Single Carrier QAM Modulator

Abstract

The block diagram of the conventional QAM modulator is shown in Figure 2.4. The output of the QAM modulator is

$$ \begin{gathered} {I_{out}}\left( n \right) = I\left( n \right)\cos \left( {{\omega _{QDDS}}n} \right) + Q\left( n \right)\sin \left( {{\omega _{QDDS}}n} \right) \hfill \\ {Q_{out}}\left( n \right) = Q\left( n \right)\cos \left( {{\omega _{QDDS}}n} \right) - I\left( n \right)\sin \left( {{\omega _{QDDS}}n} \right), \hfill \\ \end{gathered} $$

((12.1))

where ω_DDS is the output frequency of the quadrature direct digital synthesizer (QDDS), and I(n)> Q(n) are pulse shaped and interpolated quadrature data symbols [Tan95a]. In the base station, the multi-user I/Q data is combined and weighted and so the input of the I/Q branches is 12 bits in Table 12.1. The specifications are not so strict in Table 12.1 as in Table 11.1 because it is possible to use steep analog bandpass filters around the single carrier signal in Figure 11.2, and the adjacent channels’ power around the single carrier signal can be further reduced.