Method and apparatus for data driven compression for MIMO precoding feedback

Abstract

A method for data driven multiple-input multiple-output (MIMO) pre-decoder compression is described herein. A method is provided that may include receiving one or more Channel State Information (CSI) Reference Signals (RSs) using a plurality of sub-bands. The method includes transmitting a report indicating coherence time information respectively associated with the plurality of sub-bands, where the coherence time information respectively associated with the plurality of sub-bands is determined based on the CSI determined from the received CSI-RS. The method includes receiving at least one second CSI-RS using the at least one sub-band of the plurality of sub-bands. The method comprises transmitting feedback to the transmitter, the feedback comprising compression information indicating, for the at least one sub-band of the plurality of sub-bands, a suggested precoding parameter determined based on the received at least one second CSI-RS, wherein the feedback is transmitted within a coherence time associated with the at least one of the plurality of sub-bands.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 388,132, filed on July 11, 2022, the contents of which are incorporated herein by reference. Background Art

[0003] Adopting channel adaptive signaling in wireless communication systems can produce huge improvements on almost any performance metric. These adaptive techniques may require channel knowledge at the transmitter. Unfortunately, channel knowledge may not be directly exploited in frequency division duplex systems. However, having the receiver feed back some bits about the channel conditions (such as channel quality, grade, etc.) can allow near-optimal adaptation. This channel information transmitted from the receiver to the transmitter is usually called limited or limited rate feedback. Through carefully designed feedback, perfect transmitter channel knowledge that would otherwise be unattainable can be achieved with near-optimal performance. Summary of the invention

[0004] Methods for data-driven multiple-input multiple-output (MIMO) pre-decoder compression are described herein. A method may include receiving one or more channel state information (CSI) reference signals (RS) using multiple subbands. The method includes sending a report indicating coherence time information associated with the multiple subbands, respectively, wherein the coherence time information associated with the multiple subbands, respectively, is determined based on CSI determined from the received CSI-RS. The method includes receiving at least one second CSI-RS using at least one of the multiple subbands. The method includes sending feedback to the transmitter, the feedback including compression information, the compression information indicating a recommended pre-decoding parameter determined based on the received at least one second CSI-RS for the at least one subband of the multiple subbands, wherein the feedback is sent within a coherence time associated with the at least one subband of the multiple subbands. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] A more detailed understanding may be obtained from the following description given by way of example in conjunction with the accompanying drawings, in which like reference numerals indicate like elements, and in which:

[0006] Figure 1A is a system diagram illustrating an example communication system in which one or more disclosed embodiments may be implemented;

[0007] Figure 1B is an example of an embodiment in which Figure 1A A system diagram of an example wireless transmit / receive unit (WTRU) for use within an illustrated communication system;

[0008] Figure 1Cis an example of an embodiment in which Figure 1A A system diagram of an example Radio Access Network (RAN) and an example Core Network (CN) used within the illustrated communication system;

[0009] Figure 1D is an example of an embodiment in which Figure 1A A system diagram of another example RAN and another example CN used within the illustrated communication system;

[0010] Figure 2 is a diagram of a MIMO system according to at least one embodiment described herein;

[0011] Figure 3 is a flow chart illustrating steps of online training / retraining that may be performed by a transmitter in a MIMO system;

[0012] Figure 4 is a flow chart illustrating the steps of online training / retraining that may be performed by a receiver in a MIMO system

[0013] Figure 5 An example of a compression ratio index lookup table is illustrated;

[0014] Figure 6 is a signaling flow diagram describing an example of signaling that may be performed between a transmitter and a receiver for online training or retraining;

[0015] Figure 7 is a flow chart illustrating steps of real-time link adaptation that may be performed by a transmitter in a MIMO system;

[0016] Figure 8 is a flow chart illustrating the steps of real-time link adaptation that may be performed by a receiver in a MIMO system

[0017] Fig. 9 is a schematic diagram illustrating an example of signaling between a transmitter and a receiver that perform real-time link adaptation. DETAILED DESCRIPTION

[0018] Figure 1A1 is a diagram illustrating an example communication system 100 in which one or more disclosed embodiments may be implemented. The communication system 100 may be a multiple access system that provides content such as voice, data, video, messaging, broadcast, etc. to multiple wireless users. The communication system 100 may enable multiple wireless users to access such content through sharing of system resources (including wireless bandwidth). For example, the communication system 100 may employ 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), single carrier FDMA (SC-FDMA), zero tail unique word discrete Fourier transform spread OFDM (ZT-UW-DFT-S-OFDM), unique word OFDM (UW-OFDM), resource block filtered OFDM, filter bank multi-carrier (FBMC), etc.

[0019] like Figure 1A As shown, the communication system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) 104, a core network (CN) 106, a public switched telephone network (PSTN) 108, the Internet 110 and other networks 112, but it should be understood that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and / or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d (any of which may be referred to as a station (STA)) may be configured to send and / or receive wireless signals and may include user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscription-based unit, a pager, a cellular phone, a personal digital assistant (PDA), a smart phone, a laptop, a netbook, a personal computer, a wireless sensor, a hotspot or Mi-Fi device, an Internet of Things (IoT) device, a watch or other wearable device, a head-mounted display (HMD), a vehicle, a drone, medical devices and applications (e.g., remote surgery), industrial devices and applications (e.g., robots and / or other wireless devices operating in an industrial and / or automated process chain environment), a consumer electronic device, a device operating on a commercial and / or industrial wireless network, etc. Any of the WTRUs 102a, 102b, 102c, and 102d may be interchangeably referred to as a UE.

[0020] The communication system 100 may also include a base station 114a and / or a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the CN 106, the Internet 110, and / or other networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node B, an evolved Node B (eNB), a Home Node B, a Home evolved Node B, a next generation Node B such as a gNode B (gNB), a new radio (NR) Node B, a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0021] The base station 114a may be part of the RAN 104, which may also include other base stations and / or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), a relay node, etc. The base station 114a and / or the base station 114b may be configured to send and / or receive wireless signals on one or more carrier frequencies, which may be referred to as a cell (not shown). These frequencies may be in a licensed spectrum, an unlicensed spectrum, or a combination of licensed and unlicensed spectrums. A cell may provide coverage of wireless services to a specific geographic area, which may be relatively fixed or may change over time. The cell may be further divided into cell sectors. For example, a cell associated with the base station 114a may be divided into three sectors. Therefore, in one embodiment, the base station 114a may include three transceivers, i.e., one transceiver for each sector of the cell. In one embodiment, the base station 114a may employ multiple-input multiple-output (MIMO) technology and may utilize multiple transceivers for each sector of the cell. For example, beamforming may be used to send and / or receive signals in a desired spatial direction.

[0022] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, centimeter wave, micrometer wave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0023] More specifically, as noted above, the communication system 100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, etc. For example, the base station 114a in the RAN 104 and the WTRUs 102a, 102b, 102c may implement a radio technology, such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), that may use Wideband CDMA (WCDMA) to establish the air interface 116. WCDMA may include communication protocols, such as High Speed ​​Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA may include High Speed ​​Downlink (DL) Packet Access (HSDPA) and / or High Speed ​​Uplink (UL) Packet Access (HSUPA).

[0024] In one embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA) that may establish the air interface 116 using Long Term Evolution (LTE) and / or Advanced LTE (LTE-A) and / or Advanced LTE Pro (LTE-A Pro).

[0025] In one embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology (such as NR radio access) that may establish the air interface 116 using NR.

[0026] In one embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement multiple radio access technologies. For example, the base station 114a and the WTRUs 102a, 102b, 102c may together implement LTE radio access and NR radio access, for example using dual connectivity (DC) principles. Thus, the air interface utilized by the WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and / or transmissions transmitted to / from multiple types of base stations (e.g., eNBs and gNBs).

[0027] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies such as IEEE 802.11 (i.e., Wireless Fidelity (WiFi)), IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile Communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), etc.

[0028] Figure 1A The base station 114b in the example may be, for example, a wireless router, a Home NodeB, a Home eNodeB, or an access point, and may utilize any suitable RAT to facilitate wireless connectivity in a local area, such as a business location, a home, a vehicle, a campus, an industrial facility, an air corridor (e.g., for use by drones), a road, and the like. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR, etc.) to establish a micro-micro cell base station or a femto cell base station. As Figure 1A As shown, the base station 114b may have a direct connection to the Internet 110. Therefore, the base station 114b may not be required to access the Internet 110 via the CN 106.

[0029] The RAN 104 may be in communication with the CN 106, which may be any type of network configured to provide voice, data, applications, and / or Voice over Internet Protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may have different quality of service (QoS) requirements, such as different throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, etc. The CN 106 may provide call control, billing services, mobile location-based services, prepaid calling, Internet connectivity, video distribution, etc., and / or perform high-level security functions, such as user authentication. Although not described in detail in the accompanying drawings, the CN 106 may be configured to provide voice, data, applications, and / or Voice over Internet Protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. Figure 1AAlthough not shown in the figure, it will be appreciated that the RAN 104 and / or the CN 106 may be in direct or indirect communication with other RANs that employ the same RAT as the RAN 104 or a different RAT. For example, in addition to being connected to the RAN 104, which may utilize NR radio technology, the CN 106 may also be in communication with another RAN (not shown) that employs GSM, UMTS, CDMA 2000, WiMAX, E-UTRA, or WiFi radio technology.

[0030] The CN 106 may also act as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or other networks 112. The PSTN 108 may include a circuit-switched telephone network that provides plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and / or the Internet Protocol (IP) in the TCP / IP Internet protocol suite. The networks 112 may include wired communication networks and / or wireless communication networks owned and / or operated by other service providers. For example, the networks 112 may include another CN connected to one or more RANs, which may employ the same RAT as the RAN 104 or a different RAT.

[0031] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communication system 100 may include multi-mode capabilities (e.g., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks via different wireless links). Figure 1A The illustrated WTRU 102c may be configured to communicate with the base station 114a, which may employ a cellular-based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

[0032] Figure 1B is a system diagram illustrating an example WTRU 102. Figure 1B As shown, the WTRU 102 may include, among other things, a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keypad 126, a display / touchpad 128, non-removable memory 130, removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and / or other peripherals 138. It will be appreciated that the WTRU 102 may include any sub-combination of the foregoing elements while remaining consistent with an embodiment.

[0033] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), any other type of integrated circuit (IC), a state machine, etc. The processor 118 may perform signal decoding, data processing, power control, input / output processing, and / or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit / receive element 122. Although Figure 1B The processor 118 and the transceiver 120 are depicted as separate components, but it is understood that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0034] The send / receive element 122 may be configured to send a signal to a base station (e.g., base station 114a) or receive a signal from the base station via an air interface 116. For example, in one embodiment, the send / receive element 122 may be an antenna configured to send and / or receive an RF signal. In one embodiment, the send / receive element 122 may be a transmitter / detector configured to send and / or receive, for example, an IR, UV or visible light signal. In another embodiment, the send / receive element 122 may be configured to send and / or receive both an RF signal and an optical signal. It should be understood that the send / receive element 122 may be configured to send and / or receive any combination of wireless signals.

[0035] Although the transmit / receive element 122 Figure 1B Although depicted as a single element in the figure, the WTRU 102 may include any number of transmit / receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0036] The transceiver 120 may be configured to modulate signals to be transmitted by the transmit / receive element 122 and to demodulate signals received by the transmit / receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. For example, the transceiver 120 may include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as NR and IEEE 802.11.

[0037] The processor 118 of the WTRU 102 may be coupled to and may receive user input data from a speaker / microphone 124, a keypad 126, and / or a display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or an organic light emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128. In addition, the processor 118 may access information from and store data in any type of suitable memory, such as a non-removable memory 130 and / or a removable memory 132. The non-removable memory 130 may include a random access memory (RAM), a read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from and store data in a memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown).

[0038] The processor 118 may receive power from the power source 134, and may be configured to distribute and / or control power to the other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel-metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, etc.

[0039] The processor 118 may also be coupled to the GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to or in lieu of the information from the GPS chipset 136, the WTRU 102 may receive location information from a base station (e.g., base stations 114a, 114b) over the air interface 116 and / or determine its location based on the timing of signals received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by any suitable location-determination method while remaining consistent with an embodiment.

[0040] The processor 118 may also be coupled to other peripherals 138, which may include one or more software modules and / or hardware modules that provide additional features, functionality, and / or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an electronic compass, a satellite transceiver, a digital camera (for photos and / or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands-free headset, module, FM radio unit, digital music player, media player, video game player module, Internet browser, virtual reality and / or augmented reality (VR / AR) device, activity tracker, etc. The peripheral device 138 may include one or more sensors. The sensor may be one or more of the following: a gyroscope, an accelerometer, a Hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor; a geolocation sensor, an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, a humidity sensor, etc.

[0041] The WTRU 102 may include a full-duplex radio for which transmission and reception of some or all of the signals (e.g., associated with specific subframes for both UL (e.g., for transmission) and DL (e.g., for reception)) may be concurrent and / or simultaneous. The full-duplex radio may include an interference management unit for reducing and / or substantially eliminating self-interference via hardware (e.g., a choke) or via signal processing performed by a processor (e.g., a separate processor (not shown) or via the processor 118). In one embodiment, the WTRU 102 may include a half-duplex radio for which transmission and reception of some or all of the signals (e.g., associated with specific subframes for both UL (e.g., for transmission) or DL ​​(e.g., for reception)) may be concurrent and / or simultaneous.

[0042] Figure 1C 1 is a system diagram illustrating the RAN 104 and the CN 106 in accordance with an embodiment. As noted above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the CN 106.

[0043] The RAN 104 may include evolved Node-Bs 160a, 160b, 160c, though it will be appreciated that the RAN 104 may include any number of evolved Node-Bs while remaining consistent with an embodiment. The evolved Node-Bs 160a, 160b, 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the evolved Node-Bs 160a, 160b, 160c may implement MIMO technology. Thus, the evolved Node-B 160a, for example, may use multiple antennas to transmit wireless signals to and / or receive wireless signals from the WTRU 102a.

[0044] Each of the evolved Node Bs 160a, 160b, 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, etc. Figure 1C As shown, the eNode-Bs 160a, 160b, 160c may communicate with one another via an X2 interface.

[0045] Figure 1C The illustrated CN 106 may include a mobility management entity (MME) 162, a serving gateway (SGW) 164, and a packet data network (PDN) gateway (PGW) 166. Although the foregoing elements are depicted as part of the CN 106, it should be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0046] The MME 162 may be connected to each of the evolved Node-Bs 162a, 162b, 162c in the RAN 104 via an S1 interface and may serve as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation / deactivation, selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, 102c, etc. The MME 162 may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM and / or WCDMA.

[0047] The SGW 164 may be connected to each of the evolved Node-Bs 160a, 160b, 160c in the RAN 104 via an S1 interface. The SGW 164 may generally route and forward user data packets to / from the WTRUs 102a, 102b, 102c. The SGW 164 may perform other functions, such as anchoring the user plane during an inter-evolved Node-B handover, triggering paging when DL data is available for the WTRUs 102a, 102b, 102c, managing and storing the context of the WTRUs 102a, 102b, 102c, and the like.

[0048] The SGW 164 may be connected to the PGW 166, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0049] The CN 106 may facilitate communications with other networks. For example, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. For example, the CN 106 may include, or may be in communication with, an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired networks and / or wireless networks owned and / or operated by other service providers.

[0050] Although the WTRU Figures 1A to 1D Although described as wireless terminals, it is contemplated that in certain representative embodiments, such terminals may (eg, temporarily or permanently) use a wired communications interface with a communications network.

[0051] In a representative embodiment, the other network 112 may be a WLAN.

[0052] A WLAN in infrastructure basic service set (BSS) mode may have an access point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP may have access or an interface to a distribution system (DS) or another type of wired / wireless network that carries traffic to and / or carries traffic away from the BSS. Traffic originating from outside the BSS and going to the STA may be reached by the AP and may be delivered to the STA. Traffic originating from the STA and going to a target outside the BSS may be transmitted to the AP to be delivered to the corresponding target. Traffic between STAs within the BSS may be transmitted by the AP, for example, wherein the source STA may transmit traffic to the AP, and the AP may deliver traffic to the target STA. Traffic between STAs within the BSS may be considered and / or referred to as point-to-point traffic. Direct link establishment (DLS) may be used to transmit point-to-point traffic between the source STA and the target STA (e.g., directly between them). In certain representative embodiments, the DLS may use 802.11e DLS or 802.11z tunnel DLS (TDLS). A WLAN using an independent BSS (IBSS) mode may not have an AP, and STAs within or using the IBSS (eg, all STAs in the STA) may communicate directly with each other. The IBSS communication mode may sometimes be referred to herein as an "ad-hoc" communication mode.

[0053] When using the 802.11ac infrastructure operating mode or a similar operating mode, the AP may send beacons on a fixed channel, such as a primary channel. The primary channel may be a fixed width (e.g., a 20 MHz wide bandwidth) or a dynamically set width. The primary channel may be a working channel of the BSS and may be used by the STA to establish a connection with the AP. In certain representative embodiments, carrier sense multiple access / collision avoidance (CSMA / CA) may be implemented, for example, in an 802.11 system. For CSMA / CA, a STA (e.g., each STA) (including the AP) may listen to the primary channel. If the primary channel is listened / detected and / or determined to be busy by a particular STA, the particular STA may back off. One STA (e.g., only one station) may transmit at any given time in a given BSS.

[0054] High throughput (HT) STAs may communicate using a 40 MHz wide channel, for example, via a combination of a primary 20 MHz channel and adjacent or non-adjacent 20 MHz channels to form a 40 MHz wide channel.

[0055] Very high throughput (VHT) STA can support 20MHz, 40MHz, 80MHz and / or 160MHz wide channels. 40MHz channels and / or 80MHz channels can be formed by combining continuous 20MHz channels. 160MHz channels can be formed by combining 8 continuous 20MHz channels, or by combining two non-continuous 80MHz channels (this can be called 80+80 configuration). For 80+80 configuration, after channel coding, the data can pass through a segment parser that can divide the data into two streams. Each stream can be processed by inverse fast Fourier transform (IFFT) and time domain processing separately. These streams can be mapped to two 80MHz channels, and the data can be sent by sending STA. At the receiver of the receiving STA, the above-mentioned operation for 80+80 configuration can be reversed, and the combined data can be transmitted to the medium access control (MAC).

[0056] 802.11af and 802.11ah support operating modes below 1GHz. Channel operating bandwidths and carriers are reduced in 802.11af and 802.11ah relative to those used in 802.11n and 802.11ac. 802.11af supports 5MHz, 10MHz, and 20MHz bandwidths in the TV White Space (TVWS) spectrum, and 802.11ah supports 1MHz, 2MHz, 4MHz, 8MHz, and 16MHz bandwidths using non-TVWS spectrum. According to a representative embodiment, 802.11ah may support meter type control / machine type communication (MTC), such as MTC devices in macro coverage areas. MTC devices may have certain capabilities, such as limited capabilities, including support for (e.g., only support for) certain bandwidths and / or limited bandwidths. MTC devices may include batteries with battery life above a threshold (e.g., to maintain very long battery life).

[0057] WLAN systems that can support multiple channels and channel bandwidths (such as 802.11n, 802.11ac, 802.11af, and 802.11ah) include channels that can be designated as primary channels. The primary channel may have a bandwidth equal to the maximum common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may be set and / or limited by a STA (which supports the minimum bandwidth operation mode) from all STAs operating in the BSS. In the example of 802.11ah, for STAs (e.g., MTC-type devices) that support (e.g., only support) a 1MHz mode, the primary channel may be 1MHz wide, even if the AP and other STAs in the BSS support 2MHz, 4MHz, 8MHz, 16MHz, and / or other channel bandwidth operation modes. Carrier sensing and / or network allocation vector (NAV) settings may depend on the state of the primary channel. If the primary channel is busy, for example, because a STA (which only supports a 1MHz operation mode) is transmitting to the AP, all available bands may be considered busy even if most of the available bands remain idle.

[0058] In the United States, the available frequency band for 802.11ah is 902MHz to 928MHz. In South Korea, the available frequency band is 917.5MHz to 923.5MHz. In Japan, the available frequency band is 916.5MHz to 927.5MHz. The total bandwidth available for 802.11ah is 6MHz to 26MHz, depending on the country code.

[0059] Figure 1D1 is a system diagram illustrating the RAN 104 and the CN 106 in accordance with an embodiment. As noted above, the RAN 104 may employ NR radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the CN 106.

[0060] The RAN 104 may include gNBs 180a, 180b, 180c, though it will be appreciated that the RAN 104 may include any number of gNBs while remaining consistent with an embodiment. The gNBs 180a, 180b, 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the gNBs 180a, 180b, 180c may implement MIMO technology. For example, the gNBs 180a, 180b may utilize beamforming to send signals to and / or receive signals from the gNBs 180a, 180b, 180c. Thus, the gNB 180a may, for example, use multiple antennas to send wireless signals to and / or receive wireless signals from the WTRU 102a. In one embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, the gNB 180a may transmit multiple component carriers to the WTRU 102a (not shown). A subset of these component carriers may be on an unlicensed spectrum, while the remaining component carriers may be on a licensed spectrum. In one embodiment, the gNBs 180a, 180b, 180c may implement coordinated multi-point (CoMP) technology. For example, the WTRU 102a may receive coordinated transmissions from the gNB 180a and gNB 180b (and / or gNB 180c).

[0061] The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using transmissions associated with a set of parameters that may be scalable. For example, OFDM symbol spacing and / or OFDM subcarrier spacing may vary for different transmissions, different cells, and / or different portions of the wireless transmission spectrum. The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using subframes or transmit time intervals (TTIs) of varying or scalable lengths (e.g., containing varying numbers of OFDM symbols and / or varying absolute time lengths over time).

[0062] The gNBs 180a, 180b, 180c may be configured to communicate with the WTRUs 102a, 102b, 102c in a standalone configuration and / or a non-standalone configuration. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c while not accessing other RANs (e.g., such as the eNodeBs 160a, 160b, 160c). In a standalone configuration, the WTRUs 102a, 102b, 102c may use one or more of the gNBs 180a, 180b, 180c as mobility anchor points. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using signals in an unlicensed band. In a non-standalone configuration, the WTRUs 102a, 102b, 102c may communicate / connect with the gNB 180a, 180b, 180c while also communicating / connecting with another RAN, such as the eNodeB 160a, 160b, 160c. For example, the WTRUs 102a, 102b, 102c may implement the DC principle to communicate with one or more gNBs 180a, 180b, 180c and one or more eNodeBs 160a, 160b, 160c substantially simultaneously. In a non-standalone configuration, the eNodeB 160a, 160b, 160c may act as a mobility anchor for the WTRUs 102a, 102b, 102c, and the gNB 180a, 180b, 180c may provide additional coverage and / or throughput for serving the WTRUs 102a, 102b, 102c.

[0063] Each of the gNBs 180a, 180b, 180c may be associated with a specific cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in UL and / or DL, support of network slicing, interworking between DC, NR and E-UTRA, routing of user plane data towards user plane functions (UPFs) 184a, 184b, routing of control plane information towards access and mobility management functions (AMFs) 182a, 182b, etc. Figure 1D As shown, gNBs 180a, 180b, and 180c may communicate with each other via an Xn interface.

[0064] Figure 1DThe illustrated CN 106 may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one session management function (SMF) 183a, 183b, and possible data networks (DNs) 185a, 185b. Although the aforementioned elements are depicted as part of the CN 106, it should be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0065] The AMF 182a, 182b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 via the N2 interface and may act as a control node. For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRU 102a, 102b, 102c, support of network slicing (e.g., handling of different protocol data unit (PDU) sessions with different requirements), selecting a specific SMF 183a, 183b, management of registration areas, termination of non-access stratum (NAS) signaling, mobility management, etc. The AMF 182a, 182b may use network slicing in order to customize CN support for the WTRU 102a, 102b, 102c based on the type of services utilized by the WTRU 102a, 102b, 102c. For example, different network slices may be established for different use cases, such as services relying on ultra-reliable low latency (URLLC) access, services relying on enhanced massive mobile broadband (eMBB) access, services for MTC access, etc. The AMF 182a, 182b may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro, and / or non-3GPP access technologies, such as WiFi.

[0066] The SMF 183a, 183b may be connected to the AMF 182a, 182b in the CN 106 via the N11 interface. The SMF 183a, 183b may also be connected to the UPF 184a, 184b in the CN 106 via the N4 interface. The SMF 183a, 183b may select and control the UPF 184a, 184b, and configure the traffic routing through the UPF 184a, 184b. The SMF 183a, 183b may perform other functions, such as managing and allocating UE IP addresses, managing PDU sessions, controlling policy implementation and QoS, providing DL data notification, etc. The PDU session type may be IP-based, non-IP-based, Ethernet-based, etc.

[0067] The UPF 184a, 184b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 via the N3 interface, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The UPF 184, 184b may perform other functions, such as routing and forwarding packets, enforcing user plane policies, supporting multi-homed PDU sessions, handling user plane QoS, buffering DL packets, providing mobility anchoring, etc.

[0068] The CN 106 may facilitate communications with other networks. For example, the CN 106 may include or may communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired networks and / or wireless networks owned and / or operated by other service providers. In one embodiment, the WTRUs 102a, 102b, 102c may be connected to the DNs 185a, 185b via the UPFs 184a, 184b via the N3 interfaces to the UPFs 184a, 184b and the N6 interfaces between the UPFs 184a, 184b and the local DNs 185a, 185b.

[0069] Given that Figures 1A to 1D as well as Figures 1A to 1D Corresponding to the description of the present invention, one or more or all of the functions described herein with reference to one or more of the following items may be performed by one or more simulation devices (not shown): WTRU102a to 102d, base station 114a to 114b, evolved Node B 160a to 160c, MME 162, SGW 164, PGW 166, gNB180a to 180c, AMF 182a to 182b, UPF 184a to 184b, SMF 183a to 183b, DN 185a to 185b and / or any other device described herein. The simulation device may be one or more devices configured to mimic one or more or all of the functions described herein. For example, the simulation device can be used to test other devices and / or simulate network and / or WTRU functions.

[0070] The simulation device may be designed to implement one or more tests of other devices in a laboratory environment and / or in an operator network environment. For example, one or more simulation devices may perform one or more functions or all functions while being fully or partially implemented and / or deployed as part of a wired and / or wireless communication network in order to test other devices within the communication network. One or more simulation devices may perform one or more functions or all functions while being temporarily implemented / deployed as part of a wired and / or wireless communication network. The simulation device may be directly coupled to another device for the purpose of testing and / or performing tests using over-the-air wireless communications.

[0071] One or more simulation devices can perform one or more (including all) functions without being implemented / deployed as part of a wired and / or wireless communication network. For example, the simulation device can be used in a test scenario in a test laboratory and / or a non-deployed (e.g., testing) wired and / or wireless communication network to implement testing of one or more components. One or more simulation devices can be test equipment. Direct RF coupling and / or wireless communication via an RF circuit system (e.g., which can include one or more antennas) can be used by the simulation device to send and / or receive data.

[0072] MIMO precoding is a technique used in wireless communication systems to improve the performance and capacity of the system. MIMO systems can achieve increased diversity by processing the transmitted signal at the transmitter before sending the transmitted signal through multiple antennas, utilizing spatial dimensions and multiplexing gain to achieve higher data rates and better reliability. A common method to achieve these benefits is to use multiple transmit antennas and / or multiple receive antennas. In traditional MIMO precoding schemes, each transmit antenna may require a separate radio frequency (RF) chain, including a digital-to-analog converter (DAC), analog components, and a power amplifier. This may lead to increased hardware complexity, power consumption, and cost. The analog components in the RF chain can be controlled based on the precoding weights calculated in the digital baseband processing stage. The precoding weights can be used to optimize transmission based on available channel information, and can, for example, maximize signal power, minimize interference, or balance multiple goals. During the precoding stage, the transmitted signal can be optimized based on channel conditions. Some MIMO systems can utilize hybrid precoding, which combines analog and digital precoding. In hybrid precoding, the transmit signal is split into two stages: analog precoding performed in the RF domain and digital precoding performed in the baseband domain. This approach can significantly reduce the number of RF chains required while still achieving most of the performance benefits of MIMO.

[0073] The transmitter may use feedback information to determine precoding parameters, such as precoding or beamforming weights. The receiver in a MIMO system may provide limited feedback about channel conditions through channel state information (CSI), which may include channel quality indicator (CQI), channel rank indicator (RI), precoder matrix indicator (PMI), interference level, received power, or other information. The type of information fed back by the receiver may depend on network requirements. The value of the feedback sent may vary based on the system scenario. The feedback may constitute parameters that the receiver considers suitable for multi-antenna precoding based on its observation of channel conditions. It should be understood that although the transmitter may use the feedback of the receiver to determine the actual precoding parameters, the feedback may not impose restrictions on the precoding matrix subsequently used by the transmitter. For example, the transmitter may base its decision on feedback supporting other precoding parameters received from another device (or multiple other devices).

[0074] The receiver can determine such feedback by channel estimation, where the receiver receives a reference signal (e.g., CSI-RS) from the transmitter using configured or known resources. These signals are transmitted through the antennas and are designed to enable the receiver to estimate the channel response of each transmit-receive antenna pair. Based on the channel estimate, the receiver can construct a channel matrix, which may be referred to as a channel matrix or a channel response matrix. The matrix may represent the channel gain and phase shift for each antenna pair. In order to reduce feedback overhead, the receiver can quantize the estimated channel matrix by mapping continuous values ​​from the channel matrix to discrete values ​​that can be effectively sent back to the transmitter. The quantized CSI can be represented by a finite number of bits or symbols.

[0075] The feedback may be communicated by various means, such as a dedicated control channel, an uplink transmission, or a dedicated feedback channel. For example, a receiver sending feedback may use a low-rate data stream on the reverse side of the link to communicate information of the channel to a transmitter on the forward side of the link. In this case, the receiver may communicate feedback information associated with a downlink carrier frequency channel on an uplink carrier frequency.

[0076] Figure 2 is an illustration of a MIMO system in accordance with at least one embodiment described herein. Figure 2 2 shows the transmission of channel information feedback from the receiver 220 to the transmitter 210. The receiver 220 may be a WTRU, but in some embodiments, the receiver may be a UE, a base station (BS), a Node B, a transmit receive point (TRP), a remote radio head (RRH), a STA, an AP, or any multi-antenna device. Similarly, the transmitter 210 may be a WTRU, a UE, a base station (BS), a Node B, a transmit receive point (TRP), a remote radio head (RRH), a STA, an AP, or any multi-antenna device. Figure 2In some embodiments consistent with the illustration of FIG. 1 , transmitter 210 may be configured to use multiple antennas to transmit a transmission to receiver 220. The transmission may include data associated with one or more data streams, s(k).

[0077] Receiver 220 may use one or more reference symbols sent by transmitter 210 to obtain knowledge of the downlink channel. When estimating the channel, receiver 220 may select a pre-decoder from codebook 230, which is known to both receiver 220 and transmitter 210. Codebook 230 may include a set of pre-decoders. Each of the pre-decoders can be customized / designed according to the specific channel distribution assumed. The codebook has a size of 2 B For example, the parameters associated with the selected precoder may correspond to channel eigenvalues, phase quantization values, or a quantized channel matrix. Figure 2 The selection of a pre-decoder from the codebook 230 is shown because the receiver 220 sends a signal providing an indication of the pre-decoding parameters corresponding to the selected pre-decoder. Figure 2 As shown, the receiver 220 may transmit a message including feedback information to the transmitter 210. The feedback information may include, for example, a precoding matrix indicator (PMI), which may be an index corresponding to a precoder selected from the codebook 230. The parameter B may be the number of bits used to convey the index.

[0078] Through this feedback, receiver 220 can provide information to transmitter 210 to infer how to best adapt the signal based on the state of the channel. Figure 2 As shown, the transmitter 210 may select a precoding matrix from a codebook based on the PMI transmitted by the receiver 220, for example.

[0079] The number of feedback bits required to convey channel information may depend on the codebook size. B The receiver 220 may indicate that the B bits of the selected precoder may be transmitted via the feedback channel. It should be noted that the rate and / or signal-to-noise ratio (SNR) may be useful information to facilitate communication and may also be fed back.

[0080] Having discussed the codebook-based feedback of the receiver, it is also important to note that the channel state information conveyed in the feedback from the receiver 220 may be outdated or may suffer from feedback errors (e.g., due to hardware impairments). Due to these errors, the transmitter 210 may need to adapt the transmit power and / or data rate due to the imperfect channel state information (CSIT) at the transmitter. In order to effectively utilize the imperfect CSIT, it may be important to consider the error statistics of the CSIT in link adaptation. However, it may be difficult for the transmitter to obtain and track the error statistics because they may depend on the channel environment and the Doppler spectrum. In such cases, ACK / NAK signaling from the upper layer ARQ may be useful to achieve closed-loop adaptation.

[0081] Furthermore, while understanding the benefits of limited rate feedback, it is also important to recognize the drawbacks. Using feedback on one side of the link to increase the achievable data rate may require additional overhead on the other side. In practice, the overhead required to provide feedback may be non-negligible. For example, in a 5G NR system, the overhead involved in high-resolution feedback for a multi-user scenario may be on the order of hundreds of bits. This may significantly reduce the throughput of the system.

[0082] The embodiments described herein can address various technical shortcomings and challenges in the existing pre-decoding / codebook design of MIMO systems in the face of time-varying channel conditions. Among these technical challenges, the selection of pre-decoding parameters (e.g., PMI, RI, etc.) based on the channel estimation performed by the receiver may be inaccurate for at least the following reasons, as briefly expressed in the above paragraphs. Hardware defects caused by nonlinear components may distort channel estimates. Due to channel aging, the delay in the feedback transmitted by the receiver to the transmitter may make the indication PMI received by the transmitter outdated. The codebook-based pre-decoder can be determined based on a fixed probability distribution to represent the wireless channel (e.g., based on an urban, rural or other environment / ), which can also cause high quantization errors. On the other hand, the transmission of a non-codebook-based pre-decoder that can capture CSI more accurately may significantly increase the overhead in an FDD system. Therefore, in order to improve performance while reducing feedback overhead, pre-decoder compression and feedback techniques that capture CSI and hardware nonlinear properties may be required.

[0083] Various solutions to address the above challenges are proposed herein. In the following paragraphs, methods for data-driven MIMO precoder compression and feedback to improve quality of service (e.g., BER, rate) and reduce feedback overhead based on observed data are described. Some proposed techniques may allow the receiver to signal a compressed precoder, and some proposed feedback techniques may allow the transmitter to decompress the precoder with low overhead under time-varying channel conditions. In the embodiments proposed herein, "indication of a precoder" may refer to information indicating a set of precoding parameters (PMI, RI, CQI, etc.), indices associated with the precoding parameters, precoding matrices, multiple transmission layers (i.e., N) that can be used for multi-antenna transmission, and multiple transmission layers (i.e., N) that can be used for multi-antenna transmission. L ) and / or CSI reports. The terms "CSI report", "precoder indication", "precoder" and "feedback" may be used interchangeably herein. The term "compressed precoder" may refer to compressed (or encoded) data that provides an indication of precoding parameters.

[0084] Figure 3 and Figure 4 It is a flowchart illustrating the steps that can be performed when a data-driven pre-decoder compression technique is adopted. Data-driven MIMO pre-decoder compression can be implemented by utilizing channel estimation performed by a receiver. This can be achieved by designing a function mapping between channel estimation and pre-decoder selection using a data-driven method including (i.e.) machine learning, an autoencoder, etc. Compared with the pre-decoding techniques of the prior art, these techniques may include determining a pre-decoder that is suitable for the CSI observed at the transmitter during data transmission. In other words, the receiver can transmit feedback to the transmitter in real time, and the feedback includes a compressed indication of pre-decoding parameters, wherein the pre-decoding parameters are based on channel estimates observed over a period of time. The transmitter can decompress the compressed indication of the pre-decoding parameters fed back by the receiver by, for example, using the decoder counterpart of the encoder adopted at the receiver. As will be explained in further detail herein, the decompression of the compressed indication of the pre-decoding parameters may be error-prone. For example, errors in compression or decompression may result in differences between the recommended pre-decoding parameters determined by the receiver for the channel and the decompression parameters derived by the transmitter from the compressed information received by the receiver. The degree of error experienced may vary based on, for example, the compression ratio used by the receiver to compress the proposed pre-coding parameters. Thus, adaptation of the compression ratio may be provided to the pre-decoder depending on the BER / rate requirements. This approach may provide better performance in terms of BER / rate and provide low overhead for pre-decoder feedback.

[0085] Some embodiments may provide online training / retraining. Online training / retraining may refer to a data-driven pre-decoder compression technique, in which computing resources at the network are used (e.g., by a transmitter in a MIMO system, by a base station, by a node B, or by another network node) to develop a functional mapping between uncompressed pre-decoding parameters and compressed symbols for conveying pre-decoding parameters. A more detailed step-by-step procedure according to at least one embodiment is given in the following paragraphs. In the described model, one or more assumptions related to the setting and other key aspects may be necessary. For example, it may be assumed that the transmitter is implemented with a decoder (e.g., an automatic encoder-decoder based on an AI model) for decompression of a compressed pre-decoder, and the receiver may be implemented with an encoder (e.g., an automatic encoder based on an AI model or an AI model based on transfer learning) for compression of the pre-decoder. The initial weights of the encoder and decoder may be determined as follows. For online training, the initial weights may be randomly assigned. For retraining, the initial weights may be predetermined. For example, the initial weights may be calculated via offline training and stored in a database.

[0086] Figure 3 is a flowchart illustrating the steps of online training / retraining that can be performed by a transmitter in a MIMO system. As shown at 310, the transmitter can configure the receiver with resources (i.e., time domain and frequency domain resources) for receiving CSI-RS (in addition or alternatively, with resources for receiving downlink reference signals), and can send CSI-RS. The receiver configured to receive CSI-RS can perform channel estimation on the configured CSI-RS resources to determine CSI. The receiver can determine a downlink transmit precoder (i.e., a set of suitable precoding parameters that the transmitter can use to send downlink signals). In order to reduce the overhead when transmitting feedback to the transmitter, the receiver can use a precoder compression encoder (e.g., using an AI model) and request an uplink grant at the downlink frequency.

[0087] In some embodiments, as shown at 320, the transmitter may configure one or more time slots for the receiver to transmit signals in the uplink using one or more downlink frequencies, the transmitter sends CSI-RS at these downlink frequencies, and the receiver will estimate CSI and determine the downlink transmit pre-decoder for these downlink frequencies. This can enable training of the decoder at the transmitter and the encoder at the receiver.

[0088] For example, as shown at 330, the transmitter may receive a reference signal (e.g., a sounding reference signal) based on the downlink frequency and time slot indicated to the receiver. The transmitter may also receive a compressed indication of a predecoder determined by the receiver from an earlier transmitted CSI-RS. The transmitter may decode the compressed indication of the predecoder of the receiver to decompress the compressed indication of the predecoder. The transmitter may perform channel estimation of the reference signal to determine the true predecoder of the downlink frequency. As shown at 340, for the same downlink frequency, the transmitter may compare the true predecoder with the decompressed predecoder. The transmitter may use different metrics (e.g., normalized mean square error (l2 norm), chord distance, or other metrics) to measure the loss between the decompressed predecoder and the true predecoder. This may enable the transmitter to calculate the error between the decompressed predecoder and the true predecoder for training a model (e.g., a deep neural network (DNN) or another type of AI / ML model) for predicting the precoding weights to be used by the decoder and / or encoder.

[0089] In some cases, such as in a frequency division duplex (FDD) system (or, for systems where switching may not be feasible), the transmitter may request the receiver to send explicit information indicating the true pre-decoder weights using a physical uplink control channel (PUCCH) and / or a physical uplink shared channel (PUSCH) transmission or using other logically equivalent channels or messages. For example, the explicit information indicating the true pre-decoder weights may include an uncompressed indication of the pre-decoder weights.

[0090] In some embodiments, as shown at 350, the process can be repeated for different compression ratios, which can achieve online training / retraining. For example, during training, the transmitter-receiver pair can continue the process of configuring CSI-RS, time slots for switching to downlink frequency, receiving sounding reference signals (SRS), etc. until the training model converges, or until the observed error measured using a loss function (e.g., normalized mean square error (l2 norm), chord distance) reaches a minimum level. To this end, the following cases can be considered. In some options, different DNN (or AI / ML model) weights can be designed for different compression ratios. In some options, a unified DNN (or AI / ML model) model can be designed for different compression ratios.

[0091] Figure 44 is a flow chart illustrating steps of online training / retraining that may be performed by a receiver in a MIMO system. As shown at 410, the receiver receives configuration information for receiving CSI-RS. The receiver may perform channel estimation based on the configuration information to determine the CSI. As shown at 420, the receiver may determine an appropriate downlink transmit precoder. To reduce overhead when transmitting feedback to the transmitter, the WTRU may use a precoder compression encoder (e.g., using an AI model) and request an uplink grant in the downlink frequency (or frequencies) for which the CSI was determined.

[0092] At 430, the receiver receives configuration information indicating one or more time slots in which the receiver can use a downlink frequency (or multiple frequencies) for transmission. The received configuration information may indicate the downlink frequency to be used by the receiver. The downlink frequency may be the frequency at which the receiver determines the CSI. The receiver may switch to the downlink frequency during the indicated time slot. At 440, the receiver may use the configured time slot and downlink frequency, switch to the downlink frequency, and send a reference signal (e.g., SRS) for the transmitter to estimate. The receiver may also transmit a compression indication of the predecoder (e.g., transmitted via a PUSCH or using another logically equivalent channel). At 450, the receiver may repeat one or more of the previous steps (e.g., for different compression ratios).

[0093] Figure 5 An example of a compression ratio index lookup table is illustrated. The compression ratio index lookup table is a tabular representation of the association between the compression ratio index, modulation coding scheme (MCS), and efficiency / BER. It should be understood that the association between the compression ratio index and the MCS and the association between the compression ratio index and the efficiency / BER can be optional features that can be determined by the model (i.e., DNN or another type of AI / ML model).

[0094] Figure 6 is a signaling flow diagram describing an example of signaling that may be performed between a transmitter and a receiver for online training or retraining. Figure 6 The example shown can be similarly used for different compression ratios. Figure 6As shown, at 610, the transmitter may configure the receiver to receive CSI-RS and may use the downlink frequency to send CSI-RS. The receiver and / or the transmitter may use CSI-RS to train a model for pre-coding compression at a specific compression ratio. The receiver may measure the CSI-RS and determine the pre-decoder of the channel using a pre-decoder compression model with a specific compression ratio. At 620, the receiver may request resources in the downlink frequency for uplink transmission of the reference signal. At 630, the transmitter may configure the receiver with one or more time slots to transmit the uplink transmission at the downlink frequency. Then, at 640, the receiver may switch to the downlink frequency before sending the SRS and the compression indication of the determined pre-decoder in the configured time slot. The transmitter may determine the true pre-decoder of the channel based on the received SRS and may decompress (or decode) the compression indication of the pre-decoder. The transmitter may calculate the error between the true pre-decoder and the decompression decoder. The calculated error can be used to train the AI / ML model of pre-decoder compression. At 650, the transmitter retransmits the CSI-RS for pre-decoder compression, possibly using a different compression ratio. Figure 6 As shown, at least steps 640 and 650 may be repeated until the AI / ML model converges, or until the calculated decompression error is below a threshold.

[0095] Embodiments involving real-time link adaptation and precoding parameter inference are described herein. As will be described in more detail below, the following embodiments may be implemented by a participant in a MIMO system including at least one transmitter and at least one receiver. The embodiments described herein may be implemented in conjunction with (or in parallel with) the embodiments described above regarding online training / retraining. Alternatively, the embodiments described herein may be implemented independently of the embodiments described above regarding online training / retraining.

[0096] In some embodiments described in more detail in the following paragraphs, participants in a MIMO system may utilize channel coherence to reduce the overhead of signaling a pre-decoder. Channel coherence may refer to the time-frequency region over which channel conditions remain constant. Similarly, coherence time may represent the time over which channel characteristics (e.g., path loss, delay, and fading) remain constant, and coherence bandwidth may refer to the frequency range over which the above characteristics remain constant. For example, channel coherence may fluctuate based on the environment, the mobility of the user, and the frequency of the user's operation. A receiver in a MIMO system may be configured to estimate channel coherence, coherence time, and / or coherence bandwidth by measuring channel characteristics. For example, when measuring CSI-RS to determine channel state information, the receiver may implicitly estimate channel coherence. Another method for estimating changes in channel conditions may be to measure Doppler spread, which may be related to the user's speed and carrier frequency. Doppler spread may be estimated based on changes in the phase or frequency of the received signal over time. For example, the inverse of the maximum Doppler shift (Doppler frequency) may be used as an approximation of the coherence time. Other metrics such as received signal strength indicator (RSSI), reference signal received quality (RSRQ), or channel quality indicator (CQI) can provide insight into how quickly channel conditions change.A similar approach can be used by the transmitter to estimate channel coherence.

[0097] Figure 7 is a flow chart illustrating steps of real-time data driven precoder compression that may be performed by a transmitter. As shown at 710, the transmitter may send a CSI-RS to a receiver. In some embodiments, depending on the transmission requirements of the transmitter, the transmitter may configure the receiver with a precoder compression index for each subband (i.e., corresponding to a specific precoder compression ratio). The precoder compression index may be associated with the precoder compression ratio and / or MCS, substantially as Figure 5 As shown in the table above. More specifically, for high resolution requirements (e.g., for MU-MIMO implementation), the transmitter may configure the receiver with a lower compression ratio, while for low resolution requirements (e.g., for SU-MIMO implementation), the transmitter may configure the receiver with a higher compression ratio. In addition, in scenarios where the channel is frequency selective, or where the channel experiences different interference levels for different subcarriers, the transmitter may configure different compression ratios for different subbands. In some embodiments, for use cases when the highest resolution indication is required, the transmitter may request the receiver to provide an uncompressed indication of the pre-decoder.

[0098] In some embodiments, such as those that exploit channel coherence to reduce pre-decoder signaling overhead, the transmitter may request the receiver to feed back its instructions to the pre-decoder within a given time frame. The time frame may be specified as a certain percentage of the coherence time. The transmitter may also receive a report indicating the channel coherence time and / or frequency correlation information for different sub-bands.

[0099] As shown at 720, the transmitter may receive feedback from the receiver, the feedback including a compression indication of the pre-decoder. Figure 7 In other embodiments not shown in FIG. 1 , such as those in which the transmitter requests an uncompressed indication of the predecoder, the indication of the predecoder may be uncompressed and may indicate the predecoder at the highest possible resolution.

[0100] At 730, the transmitter may use a decompressor (or decoder) model to decompress the compressed indication of the pre-decoder. The decompressor / decoder model may be an AI / ML model that is trained via an online training / retraining method, fully described herein.

[0101] At 740, the transmitter sends data to the receiver. The transmitted data may be precoded according to the precoding parameters fed back by the receiver.

[0102] In some embodiments, as shown at 750, the transmitter may receive a report indicating a key performance indicator (KPI) from the receiver. The KPI may include, for example, one or more of a bit error rate (BER), a signal-to-noise ratio (SNR), a latency metric, or a data rate. The report may include, for example, an indication that the KPI is below a threshold (e.g., a preconfigured threshold) for a given one or more time frames (e.g., an average of the KPI over multiple time frames is below a preconfigured threshold). In some embodiments, as shown at 760, the transmitter may, for example, initiate retraining of a pre-decoder compression model. The transmitter may initiate retraining based on determining that one or more transmission requirements or parameters are not met. It may be determined based on a report or KPI received from the receiver that a transmission requirement or parameter is not met. When initiating retraining, the transmitter and / or receiver may perform steps for online training / retraining according to one or more embodiments provided herein.

[0103] Figure 8is a flow chart illustrating the steps of real-time data-driven pre-decoder compression that may be performed by a receiver. As shown at 810, the receiver receives a CSI-RS and configuration information indicating a compression ratio with which the receiver's instructions to the pre-decoder are compressed. At 820, the receiver estimates the CSI based on the received CSI-RS and determines pre-decoder parameters for the channel. The receiver may utilize a pre-decoder compression model (e.g., using an autoencoder or a transfer learning-based model) and feedback an indication of pre-decoding parameters compressed using the configured compression ratio. In some embodiments, the receiver may also transmit an indication of a recommended compression ratio. For example, the receiver may adaptively indicate a higher compression ratio to be used to reduce overhead, or indicate a lower compression ratio to improve performance of subsequent transmissions (e.g., reduce decompression errors). The indication of the adaptive compression ratio provided by the receiver may be based on a lookup table (e.g., such as Figure 5 as shown) or simple up / down commands.

[0104] To further reduce the feedback overhead, the receiver may perform one or more of the following steps / procedures. The receiver may exploit the correlation of the CSI over time (channel coherence), for example, by reporting a compressed pre-decoder only after a certain percentage of the channel coherence time has elapsed. Since the coherence time between different sub-bands may be different, the channel conditions in different sub-bands may vary over time, depending on environmental changes. The receiver may send an indication of the pre-decoder for each sub-band based on the coherence time of each sub-band. The receiver may also exploit the correlation coefficients across sub-bands to obtain a low-overhead compressed pre-decoder matrix. In Figure 8 In an embodiment not shown in , the receiver may report the coherence time for each subband as well as the subband frequency correlation information. The receiver may receive an uplink grant based on the coherence time to indicate the compressed precoder matrix for each subband individually.

[0105] In some embodiments, as shown at 830, the receiver may receive pre-decoded symbols from the transmitter (i.e., pre-decoded symbols based on compression indications of the receiver's pre-decoder). At 840, the receiver may determine a key performance indicator (KPI) reflecting the performance of the pre-decoder (e.g., SNR / BER). For example, the receiver may determine whether to report the KPI to the transmitter based on the KPI. The receiver may transmit a request for CSI-RS transmission to the transmitter to determine the pre-decoder, and may feed back an indication of the determined pre-decoder without compression (e.g., omitting the auto-encoder). The receiver may also or alternatively transmit a message to the transmitter indicating that the transmitter should continue data transmission without adopting a compression-decompression model (e.g., without using an auto-encoder).

[0106] The receiver may receive data from the transmitter. The receiver may measure performance (e.g., BER / SNR) based on the received data. If the performance metric is insufficient (i.e., the performance metric does not meet a threshold), the receiver may determine that the channel condition is poor, and the receiver may transmit an indication to the transmitter to switch to data transmission based on the autoencoder model. If the performance metric is sufficient, the receiver may determine that the autoencoder model needs to be recalibrated. The receiver may then indicate to the transmitter that the autoencoder model parameters are in error and request retraining of the autoencoder model.

[0107] Fig. 9 is a schematic diagram illustrating an example of signaling between a transmitter and a receiver that performs real-time link adaptation. Fig. 9 As shown, at 905, the transmitter may transmit a first CSI-RS in different subbands. At 910, the receiver receives the CSI-RS from the transmitter and feeds back a coherence time value for each subband. Fig. 9 In some embodiments shown, at 915, the receiver may suggest a pre-decoder compression ratio value, which may depend on the requirements, capabilities, or limitations of the receiver. At 920, the transmitter transmits a second CSI-RS and configures the receiver with a compression value index for each subband. The compression value index may correspond to the compression ratio configured for each subband. At 925, the transmitter configures the receiver with a CSI reporting time interval, which may be based on the coherence time of each subband. For example, the CSI reporting time interval may specify that the receiver transmit a CSI report for each subband before a certain percentage of the coherence time has passed.

[0108] As shown at 930, the receiver may transmit a CSI report (e.g., including a compressed indication of a predecoder for each subband) to the transmitter. The timing of the CSI report may be based on the CSI reporting time interval provided by the transmitter. At 935, the transmitter may use the predecoder determined from the compressed indication of the receiver's predecoder to send data. In some embodiments, as shown at 940, the receiver measures a KPI (e.g., BER) and may request the transmitter to transmit a third CSI-RS. After receiving the third CSI-RS, the receiver may determine the predecoder again and provide the transmitter with an uncompressed indication of the predecoder. At 945, the transmitter may send a fourth CSI-RS to enable the receiver to measure the performance of the MIMO system following the receiver's uncompressed indication of the predecoder. At 950, if the performance reaches a threshold, the receiver may request retraining of the predecoder compression model.

[0109] Although the solutions described herein explicitly consider New Radio (NR) or Long Term Evolution (LTE) and LTE-Advanced (LTE-A) standards, it should be understood that the solutions described herein are not limited to systems operating according to these standards and that the solutions proposed herein may also be applicable to other wireless systems.

[0110] Although features and elements are described above in specific combinations, it will be understood by those of ordinary skill in the art that each feature or element may be used alone or in any combination with other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (sent via a wired or wireless connection) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, read-only memory (ROM), random access memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media (such as built-in hard disks and removable disks), magneto-optical media, and optical media (such as CD-ROM disks and digital versatile disks (DVDs)). A processor associated with software may be used to implement a radio frequency transceiver for a WTRU, UE, terminal, base station, RNC, or any host computer.

Claims

1. A method performed by a receiver in a multiple-input multiple-output (MIMO) system, the method comprising: receiving a first channel state information (CSI) reference signal (CSI-RS) from a transmitter using a plurality of subbands; sending a report to the transmitter, the report indicating coherence time information respectively associated with the plurality of subbands, wherein the coherence time information respectively associated with the plurality of subbands is determined based on CSI determined from the received CSI-RS; receiving configuration information from the transmitter, the configuration information indicating at least one compression ratio respectively associated with at least one of the plurality of subbands; receiving at least one second CSI-RS from the transmitter using the at least one subband of the plurality of subbands; as well as sending feedback to the transmitter, the feedback comprising compression information indicating, for the at least one subband of the plurality of subbands, a recommended precoding parameter determined based on the received at least one second CSI-RS, wherein the feedback is sent within a coherence time associated with the at least one subband of the plurality of subbands, and wherein the compression information is compressed based on one of the at least one compression ratios respectively associated with the at least one subband of the plurality of subbands.

2. The method according to claim 1, comprising: receiving, from the transmitter, data including symbols precoded based on the feedback using the at least one subband of the plurality of subbands, the feedback including compressed information indicating a suggested precoding parameter; and Under the condition that the received data does not meet the required quality threshold: sending a request to the transmitter to send a third CSI-RS, the third CSI-RS including non-precoded symbols; receiving a third CSI-RS, wherein the third CSI-RS includes non-precoded symbols; and On the condition that the third CSI-RS including the non-precoded symbol does not meet a required quality threshold, a message is sent to the transmitter, the message including a request to retrain a precoder compression model.

3. The method of claim 1 , comprising sending a message to the transmitter, the message indicating one or more recommended compression ratios associated with at least one of the plurality of subbands, wherein the received configuration information indicating the at least one compression ratio comprises the indicated one or more recommended compression ratios associated with the at least one of the plurality of subbands.

4. The method according to claim 1, the method comprising receiving configuration information indicating a CSI reporting time interval from the transmitter, wherein: The feedback is sent within a window equal to a percentage of the coherence time associated with the at least one subband of the plurality of subbands based on the indicated CSI reporting time interval.

5. The method of claim 1 , wherein the coherence time associated with a first subband of the plurality of subbands is different from a coherence time associated with a second subband of the plurality of subbands, and wherein the first subband of the plurality of subbands and the second subband of the plurality of subbands experience different channel conditions.

6. The method of claim 2, wherein the at least one compression ratio is respectively associated with at least one bit error rate (BER), wherein whether the received data does not meet a required quality threshold is determined based on the at least one BER associated with the at least one subband of the plurality of subbands.

7. A receiver configured to operate in a multiple-input multiple-output (MIMO) system, the receiver comprising: processor; Transceiver; and At least two antennas; The processor, the transceiver, and the at least two antennas are configured to receive a first channel state information (CSI) reference signal (CSI-RS) from a transmitter using a plurality of subbands; The processor, the transceiver, and the at least two antennas are configured to send a report to the transmitter, the report indicating coherence time information respectively associated with the plurality of subbands, wherein the coherence time information respectively associated with the plurality of subbands is determined based on CSI determined from the received CSI-RS; The processor, the transceiver, and the at least two antennas are configured to receive configuration information from the transmitter, the configuration information indicating at least one compression ratio respectively associated with at least one subband of the plurality of subbands; The processor, the transceiver, and the at least two antennas are configured to receive at least one second CSI-RS from the transmitter using the at least one subband of the plurality of subbands; and The processor, the transceiver, and the at least two antennas are configured to send feedback to the transmitter, the feedback comprising compressed information indicating, for the at least one subband of the plurality of subbands, a recommended precoding parameter determined based on the received at least one second CSI-RS, wherein the feedback is sent within a coherence time associated with the at least one subband of the plurality of subbands, and wherein the compressed information is compressed based on one of the at least one compression ratios respectively associated with the at least one subband of the plurality of subbands.

8. The receiver of claim 7, the processor, the transceiver, and the at least two antennas configured to receive data including symbols precoded based on the feedback from the transmitter using the at least one subband of the plurality of subbands, the feedback including compressed information indicating a suggested precoding parameter; and Under the condition that the received data does not meet the required quality threshold: The processor, the transceiver, and the at least two antennas are configured to send a request to the transmitter to send a third CSI-RS, the third CSI-RS comprising non-precoded symbols; The processor, the transceiver, and the at least two antennas are configured to receive a third CSI-RS, the third CSI-RS comprising non-precoded symbols; and Under the condition that the third CSI-RS including the non-precoded symbol does not meet the required quality threshold, the processor, the transceiver and the at least two antennas are configured to send a message to the transmitter, the message including a request to retrain a precoder compression model.

9. The receiver of claim 7, wherein the processor, the transceiver, and the at least two antennas are configured to send a message to the transmitter, the message indicating one or more recommended compression ratios associated with at least one of the plurality of subbands, wherein the received configuration information indicating the at least one compression ratio includes the indicated one or more recommended compression ratios associated with the at least one of the plurality of subbands.

10. The receiver according to claim 7, wherein the processor, the transceiver and the at least two antennas are configured to receive configuration information indicating a CSI reporting time interval from the transmitter, wherein: The feedback is sent within a window equal to a percentage of the coherence time associated with the at least one subband of the plurality of subbands based on the indicated CSI reporting time interval.

11. The receiver of claim 7, wherein the coherence time associated with a first subband of the plurality of subbands is different from a coherence time associated with a second subband of the plurality of subbands, and wherein the first subband of the plurality of subbands and the second subband of the plurality of subbands experience different channel conditions.

12. The receiver of claim 8, wherein the at least one compression ratio is respectively associated with at least one bit error rate (BER), wherein whether the received data does not meet a required quality threshold is determined based on the at least one BER associated with the at least one subband of the plurality of subbands.

13. A transmitter configured to operate in a multiple-input multiple-output (MIMO) system, the transmitter comprising: processor; Transceiver; and At least two antennas; The processor, the transceiver, and the at least two antennas are configured to transmit at least one channel state information (CSI) reference signal (CSI-RS) using at least one downlink frequency; The processor, the transceiver, and the at least two antennas are configured to receive a message from a receiver operating in the MIMO system, the message requesting authorization for an uplink transmission to be sent using the at least one downlink frequency; The processor, the transceiver, and the at least two antennas are configured to, in response to the message requesting the grant, send configuration information to the receiver, the configuration information indicating at least one time slot for sending the uplink transmission using the at least one downlink frequency; The processor, the transceiver, and the at least two antennas are configured to receive at least one sounding reference signal (SRS); The processor, the transceiver, and the at least two antennas are configured to receive feedback from the receiver, the feedback comprising compressed information indicating a suggested precoding parameter; The processor is configured to determine, based on the received at least one SRS, a precoding parameter to be used for transmission at the downlink frequency; The processor is configured to decompress the compressed information indicating the suggested precoding parameters using an artificial intelligence / machine learning (AI / ML) based automatic decoder model, the AI / ML based automatic decoder model being configured with a set of initial weights; and The processor is configured to compare the determined precoding parameters with the suggested precoding parameters to determine a loss metric associated with the compression information indicative of the suggested precoding parameters.

14. The transmitter of claim 13, configured to train the AI / ML based automatic decoder, The processor, the transceiver, and the at least two antennas are configured to transmit a second CSI-RS using at least one downlink frequency; The processor, the transceiver, and the at least two antennas are configured to receive a second message from the receiver requesting a second authorization for a second uplink transmission sent using the at least one downlink frequency; The processor, the transceiver, and the at least two antennas are configured to, in response to the second message requesting the grant, send second configuration information to the receiver, the second configuration information indicating a second at least one time slot for sending the second uplink transmission using the at least one downlink frequency; The processor, the transceiver, and the at least two antennas are configured to receive a second at least one SRS; The processor, the transceiver, and the at least two antennas are configured to receive second feedback from the receiver, the second feedback comprising second compressed information indicating a second suggested precoding parameter; The processor is configured to determine, based on the received at least one SRS, a second precoding parameter to be used for transmission at the downlink frequency; The processor is configured to decompress the second compressed information indicating the second suggested precoding parameters using an AI / ML based automatic decoder model, the AI / ML based automatic decoder model being configured with a set of updated weights; and The processor is configured to compare a second determined precoding parameter with the second suggested precoding parameter to determine a second loss metric associated with the compression information indicative of the suggested precoding parameter.

15. The transmitter of claim 14, the transmitter being configured to stop training the AI / ML-based auto-decoder model based on a determination that the determined second loss metric is an acceptable value.

16. The transmitter of claim 13, wherein the compressed information and the second compressed information are compressed using different compression ratios.

17. The transmitter of claim 13, the processor, the transceiver, and the at least two antennas configured to send a request to the receiver for uncompressed information indicating the suggested precoding parameters.

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