WO2019222875A1

WO2019222875A1 - Techniques and apparatuses for configuring demodulation reference signals in grant-free uplink non-orthogonal multiple access systems

Info

Publication number: WO2019222875A1
Application number: PCT/CN2018/087625
Authority: WO
Inventors: Qiaoyu Li; Chao Wei; Hao Xu
Original assignee: Qualcomm Incorporated
Priority date: 2018-05-21
Filing date: 2018-05-21
Publication date: 2019-11-28

Abstract

Some techniques and apparatuses described herein improve network performance by reducing the likelihood of demodulation reference signal (DMRS) collisions between multiple user equipment (UEs) that repeat DMRS sequences across multiple subframes in a grant-free uplink non-orthogonal multiple access (NOMA) communication system. For example, some techniques and apparatuses described herein permit a UE to select a DMRS sequence and/or an orthogonal cover code (OCC) based at least in part on a transmission opportunity in which the UE is to begin transmission of the DMRS sequence, thereby reducing a likelihood of collision across transmission opportunities. In this way, cross-subframe DMRS collisions may be reduced and cross-subframe CSI estimation may be improved, thereby leading to more accurate CSI estimations and improving network performance. Furthermore, some techniques and apparatuses described herein reduce complexity associated with detecting DMRS sequences by reducing a number of blind detection hypothesis operations performed by a base station.

Description

TECHNIQUES AND APPARATUSES FOR CONFIGURING DEMODULATION REFERENCE SIGNALS IN GRANT-FREE UPLINK NON-ORTHOGONAL MULTIPLE ACCESS SYSTEMS

BACKGROUND Field

Aspects of the present disclosure generally relate to wireless communication, and more particularly to techniques and apparatuses for configuring demodulation reference signals in grant-free uplink non-orthogonal multiple access (NOMA) systems.

Background

Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, and/or the like) . Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, orthogonal frequency-division multiple access (OFDMA) systems, single-carrier frequency-division multiple access (SC-FDMA) systems, time division synchronous code division multiple access (TD-SCDMA) systems, and Long Term Evolution (LTE) . LTE/LTE-Advanced is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by the Third Generation Partnership Project (3GPP) .

A wireless communication network may include a number of base stations (BSs) that can support communication for a number of user equipment (UEs) . A UE may communicate with a BS via the downlink and uplink. The downlink (or forward link) refers to the communication link from the BS to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the BS. As will be described in more detail herein, a BS may be referred to as a Node B, a gNB, an access point (AP) , a radio head, a transmit receive point (TRP) , a 5G BS, a 5G Node B, and/or the like.

The above multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless communication devices to communicate on a municipal, national, regional, and even global level. 5G, which may also be referred to as New radio (NR) , is a set of enhancements to the LTE mobile standard promulgated by the Third Generation Partnership Project (3GPP) . 5G is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using OFDM with a cyclic prefix (CP) (CP-OFDM) on the downlink (DL) , using CP-OFDM and/or SC-FDM (e.g., also known as discrete Fourier transform spread ODFM (DFT-s-OFDM) ) on the uplink (UL) , as well as supporting beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE and 5G technologies. Preferably, these improvements should be applicable to other multiple access technologies and the telecommunication standards that employ these technologies.

SUMMARY

Some UEs, such as lower power narrowband Internet of Things (NB IoT) UEs, may repeat transmissions in a time domain (e.g., in multiple subframes, slots, and/or the like) to provide coverage enhancement and increase a likelihood of successful reception, by a base station, of a signal transmitted by the UE. For example, a UE may repeat a demodulation reference signal (DMRS) sequence together with repetition of data in multiple subframes so that a base station can combine DMRS sequences received in multiple subframes to obtain a more accurate estimate of channel state information (CSI) for the UE. In addition, a UE may also randomly determine a transmission opportunity, in the time domain, in which to start transmitting an initial transmission of data and/or the DMRS sequence. However, when multiple UEs are transmitting DMRS sequences to aid the CSI estimation for grant-free uplink non-orthogonal multiple access (NOMA) communication systems, each UE is supposed to randomly select its own DMRS sequence from a predefined set of DMRS sequences. Thus, there is a high likelihood that DMRS sequences from multiple UEs will collide, especially when the DMRS sequences are repeated over multiple subframes (e.g., leading to cross-subframe DMRS collisions) . Particularly, a UE starting transmission in a later transmission opportunity may select the same DMRS sequence as the DMRS sequence selected by another UE starting transmission in an earlier transmission opportunity. In such a case, parts of the subframes of both these UEs would have DMRS collisions. However, the base station may not be able to properly detect such partial collision and the cross-subframe CSI estimation performance can become degraded. As a result, the base station may be unable to accurately estimate CSI for the UEs, which may lead to sub-optimal configurations and poor network performance.

Some techniques and apparatuses described herein improve network performance by reducing the likelihood of DMRS collisions between multiple UEs that repeat DMRS sequences across multiple subframes in a grant-free uplink NOMA communication system. For example, some techniques and apparatuses described herein permit a UE to select a DMRS sequence based at least in part on a transmission opportunity in which the UE is to begin transmission of the DMRS sequence, thereby reducing a likelihood of collision across transmission opportunities. In this way, cross-subframe DMRS collisions may be reduced and cross-subframe CSI estimation may be improved, thereby leading to more accurate CSI estimations and improving network performance. Furthermore, some techniques and apparatuses described herein reduce a complexity associated with detecting DMRS sequences for UE transmission detection by reducing a number of blind detection hypothesis operations performed by a base station. For example, the base station may perform blind detection using a subset of DMRS sequences associated with a transmission opportunity in which a DMRS sequence is transmitted by the UE. When DMRS selection is associated with a transmission opportunity, such blind detection can be performed, for the UEs starting transmission from the same transmission opportunity, with a much lower detection dimension as compared DMRS selection that is not associated with a transmission opportunity.

In an aspect of the disclosure, a method, a user equipment (UE) , an apparatus, and a computer program product are provided.

In some aspects, the method may by performed by a UE. The method may include determining a transmission opportunity in a time domain, wherein the transmission opportunity is selected from a plurality of transmission opportunities associated with the UE for grant-free uplink non-orthogonal multiple access (NOMA) transmissions with repetition over multiple subframes; randomly selecting a demodulation reference signal (DMRS) sequence, for a grant-free uplink NOMA transmission, from a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions, wherein the subset of all DMRS sequences is determined based at least in part on the transmission opportunity, wherein different subsets of DMRS sequences are associated with different transmission opportunities, and wherein DMRS sequences in the different subsets are exclusive to the respective subsets; scrambling the DMRS sequence using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) ; and transmitting the scrambled DMRS sequence in the transmission opportunity.

In some aspects, the UE may include a memory and one or more processors operatively coupled to the memory. The memory and the one or more processors may be configured to determine a transmission opportunity in a time domain, wherein the transmission opportunity is selected from a plurality of transmission opportunities associated with the UE for grant-free uplink non-orthogonal multiple access (NOMA) transmissions with repetition over multiple subframes; randomly select a demodulation reference signal (DMRS) sequence, for a grant-free uplink NOMA transmission, from a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions, wherein the subset of all DMRS sequences is determined based at least in part on the transmission opportunity, wherein different subsets of DMRS sequences are associated with different transmission opportunities, and wherein DMRS sequences in the different subsets are exclusive to the respective subsets; scramble the DMRS sequence using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) ; and transmit the scrambled DMRS sequence in the transmission opportunity.

In some aspects, the apparatus may include means for determining a transmission opportunity in a time domain, wherein the transmission opportunity is selected from a plurality of transmission opportunities associated with the apparatus for grant-free uplink non-orthogonal multiple access (NOMA) transmissions with repetition over multiple subframes; means for randomly selecting a demodulation reference signal (DMRS) sequence, for a grant-free uplink NOMA transmission, from a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions, wherein the subset of all DMRS sequences is determined based at least in part on the transmission opportunity, wherein different subsets of DMRS sequences are associated with different transmission opportunities, and wherein DMRS sequences in the different subsets are exclusive to the respective subsets; means for scrambling the DMRS sequence using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) ; and means for transmitting the scrambled DMRS sequence in the transmission opportunity.

In some aspects, the computer program product may include a non-transitory computer-readable medium storing one or more instructions. The one or more instructions, when executed by one or more processors of a UE, may cause the one or more processors to determine a transmission opportunity in a time domain, wherein the transmission opportunity is selected from a plurality of transmission opportunities associated with the UE for grant-free uplink non-orthogonal multiple access (NOMA) transmissions with repetition over multiple subframes; randomly select a demodulation reference signal (DMRS) sequence, for a grant-free uplink NOMA transmission, from a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions, wherein the subset of all DMRS sequences is determined based at least in part on the transmission opportunity, wherein different subsets of DMRS sequences are associated with different transmission opportunities, and wherein DMRS sequences in the different subsets are exclusive to the respective subsets; scramble the DMRS sequence using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) ; and transmit the scrambled DMRS sequence in the transmission opportunity.

In some aspects, the method may by performed by a UE. The method may include selecting a demodulation reference signal (DMRS) sequence for a grant-free uplink non-orthogonal multiple access (NOMA) transmission with repetition over multiple subframes, wherein the DMRS sequence is randomly selected from a predefined set of DMRS sequences; and transmitting the DMRS sequence in a transmission opportunity.

In some aspects, the UE may include a memory and one or more processors operatively coupled to the memory. The memory and the one or more processors may be configured to select a demodulation reference signal (DMRS) sequence for a grant-free uplink non-orthogonal multiple access (NOMA) transmission with repetition over multiple subframes, wherein the DMRS sequence is randomly selected from a predefined set of DMRS sequences; and transmit the DMRS sequence in a transmission opportunity.

In some aspects, the apparatus may include means for selecting a demodulation reference signal (DMRS) sequence for a grant-free uplink non-orthogonal multiple access (NOMA) transmission with repetition over multiple subframes, wherein the DMRS sequence is randomly selected from a predefined set of DMRS sequences; and means for transmitting the DMRS sequence in a transmission opportunity.

In some aspects, the computer program product may include a non-transitory computer-readable medium storing one or more instructions. The one or more instructions, when executed by one or more processors of a UE, may cause the one or more processors to select a demodulation reference signal (DMRS) sequence for a grant-free uplink non-orthogonal multiple access (NOMA) transmission with repetition over multiple subframes, wherein the DMRS sequence is randomly selected from a predefined set of DMRS sequences; and transmit the DMRS sequence in a transmission opportunity.

Aspects generally include a method, apparatus, system, computer program product, non-transitory computer-readable medium, user equipment, base station, wireless communication device, and processing system as substantially described herein with reference to and as illustrated by the accompanying drawings and specification.

The foregoing has outlined rather broadly the features and technical advantages of examples according to the disclosure in order that the detailed description that follows may be better understood. Additional features and advantages will be described hereinafter. The conception and specific examples disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. Such equivalent constructions do not depart from the scope of the appended claims. Characteristics of the concepts disclosed herein, both their organization and method of operation, together with associated advantages will be better understood from the following description when considered in connection with the accompanying figures. Each of the figures is provided for the purpose of illustration and description, and not as a definition of the limits of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is diagram illustrating an example of a wireless communication network.

FIG. 2 is a diagram illustrating an example of a base station in communication with a user equipment (UE) in a wireless communication network.

FIGs. 3-8 are diagrams illustrating examples of configuring demodulation reference signals in grant-free uplink non-orthogonal multiple access (NOMA) systems.

FIGs. 9 and 10 are flow charts of methods of wireless communication.

FIG. 11 is a conceptual data flow diagram illustrating the data flow between different modules/means/components in an example apparatus.

FIG. 12 is a diagram illustrating an example of a hardware implementation for an apparatus employing a processing system.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purposes of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, and/or the like (collectively referred to as “elements” ) . These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or any combination of elements may be implemented with a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, digital signal processors (DSPs) , field programmable gate arrays (FPGAs) , programmable logic devices (PLDs) , state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, and/or the like, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

Accordingly, in one or more example embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise a random-access memory (RAM) , a read-only memory (ROM) , an electrically erasable programmable ROM (EEPROM) , compact disk ROM (CD-ROM) or other optical disk storage, magnetic disk storage or other magnetic storage devices, combinations of the aforementioned types of computer-readable media, or any other medium that can be used to store computer executable code in the form of instructions or data structures that can be accessed by a computer.

It is noted that while aspects may be described herein using terminology commonly associated with 3G and/or 4G wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems, such as 5G and later, including 5G technologies.

FIG. 1 is a diagram illustrating a network 100 in which aspects of the present disclosure may be practiced. The network 100 may be an LTE network or some other wireless network, such as a 5G network. Wireless network 100 may include a number of BSs 110 (shown as BS 110a, BS 110b, BS 110c, and BS 110d) and other network entities. A BS is an entity that communicates with user equipment (UEs) and may also be referred to as a base station, a 5G BS, a Node B, a gNB, a 5G NB, an access point, a transmit receive point (TRP) , and/or the like. Each BS may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to a coverage area of a BS and/or a BS subsystem serving this coverage area, depending on the context in which the term is used.

A BS may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or another type of cell. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscription. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscription. A femto cell may cover a relatively small geographic area (e.g., a home) and may allow restricted access by UEs having association with the femto cell (e.g., UEs in a closed subscriber group (CSG) ) . A BS for a macro cell may be referred to as a macro BS. A BS for a pico cell may be referred to as a pico BS. A BS for a femto cell may be referred to as a femto BS or a home BS. In the example shown in FIG. 1, a BS 110a may be a macro BS for a macro cell 102a, a BS 110b may be a pico BS for a pico cell 102b, and a BS 110c may be a femto BS for a femto cell 102c. A BS may support one or multiple (e.g., three) cells. The terms “eNB” , “base station” , “5G BS” , “gNB” , “TRP” , “AP” , “node B” , “5G NB” , and “cell” may be used interchangeably herein.

In some examples, a cell may not necessarily be stationary, and the geographic area of the cell may move according to the location of a mobile BS. In some examples, the BSs may be interconnected to one another and/or to one or more other BSs or network nodes (not shown) in the access network 100 through various types of backhaul interfaces such as a direct physical connection, a virtual network, and/or the like using any suitable transport network.

Wireless network 100 may also include relay stations. A relay station is an entity that can receive a transmission of data from an upstream station (e.g., a BS or a UE) and send a transmission of the data to a downstream station (e.g., a UE or a BS) . A relay station may also be a UE that can relay transmissions for other UEs. In the example shown in FIG. 1, a relay station 110d may communicate with macro BS 110a and a UE 120d in order to facilitate communication between BS 110a and UE 120d. A relay station may also be referred to as a relay BS, a relay base station, a relay, and/or the like.

Wireless network 100 may be a heterogeneous network that includes BSs of different types, e.g., macro BSs, pico BSs, femto BSs, relay BSs, and/or the like. These different types of BSs may have different transmit power levels, different coverage areas, and different impact on interference in wireless network 100. For example, macro BSs may have a high transmit power level (e.g., 5 to 40 Watts) whereas pico BSs, femto BSs, and relay BSs may have lower transmit power levels (e.g., 0.1 to 2 Watts) .

A network controller 130 may couple to a set of BSs and may provide coordination and control for these BSs. Network controller 130 may communicate with the BSs via a backhaul. The BSs may also communicate with one another, e.g., directly or indirectly via a wireless or wireline backhaul.

UEs 120 (e.g., 120a, 120b, 120c) may be dispersed throughout wireless network 100, and each UE may be stationary or mobile. A UE may also be referred to as an access terminal, a terminal, a mobile station, a subscriber unit, a station, etc. A UE may be a cellular phone (e.g., a smart phone) , a personal digital assistant (PDA) , a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a tablet, a camera, a gaming device, a netbook, a smartbook, an ultrabook, medical device or equipment, biometric sensors/devices, wearable devices (smart watches, smart clothing, smart glasses, smart wrist bands, smart jewelry (e.g., smart ring, smart bracelet) ) , an entertainment device (e.g., a music or video device, or a satellite radio) , a vehicular component or sensor, smart meters/sensors, industrial manufacturing equipment, a global positioning system device, or any other suitable device that is configured to communicate via a wireless or wired medium.

Some UEs may be considered machine-type communication (MTC) or evolved or enhanced machine-type communication (eMTC) UEs. MTC and eMTC UEs include, for example, robots, drones, remote devices, such as sensors, meters, monitors, location tags, etc., that may communicate with a base station, another device (e.g., remote device) , or some other entity. A wireless node may provide, for example, connectivity for or to a network (e.g., a wide area network such as Internet or a cellular network) via a wired or wireless communication link. Some UEs may be considered Internet-of-Things (IoT) devices, and/or may be implemented as may be implemented as NB-IoT (narrowband internet of things) devices. Some UEs may be considered a Customer Premises Equipment (CPE) . UE 120 may be included inside a housing that houses components of UE 120, such as processor components, memory components, and/or the like.

In general, any number of wireless networks may be deployed in a given geographic area. Each wireless network may support a particular RAT and may operate on one or more frequencies. A RAT may also be referred to as a radio technology, an air interface, and/or the like. A frequency may also be referred to as a carrier, a frequency channel, and/or the like. Each frequency may support a single RAT in a given geographic area in order to avoid interference between wireless networks of different RATs. In some cases, 5G RAT networks may be deployed.

5G may refer to radios configured to operate according to a new air interface (e.g., other than Orthogonal Frequency Divisional Multiple Access (OFDMA) -based air interfaces) or fixed transport layer (e.g., other than Internet Protocol (IP) ) . In aspects, 5G may utilize OFDM with a CP (herein referred to as cyclic prefix OFDM or CP-OFDM) and/or SC-FDM on the uplink, may utilize CP-OFDM on the downlink and include support for half-duplex operation using TDD. In aspects, 5G may, for example, utilize OFDM with a CP (herein referred to as CP-OFDM) and/or discrete Fourier transform spread orthogonal frequency-division multiplexing (DFT-s-OFDM) on the uplink, may utilize CP-OFDM on the downlink and include support for half-duplex operation using TDD. 5G may include Enhanced Mobile Broadband (eMBB) service targeting wide bandwidth (e.g., 80 megahertz (MHz) and beyond) , millimeter wave (mmW) targeting high carrier frequency (e.g., 60 gigahertz (GHz) ) , massive MTC (mMTC) targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra reliable low latency communications (URLLC) service.

A single component carrier bandwidth of 100 MHZ may be supported. 5G resource blocks may span 12 sub-carriers with a sub-carrier bandwidth of 75 kilohertz (kHz) over a 0.1 ms duration. Each radio frame may include 50 subframes with a length of 10 ms. Consequently, each subframe may have a length of 0.2 ms. Each subframe may indicate a link direction (e.g., DL or UL) for data transmission and the link direction for each subframe may be dynamically switched. Each subframe may include DL/UL data as well as DL/UL control data.

In some aspects, a UE 120 may transmit information to a base station 110 using a grant-free uplink non-orthogonal multiple access (NOMA) communication. In this case, transmissions from the UE 120 to the base station 110 may not be scheduled by the base station 110 using an uplink grant. The UE 120 may transmit data to the base station 110 using grant-free uplink NOMA communications, and/or may transmit reference signals to the base station 110 using grant-free uplink NOMA communications. For example, the UE 120 may transmit a demodulation reference signal (DMRS) to the base station 110 using grant-free uplink NOMA communications. The base station 110 may use the DMRS to determine channel state information (CSI) for the UE 120, and may use the CSI to configure one or more parameters for communications with or by the UE 120. Additional details are described elsewhere herein.

As indicated above, FIG. 1 is provided merely as an example. Other examples are possible and may differ from what was described with regard to FIG. 1.

FIG. 2 shows a block diagram 200 of a design of base station 110 and UE 120, which may be one of the base stations and one of the UEs in FIG. 1. Base station 110 may be equipped with T antennas 234a through 234t, and UE 120 may be equipped with R antennas 252a through 252r, where in general T ≥ 1 and R ≥ 1.

At base station 110, a transmit processor 220 may receive data from a data source 212 for one or more UEs, select one or more modulation and coding schemes (MCS) for each UE based at least in part on channel quality indicators (CQIs) received from the UE, process (e.g., encode and modulate) the data for each UE based at least in part on the MCS (s) selected for the UE, and provide data symbols for all UEs. Transmit processor 220 may also process system information (e.g., for semi-static resource partitioning information (SRPI) , and/or the like) and control information (e.g., CQI requests, grants, upper layer signaling, and/or the like) and provide overhead symbols and control symbols. Transmit processor 220 may also generate reference symbols for reference signals (e.g., the CRS) and synchronization signals (e.g., the primary synchronization signal (PSS) and secondary synchronization signal (SSS) ) . A transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, the overhead symbols, and/or the reference symbols, if applicable, and may provide T output symbol streams to T modulators (MODs) 232a through 232t. Each modulator 232 may process a respective output symbol stream (e.g., for OFDM and/or the like) to obtain an output sample stream. Each modulator 232 may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. T downlink signals from modulators 232a through 232t may be transmitted via T antennas 234a through 234t, respectively. According to various aspects described in more detail below, the synchronization signals can be generated with location encoding to convey additional information.

At UE 120, antennas 252a through 252r may receive the downlink signals from base station 110 and/or other base stations and may provide received signals to demodulators (DEMODs) 254a through 254r, respectively. Each demodulator 254 may condition (e.g., filter, amplify, downconvert, and digitize) a received signal to obtain input samples. Each demodulator 254 may further process the input samples (e.g., for OFDM and/or the like) to obtain received symbols. A MIMO detector 256 may obtain received symbols from all R demodulators 254a through 254r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive (RX) processor 258 may process (e.g., demodulate and decode) the detected symbols, provide decoded data for UE 120 to a data sink 260, and provide decoded control information and system information to a controller/processor 280. A channel processor may determine RSRP, RSSI, RSRQ, CQI, and/or the like.

On the uplink, at UE 120, a transmit processor 264 may receive and process data from a data source 262 and control information (e.g., for reports comprising RSRP, RSSI, RSRQ, CQI, and/or the like) from controller/processor 280. Transmit processor 264 may also generate reference symbols for one or more reference signals. The symbols from transmit processor 264 may be precoded by a TX MIMO processor 266 if applicable, further processed by modulators 254a through 254r (e.g., for DFT-s-OFDM, CP-OFDM, and/or the like) , and transmitted to base station 110. At base station 110, the uplink signals from UE 120 and other UEs may be received by antennas 234, processed by demodulators 232, detected by a MIMO detector 236 if applicable, and further processed by a receive processor 238 to obtain decoded data and control information sent by UE 120. Receive processor 238 may provide the decoded data to a data sink 239 and the decoded control information to controller/processor 240. Base station 110 may include communication unit 244 and communicate to network controller 130 via communication unit 244. Network controller 130 may include communication unit 294, controller/processor 290, and memory 292.

Controller/processor 240 of base station 110, controller/processor 280 of UE 120, and/or any other component (s) of Fig. 2 may perform one or more techniques associated with configuring demodulation reference signals in grant-free uplink non-orthogonal multiple access (NOMA) systems, as described in more detail elsewhere herein. For example, controller/processor 240 of base station 110, controller/processor 280 of UE 120, and/or any other component (s) of Fig. 2 may perform or direct operations of, for example, method 900 of FIG. 9, method 1000 of FIG. 10, and/or other processes as described herein.

Memories

242 and 282 may store data and program codes for BS 110 and UE 120, respectively. A scheduler 246 may schedule UEs for data transmission on the downlink and/or uplink.

As indicated above, FIG. 2 is provided merely as an example. Other examples are possible and may differ from what was described with regard to FIG. 2.

In a grant-free uplink non-orthogonal multiple access (NOMA) communication system, a UE (e.g., UE 120 and/or the like) may transmit an uplink communication without first receiving an uplink grant that schedules transmission of the uplink communication. Furthermore, in a grant-free NOMA communication system, the UE may randomly select a demodulation reference signal (DMRS) sequence from a pool of DMRS sequences, and may transmit the randomly selected DMRS sequence to a base station (e.g., base station 110 and/or the like) in a transmission opportunity (e.g., a physical uplink control channel (PUCCH) opportunity, a physical uplink shared channel (PUSCH) opportunity, and/or the like) . The base station may use the DMRS sequence to estimate channel state information (CSI) for the UE, which may be used to configure communications with or by the UE.

Some UEs, such as low power narrowband Internet of Things (NB IoT) UEs, may repeat transmissions in a time domain (e.g., in multiple subframes, slots, and/or the like) to provide coverage enhancement and increase a likelihood of successful reception, by a base station, of a signal transmitted by the UE. For example, a UE may repeat a demodulation reference signal (DMRS) sequence together with repetition of data in multiple subframes so that a base station can combine DMRS sequences received in multiple subframes to obtain a more accurate estimate of channel state information (CSI) for the UE. In addition, a UE may also randomly determine a transmission opportunity, in the time domain, in which to start transmitting an initial transmission of data and/or the DMRS sequence. However, when multiple UEs are transmitting DMRS sequences to aid the CSI estimation for grant-free uplink non-orthogonal multiple access (NOMA) communication systems, each UE is supposed to randomly select its own DMRS sequence from a predefined set of DMRS sequences. Thus, there is a high likelihood that DMRS sequences from multiple UEs will collide, especially when the DMRS sequences are repeated over multiple subframes (e.g., leading to cross-subframe DMRS collisions) . Particularly, a UE starting transmission in a later transmission opportunity may select the same DMRS sequence as the DMRS sequence selected by another UE starting transmission in an earlier transmission opportunity. In such a case, parts of the subframes of both these UEs would have DMRS collisions. However, the base station may not be able to properly detect such partial collision and the cross-subframe CSI estimation performance can become degraded. As a result, the base station may be unable to accurately estimate CSI for the UEs, which may lead to sub-optimal configurations and poor network performance.

FIG. 3 is a diagram illustrating an example 300 of configuring demodulation reference signals in grant-free uplink NOMA systems.

As shown by reference number 305, a first group of UEs 120, shown as UE _1, ₁, UE _1, ₂, and UE _1, ₃, may begin transmitting DMRS sequences in a first transmission opportunity 310, and may repeat the DMRS sequences over multiple subframes. As shown by reference number 315, a second group of UEs 120, shown as UE _2, ₁, and UE _2, ₂, may begin transmitting DMRS sequences in a second transmission opportunity 320, and may repeat the DMRS sequences over multiple subframes. As shown by reference number 325, a d ^th group of UEs 120, shown as UE _d, ₁, UE _d, ₂, and UE _d, ₃, may begin transmitting DMRS sequences in a d ^th transmission opportunity 330 (e.g., out of D possible transmission opportunities, where d ≤ D) , and may repeat the DMRS sequences over multiple subframes. The UEs 120 may operate in a grant-free uplink NOMA communication system where the UEs 120 select the DMRS sequence to be transmitted (e.g., rather than being configured by a base station 110 with a DMRS sequence to be transmitted) .

For example, a UE 120 may randomly select a DMRS sequence from a predefined set of DMRS sequences, may transmit the randomly selected DMRS sequence in a transmission opportunity, and may repeat the DMRS sequence over multiple subframes. In some aspects, the multiple subframes are consecutive valid subframes. As used herein, a valid subframe may refer to a subframe in which a DMRS sequence is permitted to be transmitted, which may exclude a subframe in which a broadcast signal or a control signal is to be transmitted. For example, a valid subframe may not include a subframe in which a primary synchronization signal (PSS) (e.g., a narrowband PSS (NPSS) ) is transmitted, may not include a subframe in which a secondary synchronization signal (SSS) (e.g., a narrowband SSS (NSSS) ) is transmitted, may not include a subframe in which a physical broadcast channel (PBCH) communication (e.g., a narrowband PBCH (NPBCH) ) is transmitted, may not include a subframe in which a narrowband reference signal (NRS) is transmitted, and/or the like.

In example 300, the UEs 120 in each group may randomly select a DMRS sequence from a predefined set of DMRS sequences that includes all DMRS sequences permitted for grant-free uplink NOMA transmissions (e.g., a pool of N DMRS sequences, where N is the total number of permitted DMRS sequences) . In this case, selection of a DMRS sequence may not depend on a transmission opportunity in which transmission of the DMRS sequence begins. This may conserve resources of the UE 120 due to low complexity of selecting and processing DMRS sequences. However, this may result in a relatively high likelihood of DMRS collision as compared to selecting a DMRS sequence based at least in part on a transmission opportunity because UEs 120 across different groups may select the same DMRS sequence. For example, as shown by reference number 335, UE _1, ₂ and UE _d, ₃ may select the same DMRS sequence, resulting in a DMRS collision (e.g., for one or more transmissions and/or repetitions of the DMRS sequence) .

Furthermore, a base station 110 will need to perform blind detection using all possible DMRS sequences for each UE 120 and each transmission opportunity, which results in higher detection complexity and use of additional base station resources (e.g., memory, processing power, and/or the like) as compared to performing blind detection using a subset of DMRS sequences based at least in part on a transmission opportunity, as described in more detail below.

As indicated above, FIG. 3 is provided as an example. Other examples are possible and may differ from what was described with respect to FIG. 3.

FIG. 4 is a diagram illustrating another example 400 of configuring demodulation reference signals in grant-free uplink NOMA systems.

As shown by reference number 405, a first group of UEs 120 may begin transmitting DMRS sequences in a first transmission opportunity 410, in a similar manner as described above in connection with FIG. 3. As shown by reference number 415, a second group of UEs 120 may begin transmitting DMRS sequences in a second transmission opportunity 420, in a similar manner as described above in connection with FIG. 3. As shown by reference number 425, a d ^th group of UEs 120 may begin transmitting DMRS sequences in a d ^th transmission opportunity 430, in a similar manner as described above in connection with FIG. 3. The UEs 120 may operate in a grant-free uplink NOMA communication system where the UEs 120 select the DMRS sequence to be transmitted (e.g., rather than being configured by a base station 110 with a DMRS sequence to be transmitted) . For example, a UE 120 may randomly select a DMRS sequence from a predefined set of DMRS sequences, may transmit the randomly selected DMRS sequence in a transmission opportunity, and may repeat the DMRS sequence over multiple subframes. In some aspects, the multiple subframes are consecutive valid subframes, as described above in connection with FIG. 3.

In example 400, the UEs 120 in each group may randomly select a DMRS sequence from a predefined set of DMRS sequences that includes all DMRS sequences permitted for grant-free uplink NOMA transmissions, in a similar manner as described above in connection with Fig. 3. Furthermore, a UE 120 may scramble a selected DMRS sequence using a scrambling sequence (e.g., applied to the resource elements that carry the DMRS sequence) .

As shown by reference number 435, the UE 120 may determine the scrambling sequence based at least in part on an orthogonal cover code (OCC) . In some aspects, the UE 120 may randomly select the OCC from a set of OCCs. Thus, by randomly selecting a DMRS sequence and an OCC to be applied to the DMRS sequence, the total number of distinguishable signals may be increased (e.g., as compared to random selection of only a DMRS sequence without applying an OCC to the DMRS sequence) . For example, for pool of N DMRS sequences, where N is the total number of permitted DMRS sequences, the size of the pool may be increased to N × X distinguishable signals, where X is the total number of OCCs that can be selected. For example, using OCC-4 with 4 possible OCCs, the size of the pool may be increased from N to 4N.

In this case, selection of a DMRS sequence and/or the OCC may not depend on a transmission opportunity in which transmission of the DMRS sequence begins. This may conserve resources of the UE 120 due to low complexity of selecting and processing DMRS sequences. However, this may result in a relatively high likelihood of DMRS collision as compared to selecting a DMRS sequence and/or an OCC based at least in part on a transmission opportunity because UEs 120 across different groups may select the same DMRS sequence and the same OCC (e.g., a time-aligned OCC) . For example, as shown by reference number 440, UE _1, ₂ and UE _d, ₃ may select the same DMRS sequence and the same OCC, resulting in a DMRS collision (e.g., for one or more transmissions and/or repetitions of the DMRS sequence) .

Furthermore, a base station 110 will need to perform blind detection using all possible DMRS sequences and all possible OCCs for each UE 120 and each transmission opportunity, which results in higher detection complexity and use of additional base station resources (e.g., memory, processing power, and/or the like) as compared to performing blind detection using a subset of DMRS sequences and/or a subset of OCCs based at least in part on a transmission opportunity, as described in more detail below.

As indicated above, FIG. 4 is provided as an example. Other examples are possible and may differ from what was described with respect to FIG. 4.

FIG. 5 is a diagram illustrating another example 500 of configuring demodulation reference signals in grant-free uplink NOMA systems.

As shown by reference number 505, a first group of UEs 120, shown as UE _1, ₁, UE _1, ₂, and UE _1, ₃, may begin transmitting DMRS sequences in a first transmission opportunity 510. As shown by reference number 515, a second group of UEs 120, shown as UE _2, ₁, and UE _2, ₂, may begin transmitting DMRS sequences in a second transmission opportunity 520. As shown by reference number 525, a third group of UEs 120, shown as UE _3, ₁, UE _3, ₂, and UE _3, ₃, may begin transmitting DMRS sequences in a third transmission opportunity 530. As shown by reference number 535, a fourth group of UEs 120, shown as UE _4, ₁ , may begin transmitting DMRS sequences in a fourth transmission opportunity 540. In example 500, the number of transmission opportunities D is equal to 4, but other numbers of transmission opportunities are possible. The UEs 120 may operate in a grant-free uplink NOMA communication system, and may repeat the DMRS sequences over multiple subframes.

For example, a UE 120 may randomly select a DMRS sequence from a predefined set of DMRS sequences, may transmit the randomly selected DMRS sequence in a transmission opportunity, and may repeat the DMRS sequence over multiple subframes. In some aspects, the multiple subframes are consecutive valid subframes, as described above in connection with FIG. 3.

In example 500, the UEs 120 in each group may randomly select a DMRS sequence from a predefined set of DMRS sequences that includes all DMRS sequences permitted for grant-free uplink NOMA transmissions, in a similar manner as described above in connection with Fig. 3. Furthermore, a UE 120 may scramble a selected DMRS sequence using a scrambling sequence (e.g., applied to the resource elements that carry the DMRS sequence) , which may be determined based at least in part on an OCC.

As shown in FIG. 5, in some aspects, the UE 120 may select an OCC based at least in part on a transmission opportunity in which the UE 120 begins transmission of the DMRS sequence. In this case, different OCCs may be associated with different transmission opportunities. For example, as shown, the first transmission opportunity 510 may be associated with a first OCC 545 of (1, 1, 1, 1) , the second transmission opportunity 520 may be associated with a second OCC 550 of (1, 1, 1, -1) , the third transmission opportunity 530 may be associated with a third OCC 555 of (1, 1, -1, -1) , and the fourth transmission opportunity 540 may be associated with a fourth OCC 560 of (1, -1, -1, -1) . In this case, X consecutive transmission opportunities may be associated with a unique OCC, where X is the total number of OCCs that can be selected. For example, using OCC-4 with 4 possible OCCs, 4 consecutive transmission opportunities may use unique OCCs, as shown in FIG. 5. As further shown, consecutive transmission opportunities may be separated by a number of valid subframes equal to a length of the OCC (e.g., a total number of OCCs that can be selected by the UE 120) . For example, the UE 120 may select and/or be configured to use an OCC with a length determined based at least in part on the number of subframes (e.g., valid subframes) between consecutive transmission opportunities.

In this case, selection of a DMRS sequence may not depend on a transmission opportunity in which transmission of the DMRS sequence begins, but selection of an OCC may depend on a transmission opportunity in which transmission of the DMRS sequence begins. This may conserve resources of the UE 120 due to low complexity of selecting and processing DMRS sequences, and may reduce the likelihood of DMRS collisions across transmission opportunities due to the use of different OCCs in different transmission opportunities. Furthermore, a base station 110 may perform detection using an OCC determined based at least in part on the transmission opportunity, rather than performing blind detection using all possible OCCs for each transmission opportunity. This may result in lower detection complexity and may use fewer base station resources as compared to performing blind detection using all possible OCCs in every transmission opportunity.

However, this technique may result in a relatively high likelihood of DMRS collision as compared to selecting a DMRS sequence based at least in part on a transmission opportunity because UEs 120 within the same group may select the same DMRS sequence in some cases, and may always select the same OCC (e.g., because the same OCC is used for UEs 120 in the same group) . In some aspects, a UE 120 may select a DMRS sequence based at least in part on a transmission opportunity, as described in more detail below.

As indicated above, FIG. 5 is provided as an example. Other examples are possible and may differ from what was described with respect to FIG. 5.

FIG. 6 is a diagram illustrating another example 600 of configuring demodulation reference signals in grant-free uplink NOMA systems.

As shown by reference number 605, a first group of UEs 120 may begin transmitting DMRS sequences in a first transmission opportunity 610. As shown by reference number 615, a second group of UEs 120 may begin transmitting DMRS sequences in a second transmission opportunity 620. As shown by reference number 625, a d ^th group of UEs 120 may begin transmitting DMRS sequences in a d ^th transmission opportunity 630. The UEs 120 may operate in a grant-free uplink NOMA communication system where the UEs 120 select the DMRS sequence to be transmitted (e.g., rather than being configured by a base station 110 with a DMRS sequence to be transmitted) . For example, a UE 120 may randomly select a DMRS sequence from a predefined set of DMRS sequences, may transmit the randomly selected DMRS sequence in a transmission opportunity, and may repeat the DMRS sequence over multiple subframes. In some aspects, the multiple subframes are consecutive valid subframes, as described above in connection with FIG. 3.

In some aspects, the predefined set of DMRS sequences may be a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions. In this case, the UE 120 may determine the predefined set of DMRS sequences based at least in part on a transmission opportunity in which the UE 120 is to begin transmission of a DMRS sequence. As shown, different transmission opportunities may be associated with different subsets of DMRS sequences. For example, the first transmission opportunity 610 may be associated with a first subset of DMRS sequences 635, the second transmission opportunity 620 may be associated with a second subset of DMRS sequences 640, the d ^th transmission opportunity 630 may be associated with a d ^th subset of DMRS sequences 645, and/or the like. In some aspects, each different subset of DMRS sequences is mutually exclusive. For example, the DMRS sequences included in different subsets may be exclusive to the respective subsets. In some aspects, the number of DMRS sequences included in a subset may be determined based at least in part a total number of permitted DMRS sequences N divided by a number of possible transmission opportunities and/or subsets D (e.g., the size of a subset may be N /D, in some cases) . In some aspects, the UE 120 may determine a subset from which to select a DMRS sequence using a transmission opportunity index that maps to a subset.

In this case, selection of a DMRS sequence may depend on a transmission opportunity in which transmission of the DMRS sequence begins. This may reduce the likelihood of DMRS collisions across transmission opportunities due to the use of different DMRS sequences in different transmission opportunities. Furthermore, a base station 110 may perform blind detection using a subset of DMRS sequences determined based at least in part on the transmission opportunity, rather than performing blind detection using all possible DMRS sequences for each transmission opportunity, which may result in lower detection complexity and may use fewer base station resources.

As indicated above, FIG. 6 is provided as an example. Other examples are possible and may differ from what was described with respect to FIG. 6.

FIG. 7 is a diagram illustrating another example 700 of configuring demodulation reference signals in grant-free uplink NOMA systems.

As shown by reference number 705, a first group of UEs 120 may begin transmitting DMRS sequences in a first transmission opportunity 710. As shown by reference number 715, a second group of UEs 120 may begin transmitting DMRS sequences in a second transmission opportunity 720. As shown by reference number 725, a third group of UEs 120 may begin transmitting DMRS sequences in a third transmission opportunity 730. As shown by reference number 735, a fourth group of UEs 120 may begin transmitting DMRS sequences in a fourth transmission opportunity 740. The UEs 120 may operate in a grant-free uplink NOMA communication system where the UEs 120 select the DMRS sequence to be transmitted (e.g., rather than being configured by a base station 110 with a DMRS sequence to be transmitted) . For example, a UE 120 may randomly select a DMRS sequence from a predefined set of DMRS sequences, may scramble the DMRS sequence based at least in part on an OCC, may transmit the scrambled DMRS sequence in a transmission opportunity, and may repeat the scrambled DMRS sequence over multiple subframes. In some aspects, the multiple subframes are consecutive valid subframes, as described above in connection with FIG. 3.

In some aspects, the predefined set of DMRS sequences may be a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions. In this case, the UE 120 may determine the predefined set of DMRS sequences based at least in part on a transmission opportunity in which the UE 120 is to begin transmission of a DMRS sequence. As shown, different transmission opportunities may be associated with different subsets of DMRS sequences. For example, the first transmission opportunity 710 may be associated with a first subset of DMRS sequences 745, the second transmission opportunity 720 may be associated with a second subset of DMRS sequences 750, the third transmission opportunity 730 may be associated with a third subset of DMRS sequences 755, the fourth transmission opportunity 740 may be associated with a fourth subset of DMRS sequences 760, and/or the like. In some aspects, each different subset of DMRS sequences is mutually exclusive. For example, the DMRS sequences included in different subsets may be exclusive to the respective subsets. In some aspects, the number of DMRS sequences included in a subset may be determined based at least in part a total number of permitted DMRS sequences N divided by a number of possible transmission opportunities and/or subsets D (e.g., the size of a subset may be N /D, in some cases) . In some aspects, the UE 120 may determine a subset from which to select a DMRS sequence using a transmission opportunity index that maps to a subset.

Additionally, or alternatively, a UE 120 may scramble a selected DMRS sequence using a scrambling sequence (e.g., applied to the resource elements that carry the DMRS sequence) . The UE 120 may determine the scrambling sequence based at least in part on an OCC. As shown, the UE 120 may randomly select the OCC from a set of OCCs. As further shown, consecutive transmission opportunities may be separated by a number of valid subframes equal to a length of the OCC (e.g., a total number of OCCs that can be selected by the UE 120) . For example, the UE 120 may select and/or be configured to use an OCC with a length determined based at least in part on the number of subframes (e.g., valid subframes) between consecutive transmission opportunities.

In example 700, a UE 120 may determine a transmission opportunity, in a time domain, in which the UE 120 is to begin transmitting a DMRS sequence. The transmission opportunity may be selected from a plurality of transmission opportunities associated with the UE 120 (e.g., configured for the UE 120 in a radio resource control (RRC) message, system information, and/or the like) . The plurality of transmission opportunities may be associated with grant-free uplink NOMA transmissions with repetition over multiple subframes. The UE 120 may determine a subset of DMRS sequences based at least in part on the transmission opportunity, and may randomly select a DMRS sequence from the subset. As indicated above, different subsets may be associated with different transmission opportunities, and DMRS sequences included in a subset may be exclusive to that subset. After selecting a DMRS sequence from the subset, the UE 120 may scramble the DMRS sequence using a scrambling sequence determined based at least in part on an OCC, and may transmit the scrambled DMRS sequence in the transmission opportunity. In example 700, the UE 120 may randomly select the OCC from a set of OCCs.

In this case, selection of a DMRS sequence may depend on a transmission opportunity in which transmission of the DMRS sequence begins. This may reduce the likelihood of DMRS collisions across transmission opportunities due to the use of different DMRS sequences in different transmission opportunities. Furthermore, by randomly selecting and applying an OCC to the DMRS sequence, the total number of distinguishable signals may be increased (e.g., as compared to not applying an OCC to the DMRS sequence) . Furthermore, a base station 110 may perform blind detection using a subset of DMRS sequences determined based at least in part on the transmission opportunity, rather than performing blind detection using all possible DMRS sequences for each transmission opportunity, which may result in lower detection complexity and may use fewer base station resources.

As indicated above, FIG. 7 is provided as an example. Other examples are possible and may differ from what was described with respect to FIG. 7.

FIG. 8 is a diagram illustrating another example 800 of configuring demodulation reference signals in grant-free uplink NOMA systems.

In example 800, a UE 120 may randomly select a DMRS sequence from a predefined set of DMRS sequences, may scramble the DMRS sequence based at least in part on an OCC, may transmit the scrambled DMRS sequence in a transmission opportunity, and may repeat the scrambled DMRS sequence over multiple subframes (e.g., consecutive valid subframes) . The predefined set of DMRS sequences may be a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions. In this case, the UE 120 may determine the predefined set of DMRS sequences based at least in part on a transmission opportunity in which the UE 120 is to begin transmission of a DMRS sequence. As described elsewhere herein, different transmission opportunities may be associated with different subsets of DMRS sequences, and each different subset of DMRS may be mutually exclusive. Furthermore, the UE 120 may scramble a selected DMRS sequence using a scrambling sequence, which may be determined sequence based at least in part on an OCC.

In example 800, the UE 120 may select an OCC based at least in part on a transmission opportunity, in a similar manner as described above in connection with FIG. 5. In this case, different OCCs may be associated with different transmission opportunities. In some aspects, the UE 120 may select the OCC based at least in part on dividing an index of the transmission opportunity (e.g., d) by a square root of a number of transmission opportunities (e.g., D) included in a plurality of transmission opportunities associated with the UE for grant-free uplink NOMA transmissions with repetition over multiple subframes, and by performing a ceiling operation to round a result of the dividing (e.g., d /D) to a nearest integer that is greater than the result (e.g., to provide a positive integer for an OCC index and/or an OCC group index) . In some aspects, the result may be rounded to another nearest integer (e.g., by performing a floor operation) . The integer may represent an OCC index, and the UE 120 may select the OCC using the OCC index. In this case, and as shown, consecutive transmission opportunities may occur in consecutive valid subframes.

After selecting an OCC, the UE 120 may scramble the DMRS sequence in the time domain using the selected OCC. In this case, different subframes in which the DMRS sequence is repeated may be associated with different bits of the OCC. For example, a first subframe associated with the transmission opportunity (e.g., a subframe in which the transmission opportunity begins) may be associated with a first bit of the OCC, a second subframe associated with the transmission opportunity (e.g., a next consecutive valid subframe) may be associated with a second bit of the OCC, and so on.

In some aspects, the UE 120 may scramble a selected DMRS sequence using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on a selected OCC, and wherein a first subframe of the transmission opportunity is associated with a first bit of the OCC, a second subframe of the transmission opportunity is associated with a second bit of the OCC, and so on (e.g., for each bit of the OCC, where each bit of the OCC is associated with a different subframe) . The first bit and the second bit may be consecutive bits of the OCC and the first subframe and the second subframe may be consecutive valid subframes. Thus, in some aspects, consecutive bits of the OCC correspond to consecutive valid subframes in which the scrambled DMRS sequence is transmitted. In some aspects, an initial bit of the OCC may be applied to an initial subframe of the transmission opportunity regardless of the transmission opportunity (e.g., regardless of a group to which the UE 120 belongs and/or regardless of a subframe in which the transmission opportunity begins) .

In some aspects, such as when a number of bits of the OCC is less than a number of repetitions of the DMRS sequence, after a last bit of the OCC is associated with a subframe of the transmission opportunity, an initial bit of the OCC is associated with a next consecutive subframe of the transmission opportunity. For example, an initial bit of the OCC may be applied to the DMRS sequence transmitted in an initial subframe of the transmission opportunity, a second bit of the OCC (e.g., immediately following the initial bit) may be applied to the DMRS sequence transmitted in a second subframe of the transmission opportunity (e.g., immediately following the initial subframe) , and so on, until a final subframe of the transmission opportunity is reached or a final bit of the OCC is applied to the DMRS sequence in a subframe of the transmission opportunity. If the final bit of the OCC is applied before the final subframe of the transmission opportunity, then the initial bit of the OCC may be applied to a next consecutive valid subframe after a subframe in which the final bit is applied, and so on until the final subframe of the transmission opportunity is reached.

In example 800, a UE 120 may determine a transmission opportunity, in a time domain, in which the UE 120 is to begin transmitting a DMRS sequence. The transmission opportunity may be selected from a plurality of transmission opportunities associated with the UE 120. The plurality of transmission opportunities may be associated with grant-free uplink NOMA transmissions with repetition over multiple subframes. The UE 120 may determine a subset of DMRS sequences based at least in part on the transmission opportunity, and may randomly select a DMRS sequence from the subset. As indicated above, different subsets may be associated with different transmission opportunities, and DMRS sequences included in a subset may be exclusive to that subset. After selecting a DMRS sequence from the subset, the UE 120 may scramble the DMRS sequence using a scrambling sequence determined based at least in part on an OCC, and may transmit the scrambled DMRS sequence in the transmission opportunity. In example 800, the UE 120 may determine the OCC based at least in part on the transmission opportunity, as described above, and may associate different bits of the OCC with different subframes associated with the transmission opportunity.

In this case, selection of a DMRS sequence and selection of an OCC may depend on a transmission opportunity in which transmission of the DMRS sequence begins. This may reduce the likelihood of DMRS collisions across transmission opportunities due to the use of different DMRS sequences in different transmission opportunities. Furthermore, by applying an OCC to the DMRS sequence as described above (e.g., by applying different OCC bits to different subframes) , the total number of distinguishable signals may be increased (e.g., as compared to not applying an OCC to the DMRS sequence) . Furthermore, a base station 110 may perform blind detection using a subset of DMRS sequences and/or a particular OCC determined based at least in part on the transmission opportunity, rather than performing detection using all possible DMRS sequences and/or OCCs for each transmission opportunity, which may result in lower detection complexity and may use fewer base station resources.

In this case, if different UEs 120 select the same DMRS sequence (e.g., from a same subset of DMRS sequences associated with a transmission opportunity) but different OCCs, then the base station 110 can distinguish and separately detect the DMRS sequences of the different UEs 120 because the different OCCs are time-aligned. As a result, the DMRS sequences of the different UEs can be separated due to the application of different time-aligned OCCs. Furthermore, if different UEs 120 select the same OCC but different DMRS sequences, then the base station 110 can distinguish and separately detect the DMRS sequences of the different UEs 120 because application of the OCC does not change cross-correlation characteristics of different DMRS sequences, thus making the different DMRS sequences distinguishable even after application of the OCC.

As indicated above, FIG. 8 is provided as an example. Other examples are possible and may differ from what was described with respect to FIG. 8.

FIG. 9 is a flow chart of a method 900 of wireless communication. The method 900 may be performed by UE (e.g., the UE 120 of FIGs. 1-8, the apparatus 1102/1102’of FIG. 11 and/or 12, and/or the like) .

At 910, the UE may determine a transmission opportunity in a time domain. For example, the UE (e.g., using controller/processor 280 and/or the like) may determine a transmission opportunity in a time domain, as described above in connection with FIGs. 3-8. In some aspects, the transmission opportunity is selected from a plurality of transmission opportunities associated with the UE for grant-free uplink NOMA transmissions with repetition over multiple subframes.

At 920, the UE may randomly select a demodulation reference signal (DMRS) sequence, for a grant-free uplink NOMA transmission, from a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions, wherein the subset of all DMRS sequences is determined based at least in part on the transmission opportunity, wherein different subsets of DMRS sequences are associated with different transmission opportunities, and wherein DMRS sequences in the different subsets are exclusive to the respective subsets. For example, the UE (e.g., using controller/processor 280 and/or the like) may randomly select a DMRS sequence, for a grant-free uplink NOMA transmission, from a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions, as described above in connection with FIGs. 3-8. In some aspects, the subset of all DMRS sequences is determined based at least in part on the transmission opportunity. In some aspects, different subsets of DMRS sequences are associated with different transmission opportunities. In some aspects, DMRS sequences in the different subsets are exclusive to the respective subsets.

At 930, the UE may scramble the DMRS sequence using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) . For example, the UE (e.g., using controller/processor 280 and/or the like) may scramble the DMRS sequence using a scrambling sequence in a time domain, as described above in connection with FIGs. 3-8. In some aspects, the scrambling sequence is determined based at least in part on an OCC.

At 940, the UE may transmit the scrambled DMRS sequence in the transmission opportunity. For example, the UE (e.g., using controller/processor 280, transmit processor 264, TX MIMO processor 266, MOD 254, antenna 252, and/or the like) may transmit the scrambled DMRS sequence in the transmission opportunity, as described above in connection with FIGs. 3-8.

Method 900 may include additional aspects, such as any single aspect or any combination of aspects described below and/or in connection with one or more other processes described elsewhere herein.

In some aspects, the OCC is randomly selected from a set of OCCs. In some aspects, consecutive transmission opportunities, of the plurality of transmission opportunities, are separated by a number of valid subframes equal to a length of the OCC. In some aspects, the number of valid subframes excludes one or more subframes reserved for broadcast signals or control signals.

In some aspects, the OCC is selected based at least in part on the transmission opportunity, wherein different OCCs are associated with different transmission opportunities. In some aspects, consecutive transmission opportunities, of the plurality of transmission opportunities, occur in consecutive valid subframes. In some aspects, the consecutive valid subframes exclude one or more subframes reserved for broadcast signals or control signals. In some aspects, the OCC is selected based at least in part on dividing an index of the transmission opportunity by a square root of a number of transmission opportunities included in the plurality of transmission opportunities, and performing a ceiling operation to round a result of the dividing to a nearest integer that is greater than the result, wherein the integer represents an OCC index used for selection of the OCC. In some aspects, the scrambled DMRS sequence is repeated over multiple subframes.

In some aspects, different bits of the OCC are applied to different subframes in which the scrambled DMRS sequence is repeated. In some aspects, a first bit of the OCC is associated with the scrambled DMRS sequence transmitted in a first subframe of the transmission opportunity and a second bit of the OCC is associated with the scrambled DMRS sequence transmitted in a second subframe of the transmission opportunity, wherein the first bit and the second bit are consecutive bits of the OCC and the first subframe and the second subframe are consecutive valid subframes. In some aspects, consecutive bits of the OCC correspond to consecutive valid subframes in which the scrambled DMRS sequence is transmitted. In some aspects, after a last bit of the OCC is associated with a subframe of the transmission opportunity, an initial bit of the OCC is associated with a next consecutive subframe of the transmission opportunity, wherein a number of bits of the OCC is less than a number of repetitions of the DMRS sequence. In some aspects, the multiple subframes are consecutive valid subframes that do not include a broadcast signal or a control signal.

Although FIG. 9 shows example blocks of a method of wireless communication, in some aspects, the method may include additional blocks, fewer blocks, different blocks, or differently arranged blocks than those shown in FIG. 9. Additionally, or alternatively, two or more blocks shown in FIG. 9 may be performed in parallel.

FIG. 10 is a flow chart of a method 1000 of wireless communication. The method 1000 may be performed by a UE (e.g., the UE 120 of FIGs. 1-8, the apparatus 1102/1102’of FIG. 11 and/or 12, and/or the like) .

At 1010, the UE may select a demodulation reference signal (DMRS) sequence for a grant-free uplink non-orthogonal multiple access (NOMA) transmission with repetition over multiple subframes, wherein the DMRS sequence is randomly selected from a predefined set of DMRS sequences. For example, the UE (e.g., using controller/processor 280 and/or the like) may select a DMRS sequence for a grant-free uplink NOMA transmission with repetition over multiple subframes, as described above in connection with FIGs. 3-8. In some aspects, the DMRS sequence is randomly selected from a predefined set of DMRS sequences.

At 1020, the UE may transmit the DMRS sequence in a transmission opportunity. For example, the UE (e.g., using controller/processor 280, transmit processor 264, TX MIMO processor 266, MOD 254, antenna 252, and/or the like) may transmit the DMRS sequence in a transmission opportunity, as described above in connection with FIGs. 3-8.

At 1030, the UE may repeat the DMRS sequence over multiple subframes. For example, the UE (e.g., using controller/processor 280, transmit processor 264, TX MIMO processor 266, MOD 254, antenna 252, and/or the like) may repeat the DMRS sequence over multiple subframes, as described above in connection with FIGs. 3-8.

Method 1000 may include additional aspects, such as any single aspect or any combination of aspects described below and/or in connection with one or more other processes described elsewhere herein.

In some aspects, the DMRS sequence is repeated over multiple subframes. In some aspects, the multiple subframes are consecutive valid subframes that do not include a broadcast signal or a control signal. In some aspects, the predefined set of DMRS sequences includes all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions.

In some aspects, the DMRS sequence is scrambled using a scrambling sequence, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) . In some aspects, the OCC is randomly selected from a set of OCCs. In some aspects, the OCC is selected based at least in part on the transmission opportunity. In some aspects, different OCCs are associated with different transmission opportunities. In some aspects, consecutive transmission opportunities are separated by a number of valid subframes equal to a length of the OCC. In some aspects, the number of valid subframes excludes one or more subframes reserved for broadcast signals or control signals.

In some aspects, the predefined set of DMRS sequences is a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions. In some aspects, the predefined set of DMRS sequences is determined based at least in part on the transmission opportunity, wherein different subsets of DMRS sequences are associated with different transmission opportunities. In some aspects, DMRS sequences in the different subsets of DMRS sequences are exclusive to the respective subsets.

In some aspects, the DMRS sequence is scrambled using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) that is randomly selected from a set of OCCs. In some aspects, consecutive transmission opportunities are separated by a number of subframes equal to a length of the OCC. In some aspects, the number of subframes excludes one or more subframes reserved for broadcast signals or control signals.

In some aspects, the DMRS sequence is scrambled using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) that is selected based at least in part on the transmission opportunity, wherein different OCCs are associated with different transmission opportunities. In some aspects, the OCC is selected based at least in part on dividing an index of the transmission opportunity by a square root of a number of transmission opportunities included in a plurality of transmission opportunities associated with the UE for grant-free uplink NOMA transmissions with repetition over multiple subframes, and performing a ceiling operation to round a result of the dividing to a nearest integer that is greater than the result, wherein the integer represents an OCC index used for selection of the OCC.

In some aspects, different bits of the OCC are applied to different subframes in which the DMRS sequence is repeated. In some aspects, a first bit of the OCC is associated with the DMRS sequence transmitted in a first subframe of the transmission opportunity and a second bit of the OCC is associated with the DMRS sequence transmitted in a second subframe of the transmission opportunity, wherein the first bit and the second bit are consecutive bits of the OCC and the first subframe and the second subframe are consecutive valid subframes. In some aspects, consecutive bits of the OCC correspond to consecutive valid subframes in which the scrambled DMRS sequence is transmitted. In some aspects, after a last bit of the OCC is associated with a subframe of the transmission opportunity, an initial bit of the OCC is associated with a next consecutive subframe of the transmission opportunity, wherein a number of bits of the OCC is less than a number of repetitions of the DMRS sequence.

In some aspects, consecutive transmission opportunities occur in consecutive valid subframes. In some aspects, the consecutive valid subframes exclude one or more subframes reserved for broadcast signals or control signals.

Although FIG. 10 shows example blocks of a method of wireless communication, in some aspects, the method may include additional blocks, fewer blocks, different blocks, or differently arranged blocks than those shown in FIG. 10. Additionally, or alternatively, two or more blocks shown in FIG. 10 may be performed in parallel.

FIG. 11 is a conceptual data flow diagram 1100 illustrating the data flow between different modules/means/components in an example apparatus 1102. The apparatus 1102 may be a UE. In some aspects, the apparatus 1102 includes a reception module 1104, a determination module 1106, a selection module 1108, a scrambling module 1110, a transmission module 1112, and/or the like.

In some aspects, the reception module 1104 may receive information 1114, from a base station 1150, regarding grant-free uplink NOMA transmissions (e.g., information identify a plurality of transmission opportunities, an OCC configuration, sets of DMRS sequences, and/or the like) . In some aspects, the reception module 1104 may provide such information to the determination module 1106 as information 1116 and/or to the selection module 1108 as information 1118. The determination module 1106 may determine a transmission opportunity for transmission of a DMRS sequence. In some aspects, the determination module 1106 may indicate the transmission opportunity to the selection module 1108 as information 1120. The selection module 1108 may select, using information 1118 and/or information 1120, a DMRS sequence and/or an OCC. In some aspects, the selection module 1108 may indicate the DMRS sequence to the transmission module 1112 as information 1122, and the transmission module 1112 may transmit the DMRS sequence, in the transmission opportunity, to the base station 1150 as information 1128. Additionally, or alternatively, the selection module 1108 may indicate the DMRS sequence and the OCC to the scrambling module 1110 as information 1124, and the scrambling module 1110 may scramble the DMRS sequence based at least in part on the OCC. The scrambling module 1110 may provide the scrambled DMRS sequence to the transmission module 1112 as information 1126, and the transmission module 1112 may transmit the scrambled DMRS sequence, in the transmission opportunity, to the base station 1150 as information 1128. Additionally, or alternatively, the transmission module 1112 may repeat transmission of the DMRS sequence.

The apparatus may include additional modules that perform each of the blocks of the algorithm in the aforementioned method 900 of FIG. 9, method 1000 of FIG. 10, and/or the like. As such, each block in the aforementioned method 900 of FIG. 9, method 1000 of FIG. 10, and/or the like may be performed by a module and the apparatus may include one or more of those modules. The modules may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or a combination thereof.

The number and arrangement of modules shown in FIG. 11 are provided as an example. In practice, there may be additional modules, fewer modules, different modules, or differently arranged modules than those shown in FIG. 11. Furthermore, two or more modules shown in FIG. 11 may be implemented within a single module, or a single module shown in FIG. 11 may be implemented as multiple, distributed modules. Additionally, or alternatively, a set of modules (e.g., one or more modules) shown in FIG. 11 may perform one or more functions described as being performed by another set of modules shown in FIG. 11.

FIG. 12 is a diagram 1200 illustrating an example of a hardware implementation for an apparatus 1102′employing a processing system 1202. The apparatus 1102′may be a UE.

The processing system 1202 may be implemented with a bus architecture, represented generally by the bus 1204. The bus 1204 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 1202 and the overall design constraints. The bus 1204 links together various circuits including one or more processors and/or hardware modules, represented by the processor 1206, the

modules

1104, 1106, 1108, 1110, and/or 1112, and the computer-readable medium /memory 1208. The bus 1204 may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

The processing system 1202 may be coupled to a transceiver 1210. The transceiver 1210 is coupled to one or more antennas 1212. The transceiver 1210 provides a means for communicating with various other apparatus over a transmission medium. The transceiver 1210 receives a signal from the one or more antennas 1212, extracts information from the received signal, and provides the extracted information to the processing system 1202, specifically the reception module 1104. In addition, the transceiver 1210 receives information from the processing system 1202, specifically the transmission module 1112, and based at least in part on the received information, generates a signal to be applied to the one or more antennas 1212. The processing system 1202 includes a processor 1206 coupled to a computer-readable medium /memory 1208. The processor 1206 is responsible for general processing, including the execution of software stored on the computer-readable medium /memory 1208. The software, when executed by the processor 1206, causes the processing system 1202 to perform the various functions described supra for any particular apparatus. The computer-readable medium /memory 1208 may also be used for storing data that is manipulated by the processor 1206 when executing software. The processing system further includes at least one of the

modules

1104, 1106, 1108, 1110, and/or 1112. The modules may be software modules running in the processor 1206, resident/stored in the computer readable medium /memory 1208, one or more hardware modules coupled to the processor 1206, or a combination thereof. The processing system 1202 may be a component of the UE 120 and may include the memory 282 and/or at least one of the TX MIMO processor 266, the RX processor 258, and/or the controller/processor 280.

In some aspects, the apparatus 1102/1102′for wireless communication includes means for determining a transmission opportunity in a time domain, wherein the transmission opportunity is selected from a plurality of transmission opportunities associated with the UE for grant-free uplink non-orthogonal multiple access (NOMA) transmissions with repetition over multiple subframes; means for randomly selecting a demodulation reference signal (DMRS) sequence, for a grant-free uplink NOMA transmission, from a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions, wherein the subset of all DMRS sequences is determined based at least in part on the transmission opportunity, wherein different subsets of DMRS sequences are associated with different transmission opportunities, and wherein DMRS sequences in the different subsets are exclusive to the respective subsets; means for scrambling the DMRS sequence using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) ; means for transmitting the scrambled DMRS sequence in the transmission opportunity; and/or the like. Additionally, or alternatively, the apparatus 1102/1102′for wireless communication includes means for selecting a demodulation reference signal (DMRS) sequence for a grant-free uplink non-orthogonal multiple access (NOMA) transmission with repetition over multiple subframes, wherein the DMRS sequence is randomly selected from a predefined set of DMRS sequences; means for transmitting the DMRS sequence in a transmission opportunity; and/or the like. The aforementioned means may be one or more of the aforementioned modules of the apparatus 1102 and/or the processing system 1202 of the apparatus 1102′configured to perform the functions recited by the aforementioned means. As described supra, the processing system 1202 may include the TX MIMO processor 266, the RX processor 258, and/or the controller/processor 280. As such, in one configuration, the aforementioned means may be the TX MIMO processor 266, the RX processor 258, and/or the controller/processor 280 configured to perform the functions recited by the aforementioned means.

FIG. 12 is provided as an example. Other examples are possible and may differ from what was described in connection with FIG. 12.

It is understood that the specific order or hierarchy of blocks in the processes /flow charts disclosed is an illustration of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes /flow charts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” The word “exemplary” is used herein to mean “serving as an example, instance, or illustration. ” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C, ” “at least one of A, B, and C, ” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C, ” “at least one of A, B, and C, ” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for. ”

Claims

A method of wireless communication performed by a user equipment (UE) , comprising:

determining a transmission opportunity in a time domain, wherein the transmission opportunity is selected from a plurality of transmission opportunities associated with the UE for grant-free uplink non-orthogonal multiple access (NOMA) transmissions with repetition over multiple subframes;

randomly selecting a demodulation reference signal (DMRS) sequence, for a grant-free uplink NOMA transmission, from a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions, wherein the subset of all DMRS sequences is determined based at least in part on the transmission opportunity, wherein different subsets of DMRS sequences are associated with different transmission opportunities, and wherein DMRS sequences in the different subsets are exclusive to the respective subsets;

scrambling the DMRS sequence using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) ; and

transmitting the scrambled DMRS sequence in the transmission opportunity.
The method of claim 1, wherein the OCC is randomly selected from a set of OCCs.
The method of claim 2, wherein consecutive transmission opportunities, of the plurality of transmission opportunities, are separated by a number of valid subframes equal to a length of the OCC.
The method of claim 3, wherein the number of valid subframes excludes one or more subframes reserved for broadcast signals or control signals.
The method of claim 1, wherein the OCC is selected based at least in part on the transmission opportunity, wherein different OCCs are associated with different transmission opportunities.
The method of claim 5, wherein consecutive transmission opportunities, of the plurality of transmission opportunities, occur in consecutive valid subframes.
The method of claim 6, wherein the consecutive valid subframes exclude one or more subframes reserved for broadcast signals or control signals.
The method of claim 5, wherein the OCC is selected based at least in part on dividing an index of the transmission opportunity by a square root of a number of transmission opportunities included in the plurality of transmission opportunities, and performing a ceiling operation to round a result of the dividing to a nearest integer that is greater than the result, wherein the integer represents an OCC index used for selection of the OCC.
The method of claim 5, wherein different bits of the OCC are applied to different subframes in which the scrambled DMRS sequence is repeated.
The method of claim 5, wherein a first bit of the OCC is associated with the scrambled DMRS sequence transmitted in a first subframe of the transmission opportunity and a second bit of the OCC is associated with the scrambled DMRS sequence transmitted in a second subframe of the transmission opportunity, wherein the first bit and the second bit are consecutive bits of the OCC and the first subframe and the second subframe are consecutive valid subframes.
The method of claim 5, wherein consecutive bits of the OCC correspond to consecutive valid subframes in which the scrambled DMRS sequence is transmitted.
The method of claim 11, wherein after a last bit of the OCC is associated with a subframe of the transmission opportunity, an initial bit of the OCC is associated with a next consecutive subframe of the transmission opportunity, wherein a number of bits of the OCC is less than a number of repetitions of the DMRS sequence.
The method of claim 1, wherein the scrambled DMRS sequence is repeated over multiple subframes.
The method of claim 13, wherein the multiple subframes are consecutive valid subframes that do not include a broadcast signal or a control signal.
A method of wireless communication performed by a user equipment (UE) , comprising:

selecting a demodulation reference signal (DMRS) sequence for a grant-free uplink non-orthogonal multiple access (NOMA) transmission with repetition over multiple subframes, wherein the DMRS sequence is randomly selected from a predefined set of DMRS sequences; and

transmitting the DMRS sequence in a transmission opportunity.
The method of claim 15, wherein the DMRS sequence is repeated over multiple subframes.
The method of claim 16, wherein the multiple subframes are consecutive valid subframes that do not include a broadcast signal or a control signal.
The method of claim 15, wherein the predefined set of DMRS sequences includes all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions.
The method of claim 15, wherein the DMRS sequence is scrambled using a scrambling sequence, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) .
The method of claim 19, wherein the OCC is randomly selected from a set of OCCs.
The method of claim 19, wherein the OCC is selected based at least in part on the transmission opportunity.
The method of claim 21, wherein different OCCs are associated with different transmission opportunities.
The method of claim 21, wherein consecutive transmission opportunities are separated by a number of valid subframes equal to a length of the OCC.
The method of claim 23, wherein the number of valid subframes excludes one or more subframes reserved for broadcast signals or control signals.
The method of claim 13, wherein the predefined set of DMRS sequences is a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions.
The method of claim 25, wherein the predefined set of DMRS sequences is determined based at least in part on the transmission opportunity, wherein different subsets of DMRS sequences are associated with different transmission opportunities.
The method of claim 26, wherein DMRS sequences in the different subsets of DMRS sequences are exclusive to the respective subsets.
The method of claim 25, wherein the DMRS sequence is scrambled using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) that is randomly selected from a set of OCCs.
The method of claim 28, wherein consecutive transmission opportunities are separated by a number of subframes equal to a length of the OCC.
The method of claim 29, wherein the number of subframes excludes one or more subframes reserved for broadcast signals or control signals.
The method of claim 25, wherein the DMRS sequence is scrambled using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) that is selected based at least in part on the transmission opportunity, wherein different OCCs are associated with different transmission opportunities.
The method of claim 31, wherein the OCC is selected based at least in part on dividing an index of the transmission opportunity by a square root of a number of transmission opportunities included in a plurality of transmission opportunities associated with the UE for grant-free uplink NOMA transmissions with repetition over multiple subframes, and performing a ceiling operation to round a result of the dividing to a nearest integer that is greater than the result, wherein the integer represents an OCC index used for selection of the OCC.
The method of claim 31, wherein different bits of the OCC are applied to different subframes in which the DMRS sequence is repeated.
The method of claim 31, wherein a first bit of the OCC is associated with the DMRS sequence transmitted in a first subframe of the transmission opportunity and a second bit of the OCC is associated with the DMRS sequence transmitted in a second subframe of the transmission opportunity, wherein the first bit and the second bit are consecutive bits of the OCC and the first subframe and the second subframe are consecutive valid subframes.
The method of claim 31, wherein consecutive bits of the OCC correspond to consecutive valid subframes in which the scrambled DMRS sequence is transmitted.
The method of claim 35, wherein after a last bit of the OCC is associated with a subframe of the transmission opportunity, an initial bit of the OCC is associated with a next consecutive subframe of the transmission opportunity, wherein a number of bits of the OCC is less than a number of repetitions of the DMRS sequence.
The method of claim 25, wherein consecutive transmission opportunities occur in consecutive valid subframes.
The method of claim 37, wherein the consecutive valid subframes exclude one or more subframes reserved for broadcast signals or control signals.
A user equipment (UE) for wireless communication, comprising:

memory; and

one or more processors operatively coupled to the memory, the memory and the one or more processors configured to:

determine a transmission opportunity in a time domain, wherein the transmission opportunity is selected from a plurality of transmission opportunities associated with the UE for grant-free uplink non-orthogonal multiple access (NOMA) transmissions with repetition over multiple subframes;

randomly select a demodulation reference signal (DMRS) sequence, for a grant-free uplink NOMA transmission, from a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions, wherein the subset of all DMRS sequences is determined based at least in part on the transmission opportunity, wherein different subsets of DMRS sequences are associated with different transmission opportunities, and wherein DMRS sequences in the different subsets are exclusive to the respective subsets;

scramble the DMRS sequence using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) ; and

transmit the scrambled DMRS sequence in the transmission opportunity.
The UE of claim 39, wherein the OCC is randomly selected from a set of OCCs.
The UE of claim 40, wherein consecutive transmission opportunities, of the plurality of transmission opportunities, are separated by a number of valid subframes equal to a length of the OCC.
The UE of claim 41, wherein the number of valid subframes excludes one or more subframes reserved for broadcast signals or control signals.
The UE of claim 39, wherein the OCC is selected based at least in part on the transmission opportunity, wherein different OCCs are associated with different transmission opportunities.
The UE of claim 43, wherein consecutive transmission opportunities, of the plurality of transmission opportunities, occur in consecutive valid subframes.
The UE of claim 44, wherein the consecutive valid subframes exclude one or more subframes reserved for broadcast signals or control signals.
The UE of claim 43, wherein the OCC is selected based at least in part on dividing an index of the transmission opportunity by a square root of a number of transmission opportunities included in the plurality of transmission opportunities, and performing a ceiling operation to round a result of the dividing to a nearest integer that is greater than the result, wherein the integer represents an OCC index used for selection of the OCC.
The UE of claim 43, wherein different bits of the OCC are applied to different subframes in which the scrambled DMRS sequence is repeated.
The UE of claim 43, wherein a first bit of the OCC is associated with the scrambled DMRS sequence transmitted in a first subframe of the transmission opportunity and a second bit of the OCC is associated with the scrambled DMRS sequence transmitted in a second subframe of the transmission opportunity, wherein the first bit and the second bit are consecutive bits of the OCC and the first subframe and the second subframe are consecutive valid subframes.
The UE of claim 43, wherein consecutive bits of the OCC correspond to consecutive valid subframes in which the scrambled DMRS sequence is transmitted.
The UE of claim 49, wherein after a last bit of the OCC is associated with a subframe of the transmission opportunity, an initial bit of the OCC is associated with a next consecutive subframe of the transmission opportunity, wherein a number of bits of the OCC is less than a number of repetitions of the DMRS sequence.
The UE of claim 39, wherein the scrambled DMRS sequence is repeated over multiple subframes.
The UE of claim 51, wherein the multiple subframes are consecutive valid subframes that do not include a broadcast signal or a control signal.
A user equipment (UE) for wireless communication, comprising:

memory; and

one or more processors operatively coupled to the memory, the memory and the one or more processors configured to:

select a demodulation reference signal (DMRS) sequence for a grant-free uplink non-orthogonal multiple access (NOMA) transmission with repetition over multiple subframes, wherein the DMRS sequence is randomly selected from a predefined set of DMRS sequences; and

transmit the DMRS sequence in a transmission opportunity.
The UE of claim 53, wherein the DMRS sequence is repeated over multiple subframes.
The UE of claim 54, wherein the multiple subframes are consecutive valid subframes that do not include a broadcast signal or a control signal.
The UE of claim 53, wherein the predefined set of DMRS sequences includes all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions.
The UE of claim 53, wherein the DMRS sequence is scrambled using a scrambling sequence, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) .
The UE of claim 57, wherein the OCC is randomly selected from a set of OCCs.
The UE of claim 57, wherein the OCC is selected based at least in part on the transmission opportunity.
The UE of claim 59, wherein different OCCs are associated with different transmission opportunities.
The UE of claim 59, wherein consecutive transmission opportunities are separated by a number of valid subframes equal to a length of the OCC.
The UE of claim 61, wherein the number of valid subframes excludes one or more subframes reserved for broadcast signals or control signals.
The UE of claim 53, wherein the predefined set of DMRS sequences is a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions.
The UE of claim 63, wherein the predefined set of DMRS sequences is determined based at least in part on the transmission opportunity, wherein different subsets of DMRS sequences are associated with different transmission opportunities.
The UE of claim 64, wherein DMRS sequences in the different subsets of DMRS sequences are exclusive to the respective subsets.
The UE of claim 63, wherein the DMRS sequence is scrambled using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) that is randomly selected from a set of OCCs.
The UE of claim 66, wherein consecutive transmission opportunities are separated by a number of subframes equal to a length of the OCC.
The UE of claim 67, wherein the number of subframes excludes one or more subframes reserved for broadcast signals or control signals.
The UE of claim 63, wherein the DMRS sequence is scrambled using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) that is selected based at least in part on the transmission opportunity, wherein different OCCs are associated with different transmission opportunities.
The UE of claim 69, wherein the OCC is selected based at least in part on dividing an index of the transmission opportunity by a square root of a number of transmission opportunities included in a plurality of transmission opportunities associated with the UE for grant-free uplink NOMA transmissions with repetition over multiple subframes, and performing a ceiling operation to round a result of the dividing to a nearest integer that is greater than the result, wherein the integer represents an OCC index used for selection of the OCC.
The UE of claim 69, wherein different bits of the OCC are applied to different subframes in which the DMRS sequence is repeated.
The UE of claim 69, wherein a first bit of the OCC is associated with the DMRS sequence transmitted in a first subframe of the transmission opportunity and a second bit of the OCC is associated with the DMRS sequence transmitted in a second subframe of the transmission opportunity, wherein the first bit and the second bit are consecutive bits of the OCC and the first subframe and the second subframe are consecutive valid subframes.
The UE of claim 69, wherein consecutive bits of the OCC correspond to consecutive valid subframes in which the scrambled DMRS sequence is transmitted.
The UE of claim 73, wherein after a last bit of the OCC is associated with a subframe of the transmission opportunity, an initial bit of the OCC is associated with a next consecutive subframe of the transmission opportunity, wherein a number of bits of the OCC is less than a number of repetitions of the DMRS sequence.
The UE of claim 63, wherein consecutive transmission opportunities occur in consecutive valid subframes.
The UE of claim 75, wherein the consecutive valid subframes exclude one or more subframes reserved for broadcast signals or control signals.
A non-transitory computer-readable medium storing one or more instructions for wireless communication, the one or more instructions comprising:

one or more instructions that, when executed by one or more processors of a user equipment (UE) , cause the one or more processors to:

determine a transmission opportunity in a time domain, wherein the transmission opportunity is selected from a plurality of transmission opportunities associated with the UE for grant-free uplink non-orthogonal multiple access (NOMA) transmissions with repetition over multiple subframes;

randomly select a demodulation reference signal (DMRS) sequence, for a grant-free uplink NOMA transmission, from a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions, wherein the subset of all DMRS sequences is determined based at least in part on the transmission opportunity, wherein different subsets of DMRS sequences are associated with different transmission opportunities, and wherein DMRS sequences in the different subsets are exclusive to the respective subsets;

scramble the DMRS sequence using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) ; and

transmit the scrambled DMRS sequence in the transmission opportunity.
An apparatus for wireless communication, comprising:

means for determining a transmission opportunity in a time domain, wherein the transmission opportunity is selected from a plurality of transmission opportunities associated with the apparatus for grant-free uplink non-orthogonal multiple access (NOMA) transmissions with repetition over multiple subframes;

means for randomly selecting a demodulation reference signal (DMRS) sequence, for a grant-free uplink NOMA transmission, from a subset of all DMRS sequences permitted to be used for grant-free uplink NOMA transmissions, wherein the subset of all DMRS sequences is determined based at least in part on the transmission opportunity, wherein different subsets of DMRS sequences are associated with different transmission opportunities, and wherein DMRS sequences in the different subsets are exclusive to the respective subsets;

means for scrambling the DMRS sequence using a scrambling sequence in a time domain, wherein the scrambling sequence is determined based at least in part on an orthogonal cover code (OCC) ; and

means for transmitting the scrambled DMRS sequence in the transmission opportunity.
A non-transitory computer-readable medium storing one or more instructions for wireless communication, the one or more instructions comprising:

one or more instructions that, when executed by one or more processors of a user equipment (UE) , cause the one or more processors to:

select a demodulation reference signal (DMRS) sequence for a grant-free uplink non-orthogonal multiple access (NOMA) transmission with repetition over multiple subframes, wherein the DMRS sequence is randomly selected from a predefined set of DMRS sequences; and

transmit the DMRS sequence in a transmission opportunity.
An apparatus for wireless communication, comprising:

means for selecting a demodulation reference signal (DMRS) sequence for a grant-free uplink non-orthogonal multiple access (NOMA) transmission with repetition over multiple subframes, wherein the DMRS sequence is randomly selected from a predefined set of DMRS sequences; and

means for transmitting the DMRS sequence in a transmission opportunity.