In software versions 2.0 and earlier, in Custom OFDM resource allocation, the Symbol Index and Subcarrier Index had a global mapping, meaning that all the subcarriers defined in the Subcarrier Index were allocated in all the symbols defined in the Symbol Index. For some signals, especially those with scattered pilot, this manner was not convenient enough for the user to configure it. The user had to split a single pilot into several resource blocks, and sometimes may need to write some code to generate the interleaved payload bits or IQ values.
The solution to this issue (software versions 3.0 and later) is to support 1-to-1 mapping between the Symbol Index and the Subcarrier Index by introducing a new syntax with Group ID. That is, the individual symbol/subcarrier or a range of symbols/subcarriers can be assigned an ID. And only the symbol/subcarrier groups with the same ID will be allocated to current resource block. This new syntax can be combined with legacy syntax, while the legacy syntax still allocates symbol/subcarrier in a global manner.
The syntax format is like below:
{n|xxxxx}
where n = 1….N is the group ID,
xxxx is the individual or range of symbols/subcarriers with legacy format
n = 0 is a global ID, which means {0|xxxx} is actually equivalent to xxxx (legacy format) itself, and will be allocated with all the resources in Symbol Index or Subcarrier Index. When there is no corresponding group defined (i.e. group 1 only defined in Symbol Index but not in Subcarrier Index), the group mapping will be ignored and it only maps to those resources in global group if they exist.
For example:
Symbol Index = {1|0},{2|1},2:3
Subcarrier Index = {1|-24:4:-4},{2|4:4:24},10
In this resource block, group 1 is allocated with subcarrier -24:4:-4 only in symbol 0, and group 2 is allocated with subcarriers 4:4:24 only in symbol 1. Symbol 2 and 3 belong to the global group and will be allocated with all the subcarriers -24:4:-4, 4:4:24 and 10. Subcarrier 10 belongs to global group and will be allocated in all symbols from 0 to 3. See the red areas of the resource mapping graph below. The data symbol to resource mapping order is not changed and also applicable to the new syntax.
When the new group ID syntax is used in either Symbol Index or Subcarrier Index, the ‘Repeat Every x Symbols’ in IQ values editor will be disabled and x is always set to 0, because there is no repetition between symbols.