Digital Modulation: The Basic Principles

Abstract

The modulation methods used in most fifth generation (5G) wireless transport links are largely various versions of quadrature amplitude modulation (QAM). At the low end of modulation order, we find BPSK, which is not QAM, followed by QPSK, which is really 4-QAM. At the high end, we find 8192-QAM and in a few instances 16384-QAM, referred to also as 16 K-QAM. The QAM modulation order can be 2²ⁿ or 2²ⁿ⁺¹ where n is an integer of value 1 or above. These are the methods, therefore, that we are going to study in this chapter, along with a number of schemes involved in their realization such as up- and downconversion and carrier and symbol timing recovery. In these methods, baseband signals linearly modulate an RF carrier. Ideally, we would like to cut to the chase and study these methods immediately. This is not what we will do, however. First, the fundamentals of baseband transmission techniques will be reviewed, as these form the foundation upon which the techniques involving the linear modulation of an RF carrier are based. This approach will allow us to gain a strong intuitive understanding of digital modulation and the spectral efficiency and bit error rate characteristics thereof.