  Determining the mechanism responsible for the plasma heating and particle
acceleration is a fundamental problem in the study of the heliosphere. Due to
efficient wave-particle interactions of ion-scale waves with charged particles,
these waves are widely believed to be a major contributor to ion energization,
and their contribution considerably depends on the wave occurrence rate. By
analyzing the radial distribution of quasi-monochromatic ion-scale waves
observed by the Parker Solar Probe, this work shows that the wave occurrence
rate is significantly enhanced in the near-Sun solar wind, specifically
21%$-$29% below 0.3 au, in comparison to 6%$-$14% beyond 0.3 au. The radial
decrease of the wave occurrence rate is not only induced by the sampling effect
of a single spacecraft detection, but also by the physics relating to the wave
excitation, such as the enhanced ion beam instability in the near-Sun solar
wind. This work also shows that the wave normal angle $\theta$, the absolute
value of ellipticity $\epsilon$, the wave frequency $f$ normalized by the
proton cyclotron frequency $f_{\mathrm{cp}}$, and the wave amplitude $\delta B$
normalized by the local background magnetic field $B_0$ slightly vary with the
radial distance. The median values of $\theta$, $|\epsilon|$, $f$, and $\delta
B$ are about $9^\circ$, $0.73$, $3f_{\mathrm{cp}}$, and $0.01B_0$,
respectively. Furthermore, this study proposes that the wave mode nature of the
observed left-handed and right-handed polarized waves corresponds to the
Alfv\'en ion cyclotron mode wave and the fast-magnetosonic whistler mode wave,
respectively.
