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US-12621023-B2 - Receiver, transmitter, system and method employing space-delay precoding

US12621023B2US 12621023 B2US12621023 B2US 12621023B2US-12621023-B2

Abstract

A receiver processes a radio signal received via a radio channel from a transmitter employing a plurality of antenna ports, determines complex precoder coefficients and delays of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel, and feeds back, explicitly or implicitly, delays and the complex precoder. The space-delay precoder has a dual-stage structure having a spatial codebook matrix including spatial beamforming vectors, a frequency-domain codebook matrix, and a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices. The frequency-domain codebook matrix is defined by a sub-matrix of a DFT matrix, which the sub-matrix of the DFT matrix is associated with a range of delay values.

Inventors

  • Venkatesh Ramireddy
  • Markus LANDMANN
  • Marcus Grossmann

Assignees

  • Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.

Dates

Publication Date
20260505
Application Date
20240325

Claims (19)

  1. 1 . A receiver, configured to receive and process a radio signal received via a radio channel from a transmitter employing a plurality of antenna ports, determine, based on the received signal, complex precoder coefficients and delays of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel, and feed back to the transmitter the determined delays explicitly or implicitly and the determined complex precoder coefficients explicitly or implicitly, wherein the space-delay precoder comprises a dual-stage structure comprising: a spatial codebook matrix comprising spatial beamforming vectors, a frequency-domain codebook matrix, wherein each vector of the frequency-domain codebook matrix is associated with a delay or a delay difference, and a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices, wherein the frequency-domain codebook matrix is defined by a sub-matrix of a DFT matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay values, and wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix or only a part of the DFT matrix, and wherein the frequency-domain codebook matrix is defined by the first N columns of the DFT matrix, or the first N 1 columns and the last N 2 columns of the DFT matrix, or the i 1 :i 2 columns of the DFT matrix, or i 1 :i 2 columns and i 3 :i 4 columns of the DFT matrix.
  2. 2 . The receiver of claim 1 , wherein the delays are associated with only a part of a DFT matrix so that the frequency-domain codebook matrix is defined by a sub-matrix of the DFT matrix, wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix and is associated with a range of delay values.
  3. 3 . The receiver of claim 1 , wherein the delays are associated with only a part of a DFT matrix so that the frequency-domain codebook matrix is defined by a sub-matrix of a DFT matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay values.
  4. 4 . The receiver of claim 1 , wherein a DFT matrix used for constructing the frequency-domain codebook matrix is an oversampled DFT-matrix D=[d 0 , d 1 , . . . , d SO f−1 ], where d i = [ 1 e - j ⁢ 2 ⁢ π ⁢ i O f ⁢ S … e - j ⁢ 2 ⁢ π ⁢ i ⁡ ( S - 1 ) O f ⁢ S ] T ∈ ℂ S × 1 , i ε , j=√{square root over (−1)} with O f being the oversampling factor of the DFT-matrix and S=total number of subcarriers, or subbands, or physical resource blocks, wherein, when O f =1, the frequency-domain codebook matrix is given by an S×S DFT-matrix, and wherein, when O f >1, the frequency-domain codebook matrix is given by an oversampled DFT-matrix of size S×(O f S−1).
  5. 5 . The receiver of claim 1 , wherein the frequency domain codebook matrix is defined by the sub-matrix of the DFT matrix such that the size of the frequency domain codebook matrix is reduced over the frequency-domain codebook defined by the full DFT matrix, or wherein the frequency domain codebook matrix is defined by the sub-matrix of the DFT matrix such that the size of the frequency domain codebook matrix is reduced over the frequency-domain codebook defined by the full DFT matrix with O f =1.
  6. 6 . The receiver of claim 1 , wherein the sub-matrix of the DFT matrix is selected dependent on a delay spread of a beam-formed channel impulse response acquired when combining the selected beams of the spatial codebook matrix with a MIMO channel impulse response.
  7. 7 . The receiver of claim 1 , wherein a subset of the delays associated with a subset of the spatial beams of a transmission layer is identical, or the number of delays for a subset of the spatial beams of a transmission layer is identical, or a subset of the delays is identical for a subset of the spatial beams and transmission layers.
  8. 8 . The receiver of claim 1 , wherein the number of delays and the delays per beam is identical for a transmission layer, so that all beams of a transmission layer are associated with the same delays.
  9. 9 . The receiver of claim 1 , wherein the precoding matrix is represented by F ( r ) = α ( r ) [ ∑ u = 1 U ( r ) b u ( r ) ∑ d = 1 D u ( r ) γ 1 , u , d ( r ) ⁢ d 1 , u , d ( r ) ⁢ T ∑ u = 1 U ( r ) b u ( r ) ∑ d = 1 D u ( r ) γ 2 , u , d ( r ) ⁢ d 2 , u , d ( r ) ⁢ T ] ∈ ℂ N t ⁢ S × 1 , wherein N t is the number of antenna ports of the transmitter, U (r) is the number of beams for the r-th layer, D u ( r ) is the number of delays for the r-th layer and u-th beam, d p , u , d ( r ) is the d-th delay vector of size S×1 associated with the r-th layer, u-th spatial beam and the p-th polarization of the transmitter antenna array; b u ( r ) is the u-th spatial beam associated with the r-th layer; γ p , u , d ( r ) is a scalar delay-beam complex combining coefficient associated with the r-th layer, u-th spatial beam, d-th delay and the p-th polarization of the transmitter antenna array, and α (r) is a normalization factor to ensure that the average total transmission power over all precoder layers is equal to a fixed value.
  10. 10 . The receiver of claim 1 , wherein the receiver is configured to feed back the delays of the space-delay precoder explicitly or implicitly, the implicit feedback using a delay identifier indicating indices associated with respective column vectors of the frequency-domain codebook matrix, wherein the implicit delay feedback comprises one or more delay identifiers, DI, each delay identifier indicating a set of L indices which are associated with column vectors of the frequency-domain codebook matrix D, L=total number of delays, and wherein the number of indices in the DIs is identical or different with respect to the spatial beams.
  11. 11 . The receiver of claim 10 , wherein the feedback comprises, in addition to beam-specific DIs that comprise indices for specific spatial beams, a common DI common to X (X=1 . . . PU) spatial beams, the common DI denoting indices common to X spatial beams.
  12. 12 . The receiver of claim 10 , wherein the feedback comprises a precoding matrix identifier, PMI, indicating a first number of indices indicating respective spatial beamforming vectors of the radio signal, a second number of indices indicating the respective complex delay-domain combining-coefficients, and a third number of indices indicating the delays comprised in the delay identifier(s).
  13. 13 . The receiver of claim 1 , wherein the entries of the spatial codebook matrix are represented by N/2-length column vectors, with N being the number of antenna ports, where the m-th vector (m=1, . . . , N/2) comprises a single 1 at the m-th position and zeros elsewhere.
  14. 14 . A transmitter, comprising: an antenna array comprising a plurality of antennas for a wireless communication with one or more receivers; and one or more precoders connected to the antenna array, the precoder to apply a set of beamforming weights to one or more antennas of the antenna array to form, by the antenna array, one or more transmit beams, wherein the transmitter is configured to determine the beamforming weights responsive to a feedback received from a receiver, the feedback indicating delays, explicitly or implicitly, and complex precoder coefficients, explicitly or implicitly, of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel, wherein the space-delay precoder comprises a dual-stage structure comprising: a spatial codebook matrix including spatial beamforming vectors, a frequency-domain codebook matrix, wherein each vector of the frequency-domain codebook matrix is associated with a delay or a delay difference, and a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices, and wherein the frequency-domain codebook matrix is defined by a sub-matrix of a DFT matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay values or a range of delay difference values, and wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix or only a part of the DFT matrix, and wherein the frequency-domain codebook matrix is defined by the first N columns of the DFT matrix, or the first N 1 columns and the last N 2 columns of the DFT matrix, or the i 1 :i 2 columns of the DFT matrix, or i 1 :i 2 columns and i 3 :i 4 columns of the DFT matrix.
  15. 15 . A wireless communication network, comprising: at least one receiver of claim 1 , and at least one Transmitter, comprising: an antenna array comprising a plurality of antennas for a wireless communication with one or more receivers; and one or more precoders connected to the antenna array, the precoder to apply a set of beamforming weights to one or more antennas of the antenna array to form, by the antenna array, one or more transmit beams, wherein the transmitter is configured to determine the beamforming weights responsive to a feedback received from a receiver, the feedback indicating delays, explicitly or implicitly, and complex precoder coefficients, explicitly or implicitly, of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel, wherein the space-delay precoder comprises a dual-stage structure comprising: a spatial codebook matrix including spatial beamforming vectors, a frequency-domain codebook matrix, wherein each vector of the frequency-domain codebook matrix is associated with a delay or a delay difference, and a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices, and wherein the frequency-domain codebook matrix is defined by a sub-matrix of a DFT matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay values or a range of delay difference values, and wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix or only a part of the DFT matrix, and wherein the frequency-domain codebook matrix is defined by the first N columns of the DFT matrix, or the first N 1 columns and the last N 2 columns of the DFT matrix, or the i 1 :i 2 columns of the DFT matrix, or i 1 :i 2 columns and i 3 :i 4 columns of the DFT matrix.
  16. 16 . A method, comprising: receiving and processing a radio signal received via a radio channel from a transmitter employing a plurality of antenna ports, determining, based on the received signal, complex precoder coefficients and delays of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel, and feeding back to the transmitter the determined delays explicitly or implicitly and the determined complex precoder coefficients explicitly or implicitly, wherein the space-delay precoder comprises a dual-stage structure comprising: a spatial codebook matrix including spatial beamforming vectors, a frequency-domain codebook matrix, wherein each vector of the frequency- domain codebook matrix is associated with a delay or a delay difference, and a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices, and wherein the frequency-domain codebook matrix is defined by a sub-matrix of a DFT matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay values or a range of delay difference values, and wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix or only a part of the DFT matrix, and wherein the frequency-domain codebook matrix is defined by the first N columns of the DFT matrix, or the first N 1 columns and the last N 2 columns of the DFT matrix, or the i 1 :i 2 columns of the DFT matrix, or i 1 :i 2 columns and i 3 :i 4 columns of the DFT matrix.
  17. 17 . A method for forming one or more beams for a wireless communication among a transmitter and one or more receivers, the method comprising: applying a set of beamforming weights to one or more antennas of an antenna array to form, by the antenna array, one or more transmit beams, wherein the beamforming weights are determined responsive to a feedback received from a receiver, the feedback indicating delays, explicitly or implicitly, and complex precoder coefficients, explicitly or implicitly, of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel, wherein the space-delay precoder comprises a dual-stage structure comprising: a spatial codebook matrix including spatial beamforming vectors, a frequency-domain codebook matrix, wherein each vector of the frequency-domain codebook matrix is associated with a delay or a delay difference, and a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices, and wherein the frequency-domain codebook matrix is defined by a sub-matrix of a DFT matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay values or a range of delay difference values, and wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix or only a part of the DFT matrix, and wherein the frequency-domain codebook matrix is defined by the first N columns of the DFT matrix, or the first N 1 columns and the last N 2 columns of the DFT matrix, or the i 1 :i 2 columns of the DFT matrix, or i 1 :i 2 columns and i 3 :i 4 columns of the DFT matrix.
  18. 18 . A non-transitory digital storage medium having stored thereon a computer program for performing, when said computer program is run by a computer, a method, comprising: receiving and processing a radio signal received via a radio channel from a transmitter employing a plurality of antenna ports, determining, based on the received signal, complex precoder coefficients and delays of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel, and feeding back to the transmitter the determined delays explicitly or implicitly and the determined complex precoder coefficients explicitly or implicitly, wherein the space-delay precoder comprises a dual-stage structure comprising: a spatial codebook matrix including spatial beamforming vectors, a frequency-domain codebook matrix, wherein each vector of the frequency-domain codebook matrix is associated with a delay or a delay difference, and a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices, and wherein the frequency-domain codebook matrix is defined by a sub-matrix of a DFT matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay values or a range of delay difference values, and wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix or only a part of the DFT matrix, and wherein the frequency-domain codebook matrix is defined by the first N columns of the DFT matrix, or the first N 1 columns and the last N 2 columns of the DFT matrix, or the i 1 :i 2 columns of the DFT matrix, or i 1 :i 2 columns and i 3 :i 4 columns of the DFT matrix.
  19. 19 . A non-transitory digital storage medium having stored thereon a computer program for performing, when said computer program is run by a computer, a method for forming one or more beams for a wireless communication among a transmitter and one or more receivers, the method comprising: applying a set of beamforming weights to one or more antennas of an antenna array to form, by the antenna array, one or more transmit beams, wherein the beamforming weights are determined responsive to a feedback received from a receiver, the feedback indicating delays, explicitly or implicitly, and complex precoder coefficients, explicitly or implicitly, of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel, wherein the space-delay precoder comprises a dual-stage structure comprising: a spatial codebook matrix including spatial beamforming vectors, a frequency-domain codebook matrix, wherein each vector of the frequency-domain codebook matrix is associated with a delay or a delay difference, and a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices, and wherein the frequency-domain codebook matrix is defined by a sub-matrix of a DFT matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay values or a range of delay difference values, and wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix or only a part of the DFT matrix, and wherein the frequency-domain codebook matrix is defined by the first N columns of the DFT matrix, or the first N 1 columns and the last N 2 columns of the DFT matrix, or the i 1 :i 2 columns of the DFT matrix, or i 1 :i 2 columns and i 3 :i 4 columns of the DFT matrix.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation of copending U.S. patent application Ser. No. 17/159,964, filed Jan. 27, 2021, which in turn is a continuation of copending International Application No. PCT/EP2018/073254, filed Aug. 29, 2018, which is incorporated herein by reference in its entirety. BACKGROUND OF THE INVENTION The present invention concerns the field of wireless communication systems, such as a mobile communication network. Embodiments of the present invention relate to wireless communication systems employing precoding with reduced feedback, e.g., space-delay wideband MIMO (Multiple Input Multiple Output) precoding for mmWave systems FIG. 1 is a schematic representation of an example of a wireless network 100 including a core network 102 and a radio access network 104. The radio access network 104 may include a plurality of base stations eNB1 to eNB5, each serving a specific area surrounding the base station schematically represented by respective cells 1061 to 1065. The base stations are provided to serve users within a cell. A user may be a stationary device or a mobile device. Further, the wireless communication system may be accessed by mobile or stationary IoT devices which connect to a base station or to a user. The mobile devices or the IoT devices may include physical devices, ground based vehicles, such as robots or cars, aerial vehicles, such as manned or unmanned aerial vehicles (UAVs), the latter also referred to as drones, buildings and other items having embedded therein electronics, software, sensors, actuators, or the like as well as network connectivity that enable these devices to collect and exchange data across an existing network infrastructure. FIG. 1 shows an exemplary view of only five cells, however, the wireless communication system may include more such cells. FIG. 1 shows two users UE1 and UE2, also referred to as user equipment (UE), that are in cell 1062 and that are served by base station eNB2. Another user UE3 is shown in cell 1064 which is served by base station eNB4. The arrows 1081, 1082 and 1083 schematically represent uplink/downlink connections for transmitting data from a user UE1, UE2 and UE3 to the base stations eNB2, eNB4 or for transmitting data from the base stations eNB2, eNB4 to the users UE1, UE2, UE3. Further, FIG. 1 shows two IoT devices 1101 and 1102 in cell 1064, which may be stationary or mobile devices. The IoT device 1101 accesses the wireless communication system via the base station eNB4 to receive and transmit data as schematically represented by arrow 1121. The IoT device 1102 accesses the wireless communication system via the user UE3 as is schematically represented by arrow 1122. The respective base station eNB1 to eNB5 are connected to the core network 102 and/or with each other via respective backhaul links 1141 to 1145, which are schematically represented in FIG. 1 by the arrows pointing to the “core”. The core network 102 may be connected to one or more external networks. For data transmission a physical resource grid may be used. The physical resource grid may comprise a set of resource elements to which various physical channels and physical signals are mapped. For example, the physical channels may include the physical downlink and uplink shared channels (PDSCH, PUSCH) carrying user specific data, also referred to as downlink and uplink payload data, the physical broadcast channel (PBCH) carrying for example a master information block (MIB) and a system information block (SIB), the physical downlink and uplink control channels (PDCCH, PUCCH) carrying for example the downlink control information (DCI), etc. For the uplink, the physical channels may further include the physical random access channel (PRACH or RACH) used by UEs for accessing the network once a UE synchronized and obtained the MIB and SIB. The physical signals may comprise reference signals (RS), synchronization signals and the like. The resource grid may comprise a frame having a certain duration in the time domain and a given bandwidth in the frequency domain. The frame may have a certain number of subframes of a predefined length, and each subframe may include symbols, like OFDM symbols. The wireless communication system may operate, e.g., in accordance with the LTE-Advanced pro standard or the 5G or NR (New Radio) standard. The wireless communication system may be any single-tone or multicarrier system based on frequency-division multiplexing, like the orthogonal frequency-division multiplexing (OFDM) system, the orthogonal frequency-division multiple access (OFDMA) system, or any other IFFT-based signal with or without CP, e.g. DFT-s-OFDM. Other waveforms, like non-orthogonal waveforms for multiple access, e.g. filter-bank multicarrier (FBMC), generalized frequency division multiplexing (GFDM) or universal filtered multi carrier (UFMC), may be used. In a wireless communication system like to one depicted schematically in FIG. 1, m