Methods of subframe pairing for measurement gap length configuration in dual connectivity

1. A method by a user equipment, UE, configured in asynchronous dual connectivity, DC, the method comprising:

receiving from a network node, configuration information of a measurement gap length in a master cell group, MCG, for performing one or more radio measurements;

configuring a measurement gap length of at least seven subframes in a secondary cell group, SCG, using subframe pairs, the subframe pairs constituted between the MCG and the SCG with respect to the measurement gap length in the MCG on which the measurement gap length in the SCG is configured;

wherein the MCG measurement gap precedes the SCG measurement gap, the first subframe of the measurement gap length in the SCG is the subframe in the SCG that is identified as starting immediately after the start of the MCG measurement gap;

preventing transmission and reception of data in SCG in the subframe immediately before the first subframe of the measurement gap length of the SCG; and

performing one or more radio measurements in the SCG within the configured measurement gap length.

2. The method of claim 1 , further comprising:

determining a synchronization level of signals received at the UE from subframe boundaries of the MCG and the SCG; and

determining based on the synchronization level whether or not to perform the determining subframe pairs between the MCG and the SCG.

3. The method of claim 2 , wherein determining synchronization level of signals received at the UE from subframe boundaries of the MCG and the SCG, comprises:

determining the synchronization level based on a received time difference of signals received at the UE from the MCG and the SCG.

4. The method of claim 1 , further comprising identifying the subframe in the SCG that starts after a defined subframe in a MCG gap; and

wherein configuring the measurement gap length of at least seven subframes in the SCG using the subframe pairs, comprises configuring the measurement gap length in the SCG using the subframe in the SCG that is identified as starting after the defined subframe in the MCG gap.

5. The method of claim 4 , wherein the defined subframe in the MCG gap is the first subframe in a measurement gap of the MCG.

6. The method of claim 1 , further comprising preventing transmission and reception of data in SCG in a subframe immediately after the last subframe of the measurement gap length of the SCG.

7. A user equipment, UE, configured in asynchronous dual connectivity, DC, and comprising:

a processor and a memory, the memory comprising executable instructions that when executed by the processor cause the processor to:

receive from a network node, configuration information of a measurement gap length in a master cell group, MCG, for performing one or more radio measurements;

configure a measurement gap length of at least seven subframes in a secondary cell group, SCG, using subframe pairs, the subframe pairs constituted between the MCG and the SCG with respect to the measurement gap length in the MCG on which the measurement gap length in the SCG is configured;

wherein the MCG measurement gap precedes the SCG measurement gap, the first subframe of the measurement gap length in the SCG is the subframe in the SCG that is identified as starting immediately after the start of the MCG measurement gap;

prevent transmission and reception of data in SCG in the subframe immediately before the first subframe of the measurement gap length of the SCG; and

perform one or more radio measurements in the SCG within the configured measurement gap length.

8. The UE of claim 7 , where the UE is further configured to:

determine a synchronization level of signals received at the UE from subframe boundaries of the MCG and the SCG; and

determine based on the synchronization level whether or not to perform the determining subframe pairs between the MCG and the SCG.

9. The UE of claim 8 , wherein determining a synchronization level of signals received at the UE from subframe boundaries of the MCG and the SCG, comprises:

determining the synchronization level based on a received time difference of signals received at the UE from the MCG and the SCG.

10. The UE of claim 7 , wherein the UE is further configured to:

identify the subframe in the SCG that starts after a defined subframe in a MCG gap; and

configure the measurement gap length of at least seven subframes in the SCG using the subframe pairs the SCG using the determined subframe pairs, comprises configuring the measurement gap length in the SCG using the subframe in the SCG that is identified as starting after the defined subframe in the MCG gap.

11. The UE of claim 7 , wherein the UE is further configured to prevent transmission and reception of data in the SCG in a subframe immediately after the last subframe of the measurement gap length of the SCG.

12. A method by a network node serving a user equipment, UE, configured in asynchronous dual connectivity, DC, the method comprising:

determining synchronization level of signals received at the UE from subframe boundaries of a master cell group, MCG, and a secondary cell group, SCG;

determining one of the UE is configured in unsynchronized DC or the network node cannot ascertain from the synchronization level whether the UE operates in unsynchronized DC or synchronized DC;

based on the determining that the UE is configured in unsynchronized DC or that the network node cannot ascertain from the synchronization level whether the UE operates in unsynchronized DC or synchronized DC,

selecting one of a plurality of pre-defined rules based on one or more criteria, wherein the selected one of the pre-defined rules enables the UE to pair subframes from the MCG and the SCG to determine a first measurement gap length in the MCG and a second measurement gap length of at least seven subframes in the SCG, wherein the first subframe of the measurement gap length in the SCG is the subframe in the SCG that is identified as starting immediately after the start of the MCG measurement gap, wherein the MCG measurement gap precedes the SCG measurement gap;

configuring the UE with the selected one of the plurality of pre-defined rules, the selected one of the plurality of pre-defined rules comprising an instruction to prevent transmission and reception of data at the UE in the SCG in a subframe immediately before the first subframe of the second measurement gap length; and

configuring the UE with the second measurement gap length for operating to perform one or more radio measurements based on the second measurement gap length.

13. The method of claim 12 , wherein configuring the UE with the selected one of the plurality of pre-defined rules, comprises:

transmitting configuration information to configure the UE to determine subframe pairs between the MCG and the SCG with respect to the first measurement gap length in the MCG on which the second measurement gap length in the SCG can be configured.

14. The method of claim 13 , wherein transmitting configuration information to configure the UE to determine subframe pairs between the MCG and the SCG with respect to the first measurement gap length in the MCG on which the second measurement gap length in the SCG can be configured, comprises:

transmitting the configuration information to configure the UE to identify one of the subframe pairs as a subframe in the MCG and a subframe in the SCG that overlap with each other in a defined time slot.

15. The method of claim 13 , wherein transmitting configuration information to configure the UE to determine subframe pairs between the MCG and the SCG with respect to the first measurement gap length in the MCG on which the second measurement gap length in the SCG can be configured, comprises:

transmitting the configuration information to configure the UE to identify a subframe in the SCG that starts after a defined subframe in a MCG gap.

16. The method of claim 12 , further comprising:

scheduling resources for assignment to UEs so that the UE is not scheduled for transmission in a subframe before or after the second measurement gap length.

17. The method of claim 16 , further comprising:

scheduling resources for assignment to another UE that can transmit in the subframe before or after the second measurement gap length.

18. A network node serving a user equipment, UE, configured in asynchronous dual connectivity, DC, the network node comprising:

a processor and a memory, the memory comprising executable instructions that when executed by the processor cause the processor to:

determine synchronization level of signals received at the UE from subframe boundaries of a master cell group, MCG, and a secondary cell group, SCG;

determine one of the UE is configured in unsynchronized DC or the network node cannot ascertain from the synchronization level whether the UE operates in unsynchronized DC or synchronized DC;

based on determining that the UE is configured in unsynchronized DC or that the network node cannot ascertain from the synchronization level whether the UE operates in unsynchronized DC or synchronized DC,

select one of a plurality of pre-defined rules based on one or more criteria, wherein the selected one of the pre-defined rules enables the UE to pair subframes from the MCG and the SCG to determine a first measurement gap length in the MCG and a second measurement gap length of at least seven subframes in the SCG, wherein the first subframe of the measurement gap length in the SCG is the subframe in the SCG that is identified as starting immediately after the start of the MCG measurement gap, wherein the MCG measurement gap precedes the SCG measurement gap;

configure the UE with the selected one of the plurality of pre-defined rules, the selected one of the plurality of pre-defined rules comprising an instruction to prevent transmission and reception of data at the UE in the SCG in a subframe immediately before the first subframe of the second measurement gap length; and

configure the UE with the second measurement gap length for operating to perform one or more radio measurements based on the second measurement gap length.