CN112425248A

CN112425248A - Enhanced RS transmission for RLM in NR unlicensed spectrum

Info

Publication number: CN112425248A
Application number: CN201880095664.7A
Authority: CN
Inventors: 孟艳; 陶涛; 刘建国; 骆喆; 武卓; 沈钢
Original assignee: Nokia Shanghai Bell Co Ltd; Nokia Networks Oy
Current assignee: Nokia Shanghai Bell Co Ltd; Nokia Oyj
Priority date: 2018-05-15
Filing date: 2018-05-15
Publication date: 2021-02-26
Anticipated expiration: 2038-05-15
Also published as: WO2019218142A1; CN112425248B

Abstract

Determining, by the transmitter, whether an LBT procedure performed in a current cycle is successful for the unlicensed spectrum, and performing one of: in response to the LBT procedure being successful, transmitting a first reference signal(s) on the unlicensed spectrum at a predetermined location in a current cycle; or, in response to the LBT procedure being unsuccessful, attempting to transmit the second reference signal(s) over the unlicensed spectrum within the time window in the current cycle based on other LBT procedure(s) operating within the time window in the current cycle. The receiver detects the first reference signal(s) and: in response to a successful detection, performing processing using the first reference signal(s); or blindly detecting the second reference signal(s) over the unlicensed spectrum within a time window in the current cycle in response to the detection being unsuccessful.

Description

Enhanced RS transmission for RLM in NR unlicensed spectrum

Technical Field

The present invention relates generally to wireless communications, and more particularly to reference signal usage in unlicensed spectrum.

Background

This section is intended to provide a background or context to the invention that is discussed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented, or described. Thus, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description of the present application and is not admitted to be prior art by inclusion in this section. Abbreviations that may be found in the specification and/or drawings are defined at the beginning of the detailed description section below.

In order to monitor the downlink radio link quality to indicate the out-of-sync/in-sync status indication to higher layers, the UE should measure the Reference Signal (RS) and compare it with the thresholds Qout and Qin. See, e.g., 3GPP TS 36.133V15.2.0 (2018-03). When the estimated downlink radio link quality becomes worse than the threshold Qout, the physical layer in the UE will send an out-of-sync (OOS) indication to higher layers. When the estimated downlink radio link quality becomes better than the threshold Qin, the physical layer in the UE will send a synchronization (IS) indication to the higher layers. Therefore, RS measurement is a key function of Radio Link Monitoring (RLM) of the physical layer.

RS measurements depend on RS design and transmission. In Long Term Evolution (LTE), the physical layer in the UE should monitor the downlink quality based on cell-specific reference signals (CRS) transmitted at each Downlink (DL) subframe and evaluate the radio link quality of each radio frame. In the NR design, both the Synchronization Signal Block (SSB) and the channel state information reference signal (CSI-RS) may be used as RLM reference signals. See final report 3GPP TSG RAN WG1# 91: MCC Support, "Draft Report of 3GPP TSG RAN WG1#91v0.2.0(Reno, USA,27th November-1st December 2017)", printed on 3GPP TSG RAN WG1 Meeting #92, R1-180xxxx, Athens, Greece,2018, 2.month, 26 days to 3.month, 2 days. In the case of CSI-RS based RLM, the RLM-RS resource is the configured UE-specific RRC. In the case of SSB-based RLM, the RLM-RS resource may be a configured UE-specific or cell-specific RRC. Both RLM-RSs are transmitted periodically. Therefore, the UE should monitor the downlink quality based on the SSB or CSI-RS and evaluate the downlink radio link quality per cycle in the NR system.

In the unlicensed spectrum, prior to transmission on the unlicensed carrier, the device should apply Listen Before Talk (LBT) to ensure that the target carrier is idle before accessing the unlicensed carrier. Due to LBT failure, the transmission of RLM-RS may be blocked, resulting in inefficient RLM measurements. To overcome the uncertainty problem of channel availability due to LBT, multifire (mf) makes RLM measurements with Discovery Rs (DRS) in a predictable DRS transmission window (DTxW). See MFA TS 36.133V1.0.0(2017-12), Release 1.0, especially section 7.6, "Radio Link Monitoring". Since the gNB (base station in NR) may attempt to periodically transmit DRSs in DTxW, the presence of DRSs may be expected. CRS, on the other hand, is used for RLM measurements outside of DTxW.

Additional details regarding RLM measurements in unlicensed spectrum are described below.

Disclosure of Invention

This section is intended to include examples, and not limitations.

An exemplary embodiment is a method comprising: determining, by the base station, whether a listen-before-talk procedure performed in a current cycle is successful for the unlicensed spectrum; and in response to the determination, performing, by the base station, one of: in response to the listen-before-talk procedure being successful, transmitting one or more first reference signals over the unlicensed spectrum at a predetermined location in a current cycle; or in response to the listen-before-talk procedure being unsuccessful, attempting to transmit one or more second reference signals over the unlicensed spectrum within a time window in the current cycle based on at least one other listen-before-talk procedure operating within the time window in the current cycle.

Another exemplary embodiment comprises a computer program comprising code for performing the method of the above paragraph when the computer program is run on a processor. A computer program according to this paragraph, wherein the computer program is a computer program product comprising a computer readable medium bearing computer program code embodied therein for use with a computer.

An exemplary apparatus includes one or more processors and one or more memories including computer program code. The one or more memories and the computer program code are configured to, with the one or more processors, cause the apparatus to perform at least the following: determining, by the base station, whether a listen-before-talk procedure performed in a current cycle is successful for the unlicensed spectrum; and responsive to the determination, performing, by the base station, one of: in response to the listen-before-talk procedure being successful, transmitting one or more first reference signals over the unlicensed spectrum at a predetermined location in a current cycle; or in response to the listen-before-talk procedure being unsuccessful, attempting to transmit one or more second reference signals over the unlicensed spectrum within a time window in the current cycle based on at least one other listen-before-talk procedure operating within the time window in the current cycle.

An exemplary computer program product comprises a computer-readable storage medium bearing computer program code embodied therein for use with a computer. The computer program code includes: code for determining, by the base station, whether a listen-before-talk procedure performed in a current cycle is successful for the unlicensed spectrum; and code for performing, by the base station in response to the determination, one of: in response to the listen-before-talk procedure being successful, transmitting one or more first reference signals over the unlicensed spectrum at a predetermined location in a current cycle; or in response to the listen-before-talk procedure being unsuccessful, attempting to transmit one or more second reference signals over the unlicensed spectrum within a time window in the current cycle based on at least one other listen-before-talk procedure operating within the time window in the current cycle.

In another exemplary embodiment, an apparatus comprises: means for determining, by the base station, whether a listen-before-talk procedure performed in a current cycle is successful for the unlicensed spectrum; and means for performing, by the base station in response to the determination, one of: in response to the listen-before-talk procedure being successful, transmitting one or more first reference signals over the unlicensed spectrum at a predetermined location in a current cycle; or in response to the listen-before-talk procedure being unsuccessful, attempting to transmit one or more second reference signals over the unlicensed spectrum within a time window in the current cycle based on at least one other listen-before-talk procedure operating within the time window in the current cycle.

In an exemplary embodiment, a method is disclosed, the method comprising: detecting, by a user equipment, one or more first reference signals in an unlicensed spectrum at a predetermined location in a current cycle; and in response to the detection, performing, by the user equipment, one of: in response to a detection success, performing processing using one or more first reference signals; or in response to the detection being unsuccessful, blind detecting one or more second reference signals over the unlicensed spectrum within a time window in the current cycle.

An exemplary apparatus includes one or more processors and one or more memories including computer program code. The one or more memories and the computer program code are configured to, with the one or more processors, cause the apparatus to perform at least the following: detecting, by a user equipment, one or more first reference signals in an unlicensed spectrum at a predetermined location in a current cycle; and in response to the detection, performing, by the user equipment, one of: in response to a detection success, performing processing using one or more first reference signals; or in response to the detection being unsuccessful, blind detecting one or more second reference signals over the unlicensed spectrum within a time window in the current cycle.

An exemplary computer program product comprises a computer-readable storage medium bearing computer program code embodied therein for use with a computer. The computer program code includes: code for detecting, by a user equipment, one or more first reference signals in an unlicensed spectrum at a predetermined location in a current cycle; and code for performing, by the user equipment in response to the detecting, one of: in response to a detection success, performing processing using one or more first reference signals; or in response to the detection being unsuccessful, blind detecting one or more second reference signals over the unlicensed spectrum within a time window in the current cycle.

In another exemplary embodiment, an apparatus comprises: means for detecting, by a user equipment, one or more first reference signals in an unlicensed spectrum at a predetermined location in a current cycle; and means for performing, by the user equipment in response to the detecting, one of: in response to a detection success, performing processing using one or more first reference signals; or in response to the detection being unsuccessful, blind detecting one or more second reference signals over the unlicensed spectrum within a time window in the current cycle.

Drawings

In the drawings:

FIG. 1 is a block diagram of one possible and non-limiting exemplary system in which exemplary embodiments may be practiced;

FIG. 2 shows an example of RLM-RS transmission in NR-U;

fig. 3 shows an example for the proposed RLM-RS transmission in the NR-U in an exemplary embodiment;

fig. 4 is a logic flow diagram performed by a gNB for enhanced RS transmission for RLM in NR unlicensed spectrum in accordance with an example embodiment;

FIG. 4A is a graphical illustration of sub-windows within a time window and possible parameters associated therewith; and

fig. 5 is a logic flow diagram executed by a user equipment for enhanced RS transmission for RLM in NR unlicensed spectrum in accordance with an example embodiment.

Detailed Description

The following abbreviations that may be found in the specification and/or the drawings are defined as follows:

3 GPP: third generation partnership project

5G: fifth generation

CRS: cell specific reference signal

CSI-RS: channel state information reference signal

DL: downlink (from base station to UE)

DMRS: demodulation reference signal

DRS: discovery reference signal

DTxW: DRS Transmission Window

eNB (or eNodeB): evolved node B (e.g., LTE base station)

gNB (or gnnodeb): base station for 5G/NR

I/F: interface

IS: synchronization

L1: physical layer

LBT: listen before talk

LTE: long term evolution

MF：MultiFire

MFA: multi fire alliance

MME: mobility management entity

NCE: network control element

NR: new radio

NR-U: NR unlicensed

N/W: network

OOS: out of synchronization

PDCCH: physical downlink control channel

PDSCH: physical downlink shared channel

RLF: radio link failure

RLM: radio link monitoring

RRC: radio resource control

RRH: remote radio head

And RS: reference signal

Rx: receiver with a plurality of receivers

SGW: service gateway

And (3) SSB: synchronous signal block

syn: synchronization

TS: specification of the technology

Tx: emitter

UE: user equipment (e.g., wireless devices, typically mobile devices)

WG: working group

The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described in the detailed description are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims.

Example embodiments herein describe techniques for enhanced RS transmission for RLM in NR unlicensed spectrum. Having described a system in which the illustrative embodiments may be used, additional description of these techniques is presented.

Turning to fig. 1, a block diagram of one possible and non-limiting exemplary system in which the exemplary embodiments may be practiced is shown. In fig. 1, a User Equipment (UE)110 is in wireless communication with a wireless network 100. The UE is wireless, typically a mobile device that can access a wireless network. UE 110 includes one or more processors 120, one or more memories 125, and one or more transceivers 130 interconnected by one or more buses 127. Each of the one or more transceivers 130 includes a receiver Rx 132 and a transmitter Tx 133. The one or more buses 127 may be address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, an optical fiber, or other optical communication device, and so forth. One or more transceivers 130 are connected to one or more antennas 128. The one or more memories 125 include computer program code 123. UE 110 includes RLM module 140, RLM module 140 including one or both of portions 140-1 and/or 140-2, RLM module 140 may be implemented in a variety of ways. The RLM module 140 may be implemented in hardware as RLM module 140-1, such as part of one or more processors 120. The RLM module 140-1 may also be implemented as an integrated circuit or by other hardware, such as a programmable gate array. In another example, the RLM module 140 may be implemented as RLM module 140-2, with the RLM module 140-2 being implemented as computer program code 123 and being executed by the one or more processors 120. For example, the one or more memories 125 and the computer program code 123 may be configured to, with the one or more processors 120, cause the user equipment 110 to perform one or more of the operations described herein. UE 110 communicates with gNB170 via radio link 111.

The gbb 170 is a base station that provides access to the wireless network 100 for wireless devices, such as UE 110. The gNB170 is a base station for 5G (also referred to as New Radio (NR)). The gNB170 may also be an eNB (evolved NodeB) base station for LTE (long term evolution), or any other suitable base station. The gNB170 includes one or more processors 152, one or more memories 155, one or more network interfaces (N/W I/F)161, and one or more transceivers 160 interconnected by one or more buses 157. Each of the one or more transceivers 160 includes a receiver Rx 162 and a transmitter Tx 163. One or more transceivers 160 are connected to one or more antennas 158. The one or more memories 155 include computer program code 153. The gNB170 includes an RLM module 150, the RLM module 150 including one or both of the portions 150-1 and/or 150-2, and the RLM module 150 may be implemented in a variety of ways. The RLM module 150 may be implemented in hardware as RLM module 150-1, such as part of one or more processors 152. The RLM module 150-1 may also be implemented as an integrated circuit or by other hardware, such as a programmable gate array. In another example, RLM module 150 may be implemented as RLM module 150-2, RLM module 150-2 being implemented as computer program code 153 and being executed by one or more processors 152. For example, the one or more memories 155 and the computer program code 153 are configured, with the one or more processors 152, to cause the gNB170 to perform one or more of the operations as described herein. One or more network interfaces 161 communicate over a network, such as via

links

176 and 131. Two or more gnbs 170 communicate using, for example, link 176. The link 176 may be wired or wireless or both and may implement, for example, an X2 interface.

The one or more buses 157 may be address, data, or control buses, and may include any interconnection mechanism, such as a series of wires on a motherboard or integrated circuit, an optical fiber or other optical communication device, a wireless channel, or the like. For example, one or more transceivers 160 may be implemented as Remote Radio Heads (RRHs) 195, while other elements of the gNB170 are physically located at a different location than the RRHs, and one or more buses 157 may be implemented in part as fiber optic cables to connect the other elements of the gNB170 to the RRHs 195.

The wireless network 100 may include a Network Control Element (NCE)190, and the NCE 190 may include MME (mobility management entity)/SGW (serving gateway) functionality and provide connectivity to other networks such as a telephone network and/or a data communication network (e.g., the internet). The gNB170 is coupled to the NCE 190 via link 131. Link 131 may be implemented as, for example, an S1 interface. NCE 190 includes one or more processors 175, one or more memories 171, and one or more network interfaces (N/W I/F)180 interconnected by one or more buses 185. The one or more memories 171 include computer program code 173. The one or more memories 171 and the computer program code 173 are configured to, with the one or more processors 175, cause the NCE 190 to perform one or more operations.

Wireless network 100 may implement network virtualization, which is the process of combining hardware and software network resources and network functions into a single software-based management entity (i.e., a virtual network). Network virtualization involves platform virtualization, which is often combined with resource virtualization. Network virtualization can be divided into external (combining many networks or parts of networks into virtual units) or internal (providing network-like functionality to software containers on a single system). Note that the virtualized entities resulting from network virtualization are still implemented to some extent using hardware such as the

processor

152 or 175 and the

memories

155 and 171, and such virtualized entities also produce technical effects.

The computer-

readable memories

125, 155, and 171 may be of any type suitable to the local technical environment, and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory, and removable memory. The computer

readable memories

125, 155 and 171 may be means for performing a storage function.

Processors

120, 152, and 175 may be of any type suitable to the local technical environment, and may include, by way of non-limiting example, one or more of the following: general purpose computers, special purpose computers, microprocessors, Digital Signal Processors (DSPs) and processors based on a multi-core processor architecture.

Processors

120, 152, and 175 may be means for performing functions such as controlling UE 110, gNB170, and other functions described herein.

In general, the various embodiments of the user device 110 can include, but are not limited to, cellular telephones (such as smart phones), tablet computers, Personal Digital Assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, image capture devices (such as digital cameras) having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback appliances having wireless communication capabilities, internet appliances permitting wireless internet access and browsing, tablet computers having wireless communication capabilities, and portable devices or terminals that incorporate combinations of such functions.

Having thus introduced a suitable but non-limiting technical context for practicing the exemplary embodiments of this invention, the exemplary embodiments will now be described in greater detail.

Exemplary embodiments relate to an NR-U system. For more details on the NR-U system and the frequency bands that may be involved, see for example Qualcomm Incorporated, "visited SID on NR-based Access to Unlicensed Spectrum", RP-172021,3GPP TSG RAN Meeting #77, Sapporo, Japan, 11 th-14 th 9 th 2017. This is a 3GPP work item description, also known as "studio on NR-based Access to Ullicensed Spectrum".

As described above, CRS is cell-specific and is transmitted at every DL subframe. Since there are multiple transmission samples in one radio frame, it can help to ensure that the UE can access the radio link quality at least once per radio frame. Therefore, RLM measurements in MF that rely on DRS and CRS are feasible.

However, in the NR-U system, RLM-RSs (SSB and CSI-RS) may be transmitted once per cycle at a fixed location. Thus, the potential measurement samples may be much fewer than in MF systems, especially for long period RSs (e.g., where a relatively long period of time elapses between RSs).

Furthermore, due to LBT failure in the unlicensed spectrum, the transmission of the RS may also be dropped, as shown in fig. 2, which means that the UE 100 cannot accurately and quickly track the radio link status. Fig. 2 shows attempted transmission of the RLM-RS over time with a period 240, and each cycle 210-1 through 210-5 has a period corresponding to the period 240. As shown in fig. 2, the gNB170 sends an RLM-RS transmission 220 in loop 210-1 (as well as loops 210-4 and 210-5), but once the gNB170 misses an RS transmission point due to the dropped RLM-RS transmission 230 in loops 210-2 and 210-3 (e.g., due to a corresponding LBT failure), the gNB170 must wait until the next loop (loop 210-4 in this example) has an opportunity to transmit. In case of a high LBT blocking rate, the UE 110 will not know the radio link status for one or several cycles (in this example several cycles 210-2 and 210-3). Of course, the UE is also unable to report the indication to higher layers, in which case a Radio Link Failure (RLF) statement may result.

It is beneficial to introduce enough instances of RS transmission to make RLM evaluations while attempting to reuse existing RSs in the NR. Example embodiments herein aim to provide options to provide a number of potential RS transmission opportunities for RLM measurements in NR unlicensed spectrum.

An overview of exemplary embodiments is now provided. An exemplary embodiment proposes a robust RLM-RS transmission scheme based on LBT results to facilitate RLM measurements to reliably monitor radio link quality. When a legacy periodic RLM-RS transmission 220 is blocked by a discarded RLM-RS transmission 230 (e.g., and corresponding LBT failure), the exemplary RS extended transmission scheme may be triggered to transmit opportunistic RLM-RS in a flexible time window. The detailed design of the proposed RS transmission mainly includes two aspects: (1) RS extension scheme, and (2) flexible time window. These will be briefly described below.

(1) RS extension scheme

Regarding the RS extension scheme, several RSs are introduced in the scheme for opportunistic transmission. The RS includes not only the conventional RLM-RS but also the temporary RLM-RS (or vice versa).

a) The legacy RLM-RS may be different from the original blocked periodic RS. For example, it may not involve retransmission of the original blocked RS. That is, it may be a retransmission of the original blocked RS or other periodic RS. In other words, it is not limited to the original blocked RS only. Instead, it may cover more RSs. For example, if the original, blocked RLM-RS is SSB1, the legacy RLM-RS may be SSB1 or SSB 2.

b) The temporary RLM-RS may be, for example, a group-common DMRS in the PDCCH or a UE-specific DMRS in the PDCCH or a DMRS in the PDSCH.

(2) Flexible time window

With regard to flexible time windows, a time window may be dynamically triggered when certain conditions are met. The time window allows the gNB170 (e.g., or eNB) to transmit opportunistic RSs in the time window after LBT blocks one or several consecutive periods of legacy RS transmission.

The time window may be flexible and may be configured as follows:

a) the time window may be a plurality of consecutive time slots or a plurality of non-consecutive sub-windows. Each sub-window may include several consecutive time slots.

b) The location of the time window (including the starting location and length) may be configured by RRC signaling. The starting position may be indicated by a relative offset within the subframe position of the conventional periodic RLM-RS. The offset is relative to a time position of the periodic RLM-RS.

Now, an overview has been provided and more details will be provided. In particular, exemplary proposals are set forth in the context of using multiple embodiments.

In unlicensed spectrum, RLM-RS transmissions will be blocked by LBT failures and corresponding dropped RLM-RS transmissions 230, which will affect the performance of RLM measurements. In the present disclosure, an enhanced RS transmission scheme is proposed to overcome the LBT problem in the NR unlicensed spectrum (NR-U) by artificially increasing a plurality of transmission points in addition to the normal periodic RS transmission.

In the present disclosure, an exemplary proposed RS transmission scheme will be explained in detail, specifically including: when and where the opportunistic RLM-RS is transmitted, which opportunistic RLM-RS is transmitted, and detailed operations at the gNB170 and the UE 110. To illustrate the exemplary proposal more clearly, fig. 3 shows an example of the proposed RLM-RS transmission in the NR-U.

FIG. 3 shows five cycles 210-n, 210-n +1, 210-n +2, 210-n +3, and 210-n +4, each cycle having the same period 240. The first cycle 210-n has normal RLM-RS transmissions 220. The second loop 210-n +1 and the third loop 210-n +2 have an LBT failure and a corresponding dropped RLM-RS transmission 230. The fourth cycle 210-n +3 and 210-n +4 has normal RLM-RS transmissions 220. Due to the LBT failure in the second and third cycles 210-n +1 and 210-n +2 and the corresponding dropped RLM-RS transmission 230, an offset 310 is used between the time position of the dropped RLM-RS transmission 230 and the time position of the activated time window 330 (e.g., the beginning thereof), and there is an opportunistic RLM-RS transmission 320-1, 320-2 in each time window 330-1, 330-2, respectively.

(1) Time-to-place transmission of opportunistic RLM-RS 320

The position of the time window 330 may be indicated by a relative frame number that is related to the position of the normal periodic RLM-RS signal. The relative frame number may be indicated by an offset 310 from the location of the periodic RLM-RS signal (e.g., the dropped RLM-RS transmission 230). In some embodiments, the time window 330 may be represented by an offset 310 and a length of time 380 (also referred to as length 380) of the RRC signaling. In FIG. 3, the start of the time window 330-1 between cycle # n +1(210-n +1) and cycle # n +2(210-n +2) may be indicated by an offset 310 relative to the location of the periodic RLM-RS signal at cycle # n +1(210-n +1) (i.e., the discarded RLM-RS transmission 230).

The activated time window 330 is implicitly and dynamically triggered only when one or several consecutive normal periodic RLM-RS transmissions 220 fail. For simplicity of illustration, it is assumed that the time window 330 is triggered after one periodic RLM-RS is lost in a transmission opportunity, as shown in FIG. 3. In FIG. 3, in response to a normal periodic RLM-RS transmission 220 failing in cycle # n +1(210-n +1), a time window 330-1 between cycle # n +1(210-n +1) and cycle # n +2(210-n +2) has been activated. The gNB170 will attempt to transmit an opportunistic RLM-RS transmission 320-1 (and corresponding signal) within the active time window 330-1. Similarly, in response to a normal periodic RLM-RS transmission 220 failing at cycle # n +2(210-n +2), a time window 330-2 between cycle # n +2(210-n +2) and cycle # n +3(210-n +3) has been activated. The gNB170 will attempt to transmit an opportunistic RLM-RS transmission 320-2 (and corresponding signal) within the active time window 330-2. Note that in this example, the opportunistic RLM-RS transmissions 320-1, 320-2 are at different (temporal) locations within their respective time windows 330-1, 330-2.

(2) What kind of opportunistic RLM-RS is to be transmitted

In the present disclosure, in exemplary embodiments, it is proposed to reuse existing DMRS signals as opportunistic RLM-RS signals in addition to configured RLM-RS signals (in some embodiments). Thus, the opportunistic RLM-RS signal may comprise two parts: DMRS signals 360 and configured RLM-RS signals 350. The configured signal 350 may be SSB 350-1 or CSI-RS 350-2 in an NR system. The DMRS signal 360 may be a common group DMRS in PDCCH360-1, or a UE specific DMRS in PDCCH 360-2, or a DMRS in PDSCH 360-3.

In the activated time window 330, if the DMRS signal 360 is transmitted at the PDCCH or PDSCH, there is no need to transmit the configured RLM-RS signal 350. Transmitting only the DMRS signals 360 reduces resource overhead to avoid additional configured RLM-RS signal 350 transmissions, as the gNB170 only needs to transmit the DMRS signals 360. Of course, if DMRS signals 360 are not transmitted within the active time window 330, the gNB170 needs to transmit the configured RLM-RS signals 350.

It should be noted that the normal RLM-RS transmission 220 will also be referred to as a normal RLM-RS signal 220. Similarly, opportunistic RLM-RS transmissions 320 will be referred to as opportunistic RLM-RS signals 320.

(3) Exemplary detailed operations at gNB170 and UE 110

At the gNB transmitter, either normal RLM-RS or opportunistic RLM-RS transmission will be performed based on the LBT results. When LBT is successful, the gNB170 will periodically transmit normal RLM-RS at predefined locations. Time window 330 will be triggered (e.g., instantaneously) when normal periodic RLM-RS transmissions are blocked by LBT failures and corresponding dropped RLM-RS transmissions 230, and when gNB170 acquires a channel in time window 330, gNB170 will send opportunistic RLM-RS.

At the UE receiver, two layers of detection are used. First, the UE 110 will first detect whether the normal periodic RLM-RS220 is at a predefined location. Then, if no normal RLM-RS22 is detected, the UE 110 starts to blindly detect opportunistic RLM-RS within the time window. Take fig. 3 as an example. The normal periodic RLM-RS signal at cycle # n (210-n) has been successfully transmitted and the time window 330 is not triggered. However, normal periodic RLM-RS signaling at cycle # n +1(210-n +1) has been blocked by LBT. Thus, the time window 330-1 between cycle # n +1(210-n +1) and cycle # n +2(210-n +2) is triggered to begin after one offset 310 from the location of the dropped RLM-RS transmission 230 at cycle # n +1(210-n + 1). The gNB170 will then attempt to transmit an opportunistic RLM-RS signal 320-1 within the time window 330-1. If the LBT succeeds in one of the transmission slots within window 330-1, then the gmb 170 transmits an opportunistic RS signal 320. Similarly, the time window 330-2 between cycle # n +2(210-n +2) and cycle # n +3(210-n +3) is triggered to begin after one offset 310 from the location of the dropped RLM-RS transmission 230 at cycle # n +2(210-n + 2). The gNB170 will then attempt to transmit an opportunistic RLM-RS signal 320-2 within the time window 330-2. If the LBT succeeds in one of the transmission slots within window 330-2, then the gmb 170 transmits an opportunistic RS signal 320.

Accordingly, on the UE side, the UE 110 first detects a normal periodic RLM-RS at cycle # n (210-n), cycle # n +1(210-n +1), and so on. When UE 110 does not detect a normal periodic RLM-RS220 at cycle # n +1(210-n +1) (e.g., detection fails), UE 110 will attempt to blindly detect opportunistic RLM-RS 320 within time window 330-1 between cycle # n +1 and cycle # n + 2. Similarly, when the UE 110 does not detect the normal periodic RLM-RS220 at cycle # n +2(210-n +2) (e.g., detection fails), the UE 110 will attempt to blindly detect the opportunistic RLM-RS 320 within the time window 330-2 between cycle # n +2 and cycle # n + 3.

Fig. 4 and 5 describe these exemplary operations in more detail.

Turning to fig. 4, this figure is a logic flow diagram of enhanced RS transmission for RLM in NR unlicensed spectrum performed by a gNB in accordance with an exemplary embodiment. The figure illustrates the operation of one or more exemplary methods, the results of execution of computer program instructions embodied on a computer-readable memory, functions performed by logic implemented in hardware, and/or interconnected components for performing the functions in accordance with the exemplary embodiments. The blocks in fig. 4 are assumed to be performed by the gNB (or eNB or other network node), e.g., at least partially under control of the RLM module 150.

In block 410, the gNB170 determines one or more of the following: offset 310, length of time 380 of time window 330, N, and window parameter(s). The parameter N is described below, and the window parameter(s) are described with reference to fig. 4A. In block 420, the gNB170 sends an indication of these determined parameters to the UE 110, indicating one or more of: offset 310, length of time 380, N, and window parameter(s). The transmission may be, for example, via RRC signaling, although other signaling is also possible. It should also be noted that offset 310 and time length 380 may be configured via other means such as those described in the technical specification. For example, for the case where the time window 330 occupies "all" of the time period between the end of the LBT process and the beginning of the next cycle 210, one or both of the offset 310 and the length of time 380 may also not be necessary. The parameter N and the window parameter(s) may also be communicated or defined by other techniques, such as via a technical specification.

Additionally, with respect to N, while the example of fig. 3 shows that the time window 330 is triggered after a single LBT failure and corresponding dropped RLM-RS transmission 230, the time window 330 may be triggered after one or several LBT failures and corresponding dropped RLM-RS transmissions 230. In some embodiments, the detailed number N of failed LBTs and corresponding dropped RLM-RS transmissions 230 may be configured by the network. Thus, the parameter N is used in these embodiments to determine whether transmission (fig. 4) or detection (fig. 5) of the opportunistic RLM-RS should be performed. That is, if the number of discarded RLM-RS transmissions 230 is less than N, the time window will not be triggered. Note that this is a comparison of the number of discarded RLM-RS transmissions 230 to the threshold N, and there are many different ways to perform this comparison. In the examples of fig. 4 and 5, the number of dropped RLM-RS transmissions 230 is compared to N, and the time window is triggered in response to the number of dropped RLM-RS transmissions 230 being equal to or greater than N. However, the time window may alternatively be triggered in response to the number of dropped RLM-RS transmissions 230 being greater than (but not equal to) N. In the examples of fig. 4 and 5, the number of RLM-RS transmissions 230 dropped is indicated by a counter shown as "n". In fig. 4, the counter n is set to 0 (zero) in block 423.

The next block in fig. 4 occurs over one or more cycles 210. In block 425, gNB170 performs the LBT procedure, and in block 430, gNB170 determines whether the LBT procedure was successful. If so (yes (success), at block 440), the gNB170 performs normal RLM-RS transmission 220 (e.g., periodic transmission at a predefined location) over the unlicensed spectrum for the current cycle 210 in block 450. As described above, the RLM-RS may be one or both of a Synchronization Signal Block (SSB) and a channel state information reference signal (CSI-RS). Note that the predefined location is shown in fig. 3 at the beginning of loop 210, which has a period 240. In response to performing the normal RLM-RS transmission 220, the counter n is set (reset) to zero in block 452. As long as the LBT procedure succeeds within successive cycles 210 (i.e., cycles 210 that are adjacent to each other and successive in time), the normal RLM-RS transmission 220 may continue for multiple cycles 210.

In contrast, if the LBT procedure is unsuccessful (no (failure) at block 440), flow proceeds to

blocks

445 and 455, with parameter N being used, such as received (or otherwise configured, such as via a technical specification). Note that if parameter N is not used, flow may proceed from block 440 to block 460 (and tracking of counter N will not be performed in

blocks

423, 445, 452, and 485 as well). For the example of block 445, the gNB170 increments a counter n (n ═ n +1), and in block 455, the gNB170 compares the number of (e.g., consecutive) dropped RLM-RS transmissions 230 to a threshold. The term "contiguous" refers to "in a row," such that a plurality of discarded RLM-RS transmissions 230 will be discarded in a plurality of consecutive cycles 210 (i.e., a plurality of cycles 210 in a row in time). In this case, the comparison is between the number of consecutive discarded RLM-RS transmissions 230 (e.g., N) and N, and the timing window 330 is triggered in response to the number of discarded RLM-RS transmissions 230 (e.g., N) being equal to or greater than N. If the number of dropped RLM-RS transmissions 230 (e.g., N) is less than N (block 455 — yes), flow proceeds to block 425 where another LBT procedure is performed in a new subsequent loop 210.

If the number of dropped RLM-RS transmissions 230 (e.g., N) is equal to or greater than N (no at block 455), flow proceeds to block 460. In block 460, the gNB170 triggers (e.g., activates) the time window 330 for a length of time 380 after the offset 310. For length of time 380 of time window 330, gNB170 attempts to transmit (block 470) opportunistic RLM-RS 320 in time window 330 and, if the LBT procedure is successful, will transmit opportunistic RLM-RS 320 on the unlicensed spectrum. The transmission of RLM-RS 320 may include one or both of the configured RLM-RS signal 350 and DMRS signal 360. If there is a transmission of an opportunistic RLM-RS (yes in block 480), the counter n is set (reset) to zero in block 485 and flow proceeds to block 425 where another LBT procedure is performed for the new subsequent loop 210. If there is no transmission of opportunistic RLM-RS 320 (no at block 480), then gNB170 determines whether time length 380 has expired. If time length 380 has expired (block 490 — yes), flow proceeds to block 495 where transmission of the opportunistic RLM-RS is not performed in the time window because all LBTs were unsuccessful (i.e., none of the LBTs were successful). Flow then proceeds to block 425 where another LBT procedure is performed for the new subsequent loop 210 in block 425. If time length 380 has not expired (no at block 490), then flow returns to block 470 where at block 470 gNB170 attempts to transmit opportunistic RLM-RS 320 in time window 330.

The above description with respect to fig. 4 assumes a single time window 330. However, the time window 330 may be divided into a plurality of sub-windows. This is illustrated by fig. 4A, which is a diagram of a sub-window 415 within the time window 330, and also shows possible parameters associated therewith. The larger time window 330 may include a number of discontinuous sub-windows 415 (where a discontinuity indicates a time gap between sub-windows). In this example, there are three sub-windows 415-1, 415-2, and 415-3. The number of sub-windows 415 is shown by the number 417 of sub-windows 417. It should be noted that three are merely exemplary, and that more or fewer sub-windows may be used.

With respect to a simple way to indicate the location of the sub-windows 415, the distance between the sub-windows 415 (shown as spacing SP) may be equally spaced, and the same length of the sub-windows (shown as length L of the sub-windows) may be designed_SW). Thus, only parameters including the interval between two sub-windows (SP), the number of sub-windows in a large time window (417), or the length 380 of the time window 330 need to be configured by the network. Many other options are possible. For example, the window parameters may include the length 380 of the large time window 330, the number 417 of sub-windows 415, and the length L of the sub-windows_SW. As another example, the window parameters may include the length 380 of the large time window 330, the length L of each sub-window_SWAnd a space 418Length (e.g., SP). The number of sub-windows may be calculated based on this information. Other examples are possible.

gNB170 will perform LBT sequentially in time in sub-window 415, and if LBT succeeds, gNB170 will transmit opportunistic RLM-RS 320 in sub-window 415. For example, for each iteration through block 470, gNB170 attempts to sequentially transmit opportunistic RLM-RS 320 in time in one of sub-windows 415. For UE 110, UE 110 will detect opportunistic RLM-RSs 320 sequentially in time in sub-window 415.

Reference is made to fig. 5, which illustrates operations of one or more exemplary methods, results of execution of computer program instructions embodied on a computer-readable memory, functions performed by logic implemented in hardware, and/or interconnected components for performing the functions in accordance with the exemplary embodiments. The blocks in fig. 5 are assumed to be performed by the user equipment 110, e.g., at least partially under control of the RLM module 140.

In block 520, UE 110 receives an indication of parameters set by the network. These parameters may include one or more of the following: offset 310, length of time 380, N, and window parameter(s). As also previously mentioned, some or all of these may not be used or may be otherwise defined, such as via a technical specification. If N is used, UE 110 sets a counter N to 0 (zero) (N-0) in block 522.

In block 530, the UE 110 detects the normal periodic RLM-RS220 at the predefined location. If RLM-RS220 is detected (block 540-yes), UE 110 performs normal RLM-RS processing in block 550 and also sets (resets) counter n to zero (n-0) in block 555. If no RLM-RS220 is detected (block 540 ═ N), and if N is used, UE 110 increments a counter N (N ═ N +1) in block 542, and compares the number of consecutive dropped RLM-RS transmissions 230 (e.g., N) to the parameter N in block 545. In this example, if the number of dropped RLM-RS transmissions 230 (e.g., N) is less than N (block 545 — yes), flow proceeds to block 530 where another detection of normal periodic RLM-RS is performed in a new subsequent loop 210 in block 530. Note that if N is not used, flow may proceed from block 540 to block 560 and blocks 522, 542, 555, and 592 of manipulating the counter will not be used.

If the number of dropped RLM-RS transmissions 230 (e.g., N) is equal to or greater than N (no at block 545), flow proceeds to block 456. In block 560, the UE 110 blindly detects the opportunistic RLM-RS 320 after the offset 310 within the time window 330 (having a time length 380). If opportunistic RLM-RS 320 is found (block 570 — yes), UE 110 performs opportunistic RLM-RS processing in block 590 and sets (resets) counter n to zero (n-0) in block 592. If no opportunistic RLM-RS 320 is found (no at block 570), UE 110 determines whether time length 380 ends. If time length 380 has not ended (block 580 — no), UE 110 returns to blind detection of opportunistic RLM-RS 320 within time window 330. As described with reference to fig. 4A, if time window 330 is divided into sub-windows 415, for each iteration through block 560, UE 110 will sequentially detect opportunistic RLM-RSs 320 in time in one of the sub-windows 415. If the length of time 380 ends (block 580-yes), then the blind detection of opportunistic RLM-RSs within the time window fails in block 595. The UE 110 returns to block 530 and detects the normal periodic RLM-RS220, e.g., in the next cycle 210.

Note that in

blocks

550 and 590 of fig. 5, UE 110 performs processing on the reference signals. This process can be described as follows. In RLM, after the UE has measured the RS, the UE 110 compares the measured value with the thresholds Qout and Qin. When the estimated downlink radio link quality becomes worse than the threshold Qout, the physical layer in the UE will send an out-of-sync (OOS) indication to higher layers. When the estimated downlink radio link quality becomes better than the threshold Qin, the physical layer in the UE will send a synchronization (IS) indication to the higher layers. For higher layers, a timer is started after receiving enough consecutive OOS indications from L1. A Radio Link Failure (RLF) IS declared if not enough consecutive IS indications are received before the timer expires. The declaration of RLF results in other actions being considered or taken, such as handover or other actions.

Without in any way limiting the scope, interpretation, or application of the claims appearing below, a technical effect and advantage of one or more of the example embodiments disclosed herein is that the proposed mechanism increases RS measurement samples by transmitting opportunistic RLM-RS in configured time windows when normal RLM-RS is blocked by failed LBT. Another technical effect and advantage of one or more of the example embodiments disclosed herein is the introduction of one time window for opportunistic RLM-RS transmissions to reduce the complexity of UE detection by avoiding blind detection in all subframes between two normal RLM-RS transmission positions. Another technical effect and advantage of one or more example embodiments disclosed herein is that the proposed RS transmission scheme reuses existing DMRSs within a time window in which DMRSs are present in PDCCH or PDSCH. Thus, by avoiding additional RLM-RS transmissions in the time window, resource overhead may be reduced.

Additional examples follow.

Example 1. a method, comprising:

determining, by the base station, whether a listen-before-talk procedure performed in a current cycle is successful for the unlicensed spectrum; and

in response to the determination, performing, by the base station, one of:

transmitting one or more first reference signals over the unlicensed spectrum at a predetermined location in the current cycle in response to the listen-before-talk procedure being successful; or

In response to the listen before talk process being unsuccessful, attempting to transmit one or more second reference signals on the unlicensed spectrum within a time window of the current cycle based on at least one other listen before talk process operating within the time window of the current cycle.

Example 2. the method of example 1, further comprising:

transmitting the one or more second reference signals over the unlicensed spectrum within the time window in response to success of one of the at least one other listen-before-talk process operating within the time window of the current cycle.

Example 3. the method of example 1, further comprising

Transmitting the one or more second reference signals over the unlicensed spectrum in response to all other listen-before-talk processes running within the time window in the current cycle being unsuccessful.

Example 4. the method of any of examples 1-3, wherein attempting to transmit the one or more second reference signals over the unlicensed spectrum within the time window in the current cycle is performed only in response to a number of dropped first reference signals in a plurality of (e.g., previous) cycles, the dropped first reference signals caused by the listen-before-talk process being unsuccessful in the plurality of (e.g., previous) cycles, satisfying a threshold. In this case, the previous cycle is a (e.g., consecutive) cycle prior to the current cycle.

Example 5. a method, comprising:

detecting, by a user equipment, one or more first reference signals in an unlicensed spectrum at a predetermined location in a current cycle; and

in response to the detection, performing, by the user equipment, one of:

in response to the detection being successful, performing processing using the one or more first reference signals; or

In response to the detecting being unsuccessful, blindly detecting one or more second reference signals over the unlicensed spectrum within a time window in the current cycle.

Example 6. the method of example 5, further comprising:

in response to the blind detection being successful, processing the one or more second reference signals.

Example 7. the method of example 5, further comprising

In response to the blind detection being unsuccessful within the time window in the current cycle, performing the detection of the one or more first reference signals in the unlicensed spectrum at the predetermined location in a subsequent cycle.

Example 8 the method of any of examples 5 to 7, wherein blindly detecting the one or more second reference signals over the unlicensed spectrum within the time window in the current cycle is performed only in response to a number of dropped first reference signals of a plurality of cycles for which the dropped first reference signals determined by the first reference signals were not detected satisfying a threshold.

Example 9. the method of any of examples 1 to 8, wherein the time window is offset from a time location at which a first reference signal in the current cycle would have been transmitted if the listen-before-talk procedure succeeded but was discarded due to the listen-before-talk procedure failing.

Example 10. the method of example 9, wherein the time window has a length of time, and wherein the method further comprises: transmitting an indication of the length of time and the offset between the base station and the user equipment.

Example 11 the method of example 10, wherein the transmitting is performed using radio resource control signaling.

Example 12. the method of any of examples 1 to 11, wherein the one or more first reference signals include one or both of: at least one synchronization signal block and at least one channel state information reference signal.

Example 13. the method of any of examples 1 to 12, wherein the one or more second reference signals include one or both of: the configured radio link monitors reference signals and demodulates reference signals.

Example 14. the method of example 13, wherein the demodulation reference signal comprises one or more of: a common set of demodulation reference signals in a physical downlink control channel; a user equipment-specific demodulation reference signal in the physical downlink control channel; and demodulation reference signals in a physical downlink shared channel.

Example 15 the method of example 14, wherein the one or more first reference signals are only the demodulation reference signals and not the configured radio link monitoring reference signals.

Example 16 the method of any of examples 13 or 14, wherein the configured radio link monitoring reference signal comprises one or both of: at least one synchronization signal block and at least one channel state information reference signal.

Example 17. the method of any of examples 1 to 16, wherein the time window comprises a plurality of non-contiguous sub-windows.

Example 18 a computer program comprising program code for performing the method according to any one of examples 1 to 17.

Example 19 the computer program of example 18, wherein the computer program is a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer.

Example 20. an apparatus, comprising:

means for determining, by the base station, whether a listen-before-talk procedure performed in a current cycle is successful for the unlicensed spectrum; and

means for performing, by the base station in response to the determination, one of:

Example 21. the apparatus of example 20, further comprising:

means for transmitting the one or more second reference signals over the unlicensed spectrum within the time window in response to success of one of the at least one other listen-before-talk process operating within the time window of the current cycle.

Example 22. the apparatus of example 20, further comprising

Means for transmitting the one or more second reference signals over the unlicensed spectrum in response to all other listen-before-talk processes running within the time window in the current cycle being unsuccessful.

Example 23 the apparatus of any of examples 20 to 22, wherein attempting to transmit the one or more second reference signals over the unlicensed spectrum within the time window in the current cycle is performed only in response to a number of dropped first reference signals in a plurality of cycles, the dropped first reference signals caused by the listen-before-talk process being unsuccessful within the plurality of cycles, satisfying a threshold.

An apparatus of example 24, comprising:

means for detecting, by a user equipment, one or more first reference signals in an unlicensed spectrum at a predetermined location in a current cycle; and

means for performing, by the user equipment in response to the detecting, one of:

Example 25. the apparatus of example 24, further comprising:

means for processing the one or more second reference signals in response to the blind detection being successful.

Example 26. the apparatus of example 24, further comprising

Means for performing the detection of the one or more first reference signals in the unlicensed spectrum at the predetermined location in a subsequent cycle in response to the blind detection being unsuccessful within the time window in the current cycle.

The apparatus of any of examples 24-25, wherein blind detection of the one or more second reference signals over the unlicensed spectrum within the time window in the current cycle is performed only in response to a number of dropped first reference signals of a plurality of cycles for which the dropped first reference signals determined by the first reference signals were not detected satisfying a threshold.

Example 28 the apparatus of any of examples 20 to 27, wherein the time window is offset from a time at which the first reference signal in the current cycle would have been transmitted if the listen-before-talk procedure succeeded but was discarded due to the listen-before-talk procedure failing.

Example 29 the apparatus of example 28, wherein the time window has a length of time, and wherein the apparatus further comprises means for transmitting an indication of the length of time and the offset between the base station and the user equipment.

Example 30 the apparatus of example 29, wherein the transmitting is performed using radio resource control signaling.

Example 31 the apparatus of any of examples 20 to 30, wherein the one or more first reference signals comprise one or both of: at least one synchronization signal block and at least one channel state information reference signal.

The apparatus of any of examples 20 to 31, wherein the one or more second reference signals comprise one or both of: the configured radio link monitors reference signals and demodulates reference signals.

Example 33 the apparatus of example 32, wherein the demodulation reference signal comprises one or more of: a common set of demodulation reference signals in a physical downlink control channel; a user equipment-specific demodulation reference signal in the physical downlink control channel; and demodulation reference signals in a physical downlink shared channel.

Example 34 the apparatus of example 33, wherein the one or more first reference signals are only the demodulation reference signals and not the configured radio link monitoring reference signals.

The apparatus of any of examples 32 or 34, wherein the configured radio link monitoring reference signal comprises one or both of: at least one synchronization signal block and at least one channel state information reference signal.

Example 36. the apparatus of any of examples 20 to 35, wherein the time window comprises a plurality of non-contiguous sub-windows.

Example 37 a base station comprising any of examples 20 to 23 and examples dependent thereon.

Example 38. a user equipment comprising any one of examples 24 to 27 and examples dependent on these examples.

Example 39. an apparatus, comprising:

one or more processors; and

one or more memories including computer program code,

the one or more memories and the computer program code configured to, with the one or more processors, cause the apparatus to perform the method according to any of examples 21-17.

Example 40. an apparatus, comprising:

one or more processors; and

one or more memories including computer program code,

the one or more memories and the computer program code configured to, with the one or more processors, cause the apparatus to implement an apparatus according to any of examples 20-36.

Embodiments herein may be implemented in software (executed by one or more processors), hardware (e.g., application specific integrated circuits), or a combination of software and hardware. In an example embodiment, the software (e.g., application logic, an instruction set) is stored on any of a variety of conventional computer-readable media. In the context of this document, a "computer-readable medium" can be any medium or means that can contain, store, communicate, propagate, or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer, with one example of a computer described and depicted, for example, in FIG. 1. A computer-readable medium may include a computer-readable storage medium (e.g.,

memory

125, 155, 171 or other device) that may be any medium or means that can contain, store, and/or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer. Computer-readable storage media do not include propagated signals.

If desired, the different functions discussed herein may be performed in a different order and/or concurrently with each other. Further, if desired, one or more of the above-described functions may be optional or may be combined.

Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claims.

It is also noted herein that while the above describes example embodiments of the invention, these descriptions should not be viewed in a limiting sense. Rather, various modifications and changes may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A method, comprising:

in response to the determination, performing, by the base station, one of:

2. The method of claim 1, further comprising:

3. The method of claim 1, further comprising

4. The method of any of claims 1-3, wherein attempting to transmit the one or more second reference signals over the unlicensed spectrum within the time window in the current cycle is performed only in response to a number of dropped first reference signals in a plurality of cycles, the dropped first reference signals caused by the listen-before-talk process being unsuccessful within the plurality of cycles, satisfying a threshold.

5. A method, comprising:

in response to the detection, performing, by the user equipment, one of:

6. The method of claim 5, further comprising:

7. The method of claim 5, further comprising

8. The method according to any one of claims 5-7, wherein blindly detecting the one or more second reference signals over the unlicensed spectrum within the time window in the current cycle is performed only in response to a number of dropped first reference signals of a plurality of cycles, over which the dropped first reference signals determined by the first reference signals were not detected, satisfying a threshold.

9. The method according to any one of claims 1 to 8, wherein the time window is offset from a time position at which a first reference signal in the current cycle would have been transmitted if the listen-before-talk procedure succeeded but was discarded due to the failure of the listen-before-talk procedure.

10. The method of claim 9, wherein the time window has a length of time, and wherein the method further comprises: transmitting an indication of the length of time and the offset between the base station and the user equipment.

11. The method of claim 10, wherein the transmitting is performed using radio resource control signaling.

12. The method of any one of claims 1-11, wherein the one or more first reference signals comprise one or both of: at least one synchronization signal block and at least one channel state information reference signal.

13. The method of any of claims 1-12, wherein the one or more second reference signals comprise one or both of: the configured radio link monitors reference signals and demodulates reference signals.

14. The method of claim 13, wherein demodulating the reference signal comprises one or more of: a common set of demodulation reference signals in a physical downlink control channel; a user equipment-specific demodulation reference signal in the physical downlink control channel; and demodulation reference signals in a physical downlink shared channel.

15. The method of claim 14, wherein the one or more first reference signals are only the demodulation reference signals and not the configured radio link monitoring reference signals.

16. The method of any of claims 13 or 14, wherein configured radio link monitoring reference signals comprise one or both of: at least one synchronization signal block and at least one channel state information reference signal.

17. The method of any of claims 1-16, wherein the time window comprises a plurality of non-contiguous sub-windows.

18. A computer program comprising program code for performing the method according to any one of claims 1 to 17.

19. The computer program according to claim 18, wherein the computer program is a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer.

20. An apparatus, comprising:

21. The apparatus of claim 20, further comprising:

22. The apparatus of claim 20, further comprising

23. The apparatus of any of claims 20-22, wherein attempting to transmit the one or more second reference signals over the unlicensed spectrum within the time window in the current cycle is performed only in response to a number of dropped first reference signals in a plurality of cycles, the dropped first reference signals caused by the listen-before-talk process being unsuccessful within the plurality of cycles, satisfying a threshold.

24. An apparatus, comprising:

25. The apparatus of claim 24, further comprising:

26. The apparatus of claim 24, further comprising

27. The apparatus according to any one of claims 24-25, wherein blindly detecting the one or more second reference signals over the unlicensed spectrum within the time window in the current cycle is performed only in response to a number of dropped first reference signals of a plurality of cycles, over which the dropped first reference signals determined by the first reference signals were not detected, satisfying a threshold.

28. An apparatus according to any one of claims 20 to 27, wherein the time window is offset from a time at which a first reference signal in the current cycle would have been transmitted if the listen-before-talk procedure succeeded but was discarded due to the listen-before-talk procedure failing.

29. The apparatus of claim 28, wherein the time window has a length of time, and wherein the apparatus further comprises means for transmitting an indication of the length of time and the offset between the base station and the user equipment.

30. The apparatus of claim 29, wherein the transmitting is performed using radio resource control signaling.

31. The apparatus of any one of claims 20-30, wherein the one or more first reference signals comprise one or both of: at least one synchronization signal block and at least one channel state information reference signal.

32. The apparatus of any of claims 20-31, wherein the one or more second reference signals comprise one or both of: the configured radio link monitors reference signals and demodulates reference signals.

33. The apparatus of claim 32, wherein demodulation reference signals comprise one or more of: a common set of demodulation reference signals in a physical downlink control channel; a user equipment-specific demodulation reference signal in the physical downlink control channel; and demodulation reference signals in a physical downlink shared channel.

34. The device of claim 33, wherein the one or more first reference signals are only the demodulation reference signals and not the configured radio link monitoring reference signals.

35. The device of any of claims 32 or 34, wherein configured radio link monitoring reference signals comprise one or both of: at least one synchronization signal block and at least one channel state information reference signal.

36. An apparatus according to any one of claims 20 to 35, wherein the time window comprises a plurality of non-contiguous sub-windows.

37. A base station comprising any one of claims 20 to 23 and claims dependent thereon.

38. A user equipment comprising any one of claims 24 to 27 and claims dependent thereon.