Recherche Images Maps Play YouTube Actualités Gmail Drive Plus »
Connexion
Les utilisateurs de lecteurs d'écran peuvent cliquer sur ce lien pour activer le mode d'accessibilité. Celui-ci propose les mêmes fonctionnalités principales, mais il est optimisé pour votre lecteur d'écran.

Brevets

  1. Recherche avancée dans les brevets
Numéro de publicationUS20080273617 A1
Type de publicationDemande
Numéro de demandeUS 12/176,306
Date de publication6 nov. 2008
Date de dépôt18 juil. 2008
Date de priorité7 mai 2004
Autre référence de publicationCA2565770A1, CA2689636A1, CN102088436A, CN102088436B, EP1747652A1, US8285226, US20050249174, WO2005114939A1
Numéro de publication12176306, 176306, US 2008/0273617 A1, US 2008/273617 A1, US 20080273617 A1, US 20080273617A1, US 2008273617 A1, US 2008273617A1, US-A1-20080273617, US-A1-2008273617, US2008/0273617A1, US2008/273617A1, US20080273617 A1, US20080273617A1, US2008273617 A1, US2008273617A1
InventeursStein A. Lundby, Steven J. Howard, Jay Rodney Walton
Cessionnaire d'origineQualcomm Incorporated
Exporter la citationBiBTeX, EndNote, RefMan
Liens externes: USPTO, Cession USPTO, Espacenet
Steering diversity for an ofdm-based multi-antenna communication system
US 20080273617 A1
Résumé
A transmitting entity uses different steering vectors for different subbands to achieve steering diversity. Each steering vector defines or forms a beam for an associated subband. Any steering vector may be used for steering diversity. The steering vectors may be defined such that the beams vary in a continuous instead of abrupt manner across the subbands. This may be achieved by applying continuously changing phase shifts across the subbands for each transmit antenna. As an example, the phase shifts may change in a linear manner across the subbands for each transmit antenna, and each antenna may be associated with a different phase slope. The application of linearly changing phase shifts to modulation symbols in the frequency domain may be achieved by either delaying or circularly shifting the corresponding time-domain samples.
Images(12)
Previous page
Next page
Revendications(18)
1. A method of transmitting data in a wireless communication system, comprising:
obtaining input symbols to be transmitted on a plurality of frequency subbands of a plurality of antennas;
modifying an input symbol for each frequency subband of each antenna with a phase shift selected for the frequency subband and the respective antenna to generate a phase-shifted symbol for the frequency subband and the respective antenna; and
processing phase-shifted symbols for the plurality of frequency subbands of each antenna to obtain a sequence of samples for the respective antenna.
2. The method of claim 1, further comprising:
applying linearly varying phase shifts across the plurality of frequency subbands for each antenna.
3. The method of claim 1, further comprising:
applying a different phase slope across the plurality of frequency subbands for each antenna.
4. The method of claim 1, further comprising:
applying continuously varying phase shifts across the plurality of frequency subbands for each antenna.
5. The method of claim 4, further comprising:
determining the continuously varying phase shifts across the frequency subbands for each antenna based on a function selected for the respective antenna.
6. The method of claim 1, wherein the processing the phase-shifted symbols comprises
performing orthogonal frequency division multiplexing (OFDM) modulation on the phase-shifted symbols for the plurality of frequency subbands of each antenna to obtain the sequence of samples for the respective antenna.
7. An apparatus in a wireless communication system, comprising:
a spatial processor to obtain input symbols to be transmitted on a plurality of frequency subbands of a plurality of antennas and to modify an input symbol for each frequency subband of each antenna with a phase shift selected for the frequency subband and the respective antenna to generate a phase-shifted symbol for the frequency subband and the respective antenna; and
a modulator to process phase-shifted symbols for the plurality of frequency subbands of each antenna to obtain a sequence of samples for the respective antenna.
8. The apparatus of claim 7, wherein the spatial processor applies linearly varying phase shifts across the plurality of frequency subbands for each antenna.
9. The apparatus of claim 7, wherein the spatial processor applies a different phase slope across the plurality of frequency subbands for each antenna.
10. The apparatus of claim 7, wherein the spatial processor applies continuously varying phase shifts across the plurality of frequency subbands for each antenna.
11. An apparatus in a wireless communication system, comprising:
means for obtaining input symbols to be transmitted on a plurality of frequency subbands of a plurality of antennas;
means for modifying an input symbol for each frequency subband of each antenna with a phase shift selected for the frequency subband and the respective antenna to generate a phase-shifted symbol for the frequency subband and the respective antenna; and
means for processing phase-shifted symbols for the plurality of frequency subbands of each antenna to obtain a sequence of samples for the respective antenna.
12. The apparatus of claim 11, further comprising:
means for applying linearly varying phase shifts across the plurality of frequency subbands for each antenna.
13. The apparatus of claim 11, further comprising:
means for applying a different phase slope across the plurality of frequency subbands for each antenna.
14. The apparatus of claim 11, further comprising:
means for applying continuously varying phase shifts across the plurality of frequency subbands for each antenna.
15. A computer-program apparatus for processing data in a wireless communication system comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors and the instructions comprising:
instructions for processing data to obtain an input sequence of time-domain samples;
instructions for obtaining input symbols to be transmitted on a plurality of frequency subbands of a plurality of antennas;
instructions for modifying an input symbol for each frequency subband of each antenna with a phase shift selected for the frequency subband and the respective antenna to generate a phase-shifted symbol for the frequency subband and the respective antenna; and
instructions for processing phase-shifted symbols for the plurality of frequency subbands of each antenna to obtain a sequence of samples for the respective antenna.
16. The computer-program apparatus of claim 15, further comprising:
instructions for applying linearly varying phase shifts across the plurality of frequency subbands for each antenna.
17. The computer-program apparatus of claim 15, further comprising:
instructions for applying a different phase slope across the plurality of frequency subbands for each antenna.
18. The computer-program apparatus of claim 15, further comprising:
instructions for applying continuously varying phase shifts across the plurality of frequency subbands for each antenna.
Description
    CLAIM OF PRIORITY
  • [0001]
    This application is a continuation of, and claims the benefit of priority from, U.S. patent application Ser. No. 11/066,771, filed Feb. 24, 2005 and entitled “Steering Diversity for an OFDM-Based Multi-Antenna Communication System,” which claims the benefit of priority from U.S. Provisional Patent Application Ser. No. 60/569,103, filed May 7, 2004 and entitled “Steering Diversity for an OFDM-Based Multi-Antenna Communication System,” both of which are assigned to the assignee hereof and are fully incorporated herein by reference for all purposes.
  • FIELD
  • [0002]
    The present invention relates generally to communication, and more specifically to data transmission in a multi-antenna communication system that utilizes orthogonal frequency division multiplexing (OFDM).
  • BACKGROUND
  • [0003]
    OFDM is a multi-carrier modulation technique that effectively partitions the overall system bandwidth into multiple (K) orthogonal subbands, which are also referred to as tones, subcarriers, bins, and frequency channels. With OFDM, each subband is associated with a respective subcarrier that may be modulated with data. OFDM is widely used in various wireless communication systems, such as those that implement the well-known IEEE 802.11a and 802.11g standards. IEEE 802.11a and 802.11g generally cover single-input single-output (SISO) operation whereby a transmitting device employs a single antenna for data transmission and a receiving device normally employs a single antenna for data reception.
  • [0004]
    A multi-antenna communication system may support communication for both single-antenna devices and multi-antenna devices. In this system, a multi-antenna device may utilize its multiple antennas for data transmission to a single-antenna device. The multi-antenna device and the single-antenna device may implement any one of a number of conventional transmit diversity schemes in order to obtain transmit diversity and improve performance for the data transmission. One such transmit diversity scheme is described by S. M. Alamouti in a paper entitled “A Simple Transmit Diversity Technique for Wireless Communications,” IEEE Journal on Selected Areas in Communications, Vol. 16, No. 8, October 1998, pp. 1451-1458. For the Alamouti scheme, the transmitting device transmits each pair of modulation symbols from two antennas in two symbol periods, and the receiving device combines two received symbols obtained in the two symbol periods to recover the pair of modulation symbols sent by the transmitting device. The Alamouti scheme as well as most other conventional transmit diversity schemes require the receiving device to perform special processing, which may be different from scheme to scheme, in order to recover the transmitted data and obtain the benefits of transmit diversity.
  • [0005]
    A “legacy” single-antenna device may be designed for SISO operation only, as described below. This is normally the case if the wireless device is designed for the IEEE 802.11a or 802.11g standard. Such a legacy single-antenna device would not be able to perform the special processing required by most conventional transmit diversity schemes. Nevertheless, it is still highly desirable for a multi-antenna device to transmit data to the legacy single-antenna device in a manner such that greater reliability and/or improved performance can be achieved.
  • [0006]
    There is therefore a need in the art for techniques to achieve transmit diversity in an OFDM-based system, especially for legacy single-antenna devices.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • [0007]
    FIG. 1 shows a multi-antenna system with an access point and user terminals.
  • [0008]
    FIG. 2 shows a block diagram of a multi-antenna transmitting entity, a single-antenna receiving entity, and a multi-antenna receiving entity.
  • [0009]
    FIG. 3 shows an OFDM waveform in the frequency domain.
  • [0010]
    FIG. 4 shows a block diagram of an OFDM modulator.
  • [0011]
    FIG. 5 shows a model for transmission with steering diversity for one subband.
  • [0012]
    FIG. 6 shows a transmit (TX) spatial processor and an OFDM modulator.
  • [0013]
    FIG. 7 shows plots of linear phase shifts across subbands for four antennas.
  • [0014]
    FIGS. 8A and 8B show two embodiments for achieving linear phase shifts using different delays for time-domain samples.
  • [0015]
    FIG. 8C shows transmissions from T transmit antennas for the embodiments shown in FIGS. 8A and 8B.
  • [0016]
    FIG. 9A shows an embodiment for achieving linear phase shifts using circular shifts for time-domain samples.
  • [0017]
    FIG. 9B shows transmissions from T transmit antennas for the embodiment shown in FIG. 9A.
  • DETAILED DESCRIPTION
  • [0018]
    The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.
  • [0019]
    FIG. 1 shows a multi-antenna system 100 with an access point (AP) 110 and user terminals (UTs) 120. An access point is generally a fixed station that communicates with the user terminals and may also be referred to as a base station or some other terminology. A user terminal may be fixed or mobile and may also be referred to as a mobile station, a wireless device, a user equipment (UE), or some other terminology. For a centralized architecture, a system controller 130 couples to the access points and provides coordination and control for these access points.
  • [0020]
    Access point 110 is equipped with multiple antennas for data transmission and reception. Each user terminal 120 may be equipped with a single antenna or multiple antennas for data transmission and reception. A user terminal may communicate with the access point, in which case the roles of access point and user terminal are established. A user terminal may also communicate peer-to-peer with another user terminal. In the following description, a transmitting entity is equipped with multiple (T) transmit antennas, and a receiving entity may be equipped with a single antenna or multiple (R) antennas. A multiple-input single-output (MISO) transmission exists when the receiving entity is equipped with a single antenna, and a multiple-input multiple-output (MIMO) transmission exists when the receiving entity is equipped with multiple antennas.
  • [0021]
    FIG. 2 shows a block diagram of a multi-antenna transmitting entity 210, a single-antenna receiving entity 250 x, and a multi-antenna receiving entity 250 y in system 100. Transmitting entity 210 may be an access point or a multi-antenna user terminal. Each receiving entity 250 may also be an access point or a user terminal.
  • [0022]
    At transmitting entity 210, a transmit (TX) data processor 212 processes (e.g., encodes, interleaves, and symbol maps) traffic/packet data and generates data symbols. As used herein, a “data symbol” is a modulation symbol for data, a “pilot symbol” is a modulation symbol for pilot (which is data that is known a priori by both the transmitting and receiving entities), a “transmit symbol” is a symbol to be sent from a transmit antenna, and a “received symbol” is a symbol obtained from a receive antenna. A TX spatial processor 220 receives and demultiplexes pilot and data symbols onto the proper subbands, performs spatial processing as appropriate, and provides T streams of transmit symbols for the T transmit antennas. An OFDM modulator (Mod) 230 performs OFDM modulation on the T transmit symbol streams and provides T streams of samples to T transmitter units (TMTR) 232 a through 232 t. Each transmitter unit 232 processes (e.g., converts to analog, amplifies, filters, and frequency upconverts) its transmit symbol stream and generates a modulated signal. Transmitter units 232 a through 232 t provide T modulated signals for transmission from T antennas 234 a through 234 t, respectively.
  • [0023]
    At single-antenna receiving entity 250 x, an antenna 252 x receives the T transmitted signals and provides a received signal to a receiver unit (RCVR) 254 x. Receiver unit 254 x performs processing that is complementary to the processing performed by transmitter units 232 and provides a stream of samples. An OFDM demodulator (Demod) 260 x performs OFDM demodulation on the sample stream to obtain received data and pilot symbols, provides the received data symbols to a detector 270 x, and provides the received pilot symbols to a channel estimator 284 x within a controller 280 x. Channel estimator 284 x derives channel estimates for the effective SISO channels between transmitting entity 210 and receiving entity 250 x for subbands used for data transmission. Detector 270 x performs detection on the received data symbols for each subband based on the effective SISO channel estimate for that subband and provides a stream of detected symbols for all subbands. A receive (RX) data processor 272 x then processes (e.g., symbol demaps, deinterleaves, and decodes) the detected symbol stream and provides decoded data.
  • [0024]
    At multi-antenna receiving entity 250 y, R antennas 252 a through 252 r receive the T transmitted signals, and each antenna 252 provides a received signal to a respective receiver unit 254. Each receiver unit 254 processes a respective received signal and provides a sample stream to an associated OFDM demodulator 260. Each OFDM demodulator 260 performs OFDM demodulation on its sample stream to obtain received data and pilot symbols, provides the received data symbols to an RX spatial processor 270 y, and provides the received pilot symbols to a channel estimator 284 y within a controller 280 y. Channel estimator 284 y derives channel estimates for the actual or effective MIMO channels between transmitting entity 210 and receiving entity 250 y for subbands used for data transmission. Controller 280 y derives spatial filter matrices based on the MIMO channel estimates. RX spatial processor 270 y performs receiver spatial processing (or spatial matched filtering) on the received data symbols for each subband with the spatial filter matrix derived for that subband and provides detected symbols for the subband. An RX data processor 272 y then processes the detected symbols for all subbands and provides decoded data.
  • [0025]
    Controllers 240, 280 x, and 280 y control the operation of the processing units at transmitting entity 210 and receiving entities 250 x and 250 y, respectively. Memory units 242, 282 x, and 282 y store data and/or program code used by controllers 240, 280 x, and 280 y, respectively.
  • [0026]
    FIG. 3 shows an OFDM waveform in the frequency domain. OFDM provides K total subbands, and the subcarrier for each subband may be individually modulated with data. Of the K total subbands, ND subbands may be used for data transmission, NP subbands may be used for pilot transmission, and the remaining NG subbands may be unused and serve as guard subbands, where K=ND+NP+NG. For example, 802.11a utilizes an OFDM structure that has 64 total subbands, of which 48 subbands are used for data transmission, 4 subbands are used for pilot transmission, and 12 subbands are unused. In general, system 100 may utilize any OFDM structure with any number of data, pilot, guard, and total subbands. For simplicity, the following description assumes that all K subbands are usable for data and pilot transmission.
  • [0027]
    FIG. 4 shows a block diagram of OFDM modulator 230 at transmitting entity 210. The data to be transmitted (or information bits) is typically first encoded to generate code bits, which are then interleaved. The interleaved bits are then grouped into B-bit binary values, where B≧1. Each B-bit value is then mapped to a specific modulation symbol based on a modulation scheme selected for use (e.g., M-PSK or M-QAM, where M=2B). Each modulation symbol is a complex value in a signal constellation for the selected modulation scheme. In each OFDM symbol period, one modulation symbol may be transmitted on each subband. (A signal value of zero, which is also called a zero symbol, is usually provided for each unused subband.) An inverse discrete Fourier transform (IDFT) unit 432 receives K modulation symbols for the K subbands in each OFDM symbol period, transforms the K modulation symbols to the time domain with a K-point IDFT, and provides a “transformed” symbol that contains K time-domain samples. Each sample is a complex-value to be transmitted in one sample period. A parallel-to-serial (P/S) converter 434 serializes the K samples for each transformed symbol. A cyclic prefix generator 436 then repeats a portion (or C samples) of each transformed symbol to form an OFDM symbol that contains K+C samples. The cyclic prefix is used to combat inter-symbol interference (ISI) caused by frequency selective fading, which is a frequency response that varies across the overall system bandwidth. An OFDM symbol period (which is also referred to herein as simply a “symbol period”) is the duration of one OFDM symbol and is equal to K+C sample periods.
  • [0028]
    In system 100, a MISO channel exists between a multi-antenna transmitting entity and a single-antenna receiving entity. For an OFDM-based system, the MISO channel formed by the T antennas at the transmitting entity and the single antenna at the receiving entity may be characterized by a set of K channel response row vectors, each of dimension 1×T, which may be expressed as:
  • [0000]

    h (k)=[h 0(k)h 1(k) . . . h T−1(k)], for k=0, . . . , K−1,  Eq (1)
  • [0000]
    where k is an index for subband and hi(k), for i=0, . . . , T−1, denotes the coupling or complex gain between transmit antenna i and the single receive antenna for subband k. For simplicity, the MISO channel response h(k) is shown as a function of only subband k and not time.
  • [0029]
    If the transmitting entity has an accurate estimate of the MISO channel response, then it may perform spatial processing to direct a data transmission toward the receiving entity. However, if the transmitting entity does not have an accurate estimate of the wireless channel, then the T transmissions from the T antennas cannot be intelligently adjusted based on the wireless channel.
  • [0030]
    When an accurate channel estimate is not available, the transmitting entity may transmit data from its T antennas to the single-antenna receiving entity using steering diversity to achieve transmit diversity, greater reliability, and/or improved performance. With steering diversity, the transmitting entity performs spatial processing such that the data transmission observes different effective channels across the subbands used for data transmission. Consequently, performance is not dictated by a bad channel realization. The spatial processing for steering diversity is also such that the single-antenna receiving entity can perform the normal processing for SISO operation (and does not need to do any other special processing for transmit diversity) in order to recover the data transmission and enjoy the benefits of transmit diversity. For clarity, the following description is generally for one OFDM symbol, and the index for time is omitted.
  • [0031]
    FIG. 5 shows a model for transmission with steering diversity for one subband k from multi-antenna transmitting entity 210 to single-antenna receiving entity 250 x. A modulation symbol s(k) to be sent on subband k is spatially processed with T complex weights (or scalar values) v0(k) through vT−1(k) to obtain T transmit symbols for subband k, which are then processed and sent from the T transmit antennas. The T transmit symbols for subband k observe channel responses of h0(k) through hT−1(k).
  • [0032]
    The transmitting entity performs spatial processing for each subband k for steering diversity, as follows:
  • [0000]

    x (k)= v (ks(k), for k=0, . . . , K−1,  Eq(2)
  • [0000]
    where s(k) is a modulation symbol to be sent on subband k;
      • v(k)=[v0(k)v1(k) . . . vT−1(k)]T is a T×1 steering vector for subband k;
      • x(k)=[x0(k)x1(k) . . . xT−1(k)]T is a T×1 vector with T transmit symbols to be sent from the T transmit antennas on subband k; and
      • T” denotes a transpose.
        In general, the modulation symbol s(k) may be any real or complex value (e.g., a signal value of zero) and does not need to be from a signal constellation.
  • [0036]
    The received symbols at the receiving entity for each subband k may be expressed as:
  • [0000]
    r ( k ) = h _ ( k ) · x _ ( k ) + n ( k ) , = h _ ( k ) · v _ ( k ) · s ( k ) + n ( k ) , = h eff ( k ) · s ( k ) + n ( k ) , for k = 0 , , K - 1 , Eq ( 3 )
  • [0000]
    where r(k) is a received symbol for subband k;
      • heff(k) is an effective SISO channel response for subband k, which is heff(k)=h(k)·v(k); and
      • n(k) is the noise for subband k.
  • [0039]
    As shown in equation (3), the spatial processing by the transmitting entity for steering diversity results in the modulation symbol s(k) for each subband k observing the effective SISO channel response heff(k), which includes the actual MISO channel response h(k) and the steering vector v(k) for that subband. The receiving entity can estimate the effective SISO channel response heff(k), for example, based on pilot symbols received from the transmitting entity. The receiving entity can then perform detection or matched filtering on the received symbol r(k) for each subband k with the effective SISO channel response estimate ĥeff(k) for that subband to obtain a detected symbol ŝ(k), which is an estimate of the modulation symbol s(k) transmitted on the subband.
  • [0040]
    The receiving entity may perform matched filtering as follows:
  • [0000]
    s ^ ( k ) = h ^ eff * ( k ) · r ( k ) h ^ eff ( k ) 2 = s ( k ) + n ( k ) , Eq ( 4 )
  • [0000]
    where “*” denotes a conjugate and n′(k) is the noise after the matched filtering. The detection operation in equation (4) is the same as would be performed by the receiving entity for a SISO transmission. However, the effective SISO channel response estimate, ĥeff(k), is used for detection instead of a SISO channel response estimate, ĥ(k).
  • [0041]
    For steering diversity, the receiving entity does not need to know whether a single antenna or multiple antennas are used for data transmission and also does not need to know the steering vector used for each subband. The receiving entity can nevertheless enjoy the benefits of transmit diversity if different steering vectors are used across the subbands and different effective SISO channels are formed for these subbands. A data transmission sent across multiple subbands would then observe an ensemble of different effective SISO channels across the subbands used for data transmission.
  • [0042]
    FIG. 6 shows a block diagram of a TX spatial processor 220 a and an OFDM modulator 230 a, which are an embodiment of TX spatial processor 220 and OFDM modulator 230, respectively, in FIG. 2. TX spatial processor 220 a receives K modulation symbols (or generically, input symbols) s(0) through s(K−1) for the K subbands for each OFDM symbol period. Within TX spatial processor 220 a, a different set of K multipliers 620 multiplies the K modulation symbols with a set of K weights vi(0) through vi(K−1)) for each transmit antenna i and provides K weighted symbols for that antenna. The modulation symbol s(k) for each subband k is transmitted from all T antennas and is multiplied with T weights v0(k) through vT−1(k) for the T transmit antennas for that subband. TX spatial processor 220 a provides T sets of K weighted symbols for the T transmit antennas.
  • [0043]
    Within OFDM modulator 230 a, the set of K weighted symbols for each transmit antenna i is transformed to the time-domain by a respective IDFT unit 632 to obtain a transformed symbol for that antenna. The K time-domain samples for the transformed symbol for each transmit antenna i are serialized by a respective P/S converter 634 and further appended with a cyclic prefix by a cyclic prefix generator 636 to generate an OFDM symbol for that antenna. The OFDM symbol for each transmit antenna i is then conditioned by transmitter unit 232 for that antenna and transmitted via the antenna.
  • [0044]
    For steering diversity, the transmitting entity uses different steering vectors for different subbands, with each steering vector defining or forming a beam for the associated subband. In general, it is desirable to use as many different steering vectors as possible across the subbands to achieve greater transmit diversity. For example, a different steering vector may be used for each of the K subbands, and the set of K steering vectors used for the K subbands may be denoted as {v(k)}. For each subband, the steering vector may be the same over time or may change, e.g., from symbol period to symbol period.
  • [0045]
    In general, any steering vector may be used for each of the K subbands for steering diversity. However, to ensure that performance is not degraded for single-antenna devices that are not aware of the steering diversity being performed and further rely on some correlation across the subbands, the steering vectors may be defined such that the beams vary in a continuous instead of abrupt manner across the subbands. This may be achieved by applying continuously changing phase shifts across the subbands for each transmit antenna. As an example, the phase shifts may change in a linear manner across the subbands for each transmit antenna, and each antenna may be associated with a different phase slope, as described below. The application of linearly changing phase shifts to modulation symbols in the frequency domain may be achieved by temporally modifying (e.g., either delaying or circularly shifting) the corresponding time-domain samples. If different steering vectors are used for different subbands, then the modulation symbols for these subbands are beamed in different directions by the array of N transmit antennas. If encoded data is spread over multiple subbands with different steering, then decoding performance will likely improve due to the increased diversity.
  • [0046]
    If the steering vectors for adjacent subbands generate beams in very different directions, then the effective SISO channel response heff(k) would also vary widely among the adjacent subbands. Some receiving entities may not be aware of steering diversity being performed, such as legacy single-antenna devices in an IEEE 802.11a system. These receiving entities may assume that the channel response varies slowly across the subbands and may perform channel estimation in a manner to simplify the receiver design. For example, these receiving entities may estimate the channel response for a subset of the K total subbands and use interpolation or some other techniques to derive estimates of the channel response for the other subbands. The use of abruptly changing steering vectors (e.g., pseudo-random steering vectors) may severely degrade the performance of these receiving entities.
  • [0047]
    To provide transmit diversity and avoid degrading the performance of legacy receiving entities, the steering vectors may be selected such that (1) different beams are used for different subbands and (2) the beams for adjacent subbands have smooth instead of abrupt transitions. The weights to use for the K subbands of the T transmit antennas may be expressed as:
  • [0000]
    V _ = [ v _ ( 0 ) v _ ( 1 ) v _ ( K - 1 ) ] = [ v 0 ( 0 ) v 0 ( 1 ) v 0 ( K - 1 ) v 1 ( 0 ) v 1 ( 1 ) v 1 ( K - 1 ) v T - 1 ( 0 ) v T - 1 ( 1 ) v T - 1 ( K - 1 ) ] , Eq ( 5 )
  • [0000]
    where V is a T×K matrix of weights for the K subbands of the T transmit antennas.
  • [0048]
    In an embodiment, the weights in the matrix V are defined as follows:
  • [0000]
    v i ( k ) = B ( i ) · j 2 π · i · k K , for i = 0 , , T - 1 and k = 0 , , K - 1 , Eq ( 6 )
  • [0000]
    where B(i) is a complex gain for transmit antenna i;
      • vi(k) is the weight for subband k of transmit antenna i; and
      • j is the imaginary value defined by j=√{square root over (−1)}.
  • [0051]
    The magnitude of the complex gain for each transmit antenna may be set to one, or ∥B(i)∥=1.0 for i=0, . . . , T−1. The weights shown in equation (6) correspond to a progressive phase shift for each subband and antenna. These weights effectively form a slightly different beam for each subband for a linear array of T equally spaced antennas.
  • [0052]
    In a specific embodiment, the weights are defined as follows:
  • [0000]
    v i ( k ) = - j π · i · j 2 π · i · k K = j 2 π i K · ( k - K 2 ) , Eq ( 7 )
  • [0000]
    for i=0, . . . , T−1 and k=0, . . . , K−1. The embodiment shown in equation (7) uses B(i)=e−jπ·i for equation (6). This results in a different phase shift being applied to each antenna.
  • [0053]
    FIG. 7 shows plots of the phase shifts for each transmit antenna for a case with T=4. The center of the K subbands is typically considered to be at zero frequency, as shown in FIG. 3. The weights generated based on equation (7) may be interpreted as creating a linear phase shift across the K subbands. Each transmit antenna i, for i=0, . . . , T−1, is associated with a phase slope of 2π·i/K. The phase shift for each subband k, for k=0, . . . , K−1, for each transmit antenna i is given as 2π·i·(k−K/2)/K. The use of B(i)=e−jπ·i result in subband k=K/2 observing a phase shift of zero.
  • [0054]
    The weights derived based on equation (7) may be viewed as a linear filter having a discrete frequency response of Gi(k′), which may be expressed as:
  • [0000]
    G i ( k ) = v i ( k + K / 2 ) = j 2 π i · k K , Eq ( 8 )
  • [0000]
    for i=0, . . . , T−1 and k′=(−K/2), . . . , (K/2−1). The subband index k is for a subband numbering scheme that places the zero frequency at subband Ncenter=K/2, as shown in FIG. 3. The subband index k′ is a shifted version of the subband index k by K/2, or k′=k−K/2. This results in subband zero being at zero frequency for the new subband numbering scheme with the index k′. Ncenter may be equal to some other value instead of K/2 if the index k is defined in some other manner (e.g., k=1, . . . , K) or if K is an odd number.
  • [0055]
    A discrete time-domain impulse response gi(n) for the linear filter may be obtained by performing a K-point IDFT on the discrete frequency response Gi(k′). The impulse response gi(n) may be expressed as:
  • [0000]
    g i ( n ) = 1 K · k = - K / 2 K / 2 - 1 G i ( k ) · j2π n · k K , = 1 K · k = - K / 2 K / 2 - 1 j 2 π i · k K · j 2 π n · k K , = 1 K · k = - K / 2 K / 2 - 1 j 2 π k K ( i + n ) , = { 1 for n = - i 0 otherwise Eq ( 9 )
  • [0000]
    where n is an index for sample period and has a range of n=0, . . . , K−1. Equation (9) indicates that the impulse response gi(n) for transmit antenna i has a single unit-value tap at a delay of i sample periods and is zero at all other delays.
  • [0056]
    The spatial processing with the weights defined as shown in equation (7) may be performed by multiplying the K modulation symbols for each transmit antenna i with the K weights vi(0) through vi(K−1) for that antenna and then performing a K-point IDFT on the K weighted symbols. Equivalently, the spatial processing with these weights may be achieved by (1) performing a K-point IDFT on the K modulation symbols to obtain K time-domain samples, and (2) performing a circular convolution of the K time-domain samples with the impulse response gi(n), which has a single unit-value tap at a delay of i sample periods.
  • [0057]
    FIG. 8A shows a block diagram of a TX spatial processor 220 b and an OFDM modulator 230 b, which are another embodiment of TX spatial processor 220 and OFDM modulator 230, respectively, in FIG. 2. OFDM modulator 220 b receives K modulation symbols s(0) through s(K−1) for the K subbands for each OFDM symbol period. Within OFDM modulator 230 b, an IDFT unit 832 performs a K-point IDFT on the K modulation symbols and provides K time-domain samples. A P/S converter 834 serializes the K time-domain samples. A cyclic prefix generator 836 then appends a C-sample cyclic prefix and provides an OFDM symbol containing K+C samples to TX spatial processor 220 b. TX spatial processor 220 b includes T digital delay units 822 a through 822 t for the T transmit antennas. Each delay unit 822 receives and delays the OFDM symbol from OFDM demodulator 230 b by a different amount determined by the associated transmit antenna. In particular, delay unit 822 a for transmit antenna 234 a delays the OFDM symbol by zero sample period, delay unit 822 b for transmit antenna 234 b delays the OFDM symbol by one sample period, and so on, and delay unit 822 t for transmit antenna 234 t delays the OFDM symbol by T−1 sample periods. The subsequent processing by transmitter units 232 is as described above.
  • [0058]
    FIG. 8B shows a block diagram of OFDM modulator 230 b and a TX spatial processor 220 c, which is yet another embodiment of TX spatial processor 220 in FIG. 2. OFDM modulator 220 b performs OFDM modulation on K modulation symbols for each OFDM symbol period as described above for FIG. 8A. Transmitter unit 232 then receives and conditions the OFDM symbol for each symbol period to generate a modulated signal. TX spatial processor 220 c provides time delay in the analog domain. TX spatial processor 220 c includes T analog delay units 824 a through 824 t for the T transmit antennas. Each delay unit 824 receives and delays the modulated signal by a different amount determined by the associated transmit antenna. In particular, delay unit 824 a for the first transmit antenna 234 a delays the modulated signal by zero seconds, delay unit 824 b for the second transmit antenna 234 b delays the modulated signal by one sample period (or Tsam seconds), and so on, and delay unit 824 t for the T-th transmit antenna 234 t delays the modulated signal by (T−1) sample periods (or (T−1)·Tsam seconds). A sample period is equal to Tsam=1/(BW·(K+C)), where BW is the overall bandwidth of the system in Hertz.
  • [0059]
    FIG. 8C shows a timing diagram for the T transmissions from the T transmit antennas for the embodiments shown in FIGS. 8A and 8B. The same OFDM symbol is transmitted from each of the T transmit antennas. However, the OFDM symbol sent from each transmit antenna is delayed by a different amount. The T delayed and non-delayed OFDM symbols for the T antennas may be viewed as T different versions of the same OFDM symbol.
  • [0060]
    For the embodiments shown in equations (7) through (9) and FIGS. 8A through 8C, the delays for the T transmit antennas are in integer numbers of sample periods. Phase slopes that result in non-integer delays for the T transmit antennas (or B(i)=e−jπi/L, where L>1) may also be implemented. For example, the time-domain samples from OFDM modulator 230 b in FIG. 8A may be up-sampled to a higher rate (e.g., with a period of Tupsam=Tsam/L), and the higher rate samples may be delayed by digital delay units 822 by integer numbers of the higher rate sample period (Tupsam). Alternatively, analog delay units 824 in FIG. 8B may provide delays in integer numbers of Tupsam (instead of Tsam).
  • [0061]
    When the number of transmit antennas is less than the cyclic prefix length (or T<C), the cyclic prefix appended to each OFDM symbol makes a linear delay by digital delay units 822 or analog delay units 824 appears like a circular rotation for the circular convolution with the time-domain impulse response gi(n). The weights as defined in equation (7) may thus be implemented by a time delay of i sample periods for each transmit antenna i, as shown in FIGS. 8A through 8C. However, as shown in FIG. 8C, the OFDM symbol is transmitted from the T transmit antennas at different delays, which reduces the effectiveness of the cyclic prefix to protect against multipath delay.
  • [0062]
    The IDFT of K weighted symbols (which are obtained by multiplying K modulation symbols with the phase slope shown in equation (7)) provides a time-domain sample sequence that is equal to a circular shift of the K time-domain samples from the IDFT of the K (original unweighted) modulation symbols. The spatial processing may thus be performed by circularly shifting these K time-domain samples.
  • [0063]
    FIG. 9A shows a block diagram of an OFDM modulator 230 d and a TX spatial processor 220 d, which are yet another embodiment of OFDM modulator 230 and TX spatial processor 220, respectively, in FIG. 2. Within OFDM modulator 230 d, an IDFT unit 932 performs a K-point IDFT on the K modulation symbols and provides K time-domain samples, and a P/S converter 934 serializes the K time-domain samples. TX spatial processor 220 d includes T circular shift units 922 a through 922 t for the T transmit antennas. Each unit 922 receives the K time-domain samples from P/S converter 934, performs a circular shift of the K time-domain samples by i samples for transmit antenna i, and provides a circular-shifted transformed symbol containing K samples. In particular, unit 922 a performs a circular shift by 0 sample for transmit antenna 234 a, unit 922 b performs a circular shift by 1 sample for transmit antenna 234 b, and so on, and unit 922 t performs a circular shift by (T−1) samples for transmit antenna 234 t. T cyclic prefix generators 936 a through 936 t receive the circular-shifted transformed symbols from units 922 a through 922 t, respectively. Each cyclic prefix generator 936 appends a C-sample cyclic prefix to its circular-shifted transformed symbol and provides an OFDM symbol containing (K+C) samples. The subsequent processing by transmitter units 232 a through 232 t is as described above.
  • [0064]
    FIG. 9B shows a timing diagram for the T transmissions from the T transmit antennas for the embodiment shown in FIG. 9A. A different version of the OFDM symbol is generated for each of the T transmit antennas by circularly shifting a different amount. However, the T different versions of the OFDM symbol are sent from the T transmit antennas at the same time.
  • [0065]
    The embodiments shown in FIGS. 8A, 8B, and 9A illustrate some of the ways in which spatial processing for steering diversity may be performed. In general, the spatial processing for steering diversity may be performed in various manners and at various locations within the transmitting entity. For example, the spatial processing may be performed in the time-domain or the frequency-domain, using digital circuitry or analog circuitry, prior to or after the OFDM modulation, and so on.
  • [0066]
    Equations (6) and (7) represent a function that provides linearly changing phase shifts across the K subbands for each transmit antenna. The application of linearly changing phase shifts to modulation symbols in the frequency domain may be achieved by either delaying or circularly shifting the corresponding time-domain samples, as described above. In general, the phase shifts across the K subbands for each transmit antenna may be changed in a continuous manner using any function so that the beams are varied in a continuous instead of abrupt manner across the subbands. A linear function of phase shifts is just one example of a continuous function. The continuous change ensures that the performance for single-antenna devices that rely on some amounts of correlation across the subbands (e.g., to simplify channel estimation) is not degraded.
  • [0067]
    In the description above, steering diversity is achieved for a transmission of one modulation symbol on each subband in each symbol period. Multiple (S) modulation symbols may also be sent via the T transmit antennas on one subband in one symbol period to a multi-antenna receiving entity with R receive antennas using steering diversity, where S≦min {T, R}
  • [0068]
    The steering diversity techniques described herein may be used for various wireless systems. These techniques may also be used for the downlink (or forward link) as well as the uplink (or reverse link). Steering diversity may be performed by any entity equipped with multiple antennas.
  • [0069]
    Steering diversity may be used in various manners. For example, a transmitting entity (e.g., an access point or a user terminal) may use steering diversity to transmit to a receiving entity (e.g., another access point or user terminal) when accurate information about the wireless channel is not available. Accurate channel information may not be available due to various reasons such as, for example, a feedback channel that is corrupted, a system that is poorly calibrated, the channel conditions changing too rapidly for the transmitting entity to use/adjust beam steering on time, and so on. The rapidly changing channel conditions may be due to, for example, the transmitting and/or receiving entity moving at a high velocity.
  • [0070]
    Steering diversity may also be used for various applications in a wireless system. In one application, broadcast channels in the system may be transmitted using steering diversity as described above. The use of steering diversity allows wireless devices in the system to possibly receive the broadcast channels with improved reliability, thereby increasing the range of the broadcast channels. In another application, a paging channel is transmitted using steering diversity. Again, improved reliability and greater coverage may be achieved for the paging channel via the use of steering diversity. In yet another application, an 802.11a access point uses steering diversity to improve the performance of user terminals under its coverage area.
  • [0071]
    The steering diversity techniques described herein may be implemented by various means. For example, these techniques may be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing units used to perform spatial processing for steering diversity may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.
  • [0072]
    For a software implementation, the steering diversity techniques may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit (e.g., memory unit 242 in FIG. 2) and executed by a processor (e.g., controller 240). The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.
  • [0073]
    The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Citations de brevets
Brevet cité Date de dépôt Date de publication Déposant Titre
US5668837 *3 févr. 199516 sept. 1997Ericsson Inc.Dual-mode radio receiver for receiving narrowband and wideband signals
US5757845 *9 févr. 199526 mai 1998Ntt Mobile Communications NetworkAdaptive spread spectrum receiver
US6118758 *23 déc. 199612 sept. 2000Tellabs Operations, Inc.Multi-point OFDM/DMT digital communications system including remote service unit with improved transmitter architecture
US6175743 *1 mai 199816 janv. 2001Ericsson Inc.System and method for delivery of short message service messages to a restricted group of subscribers
US6198775 *28 avr. 19986 mars 2001Ericsson Inc.Transmit diversity method, systems, and terminals using scramble coding
US6218985 *15 avr. 199917 avr. 2001The United States Of America As Represented By The Secretary Of The NavyArray synthesis method
US6298035 *21 déc. 19992 oct. 2001Nokia Networks OyEstimation of two propagation channels in OFDM
US6351499 *15 déc. 199926 févr. 2002Iospan Wireless, Inc.Method and wireless systems using multiple antennas and adaptive control for maximizing a communication parameter
US6441786 *20 juil. 200127 août 2002Motorola, Inc.Adaptive antenna array and method for control thereof
US6452981 *5 nov. 199917 sept. 2002Cisco Systems, IncSpatio-temporal processing for interference handling
US6473467 *30 mars 200029 oct. 2002Qualcomm IncorporatedMethod and apparatus for measuring reporting channel state information in a high efficiency, high performance communications system
US6542556 *31 mars 20001 avr. 2003Nokia Mobile Phones Ltd.Space-time code for multiple antenna transmission
US6618454 *17 déc. 19989 sept. 2003At&T Corp.Diversity coded OFDM for high data-rate communication
US6678263 *17 sept. 199913 janv. 2004Hughes Electronics CorporationMethod and constructions for space-time codes for PSK constellations for spatial diversity in multiple-element antenna systems
US6711124 *25 mai 200123 mars 2004Ericsson Inc.Time interval based channel estimation with transmit diversity
US6711528 *10 févr. 200323 mars 2004Harris CorporationBlind source separation utilizing a spatial fourth order cumulant matrix pencil
US6763073 *15 juin 200113 juil. 2004Lucent Technologies Inc.Wireless communications system having a space-time architecture employing multi-element antennas at both the transmitter and receiver
US6842487 *22 sept. 200011 janv. 2005Telefonaktiebolaget Lm Ericsson (Publ)Cyclic delay diversity for mitigating intersymbol interference in OFDM systems
US6847306 *16 mai 200325 janv. 2005Keyvan T. DibaEmergency traffic signal attachment
US6862271 *26 févr. 20021 mars 2005Qualcomm IncorporatedMultiple-input, multiple-output (MIMO) systems with multiple transmission modes
US6940917 *27 août 20026 sept. 2005Qualcomm, IncorporatedBeam-steering and beam-forming for wideband MIMO/MISO systems
US6999472 *30 mai 200114 févr. 2006Nokia Mobile Phones LimitedApparatus, and associated method, for space-time encoding, and decoding, data at a selected code rate
US7031669 *9 juin 200318 avr. 2006Cognio, Inc.Techniques for correcting for phase and amplitude offsets in a MIMO radio device
US7061969 *20 juil. 200413 juin 2006Cingular Wireless Ii, LlcVertical adaptive antenna array for a discrete multitone spread spectrum communication system
US7065156 *31 août 200020 juin 2006Nokia Mobile Phones Ltd.Hopped delay diversity for multiple antenna transmission
US7079870 *13 févr. 200418 juil. 2006Ipr Licensing, Inc.Compensation techniques for group delay effects in transmit beamforming radio communication
US7092737 *31 juil. 200215 août 2006Mitsubishi Electric Research Laboratories, Inc.MIMO systems with rate feedback and space time transmit diversity
US7095987 *15 nov. 200122 août 2006Texas Instruments IncorporatedMethod and apparatus for received uplinked-signal based adaptive downlink diversity within a communication system
US7099678 *13 févr. 200429 août 2006Ipr Licensing, Inc.System and method for transmit weight computation for vector beamforming radio communication
US7099698 *3 nov. 200329 août 2006Vivato, Inc.Complementary beamforming methods and apparatuses
US7110350 *5 mars 200419 sept. 2006University Of Florida Research Foundation, Inc.Wireless LAN compatible multi-input multi-output system
US7190734 *28 mai 200213 mars 2007Regents Of The University Of MinnesotaSpace-time coded transmissions within a wireless communication network
US7200631 *10 janv. 20033 avr. 2007Lucent Technologies Inc.Method and apparatus for determining an inverse square root of a given positive-definite hermitian matrix
US7206354 *19 févr. 200417 avr. 2007Qualcomm IncorporatedCalibration of downlink and uplink channel responses in a wireless MIMO communication system
US7227906 *11 déc. 20025 juin 2007Ntt Docomo, Inc.Radio communication method and apparatus for multiplex transmission of plural signals in the same frequency band
US7236478 *8 mai 200326 juin 2007Huawei Technologies Co., Ltd.Method and apparatus for down-link feedback multiple antenna transmission in wireless communication system
US7317750 *16 avr. 20038 janv. 2008Lot 41 Acquisition Foundation, LlcOrthogonal superposition coding for direct-sequence communications
US7324429 *23 oct. 200329 janv. 2008Qualcomm, IncorporatedMulti-mode terminal in a wireless MIMO system
US7324482 *13 janv. 200429 janv. 2008The Directv Group, Inc.Method and constructions for space-time codes for PSK constellations for spatial diversity in multiple-element antenna systems
US7327798 *21 oct. 20025 févr. 2008Lg Electronics Inc.Method and apparatus for transmitting/receiving signals in multiple-input multiple-output communication system provided with plurality of antenna elements
US7336746 *8 mars 200726 févr. 2008Qualcomm IncorporatedData transmission with spatial spreading in a MIMO communication system
US7356073 *10 sept. 20038 avr. 2008Nokia CorporationMethod and apparatus providing an advanced MIMO receiver that includes a signal-plus-residual-interference (SPRI) detector
US7359466 *24 août 200115 avr. 2008Lucent Technologies Inc.Signal detection by a receiver in a multiple antenna time-dispersive system
US7385617 *7 mai 200310 juin 2008Illinois Institute Of TechnologyMethods for multi-user broadband wireless channel estimation
US7394754 *21 nov. 20021 juil. 2008Mediatek Inc.System and method for transmitting data in a multiple-branch transmitter-diversity orthogonal frequency-division multiplexing (OFDM) system
US7522673 *21 avr. 200321 avr. 2009Regents Of The University Of MinnesotaSpace-time coding using estimated channel information
US7529177 *28 août 20025 mai 2009Agere Systems Inc.Dithering scheme using multiple antennas for OFDM systems
US7555053 *30 août 200430 juin 2009Broadcom CorporationLong training sequence for MIMO WLAN systems
US7583747 *31 mars 20051 sept. 2009University Of AlbertaMethod of systematic construction of space-time constellations, system and method of transmitting space-time constellations
US7593317 *1 août 200322 sept. 2009Panasonic CorporationRadio base station apparatus
US7653142 *13 déc. 200626 janv. 2010Qualcomm IncorporatedChannel estimation and spatial processing for TDD MIMO systems
US7742546 *8 oct. 200322 juin 2010Qualcomm IncorporatedReceiver spatial processing for eigenmode transmission in a MIMO system
US20020009125 *11 juin 200124 janv. 2002Shi Zhen LiangHigh bandwidth efficient spread spectrum modulation using chirp waveform
US20020091943 *12 déc. 200111 juil. 2002International Business Machines CorporationMethods, systems, signals and media for encouraging users of computer readable content to register
US20020102940 *19 nov. 20011 août 2002Ralf BohnkeAdaptive subcarrier loading
US20020114269 *3 oct. 200122 août 2002Onggosanusi Eko NugrohoChannel aware optimal space-time signaling for wireless communication over wideband multipath channels
US20020127978 *23 janv. 200212 sept. 2002Koninklijke Philips Electronics N.V.Radio communication system
US20030011274 *12 juil. 200216 janv. 2003Moteurs Leroy-SomerDiscoid machine
US20030016637 *25 mai 200123 janv. 2003Khayrallah Ali S.Time interval based channel estimation with transmit diversity
US20030076908 *24 août 200124 avr. 2003Huang Howard C.Signal detection by a receiver in a multiple antenna time-dispersive system
US20030108117 *7 déc. 200112 juin 2003Ketchum John W.Time-domain transmit and receive processing with channel eigen-mode decompositon for MIMO systems
US20030112745 *17 déc. 200119 juin 2003Xiangyang ZhuangMethod and system of operating a coded OFDM communication system
US20030123565 *11 déc. 20023 juil. 2003Ntt Docomo, Inc.Radio communication method and apparatus
US20030123567 *7 nov. 20023 juil. 2003Haruhiko ShigemasaTransmitter apparatus and communication system employing the same
US20030128658 *8 janv. 200210 juil. 2003Walton Jay RodResource allocation for MIMO-OFDM communication systems
US20030161282 *26 févr. 200228 août 2003Irina MedvedevMultiple-input, multiple-output (MIMO) systems with multiple transmission modes
US20030181211 *19 mars 200225 sept. 2003Javad RazavilarMethod and apparatus for dynamic channel selection in wireless modems
US20040002364 *23 janv. 20031 janv. 2004Olav TrikkonenTransmitting and receiving methods
US20040022183 *21 nov. 20025 févr. 2004Li Kuo HuiSystem and method for transmitting data in a multiple-branch transmitter-diversity orthogonal frequency-division multiplexing (OFDM) system
US20040042439 *27 août 20024 mars 2004Menon Murali ParavathBeam-steering and beam-forming for wideband MIMO/MISO systems
US20040052315 *4 oct. 200118 mars 2004Jorn ThieleckeMulti strata system
US20040066773 *1 oct. 20028 avr. 2004Atheros Communications, Inc.Decision feedback channel estimation and pilot tracking for OFDM systems
US20040081263 *24 oct. 200229 avr. 2004Lee King F.Method and apparatus for receiving diversity transmissions
US20040082356 *23 oct. 200329 avr. 2004Walton J. RodneyMIMO WLAN system
US20040085939 *23 oct. 20036 mai 2004Wallace Mark S.Channel calibration for a time division duplexed communication system
US20040086027 *16 avr. 20036 mai 2004Shattil Steve J.Orthogonal superposition coding for direct-sequence communications
US20040102157 *27 nov. 200227 mai 2004Lewis Michael E.Wireless LAN with distributed access points for space management
US20040136349 *23 oct. 200315 juil. 2004Walton J. RodneyMIMO system with multiple spatial multiplexing modes
US20040139137 *10 janv. 200315 juil. 2004Mailaender Laurence EugeneMethod and apparatus for determining an inverse square root of a given positive-definite hermitian matrix
US20040157645 *10 oct. 200312 août 2004Smith Adrian DavidSystem and method of operation an array antenna in a distributed wireless communication network
US20040165675 *20 févr. 200326 août 2004Nec CorporationIterative soft interference cancellation and filtering for spectrally efficient high-speed transmission in MIMO systems
US20050017511 *11 août 200327 janv. 2005Stephen DaltonGravity air motion concept
US20050026570 *17 juin 20043 févr. 2005Samsung Electronics Co., Ltd.TDMA transceiver including Cartesian feedback loop circuit
US20050149320 *24 déc. 20037 juil. 2005Matti KajalaMethod for generating noise references for generalized sidelobe canceling
US20050175115 *9 déc. 200411 août 2005Qualcomm IncorporatedSpatial spreading in a multi-antenna communication system
US20050180312 *18 févr. 200418 août 2005Walton J. R.Transmit diversity and spatial spreading for an OFDM-based multi-antenna communication system
US20050195733 *5 mars 20048 sept. 2005Walton J. R.Transmit diversity and spatial spreading for an OFDM-based multi-antenna communication system
US20060013250 *15 juil. 200419 janv. 2006Howard Steven JUnified MIMO transmission and reception
US20060050770 *24 janv. 20059 mars 2006Qualcomm IncorporatedReceiver structures for spatial spreading with space-time or space-frequency transmit diversity
US20060067421 *1 sept. 200530 mars 2006Qualcomm IncorporatedSpatial spreading with space-time and space-frequency transmit diversity schemes for a wireless communication system
US20070009059 *12 sept. 200611 janv. 2007Wallace Mark SEfficient computation of spatial filter matrices for steering transmit diversity in a MIMO communication system
US20080031372 *10 oct. 20077 févr. 2008Qualcomm IncorporatedBroadcast transmission with spatial spreading in a multi-antenna communication system
US20080031374 *10 oct. 20077 févr. 2008Qualcomm IncorporatedBroadcast transmission with spatial spreading in a multi-antenna communication system
US20080095121 *14 mai 200224 avr. 2008Shattil Steve JCarrier interferometry networks
US20080095282 *21 déc. 200724 avr. 2008Qualcomm IncorporatedData transmission with spatial spreading in a mimo communication system
US20100074301 *2 août 200925 mars 2010Qualcomm IncorporatedUnified mimo transmission and reception
US20100169396 *9 mars 20101 juil. 2010Qualcomm IncorporatedEfficient computation for eigenvalue decomposition and singular value decomposition of matrices
US20110142097 *15 juin 201016 juin 2011Qualcomm IncorporatedData transmission with spatial spreading in a mimo communication system
US20120213181 *1 mai 201223 août 2012Walton J RodneyTransmit diversity and spatial spreading for an ofdm-based multi-antenna communication system
Référencé par
Brevet citant Date de dépôt Date de publication Déposant Titre
US797864915 juil. 200412 juil. 2011Qualcomm, IncorporatedUnified MIMO transmission and reception
US797877824 janv. 200512 juil. 2011Qualcomm, IncorporatedReceiver structures for spatial spreading with space-time or space-frequency transmit diversity
US799106512 sept. 20062 août 2011Qualcomm, IncorporatedEfficient computation of spatial filter matrices for steering transmit diversity in a MIMO communication system
US81698895 mars 20041 mai 2012Qualcomm IncorporatedTransmit diversity and spatial spreading for an OFDM-based multi-antenna communication system
US82041499 déc. 200419 juin 2012Qualcomm IncorporatedSpatial spreading in a multi-antenna communication system
US828522624 févr. 20059 oct. 2012Qualcomm IncorporatedSteering diversity for an OFDM-based multi-antenna communication system
US829008917 mai 200716 oct. 2012Qualcomm IncorporatedDerivation and feedback of transmit steering matrix
US832584415 juin 20104 déc. 2012Qualcomm IncorporatedData transmission with spatial spreading in a MIMO communication system
US85204981 mai 201227 août 2013Qualcomm IncorporatedTransmit diversity and spatial spreading for an OFDM-based multi-antenna communication system
US85430705 juil. 200624 sept. 2013Qualcomm IncorporatedReduced complexity beam-steered MIMO OFDM system
US8744374 *9 déc. 20103 juin 2014Intel Mobile Communications Technology Dresden GmbHMethod and apparatus for data communication in LTE cellular networks
US87677012 août 20091 juil. 2014Qualcomm IncorporatedUnified MIMO transmission and reception
US882458311 mars 20132 sept. 2014Qualcomm IncorporatedReduced complexity beam-steered MIMO OFDM system
US890301618 juin 20122 déc. 2014Qualcomm IncorporatedSpatial spreading in a multi-antenna communication system
US890917431 juil. 20099 déc. 2014Qualcomm IncorporatedContinuous beamforming for a MIMO-OFDM system
US89237853 févr. 200530 déc. 2014Qualcomm IncorporatedContinuous beamforming for a MIMO-OFDM system
US8929495 *19 mars 20136 janv. 2015Fundacio Centre Technologic de Telecomunicacions de CatalunyaMethod for equalizing filterbank multicarrier (FBMC) modulations
US20050180312 *18 févr. 200418 août 2005Walton J. R.Transmit diversity and spatial spreading for an OFDM-based multi-antenna communication system
US20050249174 *24 févr. 200510 nov. 2005Qualcomm IncorporatedSteering diversity for an OFDM-based multi-antenna communication system
US20070009059 *12 sept. 200611 janv. 2007Wallace Mark SEfficient computation of spatial filter matrices for steering transmit diversity in a MIMO communication system
US20070206686 *5 janv. 20066 sept. 2007Vook Frederick WMethod and apparatus for performing cyclic-shift diversity with beamforming
US20110105063 *17 juin 20095 mai 2011Takashi YamamotoRadio communication device and signal transmission method in mimo radio communication
US20110143807 *9 déc. 201016 juin 2011Blue Wonder Communications GmbhMethod and apparatus for data communication in lte cellular networks
US20140286384 *19 mars 201325 sept. 2014Fundació Centre Tecnològic De Telecomunicacions De CatalunyaMethod for equalizing filterbank multicarrier (fbmc)modulations
Classifications
Classification aux États-Unis375/260, 375/295
Classification internationaleH04L27/26, H04L27/28, H04B7/06, H04L27/00
Classification coopérativeH04L27/2602
Classification européenneH04L27/26M1
Événements juridiques
DateCodeÉvénementDescription
20 juil. 2008ASAssignment
Owner name: QUALCOMM INCORPORATED, CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:LUNDBY, STEIN A.;HOWARD, STEVEN J.;WALTON, JAY RODNEY;REEL/FRAME:021265/0257;SIGNING DATES FROM 20050520 TO 20050526