Method for PDCCH buffer management
Approaches are described that enhance the reliability of physical downlink control channel (PDCCH) detection where the PDCCH can be transmitted repeatedly with different beams. The approaches use soft combining where the user equipment (UE) combines the soft bits from each repetition, with the combined soft bits used to jointly decode the PDCCH repetitions. To support the soft combining, the UE needs to buffer the soft bits. Buffering approaches include determining what contributes towards the buffering, including scenarios where one of the linked search sets (SSs) is dropped, what is contributed in a linked SS set pair, how the duration of buffer counting is determined, and how the UE reports its maximum buffer size capability. In scenarios where the required buffer size exceeds the UE maximum buffer size, a priority rule may be used in the PDCCH decoding using the SS sets pair, where the priority is based on the SS type, the serving cell index, the SS set ID and/or the control channel resource set (CORESET) ID.
1 . A user equipment (UE) comprising:
a radio frequency (RF) receiver configured to receive a first physical downlink control channel (PDCCH) signal and a second PDCCH signal from a base station, the second PDCCH signal being a repetition of the first PDCCH signal and sent via a different beam from the base station than that of the first PDCCH signal, the first PDCCH signal and the second PDCCH signal sharing a same control channel element (CCE) aggregation level and a starting candidate index, the first PDCCH signal and the second PDCCH signal configured by the base station to use two linked search space (SS) sets, wherein a maximum number of linked SS sets overlapping in a time domain are predefined or are determined based on reported UE capability;
processing circuitry coupled to the RF receiver, the processing circuitry configured to blindly decode the first PDCCH signal and the second PDCCH signal by obtaining respective soft-bits from the first PDCCH signal and the second PDCCH signal;
a buffer coupled to the processing circuitry and configured to buffer the respective soft-bits for a duration, wherein the buffer is incremented using one of per component carrier (CC), per bandwidth part (BWP), counted across CCs in a band, counted across CCs in a band combination, counted across CCs in a frequency range (FR), or counted per UE; and
the processing circuitry further configured to combine the respective soft-bits to jointly decode the first PDCCH signal and the second PDCCH signal.
2 . The UE of claim 1 , wherein the one of per component carrier (CC), per bandwidth part (BWP), counted across CCs in a band, counted across CCs in a band combination, counted across CCs in a frequency range (FR), or counted per UE is selected based on an RRC parameter.
3 . The UE of claim 1 , wherein the UE is engaged in a multi-downlink control information (DCI)-based multi-transmission-reception-point (multi-TRP) operation, and the buffer is incremented on a per TRP-control channel resource set (CORESET) associated with a same CORESETPoolIndex, or is counted across TRPs.
4 . The UE of claim 1 , wherein one of the two linked SS sets is dropped due to one of overbooking, QCL-TypeD collision handling, overlapping of SSB, overlapping of rate matching resources, overlapping with semi-static/dynamic uplink (UL) symbols or a physical random access channel (PRACH).
5 . The UE of claim 1 , wherein the buffer is incremented based on all linked PDCCH candidates, or the buffer is incremented based on a maximum total number of resource elements (REs) for each CCE aggregation level.
6 . The UE of claim 1 , wherein the duration of the buffer starts from a first symbol of an earliest SS set, and stops after K symbols at a last symbol of a later-ending SS set.
7 . The UE of claim 6 , wherein K is predefined, is reported as a UE capability, or is configured by a higher layer signaling.
8 . The UE of claim 1 , wherein the duration of the buffer starts from a last symbol of an earliest SS set, and stops after K symbols at a last symbol of a later-ending SS set.
9 . The UE of claim 8 , wherein K is predefined, is reported as a UE capability, or is configured by a higher layer signaling.
10 . The UE of claim 1 , wherein the UE reports an indication of a maximum supported buffer size.
11 . A method comprising:
receiving, by a user equipment (UE), a first physical downlink control channel (PDCCH) signal and a second PDCCH signal from a base station, the second PDCCH signal being a repetition of the first PDCCH signal and sent via a different beam from the base station than that of the first PDCCH signal, the first PDCCH signal and the second PDCCH signal sharing a same control channel element (CCE) aggregation level and a starting candidate index, the first PDCCH signal and the second PDCCH signal configured by the base station to use two linked search space (SS) sets, wherein a maximum number of linked SS sets overlapping in a time domain are predefined or are determined based on reported UE capability;
blindly decoding the first PDCCH signal and the second PDCCH signal by obtaining respective soft-bits from the first PDCCH signal and the second PDCCH signal;
buffering, by the UE in a buffer, the respective soft-bits for a duration, wherein the buffer is incremented using one of per component carrier (CC), per bandwidth part (BWP), counted across CCs in a band, counted across CCs in a band combination, counted across CCs in a frequency range (FR), or counted per UE; and
combining the respective soft-bits to jointly decode the first PDCCH signal and the second PDCCH signal.
12 . The method of claim 11 , wherein the one of per component carrier (CC), per bandwidth part (BWP), across CCs in a band, across CCs in a band combination, across CCs in a frequency range (FR), or per UE is selected based on an RRC parameter.
13 . The method of claim 11 , wherein the UE is engaged in a multi-downlink control information (DCI)-based multi-transmission-reception-point (multi-TRP) operation, and the buffer is incremented on a per TRP-control channel resource set (CORESET) associated with a same CORESETPoolIndex, or is counted across TRPs.
14 . The method of claim 11 , wherein one of the two linked SS sets is dropped due to one of overbooking, QCL-TypeD collision handling, overlapping of SSB, overlapping of rate matching resources, overlapping with semi-static/dynamic uplink (UL) symbols or a physical random access channel (PRACH).
15 . The method of claim 11 , wherein the buffer is incremented based on all linked PDCCH candidates, or the buffer is incremented based on a maximum total number of resource elements (REs) for each CCE aggregation level.
16 . The method of claim 11 , wherein a priority rule for incrementing the buffer is based on a type of SS, a serving cell index, an ID of a SS set, or an ID of a control channel resource set (CORESET).
17 . The method of claim 11 , further comprising dropping at least one low-priority SS set pairs to accommodate a maximum supported buffer size.
18 . The method of claim 11 , further comprising selectively decoding at least one low-priority SS set pair to accommodate a maximum supported buffer size.
19 . The method of claim 11 , further comprising dropping or selectively decoding at least one low-priority SS set pair based on a reported capability of the UE or based on a configuration transmitted by the base station.
20 . A base station comprising:
a radio frequency (RF) transceiver configured to receive an indication of a maximum supported buffer size of a user equipment (UE);
processing circuitry, coupled to the RF transceiver, configured to generate a first physical downlink control channel (PDCCH) signal and a second PDCCH signal, the second PDCCH signal being a repetition of the first PDCCH signal, the first PDCCH signal and the second PDCCH signal sharing a same control channel element (CCE) aggregation level and a starting candidate index, the first PDCCH signal and the second PDCCH signal configured to use two linked search space (SS) sets, wherein a maximum number of linked SS sets overlapping in a time domain are predefined or are determined based on reported UE capability;
the processing circuitry further configured to adjust scheduling of the first PDCCH signal or the second PDCCH signal, or to adjust priorities of the two linked SS sets based on the indication of the maximum supported buffer size;
the RF transceiver further configured to transmit the first PDCCH signal and the second PDCCH signal to the UE; and
an RRC parameter, wherein the RRC parameter causes the UE to increment a buffer using one of per component carrier (CC), per bandwidth part (BWP), count across CCs in a band, count across CCs in a band combination, count across CCs in a frequency range (FR), or count per UE.