"Once a UE is configured with carrier aggregation, the UE is capable of simultaneously receiving or transmitting on all the CCs that are aggregated. Thus, the UE may be scheduled over multiple CCs simultaneously. The scheduling of downlink assignments and uplink grants for each CC may be via an additional carrier indicator field of 0-3 bits in DCI format(s) for a single CC. In case of 0 bits, there is no carrier indicator.
"An example illustrating the carrier aggregation of 5 CCs and the corresponding carrier indicator index to CC index mapping for a PDCCH with the carrier indicator field in CC #2 is shown in FIGS. 2 and 3, respectively.
"The use of a carrier indicator in the PDCCH is not without cost. The disadvantages of having a PDCCH carrier indicator include: increased complexity in PDCCH scheduling as the scheduling may have to be performed jointly over multiple CCs. Increased payload size of up to 3 bits for DCI formats if the carrier indicator is explicitly signaled. Potential increased number of blind decoding attempts per CC if UE is expected to blindly detect whether the non-zero-bit carrier indicator field exists in a DCI format and if the CCs can have different bandwidth size.
"From the UE's point of view, the increase in blind decoding attempts for a CC is undesirable due to the increased PDCCH processing latency and increased power consumption especially if the UE is required to perform the extra blind detections all the time but the benefit of PDCCH with configurable linkage is only limited to certain scenarios.
"It would therefore be desirable to provide a method for detecting carrier aggregation that minimizes the number of PDCCH blind decoding attempts required to be performed by the UE for each CC.
"The above discussion of background art is included to explain the context of the present invention. It is not to be taken as an admission that any of the documents or other material referred to was published, known or part of the common general knowledge at the priority date of any one of the claims of this specification.
"Solution to Problem
"According to one aspect, the present invention provides a method for detecting a downlink control structure for carrier aggregation in a communications network in which data transmission is scheduled by a physical downlink control channel (PDCCH), the method including the steps of, at a UE:
"receiving higher layer signaling enabling carrier aggregation for the UE, and
"reading the PDCCHs of component carriers (CCs), wherein the downlink control information (DCI) in the PDCCHs of each CC is read according to one of a plurality of predefined formats derived from the higher layer signaling.
"The higher layer signaling allows the carrier aggregation to be turned on or off, and allows the number of blind decoding attempts as well as the payload sizes of DCI formats to be kept to minimum when cross-carrier control is not needed (depending on deployment scenario or network operator's preference). The higher-layer signaling is transmitted only to UEs with carrier aggregation capability. The default setting assumed by both the eNodeB and the UE before the higher layer signaling is sent is no cross-carrier control, i.e. all DCI formats are with zero-bit carrier indicator fields.
"As the PDCCH of each CC is read in accordance with a predetermined DCI format signaled to the UE, the UE power and latency budget for PDCCH processing per CC may be reduced.
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