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`PROVISIONAL PATENT APPLICATION COVER SHEET
`,
`
`HII
`
`This is a request for filing a PROVISIONAL APPLICATION under 37 CFR 1.53(b)(2).
`
`Docket Number
`
`6785-172
`
`Type a plus sign(+)
`inside this box "'>
`
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`RESIDENCE (CITY AND EITHER STATE OR FOREIGN COUNTRY)
`
`INVENTOR(S) / APPLICANT(S)
`
`LAST NAME
`
`FIRST NAME
`
`WILLIAMS
`
`SCHMUTZ
`
`NOLL
`
`HARPER
`
`Terrv
`
`Thomas
`
`John
`
`Donald
`
`MIDDLE
`INITIAL
`
`L.
`
`Melbourne, FL
`
`Indialantic, FL
`
`Palm Bay, FL
`
`Melbourne, FL
`
`TITLE OF THE INVENTION (230 characters max)
`
`ADAPTIVE ANTENNA ARRAY CALIBRATION SYSTEM AND METHOD
`
`CORRESPONDENCE ADDRESS
`
`Robert J. Sacco
`Akerman, Senterfitt & Eidson, P.A.
`222 Lakeview Avenue, Suite 400
`P.O. Box 3188
`West Palm Beach, Florida 33402-3188
`
`I
`
`FL
`
`I
`
`ZIP CODE
`
`33402-3188
`
`USA
`
`ENCLOSED APPLICATION PARTS check all that aooly)
`
`f
`'
`;1A'
`
`;)
`= ;:::;:
`t
`
`x:,: Specification
`
`Number of pages
`
`~'
`
`Drawmg(s)
`
`Number of sheets
`
`-
`
`~.,
`
`35
`
`I
`
`Small Entity Statement
`
`Other (specify)
`
`I COUNTRY I
`-
`-
`
`--4,-;i
`
`~.
`' (']
`
`METHOD OF PAYMENT (check one)
`
`C) - A check or money order is enclosed to cover the provisional filing fees
`-
`I 500951
`
`The Commissioner is hereby authorized to charge
`filing fees and credit Deposit Account Number:
`
`I
`
`PROVISIONAL
`FILING FEE
`AMOUNT($)
`
`$150.00
`
`X
`
`- T
`
`he invention was made by an agency of the United States Government or under a contract with an agency of the United States Government.
`[X] No
`
`[ ] Yes, the name of the U,S, Government ency and the Government contract number are: ______________
`
`_
`
`Respectfully submitted,
`
`
`
`
`
`TYPED or PRINTED NAME ---"-'N=ei'""I R='.;,.;Je=tt=er _____
`
`Date 110/~1/oD
`
`_
`
`REGISTRATION NO.
`(if appropnate)
`
`46,803
`
`VIA EXPRESS MAIL LABEL NO. EK972214040US
`
`IPR2023-00796
`Apple EX1005 Page 1
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`

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`.
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`I
`
`ADAPTIVE ANTENNA ARRAY CALIBRATION SYSTEM AND METHOD
`
`lnventor(s): T. WILLIAMS
`T. SCHMUTZ
`J. NOLL
`D. HARPER
`
`AKERMAN SENTERFITT
`
`IPR2023-00796
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`6785-172
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`BACKGROUND OF THE INVENTION
`
`Field of the Invention
`
`This invention relates to the field of RF communication systems, and more
`
`particularly to a system and method for calibration of adaptive antenna arrays.
`
`Description of the Related Art
`
`In order to remain competitive in an increasingly crowded market, wireless
`
`equipment manufacturers experience constant pressure to reduce their costs and
`
`improve performance. One way to reduce the overall cost of a cellular phone system is
`
`to re-design individual system components or software so that the system may operate
`
`more efficiently. For example, it would be desirable to supply more users while
`
`maintaining an acceptable signal quality. One method for increasing the efficiency and
`
`performance of a cellular system is through the use of adaptive antenna arrays
`
`
`
`("adaptive arrays 11). Until recently, adaptive arrays had been used almost exclusively for
`
`military anti-jam applications. Non military uses were limited by losses and signal
`
`degradation resulting from the combining of a large number of analog signals (in
`
`transmit mode) and splitting the large number of analog signals (in receive mode)
`
`required in multi-channel communication systems. The losses and degradation noted
`
`was generally more than offset by any advantage gained through employing an ,
`
`adaptive antenna array. With the advent of high speed digital signal processing, losses
`
`and signal degradation associated with analog processing to accomplish the same
`
`result are almost entirely avoided.
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`Adaptive antenna array systems provide greater range over traditional
`
`technologies due to increased antenna gain. As a carrier wave propagates through
`
`space, the signal power decreases. Since mobile subscribers cannot detect signals
`
`below a minimum threshold level of transmitted power, increasing antenna gain extends
`
`the distance a carrier wave can travel. Thus, an adaptive antenna array can increase
`
`the cell size that a given BTS can serve.
`
`An adaptive antenna array can also increase user capacity over traditional
`
`antenna technology by amplifying the signal coming from and going to the mobile user
`
`while dampening other signals coming from other directions. This ability is commonly
`
`referred to as "digital beamforming." By steering a beam and positioning multiple nulls,
`
`an adaptive array is able to reduce co-channel and adjacent channel interference. This
`
`allows each cell to use all frequencies within an operator's licensed band and may
`
`make it possible to use single frequencies more than once within a given cell.
`
`Separating multiple signals having the same frequency is possible using an adaptive
`
`array, provided the signals arrive from angles or otherwise have distinctive propagation
`
`paths. In the same manner, echos caused by multipath arrivals of a desired signal can
`
`be detected and suppressed.
`
`An antenna array consists of N identical antenna elements arranged in a
`
`particular geometry. The geometry of the array determines the amount of coverage in a
`
`given spatial region. A very commonly used array type is the uniform linear array.
`
`For any given geometry, the phases and amplitudes of the currents exciting the
`
`array elements determine the gain of the array in a certain direction. The phases and
`
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`amplitudes of the currents on the antenna array elements can be electronically adjusted
`
`such that received signals from a certain direction add in phase, and maximum gain is
`
`achieved in that direction. Due to the reciprocal nature of antennas, this approach is
`
`also generally applicable to focus the array beam for transmission as well, assuming
`
`the transmit and receive frequencies are equal or nearly equal.
`
`To adjust the amplitude and phases of the individual array currents, complex
`
`weights are placed in the signal path of each antenna element. The weighted signals
`
`are combined and the output is fed to a control unit that operates on the individual
`
`signals and their combined output to update the weights. Weight updating is usually
`
`accomplished adaptively to satisfy a chosen optimization system.
`
`There are several commonly used adaptive algorithms available for updating the
`
`weights. These include gradient based algorithms, recursive methods, and others such
`
`as the constant modulus method (CMA).
`
`For the phases and amplitudes of the various currents on the antenna array
`
`elements to be controlled, the individual (unweighted) array currents must arrive at the
`
`same instant and with the same amplitude. Consequently, the relative phase and
`
`amplitude offsets for each of the complete transmit and receive paths associated with
`
`each array element must be determined to enable proper determination of a signal's
`
`angle of arrival as well as for precise beam steering. In digital systems, the complete
`
`transmit and receive paths extend between the respective digital signal processors and
`
`the respective antenna elements.
`
`Each adaptive array antenna element requires a separate transceiver chain for
`
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`operation of the adaptive array. Thus, each antenna element is provided a dedicated
`
`receiver apparatus chain and transmit apparatus chain. For example, a receive
`
`apparatus chain may include an antenna element, cables, filters, RF electronics,
`
`physical connections, and an analog-to-digital converter, assuming the processing is
`
`digital. Due to normal manufacturing variances in the manufacture of the antenna array
`
`elements, connecting cables, and transmit and receive electronics chains, there will be
`
`differing errors and non-linearities introduced by signal paths comprising combination of
`
`these components. Thus, identical signals passing through the different elements of
`
`antenna array will emerge with different amplitudes and phases.
`
`Similarly, identical signals passing through different cables and electronics will
`
`result in distinct resulting amplitude and phase. These composite amplitude and phase
`
`errors in a given antenna signal path can be captured for a fixed reference angle (for
`
`example, north) and a set of receive and transmit calibration factors calculated to
`
`equalize the transfer functions of the various receive and transmit apparatus chains.
`
`Each antenna array element along with its corresponding cables and the corresponding
`
`receive electronics in the path from each antenna element to its respective digital signal
`
`processor shall be referred to as the "receive apparatus chain" for each antenna
`
`element. Similarly, each antenna array element along with its corresponding cables
`
`and the corresponding transmit electronics from the respective digital signal processor
`
`to the respective antenna element shall be referred to as the "transmit apparatus chain"
`
`for each antenna element. These calibration factors can be used to transmute the
`
`actual signals that are actually seen at the end of each antenna array element chain
`
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`into corresponding signals that would be expected at the end of each chain if all signal
`
`path components behaved identically.
`
`Because the transmit signals and the receive signals follow somewhat different
`
`hardware paths, the adaptive antenna system will have both transmit and a receive
`
`calibration factors. It should also be noted that the phase and amplitude shifts that
`
`occur in the receive and transmit apparatus chains are, in general, frequency
`
`dependent. Thus, in broadband applications, calibration factors must generally be
`
`determined at the plurality of carrier frequencies used.
`
`Accurate real-time calibration is required for all receive and transmit apparatus
`
`chains. Periodically, the calibration procedure must be performed as differences in the
`
`propagation path may vary during the day and from day to day due to temperature and
`
`other environmental conditions. Since there are active components involved their
`
`responses will change with time and temperature. Thus, for an adaptive antenna array
`
`to function properly, frequent calibration of the various transmit and receive apparatus
`
`chains should be performed.
`
`The complete paths for the receive apparatus chains are relatively easy to
`
`calibrate since a fixed near-field or far field transmitter can be used as a calibration
`
`source to allow the respective receive apparatus chain path delays and magnitude
`
`shifts to be calculated and stored. Unfortunately, the calibration of the transmit
`
`apparatus chain path delays and magnitude shifts are much more difficult because a
`
`single external transmitter cannot be used as a calibration reference. As a result,
`
`transmit apparatus chain calibration is generally performed with costly dedicated
`
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`hardware including near and/or far-field transmit sources or receivers.
`
`Therefore, there is a need for a method to calibrate all transmit apparatus chains
`
`and receive apparatus chains without the addition of dedicated calibration hardware
`
`such as near and/or far-field transmit sources or receivers. Moreover, such a method
`
`should preferably not impact a cellular system's traffic capacity.
`
`P1000803.DOC
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`6785-172
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`There are presently shown in the drawings embodiments which are presently
`
`preferred, it being understood, however, that the invention is not limited to the precise
`
`arrangements and instrumentalities shown.
`
`Fig. 1 shows a simplified block diagram of a wideband digital beamforming base
`
`station transceiver (BTS ).
`
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`DETAILED DESCRIPTION OF THE INVENTION
`
`Referring to FIG. 1, a simplified block diagram of a digital beamforming base
`
`transceiver station (BTS) is shown. BTS 200 shown includes a 4 element antenna
`
`array 210-213 (hereafter 210).
`
`Each antenna element has a dedicated receive apparatus chain comprising
`
`filter/duplexer 220-223 (hereafter 220), broadband digital transceiver 240-243 (hereafter
`
`240), channelizer/combiner (XMUX) 250-253 and associated connectors inclusive of
`
`digital signal processor boards 270-273 hereafter 270). In the receive mode, XMUX
`
`250 operates as a channelizer. In a broadband application, digital signal processor
`
`boards comprise a plurality of individual digital signal processors. Filter/duplexer 220
`
`performs amplification, filtering and down conversion to IF of received signals. In
`
`broadband applications, assuming multiple frequency channels are active at any given
`
`instant, received signals are multi-channel signals.
`
`The broadband digital transceiver 240 performs AID conversion then digitally
`
`down-converts the received signal. The multi-channel digital signal output by the
`
`broadband digital transceiver 240 is separated by channelizer 250 into baseband digital
`
`signals having an I and Q representation for each active channel. There is one
`
`channelizer 250 provided for each antenna element 210. In the preferred embodiment,
`
`the channelizer 250 is a FFT channelizer. The baseband digital signals, respectively
`
`associated with each antenna element 210, are then communicated to a digital array
`
`processor 260. Although shown as a separate module and positioned on the
`
`channelizer/combiner 250 side of control and timing bus 262 and switching bus 264,
`
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`digital array processor 260 can be positioned on the opposite side of buses 262 and
`
`264. Moreover, in the preferred embodiment, digital array processor 260 can be
`
`positioned on the same board as digital signal processor 270, digital signal processor
`
`270 being on the side of buses 262, 264 opposite to XMUX 250.
`
`Digital array processor 260 may be used to store the various calibration factors
`
`and angular weighting factors. Calibration factors and angular weighting factors are
`
`preferably stored separately. Calibration factors are used to compensate for relative
`
`path phase delay and amplitude variations that occur when signals traverse the various
`
`transmit and receive apparatus chains, with reference to a fixed reference angle (for
`
`example, north). The angular weighting factors are used to point the antenna beam
`
`and nulls into the desired directions (for both transmit and receive) relative to the
`
`reference angle (for example, +23 degrees north). The phases and amplitudes of the
`
`calibration factors and angular weighting factors are effectively added together to result
`
`in a net weighting factor that is applied to signals traveling in each antenna apparatus
`
`chain for each signal frequency and time slot (in TDM systems).
`
`Digital array processor 260 may be used to calculate the various calibration
`
`factors and angular weighting factors and store these factors. Through application of
`
`net weighting factors to each of the applicable apparatus chains, digital array processor
`
`260 can adjust the baseband digital signals received from and for transmission by each
`
`antenna element 210 to beamform each active channel. The net weighting factors can
`
`be resolved and applied using the recently available "Super DSP" cards, where one
`
`processor does the beamforming for a single RF carrier (all 8 time slots in GSM, for
`
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`example) and a second processor does the signal processing (modem functions).
`
`Having both processors on the same board reduces signal interconnectivity
`
`requirements and improves system reliability. Combining the processors on a single
`
`board also generally reduces system cost compared to separate board implementations
`
`when implementing adaptive antennas.
`
`For the receive path, the respective phase and amplitude net weighting factors
`
`are preferably applied after the XMUX 250 (digital channelizer) and before the DSP
`
`270. DSP 270 receives the signal components adjusted with respective net weighting
`
`factors from each receive apparatus chain output by the digital array processor 260 and
`
`demodulates these signals to recover the combined beamformed communication
`
`signal. The recovered communication signal is then communicated to the
`
`communication system via a suitable interface (not shown).
`
`System operation in the transmit direction is quite similar to the receive direction.
`
`Each antenna element has a dedicated transmit apparatus chain comprising
`
`filter/duplexer 220, multi-carrier power amplifier (MCPA) 230-233 (hereafter 230),
`
`broadband digital transceiver 240-243, channelizer/combiner 250-253 (XMUX 250)
`
`using the combiner and associated connectors inclusive of respective digital signal
`
`processors 270. Digital signal processors 270, are associated with a specific antenna
`
`element 210 and a specific frequency channel for processing respective ones of a
`
`plurality of incoming (voice/data) communication signals to be transmitted over
`
`respective frequency channels. Their processed (modulated and encoded) outputs are
`
`supplied to the digital array processor 260, which can apply appropriate net weighting
`
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`6785-172
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`factors to each active channel and for each transmit apparatus chain associated with
`
`each antenna element 210. For the transmit path, the phase and amplitude net
`
`weighting factors are preferably applied after the DSP 270 (modulation) and before the
`
`XMUX 250 (digital combiner). At these points in the signal path, each signal (RF
`
`frequency and time slot) is a baseband signal having an I and Q representation.
`
`The outputs of the digital array processor 260 for each transmit apparatus chain
`
`are input into respective combiner 250. In the preferred embodiment, there is one
`
`combiner 250 for each antenna element 210 and the combiner is an inverse FFT
`
`combiner. The FFT combiner 250 forms a multichannel digital signal which is input to
`
`the broadband digital transceiver 240, where it is upconverted to IF, D/A converted, and
`
`amplified by a high power multi-carrier power amplifier (MCPA) 230. The composite
`
`multi-frequency signal is then supplied to RF elements 220 for amplification, filtering
`
`and up conversion from IF to RF. The antenna elements 210 then each transmit the
`
`beamformed multi-frequency communication signal.
`
`Although a 4 element antenna array embodiment is shown in Fig. 1, the invention is
`
`not limited to 4 antenna elements. Note that although four DSP boards 270 are shown
`
`in Fig. 1, each may provide a plurality of digital signal processors per board. For
`
`example, 24 digital signal processors may be provided per DSP board 270. In the
`
`preferred embodiment of the invention, 96 channels are supported by BTS 200 through
`
`use of 12 RF carriers and 8 TOM time slots. A separate digital signal processors may
`
`be dedicated to each channel (timeslot), or a digital signal processor having sufficient
`
`processing speed may process multiple channels, such as all eight channels (timeslots)
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`in GSM systems.
`
`To obtain the full advantages of an adaptive antenna array, both transmitted and
`
`received signals must be calibrated so that unweighted signals traveling along the
`
`various antenna apparatus chains from respective DSPs 270 to antenna element 210
`
`each reach each antenna element 210 simultaneously and with the same amplitude.
`
`Preferably, the various transmit and receive apparatus chains are calibrated to all be
`
`within 1 to 2 degrees of phase and 0.1 db to 0.2 db in magnitude relative to each other.
`
`Similarly, all received signals by each antenna element 210 should reach their
`
`respective DSP 270 nearly simultaneously and with the nearly the same amplitude as
`
`well. Consequently, accurate determination of receive apparatus chain calibration
`
`factors and transmit apparatus chain calibration factors to and from each antenna
`
`element 210 to respective DSP 270s are generally required to implement beamforming.
`
`At the time of system installation, the physical distances between the various
`
`antenna elements are measured and recorded. This information is used to calculate
`
`and compensate for free space path time delays between the various antenna
`
`elements. For example, for a triangular 4 element system where a single antenna is
`
`placed in the center of the triangle, there are 4 unique distances to measure.
`
`In one aspect of the invention, calibrating factors for the various receive and
`
`transmit apparatus chains are determined through use of a remote device to receive,
`
`frequency shift and loopback signals transmitted by BTS 200. In the preferred
`
`embodiment, a remote wireless translating repeater ("translating repeater'') may be
`
`used as the remote device for calibration of an adaptive antenna array included in BTS
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`200. Translating repeaters may already be installed in conjunction with BTS 200 in
`
`certain cellular systems. In this case, the translating repeaters result in no added
`
`system expense. If a wireless translating repeater is not already used in the cellular
`
`system, a reduced cost modified translating repeater version can be used, the modified
`
`translating repeater having only backhaul receive and transmit functions.
`
`The method requires the total delay and magnitude shift (collectively the "signal
`
`shift") for a round trip (TD) of a loopback signal transmitted and received by BTS 200 to
`
`be measured. Round trip signal shifts between transmitting and receiving antenna
`
`apparatus chains consist of the following components:
`
`1. signal shift from the respective DSP 270 to respective transmit antenna element 210
`
`(transmit apparatus chain), referred to as TX1- TXn; plus
`
`2. delay during signal travel in free space to the remote device, referred to as D1-Dn;
`
`plus
`
`3. signal shift during remote device signal processing; plus
`
`4. delay during signal travel in free space from remote device back to respective
`
`antenna elements, referred to as D'1 - D'n (note that due to symmetry D1 =D'1;
`
`Dn=D'n), plus
`
`5. Signal shift from each receiving antenna 210 to their respective DSP 270 (receive
`
`apparatus chain), referred to as RX1-RXn.
`
`For a 4 element antenna array, 16 distinct round trip signal shifts can be measured,
`
`4 per antenna element. The translating repeater location is measured and
`
`characterized with reference to the angular position and distance between the
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`6785-172
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`translating repeater and the various BTS antenna elements 210. This is normally
`
`accomplished using a survey. This information is then stored and taken into account
`
`during calibration factor calculations to account for the differences in free space delays
`
`between the remote device, such as a translating repeater, and the various antenna
`
`elements.
`
`Method and Apparatus Employing a Remote Wireless Repeater For Calibration of a
`
`Wireless Base Station Uplink and Downlink Adaptive Antenna Array
`
`To initiate a first calibration process, a remotely positioned translating repeater is
`
`signaled by BTS 200 to enter a loopback mode by an appropriate signal. The
`
`translating repeater may be placed in the loopback mode for one frame (8 time slots in
`
`GSM). Once in the loopback mode, signals received by the translating repeater are
`
`coupled off to a low level (e.g. -40 dB), additionally attenuated frequency shifted from
`
`the transmit to receive band (for example, 80 MHZ lower for GSM-1900) and re(cid:173)
`
`transmitted back to the BTS.
`
`The BTS 200 transmits a loopback signal, such as a GSM access burst, from
`
`each antenna element, one at a time. The translating repeater receives and re(cid:173)
`
`transmits loopback signals which are received by all antenna elements of the BTS
`
`adaptive array. Signal shifts for each receive apparatus chain may be measured and
`
`calibration factors determined from resulting receive apparatus chain signal shifts
`
`measured from receipt of any one of the returned loopback signals originally
`
`transmitted by BTS from any antenna element. These values may be recorded for
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`each antenna receive chain to permit computation of calibration factors for the
`
`respective receive apparatus chains to compensate for receive signal shift differences.
`
`Similarly, round trip signal shifts can be measured. By using measured round
`
`trip signal shift data for signals transmitted and received by each antenna element and
`
`subtracting the earlier determined respective receive signal shifts and adjusting for free
`
`space delay differences, transmit apparatus chain calibration factors can be
`
`determined. These factors can be used to compensate for transmit signal shift
`
`differences from signals transmitted by each antenna element. Since signal shifts are
`
`frequency dependent, the calibration process for both transmit and receive apparatus
`
`chains are generally repeated for all carrier frequencies supported by BTS 200.
`
`Once the receive and transmit chain calibration factors are calculated and stored
`
`by the BTS, the angle of arrival for each uplink channel may be calculated and stored.
`
`In practice, angle of arrival for translating repeater transmissions relative to the BTS is
`
`known (e.g., based on a survey) at the time of installation and does not change over
`
`time. Thus, the translating repeater angle of arrival can be used as an absolute
`
`reference, permitting mobile user angle of arrivals at the BTS 200 to,be made relative to
`
`that fixed reference angle.
`
`In a multi-carrier BTS utilizing 12 RF carriers and 8 TOMA time slots, 96 full
`
`duplex channels of GSM are available. In this configuration, 96X2 values of calibration
`
`factors are stored for each antenna element and its dedicated receive apparatus chain.
`
`Thus, for a duplexed system having 96 channels and 4 antennas, 768 calibration
`
`factors are stored to support beamforming in the receive direction. After the uplink
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`angle of arrival is determined, the downlink steering angle is determined as the
`
`reciprocal direction.
`
`In actual operation, the BTS 200 uses the receive chain apparatus calibration
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`factors when an uplink signal is received by antenna elements 210 to determine the
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`angular location of the signal source, such as a mobile user. Various algorithms known
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`in the art permit accurate identification of the mobile's location, allowing the
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`determination of the angle of arrival of the mobile user's signal. Upon receipt of the
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`arriving signal, the digital array processor 260 may be used to determine the angle of
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`arrival of the incoming signal by measuring the signal shifts of the arriving signal after
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`traveling the respective receive apparatus chains of the several antenna elements 210.
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`In this determination, receive apparatus chain calibration factors already determined
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`and stored therein are used to compensate for differences in the various receive
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`apparatus chains.
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`Using the mobile user's angle of arrival, angular weighting factors can be readily
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`calculated using methods known in the art to narrow the beam to focus to the user's
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`location and to position nulls to steer toward interference sources. Angular weighting
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`factors are combined with respective calibration factors to produce appropriate net
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`weighting factors for application to the signal paths of each receive antenna chain.
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`Appropriate net weighting factors permit pointing a beam towards the mobile user and
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`up to N-1 nulls (N is the number of antenna elements) toward interference sources.
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`Similarly, using the inverse of the angle of arrival for transmitted signals, respective
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`transmit apparatus chain net weighting factors are determined to point a beam towards
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`the mobile user and up to N-1 nulls toward interference sources.
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`Translating repeaters may be used to calibrate the antenna array in either a passive
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`analog loopback repeat function or an active receive/demodulate remodulate/transmit
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`function. In the passive repeat function, downlink signal are simply frequency
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`translated and looped back to the BTS 200. In the active receive function, the
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`translating repeater can demodulate the received signal and remodulate (and frequency
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`shift) the received signal for retransmission. The active receive function can be used to
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`send additional information such as RSSI (receive signal strength) of the mobile user to
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`the BTS during calibration.
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`Transmit calibration factors are preferably constantly updated during system
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`operation because of component drift, principally due to environmental factors. For
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`example, the length of RF cables and jumpers change (and result in corresponding
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`shifts in time delays to traverse) with heating and cooling from the sun, day/night,
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`weather and other environmental factors. Devices such as surface acoustic wave
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`(SAW) filters found in both the BTS upconverter (downlink transmit) and BTS
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`downconverter (uplink receive) as part of broadband digital transceiver 240 circuitry are
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`particularly sensitive to temperature and are known to produce significant changes in
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`signal shift from modest changes in temperature.
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`Channelizer 250 separates the inputted composite digital signal comprised of all
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`active RF carriers into separate digital signals representing each RF carrier from a
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`composite signal. Using the angle of arrival data determined for mobile users for all
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`active timeslots for each RF carrier in a TOM system, net weighting factors may be
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`determined by the digital array processor 260 and be separately applied to each active
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`timeslot to point a beam towards the mobile user's location and to point one or more
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`nulls at the most intense interference sources.
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`Turning to the transmit direction, signals output by DSP 270 to the digital array
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`processor 260 are separate digital signals for each active channel (timeslot). Using the
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`reciprocal of the angle of arrival for the received signal, the digital array processor 260
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`calculates the optimum net weighting factors for the various transmit apparatus chains
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`and places these net weighting factors in each of the channel's transmit signal path at
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`the digital array processor 260 to point the transmitted antenna beam and one or more
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`nulls in the reciprocal of the uplink signal direction.
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`Assuming full channel use, the digital array processor 260 generally determines
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`optimum net weighting factors for each antenna element 210 for each of the 96 full
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`duplex signals. However, it is often not desirable to beamform the dedicated control
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`channel used as beacons, since such control channels must be generally available
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`throughout a given cell. Consequently, in the absence of major blocking structures, no
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`weighting factors will be applied to BTS 200 transmitted control channels which function
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`as beacons.
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`Calibration factors and angular weighting factors may be stored in memory
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`locations in the base station digital array processing card 260. These factors are
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`preferably stored separately. Neglecting control channels, for a cellular system having
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`96 channels and having 4 duplexed transmit/receive antennas elements, the number of
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`memory locations required is 768 (96x2x4) for calibration factors and the same number
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`for separately stored weighting factors. Angular weighting factors must generally be
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`frequently updated since the cellular user may be moving and a variety of interference
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`sources may arise.
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`Calibration of a Frequency Division Duplex (FDD) Wireless Adaptive Array Using
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`a Remote Translating Repeater
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`In another calibration method, a translating repeater is placed (or if already used
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`in the cellular system, utilized) at a known location with respect to BTS 200.