Base station and scheduling method

1. A base station comprising:

a radio transceiver configured to communicate with a plurality of radio terminals located in a first cell; and

at least one processor configured to schedule radio resources to a plurality of device-to-device (D2D) transmissions performed by a plurality of D2D communication pairs included in the plurality of radio terminals, each D2D transmission including wirelessly transmitting from one radio terminal directly to another radio terminal in each D2D communication pair without passing through the base station, wherein

the at least one processor is further configured to schedule radio resources to the plurality of D2D transmissions in accordance with an allocation rule that permits two D2D communication pairs that are not in proximity to each other to share an identical radio resource but prohibit two D2D communication pairs in proximity to each other from sharing an identical radio resource,

wherein the at least one processor is configured to:

allocate a first prioritized radio resource configured in the first cell, preferentially over another radio resource, to D2D transmission performed by a D2D communication pair in proximity to an adjacent-cell radio terminal that belongs to an adjacent cell of the first cell, and

allocate the other radio resource, preferentially over the first prioritized radio resource, to D2D transmission performed by a D2D communication pair that is not in proximity to the adjacent-cell radio terminal.

2. The base station according to claim 1 , wherein the at least one processor is configured to allocate radio resources to the plurality of D2D transmissions in accordance with a proportional fairness algorithm on which the allocation rule is imposed.

3. The base station according to claim 1 , wherein the at least one processor is configured to select a first D2D communication pair in a descending order of a scheduling metric on a first radio resource, and if the first radio resource has not been allocated to D2D transmission performed by a second D2D communication pair that has a larger scheduling metric than the first D2D communication pair and is in a proximity relationship with the first D2D communication pair, allocate the first radio resource to D2D transmission performed by the first D2D communication pair.

4. The base station according to claims 1 , wherein the first prioritized radio resource is a radio resource of which a base station of the adjacent cell prohibits use by the adjacent-cell radio terminal.

5. The base station according to claim 1 , wherein

the other radio resource includes a second prioritized radio resource configured in the adjacent cell and a non-prioritized radio resource that is set to neither the first prioritized radio resource nor the second prioritized radio resource, and

the at least one processor is configured to allocate the second prioritized radio resource, preferentially over the first prioritized radio resource and the non-prioritized radio resource, to D2D transmission performed by a D2D communication pair that is not in proximity to the adjacent-cell radio terminal.

6. The base station according to claim 1 , wherein

the plurality of D2D communication pairs include third and fourth D2D communication pairs, and

the at least one processor is configured to:

permit the third and fourth D2D communication pairs to perform their respective D2D transmissions on an identical time-frequency resource when a proximity level indicating a geographic distance between the third and fourth D2D communication pairs is at a first level;

prohibit the third and fourth D2D communication pairs from performing their respective D2D transmissions on an identical time-frequency resource and, instead, permit the third and fourth D2D communication pairs to perform their respective D2D transmissions on a plurality of time-frequency resources that have the same time domain position and have different frequency domain positions, when the proximity level is at a second level higher than the first level; and

prohibit the third and fourth D2D communication pairs from performing their respective D2D transmissions on the same time domain resource and, instead, permit the third and fourth D2D communication pairs to perform their respective D2D transmissions on a plurality of time-frequency resources having different time domain positions, when the proximity level is at a third level higher than the second level.

7. The base station according to claim 1 , wherein the at least one processor is configured to determine whether fifth and sixth D2D communication pairs included in the plurality of D2D communication pairs are in proximity to each other.

8. The base station according to claim 7 , wherein the at least one processor is configured to determine whether the fifth and sixth D2D communication pairs are in proximity to each other based on at least one of: (a) a result of detection of a neighboring radio terminal reported from either radio terminal belonging to the fifth D2D communication pair; and (b) location information of at least one radio terminal belonging to the fifth D2D communication pair and location information of at least one radio terminal belonging to the sixth D2D communication pair.

9. The base station according to claim 8 , wherein

the at least one processor is configured to receive the result of detection of a neighboring radio terminal, and

the detection result includes at least one of: (a) an identifier of each of one or more neighboring radio terminals; and (b) an identifier of each of one or more D2D communication pairs to which the one or more neighboring radio terminals belong.

10. The base station according to claim 9 , wherein the detection result further includes at least one of: (c) an identifier of a base station or a cell with which each of the one or more neighboring radio terminals is associated; (d) received signal power of a signal transmitted from each of the one or more neighboring radio terminals; and (e) the number of times of detection of the one or more neighboring radio terminals.

11. A scheduling method performed in a base station, the method comprising:

scheduling radio resources to a plurality of device-to-device (D2D) transmissions performed by a plurality of D2D communication pairs, in accordance with an allocation rule that permits two D2D communication pairs that are not in proximity to each other to share an identical radio resource but prohibits two D2D communication pairs in proximity to each other from sharing an identical radio resource, each D2D transmission including wirelessly transmitting from one radio terminal directly to another radio terminal in each D2D communication pair without passing through the base station,

wherein the scheduling comprises:

allocating a first prioritized radio resource configured in a first cell managed by the base station, preferentially over another radio resource, to D2D transmission performed by a D2D communication pair in proximity to an adjacent-cell radio terminal that belongs to an adjacent cell of the first cell, and

allocating the other radio resource, preferentially over the first prioritized radio resource, to D2D transmission performed by a D2D communication pair that is not in proximity to the adjacent-cell radio terminal.

12. The method according to claim 11 , wherein the scheduling comprises allocating radio resources to the plurality of D2D transmissions in accordance with a proportional fairness algorithm on which the allocation rule is imposed.

13. The method according to claim 11 , wherein the scheduling comprises:

selecting a first D2D communication pair in a descending order of a scheduling metric on a first radio resource; and

if the first radio resource has not been allocated to D2D transmission performed by a second D2D communication pair that has a larger scheduling metric than the first D2D communication pair and is in a proximity relationship with the first D2D communication pair, allocating the first radio resource to D2D transmission performed by the first D2D communication pair.

14. The method according to claim 11 , wherein the first prioritized radio resource is a radio resource of which a base station of the adjacent cell prohibits use by the adjacent-cell radio terminal.

15. The method according to claim 11 , wherein

the other radio resource includes a second prioritized radio resource configured in the adjacent cell and a non-prioritized radio resource that is set to neither the first prioritized radio resource nor the second prioritized radio resource, and

the scheduling comprises allocating the second prioritized radio resource, preferentially over the first prioritized radio resource and the non-prioritized radio resource, to D2D transmission performed by a D2D communication pair that is not in proximity to the adjacent-cell radio terminal.

16. The method according to claim 11 , wherein

the plurality of D2D communication pairs include third and fourth D2D communication pairs, and

the scheduling comprises:

permitting the third and fourth D2D communication pairs to perform their respective D2D transmissions on an identical time-frequency resource when a proximity level indicating a geographic distance between the third and fourth D2D communication pairs is at a first level;

prohibiting the third and fourth D2D communication pairs from performing their respective D2D transmissions on an identical time-frequency resource and, instead, permitting the third and fourth D2D communication pairs to perform their respective D2D transmissions on a plurality of time-frequency resources that have the same time domain position and have different frequency domain positions, when the proximity level is at a second level higher than the first level; and

prohibiting the third and fourth D2D communication pairs from performing their respective D2D transmissions on the same time domain resource and, instead, permitting the third and fourth D2D communication pairs to perform their respective D2D transmissions on a plurality of time-frequency resources having different time domain positions, when the proximity level is at a third level higher than the second level.

17. A non-transitory computer readable medium storing a program for causing a computer to perform a scheduling method in a base station, wherein the scheduling method comprises:

scheduling radio resources to a plurality of device-to-device (D2D) transmissions performed by a plurality of D2D communication pairs, in accordance with an allocation rule that permits two D2D communication pairs that are not in proximity to each other to share an identical radio resource but prohibits two D2D communication pairs in proximity to each other from sharing an identical radio resource, each D2D transmission including wirelessly transmitting from one radio terminal directly to another radio terminal in each D2D communication pair without passing through the base station,

wherein the scheduling comprises:

allocating a first prioritized radio resource configured in a first cell managed by the base station, preferentially over another radio resource, to D2D transmission performed by a D2D communication pair in proximity to an adjacent-cell radio terminal that belongs to an adjacent cell of the first cell, and

allocating the other radio resource, preferentially over the first prioritized radio resource, to D2D transmission performed by a D2D communication pair that is not in proximity to the adjacent-cell radio terminal.

18. The non-transitory computer readable medium according to claim 17 , wherein the scheduling comprises allocating radio resources to the plurality of D2D transmissions in accordance with a proportional fairness algorithm on which the allocation rule is imposed.

19. The non-transitory computer readable medium according to claim 17 , wherein the first prioritized radio resource is a radio resource of which a base station of the adjacent cell prohibits use by the adjacent-cell radio terminal.

20. The non-transitory computer readable medium according to claim 17 , wherein

the other radio resource includes a second prioritized radio resource configured in the adjacent cell and a non-prioritized radio resource that is set to neither the first prioritized radio resource nor the second prioritized radio resource, and

the scheduling comprises allocating the second prioritized radio resource, preferentially over the first prioritized radio resource and the non-prioritized radio resource, to D2D transmission performed by a D2D communication pair that is not in proximity to the adjacent-cell radio terminal.