Enhancements to mobility reference signals for radio link monitoring in a beam-based system

1. A method, in a user equipment (UE) comprising:

receiving, in a downlink signal having a series of subframes, a beam-formed reference signal in each of a plurality of subframes, wherein the beam-formed reference signals are received in fewer than all of the subframes of the downlink signal;

performing mobility management measurements using at least a first subset of the received beam-formed reference signals, the first subset corresponding to a first frequency or first localized range of frequencies; and

performing radio link monitoring (RLM) using a second subset of the received beam-formed reference signals, the second subset at least partly differing from the first subset and including beam-formed reference signals corresponding to a second frequency or second localized range of frequencies, the second frequency or second localized range of frequencies being spaced apart from and differing from the first frequency or first localized range of frequencies; wherein

performing RLM comprises:

measuring a value of a metric and comparing the value to a threshold that represents a predetermined downlink control channel quality, for detecting radio link failure, and

determining that the UE is in-sync or out-of-sync, based on measurements of at least some of the second subset of beam-formed reference signals.

2. A method, in an access node of a wireless communications system, the method comprising:

transmitting, in a downlink signal having a series of subframes, a beam-formed reference signal in each of a plurality of subframes, wherein the beam-formed reference signals are transmitted in fewer than all of the subframes of the downlink signal, and wherein the beam-formed reference signals include a first subset and an at least partly differing second subset, the first subset including beam-formed reference signals corresponding to a first frequency or first localized range of frequencies, and the second subset including beam-formed reference signals corresponding to a second frequency or second localized range of frequencies, the second frequency or second localized range of frequencies being spaced apart from and differing from the first frequency or first localized range of frequencies; and

configuring a user equipment (UE) to perform mobility management measurements using at least the first subset of the beam-formed reference signals and to perform radio link monitoring (RLM) using at least the second subset of the beam-formed reference signals; wherein

performing RLM comprises:

measuring a value of a metric and comparing the value to a threshold that represents a predetermined downlink control channel quality, for detecting radio link failure, and

determining that the UE is in-sync or out-of-sync, based on measurements of at least some of the second subset of beam-formed reference signals.

3. A user equipment (UE) comprising:

transceiver circuitry; and

processing circuitry operatively associated with the transceiver circuitry and configured to:

receive, using the transceiver circuitry, in a downlink signal having a series of subframes, a beam-formed reference signal in each of a plurality of subframes, wherein the beam-formed reference signals are received in fewer than all of the subframes of the downlink signal;

perform mobility management measurements using at least a first subset of the received beam-formed reference signals, the first subset corresponding to a first frequency or first localized range of frequencies; and

perform radio link monitoring (RLM) using a second subset of the received beam-formed reference signals, the second subset at least partly differing from the first subset and including beam-formed reference signals corresponding to a second frequency or second localized range of frequencies, the second frequency or second localized range of frequencies being spaced apart from and differing from the first frequency or first localized range of frequencies; wherein

performing RLM comprises:

measuring a value of a metric and comparing the value to a threshold that represents a predetermined downlink control channel quality, for detecting radio link failure, and

determining that the UE is in-sync or out-of-sync, based on measurements of at least some of the second subset of beam-formed reference signals.

4. The UE of claim 3 , wherein the beam-formed reference signals corresponding to the second frequency or second localized range of frequencies have a periodicity in time that differs from a periodicity in time for the beam-formed reference signals corresponding to the first frequency or first localized range of frequencies.

5. The UE of claim 3 , wherein the second subset further includes beam-formed reference signals corresponding to a third frequency or third localized range of frequencies, the third frequency or third localized range of frequencies being spaced apart from and differing from the first and second frequencies or first and second localized range of frequencies.

6. The UE of claim 3 , wherein the beam-formed reference signals corresponding to the first frequency or first localized range of frequencies each coincide in time with beam-formed reference signals corresponding to the second frequency or second localized range of frequencies.

7. The UE of claim 3 , wherein the processing circuitry is configured to demodulate a first control channel using one or more additional reference signals to estimate a channel for the first control channel.

8. The UE of claim 7 , wherein the first control channel is received in frequency resources at least partly overlapping frequency resources carrying the beam-formed reference signals used for performing RLM.

9. The UE of claim 3 , wherein the second subset of beam-formed reference signals comprises a beam-specific reference signal for a first beam, and wherein the processing circuitry is configured to perform RLM by performing RLM for the first beam, using the beam-specific reference signal.

10. The UE of claim 9 , wherein the beam-specific reference signal carries a beam identifier, and wherein the processing circuitry is configured to decode the beam identifier from the beam-specific reference signal.

11. The UE of claim 3 , wherein the processing circuitry is configured to receive, prior to performing said mobility management measurements, one or more first configuration parameters defining a periodicity and/or frequency location for the first subset of beam-formed reference signals.

12. The UE of claim 11 , wherein the processing circuitry is configured to receive, prior to performing said RLM, one or more second configuration parameters defining a periodicity and/or frequency location for the second subset of beam-formed reference signals.

13. An access node of a wireless communications system, comprising:

transceiver circuitry; and

processing circuitry operatively associated with the transceiver circuitry and configured to:

transmit, using the transceiver circuitry, in a downlink signal having a series of subframes, a beam-formed reference signal in each of a plurality of subframes, wherein the beam-formed reference signals are transmitted in fewer than all of the subframes of the downlink signal, and wherein the beam-formed reference signals include a first subset and an at least partly differing second subset, the first subset including beam-formed reference signals corresponding to a first frequency or first localized range of frequencies, and the second subset including beam-formed reference signals corresponding to a second frequency or second localized range of frequencies, the second frequency or second localized range of frequencies being spaced apart from and differing from the first frequency or first localized range of frequencies; and

configure a user equipment (UE) to perform mobility management measurements using at least the first subset of the beam-formed reference signals and to perform radio link monitoring (RLM) using at least the second subset of the beam-formed reference signals; wherein

performing RLM comprises:

measuring a value of a metric and comparing the value to a threshold that represents a predetermined downlink control channel quality, for detecting radio link failure, and

determining that the UE is in-sync or out-of-sync, based on measurements of at least some of the second subset of beam-formed reference signals.

14. The access node of claim 13 , wherein the beam-formed reference signals corresponding to the second frequency or second localized range of frequencies have a periodicity in time that differs from a periodicity in time for the beam-formed reference signals corresponding to the first frequency or first localized range of frequencies.

15. The access node of claim 13 , wherein the second subset further includes beam-formed reference signals corresponding to a third frequency or third localized range of frequencies, the third frequency or third localized range of frequencies being spaced apart from and differing from the first and second frequencies or first and second localized range of frequencies.

16. The access node of claim 13 , wherein the beam-formed reference signals corresponding to the first frequency or first localized range of frequencies each coincide in time with the beam-formed reference signals corresponding to the second frequency or second localized range of frequencies.

17. The access node of claim 13 , wherein the processing circuitry is configured to transmit, using the transceiver circuitry, one or more additional reference signals for use by the UE in estimating a channel for a first control channel.

18. The access node of claim 13 , wherein the processing circuitry is configured to transmit, using the transceiver circuitry, a first control channel using the same beamforming parameters used to transmit the beam-formed reference signals, in frequency resources at least partly overlapping frequency resources carrying the beam-formed reference signals.

19. The access node of claim 13 , wherein one or more of the beam-formed reference signals comprises a beam-specific reference signal for a first beam.

20. The access node of claim 19 , wherein the beam-specific reference signal carries a beam identifier, and wherein the processing circuitry is configured to decode the beam identifier from the beam-specific reference signal.

21. The access node of claim 13 , wherein the processing circuitry is configured to transmit to the UE, using the transceiver circuitry, one or more first configuration parameters defining a periodicity and/or frequency location for the first subset of beam-formed reference signals.

22. The access node of claim 21 , wherein the processing circuitry is configured to transmit to the UE, using the transceiver circuitry, one or more second configuration parameters defining a periodicity and/or frequency location for the second subset of beam-formed reference signals.

23. A non-transitory computer readable storage medium storing a computer program comprising program instructions that, when executed on at least one processing circuit of a user equipment (UE) configured for operation in a wireless communication network, configures the UE to:

receive, in a downlink signal having a series of subframes, a beam-formed reference signal in each of a plurality of subframes, wherein the beam-formed reference signals are received in fewer than all of the subframes of the downlink signal;

perform mobility management measurements using at least a first subset of the received beam-formed reference signals, the first subset corresponding to a first frequency or first localized range of frequencies; and

perform radio link monitoring (RLM) using a second subset of the received beam-formed reference signals, the second subset at least partly differing from the first subset and including beam-formed reference signals corresponding to a second frequency or second localized range of frequencies, the second frequency or second localized range of frequencies being spaced apart from and differing from the first frequency or first localized range of frequencies; wherein

performing RLM comprises:

measuring a value of a metric and comparing the value to a threshold that represents a predetermined downlink control channel quality, for detecting radio link failure, and

determining that the UE is in-sync or out-of-sync, based on measurements of at least some of the second subset of beam-formed reference signals.

24. A non-transitory computer readable storage medium storing a computer program comprising program instructions that, when executed on at least one processing circuit of an access node of a wireless communication network, configures the access node to:

transmit, in a first downlink signal having a series of subframes, a beam-formed reference signal in each of a plurality of subframes, wherein the beam-formed reference signals are transmitted in fewer than all of the subframes of the downlink signal, and wherein the beam-formed reference signals include a first subset and an at least partly differing second subset, the first subset including beam-formed reference signals corresponding to a first frequency or first localized range of frequencies, and the second subset including beam-formed reference signals corresponding to a second frequency or second localized range of frequencies, the second frequency or second localized range of frequencies being spaced apart from and differing from the first frequency or first localized range of frequencies; and

configure a user equipment (UE) to perform mobility management measurements using at least the first subset of the beam-formed reference signals and to perform radio link monitoring (RLM) using at least the second subset of the beam-formed reference signals; wherein

performing RLM comprises:

measuring a value of a metric and comparing the value to a threshold that represents a predetermined downlink control channel quality, for detecting radio link failure, and

determining that the UE is in-sync or out-of-sync, based on measurements of at least some of the second subset of beam-formed reference signals.