occupancy.
`0040 Another way to synchronize the first and second
`data streams (i.e., reduce the differential latency of the first
`and second data streams) is to embed the data sample clock
`used by the first and second RF transmitters 610, 614 in the
`RF carrier signals used to carry the first and second data
`streams over the first and second wireless links 612, 616.
`This may be accomplished by, for example, modulating each
`of the RF carrier signals associated with the first and second
`RF transmitters 610, 614 with analog subcarrier signals,
`which are synchronized with the data source sample clock
`used at the transmitting end of the system 600. The subcar
`rier signals can be detected by the respective first and second
`RF receivers 604, 608 and converted into digital clocks
`which can drive the A/D converters of the first and second
`RF receivers 604, 608.
`0041. Yet still another way to reduce the differential
`latency of the first and second data streams is to exclusive
`OR a pseudo-random noise sequence (PRNS) into the digital
`modulation of the carrier signals, similar to as is used by the
`TIA/IS-95 radio standard. If the PRNS used for the first and
`second data streams is sufficiently long, the PRNS can be
`correlated at the first and second RF receivers 604, 608, and
`the delay between the send and receive clocks can be
`deduced.
`0042 Finally, but not necessarily lastly, the differential
`latency between the first and second data streams may be
`reduced by monitoring the data buffers or delays, and
`adjusting the clock signals used by the A/D converters of the
`first and second RF receivers 604, 608. Accordingly, if the
`occupancy of a data buffer of one of the first and second RF
`receivers 604, 608 is too low (or the receive clock/sample
`clock delay is decreasing), the A/D clock is slowed down.
`Conversely, if it is determined that the occupancy of the data
`buffer is too high (or the delay is increasing), the A/D clock
`is sped up.
`0043. The first and second RF transmitters 610, 614 and
`first and second RF receivers 604, 608 may be implemented
`in various ways. Below is a description of a few examples
`of how the transmitters and receivers may be implemented.
`Those of ordinary skill in the art will appreciate and under
`stand that these transmitter and receiver implementations are
`provided here for illustrative purposes only and that other
`types of transmitters and receivers may alternatively be
`used.
`0044 FIG. 7A is a diagram of a two-stage (heterodyne)
`transmitter 700 that may be used to implement each of the
`first and second transmitters 610, 614 in the wireless system
`
`600 in FIG. 6. The two-stage transmitter 700 comprises a
`quadrature modulator 702, a first band-pass filter 704, an RF
`upconverter 706, a second band-pass filter 708 an RF power
`amplifier 710, and an antenna 712. The quadrature modu
`lator 702 is operable to receive in-phase (I) and quadrature
`(Q) channels of the first data stream from the data source 618
`and upconvert the data to an intermediate frequency (IF). If
`necessary, data from the data source 618 may be coupled to
`a signal conditioning circuit 701 to provide analog-to-digital
`conversion, filtering, amplification and/or other signal pro
`cessing functions, before the data is coupled to the baseband
`portion (i.e., baseband processor 703) of the transmitter 700.
`The first band-pass filter 704 suppresses harmonics gener
`ated by the IF modulation process and provides the filtered
`output to the RF upconverter 706, which operates to upcon
`vert the filtered IF signal to RF. The second band-pass filter
`708 removes unwanted sidebands generated by the RF
`upconversion process and couples the filtered output to an
`input of the RF power amplifier 710. The RF power ampli
`fier 710 amplifies the filtered signals and couples the data
`modulated RF signal to the antenna 712, which radiates the
`modulated RF signal to the first RF receiver 604 over the
`first single-access wireless link 612. A second two-stage
`transmitter operates similarly to upconvert and modulate the
`I and Q channels of the second data stream from the data
`source 618 onto an RF carrier signal, which is radiated to the
`second RF receiver 608 over the second single-access link
`616.
`0045 FIG. 7B is a diagram of a direct conversion (homo
`dyne) transmitter 750 that may be used to implement each of
`the first and second transmitters 610, 614 in the wireless
`system 600 in FIG. 6. The direct conversion transmitter 750
`comprises a quadrature modulator 752, a band-pass filter
`754, an RF power amplifier 756, and an antenna 758. Rather
`than using two two-stage transmitters 700 to upconvert the
`first and second data streams to RF, as is may be done with
`the two-stage transmitter 700 in FIG. 7A, two direct con
`version transmitters 750 may be used. By using a local
`oscillator frequency that is equal to the RF carrier frequency,
`the two direct conversion transmitters are operable to
`directly upconvert the first and second data streams to
`modulated RF carriers in a single upconversion process.
`0046 FIG. 8A is a diagram of a superheterodyne receiver
`800 that may be used to implement each of the first and
`second receivers 604, 608 in the wireless system 600 in FIG.
`6. The superheterodyne receiver 800 comprises a front-end
`stage, an RF downconverter, an automatic gain control
`(AGC) amplifier 816, and a baseband quadrature demodu
`lator 818. The front-end stage comprises an antenna 802, a
`first band-pass filter 804, a low-noise amplifier (LNA) 806,
`and a second band-pass filter 808. The RF dowconverter
`comprises a first mixer 810, a first local oscillator 812, and
`a third band-bass filter 814.
`0047. The first band-pass filter 804 filters the modulated
`RF signal received by the antenna 802 to preselect the
`intended frequency band of interest from noise and other
`unwanted signals, and protects the rest of the receiver 800
`from Saturation by interfering signals at the antenna 802.
`The LNA 806 amplifies the filtered signal and couples its
`output to the second band-pass filter 808, which operates as
`an image reject filter, protects the RF downconverter from
`out-of-band interferer signals, and Suppresses undesired
`spurious signals generated by the first mixer 810 of the RF
`downconverter. Filtered signals from the second band-pass
`
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`US 2008/0076489 A1
`
`Mar. 27, 2008
`
`filter 808 are coupled to the mixer 810 of the RF downcon
`verter, which operates to transfer the modulation on the RF
`signal to IF. Spurious products generated by the mixer 810
`are filtered out by the t