Use of hyphens in acronyms

I'd say the hyphen refers to the "with" in the spelled out form.

Usually, acronyms are short (2-4 letters). In this case, the term "PTPSD" does not convey its intended meaning i.e. probabilistic tree pruning sphere decoding which makes no sense.

Also, the acronym can be split up into two terms by themselves: probabilistic tree pruning, which is one thing, and sphere decoding, which is another. Thus, a hyphen is used to ensure that the two things are recognized as two separate entities which form one other when linked together.

For example, when using an acronym such as NATO, no hyphen is used as it is merely one entity (North Atlantic Treaty Organization). But when another entity is introduced, a hyphen is included, leading to the fictional SEA-NATO (South-East Asian North Atlantic Treaty Organization).

However, note that not every "with" has to be replaced by a hyphen. Basically, the rule of thumb is to follow whoever coined the acronym.

It seems to me the hyphen is not meant to represent the word "with", but rather to separate the two parts of the acronym, PTP and SD. This separation indicates that PTP-SD is made up of its two parts, and it does a better job of representing the algorithm than combining everything into one big PTPSD.

Similarly, consider the acronym CD-ROM. The hyphen here is standard, and denotes that this is a Compact Disc which uses Read Only Memory. Since ROM is itself an acronym, putting the hyphen there makes it clear that CD-ROM has something to do with ROM and isn't just an entirely new acronym.

This analysis does not cover rules on hypheting acronyms for a line-break (the acronym wraps around from one line to the next