(12)
`
`United States Patent
`Bierly et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7.260,141 B2
`Aug. 21, 2007
`
`USOO726O141B2
`
`(54) INTEGRATED BEAMFORMER/MODEM
`ARCHITECTURE
`
`(75) Inventors: Scott Bierly, Oak Hill, VA (US); Marc
`Harlacher, Herndon, VA (US); Robert
`Smarrelli, Oak Hill, VA (US); Aaron
`Weinberg, Potomac, MD (US)
`(73) Assignee: ITT Manufacturing Enterprises, Inc.,
`Wilmington, DE (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 802 days.
`(21) Appl. No.: 10/084,614
`
`(22) Filed:
`(65)
`
`Feb. 28, 2002
`Prior Publication Data
`US 20O2/O154687 A1
`Oct. 24, 2002
`
`Related U.S. Application Data
`(60) Provisional application No. 60/271,961, filed on Feb.
`28, 2001.
`(51) Int. Cl.
`H4B I/38
`H04L 5/16
`(52) U.S. Cl
`
`Oa -
`
`- - -
`
`- - - - - - - - - - - - - - - - - - - - - -
`
`375,295.375/347
`
`(2006.01)
`(2006.015
`375/in2: 375/260: 375/340:
`s
`(58) Field of Class ag s's 35936. s:2.
`s
`s
`s
`4 - 7 375 f29 s 31 6
`let
`lication file f
`h hist
`s
`S
`ee appl1cauon Ille Ior complete searcn n1story.
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`
`... 455,60
`3,986,123 A * 10/1976 Tirro et al. .....
`5,583,562 A * 12/1996 Birch et al. ................. 725 151
`5,631,898 A *
`5/1997 Dent .......................... 370,203
`5,764,187 A
`6, 1998 Rudish et al.
`5,809,422 A * 9/1998 Raleigh et al. ............. 455,449
`
`5.937,348 A * 8/1999 Cina et al. .................. 455,421
`5,943,010 A
`8, 1999 Rudish et al.
`6,052,085 A
`4/2000 Hanson et al.
`6,072,994. A *
`6/2000 Phillips et al. ................ 455,84
`
`(Continued)
`FOREIGN PATENT DOCUMENTS
`
`WO
`WO
`
`WOOOf 11800
`WO O1, 59962
`
`3, 2000
`8, 2001
`
`OTHER PUBLICATIONS
`
`Bierly, et al.; Sequential-Acquisition, Multi-Band, Multi-Channel,
`Matched Filter; U.S. Appl. No. 09/707,909, filed Nov. 8, 2000.
`Primary Examiner Jean B. Corrielus
`(74) Attorney, Agent, or Firm Edell, Shapiro & Finnan,
`LLC
`
`(57)
`
`ABSTRACT
`
`tion from IF to baseband permits parallel signal data from
`
`A transceiver employing a steerable phased-array antenna
`includes a modem architecture in which signals from each
`antenna element in the array are independently processed
`down to the individual baseband channel level, and digital
`beam forming is performed at baseband. The data rate reduc
`multiple antenna elements to be time multiplexed and seri
`ally processed at acceptable data rates at baseband with
`minimal modem hardware requirements. Both for transmit
`signal modulation and received signal demodulation, the
`computation of carrier tracking, automatic gain control
`(AGC)/power-control, and beam forming are shared by the
`same processing circuitry for all channels when performed
`at baseband. The resulting baseband circuitry is only incre
`mentally larger than that required for carrier tracking and
`AGC alone, yet accomplishes independent beam forming for
`each antenna element on each user channel.
`
`33 Claims, 3 Drawing Sheets
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`
`2
`
`IPR2023-00796
`Apple EX1001 Page 1
`
`

`

`US 7,260,141 B2
`Page 2
`
`U.S. PATENT DOCUMENTS
`ck
`6,101,399 A * 8/2000 Raleigh et al. ............. 455,561
`6,167,099 A 12/2000 Rader et al.
`6,307.506 B1* 10/2001 Despain...................... 342,368
`6,549,527 B1 * 4/2003 Tsutsui et al. .............. 370/342
`6,615,024 B1* 9/2003 Boros et al. ...
`455/67.14
`
`6,763,062 B1* 7/2004 Kohno et al. ............... 375,220
`6,768.458 B1* 7/2004 Green et al. .
`342.375
`6,831,943 B1* 12/2004 Dabak et al. ...
`375,147
`2002/0141478 A1* 10, 2002 Ozlulturk et al. ............ 375/130
`
`
`
`* cited by examiner
`
`IPR2023-00796
`Apple EX1001 Page 2
`
`

`

`U.S. Patent
`
`Aug. 21, 2007
`
`Sheet 1 of 3
`
`US 7,260,141 B2
`
`
`
`
`
`
`
`
`
`
`
`WIND, NV
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`
`IPR2023-00796
`Apple EX1001 Page 3
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`

`

`U.S. Patent
`
`Aug. 21, 2007
`
`Sheet 2 of 3
`
`US 7.260,141 B2
`
`
`
`
`
`
`
`
`
`RECEIVE DATASYMBOLS ON
`CUSER CHANNES IN PARALLEL
`
`TIME MULTIPLEXTHE PARALE
`DATASYMBOLS ON THE CCHANNEL
`TOFORMASERAL SIGNAL
`
`CO
`
`SERALLY GENERATEE COPES OF A
`BASEBAND MODULATED SIGNAL
`FOREACH DATASYMBOL
`
`02
`
`04
`
`06
`
`PHASE ADJUSTEACH BASEBAND SIGNALTO
`JOINTLY ACCOUNT FOR (ARRIER PHASE
`AND ANTENNAELEMENT BEAMFORMINGPHASE
`
`AMPLITUDE ADJUSTEACH BASEBAND SIGNAL
`TOJOINTLY ACCOUNT FOR SIGNALGAIN AND
`ANTENNAELEMENT BEAMSCALING
`
`
`
`
`
`
`
`DEMULTIPLEX SERAL BASEBAND SIGNALS
`INTO PARALLELSIGNALS CORRESPONDING
`TO INDIVIDUAL ANTENNA ELEMENTS
`ATEACH FREQUENCY CHANNEL
`
`
`
`
`
`
`
`
`
`
`
`
`
`DIGITALLY UPCONVERT DEMULTIPLEXED
`BASEBAND SIGNALS TO PRODUCE EDIGITALIFSIGNALS
`CORRESPONDING TO EANTENNAELEMENTS
`
`O
`
`UPCONVERTO RF ANDTRANSMT
`
`2
`
`FIG.)
`
`IPR2023-00796
`Apple EX1001 Page 4
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`

`

`U.S. Patent
`
`Aug. 21, 2007
`
`Sheet 3 of 3
`
`US 7,260,141 B2
`
`
`
`RECEIVE WIDEBANDRFSIGNALS
`ATEACH OF EANTENNAELEMENTS
`
`
`
`DOWNCONVERT TOF AND DIGITLE
`
`
`
`DIGITALLY DOWNCONVERTE IFSIGNALSTO
`BASEBAND TO FORM F. E PARALE BASEBAND SIGNALS
`
`2O)
`
`
`
`
`
`
`
`TIME MULTIPLEXTHE BASEBAND SIGNALS TO FORM
`SERIAL BASEBAND SIGNAL. A. F. ETHE PARALLELDATA RATE
`
`PHASE ADJUST EACH BASEBAND SIGNAL TOJOINTLY ACCOUNT
`FOR CARRIER PHASE TRACKING AND ANTENNA
`ELEMENT BEAMFORMINGPHASE
`
`AMPLITUDE ADJUST EACH BASEBAND SIGNALTO
`JOINTLY PERFORMAGC AND ANTENNAELEMENTBEAMSCALING
`
`
`
`PERFORMBEAMFORMING BY COMBININGEANTENNA
`ELEMENTSIGNALS FOREACH OFC USER DATA CHANNELS
`
`204
`
`206
`
`208
`
`
`
`PERFORMCHANNELEQUALIZATION, BASEBAND
`DEMODULATION AND SYMBODETECTION FOR
`EACH OFC USER CHANNELS
`
`))
`
`FIG.3
`
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`

`

`US 7,260,141 B2
`
`1.
`INTEGRATED BEAMFORMER/MODEMI
`ARCHITECTURE
`
`CROSS REFERENCE TO RELATED
`APPLICATION
`
`This application claims priority from U.S. Provisional
`Patent Application Ser. No. 60/271,961 entitled “Integrated
`TDMA Beamformer/Modem Architecture, filed Feb. 28,
`2001. The disclosure of this provisional patent application is
`incorporated herein by reference in its entirety.
`
`10
`
`BACKGROUND OF THE INVENTION
`
`2
`Digital beam forming is analogous to analog beam form
`ing, except that the received signal on each antenna element
`is independently digitized, and the phasing/combining
`operation is performed mathematically on the digital
`samples. The present inventors describe digital beam form
`ing techniques in U.S. patent application Ser. No. 09/778,
`854 entitled “Integrated Beam Forming/Rake/MUD CDMA
`Receiver Architecture', filed Feb. 8, 2001, the disclosure of
`which is incorporated herein by reference in its entirety.
`Conventionally, digital beam forming is done on a wideband
`signal, prior to despreading a CDMA waveform. This forces
`the computationally intense beam forming to take place at a
`much higher sampling rate, resulting in more mathematical
`operations per second, and corresponding increased hard
`ware cost. To address this shortcoming, beam forming can be
`performed at baseband, as disclosed by Hanson et al. in U.S.
`Pat. No. 6,052,085, the disclosure of which is incorporated
`herein by reference in its entirety.
`Furthermore, digital beam forming is conventionally per
`formed as a separate process, independent of symbol modu
`lation/demodulation, perhaps even as a separate product
`from the modem. In addition to the resulting inability to
`Support advanced demodulation techniques with this archi
`tecture, the cost of the beam forming function is greater as a
`stand-alone function, compared to the incremental cost of
`adding the capability to a modem. The largest cost-compo
`nent of beam forming is the complex multiplication of each
`sample for each element with the beam forming weights.
`Thus, whether stand-alone beam formers merely point in the
`direction of the signal of interest, or respond more adap
`tively to dynamic interference conditions by null-steering,
`such beam formers still lack the ability to be tightly coupled
`with potential advanced demodulation techniques.
`When combined with the modem, there is potential to
`absorb the complex multiply required for beam forming into
`computation already taking place for extremely low incre
`mental cost. In U.S. Pat. No. 5,764,187, the disclosure of
`which is incorporated herein by reference, Rudish et al.
`disclose an implementation of beam forming using digital
`direct synthesis (DDS) functions. However, Rudish does not
`Suggest or recognize potential hardware and processing
`savings in both signal transmission and reception. Specifi
`cally, Rudish does not suggest combining demodulation
`with beam forming or using hardware in a time-shared
`manner for both transmit and receive. Rudish's architecture
`is highly parallel and does lend itself to time multiplexing
`techniques which could potentially reduce hardware require
`mentS.
`Accordingly, there remains a need for an efficient, inte
`grated way of incorporating beam forming technology, for
`both transmit and receive, into base stations or transceiver
`terminals that process large number of users simultaneously
`using time division multiple access (TDMA) and/or fre
`quency division multiple access (FDMA) technology. This
`problem can be extremely computationally burdensome, and
`architectures for cost-effectively performing this processing
`are not addressed sufficiently in the prior art.
`
`SUMMARY OF THE INVENTION
`
`Therefore, in light of the above, and for other reasons that
`become apparent when the invention is fully described, an
`object of the present invention is to integrate digital beam
`forming capabilities into baseband processing functions
`
`15
`
`1. Field of the Invention
`The present invention relates to wireless communication
`transceivers and modems and, more particularly, to the
`construction of a multi-frequency, multi-channel transceiver
`system Such as might be used in a multi-user base station for
`terrestrial cellular or fixed-wireless applications.
`2. Description of the Related Art
`Directional antennas are widely used in a variety of
`communications systems to more efficiently transmit and
`receive radiated signals. Relative to an isotropic antenna,
`which transmits and receives signals equally in all direc
`tions, a directional antenna has an antenna gain pattern that
`is greater in certain directions than others, typically having
`a higher-gain main lobe several degrees wide (i.e., an
`antenna beam). Generally, a greaterantenna gain reduces the
`amount of power required to transmit and receive signals
`between two communication devices. Thus, steering the
`main lobe of a transceivers antenna gain pattern in the
`direction of another communication device facilitates com
`munication between the two devices.
`To be useful in certain applications, it may be necessary
`to rapidly point the antenna beam of a directional antenna in
`different directions. For example, base stations employed in
`cellular or wireless communication systems are required to
`communicate with several mobile communication devices at
`once. Often, the cell or region covered by the base station is
`divided into angular sectors (e.g., three 120° sectors), with
`certain antennas being responsible for communications with
`any mobile communication devices in a given sector. To
`permit virtually instantaneous redirecting of the antenna
`beam within the sector, an antenna formed of a phased array
`of independently controllable antenna elements may be
`used. The antenna beam is formed by applying appropriate
`phase and gain to the individual elements in the array.
`More specifically, beam forming is a type of spatial filter
`ing in which an array of sensor elements is controlled with
`appropriate signal processing to implement a phased array
`antenna for the purpose of shaping the antenna response
`over time in a space-varying manner (i.e., steering gain in
`Some directions, while producing attenuation or nulls in
`other directions). In a radio communications system, a signal
`arriving at each element of an antenna array will arrive at
`slightly different times due to the direction of arrival with
`respect to the antenna array plane (unless the signal has
`normal incidence to the plane, in which case the signal will
`arrive at all elements simultaneously). A phased-array
`receive antenna achieves gain in a particular direction by
`phase shifting, or time shifting, the signal from each ele
`ment, and then Summing the phase-shifted element signals
`in a signal combiner. By choosing the relative phasing of
`each element appropriately, coherence can be achieved for a
`particular direction of arrival (DOA), across a particular
`signal bandwidth.
`
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`3
`Such as modulation and demodulation carrier phase rotation
`and AGC/power-control scaling functions.
`Another object of the present invention is to efficiently
`implement a digital signal processing architecture for a
`TDMA and/or FDMA base station transceiver performing
`digital adaptive beam forming with a multi-element antenna
`array.
`A further object of the present invention is to reduce
`overall hardware and processing requirements in a multi
`user transceiver system employing antenna beam steering.
`Yet a further object of the present invention is to share
`common processing elements between modulation and
`demodulation functions in a modem.
`A still further object of the present invention is to take
`advantage of intermediate frequency (IF) to baseband data
`rate reductions to process parallel signal data in a time
`multiplexed manner at baseband to thereby reduce modem
`hardware requirements.
`Another object of the present invention is to reduce the
`size and weight of transceiver/modem equipment.
`Yet another object of the present invention is to maximize
`the amount of processing performed with a limited hardware
`SOUC.
`Still another object of the present invention is to imple
`ment transceiver/modem processing of multiple signals in a
`cost-effective manner.
`The aforesaid objects are achieved individually and in
`combination, and it is not intended that the present invention
`be construed as requiring two or more of the objects to be
`combined unless expressly required by the claims attached
`hereto.
`In accordance with the present invention, a modulator/
`demodulator (modem) architecture is presented for TDMA
`and FDMA applications. In particular, a transceiver config
`35
`ured to simultaneously communicate with multiple users,
`Such as a base station transceiver, employs a phased-array
`antenna capable of generating a steerable, directed antenna
`beam for communication with other devices. Rather than
`implementing the beam forming phase and amplitude control
`of the antenna elements in the front-end circuitry, the signals
`from each antenna element are independently processed all
`the way down to the individual baseband channel level, and
`digital beam forming is performed at baseband. While this
`approach would suggest significantly higher processing
`demands due to the separate processing for each antenna
`element, the transceiver of the present invention is imple
`mented using a symmetrical processing structure, leveraging
`the relationship of increasing computational complexity
`with decreasing computational rate from IF to baseband
`processing. Specifically, the data rate reduction from IF to
`baseband permits parallel signal data from multiple antenna
`elements to be time multiplexed and serially processed at
`acceptable data rates at baseband with minimal modem
`hardware requirements.
`55
`Further, the approach of the present invention allows the
`computation of carrier tracking, automatic gain control
`(AGC)/power-control, and beam forming to be shared by the
`same processing circuitry for all channels when performed
`at baseband. The resulting baseband circuitry is only incre
`mentally larger than that already required in the modem for
`performing carrier tracking and AGC, yet accomplishes
`independent beam forming for each antenna element on each
`user channel. For non-simultaneous transmit/receive sys
`tems, such as time division duplex (TDD), additional sav
`ings are realized by sharing wideband digital down-con
`verter (DDC) and digital up-converter (DUC) hardware as
`
`40
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`US 7,260,141 B2
`
`10
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`30
`
`4
`well as the baseband beam forming circuitry in a time
`multiplexed manner between the demodulator and modula
`tor functions.
`The above and still further objects, features and advan
`tages of the present invention will become apparent upon
`consideration of the following definitions, descriptions and
`descriptive figures of specific embodiments thereof wherein
`like reference numerals in the various figures are utilized to
`designate like components. While these descriptions go into
`specific details of the invention, it should be understood that
`variations may and do exist and would be apparent to those
`skilled in the art based on the descriptions herein.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a functional block diagram of an integrated
`TDMA/FMDA beam former/modem architecture in accor
`dance with an exemplary embodiment of the present inven
`tion.
`FIG. 2 is a functional flow diagram illustrating the signal
`processing operations associated with transmitting and
`modulating signals in accordance with the exemplary
`embodiment of the present invention.
`FIG. 3 is a functional flow diagram illustrating the signal
`processing operations associated with receiving and
`demodulating signals in accordance with the exemplary
`embodiment of the present invention.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`The following detailed explanations of FIGS. 1-3 and of
`the preferred embodiments reveal the methods and apparatus
`of the present invention. FIG. 1 is a generalized functional
`block diagram of an integrated beam former/modem archi
`tecture in accordance with an exemplary embodiment of the
`present invention. The beam former/modem architecture of
`the present invention can be employed in any communica
`tion device that transmits or receives signals from other
`communication devices. As used herein and in the claims, a
`“communication device' includes any device, mobile or
`stationary, that is capable of transmitting and/or receiving
`communication signals, including but not limited to: a
`handheld or body-mounted radio; any type of mobile or
`wireless telephone (e.g., analog cellular, digital cellular, PCS
`or satellite-based); a pager, beeper or PDA device; a radio or
`transceiver carried on, built into or embedded in a ground
`based or airborne vehicle; any portable electronic device
`equipped with wireless reception/transmission capabilities,
`including multimedia terminals capable of receiving/trans
`mitting audio, video and/or data information; and any device
`mounted in a fixed location with transmission/reception
`capabilities. The architecture of the present invention is
`particularly useful in any transceiver communication device
`requiring the use of directed antenna beams to transmit
`signals to and receive signals from a plurality of other
`communication devices used in transmission of audio, video
`and/or data information including, but not limited to, base
`stations of wireless communication systems, mobile com
`munication devices, airborne communication systems, and
`communications satellites.
`Referring to FIG. 1, the transceiver beam former/modem
`architecture includes a plurality E of transmit/receive
`antenna elements 10, 10, ..., 10, forming a phased array
`antenna which is electronically steerable via digital beam
`forming. Antenna elements 10 may have any hardware
`configuration Suitable for operating at the frequency and
`
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`US 7,260,141 B2
`
`5
`bandwidth required by the communication system in which
`the transceiver is used. In the specific implementation shown
`in FIG. 1, the transceiver employs time-division duplexing
`(TDD) in which the transceiver is alternately in a transmit
`and receive mode, relying on the phased array antenna for
`both signal transmission and reception. Accordingly, each
`antenna element 10, has a corresponding RF Switching
`element 12, selectively connecting the antenna element to
`the transmitter system and the receiver system. RF switching
`elements 12, can be a RF transmit/receive switches, circu
`lators, diplexers, hybrid splitters or any other device suitable
`for selective connecting the antenna elements to the transmit
`and receive circuitry. It should be understood, however, that
`the invention is not limited to a TDD architecture, and the
`present invention can be employed with both simultaneous
`and non-simultaneous transmit/receive schemes.
`On the receiver side, each of the antenna elements 10,
`10, . . . , 10, is coupled to a respective bandpass filter 14,
`14, ..., 14 which attenuates signal frequencies outside the
`filter's pass band. Each antenna element 10, can simulta
`neously receive signals on a plurality of different frequency
`channels F within the receiver pass band (frequency division
`multiplexing FDM). Each frequency channel is in turn
`time-division multiplexed (TDM), such that the system
`employs both time division multiple access (TDMA) and
`frequency division multiple access (FDMA) channelizing.
`The filtered RF signal from each element 10, 10, ..., 10,
`is amplified by a corresponding low-noise amplifier (LNA)
`16, 16, .
`.
`. , 16 and then processed by an analog RF
`30
`down-converter (DC) 18, 18, .
`.
`. , 18, which down
`converts the RF signal to an intermediate frequency (IF). For
`each of the E IF signals, a corresponding analog-to-digital
`(A/D) converter 19, 19, . . . . 19, digitally samples the IF
`signal at a wideband input sampling rate Fs, and the digital
`IF signal is received by a bank of digital down-converters
`(DDC) 20 to perform frequency division multiplexing
`(FDM) de-channelization.
`The DDC bank 20 includes a digital down-converter for
`each of the F frequency channels of each of the E antenna
`elements for a total of FXE digital down-converters. In
`practice, it may be possible under certain circumstances to
`perform digital down-conversion with fewer than FXE actual
`DDC devices, as will be explained herein in greater detail.
`DDC bank 20 down-converts the digital IF signal to a
`baseband frequency by decimating the digital IF signal and
`FIR filtering to bring the signal in each frequency channel of
`each antenna element down to baseband. Specifically, each
`DDC selects every R" sample for inclusion in the baseband
`signal while discarding the intervening R-1 samples, such
`that each DDC produces a decimated signal for a particular
`element and frequency channel at a sampling rate of
`
`6
`frequency channel signals from each of the E antenna
`elements down to baseband, which are then filtered by FIR
`filters.
`As shown in FIG. 1, each of the digital baseband signals
`generated in parallel by the FXE DDCs is time multiplexed
`by multiplexer (MUX) 24 into a serial signal having a rate
`of
`
`(2)
`
`The time-multiplexed serial baseband output signal of mul
`tiplexer 24 is processed at baseband as described below to
`detect data symbols for each of C user channels. It should be
`understood that the various data rates described herein relate
`to upper limits constrained by the relationships between
`factors such as the wideband sample rate, the number and
`bandwidth of frequency and time channels, the decimation/
`interpolation factor, the number of antenna elements, the
`number of users channels and input/output symbol rates.
`Accordingly, a particular architecture can be designed to
`operate up to particular clock rates in accordance with these
`relationships. However, these rate relationships do not imply
`that the hardware must be operated at the maximum
`designed rate. Thus, for example, while Fs is shown in
`equation (2) to as “equal to a particular expression, it will
`be understood that this expression represents an upper limit
`on the permissible value of Fs, in operation, Fs can be set
`at an appropriate rate up to the value of this expression.
`On the transmitter side, baseband signals are generated at
`the rate Fs and supplied to a demultiplexer (DEMUX) 26.
`The serial baseband signal stream includes time-multiplexed
`signals for each antenna element on each user channel.
`Demultiplexer 26 converts the serial baseband signal to FXE
`parallel signals, each having a rate of Fs, which are respec
`tively received by FXE digital up-converters (DUC) of a
`DUC bank 28 which performs FDM channelization of the
`baseband signals. Receiving the center frequencies of the F
`frequency channels from FDM channel NCO bank 22, DUC
`bank 28 performs the complex multiplying required to
`up-convert E signals (one for each antenna element) on each
`of the F channel frequencies into E digital IF signals.
`Further, to bring the sampling rate up to the wideband
`sampling rate Fs, required by the digital-to-analog convert
`ers 29, 29, . . . , 29, corresponding to antenna elements
`10, 10. . . . , 10, DUC bank 28 interpolates each of the E
`digital IF signals by the factor of R. After digital-to-analog
`conversion, the analog IF signal for each of E antenna
`elements is up-converted to RF by respective analog up
`converters 30, 30, . . . , 30, and amplified by respective
`power amplifiers 32, 32, . . . , 32. With RF switching
`elements 12, 12. .
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`.
`, 12 positioned to connect the
`transmit circuitry to respective antenna elements 10,
`10. . . . , 10, the amplified RF signals are transmitted via
`the antenna elements in accordance with the beam forming
`applied in the baseband processing.
`Beamforming in a multi-user modem or base station
`applications in the prior art has principally taken a non
`integrated or detached approach. In some cases, beam form
`ing rotation and combining is done in analog in the front-end
`UC/DC circuitry of the modem. In other cases, beam forming
`is performed using either analog or digital approaches as a
`distinct external apparatus from the modem. The approach
`of the present invention is to incorporate beam forming
`directly into the modem architecture. To accomplish beam
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`The factor R represents the narrowband rate reduction which
`facilitates multiplexing the multiple elements and frequency
`60
`channels in order to share baseband processing circuitry. A
`frequency division multiplexer (FDM) channel numerically
`controlled oscillator bank 22 comprises F NCOs which are
`respectively tuned to the center frequency of the F frequency
`channels. The FDM channel NCO bank 22 supplies the F
`different frequency signals used by DDC bank 20 to perform
`the complex multiplying required to bring each of the F
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`65
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`IPR2023-00796
`Apple EX1001 Page 8
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`

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`US 7,260,141 B2
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`forming, the appropriate relative signal phase and amplitude
`must be applied to the individual antenna elements to form
`an antenna beam which has a desired shape and points in a
`particular direction. To Support signal modulation and
`demodulation, baseband processors typically perform the
`functions of carrier phase tracking (involving carrier phase
`rotation) and automatic gain control (AGC) (i.e., adjusting
`the amplitude of the baseband signal to be within the
`operational range of downstream devices), although base
`band processors do not generally process carrier phase and
`amplitude on an antenna-element-by-antenna-element basis.
`In accordance with the present invention, beam forming is
`integrated into baseband processing such that beam forming
`computations are performed in a manner requiring only
`additional adders, due to integration with the existing modu
`lation/demodulation carrier phase rotation and the AGC/
`power-control Scaling functions.
`An important novel aspect of the present invention is the
`independent processing of each antenna element all the way
`from the antenna elements down to individual baseband
`channel-level processing. While increasing the baseband
`computational complexity by a factor of the number of
`antenna elements E, this approach affords significant per
`formance advantages to each user channel, permitting com
`pletely independent antenna beam patterns to be achieved
`25
`per channel when receiving, as well as individual contribu
`tions to the beam pattern when transmitting.
`Baseband processing is described in connection with
`transmission and reception of data symbols associated with
`a plurality of users. A flow diagram Summarizing the signal
`processing operations associated with modulating and trans
`mitting data symbols is shown in FIG. 2, while a flow
`diagram Summarizing the signal processing operations asso
`ciated with receiving and demodulating data symbols is
`shown in FIG. 3. Referring to FIGS. 1 and 2, Cindependent
`data streams of symbols are received in parallel on C user
`channels at a certain data rate. The input data symbols from
`the C user channels are time multiplexed by multiplexer 34
`into a serial signal having a data rate C times the input
`symbol rate, with each user channel receiving the fraction
`1/C of the time slots (operation 100 in FIG. 2). The serial
`signal is processed by a baseband modulator bank 36
`comprising C baseband modulators which respectively gen
`erate in a time-multiplexed series baseband signals from the
`input data symbols of the C user channels for processing by
`shared baseband processor 38.
`Since beam forming is to be performed at baseband, for
`each input data symbol on each user channel, baseband
`modulator bank 36 must generate E copies of each symbol
`(operation 102). Consequently, the data rate of the time
`multiplexed signal out of baseband modulator bank 36 is the
`input data symbol rate times the number of user channels C
`times the number of antenna elements E, and for each input
`data symbol time slot, baseband modulator bank 36 pro
`duces E identical baseband modulated signals in E corre
`sponding time slots. The output of the baseband modulator
`bank 36, which is supplied to shared baseband processor 38.
`is serialized in this manner so that shared baseband proces
`sor 38 can be implemented with a single complex multiplier
`and a single automatic gain control element. Shared base
`band processor 38 applies different phases and Scaling to
`each of the E copies of each symbol.
`Shared baseband processor 38 includes a carrier phase
`accumulator bank 40 comprising a single numerically con
`trolled oscillator (NCO) controlled in a time-multiplex man
`65
`ner via a memory bank of phase values corresponding to
`each user channel C (for both modulation and demodula
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`tion). The NCO supplies a rolling phase for the respective
`data channels to a phase adder 42 in a time-multiplexed
`manner. A bank of beam rotation weights 44 contains
`beam forming weights in the form of phase rotations for each
`channel and each antenna element, which are Supplied to
`phase adder 42 channel-by-channel and element-by-element
`in a time-multiplexed manner. With C independent user
`channels, E different antenna elements and both transmit and
`receive beam steering, beam rotation weight bank 44
`includes CxEx2 beam forming phase rotations. Phase adder
`42 receives the beam forming rotation weights and adjusts
`the phase Supplied by the carrier phase accumulator bank
`NCO 40 in accordance with the beam forming phases of the
`particular antenna elements. A sin/cos lookup table 46 is
`indexed by the adjusted phase value generated by phase
`adder 42 and Supplies the corresponding sine?cosine multi
`plicands to a complex multiplier 48 for adjusting the phases
`of the input time-multiplex baseband signals on a time-slot
`by-time-slot basis (operation 104).
`The phase-adjusted baseband signal in each time slot is
`then adjusted in amplitude by a scalar multiplier 50 based on
`Scaling information received from beam Scaling and AGC/
`power control processor 52 (operation 106). Like the bank
`of beam rotation weights 44, Scaling processor 52 a