WO2024132377A1 - Procédé et nœud de réseau pour la transmission de signaux à large bande vers un dispositif sans fil par formation de faisceau dans le domaine temporel - Google Patents

Procédé et nœud de réseau pour la transmission de signaux à large bande vers un dispositif sans fil par formation de faisceau dans le domaine temporel Download PDF

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Publication number
WO2024132377A1
WO2024132377A1 PCT/EP2023/083027 EP2023083027W WO2024132377A1 WO 2024132377 A1 WO2024132377 A1 WO 2024132377A1 EP 2023083027 W EP2023083027 W EP 2023083027W WO 2024132377 A1 WO2024132377 A1 WO 2024132377A1
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WIPO (PCT)
Prior art keywords
time domain
wireless device
domain beamforming
reference signal
network node
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PCT/EP2023/083027
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English (en)
Inventor
Minkeun Chung
Yi-Ju Chen
Sairamesh Nammi
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Telefonaktiebolaget Lm Ericsson (Publ)
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Publication of WO2024132377A1 publication Critical patent/WO2024132377A1/fr

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    • 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
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0686—Hybrid systems, i.e. switching and simultaneous transmission
    • H04B7/0695—Hybrid systems, i.e. switching and simultaneous transmission using beam selection
    • H04B7/06952—Selecting one or more beams from a plurality of beams, e.g. beam training, management or sweeping

Definitions

  • the present disclosure relates generally to methods and network nodes of a wireless communication network for transmission of wideband signals downlink towards a wireless device through time domain beamforming.
  • the present disclosure further relates to computer programs and carriers corresponding to the above methods and nodes.
  • MIMO Multiple Input Multiple Output
  • MIMO is an integral part of the 3 rd generation (3G) as well as the 4G wireless communication networks.5G networks will also employ MIMO.
  • massive MIMO systems as there may be hundreds of antenna elements at the transmitter side and/or the receiver side of the RAN node.
  • Nt, Nr the number of transmitter antenna elements
  • N r denotes the number of receiver antenna elements
  • Beamforming is a way of improving efficiency in a wireless communication network by concentrating and directing beams transmitted from a network node in a certain direction.
  • Fig.1 shows a schematic block diagram of a network node, in which functionality of the network node, e.g., a gNodeB, is split in three blocks or units.
  • the three blocks or units are: a baseband unit 50, which performs physical and medium access control functions within a baseband frequency range; a radio unit 60, which converts the baseband signals from baseband frequency to radio frequency signals for transmission; and an antenna unit 70 comprising the antenna elements through which the radio frequency signals are transmitted.
  • a baseband unit 50 which performs physical and medium access control functions within a baseband frequency range
  • a radio unit 60 which converts the baseband signals from baseband frequency to radio frequency signals for transmission
  • an antenna unit 70 comprising the antenna elements through which the radio frequency signals are transmitted.
  • incoming input bits are passed through a forward error correction (FEC)/rate matching unit 51 where additional parity bits are added for error protection.
  • FEC forward error correction
  • the resultant bits are then passed through a scrambling unit 52 that adds cell-specific scrambling operations for interference avoidance from neighboring cells.
  • the resultant bits are then passed through a modulator 53 that converts the bit stream to complex symbols.
  • the resultant symbols are passed through a layer mapping unit 54 that maps the resultant modulated symbols to different user layers.
  • the resultant symbols per layer are fed through a Frequency Domain Beamforming (FDBF) unit 55, which may also be called baseband precoder 55, where the resultant symbols are multiplied with FDBF weights, aka precoding coefficients.
  • FDBF Frequency Domain Beamforming
  • the resultant symbols are fed through a resource element (RE) mapping unit 56 that maps the symbols to REs assigned to the user.
  • the mapped resultant bits are then sent to the radio unit 60 over an interface between the baseband unit 50 and the radio unit 60, as one signal per antenna subarray.
  • the resultant bit streams are passed through an inverse fast Fourier transform (IFFT) block 61 for converting from frequency domain to time domain.
  • IFFT inverse fast Fourier transform
  • an IFFT block 61 is applied for each antenna subarray. That is, if there for example are 64 Transmit and Receive (TR) branches or chains, 64 IFFT blocks are needed.
  • TR Transmit and Receive
  • CP cyclic prefix
  • the resultant time domain signals per each TR branch are passed through a Digital Front End (DFE) unit 62 where the signal is converted from digital to analog domain, the analog signal is frequency converted from baseband frequency to radio by e.g., multiplying the analog baseband signal with a local oscillator radio frequency signal and the signal is eventually power amplified.
  • the amplified, radio- frequency signal per TR branch is then passed to the antenna unit 70 and wirelessly transmitted.
  • DFE Digital Front End
  • TDBF time domain beamforming
  • the TDBF unit 66 is situated after the DFE 62. Consequently, at the TDBF unit 66, beamforming weights that are individual per subarray are applied in the radio unit, after the IFFT operation.
  • the individual TDBFs may be applied using phase shifters.
  • one common signal for all subarrays is sent from the baseband unit 50 to the radio unit 60.
  • interface bandwidth between the baseband unit 50 and the radio unit 60 is lowered quite a lot compared to full frequency domain beamforming where one signal is sent per subarray over the interface between baseband and radio unit.
  • time domain beamforming In time domain beamforming, the network node has access to a plurality of different time domain beamforming codewords, each time domain beamforming codeword comprising different beamforming weights that are individual per antenna subarray/TR branch. Each time domain beamforming codeword corresponds to a transmission direction angle and the transmission direction angles of the plurality of time domain beamforming codewords are mutually different.
  • the wireless device determines channel state information (CSI) which is sent back to the network node. Based on the received CSI for the plurality of CSI-RS, the network node determines which of the time domain beamforming codewords that resulted in a received signal at the wireless device that had the highest signal quality. The network node then selects that time domain beamforming codeword to be used for time domain beamforming and transmission of traffic data to the wireless device.
  • CSI channel state information
  • a method is provided that is performed by a network node of a wireless communication network for transmission of wideband signals towards a wireless device through time domain beamforming.
  • the network node has a plurality of antenna elements.
  • a plurality of time domain beamforming codewords is defined, each time domain beamforming codeword corresponding to a transmission direction angle, the transmission direction angles of the plurality of time domain beamforming codewords being mutually different.
  • the method comprises obtaining a wirelessly transmitted reference signal and estimating an uplink (UL) transmission channel matrix between the wireless device and the network node based on the obtained reference signal.
  • the method further comprises determining a correlation matrix between each of the plurality of time domain beamforming codewords and the UL transmission channel matrix, resulting in one correlation matrix per time domain beamforming codeword, and, based on the determined correlation matrices, selecting the one of the time domain beamforming codewords which correlation matrix reveals the highest correlation between its time domain beamforming codeword and the UL transmission channel matrix of the correlation matrices of the plurality of the time domain beamforming codewords.
  • the method further comprises transmitting a wideband signal, the wideband signal being time domain beamformed with the selected time domain beamforming codeword.
  • a network node configured to operate in a wireless communication network and configured for transmission of wideband signals towards a wireless device through time domain beamforming.
  • the network node has a plurality of antenna elements, wherein a plurality of time domain beamforming codewords is defined, each time domain beamforming codeword corresponding to a transmission direction angle, the transmission direction angles of the plurality of time domain beamforming codewords being mutually different.
  • the network node comprises a processing circuitry and a memory.
  • Said memory contains instructions executable by said processing circuitry, whereby the network node is operative for obtaining a wirelessly transmitted reference signal, estimating an UL transmission channel matrix between the wireless device and the network node based on the obtained reference signal, and determining a correlation matrix between each of the plurality of time domain beamforming codewords and the UL transmission channel matrix, resulting in one correlation matrix per time domain beamforming codeword.
  • the network node is further operative for, based on the determined correlation matrices, selecting the one of the time domain beamforming codewords which correlation matrix reveals the highest correlation between its time domain beamforming codeword and the UL transmission channel matrix of the correlation matrices of the plurality of the time domain beamforming codewords, and transmitting a wideband signal, the wideband signal being time domain beamformed with the selected time domain beamforming codeword.
  • Fig.1 is a schematic block diagram of a network node according to prior art.
  • Fig.2 is a schematic block diagram of a transmitter according to prior art.
  • Fig.3 is a schematic block diagram of another transmitter according to prior art.
  • Fig.4 is a schematic diagram of a wireless communication network in which the present invention may be used.
  • Fig.5 is a flow chart illustrating a method performed by a network node, according to possible embodiments.
  • Fig.6 is a flow chart of a method performed by a network node, according to other possible embodiments.
  • Fig.7 is a flow chart of a method performed by a network node, according to other possible embodiments.
  • Fig.8 is a schematic diagram of a communication scenario in a wireless communication in which the present invention may be used.
  • Fig.9 is a schematic block diagram of a receiver according to embodiments.
  • Fig.10 is a schematic block diagram of a transmitter according to embodiments.
  • Fig.11 is a flow chart illustrating a method performed by a network node, according to possible embodiments.
  • Fig.12 is a flow chart illustrating another method performed by a network node, according to possible embodiments.
  • Fig.13 is a diagram of a Cartesian coordinate system illustrating throughput with different methods and having DL SNR in dB on the X-axis and DL throughput in bits/second on the Y-axis.
  • Fig.14 is a flow chart illustrating another method performed by a network node, according to possible embodiments.
  • Fig.15 is a block diagram illustrating a network node in more detail, according to further possible embodiments.
  • a solution is provided to improve throughput of traffic data from a network node to a wireless device when using time domain beamforming.
  • Embodiments of the solution is built upon the idea of using channel reciprocity between the UL channel and the downlink channel.
  • the network node performs UL channel estimation on a received reference signal, determines correlation between each of each of the plurality of time domain beamforming codewords and the estimated UL transmission channel, and selects for downlink transmission the time domain beamforming codeword out of the plurality of time domain beamforming codewords that had the highest correlation with the estimated UL transmission channel.
  • Fig.4 shows a wireless communication network 100 comprising a radio access network (RAN) node aka network node 130 that is in, or is adapted for, wireless communication with a wireless communication device aka wireless device 140.
  • the network node 130 provides radio access in a cell 150 covering a geographical area.
  • the wireless communication network 100 may be any kind of wireless communication network that can provide radio access to wireless devices.
  • Example of such wireless communication networks are networks based on Global System for Mobile communication (GSM), Enhanced Data Rates for GSM Evolution (EDGE), Universal Mobile Telecommunications System (UMTS), Code Division Multiple Access 2000 (CDMA 2000), Long Term Evolution (LTE), LTE Advanced, Wireless Local Area Networks (WLAN), Worldwide Interoperability for Microwave Access (WiMAX), WiMAX Advanced, as well as fifth generation (5G) wireless communication networks based on technology such as New Radio (NR), and any possible future sixth generation (6G) wireless communication network.
  • GSM Global System for Mobile communication
  • EDGE Enhanced Data Rates for GSM Evolution
  • UMTS Universal Mobile Telecommunications System
  • CDMA 2000 Code Division Multiple Access 2000
  • LTE Long Term Evolution
  • LTE Advanced Long Term Evolution
  • WLAN Wireless Local Area Networks
  • WiMAX Worldwide Interoperability for Microwave Access
  • WiMAX WiMAX Advanced
  • Examples of network nodes 130 are a base station (BS), a radio BS, a base transceiver station, a BS controller, a network controller, a Node B (NB), an evolved Node B (eNB), a gNodeB (gNB), a Multi-cell/multicast Coordination Entity, a relay node, an access point (AP), a radio AP, a remote radio unit (RRU), a remote radio head (RRH) and a multi-standard BS (MSR BS).
  • the wireless device 140 may be any type of device capable of wirelessly communicating with a network node 130 using radio signals.
  • the wireless device 140 may be a User Equipment (UE), a machine type UE or a UE capable of machine to machine (M2M) communication, a sensor, a tablet, a mobile terminal, a smart phone, a laptop embedded equipped (LEE), a laptop mounted equipment (LME), a USB dongle, a Customer Premises Equipment (CPE), an Internet of Things (IoT) device, etc.
  • UE User Equipment
  • M2M machine to machine
  • M2M machine to machine
  • M2M machine to machine
  • a sensor a tablet
  • a mobile terminal a smart phone
  • LME laptop embedded equipped
  • LME laptop mounted equipment
  • CPE Customer Premises Equipment
  • IoT Internet of Things
  • the method comprises obtaining 202 a wirelessly transmitted reference signal and estimating 204 an uplink (UL) transmission channel matrix between the wireless device 140 and the network node 130 based on the obtained reference signal.
  • UL uplink
  • the method further comprises determining 206 a correlation matrix between each of the plurality of time domain beamforming codewords and the UL transmission channel matrix, resulting in one correlation matrix per time domain beamforming codeword, and, based on the determined correlation matrices, selecting 208 the one of the time domain beamforming codewords which correlation matrix reveals the highest correlation between its time domain beamforming codeword and the UL transmission channel matrix of the correlation matrices of the plurality of the time domain beamforming codewords.
  • the method further comprises transmitting 216 a wideband signal, the wideband signal being time domain beamformed with the selected time domain beamforming codeword.
  • a correct transmission angle towards the UE can be determined more quickly than by using the prior art beam sweeping method of WO2022010394.
  • a larger number of different time domain beamforming codewords resulting in different beam transmission angles can be used compared to the beam sweeping method. Thereby, a significant performance benefit can be achieved.
  • the obtained 202 wirelessly transmitted reference signal originates from the wireless device. In other words, the reference signal is transmitted wirelessly by the wireless device and received by the network node.
  • a time domain beamforming codeword comprises a plurality of time domain beamforming weights, for example one weight per transmitter chain.
  • the weights of one codeword is selected so that when used on the transmitter, the resulting transmission beam is directed into a certain transmission direction having a certain transmission angle in relation to e.g., boresight.
  • a time domain beamforming codeword can be seen as the same as a set of time domain beamforming weights.
  • the network node has 512 transmitter and 512 receiver antenna elements and for example 128 transceiver chains.
  • a codeword in such a case comprises 128 time- domain beamforming weights, one per transceiver chain.
  • the wideband signal is time domain beamformed with the selected time domain beamforming codeword, which was determined to have the highest correlation with the UL transmission channel of all of the plurality of codewords
  • the beam created from the transmission 216 of the wideband signal from the plurality of antenna elements will be directed towards the wireless device.
  • the time domain beamforming codeword which correlation matrix reveals the highest correlation between its time domain beamforming codeword and the UL transmission channel matrix of the plurality of time domain beamforming codewords is the time domain beamforming codeword that results in the highest received energy of the correlation matrix of the plurality of time domain beamforming codewords.
  • the time domain beamforming codeword of all the plurality of time domain beamforming codewords which correlation matrix has the highest correlation signifies the time domain beamforming codeword that results in the smallest angle difference value between the transmission angle of the beam that results from the time domain beamforming codeword and the direction between the network node and wireless device.
  • both coefficients of the estimated UL channel matrix and of the time domain beamforming codeword are complex values, respectively.
  • the correlation matrix which is based on a multiplication of the UL channel matrix and the time domain beamforming codeword becomes a real-valued matrix. The highest correlation signifies a trace of the correlation matrix.
  • the method further comprises determining 207, for each of the determined 206 correlation matrices, a sum of eigenvalues, wherein the selecting 208 of the one of the time domain beamforming codewords which correlation matrix reveals the highest correlation comprises selecting the time domain beamforming codeword which correlation matrix has the largest sum of eigenvalues of the determined correlation matrices.
  • the selecting 208 of the one of the time domain beamforming codewords which correlation matrix reveals the highest correlation comprises selecting the time domain beamforming codeword which correlation matrix has the largest sum of eigenvalues of the determined correlation matrices.
  • the time domain beamforming codeword which correlation matrix has the largest sum of eigenvalues of the correlation matrices determined is the time domain beamforming codeword that has the highest correlation with the UL transmission channel matrix of the plurality of time domain beamforming codewords.
  • the highest correlation means the trace of the correlation matrix, which indicates the sum of eigenvalues of the correlation matrix. For example, let us say there are in total 10 time-domain beamforming codewords, resulting in beams with a transmission angle of 0, 5, 10, 15, 20, 25, 30, 35, 40, 45 degrees, respectively. Then there will be 10 different correlation matrices between the respective time domain beamforming codeword and the UL transmission channel matrix. For each of those 10 different correlation matrices, a sum of eigenvalues is determined.
  • the correlation matrices are determined 206 as ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ where ⁇ ⁇ is the time domain beamforming codeword matrix, ⁇ is an index between 1 and ⁇ , where ⁇ is the number of the plurality of time domain beamforming codewords, ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ , where, ⁇ ⁇ ⁇ is the estimated DL channel matrix, ⁇ ⁇ ⁇ is the estimated UL channel matrix, and the H and T in ⁇ ⁇ ⁇ and ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ defines the Hermitian transpose and the transpose of the referred respectively.
  • the method further comprises transmitting 210, to the wireless device 140, a DL reference signal beamformed with the selected one of the time domain beamforming codewords, obtaining 212 channel state information determined by the wireless device 140 based on the DL reference signal beamformed with the selected one of the time domain beamforming codewords as received at the wireless device and determining 214 a frequency domain precoding matrix based on the obtained 212 channel state information.
  • the transmitting 216 of the wideband signal comprises transmitting the wideband signal frequency domain beamformed with the determined frequency domain precoding matrix and time domain beamformed with the selected time domain beamforming codeword.
  • the frequency domain precoding matrix is preferably determined by incorporating the selected time domain beamforming codeword for beamforming a DL reference signal to determine channel state info for selecting the frequency domain precoding matrix.
  • the dimension of the frequency domain beamforming matrix is normally smaller than the dimension of the time domain beamforming codeword.
  • the reference signal is obtained 202 wirelessly transmitted over a first bandwidth that is narrower than a bandwidth of the wideband signal and within the bandwidth of the wideband signal.
  • the bandwidth of the wideband signal may be 20 MHz, where the first, narrow, bandwidth may use between 4 and 12 Physical Resource Blocks (PRBs), which corresponds to 1.5 – 5 MHz MHz.
  • PRBs Physical Resource Blocks
  • the network node 130 has a plurality of narrowband receivers, each narrowband receiver being connected to a subset of the plurality of antenna elements, the different subsets consisting of mutually different of the plurality of antenna elements.
  • each transceiver (TR) chain may have its own narrowband receiver (NBR).
  • NBR exploits higher number of TRs for UL channel estimation but only extract a part of scheduled full BW, i.e., narrowband. In case of the channel estimation for the scheduled full BW, i.e., wideband, smaller number of chains BB chains are used than the number TRs.
  • the method further comprises obtaining 201 information on channel quality of a DL signal transmitted by the network node 130 to the wireless device 140, and only when the obtained information reveals that the channel quality is above a channel quality threshold, perform the obtaining 202 of the wirelessly transmitted reference signal.
  • the method of the above embodiments is only to be performed when the channel quality is “good enough”.
  • Channel quality may be measured as Signal to Noise Ratio SNR, Signal to Interference and Noise Ratio SINR, Signal Strength, etc.
  • the method further comprises transmitting 222, to the wireless device 140, in a first probing slot, a reference signal time domain beamformed with a first time domain beamforming codeword of the plurality of time domain beamforming codewords, and receiving 224, from the wireless device 140, first channel state information determined by the wireless device 140 based on the reference signal time domain beamformed with the first time domain beamforming codeword.
  • the method further comprises transmitting 226, to the wireless device 140, in a second probing slot, a reference signal time domain beamformed with a second time domain beamforming codeword of the plurality of time domain beamforming codewords and receiving 228, from the wireless device 140, second channel state information determined by the wireless device 140 based on the reference signal time domain beamformed with the second time domain beamforming codeword.
  • the method further comprises determining 230, based on the received 224, 228 first and second channel state information, a time domain beamforming codeword out of the first and second time domain beamforming codeword that has the highest transmission quality, and transmitting 232, in a later data slot that is later in time than the first probing slot and the second probing slot, the wideband signal to the wireless device 140, the wideband signal being time domain beamformed with the determined 230 time domain beamforming codeword.
  • This embodiment describes an advantageous embodiment of how to determine which of the plurality of time domain beamforming codewords to use when channel quality is below the channel quality threshold, i.e., when the UL channel is not good enough.
  • a DL beam sweeping method is used where two or more different beams directed according to their respective time domain beamforming codewords are used for sending DL reference signals, which transmission quality are tested and evaluated based on received channel state information.
  • traffic data may also be transmitted in the first probing slot, as well as the reference signal, the traffic data is then also time domain beamformed with the first time domain beamforming codeword.
  • traffic data may be transmitted in the second probing slot, as well as the reference signal, the traffic data is then time domain beamformed with the second time domain beamforming codeword.
  • the channel quality threshold is set to 1-3 dB SNR.
  • the method further comprises determining 200 whether the wireless device 140 can transmit wirelessly a reference signal to the network node or not, and when it is determined that the wireless device can transmit a reference signal, perform the obtaining 202 of the wirelessly transmitted reference signal and when it is determined that the wireless device cannot transmit a reference signal perform the following steps, referred to in fig.7: Transmit 222, to the wireless device 140, in a first probing slot, a reference signal time domain beamformed with a first time domain beamforming codeword of the plurality of time domain beamforming codewords; receive 224, from the wireless device 140, first channel state information determined by the wireless device 140 based on the reference signal time domain beamformed with the first time domain beamforming codeword; transmit 226, to the wireless device 140, in a second probing slot, a reference signal time domain beamformed with a second codeword of the plurality of codewords; receive 228, from the wireless device 140, second channel state information determined by the wireless device 140 based on the reference signal time domain beamformed
  • This embodiment describes an advantageous embodiment of how to determine which of the plurality of time domain beamforming codewords to use when the wireless device cannot transmit a reference signal.
  • a DL beam sweeping method is used where two or more different beams directed according to their respective time domain beamforming codewords are used for sending DL reference signals, which transmission quality are tested and evaluated based on received channel state information.
  • a case when the wireless device cannot send a reference signal to the network node is at start-up, when the wireless device has not got a connection to the network node yet, for example when in a random-access procedure.
  • traffic data may also be transmitted in the first probing slot, as well as the reference signal, the traffic data is then also time domain beamformed with the first time-domain beamforming codeword.
  • traffic data may be transmitted in the second probing slot, as well as the reference signal, the traffic data is then time domain beamformed with the second time domain beamforming codeword.
  • a multi-UE massive MIMO DL with time- division duplex (TDD) operation is considered, where DL CSI can be obtained by leveraging channel reciprocity between UL and DL.
  • Fig.8 shows a multi-UE scenario with four UEs; 301, 302, 303, 304 in communication with a network node 310.
  • Fig.8 illustrates how to acquire UL channel estimates for codebook- based UE-specific beamforming exploiting channel reciprocity between UL and DL.
  • Each UE 301, 302, 303, 304 transmits its own sounding reference signal (SRS) SRS1, SRS2, SRS3, SRS4.
  • the network node 310 estimates an UL transmission channel on the received respective SRS for the respective UE.
  • the estimated UL transmission channel signifies channel coefficients between the network node ⁇ s 310 receiving antenna elements and each UE’s 301, 302, 303, 304 SRS antenna element.
  • the network node 310 uses a narrow band receiver (NBR) to configure the UEs and to estimate the UL transmission channel of each UE.
  • NBR narrow band receiver
  • An embodiment of a receiver part at the network node 310, which receiver part employs NBRs is shown in fig.9.
  • the receiver part shown comprises NBRs 410, Analog to Digital converters (ADC) 408, Low Noise Amplifiers (LNA) 406, Remote electrical tilts (RET) 404, and antenna elements.
  • ADC Analog to Digital converters
  • LNA Low Noise Amplifiers
  • RET Remote electrical tilts
  • the antenna elements are arranged as antenna subarrays 402, numbered 1-8, each subarray comprising three antenna elements.
  • the signals received at each antenna element are fed to the RETs 404.
  • the RETs 404 control the antenna pattern characteristics of each antenna subarray 402. In most implementations, the tilt of the RETs 404 is fixed.
  • TR transceiver chain
  • Each receiver chain then comprises one Low Noise Amplifier (LNA) 406, one Analog to Digital converter (ADC) 408 and one NBR 410.
  • LNA Low Noise Amplifier
  • ADC Analog to Digital converter
  • the NBRs 410 are used to configure the UEs, such as UEs 301-304 and to estimate the UL channel of each UE.
  • the concept of NBR 410 is to use only a few of PRBs (part of full bandwidth) for the UL channel estimation but utilize a higher number of receiver chains, compared to wideband channel estimation. Since only a few of PRBs is used, the complexity is reduced, compared to wideband receiver (smaller FFT size and simpler filter for the channel estimation). But it could provide better UL channel estimation with a higher number of receiver chains.
  • Fig.10 shows a block diagram of a DL OFDM transmitter according to an embodiment.
  • the OFDM transmitter comprises in a transmission direction, a channel encoder/rate matching unit 422 through which incoming input bits are passed, a scrambling unit 424, a modulator 426, a layer mapping unit 428, a precoder 430 for frequency domain beamforming, a Resource Element (RE) mapping unit 432, an IFFT and CP insertion unit 434, a time domain beamforming unit 436, a DFE 438 comprising a Digital to Analog (DAC) converter, a frequency upconverter from baseband (BB) to radio frequency (RF) and a power amplifier (PA), and antenna elements 440.
  • the above units 422-440 may be prior art units as defined in fig.2 and 3.
  • the DL OFDM transmitter has an SRS channel estimator 442 that estimates the UL transmission channel for each UE based on the uplink signals comprising SRS as received by the NBRs, for example the NBRs 410 of fig.9, and a correlation metric calculator 444.
  • the correlation metric calculator 444 determines a correlation matrix between each of the plurality of time domain beamforming (TD-BF) codewords that are stored at the OFDM transmitter and the determined UL transmission channel in matrix from, for each UE 301-304, resulting in one correlation matrix per TD-BF codeword per UE.
  • TD-BF time domain beamforming
  • the correlation metric calculator 444 selects, for each UE 301-304, the one of the TD-BF codewords which correlation matrix reveals the highest correlation between its TD-BF codeword and the UL transmission channel matrix of the correlation matrices of the plurality of the TD- BF codewords.
  • the correlation matrix calculator 444 then feds the selected TD-BF codewords, one per UE, to the TD-BF unit 436 that beamforms the signals to be sent DL to the respective UE via the DFE 438 and the antenna elements 440 with the respective selected TD-BF codeword.
  • the estimation of a channel matrix, calculation of correlation matrices and selection of TD-BF codeword may be performed according to the following:
  • the estimated UL channel matrix for the ⁇ th UE, estimated by the SRS channel estimator 442, is denoted by ⁇ ⁇ ⁇ ⁇ ⁇ C ⁇ , where ⁇ ⁇ is the number of TRs and ⁇ ⁇ the number of SRS ports.
  • a set of TD-BF codewords i.e., a TD-BF c odebook is defined as ⁇ ⁇ ⁇ ⁇ ⁇ where ⁇ ⁇ ⁇ C ⁇ is the ⁇ th TD-BF codeword; ⁇ ⁇ the number of baseband (BB) chains, and ⁇ ⁇ the number of dynamic tilt angles.
  • the TD-BF codeword ⁇ ⁇ makes BB chains steered with the tilt ⁇ ⁇ and each codeword ⁇ ⁇ is involved in different tilt angles.
  • the correlation matrix ⁇ ⁇ , ⁇ ⁇ C ⁇ for the ⁇ th UE and the ⁇ th TD-BF codewords is then defined as: ⁇ ⁇ , ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ where ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ C ⁇ .
  • the calculator unit 444 calculates the BF codeword of the codeword in the TD-BF codebook that has the highest correlation according to the correlation matrix for each UE. Index for the selected TD-BF codeword per UE is then sent to the TD-BF unit 436.
  • the selected TD-BF codeword index ⁇ ⁇ , ⁇ for the ⁇ th UE is ⁇ ⁇ , ⁇ ⁇ argm ⁇ ax ⁇ ⁇ , ⁇ where ⁇ ⁇ , ⁇ ⁇ Tr ⁇ ⁇ ⁇ , ⁇ ⁇ is the sum of eigenvalues of the matrix ⁇ ⁇ , ⁇ and Tr ⁇ is the a matrix.
  • hybrid beamforming i.e., a combination of frequency domain beamforming (FD-BF) and TD-BF
  • CSI-RS transmissions towards the UEs are proceeded right after selecting the best TD-BF codeword.
  • the network node then performs a beamformed CSI-RS transmission using the selected TD-BF codeword.
  • each UE measures channel state and sends its corresponding feedback information as a CSI report to the network node.
  • the network node determines frequency domain (FD) precoding matrix to use in the precoder 430 based on the received CSI report.
  • the network node transmits DL signals TD-BF with the selected TD-BF codeword and pre-coded with the determined FD precoding matrix.
  • the DL signals may be transmitted in the last slot or slots before the next SRS reception.
  • Fig.11 is a flowchart of an embodiment of a method according to embodiments, performed by a network node.
  • the method starts by receiving 502, through an NBR, an SRS from a scheduled UE. Based on the received SRS, an UL transmission channel is estimated 504 and a correlation metric is calculated 505 between the estimated UL transmission channel and each TD-BF codeword in a TD-BF codebook available to the network node. Then the best TD-BF codeword in the codebook is determined 506, i.e., the TD-BF codeword that has the highest correlation metric. Then, in case FD-BF is used as well as TD-FB, a CSI-RS is transmitted 508 to the UE, time domain beamformed with the best TD-BF codeword, and CSI is received 510 from the UE as feedback.
  • a CSI-RS is transmitted 508 to the UE, time domain beamformed with the best TD-BF codeword, and CSI is received 510 from the UE as feedback.
  • the network node determines 512, based on the received CSI, the FD precoding matrix to use.
  • the wideband DL signal is thereafter transmitted 514 using the best TD-BF codeword and the determined FD precoding matrix.
  • Now an embodiment of how to calculate the correlation matrix between each of the plurality of time domain beamforming codewords and the UL transmission channel matrix is described: 1) Calculate a DL channel matrix based on the UL channel estimate, wherein the UL channel estimate takes the position of the DL channel estimate thanks to channel reciprocity.2) Calculate the correlation matrix of the DL channel matrix, which is the multiplication of one of the TD-BF codewords and the DL channel estimate.3) Calculate the trace of the correlation matrix 4) Repeat steps 1) - 3) for all or at least a plurality of the TD-BF codewords of the codebook, 4) Select the TD-BF codeword that has the highest trace value.
  • Fig.12 in conjunction with fig.4, shows a method performed by a network node 130 of a wireless communication network 100 for transmission of wireless signals towards a wireless device 140 through time domain beamforming.
  • the network node 130 has a plurality of antenna elements.
  • a second set of time domain beamforming weights (TDBFW) has been determined to have a highest transmission quality for transmission to the wireless device 140 in one or more consecutive data slots, out of a plurality of different sets of TDBFWs, each of the plurality of sets of TDBFWs corresponding to a transmission direction angle, the transmission direction angles of the plurality of sets being mutually different.
  • TDBFW time domain beamforming weights
  • the method comprises transmitting 602, to the wireless device 140, in a first probing slot, a reference signal beamformed with a first set of TDBFWs of the plurality of different sets of TDBFWs, and traffic data also beamformed with the first set of TDBFWs.
  • the method further comprises receiving 604, from the wireless device 140, first channel state information determined by the wireless device 140 based on the reference signal beamformed with the first set of TDBFWs.
  • the method comprises transmitting 606, to the wireless device 140, in the one or more consecutive data slots, traffic data beamformed with the second set of TDBFWs and transmitting 608, to the wireless device 140, in a second probing slot, a reference signal beamformed with the second set of TDBFWs and other traffic data also beamformed with the second set of TDBFWs.
  • the method further comprises receiving 610, from the wireless device 140, second channel state information determined by the wireless device 140 based on the reference signal beamformed with the second set of TDBFWs.
  • the method comprises determining 620, based on the received 604, 610 first and second channel state information, a set of TDBFWs out of the first and second set of TDBFWs that has the highest transmission quality and therefore to be used for transmission of traffic data to the wireless device in a later data slot that is later in time than the first probing slot, the second probing slot and the one or more consecutive data slots.
  • extra space in the first and second probing slots i.e., the slots where the reference signals are sent, can be used for sending traffic data as well.
  • traffic data is only sent in the data slots using the set of TDBFW that was determined to have the highest transmission quality from previous transmissions.
  • the inventors have come to the conclusion that it is possible to send traffic data also in a probing slot, as long as the same set of TDBFWs is used as is used for the reference signal in the same probing slot.
  • the total throughput of traffic data will be increased.
  • the method still makes it possible to determine 620 the set of TDBFWs that has the highest transmission quality and therefore to be used for a later transmission of traffic data, based on the different sets of TDBFWs tested in the probing slots.
  • the transmitting 602 in the first probing slot of the reference signals and the traffic data uses a first modulation and coding scheme (MCS) that is more robust than a second MCS used in the transmitting 606 of the traffic data in the one or more consecutive data slots.
  • MCS modulation and coding scheme
  • the method further comprises transmitting 612 to the wireless device 140, in one or more additional consecutive data slots following the second probing slot, traffic data beamformed with the second set of TDBFWs.
  • the method further comprises transmitting 614, to the wireless device 140, in a third probing slot, a reference signal beamformed with a third set of TDBFWs of the plurality of different sets of TDBFWs, and traffic data also beamformed with the third set of TDBFWs, and receiving 616, from the wireless device 140, third channel state information determined by the wireless device 140 based on the reference signal beamformed with the third set of TDBFWs. Further, the determining 620 of the set of TDBFWs that has the highest transmission quality is performed based on the received 604, 610, 616 first, second and third channel state information so that the determining 620 is performed out of the first, the second and the third set of TDBFWs.
  • the method further comprises transmitting 618 to the wireless device 140, in one or more second additional consecutive data slots following the third probing slot, traffic data beamformed with the second set of TDBFWs.
  • CSIRS-SWEEP CSI-RS sweeping method
  • NB SRS CSI-RS sweeping method
  • LEGACY legacy method
  • CSIRS-SWEEP has better performance than NB SRS at low Signal to Noise Ratio (SNR), e.g., from -10 dB to 2 dB.
  • SNR Signal to Noise Ratio
  • NB SRS has higher DL throughput than CSIRS-SWEEP at moderate/high SNRs, i.e., above 2 dB.
  • Fig.14 shows a method for determining whether to use the NB SRS method according to any of figs.5-7 or the CSIRS-SWEEP method according to fig.12.
  • the method comprises determining 702 SNR for DL transmission from the network node to the UE, selecting 704 the CSIRS-SWEEP method or the NB SRS method based on the determined SNR, determining 706 the best TD-BF codeword for the UE using the selected 704 method, and transmitting 708 the DL signal time domain beamformed with the determined best TD-BF codeword.
  • a FD precoding matrix/codeword is determined as described e.g., in fig.6. Then the transmitted 708 DL signal is also frequency domain beamformed using the determined FD precoding matrix.
  • Fig.15 in conjunction with fig.4, describes a network node 130 configured to operate in a wireless communication network 100, and configured for transmission of wideband signals towards a wireless device 140 through time domain beamforming.
  • the network node 130 has a plurality of antenna elements, wherein a plurality of time domain beamforming codewords is defined, each time domain beamforming codeword corresponding to a transmission direction angle, the transmission direction angles of the plurality of time domain beamforming codewords being mutually different.
  • the network node 130 comprises a processing circuitry 803 and a memory 804.
  • Said memory contains instructions executable by said processing circuitry, whereby the network node 130 is operative for obtaining a wirelessly transmitted reference signal, estimating a UL transmission channel matrix between the wireless device 140 and the network node 130 based on the obtained reference signal, and determining a correlation matrix between each of the plurality of time domain beamforming codewords and the UL transmission channel matrix, resulting in one correlation matrix per time domain beamforming codeword.
  • the network node is further operative for, based on the determined correlation matrices, selecting the one of the time domain beamforming codewords which correlation matrix reveals the highest correlation between its time domain beamforming codeword and the UL transmission channel matrix of the correlation matrices of the plurality of the time domain beamforming codewords, and transmitting a wideband signal, the wideband signal being time domain beamformed with the selected time domain beamforming codeword.
  • the network node 130 is further operative for determining, for each of the determined correlation matrices, a sum of eigenvalues, wherein the selecting of the one of the time domain beamforming codewords which correlation matrix reveals the highest correlation comprises selecting the time domain beamforming codeword which correlation matrix has the largest sum of eigenvalues of the determined correlation matrices.
  • the network node 130 is operative for the determining of the correlation matrices as ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ where ⁇ ⁇ is the time domain beamforming codeword matrix, ⁇ is an index between 1 and ⁇ , where ⁇ is the number of the plurality of time domain beamforming codewords, ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ , where, ⁇ ⁇ ⁇ is the estimated DL channel matrix, ⁇ ⁇ ⁇ is the estimated UL channel matrix, and the H and T in ⁇ ⁇ ⁇ and ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ defines the Hermitian transpose and the transpose of the referred [00073]
  • the network node 130 is further operative for transmitting, to the wireless device 140, a DL reference signal beamformed with the selected one of the time domain beamforming codewords,
  • the network node is operative for the transmitting of the wideband signal by transmitting the wideband signal frequency domain beamformed with the determined frequency domain precoding matrix and time domain beamformed with the selected time domain beamforming codeword.
  • the network node 130 is operative for obtaining the reference signal wirelessly transmitted over a first bandwidth that is narrower than a bandwidth of the wideband signal and within the bandwidth of the wideband signal.
  • the network node 130 has a plurality of narrowband receivers, each narrowband receiver being connected to a subset of the plurality of antenna elements, the different subsets consisting of mutually different of the plurality of antenna elements.
  • the network node 130 is further operative for obtaining information on channel quality of a DL signal transmitted by the network node 130 to the wireless device 140, and only when the obtained information reveals that the channel quality is above a channel quality threshold, perform the obtaining of the wirelessly transmitted reference signal.
  • the network node when the obtained information reveals that the channel quality is below the channel quality threshold, the network node is operative for transmitting, to the wireless device 140, in a first probing slot, a reference signal time domain beamformed with a first time domain beamforming codeword of the plurality of time domain beamforming codewords, receiving, from the wireless device 140, first channel state information determined by the wireless device 140 based on the reference signal time domain beamformed with the first time domain beamforming codeword, transmitting, to the wireless device 140, in a second probing slot, a reference signal time domain beamformed with a second time domain beamforming codeword of the plurality of time domain beamforming codewords, and receiving, from the wireless device 140, second channel state information determined by the wireless device 140 based on the reference signal time domain beamformed with the second time domain beamforming codeword.
  • the network node 130 is further operative for determining, based on the received first and second channel state information, a time domain beamforming codeword out of the first and second time domain beamforming codeword that has the highest transmission quality, and transmitting, in a later data slot that is later in time than the first probing slot and the second probing slot, the wideband signal to the wireless device 140, the wideband signal being time domain beamformed with the determined time domain beamforming codeword.
  • the channel quality threshold is set to 1-3 dB SNR.
  • the network node 130 is further operative for determining whether the wireless device 140 can transmit wirelessly a reference signal to the network node or not, and when it is determined that the wireless device can transmit a reference signal, perform the obtaining of the wirelessly transmitted reference signal.
  • the network node is operative to transmit, to the wireless device 140, in a first probing slot, a reference signal time domain beamformed with a first time domain beamforming codeword of the plurality of time domain beamforming codewords, receive, from the wireless device 140, first channel state information determined by the wireless device 140 based on the reference signal time domain beamformed with the first time domain beamforming codeword, transmit, to the wireless device 140, in a second probing slot, a reference signal time domain beamformed with a second codeword of the plurality of codewords, receive, from the wireless device 140, second channel state information determined by the wireless device 140 based on the reference signal time domain beamformed with the second time domain beamforming codeword, determine, based on the received first and second channel state information, a time domain beamforming codeword out of the first and second time domain beamforming codeword that has the highest transmission quality, and transmit, in a later data slot that is later in time than the first probing slot and the second probing slot,
  • the network node 130 may further comprise a communication unit 802, which may be considered to comprise conventional means for wireless communication with the wireless device 140, such as a transceiver for wireless transmission and reception of signals in the communication network.
  • the communication unit 802 may also comprise conventional means for communication with other network nodes of the wireless communication network 100.
  • the instructions executable by said processing circuitry 803 may be arranged as a computer program 805 stored e.g., in said memory 804.
  • the processing circuitry 803 and the memory 804 may be arranged in a sub-arrangement 801.
  • the sub-arrangement 801 may be a micro-processor and adequate software and storage therefore, a Programmable Logic Device, PLD, or other electronic component(s)/processing circuit(s) configured to perform the methods mentioned above.
  • the processing circuitry 803 may comprise one or more programmable processor, application-specific integrated circuits, field programmable gate arrays or combinations of these adapted to execute instructions.
  • the computer program 805 may be arranged such that when its instructions are run in the processing circuitry 803, the instructions cause the network node 130 to perform the steps described in any of the described embodiments of the network node 130 and its method.
  • the computer program 805 may be carried by a computer program product connectable to the processing circuitry 803.
  • the computer program product may be the memory 804, or at least arranged in the memory.
  • the computer program product may be called a computer-readable storage medium.
  • the memory 804 may be realized as for example a Random-access memory (RAM), Read-Only Memory (ROM) or an Electrical Erasable Programmable ROM (EEPROM).
  • a carrier may contain the computer program 05.
  • the carrier may be one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or computer readable storage medium.
  • the computer-readable storage medium may be e.g., a CD, DVD or flash memory, from which the program could be downloaded into the memory 804.
  • the computer program 805 may be stored on a server or any other entity to which the network node 130 has access via the communication unit 802. The computer program 805 may then be downloaded from the server into the memory 804. [00082] Although the description above contains a plurality of specificities, these should not be construed as limiting the scope of the concept described herein but as merely providing illustrations of some exemplifying embodiments of the described concept. It will be appreciated that the scope of the presently described concept fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the presently described concept is accordingly not to be limited.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

Est divulgué un procédé mis en œuvre par un nœud de réseau (130) d'un réseau de communication sans fil (100). Le procédé comprenant les étapes suivantes : estimation d'une matrice de canal de transmission de liaison montante entre un dispositif sans fil (140) et le nœud de réseau (130) sur la base d'un signal de référence transmis sans fil obtenu et détermination d'une matrice de corrélation entre chaque mot de code d'une pluralité de mots de code de formation de faisceau dans le domaine temporel et la matrice de canal de transmission de liaison montante, ce qui permet d'obtenir une matrice de corrélation par mot de code de formation de faisceau dans le domaine temporel. Le procédé comprend en outre la sélection de l'un des mots de code de formation de faisceau dans le domaine temporel dont la matrice de corrélation révèle la corrélation la plus élevée entre son mot de code de formation de faisceau dans le domaine temporel et la matrice de canal de transmission de liaison montante des matrices de corrélation de la pluralité des mots de code de formation de faisceau dans le domaine temporel. Un signal à large bande est ensuite transmis au dispositif sans fil (140), un faisceau dans le domaine temporel étant formé avec le mot de code de formation de faisceau dans le domaine temporel sélectionné. Ainsi, le débit de données de trafic est amélioré dans une communication de liaison descendante au moyen d'une formation de faisceau dans le domaine temporel.
PCT/EP2023/083027 2022-12-20 2023-11-24 Procédé et nœud de réseau pour la transmission de signaux à large bande vers un dispositif sans fil par formation de faisceau dans le domaine temporel WO2024132377A1 (fr)

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EPPCT/EP2022/087120 2022-12-20
PCT/EP2022/087120 WO2024132119A1 (fr) 2022-12-20 2022-12-20 Procédés et nœud de réseau pour la transmission de signaux sans fil vers un dispositif sans fil par formation de faisceau dans le domaine temporel, et dispositif sans fil correspondant

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PCT/EP2023/083027 WO2024132377A1 (fr) 2022-12-20 2023-11-24 Procédé et nœud de réseau pour la transmission de signaux à large bande vers un dispositif sans fil par formation de faisceau dans le domaine temporel

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