N. Bloembergen (1949) Physica 15 386-426. (Link to Article)
Minimum labelling: 13C
PDSD stands for Proton-Driven Spin Diffusion. Magnetization is transferred from hydrogen to 13C nuclei. From here it is transferred to other 13C nuclei which are close in space. As the name of the experiment suggests, protons are involved in this transfer (though this is not specifically indicated in the diagram).
This is the most standard experiment and could be considered the solid-state euqivalent of the HSQC. It is probably the first experiment you will record on a protein sample and should help you assess the general quality of the spectra you can achieve with that sample. Essentially all 13C atoms within a certain distance of one another are correlated by cross peaks in the spectrum. In practice this means that at short mixing times all carbon atoms within one spin-system (residue) are coupled to one another (except perhaps for some longer-range pairs of atoms such as Cα and Cε). At longer mixing times correlations between residues will appear, too. Increasingly, the PDSD is being replaced by the DARR experiment, especially when using longer mixing times.