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`US 20020114269A1
`
`(l9)
`
`United States
`
`(12) Patent Application Publication (10) Pub. No.: US 2002/0114269 A1
`(43) Pub. Date: Aug. 22, 2002
`
`()nggosanusi et al.
`
`(54) CHANNELAWARE ()l’I‘IMAL SPACE-'l‘IME
`SIGNALING FOR WIRELESS
`COMMUNICA'I‘ION OVER WIDEBAND
`MULTIPATH CHANNELS
`
`(76)
`
`(3|)
`
`Inventors: Eko Nugroho Onggosanusi, Dallas,
`TX (US); Hart")t Dorm Van Veen,
`McFarland, WI (US); Akbar
`Muhammad Sayced, Madison, WI
`(US)
`Add
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`ress:
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`NIIfileS & HILLES’ S'C' .
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`Appl. No”
`Filetl‘
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`tl9t970,4t50
`Oct 3 2001
`'
`’
`Related U.S. Application Data
`
`Prov isiona] application No. 60.t237,626, filed on Oct.
`3, 20m_
`
`Publication Classification
`
`(51)
`
`Int. Cl.7 ...................................................... H04] 11100
`
`(52) U.S. Cl.
`
`............................................ 3701208; 370508
`
`(57)
`
`ABSTRACT
`
`A method and system is described for more optimally
`managing the usage of a wideband space-time multipath
`channel. The widchand space-time multipath channel
`is
`decomposed into a plurality of orthogonal sub—channels,
`where the orthogonal sub-channels having the best signaling
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`llme multipath channel into a plurality of orthogonal sub-
`channels, channel estimates are determined for each signal
`propagation path. A closed-form singular value decomposi-
`tion of the channel corresponding to each receive antenna
`before coherent combining is utilized to obtain an orthogo~
`nal decomposition of the overall effective space—time chan—
`nel after coherent combining. By using the overall ell‘ective
`space—time channel after coherent combining rather than
`before coherent combining, the complexity and correspond-
`ingly the resources required for obtaining the orthogonal
`sub-channels is significantly reduced. The method and 53’5'
`tem further provide for transmit power to be allocated
`between the selected sub-channels in order to minimize the
`effective hit—error rate for a fixed average throughput or to
`maximize average throughput for a fixed minimum efi'cctive
`bit-error rate.
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`Patent Application Publication Aug. 22, 2002 Sheet 1 0f 15
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`US 2002/0114269 A1
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`Patent Application Publication Aug. 22, 2002 Sheet 3 0f 15
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`Patent Application Publication Aug. 22, 2002 Sheet 4 0f 15
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`Patent Application Publication Aug. 22, 2002 Sheet 5 0f 15
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`Patent Application Publication Aug. 22, 20-02 Sheet 7 0f 15
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`US 2002/0114269 A1
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`Patent Application Publication Aug. 22, 2002 Sheet 8 0f 15
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`US 2002/0114269 A1
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`Patent Application Publication Aug. 22, 2002 Sheet 9 0f 15
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`US 2002/0114269 A1
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`Patent Application Publication Aug. 22, 2002 Sheet 10 0f 15
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`US 2002/0114269 A1
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`US 2002/0114269A1
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`US 2002/0114269 A1
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`US 2002/0114269 A1
`
`Aug. 22, 2002
`
`CHANNEL AWARE OI’I‘IMAL SPACE-TIME
`SIGNALING FOR WIRELESS COMMUNICATION
`OVER WIDEBAND MULTIPATH CHANNELS
`
`[0001] This application claims the benefit of US. Provi—
`sional Application Serial No. 603231626, tiled Oct. 3, 2000,
`which is hereby incorporated by reference in its entirety.
`
`[0002] This invention was made with United States gov-
`ernment support awarded by the following agencies: NSF
`ECS-9979448. The United States has certain rights in this
`invention.
`
`BACKGROUND OF THE INVENTION
`
`[0003]
`
`1. Field of the Invention
`
`[0004] The present invention relates to communication of
`one or more data signal streams over a wideba nd space-time
`multipath channel, and more particularly to the decomposi-
`tion and selection for use of one or more subchannels within
`the ntultipath channel.
`
`[0005]
`
`2. Description of Related Art
`
`[0006] The use of wireless communications has grown
`significantly over the past several years. With it the need to
`make better utilization of the available spectrum, which is
`allocated for use in wireless communications, has similarly
`grown.
`
`In order to support multiple private two—way com—
`[0007]
`mu nications, the available spectrum is generally divided into
`a plurality of minimally andlor non—interfering subchannels
`which are then dynamically allocated between users on a per
`request basis. Several techniques have been used to improve
`the utilization of the available spectrum, including improve—
`ments in frequency division, signal modulation, and spatial
`division.
`
`Improvements in frequency division techniques
`[0008]
`have enabled a greater number of subchannels to be defined
`in the allotted spectrum by allowing the available frequency
`to be divided into narrower distinct slices or frequency
`bands.
`Improvements
`in signal modulation techniques
`including signal compression,
`time division multiplexing
`and spread spectrum techniques, such as code division
`multiple access, have enabled enhancements in both signal
`quality and channel capacity. Improvements in spatial divi-
`sion techniques which have traditionally included creating
`localized transmission areas, or cells, and other techniques
`for geographically restricting signal
`transmissions, have
`enabled frequency to be reused in geographically distinct
`and non-adjacent areas.
`
`[0009] More recently spatial division techniques have
`begun to take advantage of inherent constructive and
`destructive interfering signal patterns between similar sig-
`nals originating from or received by multiple spaced apart
`antennas to more narrowly define a signal region between
`which a signal is being transmitted or received. In this way
`signal patterns can be defined in such a way so as to focus
`a signal
`transmission within a select portion of a given
`geographical area by maximizing the strength of the signal
`directed toward an intended recipient, while minimizing the
`strength of the signal directed toward non-intended recipi-
`ents for which the signal might create unwanted interfer-
`ence.
`
`In addition to inherent constructive and destructive
`[0010]
`interfering signal patterns between signals originating from
`or received by multiple spaced apart transmitting and receiv—
`ing antennas, constructive and destructive interfering signal
`patterns are also created by signals which travel between a
`transmitter and receiver via multiple signal paths. Multiple
`signal paths can result from signals which reflect off of one
`or more structures located between a particular transmitter
`and receiver as the signal
`radiates outward.
`In many
`instances the reflection of a signal can cause that portion of
`a signal’s energy to be deflected in a manner so as to never
`be received by the receiver. In other instances a portion of
`the signal’s energy could reflect off of one or more inter—
`fering surfaces and be redirected back towards the receiver.
`Regardless, various portions of a signal often reach their
`destination via one of a couple of dilIerent signal paths. A
`signal reaching its destination along difl'erent paths will
`often result in the different components of the signal arriving
`at a ditferent angle andtor arriving at a different time.
`
`In the past, the reception of the same signal at
`[0011]
`different times was generally destructive in nature and seen
`as another source of noise known as inter-symbol interfer-
`ence Inter-symbol interference resulting from reception of
`the same signal at dilferent times due to signal propagation
`along ditferent paths, generally created a limit on the rate at
`which data symbols could be transmitted. However more
`recent
`techniques have recognized that
`this inter—symbol
`interference if accounted for could also be used to enhance
`signal transmissions, once the transmission characteristics
`between the two points are known. One such technique
`includes the use of space-time beamformer technology.
`
`[0012] However one of the complications associated with
`implementing a spatially distinct transmission which con—
`structively combines the multipalh signaling characteristics
`is the amount of computational resources required to com-
`pute the transmission requirements and reception require-
`ments for establishing such a geographically discriminating
`communication connection. The amount of computational
`resources required for maintaining a spatially distinct trans—
`mission is further complicated by the fact
`that
`in many
`wireless communication applications, the transmitter and the
`receiver are in motion with respect to one another, andfor the
`objects against which the signal
`is being reflected are
`moving with respect to the transmitter andr‘or the receiver.
`Consequently, the transmission requirements and reception
`requirements may need to be recalculated or updated to take
`into account the continuously changing environment within
`which the desired communications are taking place, thereby
`making even greater demands upon the computational
`resources available for maintaining the quality of commu-
`nications.
`
`It would therefore be desirable to provide a method
`[0013]
`for managing the usage of a space-time channel and a
`channel state processing unit, which reduces the computa—
`tional resources required for maintaining a spatially distinct
`transmission including those which make use of space«time
`beamformcr technology.
`
`'Ihese and other objects, features, and advantages
`[0014]
`of this invention are evident from the following description
`of a preferred embodiment of the present invention, with
`reference to the accompanying drawings.
`
`

`

`US 2002/0114269 A1
`
`Aug. 22, 2002
`
`SUMMARY OF THE INVENTION
`
`[0015] The present invention provides a method for man—
`aging the usage of a space-time channel having a plurality of
`orthogonal sub-channels in a communication system. The
`system includes a transmitter having one or more transmit
`antennas, a receiver having one or more receive antennas,
`and one or more signal propagation paths between each of
`said one or more transmit antennas and each of said corre-
`sponding one or more receive antennas, where channel state
`in formation is available at
`the transmitter. The method
`includes estimating the channel for each signal propagation
`path. Aclosed-form orthogonal decomposition of the overall
`effective multi-input multi-output channel after coherent
`combining is used to determine one or more orthogonal
`sub-channels. The orthogonal sub-channels having preferred
`signaling characteristics from the one or more determined
`sub-channels are then selected for usage.
`
`the closed—form
`least one embodiment
`In at
`[0016]
`orthogonal decomposition is obtained for each ofa plurality
`of signal frequencies.
`
`In another embodiment, after the sub-channels for
`[001?]
`usage are selected,
`the transmit power available to the
`transmitter for transmission of one or more data streams via
`one or more corresponding selected sub-channels is allo-
`cated between the selected sub-channels.
`
`In another aspect of the invention a channel state
`[0018]
`processing unit
`is provided for use in the communication
`system. The channel state processing unit includes a central
`processing unit, which includes means for determining
`channel state information, means for estimating the channel
`for each receive antenna, means for coherently combining
`the channel estimates for each receive antenna, means for
`obtaining a closed form orthogonal decomposition of the
`coherently combined channel estimates, and means for
`selecting usage of one or more orthogonal sub-channels. In
`at least one embodiment the central processing unit includes
`a digital signal processor, where each of the means is a set
`of program operating instructions and corresponding pro-
`gram data being executed by the digital signal processor.
`
`[0019] By coherently combining the channel estimates
`across all the receive antennas a computationally less inten~
`sive closed form decomposition can be obtained for each
`receive antenna for determining the available orthogonal
`sub-channels and the channel characteristics associated
`therewith. This closed-form orthogonal decomposition of
`the overall channel after coherent combining is made pos-
`sible by a closed form singular value decomposition [SVD)
`of the channel for each receiver antenna before coherent
`combining. This is opposed to systems which contain more
`than a single receive antenna and which do not coherently
`combine channel estimates. For these systems, a determi-
`nation of orthogonal sub-channels needs to be computed
`numerically, which generally requires a significant amount
`ofcomputing resources, because a closed form solution does
`not exist.
`
`[0020] Other features and advantages of the present inven-
`tion will be apparent from the following detailed descrip—
`tion, the accompanying drawings, and the appended claims.
`BRIEF DESCRIPTION OF 'I'I'IIL DRAWINGS
`
`plurality of transmit antennas, for use in accordance with at
`least one embodiment of the present invention;
`
`[0022] FIG. 2 is an exemplary schematic block diagram of
`a single stream transmitter module for use in the transmitter
`shown in FIG. 1 according to one embodiment;
`
`[0023] FIG. 3 is an exemplary flow diagram of a method
`for transmitting a stream of data using the transmitter shown
`in FIG. 1 according to one embodiment;
`
`[0024] FIG. 4 is an exemplary schematic block diagram of
`a receiver for receiving a single stream of data transmitted
`from a transmitter like the one shown in FIG. 1, via a
`plurality of receive antennas, for use in accordance with at
`least one embodiment of the present invention;
`
`[0025] FIG. 5 is an exemplary schematic block diagram of
`a single stream receiver module for use in the receiver
`shown in FIG. 4;
`
`[0026] FIG. 6 is an exemplary flow diagram of a method
`for receiving a stream of data transmitted as shown in FIG.
`3, using the receiver shown in FIG. 4 according to one
`embodiment;
`
`[0027] FIG. 7 is a flow diagram of the method for man-
`aging the usage of a space-time channel
`including the
`identification and selection of orthogonal sub-channels for
`use in a communication system, in accordance with one
`embodiment of the present invention;
`
`[0028] FIG. 8 is an exemplary block diagram of a single~
`user minimum BER according to another embodiment;
`
`[0029] FIG. 9 is an exemplary block diagram ofa single—
`user minimum BER according to another embodiment;
`
`illustration of sorted
`[0030] FIG. 10 is an exemplar}.r
`sub-channel SNR values according to one embodiment;
`
`[0031] FIG. 11 is an exemplary illustration of cut-olf
`power according to one embodiment;
`
`FIGS. 12—15 are exemplary illustrations of alloca-
`[0032]
`tion of power and resulting BER across sub—channels
`according to one embodiment;
`
`[0033] FIG. 16 is an exemplary illustration of an elfectivc
`BER according to another embodiment;
`
`[0034] FIG. 17 is an exemplary illustration of a compari-
`son of' power allocation schemes;
`
`FIGS. 18~2l are exemplary illustrations of average
`[0035]
`relative throughput and average BER;
`
`[0036] FIG. 22 is an exemplary block. diagram of a
`general single-user multistream transmitter according to one
`embodiment;
`
`[0037] FIG. 23 is an exemplary block diagram of a
`general single-user multistream receiver according to one
`embodiment;
`
`[0038] FIG. 24 is an exemplary block diagrams of a
`general multiuscr transmitter according to one embodiment;
`and
`
`[0021] FIG. I is an exemplary schematic block diagram of
`a transmitter for transmitting a single stream of data, via a
`
`[0039] FIG. 25 is an exemplary block. diagram of a
`general multiuscr receiver according to one embodiment.
`
`

`

`US 2002/0114269 A1
`
`Aug. 22, 2002
`
`L»)
`
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`invention is susceptible of
`[0040] While the present
`embodiment in various forms, there is shown in the draw—
`ings and will hereinafter be described presently preferred
`embodiments with the understanding that the present dis-
`closure is to be considered an exempliiication of the inven-
`tion and is not intended to limit the invention to the specific
`embodiments illustrated.
`
`[0041] Generally a multi—a ntenna framework can be
`defined to include P transmit antennas embodied within one
`or more transmitters, Q receive antennas embodied within
`one or more receivers, and I.. propagation paths between the
`respective antennas. Within the multi-antenna framework,
`typically a plurality of non-interfering sub-channels can be
`defined. Transmission via the various sub-channels can be
`
`controlled through the appropriate selection of the values for
`a beamformer vector and the specific value for a frequency
`index. By carefully computing or selecting the sets of values
`from which the beamformer vector and the frequency index
`are selected, substantially orthogonal andtor non-interfering
`sub-channels can be defined.
`
`[0042] FIG. 1 illustrates an exemplary schematic block
`diagram of a transmitter 10 for transmitting a single stream
`ol‘data 12, via a plurality of transmit antennas 14. The data
`stream 12 typically comes from the output of an encoder
`combined with a modulator. The encoder corresponds to a
`certain error—correcting code, such as block code, convolu—
`tional code, concatenated code, Turbo code, or any other
`kinds. The modulator is a device that maps a binary data
`stream [composed of zeros and ones) onto a signal constel—
`lation. Examples of modulation scheme are phase shift
`keying {PSK). pulse amplitude modulation (PAM), quadra-
`ture amplitude modulation (0AM). The transmitter 10
`includes a channel state processing unit 16 and at least one
`single stream transmitter module 13 coupled to the channel
`state processing unit 16. The channel state processing unit
`16 incorporates a channel state information estimator 20
`which identifies a set of available orthogonal sub-channels
`within the channel space by analyzing the inherent gain
`associated with each signal path between each ot‘a set of one
`or more transmit antennas 14 and each of a set of one or
`more corresponding receive antennas 22, as shown in FIG.
`4. The channel state processing unit 16 additionally incor-
`porates sub-channel selection circuitry 24 and a transmit
`power allocator 26, both of which are coupled to the channel
`state information estimator 20. The sub-channel selection
`circuitry 24 selects for usage one or more sub—channels for
`use by one or more signal stream transmitter modules.
`
`[0043] The sub-channels are typically selected based upon
`the sub-channel having preferred signaling characteristics as
`determined through an analysis of the channel state infor-
`mation. In connection with selecting a sub-channel, a fre—
`quency index is selected and a corresponding set of beam-
`formcr weights
`are determined, both of which are
`respectively identified by a frequency index selector 28 and
`a beamformer weight determiner 30. Once selected,
`the
`frequency index and the set of beamformer weights are
`passed on to the single stream transmitter module 18. The
`single stream transmitter module 18 additionally receives a
`stream of data 12, often after the signal strength of the
`stream of data 12 has been modulated by a power amplifi-
`
`cation factor. The power amplification factor is determined
`by the transmit power allocator 26 as part of the channel
`state processing unit 16.
`
`[0044] While the transmitter 10 in FIG. 1 has been shown
`using one single stream transmitter module 18,
`it will be
`readily apparent to one skilled in the art that multiple single
`stream transmitter modules 18 could be coupled in parallel.
`Each single stream transmitter module 18 would receive its
`own frequency index and set of beamformer weights corre-
`sponding to the unique sub—channel selected and receive a
`unique data stream for transmission. Where multiple single
`stream transmitter modules 18 are used, the signal outputs
`from each transmitter module 18 corresponding to the same
`antenna 14 would be summed together prior to transmiSsion
`by the specific antenna 14.
`
`[0045] The single stream transmitter module 18, which is
`illustrated in greater detail
`in FIG. 2,
`includes a
`t-to-N
`demulliplexer 32 which receives the data stream via the
`single input and selectively routes the data stream to one of
`N outputs based upon the value of a frequency index (n)
`received. The N outputs, including the one through which
`the data stream is being routed, are received as a set of signal
`coefficients by an inverse discrete Fourier transformation
`circuit 34. The inverse discrete Fourier transformation cir-
`cuit 34 then converts the signal coefficients into N time
`varying output samples which define a sinusoidal signal
`having a frequency corresponding to the particular coeffi-
`cient for which the signal stream is received and an ampli—
`tude corresponding to the received value of the signal
`stream. The output of the inverse discrete Fourier transfor-
`mation circuit 34 is then coupled to a parallel to serial shift
`register 36 which serialioes the data into a time converted
`signal stream. The time converted signal stream is then
`coupled to a signal modulator 38, which modulates the
`signal stream in accordance with the chip waveform. 'Ihe
`modulated signal stream is then coupled to each of the
`transmit antennas (1, 2, .
`.
`. P) 14 after being appropriately
`weighted by the corresponding value {Wu W2, .
`.
`. W) from
`the weight vector. Where multiple single stream transmitter
`modules 18 are used, each of the weighted signal streams for
`a particular antenna 14 are summed together before being
`coupled to the corresponding antenna 14.
`
`[0046] An exemplary corresponding flow diagram is
`shown in FIG. 3, which outlines a method 100 for trans-
`mitting a stream of data using the transmitter 10 shown in
`FIG. 1 and is consistent with the signal flow discussed in
`connection with the single stream transmitter module 16
`shown in FIG. 2.
`
`[0047] More specifically, the method 100 for transmitting
`a stream of data, shown in FIG. 3, includes, in step 105,
`receiving an index frequency, a weight vector, and a stream
`of data. The stream of data is applied to an inverse discrete
`Fourier transformation circuit as a specific coefficient based
`upon the index frequency received in step 110,
`thereby
`producing a time domain signal. The time domain signal is
`then serialized in step 115. The method 100 further provides
`for modulating the serialized time domain signal with the
`chip waveform in step 120. The modulated signal is then
`weighted with each corresponding element of the weight
`vector in step 125. Each of the weighted signals is then
`coupled to the corresponding transmit antenna in step 130
`for transmitting the same.
`
`

`

`US 2002/0114269 A1
`
`Aug. 22, 2002
`
`[0048] FIG. 4 illustrates an exemplary schematic block
`diagram of a receiver 40 for receiving a single stream ofdata
`transmitted from a transmitter 10 having multiple transmit
`antennas 14 like the one shown in FIG. 1. Like the trans
`mitter 10, the receiver 40 includes a channel state processing
`unit 42 and a corresponding channel state information
`estimator 44, which similarly identifies a set of orthogonal
`sub-channels within the channel space by analyzing the
`transmission characteristics associated with each signal path
`between each of a set of one or more transmit antennas 14
`shown in FIG. 1 and each of a set of one or more corre-
`sponding receive antennas 22. In some instances, the chan~
`nel state information is determined by directly monitoring
`the characteristics of the signals received. In other instances,
`the already determined andior partially processed channel
`state information is otherwise communicated between the
`transmitter 10 and the receiver 40.
`
`[0049] The channel state pmcessing unit 42 additionally
`incorporates sub—channel selection circuitry 46, which is
`coupled to the channel state information estimator 44. The
`sub~channel selection circuitry 46 includes a frequency
`index selector 48 and a beamforrner weight determiner 50.
`Similar to the channel state information, in some instances
`the frequency index, and the corresponding set of beam-
`former weights or beamforrner weight vector are determined
`directly in both the transmitter 10 and receiver 40. In other
`instances, the frequency index and the beamforrner vector
`are determined in one and are communicated to the other.
`
`[0050] The channel state information, frequency index,
`and beamformer weight vector are supplied to a single
`stream receiver module 52, which is coupled to the channel
`state processing unit 42. Using the channel state informa-
`tion, the frequency index, and the beamformer weight vecv
`tor, the single stream receiver module 52 isolates the signal
`being transmitted on the indicated sub-channel received via
`the plurality of receive antennas 22. The isolated signal is
`then coupled to a demodulatort'detector 54 which converts
`the signal into a stream of data symbols.
`
`[0051] The receiver 40 can include additional single
`stream receiver modules 52, similar to the transmitter 10 and
`the corresponding single stream transmitter module 18
`shown in FIG. 1, where each single stream receiver module
`52 is commonly coupled to the plurality of receive antennas
`22, but is also coupled to its own demodulaton‘detector 54.
`In this way a plurality of data streams transmitted along a
`plurality of corresponding sub—channels can be received.
`
`[0052] Each single stream receiver module 52, in accor-
`dance with the illustrated embodiment shown in FIG. 5,
`includes a plurality of sample and hold circuits 56. Each
`sample and hold circuit 56 is coupled to a corresponding
`receive antenna 22. 'I'he sample and hold circuits 56 each
`sequentially stores the N time domain signal samples
`received via the receive antenna 22 coupled thereto. The N
`time domain signal samples are then sent to a respective
`discrete Fourier transformation circuit 58, which is coupled
`to each of the sample and hold circuits 56. The discrete
`Fourier transformation circuit 56 then converts the N time
`domain signal samples into N frequency domain signal
`coeflicients. Each discrete Fourier transformation circuit 58
`is. additionally coupled to a respective N-to-l multiplexer
`60, which receives the N frequency domain signal coeffi-
`cients. Each of the N-to-l multiplexers 60 also receives the
`
`frequency index signal for selecting the signal frequency
`coefficient of interest. The selected signal frequency coef-
`ficient for each of the receive antennas 22 is then modulated
`with a corresponding beam decoder weight value, and the
`resulting modulated signal frequency coefficient values are
`summed together with the other modulator] signal frequency
`coefficient values for each of the receive antennas 22.
`
`[0053] A received data stream value is determined from
`the sum of the modulated signal frequency coefficient val-
`ues. The beam decoder weight values used in determining
`the modulated signal frequency coeificient values are deter-
`mined by a beam decoder circuit 62. The beam decoder
`circuit 62 determines the beam decoder weight values based
`upon an analysis of the beamforrner weight vector (W) and
`the channel state information (CSI). The single stream
`receiver module 52 uses each sequence of received N time
`domain signal samples for determining the subsequent data
`values in the data stream received.
`
`[0054] Similar to the transmitter 10 shown in FIGS. land
`2. and corresponding method 100 illustrated in FIG. 3, an
`exemplary corresponding flow diagram which outlines a
`method 200 for receiving a stream of data using the receiver
`40 shown in FIG. 4, and corresponding single stream
`receiver module 52 shown in FIG. 5, is shown in FIG. 6.
`
`[0055] More specifically, the method 200 for receiving a
`stream of data, shown in FIG. 6, includes receiving a signal
`at each of a plurality of receive antennas, an index fre-
`quency, a weight vector, and channel rate information in step
`205. For each receive antenna, a finite number of samples
`are c