WO2020029120A1

WO2020029120A1 - Dmrs sequence group hopping for single-tone transmission

Info

Publication number: WO2020029120A1
Application number: PCT/CN2018/099415
Authority: WO
Inventors: Chao Wei; Le LIU; Alberto Rico Alvarino
Original assignee: Qualcomm Incorporated
Priority date: 2018-08-08
Filing date: 2018-08-08
Publication date: 2020-02-13

Abstract

Various aspects of the present disclosure generally relate to wireless communication. In some aspects, a user equipment may determine a hopping pattern value for a narrowband reference signal, wherein the hopping pattern value is based at least in part on a slot or subframe index associated with the narrowband reference signal and at least one of: a frame index of a frame associated with the narrowband reference signal, or a hopping pattern value for a previous reference signal; and transmit the narrowband reference signal in accordance with the hopping pattern value for the narrowband reference signal. Numerous other aspects are provided.

Description

DMRS SEQUENCE GROUP HOPPING FOR SINGLE-TONE TRANSMISSION

TECHNICAL FIELD OF THE DISCLOSURE

Aspects of the technology described below generally relate to wireless communication, and more particularly to techniques and apparatuses for demodulation reference signal (DMRS) sequence group hopping for single-tone transmission. Some techniques and apparatuses described herein enable and provide wireless communication devices and systems configured for low latency scenarios and enhanced network coverage.

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 user equipment (UE) may communicate with a base station (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 new radio (NR) 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 user equipment to communicate on a municipal, national, regional, and even global level. New radio (NR) , which may also be referred to as 5G, is a set of enhancements to the LTE mobile standard promulgated by the Third Generation Partnership Project (3GPP) . NR 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 orthogonal frequency division multiplexing (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 OFDM (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 NR technologies. Preferably, these improvements should be applicable to other multiple access technologies and the telecommunication standards that employ these technologies.

BRIEF SUMMARY OF SOME EXAMPLES

The following summarizes some aspects of the present disclosure to provide a basic understanding of the discussed technology. This summary is not an extensive overview of all contemplated features of the disclosure, and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. The sole purpose of this summary is to present some concepts of one or more aspects of the disclosure in summary form as a prelude to the more detailed description that is presented later.

In some aspects, a method of wireless communication, performed by a user equipment (UE) , may include determining a hopping pattern value for a narrowband reference signal, wherein the hopping pattern value is based at least in part on a slot or subframe index associated with the narrowband reference signal and at least one of: a frame index of a frame associated with the narrowband reference signal, or a hopping pattern value for a previous reference signal; and transmitting the narrowband reference signal in accordance with the hopping pattern value for the narrowband reference signal.

In some aspects, a UE for wireless communication may include 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 hopping pattern value for a narrowband reference signal, wherein the hopping pattern value is based at least in part on a slot or subframe index associated with the narrowband reference signal and at least one of: a frame index of a frame associated with the narrowband reference signal, or a hopping pattern value for a previous reference signal; and transmit the narrowband reference signal in accordance with the hopping pattern value for the narrowband reference signal.

In some aspects, a non-transitory computer-readable medium may store one or more instructions for wireless communication. 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 hopping pattern value for a narrowband reference signal, wherein the hopping pattern value is based at least in part on a slot or subframe index associated with the narrowband reference signal and at least one of: a frame index of a frame associated with the narrowband reference signal, or a hopping pattern value for a previous reference signal; and transmit the narrowband reference signal in accordance with the hopping pattern value for the narrowband reference signal.

In some aspects, an apparatus for wireless communication may include means for determining a hopping pattern value for a narrowband reference signal, wherein the hopping pattern value is based at least in part on a slot or subframe index associated with the narrowband reference signal and at least one of: a frame index of a frame associated with the narrowband reference signal, or a hopping pattern value for a previous reference signal; and means for transmitting the narrowband reference signal in accordance with the hopping pattern value for the narrowband reference signal.

In some aspects, a method of wireless communication, performed by a user equipment (UE) , may include determining a first set of subcarriers for a first reference signal associated with a first cell and a second set of subcarriers for a second reference signal associated with a second cell; and determining first resources of the first set of subcarriers for transmission of the first reference signal and second resources of the second set of subcarriers for transmission of the second reference signal, wherein the first resources do not collide with the second resources, and wherein the first resources and the second resources are selected using one of: a common hopping pattern, or a slot-dependent hopping pattern.

In some aspects, a UE for wireless communication may include 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 first set of subcarriers for a first reference signal associated with a first cell and a second set of subcarriers for a second reference signal associated with a second cell; and determine first resources of the first set of subcarriers for transmission of the first reference signal and second resources of the second set of subcarriers for transmission of the second reference signal, wherein the first resources do not collide with the second resources, and wherein the first resources and the second resources are selected using one of: a common hopping pattern, or a slot-dependent hopping pattern.

In some aspects, a non-transitory computer-readable medium may store one or more instructions for wireless communication. 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 first set of subcarriers for a first reference signal associated with a first cell and a second set of subcarriers for a second reference signal associated with a second cell; and determine first resources of the first set of subcarriers for transmission of the first reference signal and second resources of the second set of subcarriers for transmission of the second reference signal, wherein the first resources do not collide with the second resources, and wherein the first resources and the second resources are selected using one of: a common hopping pattern, or a slot-dependent hopping pattern.

In some aspects, an apparatus for wireless communication may include means for determining a first set of subcarriers for a first reference signal associated with a first cell and a second set of subcarriers for a second reference signal associated with a second cell; and means for determining first resources of the first set of subcarriers for transmission of the first reference signal and second resources of the second set of subcarriers for transmission of the second reference signal, wherein the first resources do not collide with the second resources, and wherein the first resources and the second resources are selected using one of: a common hopping pattern, or a slot-dependent hopping pattern.

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

So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects. The same reference numbers in different drawings may identify the same or similar elements.

Fig. 1 is a block diagram conceptually illustrating an example of a wireless communication network, in accordance with various aspects of the present disclosure.

Fig. 2 is a block diagram conceptually illustrating an example of a base station in communication with a user equipment (UE) in a wireless communication network, in accordance with various aspects of the present disclosure.

Fig. 3 is a diagram illustrating an example of determining a DMRS sequence group hopping value for a single-tone transmission, in accordance with various aspects of the present disclosure.

Fig. 4 is a diagram illustrating an example process performed, for example, by a user equipment, in accordance with various aspects of the present disclosure.

Fig. 5 is a diagram illustrating an example of determining non-colliding resources for reference signals of an enhanced machine-type communication (eMTC) UE using pi/2 binary phase shift keying (BPSK) , in accordance with various aspects of the present disclosure.

Fig. 6 is a diagram illustrating an example process performed, for example, by a user equipment, in accordance with various aspects of the present disclosure.

DETAILED DESCRIPTION

Various aspects of the disclosure are described more fully hereinafter with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings herein one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure disclosed herein, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim.

Several aspects of telecommunication systems will now be presented with reference to various apparatuses and techniques. These apparatuses and techniques 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 hardware, software, or combinations thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

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 NR technologies.

While aspects and embodiments are described in this application by illustration to some examples, those skilled in the art will understand that additional implementations and use cases may come about in many different arrangements and scenarios. Innovations described herein may be implemented across many differing platform types, devices, systems, shapes, sizes, packaging arrangements. For example, embodiments and/or uses may come about via integrated chip embodiments and/or other non-module-component based devices (e.g., end-user devices, vehicles, communication devices, computing devices, industrial equipment, retail/purchasing devices, medical devices, AI-enabled devices, and/or the like) . While some examples may or may not be specifically directed to use cases or applications, a wide assortment of applicability of described innovations may occur. Implementations may range a spectrum from chip-level or modular components to non-modular, non-chip-level implementations and further to aggregate, distributed, or original equipment manufacturer devices or systems incorporating one or more aspects of the described innovations. In some practical settings, devices incorporating described aspects and features may also necessarily include additional components and features for implementation and practice of claimed and described embodiments. For example, transmission and reception of wireless signals necessarily includes a number of components for analog and digital purposes (e.g., hardware components including one or more antennas, RF-chains, power amplifiers, modulators, buffers, processors, interleavers, adders/summers, and/or the like) . It is intended that innovations described herein may be practiced in a wide variety of devices, chip-level components, systems, distributed arrangements, end-user devices, etc. of varying sizes, shapes, and constitution.

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 or NR 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 NR BS, a Node B, a gNB, a 5G node B (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” , “NR BS” , “gNB” , “TRP” , “AP” , “node B” , “5G NB” , and “cell” may be used interchangeably herein.

In some aspects, 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 aspects, 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, and/or the like. 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, and/or the like, 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, NR or 5G RAT networks may be deployed.

In some aspects, two or more UEs 120 (e.g., shown as UE 120a and UE 120e) may communicate directly using one or more sidelink channels (e.g., without using a base station 110 as an intermediary to communicate with one another) . For example, the UEs 120 may communicate using peer-to-peer (P2P) communications, device-to-device (D2D) communications, a vehicle-to-everything (V2X) protocol (e.g., which may include a vehicle-to-vehicle (V2V) protocol, a vehicle-to-infrastructure (V2I) protocol, and/or the like) , a mesh network, and/or the like. In this case, the UE 120 may perform scheduling operations, resource selection operations, and/or other operations described elsewhere herein as being performed by the base station 110.

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 of a design 200 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 cell-specific reference signal (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 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 reference signal received power (RSRP) , received signal strength indicator (RSSI) , reference signal received quality (RSRQ) , channel quality indicator (CQI) , and/or the like. In some aspects, one or more components of UE 120 may be included in a housing.

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 DMRS sequence group hopping for single-tone transmission, 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, process 400 of Fig. 4, process 600 of Fig. 6, and/or other processes as described herein.

Memories

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

In some aspects, UE 120 may include means for determining a hopping pattern value for a narrowband reference signal, wherein the hopping pattern value is based at least in part on a slot or subframe index associated with the narrowband reference signal and at least one of: a frame index of a frame associated with the narrowband reference signal, or a hopping pattern value for a previous reference signal; means for transmitting the narrowband reference signal in accordance with the hopping pattern value for the narrowband reference signal; means for determining a first set of subcarriers for a first reference signal associated with a first cell and a second set of subcarriers for a second reference signal associated with a second cell; means for determining first resources of the first set of subcarriers for transmission of the first reference signal and second resources of the second set of subcarriers for transmission of the second reference signal, wherein the first resources do not collide with the second resources, and wherein the first resources and the second resources are selected using one of: a common hopping pattern, or a slot-dependent hopping pattern; means for transmitting at least one of the first reference signal or the second reference signal; and/or the like. In some aspects, such means may include one or more components of UE 120 described in connection with Fig. 2.

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.

A UE may transmit a reference signal for configuration of communication between the UE and a base station. One such reference signal is the demodulation reference signal (DMRS) . The DMRS may provide channel information for demodulation of uplink communications between the UE and the base station.

Some radio access technologies, such as narrowband Internet of Things (NB-IoT) and enhanced machine-type communication (eMTC) , provide for sub-physical resource block (PRB) resource allocation. For example, in NB-IoT, single-tone transmission may be supported in the uplink. A reference signal (e.g., a DMRS for the uplink transmission) for single-tone uplink transmission may be defined by the element-wise product of a 16-length Hadamard code and a Gold sequence. One example of such a reference signal may be defined as:

wherein c (n) is a Gold sequence common to all cells and wherein w (n) is a cell-dependent Hadamard code selected from a set of 16 sequences N _seq.

DMRS group hopping may be supported for single-tone transmission. Without hopping, persistent interference may occur, which may lead to incorrect channel estimation even without noise. DMRS group hopping may be performed in accordance with a hopping pattern, and resources for DMRS transmission may be selected based at least in part on a hopping pattern value determined in accordance with the hopping pattern. For example, when DMRS hopping is enabled, the selection of the Hadamard sequence index from N _seq may be defined by a group hopping pattern f _gh (n _s) and a sequence-shift pattern f _SS according to:

u= (fgh (n _s) +f _ss) mod N _seq

The hopping pattern f _gh (n _s) may be defined by:

wherein, for single-tone transmissions, n′ _s represents the slot number of the first slot of a resource unit of the reference signal and c (i) is a pseudo-random sequence that is initialized using a physical cell identifier associated with the beginning of the resource unit. A resource unit for a single-tone transmission may include 16 slots (e.g., one tone across 16 slots) , which may include 8 ms for a 15 kHz subcarrier spacing or 16 ms for a 30 kHz subcarrier spacing. Furthermore, the slot number in some RATs (e.g., LTE) may be defined within a radio frame by an index number ranging from 0 to 19. Therefore, for a single-tone transmission in a given cell, five different DMRS sequences can be used, since there are five different values of n′ _s and since the sequence group selection is reset every X subframes, wherein X is 40 for a 15 kHz subcarrier spacing or 160 for a 3.75 kHz subcarrier spacing.

In some RATs (e.g., NB-IoT using time division duplexing) , uplink transmission is permitted only in uplink subframes that are configured by higher-layer signaling. When the frame includes a number of uplink subframes that is a power of 2 and that is less than or equal to a length of a resource unit (e.g., 2, 4, 8, 16, etc. ) , then the first slot of the resource unit of the reference signal (e.g., n′ _s) may be repeated in some resource units. This may lead to persistent inter-cell interference between reference signals, such as the same interference on a first transmission of a DMRS and a retransmission of the DMRS.

Some techniques and apparatuses described herein provide determination of a hopping pattern value to avoid collision between transmissions of a reference signal. For example, some techniques and apparatuses described herein provide determination of a hopping pattern for a narrowband reference signal (e.g., a narrowband DMRS) using a slot or subframe index associated with the narrowband reference signal and a frame index of a frame associated with the narrowband reference signal. Some techniques and apparatuses described herein provide determination of a hopping pattern for a narrowband reference signal using a slot or subframe index and a hopping pattern for a previous narrowband reference signal (e.g., a previous DMRS) (e.g., in a recursive or iterative fashion) . Furthermore, the techniques and apparatuses described herein can be applied for a 3-subcarrier and 6-subcarrier multi-tone transmission when the transmission duration of the resource unit is an integer multiple of a radio frame. Still further, the techniques and apparatuses described herein can be applied for a sub-PRB physical uplink shared channel (PUSCH) transmission in eMTC. Thus, improved reliability and more efficient spectrum usage may be provided.

Fig. 3 is a diagram illustrating an example 300 of determination of DMRS group hopping values for a single-tone transmission, in accordance with various aspects of the present disclosure.

As shown in Fig. 3, and by reference number 310, a BS 110 may configure uplink subframes for the UE 120. In some aspects, the BS 110 may configure the uplink subframes as NB-IoT uplink subframes. For example, the BS 110 may provide information identifying subframes of a radio frame as downlink subframes, uplink subframes, or special subframes. In some aspects, this information may take the form of a pattern, a bitmap, and/or the like.

As shown by reference number 320, the UE 120 may determine that the UE 120 is configured with a particular number of uplink subframes per frame (e.g., per radio frame) . For example, the UE 120 may determine that a radio frame of the UE 120 includes a number of uplink subframes that is a power of 2 and that is less than a length of a resource unit. When the UE 120 is configured with the particular number of uplink subframes per frame, or when the frame includes a number of uplink slots that is a power of 2 and that is less than or equal to a length of a resource unit (e.g., 2, 4, 8, 16, etc. ) , then collision may occur with regard to starting subframes of narrowband reference signals. For example, the starting subframe of a first transmission and a retransmission of a narrowband reference signal may collide, thus causing interference and reducing demodulation performance of a receiver device.

As shown by reference number 330, the UE 120 may determine a hopping pattern value for a single-tone transmission of a narrowband reference signal. For example, the UE 120 may determine the hopping pattern value so as to avoid repeating the same DMRS sequence for the first transmission and the retransmission of the narrowband reference signal and, thus, reduce or eliminate interference and increase demodulation performance of a receiver device.

In some aspects, the UE 120 may determine the hopping pattern value based at least in part on a slot or subframe index associated with the narrowband reference signal, and based at least in part on a frame index of a frame (e.g., a radio frame) associated with the narrowband reference signal. In some aspects, the UE 120 may determine the hopping pattern value based at least in part on the slot or subframe index associated with the narrowband reference signal, and based at least in part on a hopping pattern for a previous reference signal. Each is described in turn below.

In some aspects, the UE 120 may determine the hopping pattern value based at least in part on a slot or subframe index associated with the narrowband reference signal, and based at least in part on a frame index of a frame (e.g., a radio frame) associated with the narrowband reference signal. For example, the UE 120 may reuse the group hopping pattern f _gh (n _s) described above, and may use a modified value of n′ _s that is based at least in part on the slot or subframe index and the frame index:

wherein n _f and n _s are the frame index and the slot or subframe index of the first slot of the resource unit in which the narrowband reference signal is to be transmitted.

As further shown, the hopping pattern value may be further based at least in part on a modulo of a value N _p. In some aspects, N _p may be a number such as 2^z, where z is an integer (e.g., 5, 10, 15, etc. ) . In some aspects, N _p may be a prime number, such as a prime number larger than 16 (e.g., 31 or a different prime number) . The selection of N _p may provide for different n′ _s to be used for each resource unit. In some aspects, the value of N _p may be configured for the UE 120. In some aspects, the value of N _p may be based at least in part on a resource unit length. For example, a first value (e.g., 31 or a different value) may be used for a first resource unit length (e.g., 8 ms) and a second value (e.g., 161 or a different value) may be used for a second resource unit length. In some aspects, n′ _s may be based at least in part on a resource unit index, as shown here: n′ _s= (20n _f+n _s) mod N _seq. In this way, the UE 120 may determine the hopping pattern value based at least in part on the slot or subframe index and the frame index. Thus, a first transmission and a retransmission of a narrowband reference signal in different radio frames may have different hopping pattern values, thereby reducing collision between the first transmission and the retransmission.

In some aspects, the UE 120 may determine the hopping pattern value based at least in part on an iterative hopping pattern. For example, the hopping pattern value for the narrowband reference signal may be based at least in part on a previous reference signal, or based at least in part on a resource unit of a previous reference signal. In such a case, and as an example, the UE 120 may determine the hopping pattern value for a kth resource unit according to the equation:

wherein n′ _s, k represents a slot or subframe number of the first slot of the kth resource unit. The above hopping pattern is referred to as an iterative hopping pattern since the hoping pattern value for the kth resource unit is derived in part from the hopping pattern value for the k-1st resource unit. In such a case, even when n′ _s, k is the same for all the resource units, the group hopping pattern may be different for different resource units. Thus, collisions of narrowband reference signals are reduced.

As shown by reference number 340, the UE 120 may transmit the narrowband reference signal. For example, the UE 120 may transmit the narrowband reference signal using a resource associated with the hopping pattern value. By determining the hopping pattern value using the techniques described above, the UE 120 may reduce or avoid collisions between first transmissions and retransmissions of the narrowband reference signal, thereby reducing interference and improving network performance.

In some aspects, the UE 120 may determine a hopping pattern value for an eMTC transmission. For example, the UE 120 may determine a hopping pattern for a sub-PRB PUSCH that is to be transmitted by an eMTC UE (e.g., the UE 120) . In such a case, the UE 120 may use a 2 out of 3 subcarrier configuration with pi/2 binary phase shift keying modulation, and a combination of frequency division duplexing (FDD) and time division duplexing (TDD) may be used. In such a case, the DMRS sequence and the sequence-group hopping pattern may be the same as for the single-tone transmission case in NB-IoT. For example, the UE 120 may determine that a number of uplink subframes (e.g., based at least in part on FDD and/or TDD) in a radio frame is a power of 2 equal to or less than a length of a resource unit, and may determine a hopping pattern value in accordance with the techniques described above. Thus, the techniques and apparatuses described herein are applicable for FDD and TDD for an eMTC UE.

In some aspects, the UE 120 may determine a hopping pattern value for a multi-tone transmission. For example, for a multi-tone transmission with 3 subcarriers (e.g., 3 tones) or 6 subcarriers (e.g., 6 tones) , the resource unit length may be 8 slots and 4 ms, or 4 slots and 2 ms, respectively. In such a case, the collision issue described above may arise when the transmission duration of a resource unit is an integer multiple of the length of a radio frame. For example, consider the TDD uplink/downlink configuration DSUUD DSUUD, which has 4 downlink subframes (denoted by D) , 4 uplink subframes (denoted by U) , and 2 special subframes (denoted by S) . In such a case, for a resource unit length of 4 ms, the transmission duration of one resource unit is one radio frame. Therefore, for a 3-tone transmission, the resource unit of a retransmission may start from the same slot, with the same value of n′ _s, and may therefore use the same DMRS sequence as the resource unit of a first transmission.

To avoid this collision, the UE 120 may determine a hopping pattern value using the techniques described in connection with reference number 330, above. In some aspects, the UE 120 may use the above techniques for multi-tone transmission with regard to 3-subcarrier configurations and 6-subcarrier configurations. If the UE 120 is configured to perform 12-subcarrier transmission in eMTC, the UE 120 may determine whether to use the techniques described in connection with reference number 330, or a legacy technique, based at least in part on signaling, such as system information (e.g., a system information block (SIB) ) , a radio resource configuration (RRC) message, and/or the like. Thus, the UE 120 may reduce or avoid collision for multi-tone transmissions in eMTC.

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 an example process 400 performed, for example, by a UE, in accordance with various aspects of the present disclosure. Example process 400 is an example where a UE (e.g., UE 120) performs a determination of a hopping pattern value for a single-tone transmission.

As shown in Fig. 4, in some aspects, process 400 may include determining a hopping pattern value for a narrowband reference signal, wherein the hopping pattern value is based at least in part on a slot or subframe index associated with the narrowband reference signal and at least one of a frame index of a frame associated with the narrowband reference signal, or a hopping pattern value for a previous reference signal (block 410) . For example, the UE (e.g., using controller/processor 280 and/or the like) may determine a hopping pattern for a narrowband reference signal, such as a DMRS and/or the like. In some aspects, the hopping pattern value may be based at least in part on a slot or subframe index associated with the narrowband reference signal and a frame index of a frame associated with the narrowband reference signal. In some aspects, the hopping pattern value may be based at least in part on a slot or subframe index associated with the narrowband reference signal and a hopping pattern value for a previous reference signal.

As shown in Fig. 4, in some aspects, process 400 may include transmitting the narrowband reference signal in accordance with the hopping pattern value for the narrowband reference signal (block 420) . 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 narrowband reference signal in accordance with the hopping pattern value for the narrowband reference signal. In some aspects, the UE may transmit the narrowband reference signal using particular resources based at least in part on the hopping pattern value.

Process 400 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 frame includes a number of uplink subframes that is a power of 2 and that is less than or equal to a length of a resource unit of the narrowband reference signal. In some aspects, determining the hopping pattern value for the narrowband reference signal is based at least in part on the frame including an even number of uplink subframes. In some aspects, the hopping pattern value for the narrowband reference signal is further based at least in part on a modulo of a value that is a prime number larger than a threshold value.

In some aspects, the hopping pattern value for the narrowband reference signal is further based at least in part on a modulo of a value, wherein the value is based at least in part on a length of a resource unit used to transmit the narrowband reference signal. In some aspects, the hopping pattern value for the narrowband reference signal is based at least in part on an index number of a resource unit associated with the narrowband reference signal.

In some aspects, the narrowband reference signal is associated with a first resource unit and the previous reference signal is associated with a second resource unit, and the hopping pattern value for the narrowband reference signal is based at least in part on the second resource unit. In some aspects, the second resource unit does not overlap the first resource unit and immediately precedes the first resource unit.

In some aspects, the UE is a narrowband Internet of Things UE, and the narrowband reference signal is transmitted using a single tone. In some aspects, the UE is a machine-type communication UE, and the UE uses a sub-physical resource block allocation with a 2 out of 3 subcarriers pi/2 binary phase shift keying configuration for transmission of the reference signal.

Although Fig. 4 shows example blocks of process 400, in some aspects, process 400 may include additional blocks, fewer blocks, different blocks, or differently arranged blocks than those depicted in Fig. 4. Additionally, or alternatively, two or more of the blocks of process 400 may be performed in parallel.

A UE associated with an eMTC RAT, which may be referred to herein as an eMTC UE, may transmit an uplink communication (e.g., a physical uplink shared channel (PUSCH) ) using a sub-PRB resource allocation. In such a case, the eMTC UE may use a subset of subcarriers allocated to the eMTC UE. For example, the eMTC UE may use 2 of the 3 subcarriers allocated to the eMTC UE. The UE may use a particular modulation scheme, such as pi/2 BPSK. The UE may select the 2 of the 3 subcarriers based at least in part on a cell of the UE, for example, using a cell identifier of the cell along with a modulo 2 operation. For example,

may indicate that the two subcarriers having the lowest indices among the three allocated are to be utilized, and

may indicate that the two subcarriers having the highest indices among the three allocated are utilized. This may be used to reduce interference between neighboring cells by reducing collisions of uplink communications.

Spreading (e.g., discrete Fourier transform spreading) may result in two DMRS pi/2 sequences being spread onto just one of the 2 subcarriers. For example, the two sequences may alternate on the two subcarriers. The two DMRS sequences that will create DMRS symbols alternating between the two subcarriers may be given by r ₁ (n) = B (n) and

wherein B (n) is the same as the NB-IoT single-tone transmission DMRS sequence. More particularly, the two DMRS sequences r ₁ (n) and r ₂ (n) may be input to a length-2 DFT spreading, and the output of the DFT spreading may be (r ₁ (n) + r ₂ (n) ) /2 and (r ₁ (n) -r ₂ (n) ) /2, which will be mapped to the 2 used subcarriers. As can be seen, one of the outputs is zero, which means only one of the subcarriers is actually used for each DMRS symbol, and the actually mapped subcarrier may be alternated per DMRS symbol.

However, the cell-dependent alternating DMRS pattern described above may not adequately manage the interference between neighboring cells. For example, the DMRS pattern and the subcarrier selection may both be derived from the physical cell identifier, which may lead to collision in certain tones and slots, even though the pattern is orthogonal.

Some techniques and apparatuses described herein provide for determination of non-colliding resources for transmission of narrowband reference signals in different and overlapping sets of subcarriers. For example, some techniques and apparatuses described herein provide for determination of non-colliding resources using a common hopping pattern. Some techniques and apparatuses described herein provide for determination of non-colliding resources using a slot-dependent hopping pattern. In this way, inter-cell interference for eMTC UEs is reduced and network performance is improved.

Fig. 5 is a diagram illustrating an example 500 of a determination of non-colliding resources for reference signals of an eMTC UE using pi/2 BPSK, in accordance with various aspects of the present disclosure.

As shown in Fig. 5, and by reference number 510, a BS 110 may provide a first cell and a second cell to a UE 120. In some aspects, the first cell and the second cell may be provided by different BSs 110. In some aspects, the UE 120 may be an eMTC UE 120. For example, the UE 120 may transmit a narrowband reference signal (e.g., a DMRS and/or the like) on the first cell or the second cell to improve demodulation performance of the BS 110 with regard to a PUSCH of the UE 120. In some aspects, the UE 120 may transmit the narrowband reference signal using a 2 out of 3 subcarrier pi/2 BPSK technique, as described in more detail below.

As shown by reference number 520, the UE 120 may determine a first set of subcarriers and a second set of subcarriers. For example, the UE 120 may be allocated a plurality of subcarriers (e.g., 3 subcarriers or a different number of subcarriers) . The UE 120 may select a first set of subcarriers for the first cell and a second set of subcarriers for the second cell. For example, the first set of subcarriers and the second set of subcarriers may each include two subcarriers, although other numbers of subcarriers are possible. In some aspects, the UE 120 may select the first set of subcarriers and/or the second set of subcarriers based at least in part on cell identifiers of the first cell and the second cell and/or based at least in part on a modulo 2 operation, as described in more detail elsewhere herein.

As shown by reference number 530, the UE 120 may determine first resources of the first set of subcarriers for transmission of the first reference signal and second resources of the second set of subcarriers for transmission of the second reference signal. For example, the first resources may each occupy a single tone, and may alternate between subcarriers of the first set of subcarriers. In some aspects, the second resources may each occupy a single tone, and may alternate between subcarriers of the second set of subcarriers.

In some aspects, the first resources may not collide with the second resources. For example, the UE 120 may select the first resources and the second resources using a hopping pattern so that the first resources do not collide with the second resources. In some aspects, the UE 120 may select the first resources and the second resources using a common hopping pattern (e.g., a hopping pattern that is not dependent on or derived from the cell identifier (s) of the first cell and/or the second cell) . In some aspects, the UE 120 may determine the first resources and the second resources using a slot-dependent hopping pattern. Each hopping pattern is described in turn below.

In some aspects, the UE 120 may determine the first resources and the second resources based at least in part on a common hopping pattern. For example, the UE 120 may use the same hopping pattern (e.g., the same DMRS alternating pattern) for both cells. More particularly, the UE 120 may determine the resources using the equations: r ₁ (n) = B (n) and r ₂ (n) = B (n) (-1) ⁽ⁿ⁾ where

wherein n is the transmission DMRS symbol index (or slot index, when one DMRS symbol per slot is to be used) . In this way, the common hopping pattern may not use the cell identifiers, which may reduce collision between the first cell and the second cell.

In some aspects, the UE 120 may determine the first resources and the second resources based at least in part on a slot-dependent hopping pattern. For example, the hopping pattern may be given by r ₁ (n) =B (n) and

wherein n _s (n) is the slot number to which the nth DMRS symbol is to be mapped. In some aspects, the slot-dependent hopping pattern may be advantageous in comparison to the common hopping pattern when the transmissions in the two cells are not subframe level aligned, such as, for example, when there is a one-slot shift between the two cells. In such a case, the DMRS RE mapping in the two cells using the common hopping pattern may not be orthogonal even though

is different. In this case, the slot-dependent hopping pattern may provide orthogonal DMRS mapping between neighboring cells as long as

is different for the neighboring cells.

As shown by reference number 540, the UE 120 may transmit a reference signal using the first resources and/or the second resources. For example, the UE 120 may transmit a narrowband reference signal (e.g., a DMRS and/or the like) . In some aspects, the UE 120 may transmit the first reference signal using the first resources. In some aspects, the UE 120 may transmit the second reference signal using the second resources. In this way, the UE 120 may reduce collision between neighboring cells using common hopping patterns and/or slot-dependent hopping patterns.

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 an example process 600 performed, for example, by a UE, in accordance with various aspects of the present disclosure. Example process 600 is an example where a UE (e.g., UE 120) performs a determination of non-colliding resources for reference signals of an eMTC UE using pi/2 BPSK.

As shown in Fig. 6, in some aspects, process 600 may include determining a first set of subcarriers for a first reference signal associated with a first cell and a second set of subcarriers for a second reference signal associated with a second cell (block 610) . For example, the UE (e.g., using controller/processor 280 and/or the like) may determine a first set of subcarriers and a second set of subcarriers. In some aspects, the first set of subcarriers may be associated with a first cell and the second set of subcarriers may be associated with a second cell. In some aspects, the first set of subcarriers may be for transmission of a first reference signal and the second set of subcarriers may be for transmission of a second reference signal.

As shown in Fig. 6, in some aspects, process 600 may include determining first resources of the first set of subcarriers for transmission of the first reference signal and second resources of the second set of subcarriers for transmission of the second reference signal, wherein the first resources do not collide with the second resources, and wherein the first resources and the second resources are selected using one of a common hopping pattern, or a slot-dependent hopping pattern (block 620) . For example, the UE (e.g., using controller/processor 280 and/or the like) may determine first resources of the first set of subcarriers for transmission of the first reference signal. In some aspects, the UE may determine second resources of the second set of subcarriers for transmission of the second reference signal. In some aspects, the first resources may not collide with the second resources. In some aspects, the first resources and/or the second resources may be selected using one of a common hopping pattern or a slot-dependent hopping pattern.

Process 600 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 UE is a machine-type communication UE. In some aspects, the UE uses a sub-physical resource block allocation with a 2 out of 3 subcarriers pi/2 binary phase shift keying configuration for transmission of the reference signal. In some aspects, the UE may transmit at least one of the first reference signal or the second reference signal.

In some aspects, the common hopping pattern or the slot-dependent hopping pattern is based at least in part on a hopping pattern for a narrowband Internet of Things UE. In some aspects, the common hopping pattern is used for the first cell and the second cell. In some aspects, the common hopping pattern is not derived from a cell identifier of the first cell or the second cell. In some aspects, the common hopping pattern uses a symbol index of the reference signal to determine the first resources or the second resources. In some aspects, the slot-dependent hopping pattern uses a slot index to determine the first resources or the second resources.

Although Fig. 6 shows example blocks of process 600, in some aspects, process 600 may include additional blocks, fewer blocks, different blocks, or differently arranged blocks than those depicted in Fig. 6. Additionally, or alternatively, two or more of the blocks of process 600 may be performed in parallel.

The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the aspects to the precise form disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from practice of the aspects.

As used herein, the term component is intended to be broadly construed as hardware, firmware, or a combination of hardware and software. As used herein, a processor is implemented in hardware, firmware, or a combination of hardware and software.

Some aspects are described herein in connection with thresholds. As used herein, satisfying a threshold may refer to a value being greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, and/or the like.

It will be apparent that systems and/or methods, described herein, may be implemented in different forms of hardware, firmware, or a combination of hardware and software. The actual specialized control hardware or software code used to implement these systems and/or methods is not limiting of the aspects. Thus, the operation and behavior of the systems and/or methods were described herein without reference to specific software code-it being understood that software and hardware can be designed to implement the systems and/or methods based, at least in part, on the description herein.

Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of possible aspects. In fact, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of possible aspects includes each dependent claim in combination with every other claim in the claim set. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c) .

No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. Also, as used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more. ” Furthermore, as used herein, the terms “set” and “group” are intended to include one or more items (e.g., related items, unrelated items, a combination of related and unrelated items, and/or the like) , and may be used interchangeably with “one or more. ” Where only one item is intended, the term “one” or similar language is used. Also, as used herein, the terms “has, ” “have, ” “having, ” and/or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.

Claims

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

determining a hopping pattern value for a narrowband reference signal, wherein the hopping pattern value is based at least in part on a slot or subframe index associated with the narrowband reference signal and at least one of:

a frame index of a frame associated with the narrowband reference signal, or

a hopping pattern value for a previous reference signal; and

transmitting the narrowband reference signal in accordance with the hopping pattern value for the narrowband reference signal.
The method of claim 1, wherein the frame includes a number of uplink subframes that is a power of 2 and that is less than or equal to a length of a resource unit of the narrowband reference signal.
The method of claim 1, wherein determining the hopping pattern value for the narrowband reference signal is based at least in part on the frame including a number of uplink subframes that is a power of 2 and that is less than or equal to a length of a resource unit of the narrowband reference signal.
The method of claim 1, wherein the hopping pattern value for the narrowband reference signal is further based at least in part on a modulo of a value that is a prime number larger than a threshold value.
The method of claim 1, wherein the hopping pattern value for the narrowband reference signal is further based at least in part on a modulo of a value, wherein the value is based at least in part on a length of a resource unit used to transmit the narrowband reference signal.
The method of claim 1, wherein the hopping pattern value for the narrowband reference signal is based at least in part on an index number of a resource unit associated with the narrowband reference signal.
The method of claim 1, wherein the narrowband reference signal is associated with a first resource unit and the previous reference signal is associated with a second resource unit, and wherein the hopping pattern value for the narrowband reference signal is based at least in part on the second resource unit.
The method of claim 7, wherein the second resource unit does not overlap the first resource unit and immediately precedes the first resource unit.
The method of claim 1, wherein the UE is a narrowband Internet of Things UE, and wherein the narrowband reference signal is transmitted using a single tone.
The method of claim 1, wherein the UE is a machine-type communication UE, and wherein the UE uses a sub-physical resource block allocation with a 2 out of 3 subcarriers pi/2 binary phase shift keying configuration for transmission of the reference signal.
A method of wireless communication performed by a user equipment (UE) , comprising:

determining a first set of subcarriers for a first reference signal associated with a first cell and a second set of subcarriers for a second reference signal associated with a second cell; and

determining first resources of the first set of subcarriers for transmission of the first reference signal and second resources of the second set of subcarriers for transmission of the second reference signal,

wherein the first resources do not collide with the second resources, and

wherein the first resources and the second resources are selected using one of:

a common hopping pattern, or

a slot-dependent hopping pattern.
The method of claim 11, wherein the UE is a machine-type communication UE, and wherein the UE uses a sub-physical resource block allocation with a 2 out of 3 subcarriers pi/2 binary phase shift keying configuration for transmission of the reference signal.
The method of claim 11, further comprising:

transmitting at least one of the first reference signal or the second reference signal.
The method of claim 11, wherein the common hopping pattern is used for the first cell and the second cell.
The method of claim 11, wherein the common hopping pattern is not derived from a cell identifier of the first cell or the second cell.
The method of claim 11, wherein the common hopping pattern uses a symbol index of the reference signal to determine the first resources or the second resources.
The method of claim 11, wherein the slot-dependent hopping pattern uses a slot index to determine the first resources or the second resources.
A user equipment (UE) for wireless communication, comprising:

a memory; and

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

determine a hopping pattern value for a narrowband reference signal, wherein the hopping pattern value is based at least in part on a slot or subframe index associated with the narrowband reference signal and at least one of:

a frame index of a frame associated with the narrowband reference signal, or

a hopping pattern value for a previous reference signal; and

transmit the narrowband reference signal in accordance with the hopping pattern value for the narrowband reference signal.
A user equipment (UE) for wireless communication, comprising:

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

determine a first set of subcarriers for a first reference signal associated with a first cell and a second set of subcarriers for a second reference signal associated with a second cell; and

determine first resources of the first set of subcarriers for transmission of the first reference signal and second resources of the second set of subcarriers for transmission of the second reference signal,

wherein the first resources do not collide with the second resources, and

wherein the first resources and the second resources are selected using one of:

a common hopping pattern, or

a slot-dependent hopping pattern.
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 hopping pattern value for a narrowband reference signal, wherein the hopping pattern value is based at least in part on a slot or subframe index associated with the narrowband reference signal and at least one of:

a frame index of a frame associated with the narrowband reference signal, or

a hopping pattern value for a previous reference signal; and

transmit the narrowband reference signal in accordance with the hopping pattern value for the narrowband reference signal.
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 first set of subcarriers for a first reference signal associated with a first cell and a second set of subcarriers for a second reference signal associated with a second cell; and

determine first resources of the first set of subcarriers for transmission of the first reference signal and second resources of the second set of subcarriers for transmission of the second reference signal,

wherein the first resources do not collide with the second resources, and

wherein the first resources and the second resources are selected using one of:

a common hopping pattern, or

a slot-dependent hopping pattern.
An apparatus for wireless communication, comprising:

means for determining a hopping pattern value for a narrowband reference signal, wherein the hopping pattern value is based at least in part on a slot or subframe index associated with the narrowband reference signal and at least one of:

a frame index of a frame associated with the narrowband reference signal, or

a hopping pattern value for a previous reference signal; and

means for transmitting the narrowband reference signal in accordance with the hopping pattern value for the narrowband reference signal.
An apparatus for wireless communication, comprising:

means for determining a first set of subcarriers for a first reference signal associated with a first cell and a second set of subcarriers for a second reference signal associated with a second cell; and

means for determining first resources of the first set of subcarriers for transmission of the first reference signal and second resources of the second set of subcarriers for transmission of the second reference signal,

wherein the first resources do not collide with the second resources, and

wherein the first resources and the second resources are selected using one of:

a common hopping pattern, or

a slot-dependent hopping pattern.