In 5G NR, the frequency domain scheduling range information of PDC channel and the number of OFDM symbols in time domain are encapsulated in CORESET, and the time domain start symbol information and detection period information are encapsulated in SearchSpace. It is called frequency domain scheduling range information because UE can only know that PDC will send PDC in the RB range of COERSET at this time, but can't determine which RB to send it on. Therefore, after the physical resource information, search space type (CSS or USS) and other information are determined in the PDC channel, the UE will search PDC in different search spaces according to different RNTI types. Because UE does not know the time-frequency position sent by PDC, it can only continue to demodulate the candidate set of PDC. Therefore, this process is called blind detection of PDC.
Before blind detection, the UE can know the time-frequency resource information of the PDC, the scheduling period, the CCE aggregation degree that the PDC may send (obtained by the nrofCandidates parameter in the search space) and the number of blind detections required for each aggregation degree according to the search space and the core set associated with the search space. Therefore, according to the above information, the UE can determine each PDCCH candidate set by combining the blind detection formula and decode each candidate set. Once the decoding is successful, the blind detection process will stop. The blind detection formula of PDCCH is as follows
Due to the constraints of hardware computing resources, delay and power consumption of ue, and the consideration of scheduling flexibility, the blind detection complexity of PDC is an important consideration in the design of PDC protocol. Therefore, the 38.2 13 protocol clearly defines the maximum number of PDC candidate sets in each time slot of each service cell, and the maximum number of PDC candidate sets in different SCS is shown in the following table.
In addition, the protocol also defines the maximum number of non-overlapping CCEs on each time slot of each serving cell. This is because the more non-overlapping CCEs in a time slot, the smaller the probability of PDC between different UEs in the same service cell, but at the same time, the time-frequency resource overhead of PDC will also increase. Therefore, through the provisions of the Protocol, a good balance has been achieved between the two. The maximum number of non-overlapping CCEs is shown in the following table.
As can be seen from the above two tables, when SCS increases, the number of candidate sets and the maximum number of non-overlapping CCEs decrease. This is because the large SCS is mainly used in high frequency band, and the coverage of the cell is relatively small, so the number of UE to be scheduled is relatively small.
Like 4G LTE, the identifier assigned to the UE by the wireless side in 5G NR is still called RNTI (Radio Network Temporary Identifier), and the signaling information between the UE and gNB is used as the identifier of different UEs. The scope and function of RNTI used in the above blind detection process are defined in detail in the protocol 38.438+0.
The following table shows the range of values of various types of RNTI.
Various specific functions similar to RNTI are shown in the following table.