Radio Frame Configuration

1. A method comprising: storing, in a terminal device of a cellular communication system, definitions for a first radio frame configuration defining a frame structure of a radio frame comprising at least one sub-frame dedicated only for downlink transmission, wherein the terminal device stores definitions for a plurality of different radio frame configurations each defining at least one flexible special sub-frame, wherein at least two of the plurality of different radio frame configurations have different sub-frame lengths; storing, in the terminal device, definitions for a second radio frame configuration defining a frame structure of a radio frame comprising the at least one flexible special sub-frame configurable as either a flexible special downlink sub-frame or as an a flexible special uplink sub-frame, wherein the flexible special downlink sub-frame and the flexible special uplink sub-frame both comprise an uplink part and a downlink part, and wherein both the uplink part and the downlink part carry at least one of control information and a reference signal, wherein the definitions for the plurality of different radio frame configurations comprise the definitions for the first radio frame configuration and the definitions for the second radio frame configurations; receiving, from a network element of a the cellular communication system, a radio signal carrying an information element indicating a radio frame configuration applied in a cell of the cellular communication system; and selecting, on the basis of the received information element, a radio frame configuration amongst among a set of radio frame configurations comprising at least the first radio frame configuration and the second radio frame configuration and using the selected radio frame configuration in communication with the network element in the cell, wherein, among the at least two of the plurality of different radio frame configurations having different sub-frame lengths, either: a radio frame configuration having a greater sub-frame length has a smaller sub-carrier spacing in sub-frames than another one of the at least two of the plurality of different radio frame configurations, or a radio frame configuration having a smaller sub-frame length has a larger sub-carrier spacing in sub-frames than another one of the at least two of the plurality of different radio frame configurations.

2. The method of claim 1, wherein the first radio frame configuration defines that the frame structure of the radio frame further comprises at least one sub-frame dedicated only for uplink transmission, and the at least one flexible special sub-frame comprising an uplink part and a downlink part.

3. The method of claim 1, wherein the at least one flexible special sub-frame comprises a further uplink part or a further downlink part depending on whether the at least one flexible special sub-frame is configured as the flexible special uplink sub-frame or the flexible special downlink sub-frame.

4. The method of claim 1, wherein the terminal device stores definitions for a plurality of different radio frame configurations each defining said at least one flexible special sub-frame, wherein at least two of the plurality of different radio frame configurations have a different sub-frame length.

5. The method of claim 4, wherein a radio frame configuration having a greater sub-frame length has a smaller sub-carrier spacing in sub-frames.

6. The method of claim 1, further comprising in the terminal device: receiving a flexible special sub-frame and, together with the flexible special sub-frame, an indication of whether the flexible special sub-frame is a flexible special downlink frame sub-frame or a flexible special uplink frame sub-frame; and applying, to the received flexible special sub-frame, a sub-frame structure mapped to the received indication.

7. An apparatus comprising: at least one processor, and at least one memory comprising a computer program code, wherein the processor, the memory, and the computer program code are configured to storing instructions thereon that, when executed by the at least one processor, cause the apparatus to perform at least: provide providing a first radio frame configuration defining a frame structure of a radio frame comprising at least one sub-frame dedicated only for downlink transmission, wherein the apparatus stores definitions for a plurality of different radio frame configurations each defining at least one flexible special sub-frame, wherein at least two of the plurality of different radio frame configurations have different sub-frame lengths; provide providing a second radio frame configuration defining a frame structure of a radio frame comprising the at least one flexible special sub-frame configurable as either a flexible special downlink sub-frame or as a flexible special uplink sub-frame, wherein the flexible special downlink sub-frame and the flexible special uplink sub-frame both comprise an uplink part and a downlink part, and wherein both the uplink part and the downlink part carry at least one of control information and a reference signal, wherein the definitions for the plurality of different radio frame configurations comprise one or more definitions for the first radio frame configuration and one or more definitions for the second radio frame configurations; and select, amongst selecting, from among a set of radio frame configurations comprising at least the first and second radio frame configuration, a radio frame configuration and causing transmission of a radio signal carrying an information element indicating the selected radio frame configuration, wherein, among the at least two of the plurality of different radio frame configurations having different sub-frame lengths, either: a radio frame configuration having a greater sub-frame length has a smaller sub-carrier spacing in sub-frames than another one of the at least two of the plurality of different radio frame configurations, or a radio frame configuration having a smaller sub-frame length has a larger sub-carrier spacing in sub-frames than another one of the at least two of the plurality of different radio frame configurations.

8. The apparatus of claim 7, wherein the first radio frame configuration defines that the frame structure of the radio frame further comprises at least one sub-frame dedicated only for uplink transmission and the at least one flexible special sub-frame comprising an uplink part and a downlink part.

9. The apparatus of claim 7, wherein the processor, the memory, and the computer program code are configured to cause the apparatus to provide a plurality of different radio frame configurations each defining said at least one flexible special sub-frame, wherein at least two of the plurality of different radio frame configurations have a different sub-frame length.

10. The apparatus of claim 9, wherein a radio frame configuration having a greater sub-frame length has a smaller sub-carrier spacing in sub-frames.

11. The apparatus of claim 7 8, wherein the at least one flexible special sub-frame of the second radio frame configuration has a greater maximum length of an uplink part than a maximum length of an uplink part of the at least one flexible special sub-frame of the first radio frame configuration.

12. The apparatus of claim 7, wherein the at least one flexible special sub-frame comprises a further uplink part or a further downlink part depending on whether the at least one flexible special sub-frame is configured as the flexible special uplink sub-frame or the flexible special downlink sub-frame.

13. The apparatus of claim 12, wherein the further uplink part carries uplink data and the further downlink part carries downlink data.

14. An apparatus comprising: at least one processor, and at least one memory comprising a computer program code, wherein the processor, the memory, and the computer program code are configured to storing instructions thereon that, when executed by the at least one processor, cause the apparatus to perform at least: storing, in the at least one memory, definitions for a plurality of different radio frame configurations each defining at least one flexible special sub-frame, wherein at least two of the plurality of different radio frame configurations have different sub-frame lengths, store, in the at least one memory, wherein said definitions comprise a definition for a first radio frame configuration defining a frame structure of a radio frame comprising at least one sub-frame dedicated only for downlink transmission; and store, in the at least one memory, definitions a definition for a second radio frame configuration defining a frame structure of a radio frame comprising the at least one flexible special sub-frame configurable as either a flexible special downlink sub-frame or as an a flexible special uplink sub-frame, wherein the flexible special downlink sub-frame and the flexible special uplink sub-frame both comprise an uplink part and a downlink part, and wherein both the uplink part and the downlink part carry at least one of control information and a reference signal; receive receiving, from a network element of a cellular communication system, a message carrying an information element indicating a radio frame configuration applied in a cell of the cellular communication system; and select selecting, on the basis of the received information element, a radio frame configuration amongst from among a set of radio frame configurations comprising at least the first radio frame configuration and the second radio frame configuration and using the selected radio frame configuration in communication with the network element in the cell, wherein, among the at least two of the plurality of different radio frame configurations having different sub-frame lengths, either: a radio frame configuration having a greater sub-frame length has a smaller sub-carrier spacing in sub-frames than another one of the at least two of the plurality of different radio frame configurations, or a radio frame configuration having a smaller sub-frame length has a larger sub-carrier spacing in sub-frames than another one of the at least two of the plurality of different radio frame configurations.

15. The apparatus of claim 14, wherein the first radio frame configuration defines that the frame structure of the radio frame further comprises at least one sub-frame dedicated only for uplink transmission, and the at least one flexible special sub-frame comprising an uplink part and a downlink part.

16. The apparatus of claim 14, wherein the at least one flexible special sub-frame comprises a further uplink part or a further downlink part depending on whether the at least one flexible special sub-frame is configured as the flexible special uplink sub-frame or the flexible special downlink sub-frame.

17. The apparatus of claim 16, wherein the further uplink part carries uplink data and the further downlink part carries downlink data.

18. The apparatus of claim 14, wherein the processor, the memory, and the computer program code are configured to cause the apparatus to store definitions for a plurality of different radio frame configurations each defining said at least one flexible special sub-frame, wherein at least two of the plurality of different radio frame configurations have a different sub-frame length.

19. The apparatus of claim 18, wherein a radio frame configuration having a greater sub-frame length has a smaller sub-carrier spacing in sub-frames.

20. The apparatus of claim 14 15, wherein the at least one flexible special sub-frame of the second radio frame configuration has a greater maximum length of an uplink part than a maximum length of an uplink part of the at least one flexible special sub-frame of the first radio frame configuration.

21. The apparatus of claim 14, wherein the instructions stored on the at least one memory, when executed by the at least one processor, the memory, and the computer program code are configured to further cause the apparatus to perform at least: receive receiving a flexible special sub-frame and, together with the flexible special sub-frame, an indication of whether the flexible special sub-frame is a flexible special downlink frame sub-frame or a flexible special uplink frame sub-frame; and apply applying, to the received flexible special sub-frame, a sub-frame structure mapped to the received indication.

22. An apparatus comprising: at least one processor, and at least one memory storing instructions thereon that, when executed by the at least one processor, cause the apparatus to perform at least: storing, in the at least one memory, definitions for a radio frame configuration defining a frame structure of a radio frame comprising at least one flexible special sub-frame, wherein the at least one flexible special sub-frame comprises an uplink part, a downlink part and a flexible part, wherein the uplink part is configured to carry at least control information in a physical uplink control channel, and wherein the flexible part is configurable to be used for downlink or uplink transmission; receiving, from a network element of a cellular communication system, a message carrying an information element indicating a radio frame configuration applied in the cellular communication system; selecting, on the basis of the received information element, a radio frame configuration from among a set of radio frame configurations comprising at least the radio frame configuration corresponding to the stored definitions; and using the selected radio frame configuration in communication with the network element, wherein the set of radio frame configurations support different subcarrier spacings.

23. The apparatus of claim 22, wherein the uplink part is configured to carry at least a first reference signal multiplexed with the physical uplink control channel, and wherein the downlink part is configured to carry at least control information and at least a second reference signal.

24. A method comprising: storing, in a terminal device for use in a cellular communication system, definitions for a radio frame configuration defining a frame structure of a radio frame comprising at least one flexible special sub-frame, wherein the at least one flexible special sub-frame comprises an uplink part, a downlink part and a flexible part, wherein the uplink part is configured to carry at least control information in a physical uplink control channel, and the flexible part is configurable to be used for downlink or uplink transmission; receiving, from a network element of the cellular communication system, a message carrying an information element indicating a radio frame configuration applied in the cellular communication system; selecting, on the basis of the received information element, a radio frame configuration from among a set of radio frame configurations comprising at least the radio frame configuration corresponding to the stored definitions; and using the selected radio frame configuration in communication with the network element in the cell, wherein the set of radio frame configurations supports different subcarrier spacings.

25. The method of claim 24, wherein the uplink part is configured to carry at least a first reference signal multiplexed with the physical uplink control channel, and wherein the downlink part is configured to carry at least control information and at least a second reference signal.

26. An apparatus comprising: at least one processor, and at least one memory storing instructions thereon that, when executed by the at least one processor, cause the apparatus to perform at least: receiving, from a network element of a cellular communication system, a message carrying an information element indicating a radio frame configuration applied in the cellular communication system; selecting, on the basis of the received information element, a radio frame configuration from among a set of radio frame configurations, wherein the radio frame configuration supports subcarrier spacings that are different from other subcarrier spacings supported by other radio frame configurations of the set of radio frame configurations, wherein the set of radio frame configurations comprises a radio frame configuration that defines a frame structure of a radio frame comprising at least one flexible special sub-frame, wherein the at least one flexible special sub-frame comprises an uplink part, a downlink part and a flexible part, wherein the uplink part is configured to carry at least control information, and wherein the flexible part is configurable to be used for downlink or uplink transmission; and using the selected radio frame configuration in communication with the network element.

27. The apparatus of claim 26, wherein the set of radio frame configurations further comprises a second radio frame configuration comprising at least one sub-frame dedicated only for downlink transmission, at least one sub-frame dedicated only for uplink transmission, and the at least one flexible special sub-frame comprising an uplink part and a downlink part.

28. The apparatus of claim 26, wherein two or more of the set of radio frame configurations each define the at least one flexible special sub-frame, and wherein at least two of the two or more radio frame configurations have a different sub-frame length.

29. The apparatus of claim 28, wherein a radio frame configuration having a greater sub-frame length has a smaller sub-carrier spacing in sub-frames.

30. The apparatus of claim 27, wherein the at least one flexible special sub-frame has a greater maximum length of an uplink part than a maximum length of an uplink part of the flexible special sub-frame of the second radio frame configuration.

31. The apparatus of claim 26, wherein the at least one flexible special sub-frame comprises a further uplink part or a further downlink part depending on whether the flexible part is configured for downlink or uplink transmission.

32. The apparatus of claim 31, wherein the further uplink part carries uplink data and the further downlink part carries downlink data.

33. A method comprising: receiving, from a network element of a cellular communication system, a message carrying an information element indicating a radio frame configuration applied in a cellular communication system; selecting, on the basis of the received information element, a radio frame configuration from among a set of radio frame configurations, wherein the radio frame configuration supports subcarrier spacings that are different from other subcarrier spacings supported by other radio frame configurations of the set of radio frame configurations, wherein the set of radio frame configurations comprises a radio frame configuration that defines a frame structure of a radio frame comprising at least one flexible special sub-frame, wherein the at least one flexible special sub-frame comprises an uplink part, a downlink part and a flexible part, wherein the uplink part is configured to carry at least control information, and the flexible part is configurable to be used for downlink or uplink transmission; and using the selected radio frame configuration in communication with the network element.

34. The method of claim 33, wherein the set of radio frame configurations further comprises a second radio frame configuration comprising at least one sub-frame dedicated only for downlink transmission, at least one sub-frame dedicated only for uplink transmission, and the at least one flexible special sub-frame comprising an uplink part and a downlink part.

35. The method of claim 33, wherein two or more of the set of radio frame configurations each define the at least one flexible special sub-frame, and wherein at least two of the two or more radio frame configurations have a different sub-frame length.

36. The method of claim 35, wherein a radio frame configuration having a greater sub-frame length has a smaller sub-carrier spacing in sub-frames.

37. The method of claim 34, wherein the at least one flexible special sub-frame has a greater maximum length of an uplink part than a maximum length of an uplink part of the flexible special sub-frame of the second radio frame configuration.

38. The method of claim 33, wherein the at least one flexible special sub-frame comprises a further uplink part or a further downlink part depending on whether the flexible part is configured for downlink or uplink transmission.

39. The method of claim 38, wherein the further uplink part carries uplink data and the further downlink part carries downlink data.