HK1223761B - Methods, network nodes and user equipment for adaptive radio link monitoring - Google Patents

Description

Method, network node and user equipment for adaptive radio link monitoring

Technical Field

Disclosed herein are, for example, methods, network nodes, user equipment, and computer program products for adaptive radio link monitoring (RLM).

Background Art

Radio Link Monitoring (RLM), used by user equipment (UE) to assess serving cell performance, is defined assuming a dual UE receiver implementation. Corresponding predefined and configurable parameters associated with RLM are used regardless of the UE receiver implementation and capabilities. However, it is expected that UEs with a single receiver or more than two receivers can be used. Applying existing RLM procedures and parameter settings to these new UE receiver capabilities may incorrectly assess and detect radio link issues.

The UE performs measurements on a serving cell (e.g., a primary cell) to monitor serving cell performance. This is known as radio link monitoring (RLM) measurements, or, in LTE, RLM-related measurements. For RLM, the UE monitors downlink link quality based on cell-specific reference signals to detect the downlink radio link quality of the serving cell, or PCell.

To detect the Out-of-Sync (OOS) state and In-Sync (IS) state, the UE compares the estimated DL signal quality of the serving cell with the thresholds Qout and Qin, respectively. The thresholds Qout and Qin are defined as the levels at which the downlink radio link cannot be reliably received, corresponding to an assumed block error rate of 10% and 2% for PDCCH transmissions, respectively. In non-DRX, the downlink link quality for Out-of-Sync and In-Sync is estimated using an evaluation period of 200ms and 100ms, respectively. In DRX, the downlink link quality for Out-of-Sync and In-Sync is estimated using the same evaluation period (scaled with the DRX cycle). In addition to the filtering at the physical layer (i.e., the evaluation period), the UE also applies higher-layer filtering based on network-configured parameters. This increases the reliability of Radio Link Failure Detection (RLM), thereby avoiding unnecessary radio link failures and subsequent RRC re-establishments. After detecting a certain number of consecutive OOS and RLF timer expiration, the UE declares RLF.

Assuming that the transmission parameters of PDCCCH/PCFICH for OOS and IS detection comply with Table 1 ( FIG. 1 ) and Table 2 ( FIG. 2 ), respectively, the UE is required to meet RLM (ie, OOS and IS quality targets).

In LTE, the baseline UE receiver (interchangeably referred to as a radio receiver or radio chain or IFFT/FFT) is a dual receiver (e.g., 2-way receiver diversity). UE requirements, including RLM, are defined under the assumption of a dual receiver. More complex UE receivers that can mitigate inter-cell interference were introduced in later releases (Release 11 and later). However, they still rely on a dual-receiver baseline architecture. The terms "interference mitigation (IM) receiver," "interference cancellation (IC) receiver," "interference suppression receiver," "interference rejection receiver," "interference aware receiver," "interference avoidance receiver," etc., are used interchangeably, but all belong to the category of advanced receivers or enhanced receivers.

Inter-cell interference mitigation refers to the receiver capability of mitigating interference caused by at least some signals received at the UE receiver from at least one interfering cell (e.g., an attacker cell). In Release 12 and later, UE requirements for a single receiver and more than two receivers (e.g., 4-way receiver diversity) may be introduced. Examples of well-known receiver types include IC/IM, MMSE, MMSE-IRC, Maximum Likelihood (ML), Successive Interference Cancellation (SIC), Parallel Interference Cancellation (PIC) receivers, or any combination thereof. Examples of receiver types in terms of their ability to mitigate specific types of interfering signals include CRS-IM, PSS/SSS IC, PBCH IC, PDCCH IC, PDSCH IC receivers, etc.

Machine-to-machine (M2M) communication (e.g., machine-type communication (MTC)) is used to establish communication between machines and between machines and humans. This communication may include the exchange of data, signaling, measurement data, configuration information, etc. Devices can range in size from a wallet to a base station. M2M devices are often used for applications such as sensing environmental conditions (e.g., temperature readings), metering or measurement (e.g., electricity usage), and fault or error detection. In these applications, M2M devices are activated infrequently over continuous periods, depending on the type of service, e.g., 200 ms every two seconds, 500 ms every 60 minutes, etc. M2M devices may also perform measurements on other frequencies or other RATs.

One class of M2M devices is referred to as a low-cost device type. For example, cost reduction can be achieved by having only one receiver in the UE. Further cost reduction can be achieved by having a single receiver and half-duplex FDD capability. The latter feature can suppress the need to have a duplex filter because the UE does not transmit and receive at the same time. Low-cost UEs can also implement more cost features, such as a downlink and uplink maximum transport block size (TBS) of 1000 bits and a reduced downlink channel bandwidth of 1.4 MHz for data channels (such as PDSCH). For example, a low-cost UE may include a single receiver and one or more of the following additional features: HD-FDD, a downlink and/or uplink maximum transport block size (TBS) of 1000 bits and a reduced downlink channel bandwidth of 1.4 MHz for data channels (such as PDSCH).

Another class of M2M devices is required to support enhanced UL and/or DL coverage. These devices are installed in locations where the path loss between the M2M device and the base station may be large when they are used as sensors or metering devices located in remote locations (such as the basement of a building). In these scenarios, receiving signals from the basement is very challenging. For example, the path loss may be 15-20dB worse than in normal operation. To address this challenge, the coverage in the uplink direction and/or downlink direction must be substantially enhanced. This can be achieved by using one or more of the advanced techniques for enhancing coverage in the UE and/or radio network nodes (e.g., increasing DL transmit power, increasing UL transmit power, enhanced UE receivers, signal repetition, etc.).

The UE and its serving network node need to meet radio link monitoring (RLM) requirements predefined in the standard. These requirements are based on the assumption that the UE has dual receivers (also known as two-way receiver diversity). RLM performance significantly impacts cell coverage. Network planning (e.g., cell size, distance between base station sites, etc.) also depends on RLM performance, as well as other factors (e.g., base station power class). Another type of low-cost M2M device includes a UE with a single receiver. Current RLM procedures and associated parameters for dual UE receiver implementations can impair the assessment of serving cell performance. For example, a UE may lose coverage of its serving cell and be unable to find another, stronger cell, resulting in it becoming lost in a coverage hole or dead cell area. Similarly, current RLM settings may not be suitable for high-end UEs with more than two receivers, as these settings may cause the UE to overestimate serving cell performance. This problem is further exacerbated when such high-end UEs automatically change or are configured to adapt to the number of receivers actually receiving signals. In this scenario, the UE's RLM behavior is uncertain, and this ambiguity can lead to poor serving cell performance.

Summary of the Invention

According to some embodiments, a method for adaptive radio link monitoring (RLM) includes obtaining configuration information related to a user equipment (UE) receiver configuration, wherein the UE receiver configuration is associated with the UE and implemented by the UE to receive signals from a network node. The method also includes: the network node adapting, based on the obtained configuration information, at least one radio transmission parameter associated with at least one downlink (DL) signal used by the UE to perform RLM. The method also includes: the network node transmitting at least one DL signal to the UE using the adapted at least one parameter to enable the UE to perform RLM.

In some embodiments, the configuration information includes one or more of: a maximum number of supported receivers, a current number of receivers used to receive DL signals, and an indication of the ability to mitigate interference caused by interfering signals.

In some embodiments, the step of obtaining the configuration information comprises receiving said configuration information from the UE or determining the configuration information based on one or more radio measurements performed by the UE.

In some embodiments, the obtained configuration information indicates that the UE receiver is capable of at least one of: receiving signals using a single receiver, and receiving signals using multiple receivers simultaneously.

In some embodiments, the obtained configuration information instructs the UE receiver to mitigate interference received from one or more interfering cells, wherein mitigating interference received from one or more interfering cells includes mitigating interference from at least one or more of a DL data channel, a DL control channel, and a DL physical signal received at the UE.

In some embodiments, the at least one DL signal includes one or more of a DL physical signal and a DL physical channel.

In some embodiments, the DL physical signal is one or more of a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), a channel state information reference signal (CSI-RS), and a positioning reference signal (PRS).

In some embodiments, the DL physical channel is one or more of a physical downlink control channel (PDCCH), a physical control format indicator channel (PCFICH), a physical hybrid ARQ indicator channel (PHICH), and an enhanced physical downlink control channel (E-PDCCH).

In some embodiments, the DL physical channel is a Physical Downlink Shared Channel (PDSCH).

In some embodiments, the at least one radio transmission parameter includes one or more of the following: transmit power of the DL signal, a ratio of the energy or power of the DL signal to the average energy or power of the reference signal, the number of OFDM symbols used to send the DL signal, the format of the DL signal, the aggregation level of the DL signal, and the bandwidth of the DL signal.

In some embodiments, in response to determining that the UE indicates that the UE is capable of receiving the signal with a single receiver, the step of adapting at least one radio transmission parameter includes at least one of the following: increasing the transmit power of the DL signal; increasing the ratio of the energy or power of the DL signal to the average energy or power of the reference signal; increasing the number of OFDM symbols used to send the DL signal; selecting a format of the DL signal associated with signal reception at the UE using only a single receiver; increasing the aggregation level of the DL signal; and increasing the number of repetitions of the same DL signal in the time domain.

In some embodiments, when the configuration information indicates that the UE is capable of receiving signals with multiple receivers and/or mitigating interference received from one or more interfering cells, the step of adapting at least one radio transmission parameter includes at least one of the following: reducing the transmit power of the DL signal; reducing the ratio of the energy or power of the DL signal to the average energy or power of the reference signal; reducing the number of OFDM symbols used to send the DL signal; selecting a format of the DL signal associated with signal reception at the UE using multiple receivers and/or mitigating interference received from one or more interfering cells; reducing the aggregation level of the DL signal; and reducing the number of repetitions of the same DL signal in the time domain.

In some embodiments, the step of adapting at least one radio transmission parameter enables the UE to maintain the same DL radio link out-of-sync quality target level and synchronization quality target level regardless of the UE receiver capability of receiving the DL signal from the network node, wherein the out-of-sync quality target level indicates one or more levels for declaring that the state of the UE is an out-of-sync state, and the synchronization quality target level indicates one or more levels for declaring that the state of the UE is an in-sync state.

In some embodiments, the adaptation of at least one parameter related to at least one DL signal is performed according to one or more predefined rules.

In some embodiments, the adaptation is further based on whether DL coverage enhancement is applied to the DL signal sent by the network node for the UE.

In some embodiments, the obtained receiver configuration indicates that the UE supports multiple receiver types for receiving signals from the network node, and the network node configures (702) the UE to operate with one of the multiple receiver types supported by the UE.

In some embodiments, the method further comprises: based on the obtained configuration information, the network node determining (802) whether the UE is operating in enhanced coverage mode; and based on determining that the UE is operating in enhanced coverage mode, the network node adapting (804) at least one radio transmission parameter associated with at least one downlink (DL) signal used by the UE to perform RLM.

According to some embodiments, a network node for adaptive radio link monitoring (RLM) is arranged to obtain configuration information related to a user equipment (UE) receiver configuration, wherein the UE receiver configuration is associated with the UE and implemented by the UE to receive signals from the network node. The network node is further arranged to adapt at least one radio transmission parameter associated with at least one downlink (DL) signal used by the UE to perform RLM based on the obtained configuration information. The network node is further arranged to send at least one DL signal to the UE with the adapted at least one parameter, enabling the UE to perform RLM.

In some embodiments, the network node further includes a processor and a computer-readable medium coupled to the processor, wherein the computer-readable medium contains instructions executable by the processor.

In some embodiments, the configuration information includes one or more of: a maximum number of supported receivers, a current number of receivers used to receive DL signals, and an indication of the ability to mitigate interference caused by interfering signals.

In some embodiments, obtaining the configuration information comprises receiving the configuration information from the UE or determining the configuration information based on one or more radio measurements performed by the UE.

In some embodiments, the obtained configuration information indicates that the UE receiver is capable of at least one of: receiving signals using a single receiver, and receiving signals using multiple receivers simultaneously.

In some embodiments, the obtained configuration information instructs the UE receiver to mitigate interference received from one or more interfering cells, wherein mitigating interference received from one or more interfering cells includes mitigating interference from at least one or more of a DL data channel, a DL control channel, and a DL physical signal received at the UE.

In some embodiments, the at least one DL signal includes one or more of a DL physical signal and a DL physical channel.

In some embodiments, the DL physical signal is one or more of: a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), a channel state information reference signal (CSI-RS), and a positioning reference signal (PRS).

In some embodiments, the DL physical channel is one or more of: Physical Downlink Control Channel (PDCCH), Physical Control Format Indicator Channel (PCFICH), Physical Hybrid ARQ Indicator Channel (PHICH), and Enhanced Physical Downlink Control Channel (E-PDCCH).

In some embodiments, the DL physical channel is a Physical Downlink Shared Channel (PDSCH).

In some embodiments, the at least one radio transmission parameter includes one or more of the following: transmit power of the DL signal, a ratio of the energy or power of the DL signal to the average energy or power of the reference signal, the number of OFDM symbols used to send the DL signal, the format of the DL signal, the aggregation level of the DL signal, and the bandwidth of the DL signal.

In some embodiments, in response to determining that the UE indicates that the UE is capable of receiving the signal with a single receiver, the step of adapting at least one radio transmission parameter includes at least one of the following: increasing the transmit power of the DL signal; increasing the ratio of the energy or power of the DL signal to the average energy or power of the reference signal; increasing the number of OFDM symbols used to send the DL signal; selecting a format of the DL signal associated with signal reception at the UE using only a single receiver; increasing the aggregation level of the DL signal; and increasing the number of repetitions of the same DL signal in the time domain.

In some embodiments, when the configuration information indicates that the UE is capable of receiving signals with multiple receivers and/or mitigating interference received from one or more interfering cells, the step of adapting at least one radio transmission parameter includes at least one of the following: reducing the transmit power of the DL signal; reducing the ratio of the energy or power of the DL signal to the average energy or power of the reference signal; reducing the number of OFDM symbols used to send the DL signal; selecting a format of the DL signal associated with signal reception at the UE using multiple receivers and/or mitigating interference received from one or more interfering cells; reducing the aggregation level of the DL signal; and reducing the number of repetitions of the same DL signal in the time domain.

In some embodiments, adapting at least one radio transmission parameter enables the UE to maintain the same DL radio link out-of-sync quality target level and synchronization quality target level regardless of the UE receiver capability of receiving the DL signal from the network node, wherein the out-of-sync quality target level indicates one or more levels for declaring that the state of the UE is an out-of-sync state, and the synchronization quality target level indicates one or more levels for declaring that the state of the UE is an in-sync state.

In some embodiments, the adaptation of at least one parameter related to at least one DL signal is performed according to one or more predefined rules.

In some embodiments, the adaptation is further based on whether DL coverage enhancement is applied to the DL signal sent by the network node for the UE.

In some embodiments, the obtained receiver configuration indicates that the UE supports a plurality of receiver types for receiving signals from the network node, and the network node configures the UE to operate with one of the plurality of receiver types supported by the UE.

In some embodiments, the network node is further arranged to, based on the obtained configuration information, determine whether the UE is operating in enhanced coverage mode; and based on determining that the UE is operating in enhanced coverage mode, adapt at least one radio transmission parameter associated with at least one downlink DL signal used by the UE to perform RLM.

According to some embodiments, a computer product for adaptive radio link monitoring includes a non-transitory computer-readable medium storing computer instructions for obtaining configuration information related to a user equipment (UE) receiver configuration, the UE receiver configuration being associated with the UE and implemented by the UE to receive signals from a network node. The readable medium also includes instructions for adapting at least one radio transmission parameter associated with at least one downlink (DL) signal used by the UE to perform RLM based on the obtained information. The readable medium also includes instructions for sending at least one DL signal to the UE with the adapted at least one parameter to enable the UE to perform RLM.

In accordance with some embodiments, a method for adaptive radio link monitoring includes, based on a current number of receivers used by a user equipment (UE) to receive downlink (DL) signals from a network node and/or a currently used receiver type for mitigating interference caused by an interfering signal, the UE determining a receiver configuration. The method also includes: the UE receiving at least one DL signal having at least one parameter from the network node, wherein the at least one parameter is adapted for the UE to perform RLM based on a receiver capability of the UE to receive the DL signal. The method also includes performing RLM on the DL signal received from the network node. In some embodiments, the method also includes, in response to determining to adapt the DL signal for use by the UE for the determined receiver configuration, maintaining substantially the same DL radio link desynchronization quality target and synchronization quality target regardless of the UE receiver configuration.

In some embodiments, the determination of the receiver configuration is further based on configuration information or messages received by the network node.

In some embodiments, the receiver type includes one or more of: a receiver capable of receiving signals with only a single receiver, a receiver capable of receiving signals simultaneously with multiple receivers, and a receiver capable of mitigating interference received from one or more interfering cells.

In some embodiments, the method further includes: the UE determining whether the UE is operating in DL coverage enhancement mode or is configured to operate in DL coverage enhancement mode; and if operating in DL enhanced coverage mode, the UE adapting one or more RLM-related parameters or RLM procedures based on predetermined rules.

According to some embodiments, a user equipment (UE) served by a network node for performing radio link monitoring (RLM) by monitoring downlink quality of signals sent by the network node, the UE being arranged to determine a receiver configuration based on a current number of receivers used by the UE for receiving downlink (DL) signals from the network node and/or a currently used type of receiver for mitigating interference caused by an interfering signal.

The UE is further arranged to: receive at least one DL signal having at least one parameter from the network node, wherein the at least one parameter is adapted for the UE to perform RLM according to a receiver capability of the UE for receiving the DL signal. The UE is further arranged to perform RLM on the DL signal received from the network node.

In some embodiments, the UE further includes a processor and a computer-readable medium coupled to the processor, the computer-readable medium containing instructions executable by the processor.

In some embodiments, the UE is further arranged to, in response to determining to adapt the DL signal for use by the UE for the determined receiver configuration, maintain substantially the same DL radio link out-of-sync quality target and synchronization quality target regardless of the UE receiver configuration.

In some embodiments, the determination of the receiver configuration is further based on configuration information or messages received by the network node.

In some embodiments, the receiver type includes one or more of: a receiver capable of receiving signals with only a single receiver, a receiver capable of receiving signals simultaneously with multiple receivers, and a receiver capable of mitigating interference received from one or more interfering cells.

In some embodiments, the UE is further arranged to: determine whether the UE is operating or configured to operate in DL coverage enhancement mode; and if operating in DL enhanced coverage mode, adapt one or more RLM related parameters or RLM procedures based on predetermined rules.

According to some embodiments, a computer product for managing a network node includes a non-transitory computer-readable medium storing computer instructions for determining a receiver configuration based on the current number of receivers used by a user equipment (UE) to receive downlink (DL) signals from the network node and/or the type of receivers currently used to mitigate interference caused by interfering signals. The readable medium also includes instructions for receiving at least one DL signal having at least one parameter from the network node, wherein the at least one parameter is adapted to enable the UE to perform RLM based on a receiver capability of the UE for receiving the DL signal. The readable medium also includes instructions for performing RLM on the DL signal received from the network node.

According to an embodiment, a serving network node of a UE adapts one or more radio transmission parameters of a DL signal used by the UE to perform RLM operations, wherein the adaptation is based on the UE receiver configuration and is performed to ensure consistent DL radio link performance for the serving cell regardless of the UE receiver configuration. The adaptation may be performed according to predefined rules.

According to some embodiments, a network node serving a UE obtains a receiver configuration of the UE, the receiver configuration relating to the number of receivers supported by the UE and/or the currently used or supported receiver types with respect to their interference mitigation capabilities, and/or the number of receivers actually used or currently used by the UE for receiving downlink signals to perform radio link monitoring (RLM). The network node adapts one or more radio transmission parameters of one or more downlink signals used by the UE for RLM, wherein the adaptation is based on the obtained UE receiver configuration, either according to predefined rules or autonomously. The network node also transmits the adapted downlink radio signal to enable the UE to perform RLM.

If the network node determines to use enhanced coverage mode operation to enhance the reception quality of the DL signal at the UE, the network node may further adapt one or more radio transmission parameters.

According to some embodiments, a UE served by a network node determines a current receiver configuration of the UE, the current receiver configuration relating to a currently used receiver type with respect to its ability to mitigate interference, and/or a number of receivers actually or currently used to receive downlink radio signals for performing RLM. The UE receives radio signals from a first cell served by the network node, wherein the network node adapts radio transmission parameters related to the downlink radio signals used by the UE for RLM according to the UE receiver configuration. Based on the adapted downlink radio signals received from the first cell, the UE performs RLM for the first cell while maintaining or using the same radio link quality targets for detection of out-of-sync and synchronization regardless of the UE receiver configuration, and satisfying one or more predefined requirements associated with RLM.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate various embodiments.

Figures 1 and 2 show tables for RLM.

FIG3 illustrates an example wireless communication system in accordance with some embodiments.

FIG4 is a flow chart illustrating a process according to some embodiments.

Figures 5 and 6 show the in-sync and out-of-sync plots respectively.

FIG7 is a flow chart illustrating a process according to some embodiments.

FIG8 is a flow chart illustrating a process according to some embodiments.

FIG9 is a flow chart illustrating a process according to some embodiments.

FIG10 is a block diagram of a network node according to some embodiments.

FIG11 is a block diagram of a UE according to some embodiments.

DETAILED DESCRIPTION

FIG3 illustrates an embodiment of a wireless communication system 300, including UEs 302 and 308 communicating with base stations 304 and 310, respectively. Base stations 304 and 310 provide coverage for cells 306 and 312, respectively. Cells 306 and 312 may operate at frequencies f1 and f2, respectively. Base stations 304 and 310 communicate with a network node 316 via a network 314. Network node 316 may be any network node, such as a radio network controller (RNC), a mobility management entity (MME), a mobile switching center (MSC), or a base station subsystem (BSS).

In some embodiments, the non-limiting term UE is used. A UE herein may be any type of wireless device capable of communicating with a network node or another UE via radio signals. A UE may also be a radio communication device, a target device, a device-to-device (D2D) UE, a machine-type UE, or a UE with machine-to-machine (M2M) communication capabilities, a sensor equipped with a UE, an iPad, a tablet, a mobile terminal, a smartphone, a laptop embedded device (LEE), a laptop mounted device (LME), a USB adapter, or a customer premises equipment (CPE).

In addition, in some embodiments, general terms such as "radio network node" or simply "network node (NW node)" are used. A network node may be any type of network node, including a base station, a radio base station, a base transceiver station, a base station controller, a network controller, an evolved Node B (eNB), a Node B, a relay node, an access point, a radio access point, a remote radio unit (RRU), a remote radio head (RRH), etc.

The embodiments are described using LTE concepts. However, the embodiments are applicable to any RAT or multi-RAT system where the UE regularly uses the RLM procedure or equivalent procedures to evaluate the performance of the serving cell, such as LTE FDD/TDD, WCDMA/HSPA, GSM/GERAN, WiFi, CDMA2000, etc.

Some embodiments include scenarios involving adapting RLM-related parameters taking into account UE receiver capabilities. Some embodiments include a method in a network node for adapting RLM-related radio transmission parameters taking into account UE receiver capabilities. Some embodiments include a method in a UE for adapting RLM-related parameters taking into account UE receiver capabilities.

The scenario includes at least one UE being served by a first cell (e.g. a serving cell or PCell of the UE), which is managed by a network node. The first cell operates on a first carrier frequency (f1). The UE evaluates out-of-sync (OOS) and in-sync (IS) based on DL radio signals received from the first cell to assess its DL radio quality for the purpose of radio link monitoring of the first cell. If a radio link failure occurs (e.g. caused by continuous IS monitoring), the UE initiates an RRC connection to a second cell, which may belong to carrier frequency f1 or another carrier frequency f2. Carrier frequency f1 and carrier frequency f2 may belong to the same RAT, or even to different RATs. To ensure that the UE can correctly receive signals (e.g. DL control channels, such as PDCCH/PCFICH), the network node needs to ensure that the radio transmission parameters associated with the DL control channels comply with predefined requirements for the relevant RLM.

Unlike existing systems where all UEs have dual receivers, the UE in this article can have any number of receivers (Rx) from 1 to N (for example, typically 1 to 4 Rx). In addition, a UE with multiple Rx can use any number of receivers from 1 Rx to N Rx to receive DL signals from at least one serving cell. The UE can autonomously change the number of receivers to be used, or the UE can be configured by a network node. In addition, the autonomous operation of modifying the number of receivers to be used can also be based on predefined conditions or rules. For example, if the signal quality is above a certain threshold, the UE can use N-M Rx (M < N).

According to some embodiments, a method in a network node operates according to the scenario described above. The method can be expressed in the form of rules, which can be predefined in a standard and applied by a network node that configures a UE to perform RLM. FIG4 shows an exemplary flow chart for implementing the method. The steps in the network node described below can be performed in the network node in a specific order or in any order or sequence.

Processing may begin at 400, where the network node obtains information related to the UE receiver configuration. In this regard, the network node obtains, determines, or identifies the UE receiver configuration. The UE receiver configuration may include the UE receiver capabilities (the maximum number of receivers supported by the UE or the types of receivers supported) and the current number of receivers used by the UE to receive DL signals or the types of receivers currently used. The term receiver configuration may be represented by the number of receivers supported by the UE or used to receive downlink signals from a first cell (e.g., for radio link monitoring). In another example, the receiver configuration may be determined by the type of receiver currently used to mitigate interference caused by one or more radio signals. The interference signal may come from the serving cell and/or one or more interfering cells and be received at the UE. In another example, the receiver configuration may include a combination of the two exemplary receiver configurations mentioned above (i.e., the number of receivers and the type of receivers).

In some embodiments, the determination in step 400 may be based on explicit information. For example, the network node receives explicit information related to the receiver configuration from the UE, or receives it from another network node containing such information (e.g., the UE's previous serving network node). When the network node knows the UE's receiver capabilities, the network node may also configure the UE with a certain number of receivers. In this case, the network node obtains the configured information to determine the UE's receiver configuration.

In some embodiments, the determination in step 400 may be based on implicit information. For example, the network node may determine the UE receiver configuration based on predefined rules and/or UE radio measurement results (e.g., DL signal quality, such as RSRQ or RSRP). An example of a predefined rule is that the UE may adapt its receiver configuration based on signal quality, for example, if the serving cell performance is better than the target (e.g., HARQ BLER is below a threshold, such as <1%), the UE may use fewer receivers. In another example, if the radio measurement results (e.g., RSRQ) reported by the UE are above a threshold, the network node may assume that the higher signal quality is due to the fact that the UE is using all of its receivers or more than one receiver.

According to some embodiments, the determination in step 400 may be based on both explicit and implicit information. For example, the network node may receive explicit information about the UE's receiver configuration (e.g., the maximum number of receivers supported). However, the actual number of receivers currently used by the UE is determined implicitly, for example, based on UE measurement reports.

From step 400, processing proceeds to step 402, where the network node adapts at least one radio transmission parameter associated with at least one DL signal used by the UE to perform RLM based on the obtained UE receiver configuration. For example, in this step, the network node adapts one or more radio transmission parameters associated with at least one downlink signal used by the UE to perform radio link monitoring (RLM). This adaptation is performed to enable the UE to meet one or more predetermined requirements related to RLM, thereby ensuring that the DL serving cell quality remains within acceptable limits. For example, as shown in Figures 5 and 6, for both OOS and IS detection, the DL transmit power will be increased by a certain amount for 1 Rx compared to 2 Rx. For UE implementations or configurations with 1 Rx and 2 Rx, additional parameters may also need to be adapted to achieve the same quality threshold.

Examples of radio transmission parameters include, but are not limited to: the transmit power of the DL signal, the ratio of the energy or power of the DL signal to the average energy or power of the reference signal (such as CRS), the number of OFDM symbols used to send the DL signal, the format of the DL signal (for example, the downlink control channel information (DCI) format of the DL channel), the aggregation level of the DL signal (for example, the number of control channel elements (CCE)), the bandwidth of the DL signal, and the number of repetitions of the same signal in the time domain. The DCI formats differ in their processing structure and their information content. The former is characterized by unit multiplexing, CRC attachment, channel coding, and rate matching. The latter includes downlink or uplink scheduling information, requests for aperiodic CQI reports, etc.

Examples of predetermined requirements include, but are not limited to, out-of-sync quality targets in terms of hypothetical BLER and/or SNR of DL control channels (e.g., PCFICH/PDCCH), synchronization quality targets in terms of hypothetical BLER and/or SNR of DL control channels, an evaluation period for determining signal quality for detection of OSS and IS, etc. Examples of OOS and IN BLER targets to be met by the UE are 10% and 2%, respectively.

The adaptation step can be performed according to predefined rules, or can also be determined autonomously by the network node (e.g., based on UE downlink signal quality or performance, such as UE radio measurements, BLER, etc.). When using predefined rules, the parameters and their values are specified in the standard based on at least the UE receiver configuration. In one example, two different sets of parameter values can be predefined: one for single Rx and another for dual Rx. In another example, three different sets of parameter values can be predefined: one for single Rx, another for dual Rx, and another for quad Rx. The network node then selects the set of radio transmission parameters based on the UE receiver configuration.

From step 402, processing proceeds to step 404, where the network node transmits at least one downlink signal to the UE using at least one adapted parameter to enable the UE to perform RLM. For example, the network node transmits the downlink signal based on one or more adaptive radio transmission parameters. The UE uses the transmitted downlink signal to evaluate the radio quality of the cell of the network node for the purpose of RLM. The downlink signal may be one or more downlink physical signals and/or one or more downlink physical channels. Examples of downlink physical signals are PSS, SSSS, CRS, CSI-RS, and PRS. Examples of downlink physical channels are PDSCH, PDCCH, PCFICH, PHICH, or E-PDCCH.

According to some embodiments, the network node may perform adaptation based on the radio operating mode. For example, the network node may also determine whether the UE is configured to operate in a specific radio operating mode. In this document, the radio operating mode refers to the range in which a receiver can receive signals from a radio transmitter. An example of a radio operating mode is an enhanced coverage mode or an enhanced coverage mode of operation. In this step, the network node determines whether the UE is operating in a DL enhanced coverage mode. In the enhanced coverage mode, the transmission of one or more DL signals is enhanced by signal repetition and/or increasing the transmit power of the DL signal. The enhanced coverage mode enhances the reception quality of the DL signal received at the UE, so that the UE is able to receive the signal even if the path loss is greater than usual (for example, 10-20dB greater than normal operation). If the UE operates in an enhanced coverage mode (for example, for M2M communication), the network node may take into account the enhanced coverage operation of the UE to further adapt one or more radio transmission parameters of the DL signal received by the UE. The level of adaptation may depend on the amount of enhanced coverage. For example, the adaptation may be: if a DL control channel (such as PDCCH) to be received by the UE is repeated over certain subframes (such as 10 subframes) in order to improve coverage to a certain extent (for example, the DL path loss increases by 10 dB compared to normal operation without signal repetition), then the number of symbols used to transmit the DL control channel may be reduced from 3 to 2. The adaptation of the parameters may also be performed by the network node according to predefined rules or autonomously depending on the coverage improvement.

According to some embodiments, the network node sends a request to obtain the UE's receiver configuration. For example, the network node sends an explicit request to the UE requesting the UE to report its receiver configuration, which includes the UE's receiver capabilities and/or the number of receivers currently used or activated by the UE for receiving DL signals. The request or message can be sent via RRC signaling. The request can be sent at call establishment, after the UE's cell change, periodically, or any time the network node needs to update information.

According to some embodiments, the network node configures the UE receiver. For example, if the UE supports more than one receiver, the network node may decide to modify the UE receiver configuration via higher layer signaling. Alternatively, the network node may recommend to the UE to modify the UE receiver configuration. The decision to modify the receiver configuration or to send a corresponding recommendation may be based on the UE radio performance (e.g., serving cell performance, UE radio measurement results, etc.). For example, if the serving cell performance (e.g., DL BLER of PDSCH) is above a threshold (e.g., <1%) for a certain amount of time, the network node may decide to reduce the number of receivers used for DL reception (e.g., from 4 Rx to 3 Rx). Accordingly, this will enable the UE to reduce its power consumption and extend its battery life.

In some embodiments, the value of the parameter to be adapted or selected by the network node depends on the determined number of receivers supported by the UE and/or currently used to receive one or more DL signals from at least the first cell (ie, the serving cell), which will be explained by the following example.

In one example, if the UE receiver configuration includes one receiver, the network node adapts the DL signal by: (i) increasing the transmit power of the DL signal relative to a reference value; (ii) increasing the ratio of the energy or power of the DL signal to the average energy or power of the reference signal compared to the reference value; (iii) increasing the number of OFDM symbols used to send the DL signal compared to the reference value; (iv) selecting a format of the DL signal (e.g., a DCI format of a PCFICH/PDCCH), the format of the DL signal being associated with signal reception at the UE using only a single receiver; (v) increasing the aggregation level of the DL signal compared to the reference value; or (vi) increasing the number of repetitions of the same DL signal (e.g., PDCCH, PBCH, CRS, etc.) in the time domain compared to a first reference value (e.g., first reference value = no repetition, one repetition, etc.).

In another example, if the UE receiver configuration includes more than two receivers, the network node adapts the DL signal by: (i) reducing the transmit power of the DL signal relative to a reference value; (ii) reducing the ratio of the energy or power of the DL signal to the average energy or power of the reference signal compared to the reference value; (iii) reducing the number of OFDM symbols used to send the DL signal compared to the reference value; (iv) selecting a format of the DL signal (e.g., a DCI format of PCFICH/PDCCH), the format of the DL signal being associated with signal reception at the UE using the determined receiver configuration; (v) reducing the aggregation level of the DL signal compared to the reference value; or (vi) reducing the number of repetitions of the same DL signal in the time domain compared to a second reference value (e.g., second reference value = 5, 10, etc.).

In the above example, when the UE receiver configuration includes a specific reference configuration (eg, dual receivers, such as receiver diversity), the reference value corresponds to a value of a parameter used to transmit a DL signal.

FIG7 illustrates an embodiment of a process performed by a network node. The process may begin at step 700, where the network node obtains information about a plurality of receiver types supported by a UE for receiving signals from the network node. The process proceeds to step 702, where the network node configures the UE to operate with one of the plurality of receiver types supported by the UE. The process proceeds to step 704, where the network node adapts at least one radio transmission parameter associated with at least one downlink signal used by the UE for performing RLM based on the configured receiver type for performing RLM. The process proceeds to step 706, where the network node transmits at least one downlink signal to the UE using the adapted at least one radio transmission parameter, enabling the UE to perform RLM.

FIG8 illustrates another embodiment of a process performed by a network node. The process may begin at 800, where the network node obtains information related to a UE receiver configuration associated with the UE. The process proceeds to step 802, where the network node determines whether the UE is operating in enhanced coverage mode based on the obtained information. The process proceeds to step 804, where the network node adapts at least one radio transmission parameter associated with at least one downlink (DL) signal used by the UE to perform RLM based on the determination that the UE is operating in enhanced coverage mode. The process proceeds to step 806, where the network node transmits at least one DL signal to the UE with the adapted at least one parameter to enable the UE to perform RLM.

FIG9 illustrates an embodiment of a process performed by a UE. This embodiment may be relevant to a UE operating in the aforementioned scenario, where the UE is served by a first cell managed by a network node, the first cell operating at a first carrier frequency (f1). The process may be expressed according to rules, which may be predefined in a standard and applied by the UE when performing RLM. The steps described below in the UE may be performed in a specific order or in any order or sequence in the UE.

In general, the process begins at step 900, where the UE determines a receiver configuration based on the current number of receivers used by the UE to receive DL signals from a network node and/or the type of receiver currently used to mitigate interference caused by interfering signals. In this step, the UE determines, identifies, or obtains information related to its own receiver configuration.

In one example, the receiver configuration may be determined by the number of receivers that the UE currently uses to receive downlink signals from the first cell (e.g., for radio link monitoring). In another example, the receiver configuration may be determined by the type of receiver currently used to mitigate interference caused by one or more DL signals. Examples of receiver types are intra-cell interference mitigation receivers, inter-cell interference mitigation receivers, and the like. The interference signal may be received from the serving cell and/or one or more interfering cells. In another example, the receiver configuration may include a combination of the two receiver configurations mentioned above. The UE may determine the receiver configuration related information by one or more of the following ways: obtaining information stored in a memory, by actually checking a receiver that is actively receiving a DL signal, and a receiver configuration performed by a network node. It is assumed that the UE can support two or more receivers for receiving DL signals.

From step 900, processing proceeds to step 902, where the UE receives at least one downlink signal from a network node, wherein at least one parameter in the at least one downlink signal is adapted for the UE to perform RLM based on the receiver capabilities of the UE receiving the downlink signal. In this step, the UE may receive a downlink signal from a first cell, wherein the UE uses all activated or currently configured receivers to receive the downlink signal. The UE may also determine whether the received one or more downlink signals have been adapted by the network node based on the UE receiver configuration. This determination may be performed based on the predefined rules described in step 402 of FIG. With reference to step 404 of FIG. 4 , the downlink signals that may be adapted are described.

Processing proceeds from step 902 to step 904, where the UE performs RLM on the DL signal received from the network node. In step 906, if the DL signal is adapted for use by the UE for the determined receiver configuration, the UE maintains the same DL radio link out-of-sync quality target and synchronization quality target, regardless of the UE receiver configuration. In these steps, the UE may use the received DL signal to evaluate the DL signal quality of the first cell for the purpose of performing RLM operations (e.g., Out-of-sync, In-sync detection, etc.). If the network node adapts the radio transmission parameters of the DL received signal used by the UE for RLM according to one or more predefined rules, the UE maintains or uses the same DL radio link quality target for out-of-sync and in-sync detection, regardless of the UE receiver configuration, and further satisfies one or more predefined requirements associated with RLM (e.g., Out-of-sync/In-sync detection over a predefined evaluation period). Otherwise, if the network node does not adapt the radio transmission parameters of the DL signal used for RLM according to the predefined rules, the UE may not perform RLM or may not meet the predefined requirements related to RLM.

For example, for any receiver configuration (1 Rx or 2 Rx) for OOS and IS detection, the UE uses the SNR levels corresponding to the same values of 10% PDCCH hypothetical BLER and 2% hypothetical BLER, respectively. The UE then compares these SNR levels with the DL quality measured on the DL received signal (such as CRS) to detect whether OOS or IS has occurred.

In some embodiments, the UE may notify the network node of the UE's receiver configuration, which may include the UE's receiver capabilities and/or the current number of receivers used to receive DL signals and/or the type of receivers currently used to receive DL signals. The UE may signal this information autonomously or in response to a request received from the network node.

According to some embodiments, the UE adapts RLM based on whether the UE is operating in a specific radio operating mode. For example, the UE determines whether it is operating in a DL coverage enhancement mode. This determination may be based on whether the UE has been configured to operate in an enhanced coverage mode, or the UE may detect whether one or more DL signals are enhanced (e.g., repeated multiple times, transmitted with increased power, etc.). The UE may also determine whether the network node has also adapted one or more radio transmission parameters of the DL signal transmitted by the first cell when using enhanced coverage. The UE may apply one or more of the rules related to RLM described below.

In some embodiments, if it is determined that the UE is operating in enhanced coverage mode, or if the enhanced coverage is above a threshold (e.g., DL path loss is increased by 10 dB or more compared to normal operation), the UE may further adapt one or more parameters for performing RLM. For example, according to predetermined requirements corresponding to the enhanced coverage mode (e.g., an evaluation period that is longer than the evaluation period used in normal operation (i.e., non-enhanced coverage mode), the UE may measure the DL signal quality of the DL received signal for evaluation of the OSS and ISS.

In some embodiments, assuming the UE determines that the radio transmission parameters of the DL signal for RLM are adapted by the network node to take into account the enhanced coverage mode of operation, the UE uses a conventional DL radio link quality target for detection of out-of-sync and synchronization. The conventional DL radio link quality target is used when enhanced coverage is not applied to the DL radio signal.

In some embodiments, if the UE determines that the network node does not adapt the radio transmission parameters of the DL signal for RLM according to predefined rules when using enhanced coverage, the UE may not perform RLM or the UE may not meet predefined requirements related to RLM.

According to some embodiments, the UE notifies the network node of an incomplete RLM operation. For example, if the UE determines that the network node has not adapted the radio transmission parameters related to the DL signal (to take into account the UE receiver configuration and/or DL coverage enhancement), the UE may also notify the network node that the UE cannot perform RLM, cannot meet the predetermined requirements related to RLM, or cannot guarantee that the serving cell performance (such as the target BLER) is met. The UE may also indicate the reason for the incomplete RLM operation, for example, due to the lack of adaptation of the radio transmission parameters of the DL signal by the network node.

FIG10 is a block diagram of an embodiment of a network node 316. As shown in FIG10 , the network node 316 may include or comprise a computer system (CS) 1002, which may include one or more processors 1055, such as general-purpose microprocessors and/or one or more circuits, such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), logic circuits, etc.; a network interface 1003 for connecting the network node 316 to a network; and a data storage system 1006, which may include one or more non-volatile storage devices and/or one or more volatile storage devices (e.g., random access memory (RAM)). In embodiments where the network node 316 includes the processor 1055, a computer program product (CPP) 1033 may be provided. The CPP 1033 may include or be a computer-readable medium (CRM) 1042 storing a computer program (CP) 1043 including computer-readable instructions (CRI) 1044. CRM 1042 is a non-transitory computer-readable medium, such as, but not limited to, magnetic media (e.g., a hard drive), optical media (e.g., a DVD), a solid-state device (e.g., random access memory (RAM), flash memory), etc. In some embodiments, CRI 1044 of computer program 1043 is configured such that, when executed by computer system 1002, CRI causes network node 316 to perform the steps described above (e.g., the steps described with reference to the flowcharts and messages shown in the accompanying figures). In other embodiments, network node 316 may be configured to perform the steps described herein without requiring a computer program. That is, for example, computer system 1002 may be comprised solely of one or more ASICs. Thus, the features of the embodiments described herein may be implemented in hardware and/or software.

FIG11 is a block diagram of a UE 302 according to some embodiments. As shown in FIG11 , the UE 302 may include or comprise a computer system (CS) 1102, which may include one or more processors 1155, such as general-purpose microprocessors and/or one or more circuits, such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), logic circuits, etc.; a transceiver 1105 coupled to an antenna 1122 for wirelessly transmitting and receiving data; and a data storage system 1106, which may include one or more non-volatile memory devices and/or one or more volatile memory devices (e.g., random access memory (RAM)). In embodiments where the UE 302 includes the processor 1155, a computer program product (CPP) 1133 may be provided. The CPP 1133 may include or be a computer-readable medium (CRM) 1142 storing a computer program (CP) 1143 including computer-readable instructions (CRI) 1144. CRM 1142 is a non-transitory computer-readable medium, such as, but not limited to, magnetic media (e.g., a hard drive), optical media (e.g., a DVD), a solid-state device (e.g., random access memory (RAM), flash memory), etc. In some embodiments, CRI 1144 of computer program 1143 is configured such that, when executed by computer system 1102, CRI causes UE 302 to perform the aforementioned steps (e.g., the steps described with reference to the flowcharts and messages shown in the accompanying figures). In other embodiments, UE 302 may be configured to perform the steps described herein without requiring a computer program. That is, for example, computer system 1102 may consist solely of one or more ASICs. Thus, features of the embodiments described herein may be implemented in hardware and/or software. As shown in FIG11 , UE 302 may include a display 1123, a speaker 1124, and a microphone ("Mic"), all of which are coupled to CS 1102.

Although various embodiments of the present disclosure are described herein, it should be understood that these are presented by way of example only and not limitation. Therefore, the breadth and scope of the present disclosure should not be limited by any of the above exemplary embodiments. In addition, any combination of the above elements with all possible variations is included in the present disclosure, unless otherwise indicated or otherwise clearly conflicting with the context.

Additionally, although the processes described above and shown in the accompanying drawings are shown as a series of steps, this is for illustrative purposes only. Therefore, it is contemplated that some steps may be added, some steps may be omitted, the order of steps may be rearranged, and some steps may be performed in parallel.

abbreviation

DRX Discontinuous Reception

eNB evolved node B, base station

E-UTRAN Evolved Universal Terrestrial Radio Access Network

E-UTRA Evolved Universal Terrestrial Radio Access

E-UTRA FDD E-UTRA Frequency Division Duplex

E-UTRA TDD E-UTRA Time Division Duplex

LTE Long Term Evolution

M2M Machine to Machine

PBCH Physical Broadcast Channel

PCC Primary Component Carrier

PCI Physical Cell Identifier

PSS Primary Synchronization Signal

RAT Radio Access Technology

RRC Radio Resource Control

RSRP Reference Signal Received Power

RSRQ Reference Signal Received Quality

TDD Time Division Duplex

UE User Equipment

RNC Radio Network Controller

BSC Base Station Controller

PCell Primary Cell

HSPA High Speed Packet Access

GSM Global System for Mobile Communications

UTRA Universal Terrestrial Radio Access

UTRA FDD UTRA Frequency Division Duplex

UTRA TDD UTRA Time Division Duplex

WLAN Wireless Local Area Network

GERN GSM EDGE Radio Access Network

EDGE Enhanced Data rates for GSM Evolution

CDMA2000 Code Division Multiple Access 2000

HRPD High Rate Packet Data

DL Downlink

PDCCH Physical Downlink Control Channel

DMRS Demodulation Reference Signal

PCIFICH Physical Control Format Indicator

PDSCH Physical Downlink Shared Channel

PHICH Physical Hybrid ARQ Indicator Channel

RE Resource Unit

RB Resource Block

RS reference signal

RRH Remote Radio Head

CRS Cell-specific reference signal

SSS slave synchronization signal

UE User Equipment

UL Uplink

Claims (24)

1. A method for adaptive radio link monitoring (RLM), the method comprising the following steps: The network node (316) obtains (406) configuration information related to the receiver configuration of the user equipment (UE), the receiver configuration being associated with the UE (302, 308) and implemented by the UE for receiving signals from the network node, wherein the configuration information includes the current number of receivers for receiving DL signals; The network node adapts (402) at least one radio transmission parameter associated with at least one downlink DL signal used by the UE to perform RLM based on the obtained configuration information; and The network node sends at least one DL signal (404) to the UE with at least one adapted radio transmission parameter, enabling the UE to perform RLM. 2. The method according to claim 1, wherein the step of obtaining configuration information includes receiving the configuration information from the UE. 3. The method according to claim 1 or 2, wherein the obtained configuration information indicates that the UE receiver is capable of performing at least one of the following: receiving signals with only a single receiver, and receiving signals simultaneously with multiple receivers. 4. The method according to claim 1 or 2, wherein at least one DL signal comprises one or more of a DL physical signal and a DL physical channel. 5. The method according to claim 4, wherein the DL physical signal is one or more of the following: master synchronization signal (PSS), slave synchronization signal (SSS), cell-specific reference signal (CRS), channel state information reference signal (CSI-RS), and positioning reference signal (PRS). 6. The method of claim 4, wherein the DL physical channel is one or more of the following: physical downlink control channel (PDCCH), physical control format indication channel (PCFICH), physical hybrid ARQ indication channel (PHICH), and enhanced physical downlink control channel (E-PDCCH). 7. The method according to claim 4, wherein the DL physical channel is a physical downlink shared channel (PDSCH). 8. The method according to claim 1 or 2, wherein at least one radio transmission parameter includes one or more of the following: the transmit power of the DL signal, the ratio of the energy or power of the DL signal to the average energy or power of the reference signal, the number of OFDM symbols used to transmit the DL signal, the format of the DL signal, the aggregation level of the DL signal, and the bandwidth of the DL signal. 9. The method of claim 3, wherein the step of adapting at least one radio transmission parameter in response to determining that the UE indicates that the UE can receive signals using only a single receiver comprises at least one of the following: Increase the transmission power of the DL signal. Increase the ratio of the energy or power of the DL signal to the average energy or power of the reference signal. Increase the number of OFDM symbols used to transmit DL signals. Select the format of the DL signal associated with signal reception performed at the UE using only a single receiver. Increase the aggregation level of DL signals, and Increase the number of repetitions of the same DL signal in the time domain. 10. The method of claim 3, wherein, when the configuration information indicates that the UE can receive signals with multiple receivers, the step of adapting at least one radio transmission parameter includes at least one of the following: Reduce the transmit power of the DL signal. Reduce the ratio of the energy or power of the DL signal to the average energy or power of the reference signal. Reduce the number of OFDM symbols used to transmit DL signals. The format of the selected DL signal is associated with signal reception at the UE using multiple receivers. Reduce the aggregation level of the DL signal, and Reduce the number of repetitions of the same DL signal in the time domain. 11. The method of claim 1 or 2, wherein the step of adapting at least one radio transmission parameter enables the UE to maintain the same DL radio link out-of-sync quality target level and synchronization quality target level, regardless of the UE receiver capability receiving DL signals from the network node, wherein the out-of-sync quality target level indicates one or more levels for declaring the UE's state as out of sync, and the synchronization quality target level indicates one or more levels for declaring the UE's state as synchronized. 12. The method of claim 1 or 2, wherein adaptation of at least one radio transmission parameter related to at least one DL signal is performed according to one or more predefined rules. 13. The method of claim 1 or 2, wherein the adaptation is further based on whether DL coverage enhancement has been applied to the DL signals sent by the network node to the UE. 14. The method according to claim 1 or 2, wherein, The obtained receiver configuration indicates that the UE supports multiple receiver types for receiving signals from network nodes, and The network node configures the UE (702) to operate as one of the multiple receiver types supported by the UE. 15. The method according to claim 1 or 2, further comprising the following step: The network node determines, based on the obtained configuration information, whether the UE is operating in enhanced coverage mode (802); and The network node adapts (804) at least one radio transmission parameter associated with at least one downlink DL signal used by the UE to perform RLM based on the determination that the UE is operating in enhanced coverage mode. 16. A network node (316) for adaptive radio link monitoring (RLM), the network node comprising a processor (1055) and a computer-readable medium (1042) coupled to the processor, the computer-readable medium storing instructions (1044) executable by the processor, thereby configuring the network node to perform the method according to any one of claims 1-15. 17. A non-transitory computer-readable medium (1042) storing computer instructions (1044) for causing a network node to perform the method according to any one of claims 1-15. 18. A method for adaptive radio link monitoring, the method comprising the following steps: Based on the current number of receivers used by the UE to receive downlink DL signals from the network node (316), the user equipment UE (302, 308) determines (900) the receiver configuration; The UE receives (902) at least one DL signal having at least one DL signal parameter from the network node, wherein the at least one DL signal parameter is adapted for use by the UE; The UE performs (904)RLM on DL signals received from the network node, wherein at least one DL signal parameter is adapted based on the receiver configuration. 19. The method of claim 18, further comprising: In response to determining the DL signal to be adapted for use by the UE for the determined receiver configuration, the same DL radio link out-of-sync quality target and synchronization quality target are maintained, regardless of the UE receiver configuration. 20. The method according to claim 18 or 19, wherein the determination of the receiver configuration is further based on configuration information or messages received by the network node. 21. The method of claim 18 or 19, wherein the receiver configuration includes one or more of the following: a receiver capable of receiving signals with only a single receiver, a receiver capable of receiving signals simultaneously with multiple receivers, and a receiver capable of mitigating interference received from one or more interfering cells. 22. The method according to claim 18 or 19, further comprising the step of: The UE determines whether it is operating in DL coverage enhancement mode or is configured to operate in DL coverage enhancement mode; and If operating in DL enhanced coverage mode, the UE adapts one or more RLM-related parameters or RLM procedures based on predetermined rules. 23. A user equipment (UE) (302, 308) served by a network node (316) for performing radio link monitoring (RLM) by monitoring the downlink quality of signals transmitted by the network node, the UE comprising a processor (1155) and a computer-readable medium (1142) coupled to the processor, the computer-readable medium storing instructions (1144) executable by the processor, thereby configuring the UE to perform the method according to any one of claims 18-22. 24. A non-transitory computer-readable medium (1142) storing computer instructions (1144) for causing a user equipment (UE) to perform the method according to any one of claims 18-22.