WO2019191902A1

WO2019191902A1 - Systems and methods for radio link monitoring

Info

Publication number: WO2019191902A1
Application number: PCT/CN2018/081754
Authority: WO
Inventors: Dan Yang; Li NIU; Kaiying Lv; Yajun Zhao; Li Zhang
Original assignee: Zte Corporation
Priority date: 2018-04-03
Filing date: 2018-04-03
Publication date: 2019-10-10

Abstract

A system and method for radio link monitoring are disclosed herein. In one embodiment, a method performed by a communication device includes: producing a monitoring result based on monitoring for a reference signal, wherein the monitoring comprises one of: monitoring for the reference signal at one or more predetermined reference signal sending times in a first period, and monitoring for the reference signal in a monitoring duration of the first period; and determining whether the monitoring result is used for radio link quality evaluation.

Description

SYSTEMS AND METHODS FOR RADIO LINK MONITORING

TECHNICAL FIELD

This disclosure relates generally to wireless communications and, more particularly, to systems and methods for radio link monitoring.

BACKGROUND

As the number of applications and services for digital data continues to explode, the demands and challenges placed on network resources and operators will continue to increase. Being able to deliver a wide variety of network performance characteristics that future services will demand is one of the primary technical challenges faced by service providers today. The performance requirements placed on the network will demand connectivity in terms of data rate, latency, availability, and many other parameters, all of which will vary from one service to the next. Thus, enabling a network to effectively monitor radio link quality will greatly enhance the network’s ability to meet future demands.

A user equipment (UE) may perform radio link monitoring (RLM) to monitor downlink radio link quality of a serving cell (e.g., a serving base station (BS) within a particular geographic area) in a connected state (e.g., RRC_CONNECTED) . RLM is performed by monitoring for a reference signal (RS) , sent by a BS or cell, that includes a channel state information reference signal (CSI-RS ) or synchronization signal block (SSB) . By performing RLM, a UE in a connected state with a serving cell or BS may determine whether it is in-sync or out-of-sync with respect to its serving cell.

Figure 1 illustrates how a UE may evaluate downlink radio link quality over an evaluation period 102. This evaluation, or estimation, of received RSs 104 may be compared with out-of-sync and in-sync thresholds, Qout and Qin respectively, for the purposes of RLM. These thresholds are expressed in terms of the Block Error Rate (BLER) of a hypothetical physical downlink control channel (PDCCH) transmission from the serving cell. A designation of being out-of-sync may occur when the downlink radio link quality estimated over the last (e.g., current or most recent) evaluation period becomes worse than the threshold Qout. A designation of being in-sync may occur when the downlink radio link quality evaluated over a particular period of time (e.g., the last 100 milliseconds) becomes better than the threshold Qin.

Figure 2 illustrates how out-of-sync indications 152 or in-sync indications 154 may be sent within indication intervals 156. A UE may start a network-configured radio link failure timer (referred to also as “T310” ) after a certain number of consecutive out-of-sync indications (referred to as “N310” ) . The timer is stopped if a number of consecutive in-sync indications (referred to as “N311” ) are reported by the UE (e.g., by the UE’s physical layer) . Both the out-of-sync and in-sync counters (N310 and N311) are configurable by the network. Upon expiry of the timer T310, Radio Link Failure (RLF) occurs. As a consequence, the UE turns off its transmitter to avoid interference and is required to re-establish the RRC connection within a specific time period (e.g, T _{UE-re-establish_delay}) .

SUMMARY OF THE INVENTION

The exemplary embodiments disclosed herein are directed to solving the issues relating to one or more of the problems presented in the prior art, as well as providing additional features that will become readily apparent by reference to the following detailed description when taken in conjunction with the accompany drawings. In accordance with various embodiments, exemplary systems, methods, devices and computer program products are disclosed herein. It is understood, however, that these embodiments are presented by way of example and not limitation, and it will be apparent to those of ordinary skill in the art who read the present disclosure that various modifications to the disclosed embodiments can be made while remaining within the scope of the invention.

In one embodiment, a method performed by a communication device includes: producing a monitoring result based on monitoring for a reference signal, wherein the monitoring comprises one of: monitoring for the reference signal at one or more predetermined reference signal sending times in a first period, and monitoring for the reference signal in a monitoring duration of the first period; and determining whether the monitoring result is used for radio link quality evaluation

In a further embodiment, a method performed by a communication node includes: scheduling reference signal sending times, wherein the scheduling includes one of: scheduling the reference signal sending times at one or more instances in a first period, scheduling the reference signal sending times within a sending duration within the first period, and scheduling the reference signal sending times within the first period; and sending signals at the reference signal sending times.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments of the invention are described in detail below with reference to the following Figures. The drawings are provided for purposes of illustration only and merely depict exemplary embodiments of the invention to facilitate the reader's understanding of the invention. Therefore, the drawings should not be considered limiting of the breadth, scope, or applicability of the invention. It should be noted that for clarity and ease of illustration these drawings are not necessarily drawn to scale.

Figure 1A illustrates how a UE may evaluate downlink radio link quality over an evaluation period.

Figure 1B illustrates how out-of-sync indications or in-sync indications may be sent within indication intervals.

Figure 2 illustrates an exemplary cellular communication network in which techniques disclosed herein may be implemented, in accordance with an embodiment of the present disclosure.

Figure 3 illustrates block diagrams of an exemplary base station (BS) and a user equipment (UE) device, in accordance with some embodiments of the present disclosure.

Figure 4 illustrates timing for periodic reference signal (RS) transmissions by a BS, in accordance with some embodiments of the present disclosure.

Figure 5 is a flow chart of a process of transmitting reference signals from a BS within an radio link monitoring (RLM) period, in accordance with some embodiments of the present disclosure.

Figure 6 is a flow chart of a process of receiving RSs at a UE within an RLM period, in accordance with some embodiments of the present disclosure.

Figure 7 flow chart of a process of evaluating radio link quality at a UE, in accordance with some embodiments of the present disclosure.

Figure 8 illustrates RLM periods and RLM repeat periods for RS transmission by a base station, in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Various exemplary embodiments of the invention are described below with reference to the accompanying figures to enable a person of ordinary skill in the art to make and use the invention. As would be apparent to those of ordinary skill in the art, after reading the present disclosure, various changes or modifications to the examples described herein can be made without departing from the scope of the invention. Thus, the present invention is not limited to the exemplary embodiments and applications described and illustrated herein. Additionally, the specific order or hierarchy of steps in the methods disclosed herein are merely exemplary approaches. Based upon design preferences, the specific order or hierarchy of steps of the disclosed methods or processes can be re-arranged while remaining within the scope of the present invention. Thus, those of ordinary skill in the art will understand that the methods and techniques disclosed herein present various steps or acts in a sample order, and the invention is not limited to the specific order or hierarchy presented unless expressly stated otherwise.

As described below, the discussion below may refer to functional entities, such as a BS, UE, cell, etc. (either in physical or virtual form) , which are similar to those mentioned above with respect to conventional communication systems. As would be understood by persons of ordinary skill in the art, however, such conventional functional entities do not perform the functions described below, and therefore, would need to be modified or specifically configured to perform one or more of the operations described below. Additionally, persons of skill in the art would be enabled to configure functional entities to perform the operations described herein after reading the present disclosure. The term “configured” as used herein with respect to a specified operation or function refers to a system, device, component, circuit, structure, machine, etc. that is physically or virtually constructed, programmed and/or arranged to perform the specified operation or function.

Figure 2 illustrates an exemplary wireless communication network 200 in which techniques disclosed herein may be implemented, in accordance with an embodiment of the present disclosure. The exemplary communication network 200 may overlay a geographic area 201 and include a base station (BS) 202 and a user equipment (UE) device 204 that can communicate with each other via a communication link 210 (e.g., a wireless communication channel) , and a cluster of

notional cells

226, 230, 232, 234, 236, 238 and 240. In Figure 2, the BS 202 and UE 204 are contained within the geographic boundary of cell 226. Each of the

other cells

230, 232, 234, 236, 238 and 240 may include at least one base station (BS) operating at its allocated bandwidth to provide adequate radio coverage to its intended users. For example, the BS 202 may operate at an allocated channel transmission bandwidth to provide adequate coverage to the UE 204. The BS 202 and the UE 204 may communicate via a downlink radio frame 241, and an uplink radio frame 243 respectively. Each radio frame 245/247 may be further divided into sub-frames 249/251 which may include data symbols 253/255. Accordingly, reference to a cell may also be a short hand reference to a BS with an associated coverage region or area.

In the present disclosure, the base station (BS) 202 and user equipment (UE) 204 are described herein as non-limiting examples of “communication nodes, ” generally, which can practice the methods disclosed herein. Such communication nodes may be capable of wireless and/or wired communications, in accordance with various embodiments of the invention. Each of these communication nodes may be a transmitter in one situation and a receiver in another situation. For example, a BS 202 may transmit to a UE 204, such as during a downlink (DL) , discussed further below. Therefore, the BS 202 may be a transmitter and the UE 204 may be a receiver. However, in another situation (such as during an uplink (UL) , described further below) the UE 204 may be a transmitter and the BS 202 may be a receiver. Accordingly, both the BS 202 and the UE 204 may be a receiver or a transmitter for advanced random access preamble transmissions, as will be discussed further below. In certain embodiments, a communication device may refer to a UE while a communication node may refer to a BS.

In network 200, a signal transmitted from the BS 202 may suffer from environmental and/or operating conditions that cause undesirable channel characteristics, such as Doppler spread, Doppler shift, delay spread, multipath interference, etc. mentioned above. For example, multipath signal components may occur as a consequence of reflections, scattering, and diffraction of the transmitted signal by natural and/or man-made objects. At the receiver antenna 114, a multitude of signals may arrive from many different directions with different delay times, attenuations, and phases. Generally, the time difference between the arrival moment of a first received multipath component (typically the line of sight (LOS) component) and the last received multipath component (typically a non-line of sigh (NLOS) component) is called delay spread. The combination of signals with various delay times, attenuations, and phases may create distortions such as inter-symbol interference (ISI) and inter-channel interference (ICI) in the received signal. The distortion may complicate reception and conversion of the received signal into useful information. For example, delay spread may cause ISI in the useful information (data symbols) contained in the radio frame 224. In certain embodiments, these undesirable channel characteristics may case a failure to receive signals transmitted by a BS (e.g., a reference signal sent from the BS) .

Figure 3 illustrates block diagrams of an exemplary system 300 including a base station (BS) 302 and user equipment (UE) 304 for transmitting and receiving wireless communication signals, e.g., OFDM/OFDMA signals, between each other. The system 300 may include components and elements configured to support known or conventional operating features that need not be described in detail herein. In one exemplary embodiment, system 300 can be used to transmit and receive data symbols in a wireless communication environment such as the wireless communication environment 200 of Figure 1, as described above.

The BS 302 includes a BS transceiver module 310, a BS antenna 312, a BS processor module 314, a BS memory module 316, and a network communication module 318, each module being coupled and interconnected with one another as necessary via a data communication bus 320. The UE 304 includes a UE transceiver module 330, a UE antenna 332, a UE memory module 334, and a UE processor module 336, each module being coupled and interconnected with one another as necessary via a data communication bus 340. The BS 302 communicates with the UE 304 via a communication channel (e.g., link) 350, which can be any wireless channel or other medium known in the art suitable for transmission of data as described herein.

As would be understood by persons of ordinary skill in the art, system 300 may further include any number of modules other than the modules shown in Figure 2. Those skilled in the art will understand that the various illustrative blocks, modules, circuits, and processing logic described in connection with the embodiments disclosed herein may be implemented in hardware, computer-readable software, firmware, or any practical combination thereof. To clearly illustrate this interchangeability and compatibility of hardware, firmware, and software, various illustrative components, blocks, modules, circuits, and steps are described generally in terms of their functionality. Whether such functionality is implemented as hardware, firmware, or software depends upon the particular application and design constraints imposed on the overall system. Those familiar with the concepts described herein may implement such functionality in a suitable manner for each particular application, but such implementation decisions should not be interpreted as limiting the scope of the present invention.

In accordance with some embodiments, UE transceiver 330 may be referred to herein as an "uplink" transceiver 330 that includes a RF transmitter and receiver circuitry that are each coupled to the antenna 332. A duplex switch (not shown) may alternatively couple the uplink transmitter or receiver to the uplink antenna in time duplex fashion. Similarly, in accordance with some embodiments, the BS transceiver 310 may be referred to herein as a "downlink" transceiver 310 that includes RF transmitter and receiver circuity that are each coupled to the antenna 312. A downlink duplex switch may alternatively couple the downlink transmitter or receiver to the downlink antenna 312 in time duplex fashion. The operations of the two

transceivers

310 and 330 are coordinated in time such that the uplink receiver is coupled to the uplink antenna 332 for reception of transmissions over the wireless transmission link 350 at the same time that the downlink transmitter is coupled to the downlink antenna 312. Preferably there is close time synchronization with only a minimal guard time between changes in duplex direction.

The UE transceiver 330 and the base station transceiver 310 are configured to communicate via the wireless data communication link 350, and cooperate with a suitably configured RF antenna arrangement 312/332 that can support a particular wireless communication protocol and modulation scheme. In some exemplary embodiments, the UE transceiver 308 and the base station transceiver 310 are configured to support industry standards such as the Long Term Evolution (LTE) and emerging 5G and New Radio (NR) standards, and the like. It is understood, however, that the invention is not necessarily limited in application to a particular standard and associated protocols. Rather, the UE transceiver 330 and the base station transceiver 310 may be configured to support alternate, or additional, wireless data communication protocols, including future standards or variations thereof.

In accordance with various embodiments, the BS 302 may be a next generation nodeB (gNodeB or gNB) , serving gNB, target gNB, transmission reception point (TRP) , evolved node B (eNB) , a serving eNB, a target eNB, a femto station, or a pico station, for example. In some embodiments, the UE 304 may be embodied in various types of user devices such as a mobile phone, a smart phone, a personal digital assistant (PDA) , tablet, laptop computer, wearable computing device, etc. The

processor modules

314 and 336 may be implemented, or realized, with a general purpose processor, a content addressable memory, a digital signal processor, an application specific integrated circuit, a field programmable gate array, any suitable programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof, designed to perform the functions described herein. In this manner, a processor may be realized as a microprocessor, a controller, a microcontroller, a state machine, or the like. A processor may also be implemented as a combination of computing devices, e.g., a combination of a digital signal processor and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a digital signal processor core, or any other such configuration.

Furthermore, the steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in firmware, in a software module executed by

processor modules

314 and 336, respectively, or in any practical combination thereof. The

memory modules

316 and 334 may be realized as RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. In this regard,

memory modules

316 and 334 may be coupled to the

processor modules

314 and 336, respectively, such that the

processors modules

314 and 336 can read information from, and write information to,

memory modules

316 and 334, respectively. The

memory modules

316 and 334 may also be integrated into their

respective processor modules

314 and 336. In some embodiments, the

memory modules

316 and 334 may each include a cache memory for storing temporary variables or other intermediate information during execution of instructions to be executed by

processor modules

314 and 336, respectively.

Memory modules

316 and 334 may also each include non-volatile memory or non-transitory memory for storing instructions (e.g., computer readable instructions) to be executed by the

processor modules

314 and 336, respectively.

The network communication module 318 generally represents the hardware, software, firmware, processing logic, and/or other components of the base station 302 that enable bi-directional communication between base station transceiver 310 and other network components and communication nodes configured to communication with the base station 302. For example, network communication module 318 may be configured to support internet or WiMAX traffic. In a typical deployment, without limitation, network communication module 318 provides an 802.3 Ethernet interface such that base station transceiver 310 can communicate with a conventional Ethernet based computer network. In this manner, the network communication module 318 may include a physical interface for connection to the computer network (e.g., Mobile Switching Center (MSC) ) .

As noted above, a BS operating on an unlicensed band or spectrum may perform a listen before talk (LBT) process or mechanism before sending a reference signal (RS) . A UE may not receive, or may erroneously receive, a RS should a LBT failure occur. In certain embodiments, a LBT failure can be detected as, for example, the transmission number of PRACH preambles reaching a maximum number or a transmission number of msg3 (e.g., the standard third message of a random access procedure) reaching a maximum number. Examples of LBT failures may include an RS transmission during an ongoing transmission in the unlicensed spectrum or during a prescheduled transmission in the unlicensed spectrum. Accordingly, a LBT failure may promote the probability of an out of sync indication, which may correspondingly promote RLF process or mechanism triggering.

Therefore, LBT failures may cause additional overhead for an UE by promoting RLF mechanism triggering. Also, when a BS fails to send a RS due to an LBT failure, many UEs may not detect the RS sent by the BS. Also, trigging an RLF mechanism may also cause a UE to attempt re-establishment of a RRC connection, which will cause network congestion.

The present disclosure provides various embodiments of systems and methods for radio link monitoring. In certain embodiments, radio link monitoring includes assessing a parameter value (e.g., for downlink radio link quality) associated with a reference signal against a threshold value (e.g., for the out of sync threshold/Qout or in-sync threshold/Qin) in response to a determination that the reference signal is or is not a LBT failure (e.g., does or does not violate a listen before talk (LBT) rule) .

In various embodiments, a BS may send a RS once or periodically within a RLM period. Stated another way, a BS may send a RS periodically N times, where N>1, at different times in a RLM period. Optionally, there may be a different value of N in different RLM periods. Also, as will be discussed further below, RSs may be sent at a RS sending time. RS sending times may be periodic within a RLM period. The sending of RSs may cease when a RS is sent successfully within an RLM period. Also, when a RS is not sent at a particular RS sending time, a BS may resend or send the RS again at an immediately following RS sending time (e.g., a next RS sending time) . Accordingly, in certain embodiments, a RS is sent at a RS sending time when all previous RSs are sent unsuccessfully. In further embodiments, a BS will continue to send an RS at the (n+1) th RS sending time in a RLM period only when all previous RSs are sent unsuccessfully at the front n (n<N-1) RS sending times, where n is an RS sending time counter value. In particular embodiments, no more RSs are sent in a remaining duration of an RLM period once an RS is sent successfully at the i th (i<N) RS sending time, where i is an RS sending time counter value. For ease of discussion, the RS sending time counter value may be designated as i or n in different embodiments, as will be discussed further below. However, no RSs are sent after a last or final RS sending time within a RLM period (e.g., an Nth RS sending time) .

In certain embodiments, a UE may perform RLM at a first RS sending time. The UE may detect an RS at the first RS sending time. When the UE successfully monitors or detects RS at the first RS sending time, the UE may then record the successful detection as part of the UE’s monitoring result and apply the UE’s monitoring result from the successfully detected RS to the UE’s evaluation of downlink radio link quality. Also, when the UE successfully monitors or detects the RS at the first RS sending time, the UE may then cease monitoring or detecting for RSs within the remaining duration of the RLM period. Stated another way, the UE will cease RLM within an RLM period upon successfully detecting a RS within the RLM period.

However, when the RS is not successfully detected at a first RS sending time, the UE’s layer 1 may record the detection (e.g., performance of RLM) at the first RS sending time as invalid and not apply the RS detection at the first RS sending time to an evaluation of downlink radio link quality. Also, when the RS is not successfully detected at a first RS sending time, the UE may then perform RLM at a second RS sending time after the first RS sending time. Stated another way, when a UE has not monitored any RS successfully at the front n (n<N-1) RS sending times, the Layer 1 of the UE may note all of the results as invalid monitoring results and will not apply the invalid monitoring results to the evaluation of downlink radio link quality. Also, the UE may then perform RLM at the next, or (n+1) th, RS sending time.

In certain embodiments, the UE may detect an RS at the first RS sending time. When the UE successfully monitors or detects the RS at a particular RS sending time, the UE may then record the successful detection as part of the UE’s monitoring result, cease RLM for the RLM period, and apply the UE’s monitoring result from the successfully detected RS to the UE’s evaluation of downlink radio link quality. Stated another way, when the UE successfully monitors or detects the RS at the i th (i<N) RS sending time, the UE will not perform RLM any more in the remaining duration of the RLM period. Also, the layer 1 of the UE may record the results (e.g., measurements of the RS) of the RS at the i th (i<N) RS sending time as a valid monitoring result and apply the RS measurement at the ith RS sending time to an evaluation of downlink radio link quality. However, the UE may record RS measurement results at the Nth RS sending time and apply the RS measurements at the Nth RS sending time to an evaluation of downlink radio link quality whether or not the UE has successfully monitored or detected the RS at the Nth RS sending time.

In many embodiments, a UE’s estimate of downlink radio link quality may be compared with an out-of-sync threshold Qout-A. Qout-A is equal to n* (BLER of a hypothetical Physical Downlink Control Channel (PDCCH) transmission from the serving cell) , where n is an arbitrary value and n>10%.

In certain embodiments, a layer 1 of a UE can be utilized to judge or determine when a LBT failure has occurred. The ability of a UE (e.g., a layer 1 of a UE) to judge or determine when a LBT failure has occurred may be conventional and will not be discussed in detail for brevity. When the UE has determined that a LBT failure has occurred, the UE may then elect to not apply any measurements of an RS at the RS sending time associated with the LBT failure to an evaluation of downlink radio link quality.

In certain embodiments, a UE may evaluate whether a downlink radio link quality on a configured RS resource estimated or measured at a last T _{Evaluate_out_SSB} [ms] period becomes worse than the threshold Q _out within the T _{Evaluate_out_SSB} [ms] evaluation period. This evaluation may exclude any invalid monitoring results collected during RS sending times, such as invalid monitoring results associated with an LBT failure or other RS failure.

In particular embodiments, a UE may evaluate whether a downlink radio link quality on a configured RS resource estimated or measured over a last T _{Evaluate_in_SSB} [ms] period becomes better than the threshold Q _in within the T _{Evaluate_in_SSB} [ms] evaluation period. This evaluation may exclude any invalid monitoring results collected during RS sending times, such as invalid monitoring results associated with an LBT failure or other RS failure.

In certain optional embodiments, a UE may evaluate whether a downlink radio link quality on a configured RS resource estimated or measured over a last N _{Evaluate_out_SSB} times becomes worse than the threshold Qout within the N _{Evaluate_out_SSB} times. N _{Evaluate_out_SSB} is the total number of monitoring times minus the number of monitoring failures (e.g., RS detection failures) caused by LBT failures.

In certain optional embodiments, a UE may evaluate whether a downlink radio link quality on a configured RS resource estimated over the last N _{Evaluate_in_SSB} times becomes better than the threshold Q _in within the N _{Evaluate_in_SSB} times. N _{Evaluate_in_SSB} is the total number of monitoring times minus the number of monitoring failures (e.g., RS detection failures) caused by LBT failure.

In certain optional embodiments, a layer 1 of a UE may indicate a failure type to a high layer of a UE. The failure type may be used to indicate a cause of failure in connection with monitoring for a RS at a particular RS sending time.

In certain embodiments, a UE may send secondary cell group (SCG) failure information with a failure type indicator to a BS associated with a serving cell. This may be performed when the UE determines an out-of-sync indication associated with a failure type sent from a UE’s layer 1 to a higher level layer of the UE. The failure type may indicate that LBT is the cause of a failure to monitor a RS at a particular RS sending time. Also, a BS that receives the failure type indicator may then send the failure type indicator to another BS.

In particular embodiments, a UE may initialize a RRC connection re-establishment procedure at a moment T1 after execution of RLF. The moment T1 may be a random value (e.g., a value chosen at random) between a first value V1 and a second value V2. The values of V1 and V2 may be configured by a BS or may be predefined (e.g., in system information) , and/or may be decided by a UE. In certain embodiments, the values of V1 or V2 may be configured by a BS according to a UE service priority.

In certain embodiments, different UEs may be configured differently with different parameter sets P. Each parameter set P may set values for N310, T310, and N311, as introduced above. N310 may refer to a network-configured radio link failure timer value, T310 may refer to a value or number of consecutive out-of-sync indications, and N311 may refer to a number or value of consecutive in-sync indications.

In a first exemplary embodiment, a BS (e.g., a Node B) may configure a periodicity for RS transmissions (e.g., a periodicity for RS sending times) within a RLM period. The BS may also configure a periodicity for the RLM periods. This configurable periodicity by the BS may be consistent or inconsistent. Consistent periodicity may refer to separation by a consistent or same amount of time. In contrast, inconsistent periodicity may refer to separation by different amounts of time. For example, by having consistent periodicity, all RS transmissions within an RLM period may be separated by a consistent or same amount of time. In contrast, by having inconsistent periodicity, different RS transmissions may be separated from each other by different amounts of time. In various embodiments, a BS may configure whether the periodicity for RS transmissions and/or RLM periods are consistent or inconsistent, as well as the specific amounts of time between RS transmissions and/or RLM periods. Also, in further embodiments, a BS may have different periodicity configurations for different operating situations, such as when serving different UEs, different types of UEs, or different numbers of UEs.

Figure 4 illustrates timing for periodic reference signal (RS) 402 transmissions by a BS, in accordance with some embodiments of the present disclosure. In certain embodiments, the BS may configure the periodicity of RS 402 transmission with a RLM period T, inclusive of N RS sending times. Accordingly, the BS may send the RS 402 at the times of t1 , t1+T , t1+2T , and so on. Stated another way, an RLM period T may be periodic (e.g., may repeat itself periodically) , and the RLM period T may include multiple period RS sending times. The RS sending times may be bound within an RLM period T by a quantity N, which may be counted from the value 0 to the value N-1. Accordingly, the BS may configure N-1 alternate or periodic RS sending times.

In certain embodiments, the quantity N can be different within different RLM periods T. Stated another way, a total of N RS sending times may be configured in a current RLM periods T, spanning from t1 to t1+T. A BS may send an RS based on LBT at the first RS sending time t1, and may send RSs at the remaining N-1 RS sending times.

In certain embodiments, a BS may send an RS after performing LBT at a first RS sending time t1 within an RLM period. When the BS successfully sends the RS at t1, no more RSs are to be sent within the RLM period.

In further embodiments, a BS may fail to send an RS at the first RS sending time t1 of an RLM period. This failure to send may be due to performance of LBT, such as where the performance of LBT indicated that the RS is not to be sent at the first RS sending time. Accordingly, the BS may send the RS, and perform LBT again, at the second RS sending time immediately following the first RS sending time t1. When the BS successfully sends the RS at the second sending time, no more RSs are to be sent within the RLM period. Stated another way, when the BS successfully sends the RS at the second sending time, the BS will also cease or not send the RS at any of the subsequent N-2 RS sending times within the RLM period.

In another embodiment, a BS may send an RS at a current RS sending time if the BS fails to send the RS, based on LBT performance, at all earlier RS sending times of an RLM period. Stated another way, when a BS fails to send an RS based on LBT at all of the front i-1 (i<= N-1) RS sending times, the BS will then send the RS based on LBT at the i th RS sending time. If the RS is sent successfully at the ith RS sending time, then no more RSs will be send during the remaining N-i RS sending times of the RLM period. However, if the BS fails to send an RS based on LBT at the ith RS sending time, then the BS will send the RS and perform an associated LBT process at the (i+1) th RS sending time. However, no RSs are sent after a last or final RS sending time within a RLM period (e.g., an Nth RS sending time) .

Figure 5 is a flow chart of a process 500 of transmitting reference signals from a BS within an RLM period, in accordance with some embodiments. The process 500 of transmitting reference signals from a BS within an RLM period may be performed at a BS 501, as introduced above. It is noted that the process 500 is merely an example, and is not intended to limit the present disclosure. Accordingly, it is understood that additional operations may be provided before, during, and after the process 500 of Figure 5, certain operations may be omitted, certain operations may be performed concurrently with other operations, and that some other operations may only be briefly described herein.

At operation 502, an RS may be sent at a first RS sending time t1. As noted above the first RS sending time t1 may be first of a set of RS sending times that are sequentially sent from the BS within a RLM period. Also, the RLM period may be periodic and may repeat periodically. Also, each RS sending time may be associated with a RS sending time counter value i, where i at the first RS sending time is accorded a value of 1. N may describe the total quantity of RS sending times within an RLM period. Thus, a counter value of the last RS sending time may be of a value N (e.g., i=N at the last RS sending time within a RLM period) .

At operation 504, a decision may be made as to whether the RS at the first RS sending time t1 is sent successfully, taking into consideration the rules of LBT. As noted above, LBT may dictate whether a RS may be sent or not. For example, an RS may not be sent during an ongoing transmission. A failure to send due to LBT (e.g., where LBT dictates that an RS should not be sent at a particular RS sending time) may be referred to as an LBT failure. Typically, an LBT failure is associated with a current RS sending time (e.g., an RS sending time currently under consideration) . If the RS at the first RS sending time is sent successfully, the process 500 proceeds to operation 508. If the RS at the first RS sending time is not sent successfully (e.g., due to LBT considerations) , the process 500 proceeds to operation 506.

At operation 506, the BS 501 may send the RS at the next RS sending time of the RLM period. Accordingly, the RS sending time counter i may be incremented by one (e.g., incremented by one value) . In certain embodiments where the first RS sending time is the last RS sending time,

operations

506 and 510 may be skipped and the process 500 may proceed directly to operation 512.

At operation 510, a decision may be made as to whether the RS at the next RS sending time is sent successfully, taking into consideration the rules of LBT. If the RS at the first RS sending time is sent successfully, the process 500 proceeds to operation 508. If the RS at the first RS sending time is not sent successfully (e.g., due to LBT considerations) , the process 500 proceeds to operation 512.

At operation 512, a decision may be made as to whether the next RS sending time is the last RS sending time, such that i=N. If the next RS sending time is the last RS sending time, the process 500 proceeds to operation 508. If the next RS sending time is not the last RS sending time, the process 500 proceeds to operation 506, where the further next RS sending time is processed (e.g., i is further incremented by one value) . Accordingly, a designation of the term “next” to an RS sending time refers to an immediately subsequent RS sending time, and is not indicative of a particular sending time counter value.

At operation 508, further transmission of RSs cease for the remainder of the RLM period. Stated another way, the BS will send no more RSs in the remaining duration of the RLM period.

In certain embodiments, a UE may perform RLM at a first RS sending time t1. When the UE determines that the RS has been successfully received (e.g., the UE has monitored a RS successfully at t1) , the UE may record measurement results made based upon the successfully received RS and apply such measurement results to the evaluation of downlink radio link quality (e.g., a radio link quality evaluation) . The UE may then not perform RLM during the remaining duration of the RLM period.

In further embodiments, a UE perform RLM at a first RS sending time t1. When the UE determines that the RS has not been successfully received (e.g., the UE has not monitored a RS successfully at t1) , then the UE may not record measurement results made based upon the unsuccessfully received RS. Also, any measurements made based on the unsuccessfully received RS are not applied to the evaluation of downlink radio link quality. The UE may then continue to perform RLM at the next (e.g., a second) RS sending time.

When the UE determines that the RS has been successfully received at the second RS sending time (e.g., the UE has monitored a RS successfully at the second RS sending time) , the UE may then record measurement results made based upon the successfully received or monitored RS at the second sending time and apply such measurement results to the evaluation of downlink radio link quality. The UE may then not perform RLM during the remaining duration of the RLM period.

In additional embodiments, when the UE determines that the RS has not been successfully received at any previous RS sending time (e.g., when there have been no RSs successfully received at the front (k-1) (wherein k< N) RS sending times) , then the UE may not record measurement results made based upon the unsuccessfully received RS. Also, any measurements made based on the unsuccessfully received RS are not applied to the evaluation of downlink radio link quality. The UE may then continue to perform RLM at the next or following RS sending time (e.g., the UE will continue to perform RLM at the kth RS sending time) .

When the UE determines that the RS has been successfully received at the next or following sending time (e.g., at the kth RS sending time) , the UE may record measurement results made based upon the successfully received RS and apply such measurement results to the evaluation of downlink radio link quality. The UE may then not perform RLM during the remaining duration of the RLM period.

When the UE determines that the RS has not been successfully received at the next or following sending time (e.g., at the kth RS sending time) , the UE may not record (e.g., discard) measurement results made based upon the unsuccessfully received RS. Also, any measurements made based on the unsuccessfully received RS are not applied to the evaluation of downlink radio link quality. The UE may then continue to perform RLM at the (k+1) th RS sending time (e.g., a next RS sending time) .

However, the UE will record measurement results made based upon an unsuccessfully received RS at a last RS sending time (e.g., an Nth RS sending time) and apply such measurement results to the evaluation of downlink radio link quality if there are otherwise no successfully received RSs within the RLM period. Stated another way, whether or not the UE has monitored a RS successfully at the Nth RS sending time, the UE will record measurement results of a RS at the Nth RS sending time as a valid monitoring result and apply it to the evaluation of downlink radio link quality.

Figure 6 is a flow chart of a process 600 of receiving reference signals at a UE within an RLM period, in accordance with some embodiments. The process 600 of receiving reference signals at a UE within an RLM period may be performed at a UE 601, as introduced above. It is noted that the process 600 is merely an example, and is not intended to limit the present disclosure. Accordingly, it is understood that additional operations may be provided before, during, and after the process 600 of Figure 6, certain operations may be omitted, certain operations may be performed concurrently with other operations, and that some other operations may only be briefly described herein.

At operation 602, the UE 601 may perform RLM at a first RS sending time. As noted above, the first RS sending time may be first of a set of RS sending times that are sequentially sent from the BS within a RLM period. Also, the RLM period may be periodic and may repeat periodically. Furthermore, each RS sending time may be associated with a RS receiving time counter value “k” at the UE, where “k” at the first RS sending time is accorded a value of 1. N may describe the total quantity of RS sending times within an RLM period. Thus, a counter value of the last RS sending time may be of a value N (e.g., k=N at the last RS sending time within a RLM period) .

At operation 604, a decision may be made as to whether the RS at the first RS sending time is received successfully (e.g., monitored successfully) , taking into consideration the rules of LBT. As noted above, LBT may dictate whether a RS may be sent or not. Accordingly, LBT may dictate whether a RS may be received or not, as well. For example, an RS may not be sent, or received, during an ongoing transmission. A failure to receive due to LBT (e.g., where LBT dictates that an RS should not be sent at a particular RS sending time) may also be referred to as an LBT failure. Typically, an LBT failure is associated with a current RS sending time (e.g., an RS sending time currently under consideration) . Also, a conventional UE may be able to determine whether an LBT failure has occurred via the physical layer, or a layer 1 of the UE. If the RS at the first RS sending time is received successfully, the process 600 proceeds to operation 616. If the RS at the first RS sending time is not received successfully (e.g., due to LBT considerations) , the process 600 proceeds to operation 606.

At operation 606, the UE 601 does not record measurement results made based upon the unsuccessfully received RS (e.g., a RS not received successfully, such as due to LBT considerations) . Also, any measurements made based on the unsuccessfully received RS are not applied to the evaluation of downlink radio link quality.

At operation 608, the UE 601 may perform RLM at the next RS receiving time of the RLM period. Accordingly, the RS receiving time counter “k” may be incremented by one (e.g., incremented by one value) . Furthermore, the reference to a “next” RS sending time may not be a reference to a particular RS sending time (e.g., a “second” , “third” , or “fourth” RS sending time) , but may refer to a RS sending time that immediately follows an RS sending time under current consideration.

At operation 610, a decision may be made as to whether the RS at the next RS sending time is received successfully (e.g., monitored successfully) , taking into consideration the rules of LBT. If the RS at the next RS sending time is not received successfully (e.g., due to LBT considerations) , the process 600 proceeds to operation 612. If the RS at the next RS sending time is received successfully, the process 600 proceeds to operation 616.

At operation 612, a decision may be made as to whether the next RS sending time is the last RS sending time, such that k=N. If the next RS sending time is the last RS sending time, the process 600 proceeds to operation 616. If the next RS sending time is not the last RS sending time, the process 600 proceeds to operation 606, where the further next RS sending time is processed (e.g., “i” is further incremented by one value) .

At operation 616, the UE may record measurement results made based upon an RS currently under consideration as valid and apply such measurement results to the evaluation of downlink radio link quality.

At operation 618, the UE may cease performance of RLM during the remaining duration of the RLM period. Stated another way, the UE will not process (e.g., will not listen to) any more RSs in the remaining duration of the RLM period.

In certain embodiments, such as where N=3, when the UE determines that the RS has not been successfully received (e.g., where the UE has not monitored a RS successfully at t1 due to an LBT fail) , the UE may not record measurement results made based upon the unsuccessfully received RS. Also, any measurements made based on the unsuccessfully received RS are not applied to the evaluation of downlink radio link quality. The UE may then continue to perform RLM at the next (e.g., a second) RS sending time.

If the UE determines that the RS has been successfully received at the second RS sending time (e.g., the UE has monitored a RS successfully at the second RS sending time) , the UE may then record measurement results made based upon the successfully received RS at the second sending time and apply such measurement results to the evaluation of downlink radio link quality. The UE may then not perform RLM during the remaining duration of the RLM period.

However, if the UE determines that the RS has not been successfully received at the second sending time, the UE may not record measurement results made based upon the unsuccessfully received RS at the second sending time. Also, any measurements made based on the unsuccessfully received RS are not applied to the evaluation of downlink radio link quality. The UE may then continue to perform RLM at the next (e.g., a third) RS sending time.

However, since N=3, the UE will record measurement results made based upon an unsuccessfully received RS at this last RS sending time (e.g., the third RS sending time) and apply such measurement results to the evaluation of downlink radio link quality if there are otherwise no successfully received RSs within the RLM period. Stated another way, whether or not the UE has monitored a RS successfully at the Nth RS sending time (e.g., here at the 3 ^rd sending time, since N=3) , the UE will record measurement results of a RS at the Nth RS sending time as a valid monitoring result and apply it to the evaluation of downlink radio link quality.

In a second exemplary embodiment, the evaluation of downlink radio link quality may utilize measurement results from a set number of multiple RSs. These RSs may be considered when the RSs are not associated with an LBT fail. Stated another way, the RSs that are associated with an LBT fail are not utilized in measurement results from multiple RSs. Stated yet another way, the evaluation of downlink radio link quality may utilize measurement results from a set number of multiple RSs that do not include RSs associated with an LBT fail. Also, a total number of RSs utilized for the evaluation of downlink radio link quality may be referred to as N.

In certain embodiments, out-of-sync and in-sync evaluation periods may be used for the evaluation of whether a UE and BS are out-of-sync and in-sync are T1 (measured in milliseconds (ms) ) and T2 (measured in milliseconds (ms) ) , respectively. Also, the out-of-sync and in-sync threshold used for evaluation of whether a BS and UE are out-of-sync or in-sync are Q1and Q2, respectively.

In various embodiments, a UE may perform RLM at each RS sending time separately in T1. When the UE determines that the RS has not been successfully received (e.g., the UE has not monitored a RS successfully at t1) , the UE may not record measurement results made based upon the unsuccessfully received RS. Also, any measurements made based on the unsuccessfully received RS are not applied to the evaluation of downlink radio link quality. An RS may not be successfully received when the UE has determined that an RS sent at a particular RS sending time is an LBT failure. Also, the layer 1 of a UE may determine whether the reason for an RS not being successfully received is an LBT failure. In certain embodiments, an RS that is not successfully received is removed from the N monitoring results in T1. Stated another way, the UE may not record measurement results made based upon the unsuccessfully received RS. For example, assume that the number of unsuccessful monitoring RSs due to LBT is “M” in T1, where “N” represents the total number of RSs utilized for an evaluation of downlink radio link quality. Then, when M is removed from the N RS monitoring results in the T1, only the remaining (N-M) RS monitoring results are used for downlink wireless link quality assessment.

In certain embodiments, a UE may evaluate whether the downlink radio link quality on a configured RS resource estimated (e.g., determined) over the (N-M) times in an evaluation period T1 becomes worse than the threshold Q ₁ within the evaluation period T1. When the downlink radio link quality on all the configured RS resources estimated (e.g., determined) over the (N-M) times are worse than Q ₁, layer 1 of the UE shall send an out-of-sync indication for the primary cell (PCell) or primary serving cell (PSCell) to the higher layers within the evaluation period T1.

In further embodiments, a UE may evaluate whether the downlink radio link quality on the configured RS resource estimated (e.g., determined) over the (N-M) times in an evaluation period T2 becomes better than the threshold Q2 within the evaluation period T2. When the downlink radio link quality of the PCell or PSCell estimated over the the (N-M) times in the evaluation period T2 becomes better than the threshold Q2, layer 1 of the UE shall send an in-sync indication for the PCell or PSCell to the higher layers within the evaluation period T2.

In a third exemplary embodiment, the evaluation of downlink radio link quality may utilize measurement results from multiple RSs within an RLM period. In certain embodiments, the out-of-sync and in-sync evaluation periods used for the evaluation of whether a BS and UE are out-of-sync or in-sync are N1 and N2, respectively. Also, the out-of-sync and in-sync threshold used for evaluation of whether a UE and BS are out-of-sync or in-sync are Q1 and Q2, respectively.

In particular embodiments, a number of evaluation times is represented by a counter value n and is initialized to 0 in an evaluation period. Also, as will be explained in greater detail below, the counter value n may be compared with an out-of-sync evaluation period N1 or an in-sync evaluation period N2. For example, when n=N1, all of the RSs recorded for evaluation of downlink radio link quality may then be utilized together for an evaluation of downlink radio link quality using the out-of-sync threshold Q1. Similarly, when n=N2, all of the RSs recorded for evaluation of downlink radio link quality may then be utilized together for an evaluation of downlink radio link quality using the in-sync threshold Q2.

When the UE determines that an RS has been successfully received at n+1 (e.g., the UE has monitored a RS successfully at n+1) , where n represents a counter value and starts at 0, the UE may record measurement results made based upon the successfully received RS and apply such measurement results to the evaluation of downlink radio link quality. An n value of 0 may represent a first RS sending time.

When the UE determines that the RS has not been successfully received (e.g., the UE has not monitored a RS successfully) for reasons other than an LBT failure, the UE may not record measurement results made based upon the unsuccessfully received RS for reasons other than an LBT failure. Also, any measurements made based on the unsuccessfully received RS for reasons other than an LBT failure are not applied to the evaluation of downlink radio link quality. Furthermore, the value of n may be kept unchanged until a UE has monitored a RS successfully or when a UE has monitored a RS unsuccessfully due to an LBT failure. For example, when the UE determines that an RS has not been successfully received due to an LBT failure, the UE may record measurement results made based upon the RS that had not been successfully received due to an LBT failure and apply such measurement results to the evaluation of downlink radio link quality.

So long as n is not equal to N1, the UE may continue to perform RLM at respective next RS sending times. When n is equal to N1, the UE may then begin to use the recorded RS measurements for evaluation of downlink radio link quality

Figure 7 is a flow chart of a process 700 of evaluating radio link quality at a UE, in accordance with some embodiments. The process 700 of evaluating radio link quality at a UE may be performed at a UE 701, as introduced above. It is noted that the process 700 is merely an example, and is not intended to limit the present disclosure. Accordingly, it is understood that additional operations may be provided before, during, and after the process 700 of Figure 7, certain operations may be omitted, certain operations may be performed concurrently with other operations, and that some other operations may only be briefly described herein.

At operation 702, a counter value n for RS sending times may be initialized to a counter value representing a first RS sending time within an RLM period. As noted above, the counter value may start at 0. In the current embodiment, an initialized counter value of n=0 may represent a first RS sending time.

At operation 704, the UE may perform RLM at an RS sending time associated with a current counter value, such as n=0 for a first RS sending time that has not yet undergone RLM.

At operation 706, a decision may be made as to whether the RS at the RS sending time associated with the current counter value n is received successfully (e.g., monitored successfully) . If the RS at the RS sending time associated with a current counter value n is received successfully, the process 700 proceeds to operation 708. If the RS associated with a current counter value n is not received successfully (e.g., due to not receiving an RS) , the process 700 proceeds to operation 710.

At operation 708, the current counter value may be increment by a single value (e.g., n+1) to become a new current counter value representing a next RS sending time. For example, an n of value 0 at operation 706 may be incremented to a value of 1 at operation 708.

At operation 710, a decision may be made as to whether the unsuccessfully received RS associated with a current counter value n was unsuccessfully received due to an LBT failure. As noted above, this may be determined at layer 1 of a UE in a conventional manner. If yes, the process 700 proceeds to operation 712. If no, the process 700 proceeds to operation 708.

At operation 712, a current counter value is not incremented (e.g., stays the same) when a RS is not successfully received due to an LBT failure.

At operation 714, the UE may record measurement results made based upon an RS under consideration at operation 706 as valid and apply such measurement results to the evaluation of downlink radio link quality.

At operation 716, a decision may be made as to whether the current counter value (as incremented in operation 708 or not incremented in operation 712) is the last RS sending time within an out-of-sync evaluation period N1 or an in-sync evaluation period N2. Stated another way, a decision may be made as to whether n=N1 or n=N2. If yes, the process 700 proceeds to operation 718. If no, the process 700 proceeds to operation 704.

At operation 718, all of the RSs recorded at operation 714 are utilized for an evaluation of downlink radio link quality using either the out-of-sync threshold Q1 if n=N1, or using the in-sync threshold Q2 if n=N2.

In certain embodiments, when n equal to N1, a UE may evaluate whether the downlink radio link quality on the configured RS resource estimated (e.g., determined) over the N1 times becomes worse than the threshold Q1 within the N1 times. When the downlink radio link quality on all the configured RS resources are worse than Q1, layer 1 of the UE shall send an out-of-sync indication for the PCell or PSCell.

In certain embodiments, when n is equal to N2, a UE may evaluate whether the downlink radio link quality on a configured RS resource estimated (e.g., determined) over the last N2 times becomes better than the threshold Q2 within N2 times. When the downlink radio link quality of the PCell or PSCell estimated over the last N2 times becomes better than the threshold Q2, layer 1 of the UE shall send an in-sync indication for the PCell or PSCell.

In a fourth exemplary embodiment, a UE’s estimate (e.g., determination) of downlink radio link quality may be compared with out-of-sync thresholds Q _out-A for the purpose of radio link monitoring (RLM) . Q _out-A is equal to n* (BLER of a hypothetical Physical Downlink Control Channel (PDCCH) transmission from the serving cell) , where n is an arbitrary value and n>10. In certain embodiments, n=20%.

In particular embodiments, a UE’s estimate of downlink radio link quality is compared with an in-sync thresholds Q _in-A for the purpose of radio link monitoring. Q _in-A is equal to m* (BLER of a hypothetical Physical Downlink Control Channel (PDCCH) transmission from the serving cell) , where m is an arbitrary value and m<2%. In certain embodiments, m=1%.

In a fifth exemplary embodiment, a UE may provide feedback to a BS concerning RS success or failure. When there is an RS failure, this feedback may include failure information with a failure type indicator that indicates a type of failure that caused an RS failure. In addition to sending failure information, the feedback may include other information such as failure information for other BSs aside from a serving BS or a BS associated with a serving cell.

In certain embodiments, a UE may evaluate downlink radio link quality on a configured RS resource from a secondary node B (SN) (e.g., a secondary BS that is not a primary BS associated with a current serving cell) . This evaluation may occur when higher layers of a UE receive an out-of-sync indication carrying a failure type from the layer 1 of a UE. Based on receipt of a failure type associated with the secondary node B (e.g., secondary BS) , the UE may send the failure type associated with the secondary node B (e.g., secondary BS) to a master node B (e.g., a primary BS associated with a current serving cell) . This failure type associated with the secondary node B (e.g., secondary BS) may include a secondary cell group (SCG) failure type or other SCG failure information. For example, one failure type may indicate a failure to monitor, detect, or receive a RS due to an LBT failure.

In a sixth exemplary embodiment, a BS or UE may configure aspects of timing related to RLM. In certain embodiments, a BS (e.g., a node B) may configure the periodicity of RS for RLM with T. The BS may send an RS at the time of t1 , t1+T , t1+2T , and so on.

As noted above, a UE may initialize a RRC connection re-establishment procedure at a moment T1 after execution of RLF. The moment T1 may be a random value between a first value V1 and a second value V2. The values of V1 and V2 may be configured by a BS or may be predefined (e.g., in system information) , and/or may be decided by a UE. In certain embodiments, the values of V1 or V2 may be configured by a BS according to a UE service priority.

In particular embodiments, different UEs may be configured with different parameter sets P, where each parameter set P may define the N310 (network-configured radio link failure timer value) , T310 (e.g., a value or number of consecutive out-of-sync indications) , N311 (e.g., a number or value of consecutive in-sync indications) values as discussed above.

In a seventh exemplary embodiment, a BS may repeatedly attempt to transmit an RS within an RLM period until the RS is transmitted within the RLM period or until the RLM period expires. Also, the RLM periods may not be adjacent to each other, but may repeat after a RLM repeat period.

Figure 8 illustrates RLM periods 802 and RLM repeat periods 804 for reference signal 806 transmission by a base station, in accordance with some embodiments of the present disclosure. As illustrated in Figure 8, a BS may repeatedly attempt to transmit an RS 806 within an RLM period 802 until the RS is successfully transmitted within the RLM period 802 or until the RLM period 802 expires. Also, RLM periods 802 may not be adjacent to each other, but may repeat after a RLM repeat period 804.

In certain embodiments, a BS may configure a periodicity for RS transmission with an RLM repeat period T. Accordingly, the BS may try to send (e.g., schedule) an RS at the times of t1, t1+T, t1+2T, and so on. In addition, the BS may also configure an RLM period parameter value of T1. The starting time of T1 in every period is corresponding to t1, t1+T, t1+2T, and so on.

In certain embodiments, a UE may perform RLM in within an RLM period T1 until the UE determines that an RS has been successfully received or when the RLM period T1 expires.

When the UE determines that the RS has been successfully received (e.g., the UE has monitored a RS successfully within the RLM period T1) , the UE may record measurement results made based upon the successfully received RS and apply such measurement results to the evaluation of downlink radio link quality. The UE may then not perform RLM during the remaining duration of the RLM period T1.

When the UE determines that the RS has not been successfully received, the UE may not record measurement results made based upon the unsuccessfully received RS. Also, any measurements made based on the unsuccessfully received RS are not applied to the evaluation of downlink radio link quality. The UE may then continue to perform RLM at the next RS sending time within the RLM period T1

However, the UE will record measurement results made based upon an unsuccessfully received RS at a last RS sending time and apply such measurement results to the evaluation of downlink radio link quality if there are otherwise no successfully received RSs within the RLM period. Stated another way, whether or not the UE has monitored a RS successfully at the last RS sending time within a RLM period T1, the UE will record measurement results of a RS at the last RS sending time within a RLM period T1 as a valid monitoring result with application to the evaluation of downlink radio link quality.

While various embodiments of the invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. Likewise, the various diagrams may depict an example architectural or configuration, which are provided to enable persons of ordinary skill in the art to understand exemplary features and functions of the invention. Such persons would understand, however, that the invention is not restricted to the illustrated example architectures or configurations, but can be implemented using a variety of alternative architectures and configurations. Additionally, as would be understood by persons of ordinary skill in the art, one or more features of one embodiment can be combined with one or more features of another embodiment described herein. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments.

It is also understood that any reference to an element or embodiment herein using a designation such as "first, " "second, " and so forth does not generally limit the quantity or order of those elements. Rather, these designations can be used herein as a convenient means of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements can be employed, or that the first element must precede the second element in some manner.

Additionally, a person having ordinary skill in the art would understand that information and signals can be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits and symbols, for example, which may be referenced in the above description can be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

A person of ordinary skill in the art would further appreciate that any of the various illustrative logical blocks, modules, processors, means, circuits, methods and functions described in connection with the aspects disclosed herein can be implemented by electronic hardware (e.g., a digital implementation, an analog implementation, or a combination of the two) , firmware, various forms of program or design code incorporating instructions (which can be referred to herein, for convenience, as "software" or a "software module) , or any combination of these techniques. To clearly illustrate this interchangeability of hardware, firmware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware, firmware or software, or a combination of these techniques, depends upon the particular application and design constraints imposed on the overall system. Skilled artisans can implement the described functionality in various ways for each particular application, but such implementation decisions do not cause a departure from the scope of the present disclosure.

Furthermore, a person of ordinary skill in the art would understand that various illustrative logical blocks, modules, devices, components and circuits described herein can be implemented within or performed by an integrated circuit (IC) that can include a general purpose processor, a digital signal processor (DSP) , an application specific integrated circuit (ASIC) , a field programmable gate array (FPGA) or other programmable logic device, or any combination thereof. The logical blocks, modules, and circuits can further include antennas and/or transceivers to communicate with various components within the network or within the device. A general purpose processor can be a microprocessor, but in the alternative, the processor can be any conventional processor, controller, or state machine. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other suitable configuration to perform the functions described herein.

If implemented in software, the functions can be stored as one or more instructions or code on a computer-readable medium. Thus, the steps of a method or algorithm disclosed herein can be implemented as software stored on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that can be enabled to transfer a computer program or code from one place to another. A storage media can be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer.

In this document, the term "module" as used herein, refers to software, firmware, hardware, and any combination of these elements for performing the associated functions described herein. Additionally, for purpose of discussion, the various modules are described as discrete modules; however, as would be apparent to one of ordinary skill in the art, two or more modules may be combined to form a single module that performs the associated functions according embodiments of the invention.

Additionally, one or more of the functions described in this document may be performed by means of computer program code that is stored in a “computer program product” , “computer-readable medium” , and the like, which is used herein to generally refer to media such as, memory storage devices, or storage unit. These, and other forms of computer-readable media, may be involved in storing one or more instructions for use by processor to cause the processor to perform specified operations. Such instructions, generally referred to as “computer program code” (which may be grouped in the form of computer programs or other groupings) , which when executed, enable the computing system to perform the desired operations.

Additionally, memory or other storage, as well as communication components, may be employed in embodiments of the invention. It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units, processing logic elements or domains may be used without detracting from the invention. For example, functionality illustrated to be performed by separate processing logic elements, or controllers, may be performed by the same processing logic element, or controller. Hence, references to specific functional units are only references to a suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization.

Various modifications to the implementations described in this disclosure will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other implementations without departing from the scope of this disclosure. Thus, the disclosure is not intended to be limited to the implementations shown herein, but is to be accorded the widest scope consistent with the novel features and principles disclosed herein, as recited in the claims below.

Claims

A method performed by a communication device, the method comprising:

producing a monitoring result based on monitoring for a reference signal, wherein the monitoring comprises one of:

monitoring for the reference signal at one or more predetermined reference signal sending times in a first period, and

monitoring for the reference signal in a monitoring duration of the first period; and

determining whether the monitoring result is used for radio link quality evaluation.
The method of claim 1, further comprising:

determining whether to monitor for the reference signal at a next reference signal sending time in the first period based on the monitoring result at a current reference signal sending time.
The method of claim 2, further comprising one of:

monitoring for the reference signal at the next reference signal sending time in the first period in response to producing an unsuccessful monitoring result at the current reference signal sending time; and

not monitoring for the reference signal in the first period in response to producing a successful monitoring result at the current reference signal sending time.
The method of claim 1, further comprising one of:

discarding the monitoring result in response to producing an unsuccessful monitoring result at a current reference signal sending time;

recording and applying the monitoring result for radio link quality evaluation in response to producing a successful monitoring result at the current reference signal sending time; and

recording and applying the monitoring result for radio link quality evaluation at a last reference signal sending time within the first period.
The method of claim 1, further comprising one of:

monitoring for the reference signal in the monitoring duration of the first period in response to producing an unsuccessful monitoring result at a current reference signal sending time;

ceasing the monitoring for the reference signal in the monitoring duration of the first period in response to producing a successful monitoring result at the current reference signal sending time; and

ceasing the monitoring for the reference signal at an expiration of the monitoring duration.
The method of claim 1, further comprising one of:

recording and applying the monitoring result for radio link quality evaluation in response to producing a successful monitoring result within the monitoring duration; and

recording and applying the monitoring result for radio link quality evaluation in response to an expiration of the monitoring duration.
The method of claim 1, further comprising at least one of:

discarding the monitoring result in response to producing an unsuccessful monitoring result caused by a listen before talk (LBT) failure; and

recording and applying the monitoring result for radio link quality evaluation response to producing an unsuccessful monitoring result not caused by the listen before talk (LBT) failure.
The method of claim 1, wherein the first period is periodically repeated.
The method of claim 1, wherein the monitoring duration begins at a first reference signal sending time in the first period, and is either received from a communication node or is a predefined value.
A method performed by a communication node, the method comprising:

scheduling reference signal sending times, wherein the scheduling comprises one of:

scheduling the reference signal sending times at one or more instances in a first period,

scheduling the reference signal sending times within a sending duration within the first period, and

scheduling the reference signal sending times within the first period; and

sending signals at the reference signal sending times.
The method of claim 10, further comprising one of:

sending a reference signal at a next reference signal sending time in the first period in response to the reference signal being unsuccessfully sent at a current reference signal sending time in the first period, wherein the current reference signal sending time is prior to the next reference signal sending time; and

not sending the reference signal at the next reference signal sending time in response to the reference signal being successfully sent at the current reference signal sending time.
The method of claim 10, further comprising one of :

not sending a reference signal within a remaining duration of the first period in response to the reference signal being successfully sent in the sending duration, wherein the sending duration is prior to the remaining duration; and

not sending the reference signal after an expiration of the sending duration.
The method of claim 10, wherein the first period is periodically repeated.
The method of claim 10, further comprising sending the signals at the reference signal sending times to a computing device.
The method of claim 10, further comprising:

determining a first radio resource control (RRC) connection re-establishment value and a second RRC connection re-establishment value at the communication node.
The method of claim 15, further comprising:

sending the first RRC connection re-establishment value to a communication device; and

sending the second RRC connection re-establishment value to the communication device.
The method of claim 16, wherein the communication device is configured to:

determine a delay time value chosen at random between the first RRC connection re-establishment value and the second RRC connection re-establishment value, and

delay performance of RRC connection re-establishment after radio link failure occurrence based on the delay time value.
The method of claim 16, wherein the communication device is configured to receive the signals at the reference signal sending times.
A computing device configured to carry out the method of any one of claims 1 through 18.
A non-transitory computer-readable medium having stored thereon computer-executable instructions for carrying out any one of claims 1 through 18.