
2.2.2 Memory-Less Multilevel Modulation
Modulation formats whose symbol alphabets consist of more than the absolute
minimum of two symbols are generally referred to as multilevel formats. If the
assignment of symbols to bits or to groups of bits is independent of the symbols
sent before or after, one speaks of memory-less modulation, discussed in this
section. In contrast, if the assignment is made according to certain rules for the
succession of different symbols, one speaks of modulation with memory [40],
discussed in Section 2.2.3.
Introducing more symbols to a modulation alphabet can either be done by
expanding the dimensionality of the signal