(12) United States Patent
`US 7,312,750 B2
`(10) Patent N0.:
`
` Mao et al. (45) Date of Patent: Dec. 25, 2007
`
`
`US007312750B2
`
`(54) ADAPTIVE BEAM-FORMING SYSTEM
`USING HIERARCHICAL WEIGHT BANKS
`FOR ANTENNA ARRAY IN WIRELESS
`COMMUNICATION SYSTEM
`
`7,088,288 B1 =1
`7,099,383 B2 =1
`2003/0222818 A1
`2005/0143132 A1*
`
`8/2006 Margolese et a1.
`8/2006 Struhsaker et a1.
`12/2003 Regnier et a1.
`6/2005 Proctor et a1.
`
`.......... 342/377
`......... 375/222
`
`.............. 455/561
`
`(75)
`
`Inventors: Jian Mao, Gaithersburg, MD (US);
`Oscar Frederick Somerlok, III,
`Potomac, MD (US)
`
`(73)
`
`Assignee: Comware, Inc., Rockville, MD (US)
`
`(*)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 300 days.
`
`(21)
`
`Appl. N0.: 11/071,249
`
`(22)
`
`Filed:
`
`Mar. 4, 2005
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`
`1394966 A2
`
`3/2004
`
`OTHER PUBLICATIONS
`
`Godara, L., “Application of Antenna Arrays to Mobile Communi-
`cations, Part II: Beam-Forming and Direction-of—Arrival Consider-
`ations,” Proceedings of the IEEE, vol. 85, No. 8, Aug. 1997, pp.
`1195-1245.
`
`Van Veen et a1., “Beamforming: A Versatile Approach to Spatial
`Filtering,” IEEE ASSP Magazine, Apr. 1988, pp. 4-24.
`
`(65)
`
`(60)
`
`(51)
`
`(52)
`(58)
`
`(56)
`
`Prior Publication Data
`
`* cited by examiner
`
`US 2005/0206564 A1
`
`Sep. 22, 2005
`
`Related US. Application Data
`
`Primary ExamineriDao Phan
`(74) Attorney, Agent, or FirmiPillsbury Winthrop Shaw
`Pittman, LLP
`
`Provisional application No. 60/554,408, filed on Mar.
`19, 2004.
`
`(57)
`
`ABSTRACT
`
`Int. Cl.
`
`(2006.01)
`H01Q 3/22
`(2006.01)
`H01Q 3/26
`US. Cl.
`....................................... 342/377; 342/373
`Field of Classification Search ................ 342/367,
`342/373, 377, 378, 383; 455/69, 101, 562.1
`See application file for complete search history.
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`6,049,307 A
`
`4/2000 Lim
`
`An adaptive beam-forming system using hierarchical weight
`banks for antenna arrays in wireless communication systems
`is disclosed. The present invention can be applied for both
`reception and transmission beam-forming. The hierarchical
`weight banks contain weights that are pre-calculated based
`on pre-set beam 100k directions. By comparing measure-
`ments of chosen signal quality metrics for pre-set 100k
`directions, the best weights, and thus the best beam 100k
`direction, can be selected from the weight banks.
`
`41 Claims, 10 Drawing Sheets
`
`CONNECTED TO MULTIPATH DELAY
`FRGILE ESTIMATION UNITS - 460
`
`
`
`
`I!
`
`ET" am
`___II'‘—
`
`
`
`
`
`
`
`
`mm.emu"
`uaaunsusw
`
`
`
`
`
`
`
`CONNECTED
`TO Mk0 - 480
`
`EEAMFORMING
`UNIT] was
`(I =1, 1.
`L)
`
`LG 1006
`
`1
`
`LG 1006
`
`

`

`U.S. Patent
`
`Dec. 25, 2007
`
`Sheet 1 of 10
`
`US 7,312,750 B2
`
`FIG. 1
`
`410 k. X ‘
`{
`
`-
`
`xx“— 400
`,
`
`
`
`
`
`
`
`
`
`MAXIMUM HATIOCOMBINER
`
`j
`
`wa/
`(MEG)
`9...?“
`
`Output
`
`y (n)
`
`2
`
`

`

`U.S. Patent
`
`Dec. 25, 2007
`
`Sheet 2 of 10
`
`US 7,312,750 B2
`
`FIG. 2
`
`CONNECTED TO MULTIPATH DElAY
`PROFILE ESTIMATION UNITS ~ 450
`
`
`
` MEASUREMENT
`VVEIGHT SELECTION
`
`
`‘—
`
`790
`
`CONNECTED
`TO MRC ~ 480
`
`BEAMFORMENG
`UNITI ~455
`(I =1, 2,
`
`L)
`
`3
`
`

`

`U.S. Patent
`
`Dec. 25, 2007
`
`Sheet 3 of 10
`
`US 7,312,750 B2
`
`FIG. 3
`
`900
`
`510
`
`WEIGHT BANK 1
`(1 s! TIER
`WEIGHTS)
`
`SELECT ONE LOOK DIRECTION
`
`MEASUREMENT OF SIGNAL
`QUALITY
`
`@\
`
`910
`
`DETERMINING SEQ? SIGNAL
`QUALITY LOOK
`DIRECTION
`
`920
`
`
`FOUND BESTWEIGHTS?
`
`
`
`YES
`
`APPLY WEIGHTS TO RECEIVED
`SIGNAL
`(BEMFORMING)
`
`93“
`
`WEIGHT BANK i
`NEXT TIER
`WEIGHTS
`
`
`
`
`
`
`
`4
`
`

`

`U.S. Patent
`
`Dec. 25, 2007
`
`Sheet 4 of 10
`
`US 7,312,750 B2
`
`FIG. 4
`
`
`
`
`
`l.|.l.'.|.l...I.|.Iu.|.l.l-.II.I.I.II..'.'.!1Il.'..|.I.I.II.|I.I.I...I_.I.'..I..II.lI.I.I.I.I.I.I.I.l
`
`
`rxz<mH1063
`
`mx2<mFrom;
`
`The beam direction search resolution = 15°
`
`5
`
`

`

`U.S. Patent
`
`Dec. 25, 2007
`
`Sheet 5 of 10
`
`US 7,312,750 B2
`
`FIG. 5
`
`330
`
`........... j. ..........
`
`o
`
`f
`
`1
`
`130
`
`MIRROR BEAM 700
`
`MIRROR BEAM 700
`
`
`
`MIRROR BEAM 700
`
`6
`
`

`

`U.S. Patent
`
`Dec. 25, 2007
`
`Sheet 6 of 10
`
`US 7,312,750 B2
`
`FIG. 6
`
`MI]
`
`UP
`
`UP
`
`UP
`
`425
`
`CONVERTER
`
`CONVERTER
`
`CONVERTER
`
`.35 fix-
`
`475
`
`TRANSMIT _.
`SI GNALs ( n)
`
`
`
`TRANSMIT BEAMFORMING UNIT
`
`[4"— RECEPTION BEAM
`DIRECTION
`485
`
`FROM RECEPTION
`BEAMFORMING
`
`(455 I
`
`7
`
`

`

`U.S. Patent
`
`Dec. 25, 2007
`
`Sheet 7 of 10
`
`US 7,312,750 B2
`
`FIG. 7
`
`CONNECTED -TO RECEPTION
`BEAMFORMING UNITS (465)
`
`
`
`
`
`
`
`
`RECEPTION
`BEAM
`DIRECTION
`485
`
`735
`
`510 ~ 520
`
`
`
`CONNECTION TO DIA (435)
`
`TRANSMIT
`SIGNAL s(n)
`960
`
`T
`T
`BEAMFORMING
`UNIT 475
`
`8
`
`

`

`U.S. Patent
`
`Dec. 25, 2007
`
`Sheet 8 of 10
`
`US 7,312,750 B2
`
`FIG. 8
`
`400
`
`no.0--.
`
`400
`
`
`
`Im 430
`
`DOWN
`CONVERT
`
`DEGITAL MULTIPLEXER l DEMULTIPLEXER
`
`465
`
`MULTIPATH DELAY PROFILE ESTIMATION
`
`-—_
`
`RECEPTION BEAMFORMING UNITS
`
`
`(MRC)
`
`MAXIMUM RATIO COMBINER
`
`Output y(n)
`
`455
`
`480
`
`9
`
`

`

`U.S. Patent
`
`Dec. 25, 2007
`
`Sheet 9 of 10
`
`US 7,312,750 B2
`
`404
`
`445
`
`DIA
`
`720
`
`FIG. 9
`
`402
`
`404
`
`445
`
`'75
`
`435
`
`DIA
`
`510~520
`
`WEIGHT BANKS
`
`I
`
`410
`
`420
`
`u
`
`DOWN
`
`CONVERT
`
`'7
`
`435
`
`,_ 43"
`
`
`/620 ‘
`
`SIGNAL QUALITY
`MEASUREMENT
`
`WEIGHT
`
`SELECTION
`
`I
`
`OUTPUT
`DIGITAL
`SIGNAL
`
`v(n)
`
`10
`
`10
`
`

`

`U.S. Patent
`
`Dec. 25, 2007
`
`Sheet 10 of 10
`
`US 7,312,750 B2
`
`FIG. 10
`
`404
`
`402
`
`404
`
`445
`
`435
`
`620
`
`m
`
`445
`
`410
`
`425
`
`435
`
`RECEIVED
`
`,
`
`SIGNALQUALITY
`
`SIGNAL
`
`’9' MEASUREMENT
`r— WEIGHT BANKS
`WEIGHT
`I
`
`SELECTION
`
`I
`
`51o~520
`
`720
`
`INPUT DIGITAL
`TRANSMISSION
`SIGNAL
`
`x(n)
`
`11
`
`11
`
`

`

`US 7,312,750 B2
`
`1
`ADAPTIVE BEAM-FORMING SYSTEM
`USING HIERARCHICAL W'EIGHT BANKS
`FOR ANTENNA ARRAY IN WIRELESS
`COMMUNICATION SYSTEM
`
`
`
`CROSS REFERiNC A TO R
`
` AT ATED
`APPLICATION
`
`l 19(e) to
`This application claims priority under 35 U.S.C.
`US. Provisional Application No. 60/554,408, filed Mar. 19,
`2004, the specification and drawings of which are incorpo—
`rated herein by reference.
`
`
`
`BACKGROUND OF THE INVENTION
`
`10
`
`15
`
`2
`beam—forrner. Adaptive antenna array beam—forming tech—
`nology is performed in base—band by using digital signal
`processing algorithms and the beam—forming weights are
`calculated according to weight computing algorithms. Sev—
`eral beam—forming weight computing approaches
`are
`described in the paper,
`“Beam—forming: A Versatile
`Approach to Spatial Filtering”, IEEE ASSP Magazine, Vol.
`April, 1988. pp. 4-24. Also, descriptions of beam-forming
`approaches using adaptive antenna arrays in wireless com-
`munication systems is also available in “Application of
`Antenna Array to Mobile Communications, Part 11: Beam-
`
`forming and Direction-of—Arrival Considerations” disclosed
`
`A
`
`
`
`in Proceeding of]
`A, Vol. 85, No. 8, August 1997, pp.
`1195-1245.
`
`Beam-forming with adaptive antenna arrays, yields maxi-
`mum SINR (Signal -to-1ntcrfcrcncc plus Noise Ratio) and an
`adjustable beam pattern, which allows forming the peaks to
`the desired signal (S) and nulling of interference signals (1).
`Such a system is disclosed in US. Pat. No. 6,049,307,
`which features an adaptive phased antenna array using the
`weight memory unit to adjust the beam directions. This
`patent features an adaptive phased array, and the beam
`direction is scanned by adjusting the amplitudes and phases
`of received RF signals by using a weight memory unit which
`stores pre—computed weights (amplitudes and phases of RF
`signals supplied to each antenna element).
`For the application of beam-forming technology in wire-
`less communication systems, a technically and economically
`feasible method is to use switch beam antenna array where
`the fix-beams are formed by applying phase shift to the
`individual antemia elements in the antemia array. Generally,
`in switched beam-forming technology, one of a set of
`fixed—beams is selected to the desired mobile or base station
`based on the best measurement of received signal power.
`This fixed-beam approach could oifer feasible coverage and
`capacity extension especially in a macro cell environment
`but the performance of this approach will be degraded in
`large angle spread or multipath propagation environment.
`
`
`
`SUMMARY OF THE INVENTION
`
`It will be appreciated that the beam—forming technologies
`discussed above suifer
`from various drawbacks. For
`example, the beam beam-forming technologies associated
`with switched beam array systems requires the development
`of a method of beam selection, in such a way that each
`mobile or base station can be quickly and accurately
`switched onto the correct beam that covers the area where
`the desired mobile and base station is located.
`
`the mobile terminal/base station
`For receiving modes,
`must determine which of the present beams should be
`selected in order to receive the signal from the desired
`mobile terminal/base station. Similarly, for transmission
`mode,
`the mobile terminal/base station must select
`the
`suitable beams to transmit the signal to the desired mobile
`terminal/base station. The cost of producing such a system
`is proportional the number of look directions that must be
`supported and can become expensive due to the need for one
`set of analog hardware for each beam look direction.
`For
`the beam-forming technologies associated with
`dynamically phased array systems, the direction of arrival
`(DOA) of the desired signal needs to be estimated or known
`previously in order to adjust the phase shifters to make the
`beam main lobe point to the target mobile or base station.
`This dependence 011 DOA requires complicated direction
`
`,
`
`30
`
`35
`
`4o
`
`45
`
`1. Field of the Invention
`The present invention relates wireless communications
`systems and, more particularly, to beam—forming technolo—
`gies and associated methodologies.
`2. Description of the Related Art
`Antenna array systems with desired beam-patterns have
`been considered as a solution to improve the spectral effi—
`ciency and communication quality for both uplink (mobile-
`to-base station) and downlink segments (base station-to-
`mobile) in wireless communication systems. The beam-
`forming technologies employed with anteima arrays can be
`a powerful means to increase system capacity,
`improve
`quality of service (QoS), reduce co-channel
`interference
`(CCI), and multipath fading. Generally, this is because a
`transmitter/receiver using an antenna array can increase or
`decrease antenna gain in the intended look directions (i.e.,
`approximate direction of mobile terminal location).
`There are several ways to realize such beam-forming
`technologies. For example, switch beam antenna arrays
`select a beam pattern out of a set of previously fixed beam
`patterns, depending on the receiving signal power measure—
`ment and spatial location of the desired mobile terminal or
`base station. Such systems typically comprise multiple
`antenna elements, a fixed beam-forming network, multiple
`beam power measurement units, a beam selection unit, and
`transceiver. For switch beam antenna array, the transmitting/
`receiving beam is selected by [measuring the desired signal
`power within each beam and selecting the beam having the
`largest received signal power. The received signal power
`within each beam may be averaged over the fast fading
`pattern.
`A second example of beam-forming technology is what is
`employed in dynamically phased array systems. In such
`systems, the beam pattern is modified based on the look
`direction of the desired mobile or base station via phase ,
`shifter. Dynamically phased array systems typically com-
`prise multiple antenna array elements, multiple phase
`shifters (one for each antenna element), a weight computa-
`tion unit and a power combiner. Beam-forming technology
`using dynamically phased array has the advantages of
`simple weight calculation which based on the look direc-
`tions, high directivity and easy implementation. However,
`the direction of arrival (DOA) of the desired signal needs to
`be estimated or known a priori in order to adjust the phase
`shifters and make the beam main lobe point to the target
`mobile or base station.
`A third example of beam-forming technology is what is
`used in frilly adaptive antenna arrays. The adaptive antenna
`array system typically comprises multiple (M) antenna ele-
`ments, M RF units, M down converter to convert RF signals
`into base band signals, M A/D converters, a weight com-
`putation unit to generate the beam-fonning weights, and a
`
`55
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`
`65
`
`12
`
`12
`
`

`

`US 7,312,750 B2
`
`5
`
`3
`finding algorithms and overall system performance hinges
`on the accuracy of the look direction information and
`angular spread effect.
`Finally, the bearn—forming technologies associated with
`adaptive antenna array systems, require complex weight
`computing algorithms and powerful DSP processors, which
`are expensive and consume a great deal of battery power.
`Also, the adaptive antenna array should be well calibrated.
`Further, with regard to U.S. Pat. No. 6,049,307, because the
`amplitude and phase adjusting procedure is carried out on
`the RF stage with phase shifter and the RF power corrrbiner/
`feeder/divider are analog components, the application of this
`technique would be limited cost and size in the wireless
`communication systems. Also, this technique can not be
`applied in the multipath propagation environment as the 15
`multipath components can not be separated by this tech-
`nique.
`For at least these reasons. the principles of the present
`invention, as embodied and broadly described herein, pro-
`vide for the present invention is directed to providing an
`adaptive antenna array system for a wireless communication
`system that employs a beam—forming network having a set
`of hierarchical weight banks to suppress interference and
`background noise and to improve system performance, such
`as SINR (Signal-to-Interference plus Noise Ratio) and BER
`(Bit Error Rate), within a single—path or multipath propaga—
`tion environment.
`
`20
`
`invention provides a
`the present
`In one embodiment,
`wireless communication system, comprising an antemra
`array structure having a plurality of antenna elements that
`receive and transmit radio-frequency signals, one or more
`radio-frequency units and frequency converters configured
`to transform received RF signals to receive analog base-
`band signals and transform analog transmit base—band sig—
`nals into a transmit RF signals. one or more analog-to-digital
`converters configured to convert the receive analog base-
`band signals into a receive digital base-band signals and one
`or more digital-to-analog converters configured to convert
`transmit digital base—band signals into transmit analog base—
`band signals. The wireless communication system further
`comprises a multipath delay profile estimation tmit config-
`ured to estimate delays of multipath signal components
`based on the receive digital base—band signals, and a plu—
`rality of beam-forming units configured to process the
`multipath signal corrrponents. Each of the beam-forming
`units comprise a set of hierarchical weight banks that store
`pre-calculatcd weights in accordance with pre-spocificd
`beam look directions, a digital processing unit configured to
`estimate a signal metric, select the best weights from weight
`banks based on the estimated signal metric, and apply the
`selected weights to the received and/or transmitted signal to
`shift a beam pattern to point to the best beam look direction.
`The present invention is different from prior art as the
`beam-forming procedure is performed entirely in the digital
`basc band using digital signal processing algorithms. The
`present invention has more flexibility than that of the fixed
`beam switch approach as the present invention implements
`digital beam-forming that can be implemented with software
`defined technology which reduces analog hardware costs
`and is more easily adapted and portable to different wireless
`systems.
`In the present invention, by using multiple beam-forming
`units and based on the look directions of a desired signal and
`digitally tuning the beam based on the best measurement of
`quality metric for the received signal such as instant signal
`power, SINR or BER, and with a set of pre-calculated weight
`
`30
`
`35
`
`45
`
`50
`
`6O
`
`65
`
`13
`
`4
`banks, the beam—former performance would be improved in
`angle spread and multipath propagation environments.
`The pre—calculated hierarchical weight banks are com-
`puted a priori based on data-independent beam-forming
`teclmology which uses pre—sct look directions and array
`steering vector as beam—forming weights to provide the
`generated beams with high directivity and high resolution.
`The present
`invention does not require the pre-set
`look
`directions to be absolute directions from a fixed reference.
`Rather, the pre—set look directions must only be set at some
`known interval and known ofiset angle from adjacent look
`directions. Thus, the present invention does not require any
`absolute direction-of-arrival (DOA) information to be cal-
`culated in order to perfomr beam steering.
`The pre—calculated hierarchical weight banks consist of
`weights that define beams for pre-set look directions. In the
`case of a planar field, for example,
`the azimuth can be
`divided into pre-set look directions. For each look direction
`there exists a set of weights that defines a beam, which is
`centered on that look direction. These weights are stored in
`one or rrrore tiers of weight banks, which cover all pre-set
`look directions. The weights are applied to the signal to
`create a beam pattern pointing to a specific look direction.
`When the present invention is used in a receiver, weights
`for different look directions can be applied to all or part of
`a received signal and the quality of the resulting signal from
`each beam can be compared so as to effectively search for
`the look direction that yields the highest signal quality.
`“Signal quality” may be defined as any desired signal
`attribute such as instant power of the received signal or
`SIN R of the received signal, for example. The signal quality
`metric that is used will depend on the specific application for
`which the present invention is being used. Once the best
`look direction is determined, the optimal weights are applied
`to the entire received signal. With this beam-forming pro-
`cedure,
`the SINR and BER of a received signal can be
`improved. In a wireless network, an improvement in SINR
`yields great benefits such as increased network capacity,
`
`extended coverage and lower bit-error-rates (BER).
`For multipath environments, multiple beam-forming Imits
`can be used to collect the multipath signal components if
`multipath components are collected by different beams.
`The processing time for the present invention is propor-
`tional to the number of pre-set look directions. In order to
`support more efficient algorithms to search for the best look
`direction,
`the weights are stored in hierarchical weight
`banks. An efficient
`look direction searching and weights
`selection scheme, using a binary tree structure, is presented
`in the detailed description of the present invention. ()ther
`structures may also be used for the weight banks. The
`present invention is not limited to any one particular weight
`bank structure.
`For urriforrrr linear antenna arrays, the rrrirror beam can be
`used to further reduce beam direction searching time when
`the coverage of beam direction search is greater than 180
`degree.
`When an antenna array containing parasitic antenna ele-
`ments is employed, there is at
`least one active antenna
`element connected to a radio-frequency unit, which includes
`a frequency converter configured to transform received RF
`signals to receive analog base-band signals and transform
`analog transmit base-band signals into transmit RF signals,
`one or more analog-to-digital converters configured to con-
`vert the received analog base-band signals into base-band
`signals, and one or more digital—to—analog converters con—
`figured to convert transmit digital base-band signals into
`transmit analog base-band signals. In addition to the active
`
`13
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`

`

`US 7,312,750 B2
`
`10
`
`15
`
`,
`
`30
`
`35
`
`5
`element(s), the parasitic antelma array may also include a
`plurality of parasitic antenna elements, each of which con-
`nects to either an adjustable passive impedance component
`or directly to electrical ground
`In the present invention, the adaptive beam-forming sys-
`tem is based on the measurement of a signal quality metric
`with pre-set look directions and selection of the correspond-
`ing set of pre-calculated weights to beam-form to the desired
`look direction.
`The present invention ofiers a significant improvement
`over prior art in that there is no calibration required for the
`antenna array. By eliminating the need for calibration, the
`present invention reduces manufacturing costs and compo-
`nent costs for devices employing beam-forming technology.
`For transmission beam—fonning,
`information from the
`receiver beam-forming process can be used to determine the
`best look direction for the transmission beam. For example,
`the transmitter may transmit in the same direction as the best
`receiver look direction. This is especially useful for wireless
`communication systems using time—division—duplex (TDD)
`mode of operation where uplink and downlink channels use
`the same frequency. This technique may also be used for
`frequency-division-dup1ex (FDD) wireless communication
`systems. In the presence of received multipath signals,
`transmission weights can be selected from the same weight
`bank based on the received multipath component with the
`best signal quality (i.e. transmit only in the direction of the
`best received multipath component).
`In the present invention. the reception adaptive beam—
`forming system based on the hierarchical weight banks
`includes an antenna array system where a plurality of
`antenna elements are structured as a linear array, a circular
`array, or any other two—dimensional or three—dimensional
`structure. The antelma elements may be omni-directional,
`sectored (directional), or a combination of omni-directional
`and sectored antennas. Further, the antenna elements may be
`“active” (i.e. connected to an RF receiver chain), or “para-
`sitic” (i.e. connected to an adjustable passive impedance
`component or directly to electrical ground).
`One or more RF units and down converters are used to
`transform RF signals into base band signals and are con-
`nected to one or a plurality of A/D converter units, which
`convert the analog base band signals into digital signals. An
`electronically-controlled switch may be employed to multi-
`plex signals from multiple antenna elements through a single
`RF chain, thereby enabling multiple active antenna elements
`to share a single RF chain.
`A multipath delay profile estimation unit is then used to
`estimate the delay profiles for each multipath component,
`separate the multipath components in the temporal domain ,
`and distribute these multipath signal components to multiple
`beam-fonning units. The multipath delay profile estimation
`unit detects multipath components received by the antenna
`array and separates the corresponding multipath compo-
`nents. For example,
`if two multipath components are
`received while using a three antenna array. the multipath
`delay profile estimation unit should identify a total
`two
`components and result in six outputs (i.e. two multipath
`signals from each of the three antennas). The corresponding
`multipath components from each antelma are correlated and
`forwarded to the beam-forming units. The number of beam-
`forming units employed is equal to the number of multipath
`components received. Each beam-forming unit accepts a
`number of input signals equal to the number of antemia
`elements in the array.
`Each beam-forming unit applies weights to its input
`signals in order to implement the beam-forming and deter-
`
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`mine the set of weights that yields the best output signal
`quality. Each beam-forming unit outputs one and only one
`signal.
`in a
`If multiple beam-forming units are employed (i.e.
`multipat 1 environment), a Maximum Ratio Combiner can be
`used to combine the output signals from the different beam—
`forming units.
`The apparatus for the reception adaptive beam-fonning
`system based on the hierarchical weight banks include a
`plurality of antelma elements spaced in specific structure
`(e.g. linear, circular, etc.), a multipath delay profile estima—
`tion unit which estimates the delay of multipath components
`and distributes the multipath components to the beam-
`forming units, a set of hierarchical weight banks which are
`computed off—line and pre—stored in some form of memory
`(e.g. Read-only Memory, Flash Memory, Random Access
`Memory, EPROM, etc.), and one or more receiver beam-
`forming units, which evaluate the quality of a received
`signal in various beam—formed look directions, determine
`the best look direction for each received multipath compo—
`nent of the signal and apply the appropriate weights asso-
`ciated with each look direction separately to each received
`multipath component and performs a weighted sum of the
`signals received from each antenna element. A Maximum
`Ratio Combiner may be used to combine multiple output
`multipath signal components from the beam-fonning units
`in the ca se where multiple beam-forming units
`are
`employed.
`In another embodiment of the present invention, a trans—
`mission beam-forming system for use in a wireless commu-
`nication system is described. 'lhe transmission beam-form-
`ing system includes an antenna array system and a plurality
`of RF units which may be shared with the receiver beam—
`forming system, a plurality of up-converters which trans-
`form base-band signals into RF signals, a plurality of
`digital-to-analog (D/A) conversion units which convert the
`digital signals to analog signals, and a transmit beam-
`forming unit.
`In the transmit beam-forming unit, the multipath selection
`Imit is used to select the best path from received multipath
`components based on the received signal quality metric. The
`weight selection unit uses the same set of weights as the
`receiver beam-forming units and applies these weights for
`transmission beam-forming. In the case where multiple
`signal paths were received (i.e. multipath), the transmission
`beam-forming unit may employ only the set of weights
`associated with the best received path, based on the received
`signal quality metric, and then apply that single set of
`weights to the transmitted signal. 'l'ransmitting only in the
`same direction as the best received multipath component is
`a simplification of the transmission beam—forming but may
`be desirable to simplify system designs, reduce production
`costs and reduce component costs.
`
`BRIEF DESCRIPTION OF DRAWINGS
`
`
`
`Embodiments o the invention will now be described, by
`way of example only, with reference to the accompanying
`schematic drawings in which:
`FIG. 1 depicts a receiver beam-forming system, in accor-
`dance with an embodiment of the present invention;
`FIG. 2 illustrates a receiver beam-fonning unit, in accor-
`dance with an embodiment of the present invention;
`FIG. 3 provides a flow chart for the search process to
`determine the set of weights associated with the best
`receiver look direction, in accordance with an embodiment
`of the present invention;
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`US 7,312,750 B2
`
`7
`FIG. 4 depicts a hierarchical weight bank structure based
`on a binary tree, in accordance with an embodiment of the
`present invention;
`FIG. 5 illustrates beam pattern for the mirror beam
`generated by various look directions of a uniform linear
`antenna array, in accordance with an embodiment of the
`present invention;
`FIG. 6 depicts a transmission beam-forming system for an
`antenna array in a wireless system, in accordance with an
`embodiment of the present invention; and
`FIG. 7 illustrates a transmission beam—forming unit. in
`accordance with an embodiment of the present invention;
`FIG. 8 depicts single RF receiver beam-forming system in
`accordance with an embodiment of the present invention;
`FIG. 9 illustrates a reception beam—forming system using
`an antenna array containing one or more parasitic antenna
`elements, in accordance with an embodiment of the present
`invention; and
`FIG. 10 illustrates a transmission beam—forming system
`using an antelma array containing one or more parasitic
`antenna elements, in accordance with an embodiment of the
`present invention,
`In the Figures, corresponding reference symbols indicate
`corresponding parts.
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`10
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`DETAILED DESCRIPTION OF THE
`
`INVENTION
`
`8
`units and combined by a combiner mechanism 480, such as
`a Maximum Ratio Combining (MRC) unit after beam—
`forming.
`As noted above, receiver beam-forming system comprises
`a plurality L of beam-forming units in order to process at
`least I, of multipath components. One beam-forming unit is
`assigned for each distinct multipath component. In a mul—
`tipath environment, the multipath components often arrive at
`
`the receiver from different directions. Each beam-forming
`Imit determines the best beam look direction for its assigned
`multipath component. In this way,
`the present invention
`enables a separate beam to be focused on each multipath
`component, thereby maximizing the received signal quality
`of each multipath component.
`Each of the beam—fonning units references a set of weight
`banks to detennine the best look direction weights for its
`assigned multipath component. The best look direction for
`receiving each desired signal can be determined by mea sur-
`ing a quality metric, such as, for example, instant power,
`SINR, frame error rate, bit error rate, or any other metric, for
`each pre-set beam look direction.
`A directional beam is then formed by applying a pre-
`calculated set of weights to the received signals. These
`pre-calculated weights are computed for various difierent
`look directions. The exact direction and spacing between the
`look directions depends on the direction search resolution
`and the azimuth of the desired region to be searched.
`For the weight computation in the present invention, a
`data-independent method which uses pre—set look directions
`and array steering vector as beam-forming weights provides
`the generated beams with high directivity and high resolu—
`tion. In general, data-independent methods do not require
`any information about the received or transmitted signals to
`calculate the beam-forming weights. A detailed description
`of cata-independent methods can be found in the paper,
`“Beam—forming: A Versatile Approach to Spatial Filtering”,
`
`
`
`Ir A A ASSP Magazine, Vol. April, 1988, pp. 4-24. In hier-
`archical weight banks, the pre-calculated weight vector may
`be computed off-line for the direction 9, as:
`
`
`
`1
`WW” : Mafia
`
`where M is the number of antenna elements, a(6,) is the
`array steering vector, which is the function of the direction
`01.. For the different array structure, a(Ul.) will be difierent,
`e.g. for the linear antelma array:
`a(0,-):[l expifi—j-Z-n-d/A-cos 0,) .
`.
`(M—l)-cos 0,)]7
`
`. exp(—j-2-n-d/}v-
`
`where d is the interval of the elements, A is the signal
`wavelength. The direction 6, is selected from the tree-type
`beam direction search scheme for the dilferent
`tiers in
`hierarchical weight banks.
`In order to facilitate efficient searching, the weights for
`each receiver look direction may be stored in a hierarchical
`structure, such as a binary tree or B+ tree structure. In such
`a configuration,
`the first tier of weight banks consist of
`weights for look directions that are spaced apart such that the
`entire search azimuth can be covered. The number of look
`directions in the first tier weight bank and the spacing of
`these look direction may be determined by the Rayleigh
`limitation for the number of antelmas and antenna structure
`being employed.
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`The present invention provides a wireless communication
`system employing an adaptive beam-forming network that
`utilizes hierarchical weight banks. It will be appreciated that
`such a system may be employed at either a base station or
`mobile terminal, or both.
`FIG. 1 schematically depicts a receiver beam-forming
`system, in accordance with an embodiment of the present
`invention. The system comprises an antenna array with M
`antenna elements 400. These antenna elements may be
`configured as omni-directional, sectorized, or a combination
`of omni-directional and sectorized elements.
`The antelma array feeds into a plurality of RF units 410
`and down converters 420, and then converted into digital
`signals by AD units 430. The M output digital signals from
`A/D converters are fed into a multipath delay profile esti-
`mation unit 460.
`To enhance performance in a multipath propagation envi—
`ronment, the multipath delay profile estimation unit 460 is
`used to distinguish the multipath signals and distribute the
`multipath signals to the beam-forming units 465. The delay
`profile estimation unit 460 is configured to distinguish the
`multipath components. separate the multipath components 7
`in temporal domain, as well as distribute these multipath
`signal components to different beam-forming units 465,
`labeled as l, 2,
`.
`.
`.
`, I,.
`The beam-forming units operate in the digital domain
`with digital signal processing algorithms. The Maximum
`Ratio Combiner 480 is used to combine the output signals
`from the bea