WO2001039392A1 - Technique d'acces multiple destinee a des systemes de radiocommunication numerique multifaisceaux a liaison descendante - Google Patents

Technique d'acces multiple destinee a des systemes de radiocommunication numerique multifaisceaux a liaison descendante Download PDF

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Publication number
WO2001039392A1
WO2001039392A1 PCT/US2000/042234 US0042234W WO0139392A1 WO 2001039392 A1 WO2001039392 A1 WO 2001039392A1 US 0042234 W US0042234 W US 0042234W WO 0139392 A1 WO0139392 A1 WO 0139392A1
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central node
precoder
user
multiple access
signals
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PCT/US2000/042234
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English (en)
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Peter Monsen
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Peter Monsen
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Priority to US10/110,365 priority Critical patent/US7088671B1/en
Priority to AU30830/01A priority patent/AU3083001A/en
Publication of WO2001039392A1 publication Critical patent/WO2001039392A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
    • H04W16/24—Cell structures
    • H04W16/28—Cell structures using beam steering
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0408—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas using two or more beams, i.e. beam diversity
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/1851—Systems using a satellite or space-based relay
    • H04B7/18515—Transmission equipment in satellites or space-based relays
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/204—Multiple access
    • H04B7/2041—Spot beam multiple access

Definitions

  • This invention relates generally to multiple access communication in digital radio systems, and more particularly to improvements in the multiple access communication from one or more centrally based nodes having multibeam antennas to fixed remote user terminals and/ or mobile user terminals.
  • Multiple access radio systems provide communication services for fixed remote user terminals and/or mobile user terminals.
  • Examples of multiple access radio systems include land mobile radio networks, cellular mobile radio networks, and wideband radio networks between one or more central nodes and fixed subscribers.
  • the central node in a multiple access radio system may use multibeam antennas for increasing system capacity and improving communications quality.
  • the forward link or downlink in a multiple access radio system is a communications link between a central node and a fixed remote or mobile user terminal.
  • the central node can be located at either a fixed location on the Earth in a terrestrial radio system or as part of an orbiting satellite in a satellite radio system.
  • Digital radio systems transmit and receive digital message information, e.g., computer or Internet data.
  • digital radio systems accept analog message information, e.g., voice or video data, and convert this analog information to a digital format during transmission and reception.
  • a central node transmits message information in a digital format using downlink beams defined by a multibeam antenna to a fixed remote or mobile user terminal where the receiver processes the digital message information to extract user message information.
  • the central node processing is divided between a satellite repeater and a ground-based station processor.
  • FDMA Frequency Division Multiple Access
  • TDMA Time Division Multiple Access
  • CDMA Code Division Multiple Access
  • FDMA separates users into different frequency subbands
  • TDMA separates users into different time intervals or slots
  • CDMA separates users by assigning different signature waveforms or codes to each user.
  • CDMA codes can be either orthogonal, i.e., there is no interference between synchronized users, or quasi- orthogonal, i.e., there is some small interference between users.
  • FDMA and TDMA are orthogonal multiple access (OMA) schemes because with ideal frequency filters and synchronization there is no mutual interference.
  • OMA orthogonal multiple access
  • Another example of an OMA system is CDMA with orthogonal codes.
  • Quasi- Orthogonal Multiple Access (QOMA) systems include CDMA with quasi-orthogonal codes and FDMA/TDMA with randomized frequency hopping.
  • an OMA scheme generally provides a larger system capacity than a QOMA scheme.
  • QOMA schemes for reducing interference between users to acceptable levels.
  • Interference between a user in one beam and users in other beams is normally reduced by crossbeam antenna attenuation.
  • cross-beam attenuation usually does not reduce interference enough to allow the reuse of the same orthogonal waveform or channel in adjacent beams.
  • channel management is typically required for determining when a multiple access channel can be reused in another beam.
  • the reuse factor for an orthogonal channel is defined as the number of user terminal assignments to that orthogonal channel in different beam coverage regions divided by the total number of beam coverage regions. Because the capacity of a multiple access system is proportional to the average value of the reuse factor with respect to all the multiple access channels, it is desirable to make the reuse factor for each multiple access channel as large as possible subject to interference constraints. Practical limitations on multibeam antennas typically cause the reuse factor in conventional cellular OMA systems to vary between 1 /3 and 1/ 12.
  • a QOMA radio system e.g., the uplink of a CDMA radio system in the IS-95 standard
  • the reuse factor can be unity because the crossbeam antenna attenuation can be sufficient to keep mutual interference between users in different beams to adequately small levels.
  • a QOMA radio system generally has a theoretical capacity that is less than that of an OMA radio system.
  • Conventional multiple access digital radio systems provide means for coding/ decoding message information for error correction, means for interleaving/ deinterleaving the message information, and a transmission format for the message information that includes a reference signal.
  • the reference signal is generated and transmitted at the central node and used by the user terminal receiver for obtaining channel parameters to aid in demodulating a user signal.
  • the message information is conventionally coded for transmission on both quadrature axes of a radio frequency carrier, e.g., cos ⁇ t and sin ⁇ t.
  • quadrature coding is to alternate coded symbols between the two axes.
  • Error correction coding techniques that use a complex signal constellation also exploit both quadrature axes.
  • the information rate is reduced by a factor of two relative to quadrature coding.
  • this dimension reduction provides a more robust signal form in the presence of interference.
  • the central node transmitter may include a multibeam antenna and one of these beams includes the particular user terminal.
  • the user terminal has a single antenna for receiving the downlink transmission.
  • Adaptive equalization of multiple antenna signals cannot be applied to a downlink system because these techniques must be applied at the receiver, i.e. the user terminal.
  • interference cancellation techniques that process multiuser signals with different signatures can be employed.
  • these multiuser processors are given in Linear Multiuser Detectors for Synchronous Code-Division Multiple Access Channels, R. Lupas and S. Verdu, IEEE Transactions on Information Theory, vol. IT-35, No. 1 , pp. 123- 136, Jan. 1989; Decorrelating Decision-Feedback Multiuser Detector for Synchronous Code-Division Multiple Access Channels, A. Duel- Hallen, IEEE Transactions on Communications, vol. COM-41 , No.2, pp.285- 290, Feb. 1993; and, A Family of Multiuser Decision Feedback Detectors for Asynchronous Code-Division Multiple Access Channels, A. Duel-Hallen, IEEE Transactions on Communications, vol.COM-43, Nos. 2,3,4, Feb-April 1995.
  • Transmitter Precoding in Synchronous Multiuser Communications, B.R. Vojcic and Won Mee Jang, IEEE Transactions on Communications, vol. 46, No. 10, October 1998 shows a precoding method employed at a single antenna transmitter to provide interference cancellation between quasi- orthogonal signals that have different signatures.
  • the same channels or signatures are reused in adjacent beam coverage areas so as to increase the reuse factor.
  • the multiuser processor and transmitting precoding techniques referenced above are not applicable to a downlink OMA system with a single user terminal antenna.
  • Precoding at the transmitter in a downlink system is analogous to equalization at the receiver in an uplink system.
  • Numerous algorithms for precoding i.e., beamforming, have been proposed to reduce both co-channel, ie., other user interference, and intersymbol interference in downlink transmissions.
  • An example of such an algorithm is given in Transmit Beamforming and Power Control for Cellular Wireless Systems, F. Rashid- Farrokki, K.J. Ray Lui, and L. Tasseulas, IEEE Journal on Sel. Areas of communication, vol.16, No. 8, pp. 1437- 1450, October 1998.
  • a transmitter precoding method is described for cellular systems that reduces both other user and intersymbol interference.
  • the objective according to the authors is to either reduce the frequency reuse distance or increase the channel capacity.
  • a reuse factor of unity i.e., a frequency reuse distance of zero, can be achieved nor do they introduce and combine additional elements such as error-correction coding, interleaving, and periodic channel assignment changes.
  • Future multiple access radio systems will be unsymmetrical with typically greater downlink than uplink channel capacity requirements in order to satisfy Internet downloading demands. This future unsymmetrical capacity requirement places increased emphasis on finding techniques to increase downlink capacity.
  • the capacity of a downlink system is either limited by user interference in an OMA system, which keeps the reuse factor less than unity, or theoretically limited by the choice of QOMA. It would be desirable to have a multiple access scheme that can be used to obtain a unity reuse factor in downlink transmissions from one or more central nodes to a plurality of user terminals.
  • Another object of the invention is to provide a downlink multiple access communication system that is orthogonal in each beam coverage area, and has a channel capacity greater than that of conventional quasi-orthogonal multiple access communication systems.
  • Still another object of the invention is to provide an orthogonal multiple access communication system that has a unity reuse factor.
  • a multiple access communication system including a plurality of user terminals, each including a user terminal receiver, and one or more central nodes each including a central node transmitter for transmitting digital message information to the user terminal receivers.
  • the digital message information is generally different for each user in the multiple access scheme.
  • User terminal receivers are located within a beam coverage area; and, within this area, users are assigned mutually orthogonal multiple access channels. Users in areas covered by adjacent beams reuse the same multiple access channels. Thus, interference due to antenna spillover at beam boundaries could produce interference between users assigned to different beams, but with the same multiple access channel. Reduction or elimination of this interference is accomplished in the central node transmitter by a combination of coding/interleaving, periodic channel assignment changes, precoding, and 90° phase rotations.
  • Two or more central nodes may be connected together with fixed communication links, i.e., coaxial cable, microwave radio, or fiber optic cable.
  • fixed communication links i.e., coaxial cable, microwave radio, or fiber optic cable.
  • the precoding operation at central node transmitter (s) requires estimates of cross signal transmittance values between the antenna ports and user terminal receivers. .In the preferred embodiment for nonreciprocal uplink and downlink these estimates are computed at a central node by correlating reference signals with downlink received versions of these reference signals.
  • the downlink received signals are processed to reduce bit transmission requirements and retransmitted using uplink transmission facilities.
  • the use of some of the uplink capacity to increase downlink capacity is attractive in future multiple access systems with unsymmetrical capacity requirements , i.e., downlink greater than uplink.
  • the central node transmitter contains a plurality of source processors, each of which includes an error correction coder and interleaver.
  • Digital message information for each user is coded in a single- axis error-correction coder to provide a sequence of real-valued coded symbols.
  • the restriction of the coding transformation to real values rather than quadrature values greatly improves precoding effectiveness of interference reduction.
  • This sequence is interleaved by distributing the coded symbols amongst groups or frames of coded symbols.
  • the interleaving signal is connected via an orthogonal channel assignment switch to input ports of a plurality of precoders, each of which is associated with an orthogonal multiple access channel assignment.
  • the precoders reduce potential interference at user terminals in different beam coverage areas, but with the same orthogonal channel assignment.
  • Precoder inputs are real valued, but outputs are complex valued.
  • Reduced interference is also realized by periodically changing the multiple access assignments in a predeterrnined manner so that the receiver at the user terminal can follow the channel assignment changes.
  • a channel assignment time normally would correspond to a frame of user symbols.
  • the change in channel assignments is realized at the central node transmitter by the channel assignment switch, which changes the connection between source processor outputs and precoder inputs. If there are N orthogonal channel processors and K beams in the multibeam channel, then an NK channel assignment switch between the NK interleaver signals and the NK precoder inputs can be used to periodically switch channel assignments and average the effects of other user interference.
  • each precoded signal is converted in a quadrature modulator to a modulated user signal utilizing both quadrature axes in a radio frequency carrier.
  • the real and imaginary parts of the precoded signal correspond to the quadrature axes of the modulated signal. Since all users are coded to the same quadrature axis, enhanced protection against other user interference can be realized by phase rotating some but not all of the precoded user signals by 90°.
  • the modulated signals from all the quadrature modulators corresponding to a particular antenna beam port are then added together in a beam combiner whose output is connected to the appropriate port of the multibeam antenna.
  • Each beam output of the multibeam antenna contains a multiple access signal destined for the users located in the beam coverage area associated with that beam. Because of imperfect isolation between antenna beams at any user location, the received signal is a composite of multiple access signals from multiple beams.
  • Each user terminal receiver includes an antenna for receiving the composite multiple access signal from the central node transmitter, an RF converter that converts the antenna output signal to baseband for receiver processing, a single axis demodulator that converts the baseband signal to a digital data received signal, and a deinterleaver and decoder to recover the digital message information from the digital data received signal.
  • FIG. 1 is a diagram of a multiple-access orthogonal communication system connecting a one or more central node transmitters to multiple user terminals;
  • FIG. 2 is a functional block diagram of a source processor in the central node transmitter of the present invention;
  • FIG. 3 is a functional block diagram of the central node transmitter employed in the communication system of the present invention;
  • FIG. 4 is a functional block diagram of a modulator in the central node transmitter in the present invention
  • FIG. 5 is a functional block diagram of a user terminal receiver at the user terminal in the communication system in the present invention.
  • a multiple access radio system includes user terminals that have associated digital radio communication links, i.e., forward links or downlinks, from a central node transmitter with a multibeam antenna. Further, users of each beam are assigned orthogonal multiple access (OMA) channels.
  • OMA orthogonal multiple access
  • Examples of OMA schemes that may be used with the multiple access radio system of the present invention include Frequency-Division Multiple Access (FDMA), Time-Division Multiple Access (TDMA), and Orthogonal- Waveform Code-Division Multiple Access (OCDMA), and various combinations thereof.
  • FDMA Frequency-Division Multiple Access
  • TDMA Time-Division Multiple Access
  • OCDMA Orthogonal- Waveform Code-Division Multiple Access
  • the present invention will allow the reuse of the same orthogonal waveform or channel by different users in adjacent beam coverage areas, thereby making it possible to achieve a reuse factor of 1 in the downlink of an OMA system.
  • FIG. 1 is a diagram of an OMA communication system in a downlink application.
  • a central node transmitter 1 sends digital message information to multiple user terminals 2 located in coverage areas associated with antenna beam boundaries resulting from a multibeam antenna in the central node transmitter 1.
  • FIG. 1 there are three beams that have three beam coverage areas 3 in which are located the user terminals 2.
  • User terminal UTi and UT 2 are in the upper beam coverage area 3 and use different orthogonal channels Ci and C 2 .
  • User terminals UT 3 , UT and UT5 are in the middle beam coverage area 3 and reuse orthogonal channels Ci and C 2 plus another orthogonal channel C 3 .
  • In the lower beam coverage area 3 there is only one user terminal 2 that reuses orthogonal channel C 2 .
  • FIG. 1 is also representative of a macrodiversity system. As indicated in FIG. 1 there may be multiple central node transmitters providing downlink channels to multiple beam regions. For example in FIG. 1 , beams 1 and 2 may be associated with the central node containing central node transmitter 1 but beam 3 is a downlink beam to user terminal UT 6 that is receiving downlink signals from an adjacent central node that is connected by a communication link to the central node containing central node transmitter 1.
  • the communication link is used to pass signal information so that the two central nodes can act as a single node and thereby achieve a macrodiversity effect. For uplink transmissions this macrodiversity effect might be realized by choosing the better of two uplink transmissions arriving at the two central nodes.
  • An analogous macrodiversity effect can be achieved with precoding on the downlink.
  • the precoding of user signals for beams 1 and 2 by central node transmitter 1 would be coordinated with precoding of user signals by central node transmitter 2 in order to take into account mutual interference and diversity protection.
  • user terminal message signals and cross signal transmittance values are exchanged over the communication link between the central nodes.
  • Digital message information for each user is converted in a source processor to an interleaved signal by error correction coding and interleaving of the digital message information to produce a sequence of coded/interleaved symbols.
  • the coded symbols are contained within frames or groups of data. For example, in TDMA/FDMA, a frame of data contains the coded symbols for one time slot of transmission.
  • FIG. 2 shows a source processor for a user that has been assigned the nth orthogonal channel in a mutually orthogonal set of N channels, and is destined to a user terminal that is located in beam k of a multibeam antenna with K beams.
  • the single-axis coder 4 adds redundancy in a predetermined manner so as to provide resistance to noise and interference in the reception of the user signal at the user terminal receiver.
  • the coded data is real, corresponding to a single-axis, and may be either binary or nonbinary depending on system quality and data rate requirements.
  • the single-axis coder 4 may be realized with a binary convolutional coder. Typical parameters for such a coder are rate Vz, constraint length 7, and generator functions 133, 171.
  • the single-axis coder 4 then provides the coded data to an interleaver 5, which distributes the coded data amongst multiple frames in a predetermined manner.
  • the coded data is distributed among the multiple frames as follows. If there are F digital data symbols per frame, then the F symbols are evenly distributed over F frames; e.g., symbol 1 goes in frame 1, symbol 2 goes in frame 2, and so on, until symbol F goes in frame F; and, then the process is repeated until all F frames are full.
  • the interleaver 5 may distribute the coded data into the multiple frames in other ways and still achieve a reuse factor of 1 in the downlink of the OMA system.
  • a reference generator may produce a sequence of known data symbols that is multiplexed in each frame of digital data.
  • reference data sequences include a maximum length pseudo-noise (PN) sequence with length equal to the number of reference symbols to be inserted, or alternatively each reference subburst in a frame may be a portion of a very long PN sequence.
  • the reference data can be used at the user terminal receiver for estimation of channel parameters required in demodulation of the user signal. Alternately separate test signals can be used in a downlink system for parameter estimation at the user terminal receivers. Received reference data or received test signals may also be quantized and retransmitted on an uplink transmission to the central node. At the central node correlation of downlink received reference data or test signals with originally transmitted signals will produce downlink cross signal transmitance values required for precoding operations for the next downlink transmission.
  • PN pseudo-noise
  • Each frame may include other system or user information such as central node identification, user authorization information, network status, etc. , in addition to reference data and the interleaved and coded data provided by the interleaver 5.
  • the present invention uses orthogonal channel assignments from a mutually orthogonal set and reuses these same channel assignments in each beam coverage area.
  • the limit on the number of orthogonal users is determined by the available bandwidth W and the transmitted symbol time T.
  • the maximum number of orthogonal channels per quadrature axis is equal to WT/2.
  • N must be WT/2 or less.
  • the N orthogonal channels are reused in each beam so as to achieve a reuse factor of unity.
  • the maximum number of users supported by a central node is then KWT/2. A preferred embodiment is described here corresponding to this maximum number of users.
  • the source processors have been combined into a source processor group 6, which provides coding/ interleaving for a group of K users, each of which is in a different beam coverage area.
  • a source processor group 6 which provides coding/ interleaving for a group of K users, each of which is in a different beam coverage area.
  • N WT/2 orthogonal channels, so there are N K-input/ output source processors groups shown in FIG. 3.
  • a randomization of other user interference is achieved with an orthogonal channel assignment switch 7, which switches in a predetermined variable manner the NK interleaved signals at the source processor outputs to the NK precoder inputs at frame interval boundaries.
  • the variable switch changes may be generated from a PN sequence generator or a deterministic algorithm.
  • the effect of orthogonal channel assignment changes every frame is to average other user interference in the subsequent error-correcting decoding at the user terminal.
  • the group of orthogonal channels should be confined to a frequency band that is less than the coherence bandwidth. With this restriction the precoder parameters for the next frame can be calculated from the retransmitted received signals of the old orthogonal channel for the set of interferers associated with the new orthogonal channel.
  • the N orthogonal channels in the preferred embodiment are contained in a frequency band that is less than the frequency coherence bandwidth.
  • K+k has its processed information at source processor output (n-1) K+k.
  • There are N precoders in FIG.3, wherein the nth precoder, n 0,1, 2,...N- 1, uses orthogonal channel n.
  • the connections between the K source processor outputs for a particular source group and the N precoders can be represented by the channel assignment integer I.
  • channel assignment changes are implemented at frame boundaries.
  • the frame corresponds to a time slot so that channel assignment changes could be realized at the end of each time slot.
  • the interleaving be over many frames so as to average the interference effects at the receiver after deinterleaving.
  • the variable channel assignment combined with interleaving/ deinterleaving of coded symbols results in a random user interference at the decoder of the user terminal receiver, thus improving the communication reliability of each central node to user terminal link.
  • the channel assignment pattern is preselected so the user terminal can synchronously employ the same variably selected orthogonal channel at its receiver for processing the received signal.
  • the NK outputs of the source processor groups are applied to the NK x NK channel assignment switch 7, which provides a different variable channel assignment for each frame or multiple frames of data.
  • the N precoders 8 are used to reduce interference at user terminals that share the same orthogonal channel assignment.
  • Equation (2) shows a precoding operation that has "tap spacing" equal to the symbol period, i.e., the source vectors are separated in time by one symbol period. It is known to one skilled in this art that precoding can be realized with fractional "tap spacing," wherein source vectors are separated by T/M, T being the symbol period and M being an integer greater than one. For simplicity of presentation, a preferred embodiment will be described in the subsequent Precoder Computation section with the symbol period tap spacing of equation (2).
  • the precoded data for a user group sharing the same orthogonal channel is sequentially provided to one of the modulator groups 9 in FIG. 3.
  • a single modulator is shown in more detail in FIG.4.
  • the modulator contains a 0°/90° phase shifter 10 and a quadrature modulator 11.
  • the vector component for the nth precoder and kth output is designated as q (mT,k,n). These symbol values are complex because the precoding matrices are complex.
  • the conversion is accomplished with a phase shifter and a modulator.
  • the phase shifter provides improved protection at the user terminals against other users with the same orthogonal channel assignment, but it should be understood that its use is optional.
  • the phase shifter applies a 90° phase shift to some of the K precoder outputs in order to provide additional interference protection by placing signal pairs in quadrature.
  • a phase- rotation algorithm called the maximum quadrature interference algorithm is suggested in section 3, Maximum Quadrature Interference Algorithm for P, below.
  • the rotated precoded signal in a frame is provided to a quadrature modulator 11, which converts the frame data to a modulated user signal suitable for transmission over a downlink to a user terminal receiver using a radio frequency (RF) channel.
  • RF radio frequency
  • the frame data which is complex, is converted by the quadrature modulator 11 such that the real and imaginary components are converted to the quadrature (cos ⁇ t/sin ⁇ t) axes of the modulated signal.
  • FIG. 5 illustrates a receiver at a user terminal for reconstruction of the user digital information signals.
  • FIG. 5 shows a single antenna 14 configuration followed by an RF converter 15 for shifting the RF signal to a downconverted intermediate or baseband frequency level.
  • the single axis demodulator 16 employs a locally generated pilot signal or reference signal in order to coherently demodulate the downconverted signal.
  • the deinterleaver 17 reconstructs the original frame order by reversing the interleaver function 5 in the transmitter.
  • the decoder 18 exploits the redundancy added by the transmitter single-axis coder 4 so as to reduce the likelihood of bit errors in the recovered user digital message information. Subsequent processing, e.g., digital-to-analog conversion (not shown), of the digital message information results in the message information of the particular user.
  • Precoder Computation The computation required by a precoder 8 in FIG. 3 can be accomplished in different ways.
  • the precoder solution is a function of the path gains to the K users, the cross signal transmittance resulting from the multibeam antenna, and the K 0°/90° values resulting from the phase shifter 10. These phase shift values can be summarized in a diagonal matrix P whose diagonal values are
  • the real diagonal matrix G has diagonal elements
  • Equation (5) takes into account both other user interference due to the matrix M 0 , and a combination of other user and intersymbol interference through the matrices Mi, i ⁇ 0.
  • the real component (Re) is used in equation (5) to include the coherent demodulation, which occurs at each user receiver terminal.
  • the representation of the received signal vector Eq.(5) and the precoded vector Eq.(2) is also valid for a macrodiversity technique where multiple central node transmitters are used to serve user terminals.
  • the central nodes are connected together with fixed communication links, i.e. , coaxial cable, microwave radio, or fiber optic cable.
  • the central nodes can coordinate their downlink transmissions so as to achieve a macrodiversity effect.
  • FIG. 1 let beams 1 and 2 correspond to a multibeam antenna associated with a first central node transmitter 1 and let beam 3 correspond to a single beam antenna associated with a second central node transmitter 1.
  • a particular orthogonal channel achieves a unity reuse factor in this example if it is shared amongst three users that are each in one of the three beam coverage regions 3 of FIG. 1.
  • Eq. (2) defines this macrodiversity configuration where the first central node transmitter generates the precoder components q m ⁇ and q m2 at time mT and the second central node transmitter generates the precoder component q m 3. Since the precoding in Eq. (2) requires the source values for all the user terminals, the source values for the respective control nodes must be exchanged over the fixed communication link.
  • Eq. (5) is unchanged in its form although the antenna ports are at two physically different locations. The subsequent solution Eq. ( 1 lb) for the preferred embodiment can then be applied to find the precoder matrix that is used at both central nodes in this macrodiversity example.
  • M [M 0 , ] P O O P and an expanded precoded vector has been defined as
  • the preferred embodiment computes the solution for the precoder matrix W directly and can be implemented by standard matrix inversion procedures.
  • the direct solution is applicable when the channel assignments change every frame and precoder parameters are estimated from either uplink channel parameters in a reciprocal channel configuration or from retransmitted received downlink signals.
  • a method is then given for computing the 0°/90° phase rotation matrix P.
  • the direct solution the matrices P and W can be found for each frame of transmitted data.
  • a least-means-squares (LMS) algorithm based on the noisy gradient, steepest-descent algorithm given in Adaptive Filters, I; Fundamentals, Stanford Electronics Laboratory, Stanford University, Stanford CA, Tech. Rep. 6764-6, December 1966 by B.
  • LMS least- mean-squares
  • the W matrix can be defined as a set of 2K row vectors, i.e.
  • W can be represented by the 4Kx2K real matrix
  • equation (5a) can be rewritten as
  • the minimum mean-square error solution is usually preferrable because it results in a smaller error rate. This solution is
  • the parameter ⁇ is a constant defined by the power requirements at the central node transmitter. For example, an average power constraint requires that
  • the steps for computing the P matrix are defined by an algorithm called the maximum quadrature interference algorithm.
  • the purpose of this algorithm is to iteratively find pairs of beams that have the largest coupling, and choose 0°/90° assignments so that users sharing the same orthogonal channel in these paired beam coverage areas have quadrature phase rotations.
  • Step 0 Initialize
  • Step 1 Find eligible pairs with largest cross-linked quadrature component coupling:
  • the solution for the rotational matrix P and the precoding matrix W requires knowledge of the general cross-signal matrix E.
  • the matrix elements of E may be determined from uplink measurements at the central node.
  • the matrix elements of E can be estimated at the central node by feedback to the central node of received signal values at the user terminals.
  • correlation of these received signal values with corresponding reference signal values that were transmitted on the downlink will produce estimates of these matrix elements.
  • the estimate of E can then be used to find W directly by the preferred embodiment procedure described here, or an alternative embodiment iterative technique to estimate the precoding matrix W.
  • the alternative embodiment is next described for environments where the channel switching occurs infrequently.
  • the channel assignment switch is only activated after many frames so that an adaptive recursive solution can be realized.
  • the least-mean-squares (LMS) algorithm previously referenced is an estimated gradient algorithm that tracks the optimum of a quadrature error functional. This algorithm is a well known technique for correlating received signal values with known transmitted values in order to obtain processor parameters.
  • the received vector components are realized at the user terminals at time mT + ik, wherein tk is the propagation delay to the kth user terminal.
  • the received vector components are sent back to a receiver at the central node by feedback links such that after an appropriate delay the central node has both R m and s m for adapting the next iteration.
  • the rotation matrix P is fixed for many iterations. It may be periodically reset after a channel assignment change by using the maximum quadrature interference algorithm described earlier in the invention at the beginning of a new recursion epoch.
  • the cross-signal matrices A, for a fixed P may be deduced in some applications from a combination of available parameters such as power control values, user location from Global Positioning System (GPS) measurements, and computed antenna characteristics.
  • the matrices can be estimated by a recursive algorithm at the central node using the feedback vector r m .
  • a cross-signal matrix estimation is accomplished by the recursion
  • ⁇ 2 is another step-size constant and the prerotated, transmitted vector at time mT is

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Astronomy & Astrophysics (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • General Physics & Mathematics (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

L'invention concerne un système de communication à accès multiples comprenant un émetteur (1), des terminaux utilisateurs (2), ainsi que des régions de couverture (3). Ce système utilise des accès multiples orthogonaux.
PCT/US2000/042234 1999-11-24 2000-11-22 Technique d'acces multiple destinee a des systemes de radiocommunication numerique multifaisceaux a liaison descendante WO2001039392A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US10/110,365 US7088671B1 (en) 1999-11-24 2000-11-22 Multiple access technique for downlink multibeam digital radio systems
AU30830/01A AU3083001A (en) 1999-11-24 2000-11-22 Multiple access technique for downlink multibeam digital radio systems

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US16747299P 1999-11-24 1999-11-24
US60/167,472 1999-11-24

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WO2001039392A1 true WO2001039392A1 (fr) 2001-05-31

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AU (1) AU3083001A (fr)
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Cited By (5)

* Cited by examiner, † Cited by third party
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EP2182649A1 (fr) * 2007-08-19 2010-05-05 Alcatel, Lucent Procédé et appareil pour éliminer le brouillage entre des signaux reçus par plusieurs stations mobiles
CN105049390A (zh) * 2015-07-31 2015-11-11 哈尔滨工业大学深圳研究生院 一种基于按需se枚举的复数域球解码方法及系统
CN105162739A (zh) * 2015-07-31 2015-12-16 哈尔滨工业大学深圳研究生院 一种复数域hkz规约方法及系统
CN105282066A (zh) * 2015-07-31 2016-01-27 哈尔滨工业大学深圳研究生院 一种复数域Minkowski规约方法及系统
US10700800B2 (en) 2003-05-21 2020-06-30 Regents Of The University Of Minnesota Estimating frequency-offsets and multi-antenna channels in MIMO OFDM systems

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6157811A (en) * 1994-01-11 2000-12-05 Ericsson Inc. Cellular/satellite communications system with improved frequency re-use

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6157811A (en) * 1994-01-11 2000-12-05 Ericsson Inc. Cellular/satellite communications system with improved frequency re-use

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10700800B2 (en) 2003-05-21 2020-06-30 Regents Of The University Of Minnesota Estimating frequency-offsets and multi-antenna channels in MIMO OFDM systems
US11303377B2 (en) 2003-05-21 2022-04-12 Regents Of The University Of Minnesota Estimating frequency-offsets and multi-antenna channels in MIMO OFDM systems
EP2182649A1 (fr) * 2007-08-19 2010-05-05 Alcatel, Lucent Procédé et appareil pour éliminer le brouillage entre des signaux reçus par plusieurs stations mobiles
EP2182649A4 (fr) * 2007-08-19 2014-02-26 Alcatel Lucent Procédé et appareil pour éliminer le brouillage entre des signaux reçus par plusieurs stations mobiles
KR101467960B1 (ko) * 2007-08-19 2014-12-02 알까뗄 루슨트 다수의 이동국들에 의해 수신된 신호들 사이의 간섭을 제거하는 방법 및 장치
CN105049390A (zh) * 2015-07-31 2015-11-11 哈尔滨工业大学深圳研究生院 一种基于按需se枚举的复数域球解码方法及系统
CN105162739A (zh) * 2015-07-31 2015-12-16 哈尔滨工业大学深圳研究生院 一种复数域hkz规约方法及系统
CN105282066A (zh) * 2015-07-31 2016-01-27 哈尔滨工业大学深圳研究生院 一种复数域Minkowski规约方法及系统
CN105282066B (zh) * 2015-07-31 2019-02-01 哈尔滨工业大学深圳研究生院 一种复数域Minkowski规约方法及系统
CN105049390B (zh) * 2015-07-31 2019-03-01 哈尔滨工业大学深圳研究生院 一种基于按需se枚举的复数域球解码方法及系统
CN105162739B (zh) * 2015-07-31 2019-04-05 哈尔滨工业大学深圳研究生院 一种复数域hkz规约方法及系统

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