Question: what is the difference between 16-qam and 64-qam?
Answer: 16 QAM has four bits per symbol, so to encode our 12 bits, we break them up into three groups of four, thereby only using 3 symbols. 64 QAM has a more dense symbol that represents six bits per symbol, so to encode our 12 bits, we break up the 12-bit string into two groups of six, thereby only using two symbols.