Method and apparatus for channel estimation for MIMO systems

Abstract

A method for MIMO channel estimation is provided that includes transmitting MIMO reference signals that use a non-uniform pattern of resources in space, time, frequency, and / or code and are calculated from prior knowledge. The prior knowledge is obtained from a plurality of MIMO channel samples associated with a region. At the receiving side, the MIMO reference signals are received based on a receiver-side MIMO reference signal constellation that is also a non-uniform pattern of resources in space, time, frequency, and / or code and is calculated from prior knowledge. The MIMO channel is estimated from channel measurements on the reference signals and the prior knowledge.

Description

[Technical Field]

[0001] This application relates generally to wireless communications, and more particularly to channel estimation and feedback for multiple-input multiple-output (MIMO) systems. [Background technology]

[0002] In wireless communication systems, it is important to estimate the channel. To do this, a reference signal must be known to both the transmitting and receiving devices before transmission begins. The receiving device estimates the channel by receiving and measuring the reference signal sent by the transmitting device.

[0003] Before a MIMO transmission between a base station (BS) and one or more user equipments (UEs) begins, a reference signal within the MIMO channel space must be located. In Orthogonal Frequency Division Multiplexing (OFDM) mode, the MIMO channel on each subcarrier is represented by an NxM complex matrix, where M is the number of transmitting antennas and N is the number of receiving antennas. Over L subcarriers, this MIMO channel forms a 3D channel space: LxNxM, where L is the number of subcarriers.

[0004] In 5G, reference signals are called Channel Condition Indicator-Reference Signals (CSI-RS) for the downlink and Sounding Reference Signals (SRS) for the uplink. Downlink reference signals are typically transmitted in multicast or broadcast mode, while uplink reference signals are typically transmitted in unicast mode. Reference signals in the 5G MIMO channel space are uniformly distributed across the radio resources with a density predefined in the specification.

[0005] In 6G, the number of subcarriers, transmit antennas, and receive antennas will increase dramatically. The 6G MIMO channel space may use up to 500 MHz of bandwidth with 15 kHz subcarrier spacing, resulting in 33,333 subcarriers or 2,777 resource blocks (RBs). The number of BS antennas can reach 1,024, and the number of UE antennas can reach 32. Even if only one reference signal is transmitted per RB per transmission time interval (TTI), the total number of reference signals reaches 2,777 * 1,024 * 32 = 90,996,736 per TTI, resulting in significant overhead in the measurement and feedback of channel measurements. Summary of the Invention

[0006] A method for MIMO channel estimation is provided, which includes transmitting a MIMO reference signal that uses a non-uniform pattern of resources in space, time, frequency, and / or code and is calculated from prior knowledge. The prior knowledge is obtained from a plurality of MIMO channel samples associated with a region. At the receiving side, the MIMO reference signal is received based on a receiver-side MIMO reference signal constellation that is also a non-uniform pattern of resources in space, time, frequency, and / or code and is calculated from prior knowledge. The MIMO channel is estimated from channel measurements on the reference signal and the prior knowledge. The overhead of measuring and feeding back channel measurements can be reduced by using this method. [Means for solving the problem]

[0007] According to one aspect of the present disclosure, there is provided a method for MIMO channel estimation, including: transmitting, by a transmitting device, a multiple-input multiple-output (MIMO) reference signal using a transmit MIMO reference signal pattern, the transmit MIMO reference signal pattern including a transmit MIMO reference signal constellation, the transmit MIMO reference signal constellation being a non-uniform pattern of resources in space, time, frequency, and / or code, and calculated from prior knowledge, the prior knowledge being obtained from a plurality of MIMO channel samples associated with a region; receiving, by a receiving device, the MIMO reference signal using a receive MIMO reference signal pattern, the receive MIMO reference signal pattern including a receive MIMO reference signal constellation, the receive MIMO reference signal constellation being a non-uniform pattern of resources in space, time, frequency, and / or code, and calculated from prior knowledge, the prior knowledge being obtained from a plurality of MIMO channel samples associated with a region; and estimating, by the receiving device, a MIMO channel from channel measurements on the reference signal and the prior knowledge.

[0008] In some embodiments, the method further includes, after receiving the MIMO reference signal by the receiving device, transmitting, by the receiving device, feedback based on channel measurements for the reference signal; receiving, by the transmitting device, feedback based on channel measurements for the reference signal; and estimating, by the transmitting device, the MIMO channel from the feedback.

[0009] In some embodiments, the prior knowledge is represented by a channel spatial basis matrix U, which consists of a plurality of orthonormal channel basis vectors and is obtained from a plurality of MIMO channel samples vectorized from a multidimensional MIMO channel format including space, time, frequency, and / or code.

[0010] In some embodiments, the prior knowledge represented by the channel spatial basis matrix U is associated with a region, and different prior knowledge represented by different channel spatial basis matrices U is associated with different regions.

[0011] In some embodiments, the multiple MIMO channel samples for each of the multiple different regions are reshaped and placed into a channel training matrix A composed of vectorized MIMO channel samples of length n, and the channel spatial basis matrix U is calculated as SVD(A)=UΣV H 、 where the SVD on the training matrix A is truncated by retaining the largest r singular values, where r is the defined rank, and the channel spatial basis matrix U has a size of n×r.

[0012] In some embodiments, the method further includes, before transmitting the multiple-input multiple-output (MIMO) reference signal using the transmit MIMO reference signal pattern, obtaining, by the transmitting device, prior knowledge represented by a region to which the transmitting device and the receiving device belong, a channel spatial basis matrix U associated with the region, and the transmit MIMO reference signal pattern.

[0013] In some embodiments, the transmit MIMO reference signal pattern includes a transmit MIMO reference signal constellation including reference signal positions, transmit signal values ​​for each reference signal, or a multiplexing scheme for each reference signal, each of which indicates on which subcarriers in the MIMO channel space and on which transmitting antennas a reference signal should be transmitted.

[0014] In some embodiments, the method further includes, before using the transmit MIMO reference signal pattern, obtaining, by the transmitting device, the transmit MIMO reference signal constellation and a pattern generation method from the transmit constellation.

[0015] In some embodiments, the method further includes, before using the transmit MIMO reference signal constellation, obtaining, by the transmitting device, a basic MIMO reference signal constellation and a transmit constellation generation method from the basic.

[0016] In some embodiments, the method further includes, before receiving a multiple-input multiple-output (MIMO) reference signal using the receiver MIMO reference signal pattern, obtaining, by the receiver device, prior knowledge represented by a region to which the transmitter device and the receiver device belong, a channel spatial basis matrix U associated with the region, and the receiver MIMO reference signal pattern.

[0017] In some embodiments, the receiver MIMO reference signal pattern includes a receiver MIMO reference signal constellation including reference signal positions, each of which indicates on which subcarriers in the MIMO channel space, on which transmitter antennas, and at which receiver antennas a reference signal should be transmitted, a transmitted signal value for each reference signal, or a (de)multiplexing scheme for each reference signal.

[0018] In some embodiments, the method further includes, before using the receiver MIMO reference signal pattern, obtaining, by the receiver device, the receiver MIMO reference signal constellation and a pattern generation method from the receiver constellation.

[0019] In some embodiments, the method further includes, before using the transmit MIMO reference signal constellation, obtaining, by the receiving device, a basic MIMO reference signal constellation and a receiver constellation generation method from the basic, and / or obtaining, by the receiving device, a transmit MIMO reference signal constellation and a receiver constellation generation method from the transmit.

[0020] In some embodiments, the channel spatial basis matrix U H r pivot positions are obtained from U, and the r pivot positions correspond to the basic MIMO reference signal constellation, and define the reference signal positions in the MIMO channel space by subcarriers, transmitting antennas, and receiving antennas, respectively.H is the Hermitian transpose of U, and the MIMO channel space contains that number of subcarriers, that number of transmitting antennas, and that number of receiving antennas.

[0021] In some embodiments, the pattern generation method from the transmit constellation specifies transmit signal values ​​and multiplexing schemes for each reference signal in the transmit MIMO reference signal constellation, where the multiplexing schemes include time multiplexing, frequency multiplexing, and / or code multiplexing.

[0022] In some embodiments, the pattern generation method from the receiver configuration specifies a transmit signal value and a (de)multiplexing scheme for each reference signal in the receiver MIMO reference signal configuration, and the (de)multiplexing scheme includes time (de)multiplexing, frequency (de)multiplexing, and / or code (de)multiplexing.

[0023] In some embodiments, the transmit constellation generation method from the basic merges any two reference signal positions in the basic MIMO reference signal constellation that share the same subcarrier and the same transmitting antenna but have different receiving antennas into one reference signal position in the transmit MIMO reference signal constellation.

[0024] In some embodiments, the receiver constellation generation method from base may include a base portion and include an extended portion from the base MIMO reference signal constellation to the receiver MIMO reference signal constellation, or the receiver constellation generation method from transmit includes a base portion and includes an extended portion from the transmit MIMO reference signal constellation to the receiver MIMO reference signal constellation.

[0025] In some embodiments, the base portion includes reference signal positions in the base MIMO reference signal constellation, and the extended portion includes multiple reference signal positions that share the same subcarriers and the same transmitting antennas but have different receiving antennas and are not in the base MIMO reference signal constellation.

[0026] In some embodiments, the extensions are modified and updated.

[0027] In some embodiments, the method further includes, after receiving a multiple-input multiple-output (MIMO) reference signal using the receiver MIMO reference signal pattern, measuring, by the receiver device, channels at reference signal locations indicated by the receiver MIMO reference signal pattern into a vector y before estimating, by the receiver device, the MIMO channel from channel measurements and prior knowledge for the reference signal.

[0028] In some embodiments, the MIMO channel estimation is from channel measurements and prior knowledge for reference signals, where the channel measurements for the reference signals represented in a vector y and the prior knowledge represented by a channel spatial basis matrix U are used to estimate the compact channel basis θ aug and its left inverse, which is θ aug =P Rx *U

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[0029] In some embodiments, a MIMO channel

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[0030] In some embodiments, if only a subset of the vector a of coefficients is available, the MIMO channel

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[0031] In some embodiments, only a subset of the vector of coefficients a is available, and a subset of the MIMO channels

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[0032] In some embodiments, when the extension part is changed, the receiver MIMO reference signal constellation is expressed as a constellation matrix P Rx_update and accordingly, the compact channel basis θ aug and its left inverse is θ aug =P Rx_update *U

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[0033] In some embodiments, the transmit arrangement pattern generation method is selected from among a plurality of transmit arrangement pattern generation methods.

[0034] In some embodiments, the transmit placement generation method from base is selected from among the transmit placement generation methods from base.

[0035] In some embodiments, the pattern generation method from the receiving arrangement is selected from among the pattern generation methods from the receiving arrangement.

[0036] In some embodiments, the receiver constellation generation method from base is selected from among the receiver constellation generation methods from base, or the receiver constellation generation method from transmit is selected from among the receiver constellation generation methods from transmit.

[0037] In some embodiments, the region to which the sending and receiving devices belong may include multiple sub-regions, different regions may overlap or be separate, and the sending and receiving devices may be associated with different regions.

[0038] In some embodiments, the method further includes, before the MIMO transmission begins and the regions to which the transmitting and receiving devices are associated are determined, obtaining, by the transmitting and receiving devices, prior knowledge associated with the region, a transmit MIMO reference signal pattern, and a receive MIMO reference signal pattern.

[0039] In some embodiments, the prior knowledge is represented directly by the channel spatial basis matrix U or by the compact channel matrix θ aug Or by its left inverse θ aug =P Rx *U

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[0040] In some embodiments, the transmit MIMO reference signal pattern may be explicitly signaled or may be generated from the transmit MIMO reference signal constellation in a pattern generation method from the transmit constellation.

[0041] In some embodiments, the transmit MIMO reference signal constellation may be explicitly signaled or may be generated from the base MIMO reference signal constellation in a transmit constellation generation method from the base.

[0042] In some embodiments, the receiver MIMO reference signal pattern may be explicitly signaled or may be generated from the receiver MIMO reference signal constellation in a pattern generation method from the receiver constellation.

[0043] In some embodiments, the receiver MIMO reference signal constellation may be explicitly signaled or may be generated from a base MIMO reference signal constellation in a receiver constellation generation method from base.

[0044] In some embodiments, the basic MIMO reference signal constellation may be signaled explicitly or may be based on the channel spatial basis matrix U H r pivot positions are obtained from U, and the r pivot positions correspond to the basic MIMO reference signal constellation, and define the reference signal positions in the MIMO channel space by subcarriers, transmitting antennas, and receiving antennas, respectively. H can be computed from prior knowledge represented by the channel spatial basis matrix U according to the fact that U is the Hermitian transpose of U.

[0045] In some embodiments, the explicitly signaled transmit MIMO reference signal constellation may be represented by a combination of constituent reference signal constellations, where the constituent reference signal constellations are predefined and prestored.

[0046] In some embodiments, the explicitly signaled receiver MIMO reference signal constellation may be represented by a combination of constituent receiver reference signal constellations, where the constituent receiver reference signal constellations are predefined and prestored.

[0047] In some embodiments, the feedback based on channel measurements for reference signal positions determined by the receiver's MIMO reference signal constellation may include channel measurements for reference signal positions in the vector of y.

[0048] In some embodiments, the feedback based on channel measurements for reference signal positions determined by the receiver's MIMO reference signal constellation may include:

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[0049] In some embodiments, the method comprises, by a transmitting device after receiving feedback based on channel measurements for reference signal positions comprising a vector of y:

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[0050] In some embodiments, the method comprises: by the transmitting device after receiving feedback based on channel measurements for the reference signal positions including the vector of y:

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[0051] In some embodiments, the method comprises, by a transmitting device, after receiving feedback based on channel measurements for reference signal positions comprising the vector of coefficients a or a subset a′ of the vector of coefficients: MIMO Channel

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[0052] In some embodiments, the method comprises, by a transmitting device, after receiving feedback based on channel measurements for reference signal positions comprising the vector of coefficients a or a subset a′ of the vector of coefficients: Subset of MIMO channels

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[0053] In some embodiments, the channel training matrix A is updated with a plurality of new channel samples for each of a plurality of different regions, and a new channel spatial basis matrix U, a basic MIMO reference signal constellation, a transmit MIMO reference signal pattern, a receive MIMO reference signal pattern, and a compact channel basis θ are calculated for each of the plurality of different regions. aug or the left inverse of the compact channel basis

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[0054] In some embodiments, the transmitting device is a base station and the receiving device is a user equipment (UE).

[0055] In some embodiments, the transmitting device is a user equipment (UE) and the receiving device is a base station.

[0056] In some embodiments, the sending device comprises a processor and a memory, the memory coupled to the processor, the memory storing instructions that, when executed, cause the processor to perform steps of the sending device.

[0057] In some embodiments, the receiving device comprises a processor and a memory, the memory coupled to the processor, the memory storing instructions that, when executed, cause the processor to perform steps of the receiving device.

[0058] According to another aspect of the present disclosure, there is provided a system comprising a sending device and a receiving device, wherein the sending device is configured to perform the steps performed by the sending device as described herein, and the receiving device is configured to perform the steps performed by the receiving device as described herein.

[0059] Embodiments of the present disclosure will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0060] [Figure 1] FIG. 1 is a block diagram of a communication system. [Figure 2] FIG. 1 is a block diagram of a communication system. [Figure 3] FIG. 1 is a block diagram of a communication system showing the basic component structure of an electronic device (ED) and a base station. [Figure 4] FIG. 2 is a block diagram of modules that may be used to implement or perform one or more of the steps of the embodiments of the present application. [Figure 5] 1 is a flowchart of a channel measurement and feedback method. [Figure 6] 1 shows the reshaping of m channel measurements into a channel training matrix A. [Figure 7A] An example of reduced-rank SVD for a channel training matrix A is shown below. [Figure 7B] 10 shows an example of pivot position generation. [Figure 7C] 1 shows an example of a transmit MIMO reference signal pattern design. [Figure 8] 1 is a diagram illustrating an example of a basic MIMO reference signal arrangement P. FIG. [Figure 9] FIG. 10 is a diagram illustrating an example of a receiving-side MIMO reference signal arrangement matrix PRx. [Figure 10] FIG. 10 is a diagram illustrating an example of calculation of θaug. [Figure 11] FIG. 10 is a diagram of an example of the calculation of y. [Figure 12]

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[0061] As mentioned above, the large overhead of measuring and feeding back channel measurements in the 6G MIMO channel space makes it difficult and expensive to estimate the MIMO channel using a uniform MIMO reference signal constellation scheme like 5G. The uniform MIMO reference signal constellation occupies a large portion of the time-frequency code radio resources for transmitting reference signals. Correspondingly, if required, feedback on the estimated MIMO channel will result in significant CSI overhead.

[0062] Therefore, it is not feasible to adopt a uniform MIMO reference signal constellation like that of 5G for 6G-MIMO channel estimation and feedback. A new constellation scheme and new feedback scheme for 6G-MIMO channel estimation and feedback must reduce the density of the reference signals while maintaining good performance of MIMO channel estimation.

[0063] By way of a non-limiting illustrative example, referring to FIG. 1 , a simplified schematic diagram of a communication system is provided. The communication system 100 comprises a radio access network 120. The radio access network 120 may be a next-generation (e.g., sixth-generation (6G) or later) radio access network or a legacy (e.g., 5G, 4G, 3G, or 2G) radio access network. One or more communication electrical devices (EDs) 110a-120j (commonly referred to as 110) may be interconnected to each other or connected to one or more network nodes (collectively referred to as 170a, 170b, 170c) in the radio access network 120. A core network 130 may be part of the communication system and may or may not depend on the radio access technology used in the communication system 100. The communication system 100 also comprises a public switched telephone network (PSTN) 140, the Internet 150, and other networks 160.

[0064] FIG. 2 illustrates an exemplary communication system 100. Generally, the communication system 100 enables multiple wireless or wired elements to communicate data and other content. The purpose of the communication system 100 may be to provide content such as voice, data, video, and / or text via broadcast, multicast, unicast, etc. The communication system 100 may operate by sharing resources, such as carrier spectrum bandwidth, among its components. The communication system 100 may include terrestrial and / or non-terrestrial communication systems. The communication system 100 may provide a wide range of communication services and applications (such as earth monitoring, remote sensing, passive sensing and positioning, navigation and tracking, autonomous delivery and mobility, etc.). The communication system 100 may provide high availability and robustness through cooperation between the terrestrial and non-terrestrial communication systems. For example, integrating a non-terrestrial communication system (or components thereof) into a terrestrial communication system can result in what may be considered a heterogeneous network comprising multiple layers. Compared with traditional communication networks, heterogeneous networks can achieve better overall performance through efficient multi-link cooperation, more flexible function sharing, and faster physical layer link switching between terrestrial and non-terrestrial networks.

[0065] The terrestrial and non-terrestrial communication systems can be considered subsystems of a communication system. In the illustrated example, communication system 100 includes electronic devices (EDs) 110a-110d (collectively referred to as EDs 110), radio access networks (RANs) 120a-120b, a non-terrestrial communication network 120c, a core network 130, a public switched telephone network (PSTN) 140, the Internet 150, and other networks 160. RANs 120a-120b include respective base stations (BSs) 170a-170b, which may be collectively referred to as terrestrial transmission / reception points (T-TRPs) 170a-170b. Non-terrestrial communication network 120c includes access nodes 120c, which may be collectively referred to as non-terrestrial transmission / reception points (NT-TRPs) 172.

[0066] Any ED 110 may alternatively or additionally be configured to interface with, access, or communicate with any other T-TRPs 170a-170b and NT-TRPs 172, the Internet 150, the core network 130, the PSTN 140, other networks 160, or any combination thereof. In some examples, ED 110a may communicate uplink and / or downlink transmissions with T-TRP 170a via interface 190a. In some examples, EDs 110a, 110b, and 110d may also communicate directly with each other via one or more sidelink air interfaces 190b. In some examples, ED 110d may communicate uplink and / or downlink transmissions with NT-TRP 172 via interface 190c.

[0067] Air interface 190a and air interface 190b may use similar communication technologies, such as any suitable radio access technology. For example, communication system 100 may implement one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), or single-carrier FDMA (SC-FDMA), at air interface 190a and air interface 190b. Air interface 190a and air interface 190b may utilize other, higher-dimensional signal spaces, which may include orthogonal and / or non-orthogonal dimensions.

[0068] The air interface 190c may enable communication between the ED 110d and one or more NT-TRPs 172 via a wireless link or simply a link. In some examples, the link is a dedicated connection for unicast transmissions, a connection for broadcast transmissions, or a connection between a group of EDs and one or more NT-TRPs for multicast transmissions.

[0069] The RAN 120a and RAN 120b communicate with the core network 130 to provide various services, such as voice, data, and other services, to the EDs 110a, 110b, and 110c. The RAN 120a and RAN 120b and / or the core network 130 may communicate directly or indirectly with one or more other RANs (not shown), which may or may not be served directly by the core network 130 and which may or may not employ the same radio access technology as the RAN 120a, RAN 120b, or both. The core network 130 may also serve as a gateway access between (i) the RAN 120a and RAN 120b or the EDs 110a, 110b, and 110c, or both, and (ii) other networks (such as the PSTN 140, the Internet 150, and other networks 160). Additionally, some or all of EDs 110a, 110b, and 110c may include functionality for communicating with different wireless networks over different wireless links using different wireless technologies and / or protocols. Instead of (or in addition to) wireless communication, EDs 110a, 110b, and 110c may communicate with a service provider or switch (not shown) and the Internet 150 via wired communication channels. PSTN 140 may include a circuit-switched telephone network for providing plain old telephone service (POTS). Internet 150 may include a network of computers and / or subnets and incorporate protocols such as Internet Protocol (IP), Transmission Control Protocol (TCP), and User Datagram Protocol (UDP). EDs 110a, 110b, and 110c may be multimode devices capable of operating according to multiple wireless access technologies and may incorporate multiple transceivers necessary to support such operation.

[0070] 3 illustrates another example of the ED 110 and the base stations 170a, 170b, and / or 170c. The ED 110 is used to connect people, objects, machines, etc. The ED 110 can be widely used in various scenarios, such as cellular communication, device-to-device (D2D), vehicle-to-vehicle, vehicle-to-infrastructure, vehicle-to-pedestrian, vehicle-to-vehicle, and vehicle-to-everything (V2X), peer-to-peer (P2P), machine-to-machine (M2M), machine-to-machine communication (MTC), Internet of Things (IoT), virtual reality (VR), augmented reality (AR), industrial control, autonomous driving, telemedicine, smart grid, smart furniture, smart offices, smart wearables, smart transportation, smart cities, drones, robots, remote sensing, passive sensing, positioning, navigation and tracking, autonomous delivery, and mobility.

[0071] Each ED 110 represents any suitable end-user device for wireless operation and may include (or be referred to as) a user equipment / device (UE), a wireless transmit / receive unit (WTRU), a mobile station, a fixed or mobile subscriber unit, a cellular phone, a station (STA), a machine-type communication (MTC) device, a personal digital assistant (PDA), a smartphone, a laptop, a computer, a tablet, a wireless sensor, or a consumer electronic device, a smartbook, a vehicle, an automobile, a truck, a bus, a train, or an IoT device, an industrial device, or an apparatus (e.g., a communication module, a modem, or a chip) within any of the foregoing, among other possible devices. Future generations of EDs 110 may be referred to using other terminology. Base stations 170a, 170b are T-TRPs and are hereinafter referred to as T-TRP 170. As also shown in FIG. 3, an NT-TRP is hereinafter referred to as NT-TRP 172. Each ED110 connected to the T-TRP170 and / or NT-TRP172 can be dynamically or semi-statically turned on (i.e., established, activated or enabled), turned off (i.e., released, deactivated or disabled), and / or configured depending on one or more of the availability of the connection and the need for the connection.

[0072] The ED 110 includes a transmitter 201 and a receiver 203 coupled to one or more antennas 204. Only one antenna 204 is shown. Alternatively, one, some, or all of the antennas may be panels. The transmitter 201 and the receiver 203 may be integrated as a transceiver. The transceiver is configured to modulate data or other content for transmission by at least one antenna 204 or a network interface controller (NIC). The transceiver is also configured to demodulate data or other content received by the at least one antenna 204. Each transceiver includes any suitable structure for generating signals for wireless or wired transmission and / or processing signals received wirelessly or wired. Each antenna 204 includes any suitable structure for transmitting and / or receiving wireless or wired signals.

[0073] The ED 110 includes at least one memory 208. The memory 208 stores instructions and data used, generated, or collected by the ED 110. For example, the memory 208 can store software instructions or modules executed by the processing unit(s) 210 configured to implement some or all of the functions and / or embodiments described herein. Each memory 208 includes any suitable volatile and / or non-volatile storage and retrieval device(s). Any suitable type of memory may be used, such as random access memory (RAM), read-only memory (ROM), hard disk, optical disk, subscriber identity module (SIM) card, memory stick, secure digital (SD) memory card, on-processor cache, etc.

[0074] ED 110 may further include one or more input / output devices (not shown) or interfaces (such as a wired interface to Internet 150 in FIG. 1). The input / output devices enable interaction with a user or other devices in a network. Each input / output device includes any suitable structure for providing information to or receiving information from a user, such as a speaker, microphone, keypad, keyboard, display, or touch screen, including network interface communication.

[0075] The ED 110 further includes a processor 210 for performing operations including operations related to preparing a transmission for uplink transmission to the NT-TRP 172 and / or the T-TRP 170, operations related to processing a downlink transmission received from the NT-TRP 172 and / or the T-TRP 170, and operations related to processing a sidelink transmission or reception from another ED 110. Processing operations related to preparing a transmission for uplink transmission may include operations such as encoding, modulation, transmit beamforming, and generation of symbols for transmission. Processing operations related to processing a downlink transmission may include operations such as receive beamforming, demodulation, and decoding of received symbols. Depending on the embodiment, the downlink transmission may be received by the receiver 203, possibly using receive beamforming, and the processor 210 may extract signaling from the downlink transmission (e.g., by detecting and / or decoding the signaling). One example of signaling may be a reference signal transmitted by the NT-TRP 172 and / or the T-TRP 170. In some embodiments, processor 276 performs transmit beamforming and / or receive beamforming based on beam direction instructions, e.g., beam angle information (BAI), received from T-TRP 170. In some embodiments, processor 210 may perform operations related to network access (e.g., initial access) and / or downlink synchronization, e.g., operations related to detecting synchronization sequences, decoding and obtaining system information, etc. In some embodiments, processor 210 may perform channel estimation, e.g., using reference signals received from NT-TRP 172 and / or T-TRP 170.

[0076] Although not shown, the processor 210 may form part of the transmitter 201 and / or the receiver 203. Although not shown, the memory 208 may form part of the processor 210.

[0077] The processor 210 and the processing components of the transmitter 201 and receiver 203 may each be implemented by one or more of the same or different processors configured to execute instructions stored in a memory, such as memory 208. Alternatively, some or all of the processor 210 and the processing components of the transmitter 201 and receiver 203 may be implemented using special purpose circuitry, such as a programmed field programmable gate array (FPGA), a graphics processing unit (GPU), or an application specific integrated circuit (ASIC).

[0078] In some embodiments, the T-TRP 170 may be known as a base station, base transceiver station (BTS), radio base station, network node, network device, network-side device, transmitting / receiving node, Node B, evolved Node B (eNodeB or eNB), Home eNodeB, next-generation Node B (gNB), transmission point (TP), site controller, access point (AP), or other names such as a wireless router, relay station, remote radio head, terrestrial node, terrestrial network device, terrestrial base station, baseband unit (BBU), remote radio unit (RRU), active antenna unit (AAU), remote radio head (RRH), centralized unit (CU), distributed unit (DU), positioning node, etc. The T-TRP 170 may also be a macro BS, pico BS, relay node, donor node, etc., or a combination thereof. The T-TRP 170 may refer to a forging device or an apparatus within the aforementioned devices (e.g., a communication module, modem, or chip).

[0079] In some embodiments, parts of the T-TRP 170 may be distributed. For example, some of the modules of the T-TRP 170 may be located remotely from the equipment housing the T-TRP 170's antenna and may be coupled to the equipment housing the antenna via a communications link (not shown), sometimes known as fronthaul, such as a Common Public Radio Interface (CPRI). Thus, in some embodiments, the term T-TRP 170 may also refer to network-side modules that perform processing operations such as determining the location of the ED 110, resource allocation (scheduling), message generation, and encoding / decoding, and that are not necessarily part of the equipment housing the T-TRP 170's antenna. Modules may also be coupled to other T-TRPs. In some embodiments, the T-TRP 170 may actually be multiple T-TRPs operating together to serve the ED 110, for example, via coordinated multipoint transmission.

[0080] The T-TRP 170 includes at least one transmitter 252 and at least one receiver 254 coupled to one or more antennas 256. Only one antenna 256 is shown. Alternatively, one, some, or all of the antennas may be panels. The transmitter 252 and receiver 254 may be integrated as a transceiver. The T-TRP 170 further includes a processor 260 for performing operations including operations related to preparing a transmission for downlink transmission to the ED 110, processing uplink transmissions received from the ED 110, preparing a transmission for backhaul transmission to the NT-TRP 172, and processing transmissions received over the backhaul from the NT-TRP 172. Processing operations related to preparing a transmission for downlink or backhaul transmission may include operations such as encoding, modulating, precoding (e.g., MIMO precoding), transmit beamforming, and generating symbols for transmission. Processing operations related to processing received transmissions in the uplink or over the backhaul may include operations such as receive beamforming, demodulation, and decoding of received symbols. The processor 260 may also perform operations related to network access (e.g., initial access) and / or downlink synchronization, such as generating synchronization signal block (SSB) content, generating system information, etc. In some embodiments, the processor 260 also generates beam direction indications, e.g., BAIs, that may be scheduled for transmission by the scheduler 253. The processor 260 performs other network-side processing operations described herein, such as determining the location of the ED 110, determining where the NT-TRP 172 should be deployed, etc. In some embodiments, the processor 260 may generate signaling, for example, to configure one or more parameters of the ED 110 and / or one or more parameters of the NT-TRP 172. Any signaling generated by the processor 260 is sent by the transmitter 252. It should be noted that "signaling," as used herein, may alternatively be referred to as control signaling.Dynamic signaling may be transmitted on a control channel, e.g., the Physical Downlink Control Channel (PDCCH), and static or semi-static higher layer signaling may be included in packets transmitted on a data channel, e.g., the Physical Downlink Shared Channel (PDSCH).

[0081] The scheduler 253 may be coupled to the processor 260. The scheduler 253 may be included within the T-TRP 170 or may operate separately from the T-TRP 170 and may schedule uplink, downlink, and / or backhaul transmissions, including issuing scheduling grants and / or configuring scheduling-free ("configured grants") resources. The T-TRP 170 further includes a memory 258 for storing information and data. The memory 258 stores instructions and data used, generated, or collected by the T-TRP 170. For example, the memory 258 may store software instructions or modules configured to implement some or all of the functions and / or embodiments described herein and executed by the processor 260.

[0082] Although not shown, the processor 260 may form part of the transmitter 252 and / or the receiver 254. Also, although not shown, the processor 260 may implement the scheduler 253. Although not shown, the memory 258 may form part of the processor 260.

[0083] The processing components of the processor 260, the scheduler 253, and the transmitter 252 and receiver 254 may each be implemented by one or more of the same or different processors configured to execute instructions stored in a memory, such as memory 258. Alternatively, some or all of the processing components of the processor 260, the scheduler 253, and the transmitter 252 and receiver 254 may be implemented using dedicated circuitry, such as an FPGA, a GPU, or an ASIC.

[0084] Although the NT-TRP 172 is shown as a drone by way of example only, the NT-TRP 172 may be embodied in any suitable non-terrestrial form. The NT-TRP 172 may also be known by other names, such as a non-terrestrial node, a non-terrestrial network device, or a non-terrestrial base station, in some implementations. The NT-TRP 172 includes a transmitter 272 and a receiver 274 coupled to one or more antennas 280. Only one antenna 280 is shown. Alternatively, one, some, or all of the antennas may be panels. The transmitter 272 and the receiver 274 may be integrated as a transceiver. The NT-TRP 172 further includes a processor 276 for performing operations, including operations related to preparing a transmission for downlink transmission to the ED 110, processing uplink transmissions received from the ED 110, preparing a transmission for backhaul transmission to the T-TRP 170, and processing transmissions received via the backhaul from the T-TRP 170. Processing operations related to preparing a transmission for downlink or backhaul transmission may include operations such as encoding, modulating, precoding (e.g., MIMO precoding), transmit beamforming, and generating symbols for transmission. Processing operations related to processing received transmissions in the uplink or over the backhaul may include operations such as receive beamforming, demodulation, and decoding of received symbols. In some embodiments, the processor 276 performs transmit beamforming and / or receive beamforming based on beam direction information (e.g., BAI) received from the T-TRP 170. In some embodiments, the processor 276 may generate signaling, for example, to configure one or more parameters of the ED 110. In some embodiments, the NT-TRP 172 performs physical layer processing but does not perform higher layer functions, such as functions at the medium access control (MAC) layer or the radio link control (RLC) layer. This is just one example; more generally, the NT-TRP 172 may perform higher layer functions in addition to physical layer processing.

[0085] The NT-TRP 172 further includes a memory 278 for storing information and data. Although not shown, the processor 276 may form part of the transmitter 272 and / or the receiver 274. Although not shown, the memory 278 may form part of the processor 276.

[0086] The processor 276 and the processing components of the transmitter 272 and receiver 274 may each be implemented by the same or different processor(s) configured to execute instructions stored in a memory, e.g., memory 278. Alternatively, some or all of the processing components of the processor 276 and the transmitter 272 and receiver 274 may be implemented using dedicated circuitry, such as an FPGA, GPU, or ASIC. In some embodiments, the NT-TRP 172 may actually be multiple NT-TRPs operating together to serve the EDs 110, e.g., via coordinated multipoint transmission.

[0087] T-TRP170, NT-TRP172, and / or ED110 may include other components, which have been omitted for clarity.

[0088] One or more steps of the method of the embodiments provided herein may be performed by a corresponding unit or module according to FIG. 4. FIG. 4 illustrates units or modules within a device such as the ED 110, the T-TRP 170, or the NT-TRP 172. For example, a signal may be transmitted by a transmitting unit or a transmitting module. For example, a signal may be transmitted by a transmitting unit or a transmitting module. A signal may be received by a receiving unit or a receiving module. A signal may be processed by a processing unit or a processing module. Other steps may be performed by an artificial intelligence (AI) or machine learning (ML) module. Each unit or module may be implemented using hardware, one or more components or devices that execute software, or a combination thereof. For example, one or more of the units or modules may be a programmed integrated circuit such as an FPGA, a GPU, or an ASIC. When modules are implemented using software for execution by a processor, it will be understood that, for example, the modules may be retrieved by the processor, as a whole or in part, individually or together, in a single instance or multiple instances, for processing as needed, and the modules themselves may include instructions for further deployment and instantiation.

[0089] Further details relating to ED110, T-TRP170, and NT-TRP172 are known to those skilled in the art, and therefore, these details are omitted herein.

[0090] A method for MIMO channel estimation and feedback is provided. The method is first introduced with reference to FIG. 5, followed by a detailed description of an exemplary implementation of the method steps. Block 500 involves generating a channel spatial basis matrix. This can be achieved by collecting several ground-true or quasi-ground-true MIMO channel samples within a target region, vectorizing them, and arranging them into a channel training matrix, each column of which is a vectorized MIMO channel sample. Note that, in this specification, a column represents a vector. Alternatively, a vector can be represented by a row. Mathematically, the two are equivalent to each other. In the following description, a column-wise representation is used. The channel spatial basis matrix can be obtained by constructing the leading columns of a left singular matrix resulting from a rank-reduced singular value decomposition (SVD) on the channel training matrix. Any MIMO channel within the target region can then be approximated by a linear combination of the columns of the channel spatial basis matrix. The leading columns of the left singular matrix, each mathematically called a left singular vector, constitute the channel spatial basis. Therefore, the channel spatial basis matrix is ​​orthonormal.

[0091] Next, in block 502, a basic MIMO reference signal constellation is generated by computing pivot columns on the Hermitian transpose of the channel space basis matrix obtained in block 500, for example, as described in applicant's co-pending patent application 92012665PCT01, which is incorporated herein by reference in its entirety, which discloses a general method for finding a sparse, non-uniform, and deterministic reference signal constellation in a given high-dimensional signal space. In this application, we apply this methodology, which can be used to generate a sparse, non-uniform, and deterministic basic MIMO reference signal constellation for a MIMO channel space.

[0092] Next, in block 504, a transmit MIMO reference signal constellation and a receive MIMO reference signal constellation are obtained. The transmit MIMO reference signal constellation indicates the reference signal locations in the MIMO channel space on the subcarriers and on the transmitting antennas where the reference signals should be transmitted. The corresponding receive MIMO reference signal constellation indicates the reference signal locations in the MIMO channel space on the subcarriers and on the receiving antennas where the reference signals should be received and then measured. In a MIMO transceiver embodiment, the receive MIMO reference signal constellation can include a base portion and an extended portion. The base portion includes all reference signal locations determined by the base MIMO reference signal constellation obtained in the second step 502. The extended portion includes multiple additional reference signal locations, primarily because in a MIMO transceiver, a signal from one transmit antenna is necessarily received by all receive antennas. Thus, one reference signal transmitted from a transmit antenna on a subcarrier becomes multiple reference signals from the transmit antenna on subcarriers but on different receive antennas at the receiving device side. This will be explained in more detail below. When the receiving device sends feedback to the transmitting device so that the transmitting device can estimate the MIMO channel, both the transmitting device and the receiving device must know the same receiving MIMO reference signal constellation being used. Therefore, before MIMO transmission begins, both the receiving device and the transmitting device must align with each other with respect to the receiving MIMO reference signal constellation. In an embodiment of a MIMO transceiver, the transmitting MIMO reference signal constellation is also determined by the basic MIMO reference signal constellation by merging any two reference signal positions that share the same subcarrier and the same transmitting antenna in the basic MIMO reference signal constellation.

[0093] In block 506, the transmitting device transmits reference signals at positions indicated by the transmit MIMO reference signal constellation obtained in the third step 504. Furthermore, in addition to the constellation information, the multiplexing scheme and transmit signal values ​​for each reference signal need to be specified and defined in advance before MIMO transmission begins. The transmit MIMO reference signal pattern includes not only the transmit MIMO reference signal constellation but also the multiplexing scheme and transmit signal values ​​for each reference signal in the transmit MIMO reference signal constellation. In block 508, the receiving device receives and then measures the MIMO channel on the reference signals indicated by the receive MIMO reference signal constellation obtained in the third step 504. Furthermore, in addition to the constellation information, the multiplexing scheme and reference signal values ​​for each reference signal need to be determined. The receive MIMO reference signal pattern includes the receive MIMO reference signal constellation, the multiplexing scheme for each reference signal in the receive MIMO reference signal constellation, and the transmit signal values. In some cases, the receiving device may transmit feedback to the transmitting device based on channel measurements for the reference signals in the receive MIMO reference signal constellation.

[0094] In block 510, the receiving device begins using both channel measurements for reference signals of the receiving MIMO reference signal constellation and prior knowledge represented by a channel spatial basis matrix. The receiving device measures channels on the reference signals according to the receiving MIMO reference signal pattern. The receiving device finds a vector of coefficients such that the channel measurements for the reference signals can be a linear combination of the columns of the channel spatial basis matrix obtained in block 500 weighted by the vector of coefficients. Alternatively, a compact channel spatial basis matrix is ​​employed, in which case in this step the receiver solves a determined or over-determined equation to find a vector of coefficients such that the channel measurements for the reference signals can be a linear combination of the columns of the channel spatial basis matrix obtained in block 500 weighted by the vector of coefficients. Details of the compact channel spatial basis matrix and an exemplary method for determining the compact channel spatial basis matrix are provided below.

[0095] In block 512 , from the vector of coefficients obtained in step 510 and the channel spatial basis matrix, the MIMO channel is estimated by linearly combining the columns of the channel spatial basis matrix with the vector of coefficients obtained in block 510 .

[0096] The described approach includes steps performed by a transmitting device, which can be considered a transmitting method, and steps performed by a receiving device, which can be considered a receiving method. The steps are performed in various scenarios. For example, either the BS or the UE can send the reference signal initially, resulting in different procedures.

[0097] Training Data Collection Before using this technique to propagate MIMO channel estimates, training data is collected or obtained. The training data collection involves collecting a sufficient number (m) of MIMO channel samples in the high-dimensional MIMO channel space as a channel training dataset in the target region. For best results, the MIMO channel samples randomly taken from the target region should cover typical conditions from the target region. Also, m should be much larger than the rank of the historical or empirical channel space basis. In one specific example, a rank five times larger than the historical or empirical channel space basis can be considered much larger.

[0098] All MIMO channel samples in the channel training dataset are in the same dimension or the same MIMO channel space, e.g., in the same set of subcarriers (L), the same number of transmitting antennas (M), and the same number of receiving antennas (N). The MIMO channel samples of each channel are multidimensional, with at least three dimensions (L × N × M). Note that the provided method is open and easily applicable to even higher-dimensional MIMO signal spaces. For example, timing (OFDM symbols or TTIs) can be considered as another dimension. For example, coding (mask codes) can be considered as another dimension. For simplicity, this disclosure uses a three-dimensional MIMO channel space as an example. The advantage of this method is based on prior knowledge, which assumes that there are some persistent and dominant correlations in the MIMO channel space along timing, frequency, space, and / or code. The prior knowledge, represented by a channel space basis matrix, is used to generate a sparse (low-overhead) and non-uniform MIMO reference signal constellation, but also to ensure good MIMO channel estimation performance.

[0099] All MIMO channel samples in the channel training dataset are collected from a target region covered by the same set of BS antennas. For example, the region can be a sector or a subset of a sector covered by the BS. If the target region is covered by more than one set of BS antennas, each set of BS antennas generates its own channel training dataset. A channel training dataset is associated with a region. Different channel training datasets are associated with different regions. The regions may physically overlap or be separated. Correspondingly, prior knowledge constructed from the channel training dataset is associated with the region from which the channel training dataset was collected. Correspondingly, a basic MIMO reference signal constellation constructed from prior knowledge is associated with the region to which the prior knowledge is associated. Correspondingly, both the transmit MIMO reference signal constellation and the receive MIMO reference signal constellation derived from the basic MIMO reference signal constellation are associated with the region to which the basic MIMO reference signal constellation is associated. A large region may include multiple sub-regions (smaller regions), and the training dataset can be divided into multiple sub-datasets accordingly.

[0100] Due to the target region and its unchanging environmental topology, such as buildings, there are some strong and persistent spatial correlations hidden in the channel training dataset, and these correlations, once learned from the channel training dataset, are applicable to the target region, but can also be generalized to apply to target regions and environments similar to those from which the channel training dataset is obtained.

[0101] The channel training data set may be obtained from some actual UEs or signal measurement equipment for random sampling in the target area and specific environment, or may be compiled from actual UE historical MIMO channel estimations in the target area and specific environment, or may be synthesized by modeling the target area and specific environment in a simulator.

[0102] There may be different channel training data sets for the same target area covered by different sets of BS antennas.

[0103] There may be different channel training data sets for different environments or environment-related scenarios of the same target area. For example, a first channel training data set may be obtained for a high-traffic scenario such as daytime, and a second channel training data set may be obtained for a low-traffic scenario such as nighttime. The first and second channel training data sets in this example are for the same target area, e.g., a particular street, covered by the same set of BS antennas.

[0104] The channel training data set may be static, but can be gradually updated, fully or partially, with new MIMO channel samples to follow time-varying changes in the target region and environment.

[0105] The channel training data set can be obtained using a MIMO precoder or can be obtained without using a MIMO precoder, but the channel training data set with a MIMO precoder and the channel training data set without a MIMO precoder are two different training data sets.

[0106] The channel training data set is used to capture (i.e., learn) the spatial commonalities (strong and persistent spatial correlations) of the MIMO channels in the target region.

[0107] Generating a channel training matrix from channel measurement data The m channel measurements are reshaped into a channel training matrix A. The assumption of reciprocal uplink and downlink channels can be applied so that the channel can be used for both the uplink and downlink in TDD (Time Division Duplex) mode. More specifically, each MIMO channel sample in the MIMO three-dimensional channel space (L × N × M) is reshaped into a column-oriented vector of size n × 1, where n = L * M * N. The same reshaping protocol is maintained for all MIMO channel samples in the training dataset. The reshaping protocol is reversible. In one specific example, if each value in the column-oriented vector has a position given by an index number, and each value in the MIMO three-dimensional channel space has a position given by (subcarrier index number, BS antenna index number, UE antenna index number), the index in the column-oriented vector can be associated with a 3D index according to the following formula: index number per channel sample = subcarrier index number * (M * N) + BS antenna index number * N + UE antenna index number. The column-oriented vectors are collocated column by column to form the channel training matrix A, an n × m matrix, as shown in FIG. 6. The order of juxtaposition does not matter.

[0108] Generate channel spatial basis matrix and basic reference signal constellation design The channel training matrix A is then used as input to generate a basic MIMO reference signal constellation, which is a rank-reduced singular value decomposition (SVD) on the channel training matrix A by preserving the r rank, SVD(A) = UΣV H , where the left singular matrix U is an n×r channel spatial basis matrix (orthonormal) that can (linearly) span the MIMO channel space in the target region. The channel spatial basis matrix U can represent prior knowledge of the target region. The rank r can be empirically predefined or determined with respect to the distribution of the resulting singular values. For example, only singular values ​​larger than a threshold may be preserved. The number of preserved singular values ​​is r. An example of rank-reduced SVD(A) is shown in FIG. 7A.

[0109] For a large area, it can be divided into several smaller target areas. Each target area can be assigned a region ID to identify it within the system. These target areas may or may not overlap each other. For each target area, there is a different channel training matrix A corresponding to a different set of BS antennas and a different environment or environment-related scenario. Each channel training matrix A can be assigned a channel training region ID. Generally speaking, a channel training matrix A is associated with a target area (location). This channel training matrix A, along with its channel training region ID, can be stored in the BS or other equipment (e.g., a location detection system).

[0110] If the system decides to update the channel training matrix A, it may require one or more UEs within the target region corresponding to the channel training matrix A to measure new MIMO channel samples. These new MIMO channel samples can be obtained by conventional channel estimation methods, for example, by sending densely spaced, uniformly distributed MIMO reference signals and performing interpolation. Alternatively or additionally, the MIMO channel samples may be acquired with a digital simulator that is synthesized by modeling the target region and the specific environment. These new channel measurements can be reported to the BS or other devices. The system updates the channel training matrix A by adding these new MIMO channel samples to the channel training matrix A or by replacing the oldest channel measurement in the channel training matrix A.

[0111] Each time the channel training matrix A is updated, the channel spatial basis matrix U generated from the channel training matrix A needs to be fully or partially recalculated and updated accordingly.

[0112] Each channel training matrix A is used to generate a corresponding channel spatial basis matrix U. The channel spatial basis matrix U is also associated with a target region. Therefore, each channel spatial basis matrix U derived from that channel training matrix A can be assigned the same unique channel training region ID. The channel spatial basis matrix U with that channel training region ID can be stored together with the channel training matrix A, or can be stored in a different location from the channel training matrix A. The channel spatial basis matrix U can be stored together with its channel training region ID in a BS or other equipment (e.g., a location detection system). A UE may store many different channel spatial basis matrices U and their corresponding channel training region IDs. These channel spatial basis matrices U can be sent to the UE by the BS or other equipment.

[0113] When communication needs to be established between a BS and a UE, it may first be necessary to determine which channel spatial basis matrix U to use. The channel spatial basis matrix U may be selected based on the region to which the UE belongs, the set of BS antennas, and different environments or environment-related scenarios. The location of the UE can be detected by the BS or by other devices (e.g., a location detection sensor in a detection system). When the location of the UE is detected by the BS, the BS can send location information to the UE. When the location of the UE is detected by other devices, the devices can send location information to the BS, to the UE, or to both the BS and the UE. Furthermore, different channel training matrices A and channel spatial basis matrices U associated with different regions can be stored in other devices and sent to the BS or the UE as needed. The location of the UE can also be detected by the UE itself, and the UE can report its location to the BS in the uplink.

[0114] If the location of the UE has been detected, the BS may determine which channel spatial basis matrix U to use along with other parameters, and notify the UE of the channel spatial basis matrix U in unicast, multicast, and broadcast ways in the downlink.

[0115] If the UE knows its own location, stores multiple channel spatial basis matrices U, and has knowledge about how to select the channel spatial basis matrix U, the UE can decide by itself which channel spatial basis matrix U to use along with other parameters. At the same time, with the same UE location information, the BS can independently decide to select the same channel spatial basis matrix U and other parameters. This saves control message transmission overhead before setting up MIMO communication between the BS and the UE.

[0116] If the entire MIMO channel on all subcarriers between all transmitting and receiving antennas is not required, but a subset of the MIMO channel on some subcarriers between some transmitting and receiving antennas is required, a subset U' of U can be used instead of the channel spatial basis matrix U. U is an n x r matrix, and each row of U correlates to data on a subcarrier between the transmitting and receiving antennas. U' can be generated to consist of rows of interest from U in any order. If the complete U is not required, the channel spatial basis matrix U mentioned above can be replaced with U'.

[0117] Identifying the pivot column U H (the Hermitian of U, which is also equal to the conjugate transpose of U). Alternatively, a reduced size U' as introduced above can be used in this step. U H Since the size of is r × n, the r pivot columns are HThe pivot columns can also be considered as the most important columns with respect to the properties of the channel. H An example where a particular column in is designated to be a pivot column is shown in Figure 7B. In mathematics, there are no unique combinations of r pivot columns. One method for identifying pivot columns includes performing the following steps:

[0118] 1. T=U H Take.

[0119] 2. Go through all columns of T one by one and find the column with the largest 2-norm (L2 norm, also called Euclidean norm) as the pivot column.

[0120] 3. Take the pivot column vector generated from step 2 and remove the projection in the direction of this pivot vector from each of the column vectors of T. Mark the new matrix thus generated as a new version of matrix T.

[0121] 4. Repeat steps 2 and 3 until r pivot columns are found.

[0122] Another method for identifying the pivot column includes performing the following steps.

[0123] 1. T=U H Take.

[0124] 2. Set i=1.

[0125] 3. Go through all columns of T one by one and find the column with the largest two-norm, take this vector and define p i Mark as.

[0126] 4. The vector p generated from step 3 i Take this vector p i Calculate the cross-correlation between p and all columns of T one by one. i The real part of the cross-correlation between and the columns of T is pi If the autocorrelation of is greater than a predetermined percentage threshold, record this column vector in pivot column set i.

[0127] 5. The mean vector p of the vectors in the pivot column set i i-avg Calculate.

[0128] 5. The mean vector p generated from step 5 i-avg and remove the projection of each of the column vectors of T onto this mean vector. Mark the new matrix thus produced as a new version of matrix T.

[0129] 6. Add 1 to i, i=i+1.

[0130] 7. Repeat steps 3 through 7 until i is greater than r, i.e., until r pivot column sets have been found.

[0131] 8. Select one vector from each set of pivot columns randomly or according to some rules. These r vectors form one combination of r pivot columns.

[0132] By using this alternative method, many different combinations of r pivot columns can be obtained.

[0133] Besides the two described methods, there are other alternative methods for generating these r pivot columns. Since the combination of r pivot columns is not unique, how to select the optimal combination of pivot columns is important. Therefore, the selection may depend on several criteria, such as:

[0134] 1. Performance of MIMO channel estimation: Different combinations of pivot columns may result in different channel estimation performance. Usually, the combination that performs better is preferred.

[0135] 2. Description Complexity: Because the selection of these r pivot columns is not uniform, describing one combination from a specification perspective may be easier than describing another combination. In wireless systems, both the sender and receiver should typically be informed of the RS combination in a control message. For example, a particular combination may be selected based on the fact that it can be described more compactly than other combinations. As another example, if the sender or receiver has already recorded a combination of RSs, a new combination of RSs may be selected based on the minimum update required compared to the already recorded combination of RSs.

[0136] Obviously, if the basic MIMO reference signal constellation is calculated from the same channel spatial basis matrix U at both the transmitting and receiving devices, the method for calculating the pivot columns must be the same at both sides. Some indication or signaling is used to align the methods for calculating the pivot columns at both the transmitting and receiving devices.

[0137] Therefore, the combination of these r pivot columns can be selected as a function of channel estimation performance and / or description complexity. Each pivot column corresponds to a pivot position, which can be indicated as a row index of U. According to the reshaping protocol, the pivot position indicates a specific subcarrier between a specific transmitting antenna and a specific receiving antenna in the original 3D MIMO channel space. The r pivot positions are incomplete.

[0138] The positions in the basic MIMO reference signal constellation are generated based on the r pivot positions. Recall that each pivot position in the vector is a one-to-one indicator of a position pointing to a specific subcarrier, a specific transmitting antenna, and a specific receiving antenna in the original three-dimensional MIMO channel space. The r pivot positions are the basic MIMO reference signal constellation.

[0139] There are several ways to describe the basic MIMO reference signal constellation. For example, the basic MIMO reference signal constellation can be described in a table format. Alternatively, the basic MIMO reference signal constellation can be described in a constellation matrix P, which has n columns and r rows. The order of the columns is the same as the order of the rows in the associated channel spatial basis matrix U. Each row of P represents a pivot position, i.e., a reference signal position. Note that each row contains only "1"s, which indicate one basic reference signal position. The column index of each "1" in each row indicates a specific subcarrier between a specific transmitting antenna and a specific receiving antenna, as shown in Figure 8.

[0140] If the system generates a basic MIMO reference signal constellation and the UE requests this information, the BS can send it to the UE in a unicast, multicast, or broadcast transmission in the downlink.

[0141] Under some conditions, the system predefines a method for generating a basic MIMO reference signal constellation from the channel spatial basis matrix U when the transmitting device and the receiving device have the same channel spatial basis matrix U. In the same manner, both devices can separately and independently calculate the same basic MIMO reference signal constellation. Under some conditions, the system may have multiple sets of reference signal positions in the specification as constituent reference signal constellations. Each constituent reference signal constellation includes multiple reference signal positions indicated by a subcarrier index, a transmitting antenna index, and a receiving antenna index. These indexes can be absolute or relative, with the latter being relative to some offset. The basic MIMO reference signal constellation can be approximated by a combination of several constituent reference signal constellations. If both the transmitting device and the receiving device have all or part of the constituent reference signal constellations, the basic MIMO reference signal constellation can be generated by combining several constituent reference signal constellations. Therefore, only information regarding how to combine the constituent reference signal constellations to generate the basic MIMO reference signal constellation is communicated between the transmitting device and the receiving device.

[0142] In a MIMO transceiver system, when a reference signal is transmitted from one transmitting antenna on one subcarrier, the reference signal is received by all receiving antennas on the subcarrier. In this case, the reference signal position in the basic MIMO reference signal constellation, which indicates the subcarrier, transmitting antenna, and receiving antenna, has different meanings for the transmitting device and the receiving device. The reference signal position in the transmit MIMO reference signal constellation indicates the subcarrier and transmitting antenna. The reference signal position in the receive MIMO reference signal constellation indicates the subcarrier, transmitting antenna, and receiving antenna. From the same basic MIMO reference signal constellation, the transmitting device generates a transmit MIMO reference signal constellation, and the receiving device generates a receive MIMO reference signal constellation. Alternatively, the transmitting device generates a transmit MIMO reference signal constellation from the basic MIMO reference signal constellation, and the receiving device generates a receive MIMO reference signal constellation from the transmit MIMO reference signal constellation.

[0143] In some embodiments, starting from the basic MIMO reference signal constellation, further processing is performed to generate a transmit MIMO reference signal constellation for the transmitting device and a receive MIMO reference signal constellation for the receiving device. Referring back to the specific example of FIG. 8, the basic MIMO reference signal constellation represented by the constellation matrix P in FIG. 8 indicates (among other channel measurements) a first reference signal transmitted and received on the lth subcarrier from transmitting antenna #m to receiving antenna #n, and a second reference signal transmitted and received on the same subcarrier and the same transmitting antenna but a different receiving antenna #j (j ≠ m). However, the two reference signals collide in the air. Therefore, transmission of the second reference signal symbol in this example is unnecessary and can be merged with the first reference signal. The transmitting device transmits one reference signal on the lth subcarrier from transmitting antenna #m. This reference signal position is included in the transmit MIMO reference signal constellation. The receiving device receives two reference signals on the lth subcarrier from receiving antenna #m and receiving antenna #j. Furthermore, the receiving device can select to receive more than two reference signals on the lth subcarrier of the transmitting antenna #m from up to all receiving antennas. This increases the number of reference signals at the receiving device and is called an extended reference signal. (The term "extension" refers to a mathematical term describing the extension from a determined equation to an overdetermined equation.) The extended reference signal is included in the extended portion of the receiving MIMO reference signal constellation. Generally, from a basic MIMO reference signal constellation, a transmitting MIMO reference signal constellation is obtained by merging any two reference signal positions of the basic MIMO reference signal constellation that share the same subcarrier and the same transmitting antenna but have different receiving antennas. A receiving MIMO reference signal constellation is obtained by extending one reference signal position of the basic MIMO reference signal constellation to multiple reference signal positions with the same subcarrier and the same transmitting antenna but different receiving antennas. Alternatively, a receiving MIMO reference signal constellation is obtained by extending one reference signal position of the transmitting MIMO reference signal constellation to multiple reference signal positions with the same subcarrier and the same transmitting antenna but different receiving antennas.Therefore, the basic MIMO reference signal constellation obtained directly from the pivot sequence must be modified into a MIMO channel space that generates one transmit MIMO reference signal constellation and one receive MIMO reference signal constellation.

[0144] Derived from the same basic MIMO reference signal constellation represented by the constellation matrix P, the transmit MIMO reference signal constellation is P TX and the receiver's MIMO reference signal constellation is P -RX Besides the matrix form, they can also be represented in other forms such as tables.

[0145] Mathematically, the transmit MIMO reference signal constellation (P TX ) is generated by merging any two reference signal positions in the basic MIMO reference signal constellation (P) with the same subcarrier and transmitting antenna but different receiving antennas.

[0146] In addition to the transmit MIMO reference signal constellation generated from the basic MIMO reference signal constellation, the system may define several complementary reference signal positions in addition to the basic MIMO reference signal constellation or the transmit MIMO reference signal constellation. The complementary reference signal positions may help improve MIMO channel estimation performance and / or facilitate describing the basic MIMO reference signal constellation, the transmit MIMO reference signal constellation, and / or the receiver-side MIMO reference signal constellation.

[0147] If the system generates a transmit MIMO reference signal constellation and the UE requests this information, the BS can inform the UE of the information in a unicast, multicast, or broadcast transmission in the downlink.

[0148] In some conditions, the system predefines a base-based transmission constellation generation method for generating a transmission MIMO reference signal constellation from a basic MIMO reference signal constellation.When a transmitting device and a receiving device have the same base MIMO reference signal constellation and each knows the same base-based transmission constellation generation method, they can separately generate the same transmission MIMO reference signal constellation.

[0149] In some cases, the system defines multiple base transmission configuration generation methods and a method for selecting one base transmission configuration generation method under certain conditions. The system can also select and apply one base transmission configuration generation method during runtime. When a reference signal is transmitted by a UE as a transmitting device, first, the transmitting device must have a base transmission configuration generation method defined in the specification and stored in the UE. The base transmission configuration generation method can be sent to the UE as a transmitting device from a BS as a receiving device, or from other equipment. Second, as a transmitting device, the UE needs to know which base transmission configuration generation method to use for subsequent transmissions. This can be selected by the UE as a transmitting device based on the method for selecting one base transmission configuration generation method, as previously specified. The base transmission configuration generation method can also be selected by the BS as a receiving device, which sends the selected base transmission configuration generation method to the UE as a transmitting device. A method for selecting one base-based transmission configuration generation method to use can also be sent from the BS as the receiving device to the UE as the transmitting device, or other equipment for the UE as the transmitting device can select a base-based transmission configuration generation method based on which it can generate a transmission MIMO reference signal configuration from the base MIMO reference signal configuration.

[0150] To generate a transmit MIMO reference signal constellation from the selected base-based transmit constellation generation method, a base MIMO reference signal constellation or a channel spatial basis matrix U is required.

[0151] In some conditions, the system may define a set of reference signal positions in the specification as constituent reference signal constellations. Each constellation includes several reference signal positions indicated by a subcarrier index and a transmitting antenna index. These indexes can be absolute or relative to some offset that can be defined later. A transmit MIMO reference signal constellation can be represented by combining several constituent reference signal constellations. Both the transmitting device and the receiving device store all or part of these constituent reference signal constellations. After the transmit MIMO reference signal constellation is generated, a combination of several sets of these reference signal positions can be calculated to approximate the transmit MIMO reference signal constellation as closely as possible. Then, instead of signaling the transmit MIMO reference signal constellation, only information on how to combine the transmit MIMO reference signal constellation from the constituent reference signal constellation is required. In such a case, the UE as the transmitting device and the BS as the receiving device can send instructions on how to combine the transmit MIMO reference signal constellation and which constituent reference signal constellation to combine in a unicast, multicast, or broadcast transmission in the downlink.

[0152] When it is time to transmit a reference signal, a transmit MIMO reference signal pattern is used by the transmitting device to transmit the reference signal on actual physical resources in the MIMO channel space. The transmit MIMO reference signal pattern not only indicates which transmitting antenna the transmitting device will transmit each reference signal via and on which subcarrier(s) it will transmit each reference signal, but also assigns predefined transmit signal values ​​for each reference signal and multiplexing schemes, such as OFDM symbols for timing multiplexing and mask codes for coding multiplexing, for each reference signal. The transmit MIMO reference signal pattern includes not only the transmit MIMO reference signal constellation, but also the transmit signal values ​​and multiplexing schemes for each reference signal in the transmit MIMO reference signal constellation.

[0153] A typical example of a transmit MIMO reference signal pattern is shown in Figure 7C. The transmit MIMO reference signal pattern includes several multiplexing schemes to avoid reference signal collisions in the air. In the example of Figure 7C, the transmit MIMO reference signal configuration requests that a first reference signal be transmitted on subcarrier -l on transmitter antenna #m, a second reference signal be transmitted on subcarrier -l on transmitter antenna #n, and a third reference signal be transmitted on subcarrier -(l+1) on transmitter antenna #p. Resource contention exists between the first and second reference signals on subcarrier -l of antenna #m and antenna #n. To resolve this, the transmit MIMO reference signal pattern may apply a timing multiplexing scheme to both the first and second reference signals. The first OFDM symbol transmits the first reference signal on subcarrier -l and transmitter antenna m, and the second OFDM symbol transmits the second reference signal on subcarrier -l and transmitter antenna n. The multiplexing scheme for the transmit MIMO reference signal pattern may include frequency multiplexing, time multiplexing, code multiplexing, etc. If the system generates a transmit MIMO reference signal pattern and the UE needs this information, the BS can send the information to the UE by unicast, multicast, or broadcast in the downlink.

[0154] In some conditions, the system may predefine a pattern generation method from a transmit constellation for generating a transmit MIMO reference signal pattern from the transmit MIMO reference signal constellation, in which case, when a transmitting device and a receiving device have the same transmit MIMO reference signal constellation and the same pattern generation method from the transmit constellation, they can separately generate the same transmit MIMO reference signal pattern.

[0155] The system can define pattern generation methods from multiple transmit constellations and a method for selecting which pattern generation method from the transmit constellations to use under specific conditions. The pattern generation method from the transmit constellations defines the transmit signal value and multiplexing scheme for each reference signal in the transmit MIMO reference signal constellation based on parameters such as user ID, antenna index, transmit comb number, and cyclic shift. The system can also select which pattern generation method from the transmit constellation to use during runtime. These pattern generation methods from the transmit constellation can be stored in the BS and the UE. When a reference signal is transmitted by the UE as a transmitting device, the UE needs to have a transmit MIMO reference signal pattern. The UE can generate a transmit MIMO reference signal pattern by assigning a transmit signal value and multiplexing scheme to each position in the transmit MIMO reference signal constellation according to the pattern generation method from the selected transmit constellation. How the UE obtains the transmit MIMO reference signal constellation is described in the previous section. Regarding the selected pattern generation method from the transmit constellation, the UE may store pattern generation methods from multiple transmit constellations and a method for selecting which pattern generation method from the transmit constellation to use. For example, a specification may define a pattern generation method from a plurality of transmit constellations and a method for selecting which pattern generation method from which transmit constellations to use. The UE may generate a transmit MIMO reference signal pattern based on the method for selecting which pattern generation method from which transmit constellations to use according to current conditions. When the pattern generation method from the transmit constellations to use is selected, both transmitting devices may use the pattern generation method from the transmit constellations to generate a transmit MIMO reference signal pattern from the transmit MIMO reference signal constellations.

[0156] All receiving antennas of the receiving device can receive the reference signal transmitted from one transmitting antenna on a subcarrier. For reference signals transmitted on a subcarrier, the receiver may choose to measure the channel on all receiving antennas or a subset of receiving antennas. Regarding the entire MIMO channel space, which (one or more) receiving antennas are selected by the receiving device to measure the channel are included in the receiving MIMO reference signal constellation according to the transmitting MIMO reference signal constellation or the basic MIMO reference signal constellation. The total number of all reference signals selected by the receiving device is denoted as o. The reference signal by the receiving device is transmitted from one transmitting antenna to one receiving antenna on a subcarrier, and the reference signal by the transmitting device is transmitted from one transmitting antenna on a subcarrier.

[0157] Because MIMO channel estimation utilizes the channel spatial basis matrix U, the receiver's MIMO reference signal constellation must include at least the basic MIMO reference signal constellation. The number of reference signals in the basic MIMO reference signal constellation is r. The basic MIMO reference signal constellation is the minimum set of reference signals for the receiver device to estimate the MIMO channel. Because all receiver antennas can receive the reference signal transmitted from one transmitter antenna on one subcarrier, the receiver device can acquire received signals on more receiver antennas than the transmitter antenna on subcarriers to measure the channel. Therefore, the receiver device selects o reference signals greater than or equal to r. Mathematically, when doing so (o>r), the receiver device expands the determined equation to an overdetermined equation, so that the MIMO channel estimation performance is enhanced.

[0158] An extension method for increasing the number of reference signals from r to o at the receiving device.

[0159] 1. If a transmitting device transmits a reference signal from one transmitting antenna on a subcarrier, a receiving device can receive signals from all receiving antennas on the subcarrier. The receiving device can choose to treat all or a subset of the received signals as its reference signal.

[0160] 2. If a receiving antenna is required to measure reference signals on specific subcarriers dictated by the basic MIMO reference signal constellation, it may, as a bonus, be required to measure on other subcarriers within the same OFDM symbol in which other reference signals are transmitted. The selected reference signals must include all positions in the basic MIMO reference signal constellation, or else they will be underdetermined.

[0161] The receiver's MIMO reference signal constellation can be divided into a base part containing all reference signal positions in the basic MIMO reference signal constellation and an extended part containing extra selected reference signals.

[0162] If the receiving device measures the channel on the reference signals defined by the basic MIMO reference signal constellation, only minimum MIMO channel estimation performance is guaranteed. If the receiver starts measuring the reference signals in the extended part, the MIMO channel estimation performance can be enhanced. The receiver MIMO reference signal constellation is defined by the constellation matrix P Rx More generally, it can be expressed in a similar format to the constellation matrix P of the basic MIMO reference signal constellation as a matrix with n columns and o rows. The column order is the same as the row order of the channel spatial basis matrix U. P Rx Each row of represents a reference signal over which the channel is measured. A column index of "1" in each row indicates that the reference signal on a specific subcarrier between a specific transmitting antenna and a specific receiving antenna is to be measured. Rx An example is shown in FIG.

[0163] If the receiving device can change the extension part of the receiving MIMO reference signal constellation, P Rxis detected by the receiving device by deleting rows with column index "1" whose corresponding reference signal is not used and / or adding rows with column index "1" whose corresponding reference signal is used. Rx-update Note that the basic part of the MIMO reference signal constellation on the receiving side must remain the same.

[0164] The receiver-side MIMO reference signal constellation can also be represented in tabular form.

[0165] If the system generates a receiver MIMO reference signal constellation and the UE needs this information, the BS can send it to the UE in a unicast, multicast, or broadcast transmission in the downlink.

[0166] In some conditions, the system may predefine a receiver constellation generation method from a base for generating a receiver MIMO reference signal constellation from a basic MIMO reference signal constellation, in which, when a transmitting device and a receiving device have the same basic MIMO reference signal constellation, they can separately generate the same receiver MIMO reference signal constellation.

[0167] In some conditions, the system may predefine a transmit-to-receive constellation generation method for generating a receive-side MIMO reference signal constellation from a transmit MIMO reference signal constellation, in which case, when a transmitting device and a receiving device have the same transmit MIMO reference signal constellation, they can separately generate the same receive-side MIMO reference signal constellation.

[0168] In some conditions, the receiving device may generate a receiving MIMO reference signal constellation from the transmitting MIMO reference signal constellation taking into account its own factors. For example, the receiving device may generate a receiving MIMO reference signal constellation that includes only the base part. Alternatively, the receiving device may generate a receiving MIMO reference signal constellation that includes both the base part and the extended part. If the receiving device needs to feed back channel measurements for reference signals in the receiving MIMO reference signal constellation to the transmitting device, the transmitting device needs to know the receiving MIMO reference signal constellation to estimate the MIMO channel. The receiving device needs to inform the transmitting device of the receiving MIMO reference signal constellation before MIMO transmission begins.

[0169] In some conditions, a base-based receiver constellation generation method for generating a receiver MIMO reference signal constellation from a base MIMO reference signal constellation can be defined. The system can define multiple base-based receiver constellation generation methods and / or a method for selecting which base-based receiver constellation generation method to use under specific conditions. The system can also determine which base-based receiver constellation generation method to use during runtime. When a reference signal is received by a UE as a receiving device, the UE needs to have a receiver MIMO reference signal constellation. The UE can generate this receiver MIMO reference signal constellation from the base MIMO reference signal constellation and the selected base-based receiver constellation generation method. How the UE can obtain the base MIMO reference signal constellation is described in the previous section. Regarding the base-based receiver constellation generation method, the UE may store the base-based receiver constellation generation method and a method for selecting which base-based receiver constellation generation method to use, as defined in the specification. The UE can generate a receiver MIMO reference signal constellation based on this stored information and the base-based receiver constellation generation method with reference to the current conditions. If the system determines the base-to-base receiver configuration generation method to use, the UE may have this information sent to it from the BS or other network side equipment.

[0170] Under some conditions, a transmit-to-receiver constellation generation method for generating a receiver MIMO reference signal constellation from a transmit MIMO reference signal constellation can be defined. The system can define multiple transmit-to-receiver constellation generation methods and a method for selecting which transmit-to-receiver constellation generation method to use under specific conditions. The system can also determine which transmit-to-receiver constellation generation method to use during runtime. If the reference signal is received by the UE as a receiving device, the UE needs to have a receiver MIMO reference signal constellation. The UE can generate these receiver MIMO reference signal constellations from the transmit MIMO reference signal constellation and the transmit-to-receiver constellation generation method. How the UE can obtain the transmit MIMO reference signal constellation is described in the previous section. Regarding the transmit-to-receiver constellation generation method, the UE may store multiple transmit-to-receiver constellation generation methods and a method for selecting which transmit-to-receiver constellation generation method to use, as defined in the specification. The UE can generate a receiver MIMO reference signal constellation based on the stored information and a method that references the current conditions. If the system determines which receiver constellation generation method to use, the UE may have this information transmitted to it from the BS or other network side equipment. In one example, a system-defined receiver constellation generation method from one transmit can be described as measuring on all receiver antennas.

[0171] In some conditions, the system may define multiple sets of receiver reference signal positions in the specification as constituent receiver reference signal constellations. Each constellation includes several reference signal positions indicated by a subcarrier index and a receiver antenna index. (Constituent reference signal constellations are for transmission and include several reference signal positions indicated by a subcarrier index and a transmitter antenna index.) These indexes can be absolute indexes or relative indexes with some offset that can be defined later. A receiver MIMO reference signal constellation can be represented by combining constituent receiver reference signal constellations. Both the BS and the UE store all or part of the constituent receiver reference signal constellations. Once a receiver MIMO reference signal constellation is generated, a combination of several constituent receiver reference signal constellations can be calculated to approximate the receiver MIMO reference signal constellation as closely as possible. When selecting how to combine several sets of constituent receiver reference signal constellations, several other complementary reference signal positions can be included. A new receiver MIMO reference signal constellation can be a combination of constituent receiver reference signal constellations. When the UE as a receiving device measures the channel on the reference signal, the BS as a transmitting side can send an indication of which constituent receiver reference signal configurations constitute the receiver MIMO reference signal configuration in a unicast, multicast, or broadcast transmission in the downlink.

[0172] When it is time to measure the channel on the reference signal, the receiver MIMO reference signal pattern includes the receiver MIMO reference signal constellation, transmit signal value, and (de)multiplexing scheme for each reference signal. For example, a reference signal transmitted on a specific subcarrier between a specific transmitter antenna and a specific receiver antenna is described in the transmit MIMO reference signal pattern as on which subcarrier, in which OFDM symbol, and at which signal value this reference signal is transmitted. Correspondingly, a corresponding receiver MIMO reference signal pattern can be derived from the transmit MIMO reference signal pattern to indicate which receiver antenna and which OFDM symbol measure the reference signal.

[0173] If the system generates a receiver MIMO reference signal pattern and the UE needs this information, the BS can send it to the UE via unicast, multicast, or broadcast in the downlink.

[0174] Under some conditions, the receiver can generate a receiver MIMO reference signal pattern from the receiver MIMO reference signal constellation using a defined receiver constellation pattern generation method. This receiver constellation pattern generation method may refer to the transmit signal values ​​and (de)multiplexing scheme for each reference signal in the receiver MIMO reference signal constellation. How to obtain the receiver MIMO reference signal constellation is introduced in the previous section.

[0175] In some conditions, the receiver can generate a receiver MIMO reference signal pattern from the transmit MIMO reference signal pattern and the receiver MIMO reference signal constellation. The principle of this generation method is described in the previous section. How to obtain the transmit MIMO reference signal pattern and the receiver MIMO reference signal constellation is also introduced in the previous section.

[0176] In some conditions, the system may define multiple receiver constellation pattern generation methods and a method for selecting which receiver constellation pattern generation method to use under certain conditions. The receiver constellation pattern generation method may define the transmit signal value and demultiplexing scheme for each reference signal in the receiver MIMO reference signal constellation based on parameters such as the UE ID, antenna index, transmit comb number, and cyclic shift. The system may also determine which receiver constellation pattern generation method to use during runtime. These receiver constellation pattern generation methods may be stored in the BS and the UE. When a reference signal is received by the UE as a receiving device, the UE needs to have a receiver MIMO reference signal pattern. The UE may generate this receiver MIMO reference signal pattern from the receiver MIMO reference signal constellation in a receiver constellation pattern generation method. How the UE can obtain the receiver MIMO reference signal constellation is described in the previous section. Regarding the receiver constellation pattern generation method, the UE may define multiple receiver constellation pattern generation methods, and the method for selecting which receiver constellation pattern generation method to use may be stored and / or defined in a specification. The UE can generate a receiving MIMO reference signal pattern based on this information according to the current conditions. If the selection of the receiving MIMO reference signal pattern mapping protocol to be used is determined by the system, the UE may have this information transmitted from the BS or other network side equipment to the UE.

[0177] In some conditions, the system may pre-generate transceiver MIMO reference signal pattern parameters (e.g., transmit MIMO reference signal pattern, receive MIMO reference signal pattern) for a target area or several target areas. The BS and UE may then generate the corresponding channel spatial basis matrix U and compact channel basis θ. aug (

number

[0178] Compact channel basis Based on the channel basis matrix U, but including only elements for which channel measurements are made, a compact channel basis can be generated. If a reference signal is sent by the BS, the compact channel basis can be determined as follows:

[0179] 1. Generate a receiver MIMO reference signal constellation from the basic MIMO reference signal constellation as detailed above. The generated reference signal positions are stored in a table or matrix format P Rx If the receiving device changes more reference signals in the extended part of the receiving MIMO reference signal constellation, P Rx P accordingly Rx-update needs to be updated to.

[0180] 2. A compact channel basis θ as follows: aug Calculate. θ aug =P Rx *U Alternatively, when the receiving device modifies more reference signals in the extended part of the receiving MIMO reference signal constellation, the following occurs: θ aug =P Rx-update *U

[0181] 3. Compact channel basis θ aug The left inverse of

number

[0182] As shown in Figure 10, θ augis an o×r matrix. θ aug is a column-full rank matrix, and o is always greater than or equal to r, so its left inverse is unique,

number

[0183] If the RS is sent by the UE, then the compact channel basis may be determined as follows:

[0184] 1. Generate a receiver-side MIMO reference signal constellation from the basic MIMO reference signal constellation. The generated reference signal positions are stored in a table format or a matrix format P Rx When the BS changes the reference signal in the extended part of the receiver's MIMO reference signal arrangement, P Rx P accordingly Rx-update needs to be updated to.

[0185] 2. A compact channel basis θ as follows: aug Calculate. θ aug =P Rx *U Or, when the BS changes the reference signal in the extended part of the receiving side MIMO reference signal constellation, θ aug =P Rx-update *U

[0186] 3. Compact channel basis θ aug The left inverse of

number

[0187] Under some conditions, there are some compact channel bases θ associated with the channel spatial basis matrix U. aug and their left inverse matrices

number

number

[0188] If communication is to be established between the BS and the UE, and the channel spatial basis matrix U and some basic parameters (such as the receiver MIMO reference signal constellation) are defined, then the associated compact channel basis θ aug and / or its left inverse

number

[0189] The channel measurements can then be transformed into linear combinations of vectors in the compact channel basis, and the coefficients of the linear combinations of vectors in the compact channel basis can be transformed back into channel measurements. These steps can be performed at the transmitting device or the receiving device in different embodiments, as detailed below.

[0190] To generate a linear combination of vectors in a compact channel basis, the following steps are performed.

[0191] 1. The receiving device performs channel measurements for reference signal positions indicated by the receiving MIMO reference signal constellation, and the estimated channel coefficients form a column-oriented vector y of channel measurements for the reference signals. y is an o×1 vector. Each entry of y is a channel measurement for a position indicated by the receiving MIMO reference signal constellation.

[0192] 2. y and θ aug Based on this, the linear combination vector a is

number

[0193] 3. The receiver may choose not to measure on all receiver MIMO reference signal constellations, and the size of the channel measurement value y for the reference signal is less than o × 1. Meanwhile, θ aug is also updated to match the actual measurements taken by the receiver. For example, if there are only p RS measurements taken by the receiver, then y will be of size p × 1, and θ aug The size of is r×p.

[0194] To estimate the MIMO channel from the coefficients of a linear combination of vectors in the compact channel basis, y is expressed as θ aug It can also be seen that it can be considered to be generated from *a.

[0195] In the method disclosed in 92012665PCT01, the pivot columns taken from U form a full rank r × r square matrix θ. Because θ is a full rank square matrix, its inverse exists and is unique.

[0196] In the method of the present disclosure, more receiver device antennas can be configured to measure and report the reference signals sent by the transmitter device. The receiver MIMO reference signal constellation set increases in size to o, which is larger than r. Under this condition, θ is θ aug θ aug is a slender column-rank matrix. aug The left inverse of

number

[0197] Approximated channel measurements on L subcarriers between the BS and the UE with knowledge of a and U

number

number

[0198] Overall channel estimation (

number

number

number

number

number

number

number

[0199] In the first procedure option, the BS sends a reference signal and the UE reports y. The procedure is as follows:

[0200] i. The location of the UE is detected. As described in the previous section, the channel spatial basis matrix U with the channel training region ID to be used for the current communication is determined.

[0201] ii. The BS obtains the following information about the target region and environment: the channel spatial basis matrix U, the transmit MIMO reference signal constellation, and the transmit MIMO reference signal pattern. This information can be generated by the BS or forwarded to the BS by other devices. How to obtain or generate this information is described in the previous section.

[0202] iii. The UE obtains the following information: a receiver MIMO reference signal constellation and a receiver MIMO reference signal pattern. This information or information necessary to generate this information can be sent to the UE by the BS or other devices. For example, the transmit MIMO reference signal pattern and the receiver MIMO reference signal constellation can be sent to the UE to generate the receiver MIMO reference signal pattern. The UE generates the receiver MIMO reference signal pattern as described in the previous section. The UE may also determine which extended reference signal position in the receiver MIMO reference signal constellation to use for channel measurements on the reference signal, taking into account its own factors.

[0203] iv. The BS sends a reference signal based on the transmit MIMO reference signal pattern.

[0204] v. The UE receives and measures the channel at the reference signal positions indicated by the receiver MIMO reference signal pattern to generate channel measurements for reference signal y.

[0205] vi. The UE reports y to the BS. If the UE measures only some of the reference signal positions indicated by the receiver's MIMO reference signal constellation, the UE also reports to the BS at which reference signal positions (receiver's MIMO reference signal constellation) it measured the channel.

[0206] vii.BS receives y and generates a compact channel basis θ aug , a and

number

[0207] In the second procedure option, the UE transmits the RS. The procedure is as follows:

[0208] i. The location of the UE is detected. As described in the previous section, the channel spatial basis matrix U with the channel training region ID to be used for the current communication is determined.

[0209] ii. The BS obtains the following information about the target region and environment: the channel spatial basis matrix U, the compact channel basis θ aug , the receiver's MIMO reference signal constellation, and the receiver's MIMO reference signal pattern are obtained. This information can be generated by the BS or transmitted to the BS by other devices. How to obtain or generate this information is described in the previous section.

[0210] iii. The UE obtains the following information: a transmit MIMO reference signal constellation and a transmit MIMO reference signal pattern. This information or information required to generate this information can be sent to the UE by the BS or other devices. For example, a transmit MIMO reference signal constellation can be sent to the UE to generate a transmit MIMO reference signal pattern. How to obtain or generate this information is described in the previous section.

[0211] iv. The UE sends the RS.

[0212] v. The BS measures the RS at a position indicated by the receiver's MIMO reference signal pattern or receiver's MIMO reference signal configuration information to generate y, and

number

[0213] In the third procedure option, the BS sends RS and the UE reports a or a subset of a. The procedure is as follows:

[0214] i. The location of the UE is detected. As described in the previous section, the channel spatial basis matrix U with the channel training region ID to be used for the current communication is determined.

[0215] ii. The BS obtains the following information about the target region and environment: the channel basis matrix U, the transmit MIMO reference signal constellation, and the transmit MIMO reference signal pattern. This information can be generated by the BS or forwarded to the BS by other devices. How to obtain or generate this information is described in the previous section.

[0216] viii. The UE receives the following information: the receiver MIMO reference signal constellation, the receiver MIMO reference signal pattern, and the compact channel basis θ aug or its left inverse

number

number

[0217] iii. The BS sends the RS based on the transmit MIMO reference signal pattern.

[0218] iv. The UE receives and measures the RSs at the locations indicated by the receiver's MIMO reference signal pattern and / or receiver's MIMO reference signal configuration information to generate channel measurements for RS y.

number

[0219] v. The UE reports a to the BS.

[0220] vi.BS receives a,

number

[0221] In the fourth procedure option, the BS sends RS and the UE reports a or a subset of a, and both the BS and the UE

number

[0222] vii. The location of the UE is detected. As described in the previous section, the channel spatial basis matrix U with the channel training region ID to be used for the current communication is determined.

[0223] viii. The BS obtains the following information about the target region and environment: the channel basis matrix U, the transmit MIMO reference signal constellation, and the transmit MIMO reference signal pattern. This information can be generated by the BS or forwarded to the BS by other devices. How to obtain or generate this information is described in the previous section.

[0224] ix. The UE obtains the following information: a receiver MIMO reference signal constellation, a receiver MIMO reference signal pattern, and a channel spatial basis matrix U. This information or information necessary to generate this information can be sent to the UE by the BS or other devices. For example, the UE generates a receiver MIMO reference signal pattern based on the transmit MIMO reference signal pattern and the receiver MIMO reference signal constellation. In another example, the UE derives a compact channel basis θ from U and the receiver MIMO reference signal permutation. aug How to obtain or generate this information is explained in the previous section.

[0225] ix. The BS sends a reference signal based on a transmit MIMO reference signal pattern.

[0226] x. The UE receives and measures RSs at reference signal positions indicated by the receiver's MIMO reference signal pattern and receiver's MIMO reference signal configuration information to generate channel measurements for RS y.

number

number

[0227] xi. The UE reports a or a subset of a to the BS.

[0228] xii. The BS receives a, or a subset of a,

number

[0229] In the fifth procedure option, the UE sends RS, the BS reports a or a subset of a to the UE, and both the BS and the UE receive the same

number

[0230] i. The location of the UE is detected. As described in the previous section, the channel spatial basis matrix U with the channel training region ID to be used for the current communication is determined.

[0231] ii. The BS obtains the following information about the target region and environment: the channel basis matrix U, the compact channel basis θ aug , obtain the receiver's MIMO reference signal constellation and receiver's MIMO reference signal pattern. This information can be generated by the BS or forwarded to the BS by other network side devices. How to obtain or generate this information is described in the previous section.

[0232] iii. The UE obtains the following information: transmit MIMO reference signal constellation, transmit MIMO reference signal pattern, and channel spatial basis matrix U. This information or information required to generate this information can be sent to the UE by the BS or other network side equipment. For example, the transmit MIMO reference signal constellation can be sent to the UE to generate the receive side MIMO reference signal pattern. How to obtain or generate this information is described in the previous section.

[0233] iv. The UE sends a reference signal.

[0234] v. The BS measures the channel at the reference signal position indicated by the receiver's MIMO reference signal pattern and the receiver's MIMO reference signal arrangement information to generate y, and

number

[0235] vi. The BS sends a or a subset of a to the UE.

[0236] vii.UE is a and U

number

[0237] If the entire set of channel measurements on all subcarriers between all transmitting and receiving antennas is not needed, but a subset of channel measurements on some subcarriers between some transmitting and receiving antennas, a subset U' of U can be used instead of the channel spatial basis matrix U. If U is not needed, the channel spatial basis matrix U mentioned in the previous section can be replaced by U'.

[0238] This application provides a new method for MIMO channel estimation in MIMO systems of arbitrary dimensions, especially in ultra-high dimensional T-MIMO systems.

[0239] A conventional method for solving MIMO channel estimation is to transmit a uniformly distributed reference signal constellation known to both the transmitter and receiver. When the receiver receives the reference signal, it compares the received signal with the known transmitted reference signal to measure the channel condition at the reference signal location. For locations where no reference signal is present, there are many conventional algorithms (e.g., interpolation algorithms) that can be used to calculate the channel condition.

[0240] The provided method differs from conventional channel estimation in at least the following aspects.

[0241] 1. The provided method includes a training procedure (not deep learning based on stochastic gradients) in which channel measurements within the target region are obtained before setting up the reference signal.

[0242] 2. Unlike 5G NR, where reference signals are uniformly and densely arranged, the provided reference signal design may be very sparse and non-uniform in time-frequency code resources.

[0243] 3. In the provided method, the channel spatial basis matrix (U) is different for different target regions and environments. Any channel measurement in the target region and environment is a linear combination of the channel spatial basis matrix (U). The RS is used to calculate the channel as a linear combination vector applied on the channel spatial basis matrix U. In this sense, good channel estimation performance is maintained because the prior knowledge represented by the channel spatial basis matrix U is included in the channel estimation.

[0244] In 4.5G NR, precoding is used to reduce M antenna ports to M′ antenna ports to reduce complexity, but the RS of the provided method is already very sparse and can work with or without precoding.

[0245] First example In this first example, the UE transmits a reference signal. This example begins by collecting training data.

[0246] Collecting training data This involves collecting m channel measurements in a selected target area and environment. As an example, shown in FIG. 13A, the target area is depicted within a solid-line frame. This area is covered by the same transceiver antenna of the BS. Dots within the coverage area represent m random locations. Channel measurements are measured at these m locations using a UE or signal measurement equipment. All these channel measurements are taken under the same configuration, e.g., the same set of subcarriers (L), the same BS antenna configuration, and the same terminal antenna configuration. Following the procedure introduced above, each channel measurement is vectorized and combined into a channel training matrix A, where A has a size of n × m, where n = L * M * N. The m channel measurements can be collected by the BS or other network-side equipment that can communicate with the BS.

[0247] Reference signal design The calculations included in this part can be performed by the BS or other network side devices that can communicate with the BS. In this example, the BS broadcasts the RS to the UE. Before setting up MIMO communication, the channel basis matrix, compact channel basis matrix, transmit MIMO reference signal constellation, transmit MIMO reference signal pattern, receive MIMO reference signal pattern, and receive MIMO reference signal constellation are generated.

[0248] Starting from a channel training matrix A, Define the rank r of iA. Compute the singular values ​​of A and sort these singular values ​​from largest to smallest. The number of singular values ​​greater than the threshold is the rank of A. The SVD on A is truncated by retaining the largest r singular values. SVD(A)=UΣV H U is the channel basis matrix and has size n×r.

[0249] ii.U H These r pivot positions are basic MIMO reference signal constellations. Each entry of these r basic MIMO reference signal constellations can be described as a combination of a subcarrier, a BS antenna, and a UE antenna.

[0250] An example of a basic MIMO reference signal constellation is shown in Table 1 below. For simplicity, in this example, the system has three subcarriers (L=3), three transmitting antennas (M=3), and two receiving antennas (N=2), and r is equal to 6. Each row represents U H represents the basic MIMO reference signal constellation generated from the pivot sequence above.

[0251] [Table 1]

[0252] iii. Generate a transmit MIMO reference signal constellation. This involves including each combination of subcarrier index and transmit antenna index (as shown in Table 2a) in a basic MIMO reference signal constellation, and then removing repeated entries. The transmit MIMO reference signal constellation may be in the form of a table, as shown in Table 2b.

[0253] [Table 2]

[0254] [Table 3]

[0255] iv. Design a transmit MIMO reference signal pattern based on the transmit MIMO reference signal constellation. In a practical MIMO system, only one antenna is active on one subcarrier during one period to transmit reference signals. FIG. 13B shows an example of a transmit MIMO reference signal pattern and a receive MIMO reference signal pattern. To solve the problem in the example, the transmit MIMO reference signal pattern can utilize time multiplexing by using two consecutive OFDM symbols. In one specific example, the transmit MIMO reference signal pattern includes using antenna #b1 to send the first OFDM symbol and transmitting reference signals on subcarriers #s1, #s2, and #s3, but there is no transmission on subcarriers #s1, #s2, and #s3 from antennas #b2 and #b3 during the first OFDM symbol. The second OFDM symbol is sent using antenna #b2, with RS placed on subcarrier #s1, and the second OFDM symbol is sent using antenna #b3, with RS placed on subcarrier #s2. During the second OFDM symbol, there is no transmission from antenna #b1 on subcarriers #s1 and #s2, there is no transmission from antenna #b2 on subcarrier #s2, and there is no transmission from antenna #b2 on subcarrier #s1. The transmit MIMO reference signal pattern also defines the transmit values ​​of the reference signals. Similar to time multiplexing, the transmit MIMO reference signal pattern can also employ code multiplexing. For example, two reference signals can be transmitted on the same subcarrier and the same transmitting antenna, but using different mask codes.

[0256] v. Generate a receiver-side MIMO reference signal constellation. The receiver-side MIMO reference signal constellation must include at least the basic MIMO reference signal constellation as the base part, but can also include several extended reference signals as the extended part. For example, there are two extended reference signal positions. The first extended position is for measuring the reference signal on subcarrier #3 sent by transmitter antenna #b1 using receiver antenna #u1. (Because receiver antenna #u1 is already configured to measure subcarriers #s1 and #s2 in the basic MIMO reference signal constellation, measuring on subcarrier #s3 by antenna #u1 is an optional additional task.) The second extended reference signal position is for measuring the reference signal on subcarrier #2 sent by transmitter antenna #b1 using receiver antenna #u2. It is assumed that the receiver device has sufficient resources to perform channel measurements in both the basic and extended parts. The combinations of the basic and extended reference signal positions are shown in Table 3. The number of all reference signal combinations is 8 (o equals 8). To calculate the compact channel basis, the receiver MIMO reference signal constellation is defined as the constellation matrix P Rx It is expressed by P Rx is an o×L*M*N matrix, where each row indicates a combination for making channel measurements for a reference signal.

[0257] [Table 4]

[0258] vi. Design a receiving-side MIMO reference signal pattern based on the transmitting MIMO reference signal pattern. For example, in the receiving-side MIMO reference signal configuration, the channel measurement reference signal is assigned to BS antenna #b1 and UE antenna #u1 (<s1,b1,u1> ) and #u2(<s1,b1,u2> ) should be transmitted on subcarrier #s1 between #b1 and #b2. Using a given transmit MIMO reference signal pattern, antenna #b1 sends the first reference signal on subcarrier #s1 in the first OFDM symbol. Correspondingly, as shown in FIG. 13B, receiver antennas #u1 and #u2 can measure the first reference signal sent on subcarrier #s1 in the first OFDM symbol. To solve this example, a receiver MIMO reference signal pattern can be designed by measuring on two consecutive OFDM symbols. In one specific example, the receiver MIMO reference signal pattern includes using antenna #u1 to measure on subcarriers #s1, #s2, and #s3 in the first OFDM symbol and on subcarrier #s1 in the second OFDM symbol. Using antenna #u2 to measure on subcarriers #s1, #s2, and #s3 in the first OFDM symbol and on subcarrier #s2 in the second OFDM symbol. θ aug and calculate its left inverse. θ aug =P UEMeasure *U

number

[0259] procedure Having designed the reference signal as above, the following is an exemplary operating procedure.

[0260] i. The BS has the following information about the target area and environment: the channel basis matrix U, the transmit MIMO reference signal constellation, the transmit MIMO reference signal pattern, and the receive MIMO reference signal constellation. This information can be generated by the BS or forwarded to the BS by other network side devices.

[0261] ii. The BS broadcasts a transmit MIMO reference signal pattern and receiver-side MIMO reference signal configuration information in the downlink, and also broadcasts a reference signal based on the transmit MIMO reference signal pattern.

[0262] iii. The UE decodes the RS transmission pattern and the receiver's MIMO reference signal configuration information. The UE generates a receiver's MIMO reference signal pattern based on the transmit MIMO reference signal pattern and the receiver's channel measurement capability. The UE receives and measures the RS based on the instructions provided by the receiver's MIMO reference signal pattern. iv. The UE feeds back channel measurements for RS(y) ​​in the uplink to the BS.

[0263] v. The BS receives UE feedback of channel measurements for RS(y) ​​and calculates the corresponding θ aug and

number

number

number

[0264] Example 2 In this example, it is the UE that is transmitting the RS signal.

[0265] Collecting training data This part is the same as the first example.

[0266] Reference signal design As in Example 1, the calculations involved in this part can be performed at the BS or at other network side equipment that can communicate with the BS or UE.

[0267] The same procedure as in Example 1 is taken to generate the channel basis matrix (U) and basic RS positions from the channel training matrix A. For illustrative purposes, an example with the same basic RS positions as shown in Table 1 is also used here.

[0268] i. Generate a transmit MIMO reference signal constellation. Since the reference signal is transmitted by the UE, first take the combination of subcarrier index and UE antenna index in the basic MIMO reference signal constellation (as shown in Table 4a), and then delete the repeated entries. The transmit MIMO reference signal constellation can be in the form of a table as shown in Table 4b.

[0269] [Table 5]

[0270] [Table 6]

[0271] ii. Design a transmit MIMO reference signal pattern based on the transmit MIMO reference signal configuration. The reference signal is sent by the UE, but the configuration is performed by the network. The UE is instructed when and where to send the reference signal(s). Only one UE antenna is active on one subcarrier during one period to transmit the reference signal. To solve the example, a transmit MIMO reference signal pattern by using two consecutive OFDM symbols can be used as follows (shown in FIG. 13C): send the first OFDM symbol using antenna #u1, place the RS on subcarriers #s1 and #s2, and there is no transmission on subcarriers #s1 and #s2 from antenna #u2; send the second OFDM symbol using antenna #u2, place the RS on subcarriers #s1, #s2, and #s3, and there is no transmission on subcarriers #s1, #s2, and #s3 from antenna #u1. The transmit MIMO reference signal pattern also defines reference signal values.

[0272] iii. Generate the receiver's MIMO reference signal constellation. The receiver's MIMO reference signal constellation must include at least all combinations in the basic MIMO reference signal constellation as the base part, and some extended reference signal positions as the extended part. For example, there are four positions in the extended part. The reference signal positions in the extended part are selected for the same reasons as in the previous example. It is assumed that the receiver has sufficient resources and chooses to perform measurements on both the basic MIMO reference signal constellation and the extended reference signal positions. The combinations of the basic positions and the extended reference signal positions are shown in Table 5. The number of reference signals is 10 (o is equal to 10). To calculate the compact channel basis, the RS measurement position matrix P BSMeasure is generated. P BSMeasure is an o×L*M*N matrix, where each row indicates a combination for making channel measurements for a reference signal.

[0273] [Table 7]

[0274] iv. Design the receiving side MIMO reference signal pattern based on the transmitting MIMO reference signal pattern and the receiving side channel measurement factors. The design procedure is similar to that of the previous example. The receiving side MIMO reference signal pattern solution of this example is illustrated in Figure 13C. θ aug and calculate its left inverse. θ aug =P BSMeasure *U

number

[0275] procedure Having designed the reference signal as above, the following is an exemplary operating procedure.

[0276] i. The BS has the following information about the target area and environment: the channel basis matrix U, the transmit MIMO reference signal constellation, the transmit MIMO reference signal pattern, and the receive MIMO reference signal constellation. This information can be generated by the BS or forwarded to the BS by other network side equipment.

[0277] ii. The BS broadcasts the transmit MIMO reference signal pattern in the downlink.

[0278] iii. The UE decodes the transmit MIMO reference signal pattern. Then, the UE sends a reference signal based on the instruction given by the transmit MIMO reference signal pattern.

[0279] iv. The BS generates a receiving MIMO reference signal pattern based on the transmitting MIMO reference signal pattern and the receiving channel measurement factors. The BS also generates a corresponding θ aug and

number

[0280] v. The BS receives and measures the reference signal (y) to generate channel measurements for the reference signal (y) based on instructions provided by the receiver MIMO reference signal constellation.

[0281] vi. The BS receives the MIMO channel measurements between the BS and the UE (

number

number

[0282] Example 3 In this example, the BS is responsible for the reference signal transmission. Compared to the first example, the UE has a compact channel basis θ aug or

number

number

[0283] The only difference compared to the first example is in the procedure part.

[0284] 1. The BS obtains the following information about the target region and environment: the channel basis matrix U, the compact channel basis θ aug , transmit MIMO reference signal configuration, transmit MIMO reference signal pattern, and receive side MIMO reference signal configuration. This information can be generated by the BS or transferred to the BS by other network side devices.

[0285] 2. The BS determines the transmit MIMO reference signal pattern, the receiver MIMO reference signal constellation, and the compact channel basis θ aug or

number

[0286] 3. The BS broadcasts the RS based on the transmission MIMO reference signal pattern.

[0287] 4. The UE determines the transmit MIMO reference signal pattern, the receive MIMO reference signal constellation, and the compact channel basis θ aug or

number

[0288] 5. The UE calculates the channel as a linear combination vector a,

number

[0289] 6. The UE reports the channel linear combination vector (a) or a subset of a (a') to the BS in the uplink.

[0290] 7. The BS receives UE feedback of the channel linear combination vector (a) of a or a subset (a') of a, and calculates the MIMO channel (

number

number

number

[0291] Numerous modifications and variations of the present disclosure are possible in light of the above teachings, and it is therefore to be understood that within the scope of the appended claims, the present disclosure may be practiced other than as specifically described herein. [Explanation of symbols]

[0292] 100 Communication Systems 110 Electronic Devices (ED) 120 Radio Access Network 130 Core Network 140 PSTN 150 Internet 160 other networks 170 network nodes 172 non-terrestrial transmitting and receiving points 190 Air Interface 201 Transmitter 203 Receiver 204 Antenna 208 memory 210 processors 252 Transmitter 253 Scheduler 254 receiver 256 antennas 258 memory 260 processor 272 Transmitter 274 Receiver 276 processors 278 memory 280 Antenna

Claims

1. 1. A method for MIMO channel estimation, comprising: transmitting, by a transmitting device, a multiple-input multiple-output (MIMO) reference signal using a transmit MIMO reference signal pattern, the transmit MIMO reference signal pattern including a transmit MIMO reference signal constellation, the transmit MIMO reference signal constellation being a non-uniform pattern of resources in space, time, frequency, and / or code, and computed from prior knowledge, the prior knowledge being obtained from a plurality of MIMO channel samples associated with a region; receiving, by a receiving device, a MIMO reference signal using a receiver MIMO reference signal pattern, the receiver MIMO reference signal pattern including a receiver MIMO reference signal constellation, the receiver MIMO reference signal constellation being a non-uniform pattern of resources in space, time, frequency, and / or code, and calculated from the prior knowledge, the prior knowledge being obtained from a plurality of MIMO channel samples associated with the region; estimating, by the receiving device, a MIMO channel from channel measurements for the reference signal and the prior knowledge; A method comprising:

2. After receiving the MIMO reference signal by the receiving device, transmitting, by the receiving device, feedback based on channel measurements for the reference signal; receiving, by the transmitting device, feedback based on channel measurements for the reference signal; estimating, by the transmitting device, a MIMO channel from the feedback and the prior knowledge; The method of claim 1 further comprising:

3. 2. The method of claim 1, wherein the prior knowledge is represented by a channel spatial basis matrix U, the channel spatial basis matrix U consisting of a plurality of orthonormal channel basis vectors obtained from a plurality of MIMO channel samples vectorized from a multidimensional MIMO channel format including space, time, frequency, and / or code.

4. The method of claim 3 , wherein the prior knowledge represented by a channel spatial basis matrix U is associated with a region, and different prior knowledge represented by different channel spatial basis matrices U is associated with different regions.

5. The plurality of MIMO channel samples for each of the plurality of different regions are reshaped and placed into a channel training matrix A consisting of vectorized MIMO channel samples of length n; The channel spatial basis matrix U is SVD(A)=UΣV H is based on a reduced-rank truncated singular value decomposition (SVD) of the channel training matrix A according to The SVD on the training matrix A is truncated by retaining the largest r singular values, where r is a defined rank, and the channel spatial basis matrix U has a size of n×r. The method of claim 4.

6. prior to transmitting a multiple-input multiple-output (MIMO) reference signal using a transmit MIMO reference signal pattern; obtaining, by the transmitting device, a region to which the transmitting device and the receiving device belong, the prior knowledge represented by a channel spatial basis matrix U associated with the region, and a transmit MIMO reference signal pattern. The method of claim 1 further comprising:

7. The transmission MIMO reference signal pattern is a transmit MIMO reference signal constellation including reference signal locations, each of which indicates on which subcarriers and on which transmitting antennas a reference signal should be transmitted within the MIMO channel space; Transmitted signal value for each reference signal, or Multiplexing method for each reference signal The method of claim 6, comprising at least one of:

8. Before using the transmit MIMO reference signal pattern, obtaining, by the transmitting device, a transmit MIMO reference signal constellation and a pattern generation method from the transmit constellation; 7. The method of claim 6, further comprising:

9. Before using the transmit MIMO reference signal constellation, The transmitting device obtains a basic MIMO reference signal constellation and a method for generating a transmission constellation from the basic.

9. The method of claim 8, further comprising:

10. Before receiving a multiple-input multiple-output (MIMO) reference signal using a receiver MIMO reference signal pattern, and obtaining, by the receiving device, the region to which the transmitting device and the receiving device belong, the prior knowledge represented by a channel spatial basis matrix U associated with the region, and a receiving MIMO reference signal pattern.

10. The method of any one of claims 1 to 9, further comprising:

11. The receiving side MIMO reference signal pattern is the receiver MIMO reference signal constellation includes reference signal positions, each of which indicates on which subcarrier in the MIMO channel space, on which transmitter antenna, and on which receiver antenna a reference signal should be transmitted; Transmitted signal value for each reference signal, or (De)multiplexing method for each reference signal The method of claim 10, comprising at least one of:

12. Before using the receiver's MIMO reference signal pattern, obtaining, by the receiving device, a receiving-side MIMO reference signal constellation and a pattern generation method from the receiving-side constellation; 11. The method of claim 10, further comprising:

13. Before using the transmit MIMO reference signal constellation, obtaining a basic MIMO reference signal constellation and a receiving side constellation generation method from the basic by the receiving side device; and / or obtaining a transmit MIMO reference signal constellation and a receiver constellation generation method from the transmit by the receiver device; 13. The method of claim 12, further comprising:

14. The channel spatial basis matrix U H r pivot positions are obtained from U, where the r pivot positions correspond to the basic MIMO reference signal constellation and define reference signal positions in a MIMO channel space by subcarriers, transmitting antennas, and receiving antennas, respectively; H 14. The method of claim 9 or 13, wherein U is the Hermitian transpose of U, and the MIMO channel space includes the number of subcarriers, the number of transmitting antennas, and the number of receiving antennas.

15. 9. The method of claim 8, wherein the pattern generation method from the transmission arrangement specifies a transmission signal value and a multiplexing scheme for each reference signal in the transmission MIMO reference signal arrangement, and the multiplexing scheme includes time multiplexing, frequency multiplexing, and / or code multiplexing.

16. 13. The method of claim 12, wherein the pattern generation method from the receiver arrangement specifies a transmission signal value and a (de)multiplexing scheme for each reference signal in the receiver MIMO reference signal arrangement, and the (de)multiplexing scheme includes time (de)multiplexing, frequency (de)multiplexing, and / or code (de)multiplexing.

17. 10. The method of claim 9, wherein the method for generating a transmission constellation from a basic constellation merges any two reference signal positions in a basic MIMO reference signal constellation that share the same subcarriers and the same transmitting antenna but have different receiving antennas into one reference signal position in the transmission MIMO reference signal constellation.

18. The method of claim 13, wherein the receiver constellation generation method from the base includes a base part and may include an extension part from the base MIMO reference signal constellation to the receiver MIMO reference signal constellation, or the receiver constellation generation method from the transmission includes a base part and includes an extension part from the transmission MIMO reference signal constellation to the receiver MIMO reference signal constellation.

19. 20. The method of claim 18, wherein the basic portion includes reference signal positions in a basic MIMO reference signal constellation, and the extended portion includes multiple reference signal positions that share the same subcarriers and the same transmitting antenna but have different receiving antennas and are not in the basic MIMO reference signal constellation.

20. The method of claim 19 , wherein the extension portion is modified and updated.

21. receiving a multiple-input multiple-output (MIMO) reference signal using a receiver MIMO reference signal pattern, and before estimating a MIMO channel by the receiver device from channel measurements for the reference signal and the prior knowledge; measuring, by the receiving device, channels at the reference signal positions indicated by the receiving MIMO reference signal pattern into a vector y; The method of claim 1 further comprising:

22. The MIMO channel estimation is from the channel measurements for the reference signals and the prior knowledge, where the channel measurements for the reference signals represented in a vector y and the prior knowledge represented by a channel spatial basis matrix U are used to estimate the compact channel basis θ aug and its left inverse, which is i aug =P Rx *U [Equation 1] where P Rx is a constellation matrix determined by the receiver-side MIMO reference signal constellation, and the coefficient vector a is [Equation 2] and the MIMO channel is determined according to [Equation 3] teeth, [Equation 4] The method of claim 1, wherein the estimated value is determined according to:

23. Subset of MIMO channels [Equation 5] If needs to be estimated, [Equation 6] where U′ is a subset of the channel spatial basis matrix U, 23. The method of claim 22.

24. If only a subset of the coefficient vector a is available, the MIMO channel [Equation 7] teeth, [Equation 8] where a' is a subset of the vector coefficients of a, 23. The method of claim 22.

25. Only a subset of the coefficient vector a is available, and a subset of the MIMO channels [Equation 9] If only needs to be estimated, the MIMO channel [Equation 10] teeth, [0011] where a′ is a subset of the vector a of coefficients, and U′ is a subset of the channel spatial basis matrix U.

23. The method of claim 22.

26. When the extension part is changed, the receiver side MIMO reference signal constellation is expressed as the constellation matrix P Rx＿update and accordingly, the compact channel basis θ aug and its left inverse is i aug =P Rx＿update *U [0012] 20. The method according to claim 20, which is updated as follows:

27. The method of claim 8 , wherein the pattern generation method from the transmit arrangement is selected from a plurality of pattern generation methods from the transmit arrangement.

28. The method of claim 8, wherein the transmission arrangement generation method from the base is selected from among transmission arrangement generation methods from the base.

29. The method of claim 12, wherein the pattern generation method from the receiving arrangement is selected from among pattern generation methods from the receiving arrangement.

30. 14. The method of claim 13, wherein the receiver constellation generation method from base is selected from among the receiver constellation generation methods from base, or the receiver constellation generation method from send is selected from among the receiver constellation generation methods from send.

31. 10. The method of claim 1, wherein the region to which the sending device and receiving device belong may include multiple sub-regions, different regions may be overlapping or separated, and the sending device and receiving device may be associated with different regions.

32. Before the MIMO transmission begins and the areas to which the transmitting and receiving devices are associated are determined, obtaining, by the transmitting device and the receiving device, prior knowledge associated with the region, a transmit MIMO reference signal pattern, and a receive MIMO reference signal pattern; The method of claim 1 further comprising:

33. The prior knowledge can be represented directly by the channel spatial basis matrix U or by the compact channel matrix θ aug Or by its left inverse i aug =P Rx *U [0013] where P Rx is a constellation matrix determined by the receiver-side MIMO reference signal constellation, and the compact channel matrix θ aug 33. The method of claim 32, wherein the left inverse matrix thereof can be explicitly signaled or calculated from the channel spatial basis matrix U and the receiver-side MIMO reference signal constellation.

34. The method of claim 32, wherein the transmit MIMO reference signal pattern can be explicitly signaled or can be generated from a transmit MIMO reference signal constellation in a pattern generation method from a transmit constellation.

35. The method of claim 34, wherein the transmit MIMO reference signal constellation can be explicitly signaled or can be generated from a basic MIMO reference signal constellation in a transmit constellation generation method from a basic.

36. The method of claim 32, wherein the receiver MIMO reference signal pattern can be explicitly notified or can be generated from the receiver MIMO reference signal constellation in a pattern generation method from the receiver constellation.

37. The method of claim 36, wherein the receiver MIMO reference signal constellation can be explicitly signaled or generated from a basic MIMO reference signal constellation in a receiver constellation generation method from a basic.

38. The basic MIMO reference signal constellation can be signaled explicitly or can be calculated by the channel spatial basis matrix U H r pivot positions are obtained from U, where the r pivot positions correspond to the basic MIMO reference signal constellation and define reference signal positions in a MIMO channel space by subcarriers, transmitting antennas, and receiving antennas, respectively; H 38. The method of claim 35 or claim 37, wherein ∑ i = ∑ j ...

39. 36. The method of claim 35, wherein the explicitly signaled transmit MIMO reference signal constellation can be represented by a combination of configured reference signal constellations, the configured reference signal constellations being predefined and prestored.

40. 37. The method of claim 36, wherein the explicitly signaled receiver MIMO reference signal constellation can be represented by a combination of constituent receiver reference signal constellations, the constituent receiver reference signal constellations being predefined and prestored.

41. The method of claim 2 , wherein the feedback based on channel measurements for the reference signal positions determined by a receiver-side MIMO reference signal constellation may include channel measurements for the reference signal positions in a vector of y.

42. The feedback based on the channel measurement for the reference signal position determined by the receiver's MIMO reference signal arrangement is [0014] and a compact channel matrix θ aug or its left inverse: i aug =P Rx *U [Equation 15] In the formula, P Rx is a constellation matrix determined by the receiver-side MIMO reference signal constellation, and θ aug and [0016] The method of claim 2, wherein {right arrow over (U)} is given or can be calculated from the receiver-side MIMO reference signal constellation and the channel spatial basis matrix U.

43. after receiving feedback based on channel measurements for the reference signal positions including a vector of y; by the sending device [Equation 17] The vector coefficients of a determined according to MIMO Channel [Equation 18] but, [Equation 19] where U is the channel spatial basis matrix; estimating the MIMO channel according to 3. The method of claim 2, further comprising:

44. after receiving feedback based on channel measurements for the reference signal positions including a vector of y; by the sending device [Equation 20] a vector of coefficients a determined according to Subset of MIMO channels [0000] but, [Equation 22] where U′ is a subset of the channel spatial basis matrix U; estimating a subset of the MIMO channel according to 3. The method of claim 2, further comprising:

45. after receiving feedback based on channel measurements for the reference signal positions including the vector of coefficients a or a subset a' of the vector of coefficients; by the sending device MIMO Channel [Equation 23] but, [0000] or [Equation 25] where U is the channel spatial basis matrix; estimating the MIMO channel according to 3. The method of claim 2, further comprising:

46. after receiving feedback based on channel measurements for the reference signal positions including the vector of coefficients a or a subset a' of the vector of coefficients; by the sending device Subset of MIMO channels [Equation 26] but, [0000] or [0000] where U′ is a subset of the channel spatial basis matrix U; estimating the subset MIMO channel according to The method of claim 1 further comprising:

47. The channel training matrix A is updated with a plurality of new channel samples for each of a plurality of different regions, and a new channel spatial basis matrix U, a basic MIMO reference signal constellation, a transmit MIMO reference signal pattern, a receive MIMO reference pattern, and a compact channel basis θ are obtained for each of the plurality of different regions. aug or the left inverse of the compact channel basis [0000] is updated, The channel basis matrix U is SVD(A)=UΣV H is based on a reduced-rank truncated singular value decomposition (SVD) of the channel training matrix A according to The SVD on the training matrix A is truncated by retaining the largest r singular values, where r is the defined rank, the channel basis matrix U has size n×r, and a compact channel matrix θ aug or its left inverse: i aug =P Rx *U [Equation 30] =(θ aug H *θ aug ) －1 *θ aug H In the formula, P Rx is a constellation matrix determined by the receiver-side MIMO reference signal constellation, The method of claim 3, wherein the transmitting device and the receiving device are updated from the new channel basis matrix U, the basic MIMO reference signal constellation, the transmitting MIMO reference signal pattern, and the receiving MIMO reference pattern.

48. 48. The method of any one of claims 1 to 47, wherein the transmitting device is a base station and the receiving device is a user equipment (UE).

49. 48. The method of any one of claims 1 to 47, wherein the transmitting device is a user equipment (UE) and the receiving device is a base station.

50. 48. The apparatus of any one of claims 1 to 47, comprising a processor and a memory coupled to the processor, the memory storing instructions that, when executed, cause the processor to perform steps of a sending device.

51. 48. An apparatus according to any one of claims 1 to 47, comprising a processor and a memory, the memory coupled to the processor, the memory storing instructions that, when executed, cause the processor to perform steps of a receiving device.

52. 50. A system comprising a sending device and a receiving device, wherein the sending device is configured to perform the steps performed by the sending device in any one of claims 1 to 47, and the receiving device is configured to perform the steps performed by the receiving device in any one of claims 1 to 47.

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