In DCI format 0-0 / 0-1 / 1-0 / 1-1, frequency domain resource assignment field is a parameter which determines the size of the Payload size.
In NR / 5G - PDSCH frequency domain position introduced into, for downstream use with a number of RB Coreset # 0 and DL initial BWP also used bandwidth or the currently activated DL Active BWP bandwidth. For the uplink bandwidth has UL Active BWP UL initial BWP bandwidth or the currently active.
In accordance with section 7.3.1.0 of the 38.212 described, the whole process is divided into four steps.
Step 0
The Common Search Space DCI format 0-0 and 1-0 determine the length of the DCI format.
If the DCI format 0-0 (prior to filling Padding) smaller than the length of 1-0 DCI format, so that the same length as the filling Padding 0 after 0-0 DCI format.
If the DCI format large length DCI format 1-0 than 0-0, then destroyed the high frequency domain resource assignment to make it the same length.
Step 1
The UE Specific Search Space DCI format 0-0 and 1-0 determine the length of the DCI format.
First, the DCI format 0-0 SUL and the length is equal to non-SUL, which is shorter then the Padding bits.
Then, the DCI format is equal to 1-0 and 0-0 of the DCI format length, which is shorter then the Padding bits.
Step 2
And determining the length of DCI format 0-1 of DCI format 1-1.
DCI format 0-1 and for non-SUL SUL, by filling both the length of the Padding bits to be equal to the short length.
如果DCI format 0-1和另外一个UE Specific Search Space的DCI format 0-0/1-0长度相同，则DCI format 0-1添加1bit。
如果DCI format 1-1和另外一个UE Specific Search SpaceDCI format 0-0/1-0长度相同，则DCI format 1-1添加1bit。
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Step 3
检测的DCI size总数规则。规则主要是用于减少DCI盲检的次数。
对于一个小区来说，最多4种Payload size；对于C-RNTI对应的不同DCI Payload size个数，最多为3。
如果Step 3种的规则不满足，那么进行下面的Step 4。
Step 4
可以看下Step 2处理之后例如C-RNTI可能的Payload Size种类会有
step 0 - common search space DCI format 0-0/1-0
step 1 - UE specific search space DCI format 0-0/1-0
step 2 - UE specific serach space DCI foramt 0-1
UE specific serach space DCI foramt 1-1
如果DCI format 0-0/1-0 Common Search Space和UE Specific Search Space选取的带宽不一样的话，那么就产生了4种Payload Size了。
首先，将Step 2中的DCI format 0-1和DCI format 1-1的长度确定过程中的padding比特去除（对于DCI fomrat 0-1中non-SUL和SUL的Padding比特应该不需要去除，否则这里DCI format 0-1和non-SUL是两种Payload Size？去除的应该只是后面长度相同时候添加的Padding比特？）。
然后，对DCI format 1-0 UE Specific Search Space的带宽使用Coreset#0或者DL initial BWP，选取哪一个，规则同DCI format 1-0 Common Search Space。
DCI format 0-0 UE Specific SS的带宽使用UL initial BWP。
如果DCI format 0-0长度小于 DCI format 1-0的长度, 那么DCI format 0-0填充Padding使其长度与DCI format 1-0长度相同。
如果DCI format 0-0长度大于DCI format 1-0, 那么DCI format 0-0打掉frequency domain resource assignment的高位比特，使其两者长度相同。
Step 4的步骤其实就是UE Specific Search Space中的DCI format 0-0/1-0参照了Step 1中Common Search Space中DCI format 0-0/1-0的处理规则。
最后不期望出现 -
DCI format 0-0在某一个UE Specific Search Space的payload size和另外一个UE Specific Search Space上的DCI format 0-1的payload size一样。
DCI format 1-0在某一个UE Specific Search Space的payload size和另外一个UE Specific Search Space上的DCI format 1-1的payload size一样。
