Method for NR Radio Link Monitoring (RLM) and Evaluation Period Determination

Abstract

Methods are proposed to define UE behavior for performing synchronization signal block (SSB) based radio link monitoring (RLM) and channel state information reference signal (CSI-RS) based RLM. In a first novel aspect, if CSI-RS based RLM-RS is not QCLed to any CORESET, then UE determines that CSI-RS RLM configuration is error and does not perform RLM accordingly. In a second novel aspect, SSB for RLM and RLM CSI-RS resources are configured with different numerologies. UE perform SSB based RLM and CSI-RS based RLM based on whether the SSB and CSI-RS resources are TDMed configured by the network. In a third novel aspect, when multiple SMTC configurations are configured to UE, UE determines an SMTC period and whether SMTC and RLM-RS are overlapped for the purpose of RLM evaluation period determination.

Claims

1. A method, comprising: receiving synchronization signal block (SSB) configuration for radio link monitoring (RLM) by a user equipment (UE) in a new radio (NR) network, wherein the SSB occupies a first OFDM symbol having a first numerology; receiving channel state information reference signal (CSI-RS) configuration for RLM by the UE, wherein the configured CSI-RS resource is allocated over a second OFDM symbol having a second numerology; determining whether the SSB and the configured CSI-RS resource are Time Division Multiplexed (TDMed) responsive to the first numerology and the second numerology being different; and performing SSB based RLM and CSI-RS based RLM using the SSB and CSI-RS configuration for RLM based on whether the SSB and the configured CSI-RS resource are TDMed.

2. The method of claim 1, wherein the first numerology and the second numerology being different includes the first numerology and the second numerology having different subcarrier spacing (SCS) values.

3. The method of claim 1, wherein the first numerology and the second numerology being different includes the first numerology and the second numerology having different cyclic-shift prefix (CP) lengths.

4. The method of claim 1, wherein the performing SSB based RLM and CSI-RS based RLM based on whether the SSB and the configured CSI-RS resource are TDMed includes performing SSB based RLM and CSI-RS based RLM only when the SSB and the configured CSI-RS resource are TDMed.

5. The method of claim 1, wherein the performing SSB based RLM and CSI-RS based RLM is further based on whether the UE supports simultaneous reception over different numerologies.

6. The method of claim 5, wherein the performing SSB based RLM and CSI-RS based RLM based on whether the UE supports simultaneous reception over different numerologies includes performing SSB based RLM and CSI-RS based RLM only when the UE does NOT support simultaneous reception over different numerologies.

7. The method of claim 1, further comprising: receiving SSB measurement timing configuration (SMTC) configuration for RLM by the UE; and determining an RLM evaluation period for RLM according to the SMTC configuration for RLM based at least on an SMTC periodicity.

8. The method of claim 7, wherein the SMTC configuration comprises an SMTC periodicity, an SMTC window duration, and a timing offset.

9. The method of claim 7, wherein a first smtc1 and a second smtc2 are configured by the network, and wherein the RLM evaluation period is determined based on the shortest SMTC periodicity.

10. The method of claim 7, wherein the determining the RLM evaluation period is further based on an RLM evaluation scaling factor for channel state information reference signal (CSI-RS) based RLM, and the RLM evaluation scaling factor is associated with whether CSI-RS resources and SMTC window durations are overlapped.

11. A User Equipment (UE), comprising: a synchronization signal block (SSB) based radio link monitoring (RLM) configuration circuit that obtains SSB configuration for RLM in a new radio (NR) network, wherein the SSB occupies a first OFDM symbol having a first numerology; a channel state information reference signal (CSI-RS) based RLM configuration circuit that obtains CSI-RS configuration for RLM, wherein configured CSI-RS resource is allocated over a second OFDM symbol having a second numerology; an RLM control circuit that determines whether the SSB and the configured CSI-RS resource are Time Division Multiplexed (TDMed) responsive to the first numerology and the second numerology being different; and an RLM handling circuit that performs SSB based RLM and CSI-RS based RLM using the SSB and CSI-RS configuration for RLM based on whether the SSB and the configured CSI-RS resource are TDMed.

12. The UE of claim 11, wherein the first numerology and the second numerology being different includes the first numerology and the second numerology having different subcarrier spacing (SCS) values.

13. The UE of claim 11, wherein the first numerology and the second numerology being different includes the first numerology and the second numerology having different cyclic-shift prefix (CP) lengths.

14. The UE of claim 11, wherein the performing SSB based RLM and CSI-RS based RLM based on whether the SSB and the configured CSI-RS resource are TDMed includes performing SSB based RLM and CSI-RS based RLM only when the SSB and the configured CSI-RS resource are TDMed.

15. The UE of claim 11, wherein the performing SSB based RLM and CSI-RS based RLM is further based on whether the UE supports simultaneous reception over different numerologies.

16. The UE of claim 15, wherein the performing SSB based RLM and CSI-RS based RLM based on whether the UE supports simultaneous reception over different numerologies includes performing SSB based RLM and CSI-RS based RLM only when the UE does NOT support simultaneous reception over different numerologies.

17. The UE of claim 11, further comprising: a receiver that receives SSB measurement timing configuration (SMTC) configuration for RLM, wherein the UE determines an RLM evaluation period for RLM according to the SMTC configuration for RLM based at least on an SMTC periodicity.

18. The UE of claim 17, wherein the SMTC configuration comprises an SMTC periodicity, an SMTC window duration, and a timing offset.

19. The UE of claim 17, wherein a first smtc1 and a second smtc2 are configured by the network, and wherein the RLM evaluation period is determined based on the shortest SMTC periodicity.

20. The UE of claim 17, wherein the determining the RLM evaluation period is further based on an RLM evaluation scaling factor for channel state information reference signal (CSI-RS) based RLM, and the RLM evaluation scaling factor is associated with whether CSI-RS resources and SMTC window durations are overlapped.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention.

[0012] FIG. 1 illustrates a system diagram of a new radio (NR) wireless system with SSB and CSI-RS configured for radio link monitoring (RLM) in accordance with embodiments of the current invention.

[0013] FIG. 2 shows simplified block diagrams of a UE and a BS in accordance with embodiments of the current invention.

[0014] FIG. 3 illustrates control resource set (CORESET) configuration and CSI-RS configuration for RLM and their relationship in accordance with one novel aspect of the present invention.

[0015] FIG. 4 illustrates SSB based RLM-RS and CSI-RS based RLM-RS configured with different numerologies and corresponding RLM mechanism.

[0016] FIG. 5 illustrates RLM evaluation period determination based on SMTC configuration in accordance with one novel aspect of the present invention.

[0017] FIG. 6 illustrates one embodiment of determining whether SMTC and RLM-RS are overlapped for determining RLM evaluation period length.

[0018] FIG. 7 is a flow chart of a method for CSI-RS based RLM measurements and in accordance with embodiments of the current invention.

[0019] FIG. 8 is a flow chart of a method for SSB based and CSI-RS based RLM measurements in accordance with embodiments of the current invention.

[0020] FIG. 9 is a flow chart of a method for RLM and RLM evaluation period determination in accordance with embodiments of the current invention.

DETAILED DESCRIPTION

[0021] Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings.

[0022] FIG. 1 illustrates a system diagram of a new radio (NR) wireless system 100 with synchronization signal block (SSB) and channel state information reference signal (CSI-RS) configured for radio link monitoring (RLM) in accordance with embodiments of the current invention. Wireless communication system 100 comprises one or more wireless networks having fixed base infrastructure units, such as receiving wireless communications devices or base units 102 103, and 104, forming wireless radio access networks (RANs) distributed over a geographical region. The base units may also be referred to as an access point (AP), an access terminal, a base station (BS), a Node-B, an eNodeB, an eNB, a gNodeB, a gNB, or by other terminology used in the art. Each of the base unit 102, 103, and 104 serves a geographic area and connects to a core network 109 e.g., via links 116, 117, and 118 respectively. The base unit performs beamforming in the NR system, e.g., in both FR1 (sub7 GHz spectrum) or FR2 (Millimeter Wave frequency spectrum). Backhaul connections 113, 114 and 115 connect the non-co-located receiving base units, such as 102, 103, and 104. These backhaul connections can be either ideal or non-ideal.

[0023] A wireless communications device UE 101 in wireless system 100 is served by base station 102 via uplink 111 and downlink 112. Other UEs 105, 106, 107, and 108 are served by different base stations. UEs 105 and 106 are served by base station 102. UE 107 is served by base station 104. UE 108 is served by base station 103. Each UE may be a smart phone, a wearable device, an Internet of Things (IoT) device, a tablet, etc. For radio link monitoring (RLM) in NR, each UE can be configured to measure synchronization signal (SS) blocks (SSB) and/or channel state information (CSI) reference signal (CSI-RS). With explicit signaling, after UE is connected to a cell, the RLM RS configuration parameters can be configured through radio resource control (RRC) signaling via RadioLinkMonitoringRS, including RS type (SSB or CSI-RS) and RS ID. For CSI-RS, the parameters include CSI-RS Index that is linked to CSI-RS resource configuration, which further includes resource location in time and frequency domain and quasi-co-location (QCL) info through beam indication or transmission configuration indication (TCI) state. For SSB, the parameters include SSB Index that is used to derive SSB location in time domain. There is no QCL info for SSB. RLM RS configuration parameters can also be configured via implicit signaling, e.g., using the RS in TCI state of a COntrol REsource SET (CORESET) when no dedicated signaling for RLM in RRC is available (i.e., RadioLinkMonitoringRS is missing).

[0024] There are certain issues for SSB based RLM and CSI-RS based RLM in NR systems. First, SMTC (SSB measurement timing configuration) is provided for SSB RLM evaluation period determination. If multiple SMTC are present, how to determine the evaluation period for the overlap between RLM-RS and SMTC is ambiguous. Second, how to map CSI-RS based RLM-RS to one COntrol REsource SET (CORESET) for PDCCH parameter determination is undefined. Third, how to handle RLM when SSB for RLM and RLM CSI-RS resources are configured with different numerologies is undefined. Fourth, the definition of overlapping between CSI-RS resource and SMTC window duration is ambiguous so that RLM behavior, e.g., how to determine the RLM evaluation period is also ambiguous.

[0025] In accordance with one novel aspect, methods are proposed to define UE behavior for performing SSB based RLM and CSI-RS based RLM. In a first novel aspect, if CSI-RS based RLM-RS is not QCLed to any CORESET, then UE determines that CSI-RS RLM configuration is error and does not perform RLM accordingly. In a second novel aspect, SSB for RLM and RLM CSI-RS resources are configured with different numerologies (i.e., different SCS, CP). UE will perform SSB based RLM and CSI-RS based RLM only when the SSB and the configured CSI-RS resource are TDMed configured by the network. In a third novel aspect, when multiple SMTC configurations are configured to UE, UE determines an SMTC period for the purpose of RLM evaluation period. UE also determines whether SMTC window duration and RLM-RS resource are overlapped for the purpose of determining the RLM evaluation period.

[0026] FIG. 2 shows simplified block diagrams of a wireless devices, e.g., UE 201 and base station 202 in accordance with the current invention. Base station 202 has an antenna 226, which transmits and receives radio signals. A RF transceiver module 223, coupled with the antenna, receives RF signals from antenna 226, converts them to baseband signals and sends them to processor 222. RF transceiver 223 also converts received baseband signals from processor 222, converts them to RF signals, and sends out to antenna 226. Processor 222 processes the received baseband signals and invokes different functional modules to perform features in base station 202. Memory 221 stores program instructions and data 224 to control the operations of base station 202. Base station 202 also includes a set of control modules and circuits, such as an RLM circuit 281 that performs RLM and an RLM configuration circuit 282 that configures RLM for UEs and communicates with UEs to implement the RLM functions.

[0027] Similarly, UE 201 has an antenna 235, which transmits and receives radio signals. A RF transceiver module 234, coupled with the antenna, receives RF signals from antenna 235, converts them to baseband signals and sends them to processor 232. RF transceiver 234 also converts received baseband signals from processor 232, converts them to RF signals, and sends out to antenna 235. Processor 232 processes the received baseband signals and invokes different functional modules to perform features in mobile station 201. Memory 231 stores program instructions and data 236 to control the operations of mobile station 201. Suitable processors include, by way of example, a special purpose processor, a digital signal processor (DSP), a plurality of micro-processors, one or more micro-processor associated with a DSP core, a controller, a microcontroller, application specific integrated circuits (ASICs), file programmable gate array (FPGA) circuits, and other type of integrated circuits (ICs), and/or state machines.

[0028] UE 201 also includes a set of control modules and circuits that carry out functional tasks. These functions can be implemented in software, firmware and hardware. A processor in associated with software may be used to implement and configure the functional features of UE 201. For example, an SSB based RLM configuration circuit 291 that configures SSB and SMTC windows for RLM; a CSI-RS based RLM configuration circuit 292 that configures CSI-RS resource for RLM; an RLM control and handling circuit 293 that determines whether and how to perform RLM based on the RLM configuration; an RLM report circuit 294 transmits RLM related reports to the network.

[0029] FIG. 3 illustrates control resource set (CORESET) configuration and CSI-RS configuration for RLM and their relationship in accordance with one novel aspect of the present invention. As shown in FIG. 3, a base station can configure more than one CORESET for one UE, e.g., CORESET1 (610) and CORESET2 (620). The CORESETs are configured by the network through RRC signaling after UE is connected to a cell (i.e., UE only knows SMTC of the serving cell). The configuration parameters for CORESET include TCI state and CORESET ID. A TCI state indicates RS ID (i.e., CSI-RS ID or SSB index) and associated QCL type. A CORESET ID indicates the frequency domain resource location, duration, precoder, mapping type etc. of the CORESET. UE can determine CORESET based on different priority rules, e.g., based on CORESET index QCLed with the CSI-RS based RLM-RS.

[0030] In general, determining whether CSI-RS for RLM is QCLed to any CORESET requires time, frequency resource location, and QCL information. However, in some situations, UE may find that the CSI-RS based RLM-RS is not QCLed to any CORESET. Under such condition, UE can determine that the CSI-RS RLM configuration is error and does not perform the corresponding RLM functionality. This is because if the CSI-RS based RLM-RS is not QCLed to any CORESET, then the UE does not know how to receive control parameters over PDCCH. The 3GPP specification defines a first frequency range (FR1) and a second frequency range (FR2). In FR1 (e.g., sub7 GHz), QCL information comprises the reference for Doppler shift, Doppler spread, average delay and delay spread of the configured CSI-RS for RLM. In FR2 (e.g., mmWave), QCL information further includes spatial RX parameters, e.g. the RX beam. Therefore, QCL information in FR2 may be called spatial QCL information, and QCLed means the same RX beam.

[0031] FIG. 4 illustrates SSB based RLM-RS and CSI-RS based RLM-RS configured with different numerologies and corresponding RLM mechanism. In NR, different numerologies are supported with different OFDM frame format, e.g., different subcarrier spacing (SCS), and cyclic prefix (CP) length. Different SCS may include 60 KHz, 120 KHz, 240 KHz, 480 KHz, etc. CSI-RS based RLM-RS and SSB based RLM-RS are configurable over the same or different OFDM symbols having the same or different numerologies. As shown in FIG. 4, CSI-RS based RLM-RS and SSB based RLM-RS are multiplexed in the same OFDM symbol but do not have the same SCS, and UE may not support simultaneous receiving over different numerologies. For example, in the same OFDM symbol, CSI-RS based RLM-RS is configured with SCS=60 KHz, and SSB based RLM-RS is configured with SCS=120 kHz.

[0032] When UE does not support simultaneous reception over different numerologies (e.g., different SCS or different CP length), SSB for RLM and RLM CSI-RS resources should be TDMed configured to UE. UE will not perform SSB based RLM and CSI-RS based RLM simultaneously. Instead, UE performs SSB based RLM or CSI-RS based RLM one at a time. Note the definition for TDMed configuration means that the configured SSB and CSI-RS resources should be completely not overlapped in time domain, e.g., they do not have any overlapping in time domain. In other words, the configured SSB and CSI-RS resources should not have any overlapping and should not have any partial overlapping, especially when the OFDM symbol lengths for SSB and CSI-RS resources are different.

[0033] For RLM, UE needs to evaluate whether the downlink radio link quality on the configured RLM-RS resource estimated over a first evaluation period becomes worse than a first threshold within the first evaluation period T.sub.EVALUATE_out_SSB. UE also needs to evaluate whether the downlink radio link quality on the configured RLM-RS resource estimated over a second evaluation period becomes better than a second threshold within the second evaluation period T.sub.EVALUATE_in_SSB. For FR1 and FR2, the length of the evaluation period depends on N (RX beam scaling factor) and P (evaluation scaling factor), which in turn depends on how RLM-RS resources and SMTC occasions are configured for UE. SMTC is configured by the network through System Information or RRC signaling after UE is connected to the network (i.e., UE can know SMTC of other cells. The configuration parameters for SMTC include offset, duration, and periodicity. In general, SSBs inside SMTC are used for L3 measurements, and SSBs outside SMTC are used for L1 measurements (e.g., RLM).

[0034] Both T.sub.EVALUATE_out_SSB and T.sub.EVALUATE_in_SSB are defined for FR1 and FR2 in the 3GPP specification. For FR1, P=1/(1−T.sub.SSB/MGRP), when in the monitored cell there are measurement gaps configured for intra-frequency, inter-frequency or inter-RAT measurements, which are overlapping with some but not all occasions of the SSB; P=1, when the monitored cell there are no measurement gaps overlapping with any occasion of the SSB. For FR2, P=1/(1−T.sub.SSB/T.sub.SMTCperiod) when RLM-RS is not overlapped with measurement gap and RLM-RS is partially overlapped with SMTC occasion (T.sub.SSB<T.sub.SMTCperiod); P=3, when RLM-RS is not overlapped with measurement gap and RLM-RS is fully overlapped with SMTC period (T.sub.SSB=T.sub.SMTCperiod); P=1/(1−T.sub.SSB/MGRP−T.sub.SMTCperiod) when RLM-RS is partially overlapped with measurement gap and RLM-RS is partially overlapped with SMTC occasion (T.sub.SSB<T.sub.SMTCperiod) and SMTC occasion is not overlapped with measurement gap and (T.sub.SMTCperiod≠MGRP) or (T.sub.SMTCperiod=MGRP and TSSB<0.5*T.sub.SMTCperiod); P=1/(1−T.sub.SSB/MGRP)*3, when RLM-RS is partially overlapped with measurement gap and partially overlapped with SMTC occasion (T.sub.SSB<T.sub.SMTCperiod) and SMTC occasion is not overlapped with measurement gap and T.sub.SMTCperiod=MGRP and TSSB=0.5*T.sub.SMTCperiod; P=1/{1−T.sub.SSB/Min (T.sub.SMTCperiod, MGRP)}, when RLM-RS is partially overlapped with measurement gap and RLM-RS is partially overlapped with SMTC occasion (T.sub.SSB<T.sub.SMTCperiod) and SMTC occasion is partially or fully overlapped with measurement gap; P=1/(1−T.sub.SSB/MGRP)*3, when RLM-RS is partially overlapped with measurement gap and RLM-RS is fully overlapped with SMTC occasion (T.sub.SSB=T.sub.SMTCperiod) and SMTC occasion is partially overlapped with measurement gap (T.sub.SMTCperiod<MGRP). Similarly, the above definition also works for CSI-RS based RLM, it reuses the evaluation time by replacing T.sub.SSB.fwdarw.T.sub.CSI-RS.

[0035] FIG. 5 illustrates RLM evaluation period determination based on RLM-RS and SMTC configuration in accordance with one novel aspect of the present invention. As explained above, when RLM-RS collides with SMTC occasion in FR2, the evaluation scaling factor P is introduced and it depends on the measurement gap (MGRP), the RLM-RS (SSB) periodicity (T.sub.SSB), and the SMTC periodicity (T.sub.SMTCperiod). As depicted in 510, RLM-RS are fully overlapped with SMTC2; while as depicted in 520, RLM-RS are partially overlapped with SMTC1. However, multiple SMTC may be configured. For example, smtc1 is the primary measurement timing configuration. In addition, smtc2 is the secondary measurement timing configuration, for SS corresponding to a measurement object with PCI listed in PCI-List. For these SS, the periodicity is indicated by periodicity in smtc2 and the timing offset is equal to the offset indicated by periodicityAndOffset modulo periodicity. The periodicity in smtc2 can only be set to a value strictly shorter than the periodicity indicated by periodicityAndOffset in smtc1 (e.g. if periodicityAndOffset indicates sf10, periodicity can only be set of sf5, if periodicityAndOffset indicates sf5, smtc2 cannot be configured). If smtc2 is present, UE is configured with two SMTC configurations. These two SMTCs, smtc1 and smtc2, must have same Duration and Offset but they may have different Periodicity values. Accordingly, if smtc2 is present, to avoid ambiguity on deriving the evaluation scaling factor P in FR2, the ISMTCperiod is set to be equal to min (smtc1 Periodicity, smtc2 Periodicity). In one preferred embodiment, SMTC2 is always shorter than SMTC1, e.g. min (smtc1 Periodicity, smtc2 Periodicity)=smtc2 Periodicity.

[0036] FIG. 6 illustrates one embodiment of determining whether SMTC and CSI-RS based RLM-RS are overlapped for determining RLM evaluation period length. The evaluation scaling factor P depends on whether SMTC occasion and CSI-RS based RLM-RS are overlapped or not. However, the definition on overlap between CSI-RS based RLM-RS and SMTC occasion is ambiguous so that determination of CSI-RS based RLM evaluation period remains ambiguous. There can be different scenarios of how RLM CSI-RS and SMTC are overlapped. In a first scenario, as depicted by CSI-RS 610, the CSI-RS resource is located within the SMTC window duration. In a second scenario, CSI-RS 620 resource is located within the SMTC window duration and also within an SSB. In a third scenario, CSI-RS 630 resource is located within the SMTC window duration, but also within a scheduling availability. Accordingly, UE determines that the SMTC window duration and the CSI-RS based RLM-RS are overlapped as long as the RLM CSI-RS resource is within the SMTC window duration, regardless whether the RLM CSI-RS is located within an SSB or located within a scheduling availability inside SMTC occasion.

[0037] FIG. 7 is a flow chart of a method for CSI-RS based RLM measurements and in accordance with embodiments of the current invention. In step 701, a UE receives core resource set (CORESET) configuration in a new radio (NR) network. The CORESET configuration comprises one or more CORESETs for the UE. In step 702, the UE receives radio link monitoring (RLM) configuration comprising resource information of a plurality of channel state information reference signals (CSI-RSs) for RLM. In step 703, the UE determines whether a configured CSI-RS for RLM is Quasi-Co-Located (QCLed) to any CORESET according to the resource information of the CSI-RSs. In step 704, the UE performs RLM measurements using the configured CSI-RS for RLM only when the configured CSI-RS for RLM is QCLed to at least one CORESET.

[0038] FIG. 8 is a flow chart of a method for SSB based and CSI-RS based RLM measurements in accordance with embodiments of the current invention. In step 801, a UE receives synchronization signal block (SSB) configuration for radio link monitoring (RLM) in a new radio (NR) network. The SSB occupies a first OFDM symbol having a first numerology. In step 802, the UE receives channel state information reference signal (CSI-RS) configuration for RLM. The configured CSI-RS resource is allocated over a second OFDM symbol having a second numerology. In step 803, the UE determines whether the SSB and the configured CSI-RS resource are time division multiplexed (TDMed) responsive to the first numerology and the second numerology being different. In step 804, the UE performs SSB based RLM and CSI-RS based RLM using the SSB and CSI-RS configuration for RLM and based on whether the SSB and the CSI-RS resource are TDMed.

[0039] FIG. 9 is a flow chart of a method for RLM and RLM evaluation period determination in accordance with embodiments of the current invention. In step 901, a UE receives synchronization signal block (SSB) measurement timing configuration (SMTC) for radio link monitoring (RLM) in a new radio (NR) network. In step 902, the UE determines an RLM evaluation period according to the SMTC configuration based at least on an SMTC periodicity. In step 903, the UE performs CSI-RS based RLM using the determined RLM evaluation period.

[0040] Although the present invention has been described in connection with certain specific embodiments for instructional purposes, the present invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.