WO2022211685A1 - Procédés et appareil pour identifier un angle d'inclinaison pour un dispositif sans fil - Google Patents

Procédés et appareil pour identifier un angle d'inclinaison pour un dispositif sans fil Download PDF

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Publication number
WO2022211685A1
WO2022211685A1 PCT/SE2021/050288 SE2021050288W WO2022211685A1 WO 2022211685 A1 WO2022211685 A1 WO 2022211685A1 SE 2021050288 W SE2021050288 W SE 2021050288W WO 2022211685 A1 WO2022211685 A1 WO 2022211685A1
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WIPO (PCT)
Prior art keywords
reference signal
wireless device
measurements
tilt angle
base station
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PCT/SE2021/050288
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English (en)
Inventor
Sairamesh Nammi
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Telefonaktiebolaget Lm Ericsson (Publ)
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Application filed by Telefonaktiebolaget Lm Ericsson (Publ) filed Critical Telefonaktiebolaget Lm Ericsson (Publ)
Priority to PCT/SE2021/050288 priority Critical patent/WO2022211685A1/fr
Priority to EP21716869.9A priority patent/EP4315931A1/fr
Publication of WO2022211685A1 publication Critical patent/WO2022211685A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H04W24/02—Arrangements for optimising operational condition
    • 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
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H04W24/08—Testing, supervising or monitoring using real traffic
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H04W24/10—Scheduling measurement reports ; Arrangements for measurement reports

Definitions

  • Embodiments of the present disclosure relate to wireless communication, and, in particular, to methods and apparatus for identifying a tilt angle for radio transmissions between a wireless device and a base station.
  • 5G networks wireless devices are provided with access to a 5G core network (5GC) via a New Radio (NR) access network.
  • 5G networks There are various use cases for 5G networks including, for example, simultaneously offering one gigabit per second connections to tens of workers on the same office floor, supporting several hundreds of thousands of simultaneous connections for massive sensor deployments, and providing data rates of several tens of megabits per second for tens of thousands of users.
  • 3GPP seeks to provide improved spectral efficiency, improved coverage and enhanced signalling efficiency, whilst also reducing latency compared to 4G, or Long Term Evolution (LTE), networks.
  • LTE Long Term Evolution
  • FIG. 1 shows a signalling diagram for a typical downlink data transfer in a 5G network.
  • a gNodeB gNB sends cell-specific or user equipment (UE) specific reference signals to a UE, from which the UE computes channel estimates and various parameters for channel-state information (CSI) reporting.
  • the CSI report may, for example, comprise one or more of a channel quality indicator (CQI), a precoding matrix index (PMI), rank information (Rl) and CSI reference signal (CSI-RS) indicator (CRI), in which the CRI may indicate a particular beam that is preferred by the UE.
  • the UE sends the CSI report to the network via a feedback channel such as the Physical Uplink Control Channel (PUCCH).
  • PUCCH Physical Uplink Control Channel
  • the UE may send CSI reports periodically or on request from the network.
  • the uplink control channel carries information about hybrid automatic repeat request (HARQ) acknowledgements (HARQ-ACK) in respect of downlink data transmissions.
  • HARQ-ACK hybrid automatic repeat request acknowledgements
  • a network scheduler uses the CSI information to schedule the UE and the resulting scheduling parameters are sent to the UE via a downlink control channel such as the Physical Downlink Control Channel (PDCCH).
  • PDCCH Physical Downlink Control Channel
  • This information typically comprises the number of scheduled MIMO layers, transport block sizes, the modulation for each codeword, parameters related to HARQ, sub-band locations and/or PM Is corresponding to those sub-bands.
  • This information may be transmitted in downlink control information (DCI), for example.
  • DCI downlink control information
  • the contents of the PDCCH may vary depending on the transmission mode as well as the DCI format.
  • the UE may use the scheduling parameters to decode data transferred from the network to the UE on a downlink data channel such as the Physical Downlink Shared Channel (PDSCH).
  • a downlink data channel such as the Physical Downlink Shared Channel (PDSCH).
  • PDSCH Physical Downlink Shared Channel
  • Cell-specific reference signals are one example of a downlink reference signal.
  • downlink reference signals are predefined signals occupying specific resource elements within a downlink time-frequency grid.
  • CSI-RSs are reference signals that are used by UEs to acquire channel- state information and beam specific information such as received signal received power (RSRP) measurements for a particular beam.
  • RSRP received signal received power
  • CSI-RS may be UE-specific in that they are intended to be used for channel measurements by a single UE.
  • DM-RS Demodulation reference signals
  • DM-RS are another example of downlink reference signals.
  • DM-RS are used by UEs for channel estimation of data channels.
  • DM-RS may also be referred to as UE-specific reference signals because each demodulation reference signal is intended for channel estimation by a single UE.
  • a DM-RS for a particular UE is only transmitted within the resource blocks assigned for transmission to that UE.
  • downlink reference signals include Multicast-Broadcast Single Frequency Network (MBSFN) reference signals and positioning reference signals.
  • MBSFN Multicast-Broadcast Single Frequency Network
  • MIMO systems have been an integral part of Third Generation (3G) and 4G wireless systems because of the increase in data carrying capacity that they can provide.
  • 5G systems also employ MIMO systems in the form of massive MIMO systems in which hundreds of antennas are deployed at the transmitter and receiver sides.
  • MIMO antenna elements may be deployed at a single gNB in a massive MIMO system.
  • These deployments can provide a significantly boosted data rate, as the peak data rate of a massive MIMO system having N t transmit antennas and N r receive antennas scales with a factor of N t in a rich scattering environment compared to a single antenna system.
  • Massive MIMO systems may be implemented using advanced antenna systems (AASs), also referred to herein as active antenna array systems, in which radio frequency (RF) components such as power amplifiers and transceivers are integrated with an array of antenna elements.
  • AASs advanced antenna systems
  • RF components such as power amplifiers and transceivers are integrated with an array of antenna elements.
  • FIGs 2a and 2b show a passive antenna array system and an AAS respectively.
  • the baseband signals are boosted by a common power amplifier, which is connected to the antennas by feedback cables.
  • each antenna in the AAS of Figure 2b has an associated amplifier.
  • Using an AAS such as that illustrated in Figure 2b improves performance whilst reducing energy consumption.
  • AASs are simpler to install than passive antenna array systems and typically require less space.
  • AASs have many further applications, including cell-specific beamforming, user-specific beamforming, vertical sectorization, elevation beamforming and hybrid beamforming.
  • Optimal performance can be obtained in massive MIMO systems (such as those comprising AASs) by implementing full digital beamforming in which each antenna element is provided with separate RF circuitry that supports an independent digital signal definition to each antenna branch.
  • Figure 3a shows an architecture for achieving full digital beamforming with frequency domain beamforming. An exemplary implementation of this architecture is shown in more detail in Figure 4a.
  • signals are input to a forward error correction (FEC) code, which adds additional parity bits to the input bits for error protection.
  • FEC forward error correction
  • the coded bits are input to a scrambling unit, which performs a cell-specific scrambling operation to mitigate interference from neighbouring cells.
  • the scrambled bits are input to a modulator, which converts the input bit stream to complex symbols.
  • the symbols are input to a layer mapper, which maps the resultant modulated symbols to different layers.
  • the symbols for each layer are multiplied by a baseband precoder and input to a resource element (RE) mapper, which maps the symbols to resource elements assigned to the receiving device (e.g. a UE).
  • RE resource element
  • the digital beamforming (DBF) unit also known as a port expansion unit, maps the symbols to respective antenna elements.
  • DBF digital beamforming
  • the port expansion unit P2 BB maps the symbols from the L CSI-RS ports to Ni digital antenna elements.
  • both the precoding (Precoding and Pi BB in Figures 3a and 4a respectively) and digital beamforming (DBF and P2 BB in Figures 3a and 4a respectively) are performed in the frequency domain.
  • the DBF unit outputs a stream to an inverse fast Fourier transform (IFFT) block, which converts the stream from the frequency domain to the time domain.
  • IFFT inverse fast Fourier transform
  • the IFFT block may form part of a radio unit, for example. Although only one block is illustrated in Figure 3a, typically one IFFT block is provided per antenna such that each antenna has an associated IFFT block. Thus, for example, a system having 64 Transmit and Receive (TR) units may have 64 IFFT blocks.
  • the IFFT block outputs a time domain signal (e.g. the signal intended for a particular antenna) to a Digital to Analog (DAC) converter, which converts the signal to the analog domain.
  • the analog signal is multiplied by an analog signal generated from a local oscillator (LO) and is input to a power amplifier (PA) for amplification.
  • PA power amplifier
  • the amplified signal may be sent directly to an antenna.
  • a cell-specific tilt is often applied to the signal to improve coverage. This is achieved by outputting the signal from the PA to an Analog Phase Shifting network (APS), which applies the tilt to the signal.
  • APS Analog Phase Shifting network
  • Figure 3a thus provides an exemplary architecture for implementing full digital beamforming. Whilst this implementation optimises the performance of massive MIMO systems, it relies on providing independent signal paths between the digital interface and each antenna. As massive MIMO systems typically comprise large numbers of antenna elements, this drives up cost and power consumption, as well as the size and weight of the system. This can be particularly costly when implementing full digital beamforming in the frequency domain at high bandwidths (e.g. 100MHz), as this demands a significant signalling interface bandwidth for transmitting baseband signals to the radio.
  • Figure 3b shows an alternative architecture that addresses some of these issues by replacing the APS with a digital phase shifting network or time domain digital beamforming (TDBF) unit. An exemplary implementation of this architecture is shown in more detail in Figure 4b.
  • TDBF time domain digital beamforming
  • This architecture uses partial frequency domain beamforming, in which beamforming is partly applied in the frequency domain and partly in the time domain. For example, beamforming in the azimuth domain may be applied in the frequency domain, whereas beamforming in the elevation domain may be applied in the time domain.
  • DPD digital predistortion
  • time domain beamforming can be implemented using phase shifters, further reducing the hardware complexity.
  • full digital beamforming provides optimal performance for MIMO systems.
  • time domain digital beamforming is cheaper and more energy efficient than full digital beamforming solutions, this comes at the cost of decreased performance.
  • Replacing full digital beamforming with a time domain digital beamforming typically leads to a 10% decrease in average sector throughput at a full load, with a similar impact on throughput at cell edges.
  • a base station for a wireless communications network comprises processing circuitry and a machine-readable medium storing instructions which, when executed by the processing circuitry, cause the base station to broadcast a first reference signal at a plurality of tilt angles and, based on measurements of the first reference signal performed by one or more wireless devices in the wireless communications network, select a subset of the plurality of tilt angles for the one or more wireless devices.
  • the base station is further caused to transmit, at each tilt angle in the subset of tilt angles, a second reference signal to a wireless device in the one or more wireless devices and, based on measurements of the second reference signal performed by the wireless device, identify a tilt angle from the subset of tilt angles for communication with the wireless device.
  • a method performed by a base station in a wireless communications network comprises broadcasting a first reference signal at a plurality of tilt angles and, based on measurements of the first reference signal performed by one or more wireless devices in the wireless communications network, selecting a subset of the plurality of tilt angles for the one or more wireless devices.
  • the method further comprises transmitting, at each tilt angle in the subset of tilt angles, a second reference signal to a wireless device in the one or more wireless devices and, based on measurements of the second reference signal performed by the wireless device, identifying a tilt angle from the subset of tilt angles for communication with the wireless device.
  • a base station configured to perform the aforementioned method.
  • a computer program is provided. The computer program comprises instructions which, when executed on at least one processor of a base station, cause the base station to carry out the aforementioned method.
  • a carrier containing the computer program is provided, in which the carrier is one of an electronic signal, optical signal, radio signal, or non-transitory machine-readable storage medium.
  • Figure 1 shows a signalling procedure for channel-state information (CSI) reporting
  • Figures 2a and 2b show examples of a passive antenna array system and an active- antenna array system
  • Figures 3a, 3b, 4a and 4b show architectures for implementing beamforming
  • Figure 5 shows a communications network according to embodiments of the disclosure
  • Figure 6 shows a signalling diagram according to embodiments of the disclosure
  • Figure 7 shows a flowchart of a method according to embodiments of the disclosure
  • Figures 8a and 8b show average throughput measurements for simulations of a wireless communications network
  • Figures 9 and 10 show examples of base stations according to embodiments of the disclosure.
  • FIG. 5 shows a communications network 500 according to embodiments of the disclosure.
  • the communications network 500 may implement any suitable wireless communications protocol or technology, such as Global System for Mobile communication (GSM), Wide Code-Division Multiple Access (WCDMA), Long Term Evolution (LTE), New Radio (NR), WFi, WiMAX, or Bluetooth wireless technologies.
  • GSM Global System for Mobile communication
  • WCDMA Wide Code-Division Multiple Access
  • LTE Long Term Evolution
  • NR New Radio
  • WFi WiMAX
  • Bluetooth wireless technologies such as Bluetooth wireless technology.
  • the communications network 500 forms part of a cellular telecommunications network, such as the type developed by the 3 rd Generation Partnership Project (3GPP).
  • 3GPP 3 rd Generation Partnership Project
  • the communications network 500 comprises a base station 502 configured to provide radio services to one or more wireless devices in its coverage area.
  • the base station 502 may be, for example, a Node B, evolved Node B (eNB), a next generation Node B (gNB) or any other suitable base station.
  • eNB evolved Node B
  • gNB next generation Node B
  • the base station couples the wireless devices to a core network 506 in the communications network 500 (e.g. via a backhaul network 508).
  • a first wireless device 504a and a second wireless device 504b are shown.
  • the communications network 500 may comprise any number of wireless devices and may comprise many more wireless devices than those shown.
  • the base station 502 has antennas and transmit circuitry which permits the use of beamforming techniques to transmit wireless signals.
  • the base station may comprise an antenna array having a plurality of antenna elements.
  • the antenna array may be an advanced antenna system (AAS), which may also be referred to as an active advanced antenna system.
  • AAS advanced antenna system
  • the base station 502 may be operable to generate a transmission beam using such an antenna array by varying the amplitude and/or phase of signals provided to the multiple antenna elements so as to constructively interfere with each other in at least one direction (or angle) and destructively interfere with each other in other directions (or angles).
  • frequency-domain beamforming typically provides the best performance.
  • frequency domain beamforming refers to applying different beamforming weights for different transmission frequencies or ranges of transmission frequencies within a carrier (e.g. for different resource elements), whereas time-domain beamforming refers to applying a same beam for an entire carrier.
  • frequency-domain beamforming requires providing separate RF circuitry for each antenna element in the base station 502. This is expensive to implement, and often requires bulkier and heavier hardware that consumes more power.
  • One alternative is to use a mixed implementation in which a combination of frequency domain beamforming (implemented digitally) and time domain beamforming is used. For example, frequency domain beamforming may be used for the azimuth domain, whereas time domain beamforming may be used in the elevation domain. As time-domain beamforming can be implemented using a digital phase shifting network, this reduces the hardware complexity.
  • time-domain beamforming is not yet competitive with frequency-domain beamforming, providing average sector throughputs at a full load that are around 10% lower than a system that only uses frequency-domain beamforming.
  • Embodiments of the disclosure seek to address these and other problems by providing a base station for identifying a tilt angle to be used for communication with a wireless device.
  • the base station broadcasts a first reference signal at a plurality of tilt angles.
  • the first reference signal is measured by one or more wireless devices (e.g. in the coverage area or cell of the base station), which report the measurements to the base station.
  • the base station selects a subset of the tilt angles and transmits, to a given wireless device in the one or more wireless devices, a second reference signal at each tilt angle in the subset of tilt angles.
  • the wireless device performs measurements on the second reference signal and these measurements are used to identify, at the base station, a tilt angle to be used for communication with the wireless device.
  • the identified tilt angle may thus be used for beamforming transmission to the wireless device.
  • embodiments of the disclosure provide an efficient way to determine the tilt angle which provides the best channel for communicating with a particular wireless device. Optimising the tilt angle in this manner improves the performance of time domain beamforming, making it more competitive with frequency domain beamforming.
  • the base station 502 broadcasts a first reference signal at a plurality of tilt angles.
  • the first reference signal may be any reference signal that is suitable to be broadcast such as, for example, a synchronisation signal block (SSB) or part of an SSB (e.g. a primary synchronisation signal and/or a secondary synchronisation signal).
  • SSB synchronisation signal block
  • part of an SSB e.g. a primary synchronisation signal and/or a secondary synchronisation signal.
  • the wireless devices 504 perform measurements on the first reference signals and report the measurements to the base station 502.
  • the measurements may be, for example, received signal received power (RSRP) measurements.
  • RSRP received signal received power
  • the base station 502 uses the measurements to select a subset of the tilt angles. For example, the base station 502 may select all tilt angles for which the reported RSRP measurements are above a threshold value. In an alternative example, the base station 502 may rank the tilt angles according to the measurements and select a predetermined number of tilt angles with the highest rankings. Thus, for example, the base station 502 may select the tilt angles which are associated with the highest RSRP measurements.
  • the base station 502 transmits a second reference signal to the first wireless device 504a at each of the subset of tilt angles.
  • the same type of reference signal is sent at each of the tilt angles.
  • the base station may transmit channel state information reference signals (CSI-RSs) to the wireless device 504a at the tilt angles in the subset.
  • CSI-RSs channel state information reference signals
  • the first wireless device 504a performs measurements on the second reference signals and reports to the base station 502.
  • the first wireless device 504a may send a cell state information (CSI) report to the base station 502 comprising the measurements, for example.
  • the first wireless device 504a may indicate to the base station 502 which of the tilt angles is to be used by the base station 502.
  • the first wireless device 504a may selectively report measurements for the tilt angle with the best or optimal measurements (e.g. the tilt angle with a highest rank, channel quality index or a combination thereof).
  • the first wireless device may rank the tilt angles based on the measurements and send a ranked list to the base station 502.
  • the base station 502 Based on the measurements, the base station 502 identifies a tilt angle from the subset to be used for communicating with the first wireless device 504a. Thus, in embodiments in which the first wireless device 504a indicates a particular tilt angle to the base station 502, the base station 502 may select the tilt angle indicated by the first wireless device 504a. Alternatively, the first wireless device 504a may send the measurements to the base station 502 for the base station 502 to use to identify the tilt angle (e.g. by comparing the measurements to a threshold or by selecting the tilt angle with the best measurements).
  • the base station 502 may repeat the steps of transmitting the second reference signal and identifying a respective tilt angle for the second wireless device 504b.
  • the base station 502 may use the same method to identify respective tilt angles for any number of wireless devices.
  • the base station 502 may use the methods described herein to identify respective tilt angles for any (e.g. all) wireless devices in the coverage area of the base station 502.
  • embodiments of the disclosure reduce the overhead signalling required to identify which tilt angles are suitable for wireless devices 504 in the coverage area of the base station 502, thereby providing an efficient way to optimise time domain beamforming.
  • Figure 6 shows a communication flow between a gNode B (gNB) 602 and a user equipment (UE) 604 in a wireless communications network for identifying a tilt angle to be used by the gNB for communicating with the UE 604.
  • the wireless communications network may be the wireless communications network 500 described above in respect of Figure 5, for example.
  • the procedure begins with the gNB 602 performing an SSB sweep 606 in which the gNB 602 broadcasts an SSB at a plurality of tilt angles (e.g. three or more tilt angles).
  • the gNB 602 may, for example, broadcast the SSBs to a cell served by the gNB 602.
  • the gNB 602 does not need any knowledge of the position or preferred beam of the UE 604 in order to transmit the SSB.
  • beamforming is still employed to transmit the SSBs at each of the plurality of tilt angles.
  • the gNB 602 may be configured to use a particular number of tilt angles in the SSB sweep.
  • the gNB may be configured to transmit the SSB at three, four or five tilt angles.
  • the initial set of tilt angles may vary depending on the environment in which the gNB 602 is located. For example, a larger number of tilt angles may be used in an environment in which wireless devices are more likely to be positioned at a range of elevations (e.g. an environment with high-rise buildings) compared to, for example, a rural or flat environment. In another example, a larger number of tilt angles may be used in environments having a higher density of wireless devices (e.g. as narrower beams may be used in more congested areas). The skilled person will appreciate that there are many ways in which this initial set of tilt angles may be determined, and the present disclosure is not limited in that respect.
  • the SSB transmitted by the gNB 602 comprises a primary synchronisation signal (PSS), a secondary synchronisation signal (SSS), a physical broadcast channel (PBCH) and a Demodulation Reference Signal (DMRS) for the PBCH.
  • PSS primary synchronisation signal
  • SSS secondary synchronisation signal
  • PBCH physical broadcast channel
  • DMRS Demodulation Reference Signal
  • the sequences used by the gNB 602 for the PSS and the SSS may be determined based on the physical cell identifier (PCI) of a cell served by the gNB 602.
  • PCI physical cell identifier
  • the gNB 602 may broadcast the same SSB at each of the tilt angles since the contents of the SSB may be determined based on cell-specific parameters.
  • the contents of the SSB e.g. the sequences of the PSS and/or the SSS
  • the UE 604 receives one or more of the SSBs transmitted by the gNB 602 and performs RSRP measurements on the received SSBs. Depending on the tilt angles used, and in particular depending on the width of the beams over which the SSBs are transmitted, the UE 604 may receive some or all of the transmitted SSBs. Thus the skilled person will appreciate that the UE 604 may only be able to perform measurements on some of the SSBs transmitted by the gNB 602.
  • the UE 604 transmits 608 the RSRP measurements to the gNB 602 on a feedback channel such as the Physical Uplink Control Channel (PUCCH).
  • the UE 604 may send the RSRP measurements to the gNB 608 in one or more messages.
  • the UE 604 may send all of the measurements in a single message.
  • the UE 604 may send the RSRP measurements for each tilt angle in a respective message.
  • the gNB 602 may also receive RSRP measurements performed on the broadcasted SSBs by one or more other wireless devices (e.g. other wireless devices in the coverage area of the gNB 602).
  • the gNB 602 uses the RSRP measurements to select a subset of the plurality of tilt angles. For example, the gNB 602 may compare the RSRP measurements to a threshold value and include any tilt angles satisfying (e.g. exceeding) that threshold in the subset. In another example, the gNB 602 may, for each wireless device from which the gNB 602 receives measurements, determine the respective tilt angle with the highest RSRP measurement, and select those tilt angles to form the subset. This approach may also be generalised such that the gNB may determine, for each wireless device, a predetermined number of tilt angles having the highest RSRP measurements and form the subset from those tilt angles.
  • the subset of tilt angles is not specific to the UE 604. Rather, the gNB 602 determines a subset of tilt angles for the wireless devices from which it receives measurements.
  • the subset of tilt angles may thus, for example, be considered to be specific to the coverage area of the gNB 602 or the cell served by the gNB 602, rather than to the UE 604 itself.
  • the gNB 602 transmits 610 CSI-RSs to the UE604 at each of the tilt angles in the subset.
  • the gNB 602 thus beamforms each of the CSI-RS at a respective tilt angle when sending the CSI-RS to the UE 604.
  • the gNB 602 may use the same sequence for the CSI-RSs transmitted at different tilt angles.
  • the CSI-RSs transmitted at different tilt angles may comprise different sequences.
  • the gNB 602 may transmit 610 the CSI-RSs in one or more messages. For example, the gNB 602 may send each of the CSI-RSs to the UE 604 in a respective subframe or other time resource. That is, each CSI-RS may be transmitted at a respective tilt angle and in a respective subframe. This enables the gNB 602 to use the same time-frequency resources for the CSI-RS in each subframe. Thus the gNB 602 may use a single CSI- RS resource set in order to determine the tilt angle for the UE 604. Each CSI-RS resource set may comprise a respective CSI-RS per antenna port of the UE 604.
  • a CSI-RS resource set for a UE 604 having 16 antenna ports may comprise 16 CSI-RSs such that one CSI-RS is assigned to each antenna port.
  • the CSI-RSs in the resource set e.g. the CSI-RS for the antenna ports of the UE 604
  • the CSI-RSs in a resource set may all be transmitted in the same symbol.
  • the gNB 602 may send CSI-RSs at different tilt angles in the same subframe or other time resource.
  • the gNB 602 may send CSI-RSs at each of the tilt angles in the subset in a single subframe. Sending the CSI-RSs in a single subframe reduces the time taken to transmit the CSI-RSs to the UE 604 so that an optimal tilt angle for the UE 604 can be identified more quickly. This advantage can be achieved, albeit to a lesser effect, by sending at least two of the CSI-RSs in the same subframe.
  • This approach in which two or more CSI-RSs are transmitted at different tilt angles in the same subframe, is particularly suitable for delay-sensitive applications, such as, for example, autonomous driving, machine-type communications (MTC) or machine-to-machine (M2M) communications.
  • MTC machine-type communications
  • M2M machine-to-machine
  • the UE 604 performs measurements on the CSI-RSs received from the gNB 602.
  • the measurements may comprise one or more channel state information (CSI) parameters such as, for example, rank or rank indicator (R), channel quality indicator (CQI), precoding matrix indicator (PMI), and layer indicator (LI).
  • CSI channel state information
  • R rank or rank indicator
  • CQI channel quality indicator
  • PMI precoding matrix indicator
  • LI layer indicator
  • the measurements may further comprise one or more parameters formed from a combination of these measurements.
  • the gNB 602 may transmit the CSI-RSs in one or more subframes or other time resources.
  • UEs are often configured to average a single CSI-RS resource set received in multiple subframes when deriving channel measurements in order to increase the signal to noise ratio.
  • the UE 604 may be configured to calculate each channel measurement based on one CSI-RS such that the UE 604 performs separate measurements on each CSI-RS.
  • the gNB 602 may configure the UE 604 in this manner, using, for example, radio resource control (RRC) signalling.
  • RRC radio resource control
  • the gNB 602 may send a CSI-ReportConfig message to the UE 604 prior to sending the CSI-RSs.
  • Configuring the UE 604 in this manner ensures that each measurement is performed on a CSI-RS transmitted at a particular tilt angle, such that each measurement is indicative of the channel properties for that tilt angle.
  • the UE 604 transmits 612 the measurements to the gNB 602.
  • the UE 604 thus reports measurements of one or more of the parameters mentioned above to the gNB 602.
  • the UE 604 may, additionally or alternatively, report composite parameters calculated using a combination of two or more of these parameters.
  • the UE 604 may report measurements of R*CQI to the gNB 602.
  • the UE 604 may transmit 612 the measurements to the gNB 602 in one or more messages.
  • the UE 604 may send 612 the measurements for each tilt angle to the gNB 602 in a respective message.
  • the UE 604 may send 612 all of the measurements to the gNB 602 in a single message.
  • the UE 604 may, for example, report measurements for a particular CSI-RS immediately after the CSI-RS is received (e.g. before another CSI-RS is received).
  • the gNB 602 may delay sending the CSI-RS for another tilt angle until the measurements for the previously transmitted CSI-RS are received.
  • the gNB 602 identifies a tilt angle for the UE 604 based on the measurements.
  • the gNB 602 may select the tilt angle having a highest channel quality as indicated by the measurements, such as the tilt angle associated with the highest CQI value.
  • the gNB 602 may select the tilt angle which is associated with the highest R*CQI value.
  • the network may choose the tilt angle, L, which satisfies
  • the gNB 602 selects the tilt angle which provides the best capacity for communications with the UE 604.
  • the UE 604 sends 612 measurements of the CSI-RSs to the gNB 602 and the gNB 602 uses the received measurements to identify the best tilt angle.
  • the UE 604 may instead use the measurements to identify the tilt angle and report the identified tilt angle to the gNB 602.
  • the UE 604 may use any of the methods outlined above in respect of the gNB 602 to identify the tilt angle.
  • the UE 604 may select the tilt angle having the highest R*CQI value and indicate this tilt angle to the gNB 602.
  • the UE 604 may inform the gNB 602 of the identified tilt angle using any suitable signalling such as, for example, reporting only measurements for that tilt angle to the gNB 602 or sending an identifier for the tilt angle to the gNB 602. Identifying the tilt angle at the UE 604 means that it is not necessary to transmit measurements for all of the tilt angles to the gNB 602, thereby reducing signalling overhead.
  • the UE 604 may report measurements for some, but not all, of the tilt angles without necessarily identifying one particular tilt angle. The UE 604 may thus narrow down the list of tilt angles for the gNB 602 to consider.
  • the UE 604 may be configured with the number of tilt angles to report measurements for.
  • the UE 604 may be preconfigured with this number or the UE 604 may receive an indication of this number in signalling from the gNB 602.
  • the UE 604 may employ the same or similar methods for narrowing down the list of tilt angles as may be used (by the gNB 602 or the UE 604) to identify the tilt angle for the UE 604.
  • the UE 604 may select all tilt angles for which a given measurement is above a threshold value (e.g. all tilt angles having a CQI value above a threshold).
  • the UE 604 may rank the tilt angles according to one or more of the measurements and select a predetermined number of tilt angles with the highest rankings.
  • the UE 604 reports the measurements for the selected tilt angles to the gNB 602 in the report 612 and the gNB 602 identifies the tilt angle for the UE 604 using the measurements as described above.
  • the gNB 602 may use the identified tilt angle for any further communications with the UE 604.
  • the gNB 602 may thus schedule one or more data transmissions for the UE 604, in which the data transmissions are to be transmitted at the identified tilt angle.
  • the tilt angle may be used for time domain beamforming, such that all transmissions to the UE 604 on a particular carrier are sent at the identified tilt angle.
  • the gNB 602 may send a further CSI-RS to the UE 604 at the identified tilt angle.
  • the UE 604 reports measurements performed on the CSI-RS to the gNB 602 and the gNB 602 schedules transmissions for the UE 604 based on the reported measurements.
  • This additional signalling may substantially correspond to the communication flow described above in respect of Figure 1, with the modification that the cell-specific reference signal transmitted by the gNB is a CSI-RS transmitted at the identified tilt angle.
  • the UE 604 may thus report CSI computed from the CSI-RS on a feedback channel and the gNB 602 may determine downlink (DL) transmission parameters using the CSI and schedule one or more downlink control and/or data transmissions to be sent to the UE 604 at the identified tilt angle. Providing these additional CSI-RS measurements to the gNB enables the gNB to account for any changes in the channel when scheduling downlink transmissions.
  • DL downlink
  • the communication flow shown in Figure 6 thus provides a method by which an optimal or preferred tilt angle for a UE 604 can be identified.
  • the communication flow of Figure 6 is described as being between the gNB 602 and the UE 604, the skilled person will appreciate that this communication flow may in general be used by any base station and any wireless device.
  • the base station 502 described above in respect of Figure 5 may implement one or more of the steps performed by the gNB 602 in Figure 6.
  • the first wireless device 504a described above in respect of Figure 5 may implement one or more of the steps performed by the UE 604 in respect of Figure 6.
  • SSBs as the reference signal broadcast by the gNB 602
  • any reference signal suitable for broadcast may be used.
  • SSBs may be particularly suitable since they may be received by the UE 604 even when operating in idle mode.
  • the measurements performed by the UE 604 on the broadcasted reference signal may also differ (e.g. depending on the type of reference signal used).
  • the gNB 602 transmits CSI-RSs to the UE 604 at each of the tilt angles in the subset in the communication flow of Figure 6, the skilled person will appreciate that other reference signals may also be used.
  • the measurements performed by the UE 604 on the reference signal may also differ (e.g. depending on the type of reference signal used).
  • FIG. 7 shows a flowchart of a method 700 performed by a base station according to embodiments of the disclosure.
  • the base station may be the gNB 602 described above in respect of Figure 6, for example.
  • the base station 602 broadcasts a first reference signal at a plurality of tilt angles.
  • the first reference signal may be an SSB, for example. Broadcasting the first reference signal at a plurality of tilt angles increases the number of wireless devices that the first reference signal may be received by, whilst minimising overhead signalling.
  • the base station 602 may broadcast the first reference signal in response to a particular trigger.
  • the base station 602 may broadcast the first reference signal in response to handover of a wireless device to the base station 602 (e.g. when a wireless device enters a cell served by the base station 602).
  • the base station 602 may broadcast the first reference signal periodically (e.g. at predetermined time intervals).
  • the base station 602 selects a subset of the plurality of tilt angles for the one or more wireless devices based on measurements of the first reference signal.
  • the base station 602 thus receives measurements of the first reference signal from one or more wireless devices in its coverage area.
  • the measurements may include RSRP measurements.
  • the base station 602 may select, for each wireless device, the tilt angle associated with the highest RSRP measurement for that wireless device.
  • the subset of tilt angles may thus consist of the tilt angles associated with the highest RSRP values for the one or more wireless devices.
  • the base station 602 transmits, at each tilt angle in the subset of tilt angles, a second reference signal to a wireless device in the one or more wireless devices.
  • the wireless device may be any suitable wireless device such as the UE 604 described above in respect of Figure 6 or the first wireless device 504a described above in respect of Figure 5, for example.
  • the second reference signal is sent to the wireless device 604 specifically (e.g. the reference signal is intended for that particular wireless device 604).
  • the base station 602 may unicast the second reference signal to the wireless device 604.
  • the second reference signal may thus be considered to be wireless device (or UE)-specific in that it is intended for receipt by one wireless device. Whilst the second reference signal is intended for the wireless device 604 specifically, the skilled person will appreciate that this does not necessarily mean that the sequence used for the second reference signal is specific to the wireless device 604.
  • the base station 602 may, for example, use the same sequence for multiple wireless devices, but transmit the sequence to different wireless devices using different time-frequency resources and/or at different tilt angles.
  • the second reference signal may comprise a CSI-RS (e.g. as described above in respect of Figure 6).
  • the base station 602 identifies a tilt angle for communication with the wireless device 604 based on measurements of the second reference signal performed by the wireless device 604.
  • the base station 602 may thus receive the measurements from the wireless device and use the measurements to select the tilt angle.
  • the base station 602 may thus use the measurements to determine which tilt angle provides the best channel quality and/or capacity and select that tilt angle.
  • the base station 602 may receive CQI and rank (R) measurements from the wireless device 604 and select the tilt angle having the highest value of R*CQI.
  • the base station 602 may receive, from the wireless device 604, an indication of the tilt angle to be used for communication with the wireless device 604.
  • the base station 602 thus identifies that the tilt angle indicated in the message is to be used for communication with the wireless device 604.
  • the indication may take the form of an identifier for that tilt angle (e.g. the tilt angle itself).
  • the wireless device 604 may selectively report measurements for only the selected tilt angle.
  • the base station 602 may further schedule a transmission (e.g. a data transmission) for the wireless device at the identified tilt angle.
  • a transmission e.g. a data transmission
  • the optimal tilt angle for wireless device 604 may change as, for example, channel conditions change and/or as the wireless device 604 moves within the coverage area of the base station 602.
  • the base station 602 may repeat steps 706 and 708 to reidentify the tilt angle for the wireless device.
  • the base station 602 may repeat steps 706 and 708 at predetermined intervals or in response to a particular trigger.
  • the base station 602 may perform steps 706 and 708 in response to determining that the channel quality for the wireless device 604 has dropped below a threshold value.
  • the base station 602 perform steps 706 and 708 in response to receipt of a CSI report from the wireless device 604 indicating that the CQI has dropped below a threshold value.
  • the base station 602 may be configured to perform one or more steps of the method 700 periodically.
  • the base station 602 may be configured to repeat part of the method 700 more frequently than the rest of the method 700.
  • the base station 502 may repeat the steps 702 and 704 less frequently than steps 706 and 708.
  • the base station 502 can adapt the tilt angle for a particular wireless device to account for changes in the position of the wireless device or the channel quality, without incurring the additional signalling overhead that arises from broadcasting the first reference signal.
  • the base station 502 may thus, for example, broadcast the first reference signal (and select the subset of the plurality of tilt angles) every N slots and transmit the second reference signal (and identify the tilt angle) every M slots, in which N>M.
  • Embodiments of the disclosure thus provide methods for identifying a tilt angle for communicating with a particular wireless device. Optimising the tilt angle in this manner enables improving the performance of time domain beamforming, making it more competitive with frequency domain beamforming. As time domain beamforming is cheaper and more energy efficient than full digital beamforming solutions, this enables implementing cheaper and more efficient communications in AAS systems, whilst maintaining performance.
  • Figures 8a and 8b show the average sector throughput and average cell edge user throughput for communications with wireless devices when only a single tilt angle is used for all of the wireless devices (solid line in Figure 8a) versus when a respective tilt angle is identified for each wireless device using the methods disclosed herein (the dot-dashed line in Figure 8a). These data were obtained from simulations of a wireless communications network implemented using the simulation parameters shown in Table 1.
  • Table 1 As shown in Figure 8a, using a tilt angle selected from a set of multiple tilt angles using the methods disclosed herein improves the average sector throughput compared to conventional approaches, regardless of load. A similar increase in throughput is achieved for cell-edge users, regardless of load level. This is illustrated in Figure 8b. Embodiments of the disclosure thus enable improving average sector throughput by providing efficient methods for identifying wireless device-specific tilt angles for beamforming transmissions from a base station.
  • FIG 9 is a schematic diagram of a base station 900 according to embodiments of the disclosure.
  • the base station 900 may be, for example, the base station 502 or the gNB 602 described above in respect of Figures 5 and 6, for example.
  • the base station 900 may be operable to carry out the example method 700 described with reference to Figure 7 and possibly any other processes or methods disclosed herein. It is also to be understood that the method 700 of Figure 7 may not necessarily be carried out solely by the base station 900. At least some operations of the method can be performed by one or more other entities.
  • the base station 900 comprises processing circuitry 902 (such as one or more processors, digital signal processors, general purpose processing units, etc), a machine- readable medium 904 (e.g., memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc) and one or more interfaces 906.
  • processing circuitry 902 such as one or more processors, digital signal processors, general purpose processing units, etc
  • machine- readable medium 904 e.g., memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc
  • interfaces 906 e.g., Ethernet interfaces, etc.
  • the machine-readable medium 904 stores instructions which, when executed by the processing circuitry 902, cause the base station 900 to: broadcast a first reference signal at a plurality of tilt angles and, based on measurements of the first reference signal performed by one or more wireless devices in the wireless communications network, select a subset of the plurality of tilt angles for the one or more wireless devices.
  • the base station 900 is further caused to transmit, at each tilt angle in the subset of tilt angles, a second reference signal to a wireless device in the one or more wireless devices and, based on measurements of the second reference signal performed by the wireless device, identify a tilt angle from the subset of tilt angles for communication with the wireless device.
  • the processing circuitry 902 may be configured to directly perform the method, or to cause the base station 900 to perform the method, without executing instructions stored in the non-transitory machine-readable medium 904, e.g., through suitably configured dedicated circuitry.
  • the one or more interfaces 906 may comprise hardware and/or software suitable for communicating with other nodes of the communications network using any suitable communication medium.
  • the interfaces 906 may comprise one or more wired interfaces, using optical or electrical transmission media. Such interfaces may therefore utilize optical or electrical transmitters and receivers, as well as the necessary software to encode and decode signals transmitted via the interface.
  • the interfaces 906 may comprise one or more wireless interfaces. Such interfaces may therefore utilize one or more antennas, baseband circuitry, etc.
  • the components are illustrated coupled together in series; however, those skilled in the art will appreciate that the components may be coupled together in any suitable manner (e.g., via a system bus or suchlike).
  • the base station 900 may comprise power circuitry (not illustrated).
  • the power circuitry may comprise, or be coupled to, power management circuitry and is configured to supply the components of base station 900 with power for performing the functionality described herein.
  • Power circuitry may receive power from a power source.
  • the power source and/or power circuitry may be configured to provide power to the various components of base station 900 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component).
  • the power source may either be included in, or external to, the power circuitry and/or the base station 900.
  • the base station 900 may be connectable to an external power source (e.g., an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to the power circuitry.
  • an external power source e.g., an electricity outlet
  • the power source may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, the power circuitry.
  • the battery may provide backup power should the external power source fail.
  • Other types of power sources such as photovoltaic devices, may also be used.
  • the base station 900 may comprise a plurality of separate units over which the functionality of the base station 900 is distributed.
  • the base station 900 may thus be a distributed (e.g. modular) base station such as, for example, an Open Radio Access Network (O-RAN) node.
  • O-RAN Open Radio Access Network
  • the base station 900 may comprise a radio equipment controller (e.g. a baseband processing unit) and one or more remote radio equipment nodes (e.g. radio frequency transceivers).
  • the radio equipment nodes are not co-located with the radio equipment controller and, in particular, the radio equipment nodes may be positioned at a significant distance from the radio equipment controller such that the radio equipment controller can centrally serve a large number of remote radio equipment nodes.
  • the radio equipment controller may be directly or indirectly connected to the remote radio equipment nodes.
  • the radio equipment nodes may be connected to the radio equipment controller via one or more fibre links (e.g. lossless fibre links).
  • the interface between the units in a distributed base station be defined by the Common Public Radio Interface (CPRI), which standardizes the protocol interface between a radio equipment controller and radio equipment nodes in wireless distributed base stations to enable interoperability of equipment from different vendors.
  • CPRI Common Public Radio Interface
  • the radio equipment nodes may be connected to a common CPRI concentrator, for example.
  • the processing circuitry 902 and the machine-readable medium 904 may be comprised in, for example, a radio equipment controller which is configured to control one or more radio equipment nodes forming part of the base station 900.
  • the methods described herein e.g. the method 400
  • the processing circuitry 902 and the machine-readable medium 904 may be comprised in one of the radio equipment nodes (e.g. at a transceiver).
  • FIG 10 is a schematic diagram of a base station 1000 according to embodiments of the disclosure.
  • the base station 1000 may be, for example, the base station 502 or the gNB 602 described above in respect of Figures 5 and 6, for example.
  • the base station 1000 comprises a broadcasting unit 1002, which is configured to broadcast a first reference signal at a plurality of tilt angles.
  • the base station 1000 further comprises a selecting unit 1004, which is configured to select a subset of the plurality of tilt angles for one or more wireless devices in the wireless communications network based on measurements of the first reference signal performed by the one or more wireless devices.
  • the base station 1000 further comprises a transmitting unit 1006 and an identifying unit 1008.
  • the transmitting unit 1006 is configured to transmit, at each tilt angle in the subset of tilt angles, a second reference signal to a wireless device in the one or more wireless devices.
  • the identifying unit 1008 is configured to identify a tilt angle from the subset of tilt angles for communication with the wireless device based on measurements of the second reference signal performed by the wireless device.
  • the broadcasting unit 902, the selecting unit 904, the transmitting unit 906 and the identifying unit 908 may be configured to perform steps 702, 704, 706 and 708 (described above in respect of Figure 7) respectively.
  • the base station 1000 may comprise processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include digital signal processors (DSPs), special-purpose digital logic, and the like.
  • the processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc.
  • Program code stored in memory includes program instructions for executing one or more telecommunications and/or data communications protocols as well as instructions for carrying out one or more of the techniques described herein, in several embodiments.
  • the processing circuitry may be used to cause the broadcasting unit 1002, the selecting unit 1004, the transmitting unit 1006 and the identifying unit 1008, and any other suitable units of base station 1000 to perform corresponding functions according one or more embodiments of the present disclosure.
  • the base station 1000 may additionally comprise power-supply circuitry (not illustrated) configured to supply the base station 1000 with power.

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

Abstract

Selon un aspect, l'invention concerne une station de base pour un réseau de communication sans fil. La station de base comprend un circuit de traitement et un support lisible par machine stockant des instructions qui, lorsqu'elles sont exécutées par le circuit de traitement, amènent la station de base à diffuser un premier signal de référence à une pluralité d'angles d'inclinaison et, en fonction de mesures du premier signal de référence effectuée par un ou plusieurs dispositifs sans fil dans le réseau de communication sans fil, sélectionnent un sous-ensemble de la pluralité d'angles d'inclinaison pour le ou les dispositifs sans fil. La station de base est en outre amenée à transmettre, à chaque angle d'inclinaison dans le sous-ensemble d'angles d'inclinaison, un deuxième signal de référence à un dispositif sans fil dans le ou les dispositifs sans fil et, en fonction de mesures du deuxième signal de référence effectué par le dispositif sans fil, à identifier un angle d'inclinaison à partir du sous-ensemble d'angles d'inclinaison pour une communication avec le dispositif sans fil.
PCT/SE2021/050288 2021-03-30 2021-03-30 Procédés et appareil pour identifier un angle d'inclinaison pour un dispositif sans fil WO2022211685A1 (fr)

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PCT/SE2021/050288 WO2022211685A1 (fr) 2021-03-30 2021-03-30 Procédés et appareil pour identifier un angle d'inclinaison pour un dispositif sans fil
EP21716869.9A EP4315931A1 (fr) 2021-03-30 2021-03-30 Procédés et appareil pour identifier un angle d'inclinaison pour un dispositif sans fil

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EP2826162A1 (fr) * 2012-03-15 2015-01-21 Telefonaktiebolaget L M Ericsson (Publ) N ud et procédé de génération de signaux en forme de faisceau pour une communication en liaison descendante
US20140177745A1 (en) * 2012-12-20 2014-06-26 Motorola Mobility Llc Method and apparatus for antenna array channel feedback
US20160028519A1 (en) * 2013-01-31 2016-01-28 Chao Wei 3d mimo csi feedback based on virtual elevation ports
US20160134352A1 (en) * 2014-11-06 2016-05-12 Futurewei Technologies, Inc. System and Method for Beam-Formed Channel State Reference Signals
US20200358515A1 (en) * 2019-05-08 2020-11-12 Apple Inc. Beam Tracking Using Downlink Data Reception and Motion Sensing Information

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