This question is specifically directed at Maximilian Matthé (as you work with 5G systems), and to anyone who can shed some light.
I am trying to implement a GFDM system with a total of N = K*M symbols, where K = total number of carriers, and M = total number of subsymbols. I believe that in order to improve the Out Of Band radiation only a subset of carriers, Kon < K, are allocated to carry information while the other carriers are left as blanks.
Therefore, when mapping the data symbols (that are QAM modulated) of the allocated carriers into a 2D time frequency matrix of the size KxM, there are zeros introduced into the modulated data. This results in an extra symbol at the origin of the QAM constellation.
This seems incorrect as there is another symbol that is part of the constellation. For example, 16-QAM would now have an additional symbol at the origin as shown in the image below.
However, I feel like this might be ok because the extra symbol is at the origin, and therefore has no amplitude, phase, and surely would not require any transmission energy.
Although, on the receiver side the constellation looks like this:
So now the added symbols at zero seems to have some amplitude and phase. Would they be taking up some energy ?
So my question is, is this ok? It is justifiable at all? Or should i rather skip out adding these zeros ?