Blind decoding

1. A method, comprising:

selecting, in a system in which a communication device searches for transmissions of downlink control information for said communication device, a combination of search spaces for the transmissions by a plurality of transmission techniques of the downlink control information for the communication device, wherein said selecting comprises selecting a predefined combination from a plurality of predefined combinations, and wherein said plurality of predefined combinations comprises a predefined combination according to which no search space is assigned to transmissions of downlink control information by one of said plurality of transmission techniques; and

transmitting an indication of the result of the selected combination to said communication device.

2. A method according to claim 1 , comprising deciding how much search space to assign to transmissions of downlink control information for said communication device by one or more of said plurality of transmission techniques relative to transmissions of downlink control information for said communication device by one or more others of said plurality of transmission techniques.

3. A method according to claim 1 , wherein a plurality of aggregation levels are used for the transmission of downlink control information, and a respective search space is predefined for each aggregation level for each transmission technique; and wherein the method comprises: selecting a respective set of one or more aggregation levels for each of said plurality of transmission techniques; and transmitting an indication of the selected respective set of aggregation levels to said communication device.

4. A method according to claim 1 , wherein said selecting is performed at least partly on the basis of one or more of: (a) a size of a load on a cell in which the transmissions are made, and (b) channel state information for a wireless interface with the communication device.

5. A method according to claim 1 , wherein said plurality of transmission techniques comprise: a first transmission technique involving the transmission of one or more reference signals specific to said communication device; and a second transmission technique that does not involve transmission of one or more reference signals specific to said communication device.

6. A method according to claim 1 , wherein said plurality of transmission techniques comprise: a first transmission technique involving the transmission of both one or more reference signals specific to said communication device and one or more channel-state-information reference signals; and a second transmission technique involving transmission of one or more cell-specific reference signals.

7. A method according to claim 1 , wherein said plurality of transmission techniques comprise: a first transmission technique involving the precoding and transmission of demodulation reference signals together with the precoding and transmission of data symbols defining downlink control information, and the transmission of one or more channel state information reference signals together with the transmission of precoded data symbols defining downlink control information; and a second transmission technique that involves transmission of cell-specific reference signals together with transmission of precoded data symbols defining downlink control information.

8. An apparatus comprising:

a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to:

select, in a system in which a communication device searches for transmissions of downlink control information for said communication device, a combination of search spaces for the transmissions by a plurality of transmission techniques of the downlink control information for the communication device, wherein selecting the combination further comprises selecting a predefined combination from a plurality of predefined combinations, and wherein said plurality of predefined combinations comprises a predefined combination according to which no search space is assigned to transmissions of downlink control information by one of said plurality of transmission techniques; and

transmit an indication of the result of the selected combination to said communication device.

9. An apparatus according to claim 8 , wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to: decide how much search space to assign to transmissions of downlink control information for said communication device by one or more of said plurality of transmission techniques relative to transmissions of downlink control information for said communication device by one or more others of said plurality of transmission techniques.

10. An apparatus according to claim 8 , wherein a plurality of aggregation levels are used for the transmission of downlink control information, and a respective search space is predefined for each aggregation level for each transmission technique; and wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to: select a respective set of one or more aggregation levels for each of said plurality of transmission techniques; and transmitting an indication of the selected respective set of aggregation levels to said communication device.

11. An apparatus according to claim 8 , wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to: perform said selection at least partly on the basis of one or more of: (a) a size of a load on a cell in which the transmissions are made, and (b) channel state information for a wireless interface with the communication device.

12. An apparatus according to claim 8 , wherein said plurality of transmission techniques comprise: a first transmission technique involving the transmission of one or more reference signals specific to said communication device; and a second transmission technique that does not involve transmission of one or more reference signals specific to said communication device.

13. An apparatus according to claim 8 , wherein said plurality of transmission techniques comprise: a first transmission technique involving the transmission of both one or more reference signals specific to said communication device and one or more channel-state-information reference signals; and a second transmission technique involving transmission of one or more cell-specific reference signals.

14. A method, comprising:

receiving, at a communication device, indication of a result of a selection of a combination of search spaces for transmissions by a plurality of transmission techniques of downlink control information for said communication device; and

searching, at the communication device, for the transmissions of the downlink control information for said communication device, wherein said searching is performed on the basis of the received indication, and wherein the received indication identifies one of a plurality of predefined combinations including a predefined combination according to which no search space is assigned to transmissions of downlink control information by one of said plurality of transmission techniques.

15. A method according to claim 14 , wherein a plurality of aggregation levels are used for the transmissions of downlink control information, and a respective search space is predefined for each aggregation level for each transmission technique; and wherein the method comprises: receiving an indication of a set of aggregation levels, wherein the set comprises a set of one or more aggregation levels for each of said plurality of transmission techniques.

16. A method according to claim 14 , wherein said plurality of transmission techniques comprise: a first transmission technique involving the transmission of one or more reference signals specific to said communication device; and a second transmission technique that does not involve transmission of one or more reference signals specific to said communication device.

17. A method according to claim 14 , wherein said plurality of transmission techniques comprise: a first transmission technique involving the transmission of both one or more reference signals specific to said communication device and one or more channel-state-information reference signals; and a second transmission technique involving transmission of one or more cell-specific reference signals.

18. A method according to claim 14 , wherein said plurality of transmission techniques comprise: a first transmission technique involving the precoding and transmission of demodulation reference signals together with the precoding and transmission of data symbols defining downlink control information, and the transmission of one or more channel state information reference signals together with the transmission of precoded data symbols defining downlink control information; and a second transmission technique that involves transmission of cell-specific reference signals together with transmission of precoded data symbols defining downlink control information.

19. An apparatus, comprising:

a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to:

receive, at a communication device, indication of a result of a selection of a combination of search spaces for transmissions by a plurality of transmission techniques of downlink control information for said communication device; and

search, at the communication device, for the transmissions of the downlink control information for said communication device, wherein said searching is performed on the basis of the received indication, and wherein the received indication identifies one of a plurality of predefined combinations including a predefined combination according to which no search space is assigned to transmissions of downlink control information by one of said plurality of transmission techniques.

20. An apparatus according to claim 19 , wherein a plurality of aggregation levels are used for the transmissions of downlink control information, and a respective search space is predefined for each aggregation level for each transmission technique; and wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to: receive an indication of a set of aggregation levels, wherein the set comprises a set of one or more aggregation levels for each of said plurality of transmission techniques.

21. A method according to claim 19 , wherein said plurality of transmission techniques comprise: a first transmission technique involving the transmission of one or more reference signals specific to said communication device; and a second transmission technique that does not involve transmission of one or more reference signals specific to said communication device.

22. A method according to claim 19 , wherein said plurality of transmission techniques comprise: a first transmission technique involving the transmission of both one or more reference signals specific to said communication device and one or more channel-state-information reference signals; and a second transmission technique involving transmission of one or more cell-specific reference signals.

23. A computer program product having a non-transitory computer-readable medium encoded thereon with instructions that, when executed by a computer, cause an apparatus to perform at least the following:

selecting, in a system in which a communication device searches for transmissions of downlink control information for said communication device, a combination of search spaces for the transmissions by a plurality of transmission techniques of the downlink control information for the communication device, wherein said selecting comprises selecting a predefined combination from a plurality of predefined combinations, and wherein said plurality of predefined combinations comprises a predefined combination according to which no search space is assigned to transmissions of downlink control information by one of said plurality of transmission techniques; and

transmitting an indication of the result of the selected combination to said communication device.

24. A computer program product having a non-transitory computer-readable medium encoded thereon with instructions that, when executed by a computer, cause an apparatus to perform at least the following:

receiving, at a communication device, indication of a result of a selection of a combination of search spaces for transmissions by a plurality of transmission techniques of downlink control information for said communication device; and

searching, at the communication device, for the transmissions of the downlink control information for said communication device, wherein said searching is performed on the basis of the received indication, and wherein the received indication identifies one of a plurality of predefined combinations including a predefined combination according to which no search space is assigned to transmissions of downlink control information by one of said plurality of transmission techniques.