How to reconstruct RF signal using IQ data
The RF signal $r(t)$ is obtained from the complex baseband (IQ) signal $s(t)=x(t)+jy(t)$ in the following way:

$$r(t)=\text{Re}\{s(t)e^{j\omega_0t}\}\tag{1}$$

where $\omega_0$ is the carrier frequency (in rad/s). There are two other equivalent representations of $(1)$, where I use $s(t)=x(t)+jy(t)=a(t)e^{j\phi(t)}$:

$$\begin{align}r(t)&amp;=x(t)\cos(\omega_0t)-y(t)\sin(\omega_0t)\tag{2}\\
r(t)&amp;=a(t)\cos(\omega_0t+\phi(t))\tag{3}\end{align}$$

Eq. $(2)$ shows that the I- and Q-components are both modulated by orthogonal carriers, whereas $(3)$ shows that $r(t)$ generally exhibits amplitude modulation as well as phase modulation.

The quote in your question suggests that in the respective text the signals are all represented as discrete-time signals, hence the decimation and interpolation stages.