  Extremely large-scale array (XL-array) is envisioned to achieve super-high
spectral efficiency in future wireless networks. Different from the existing
works that mostly focus on the near-field communications, we consider in this
paper a new and practical scenario, called mixed near- and far-field
communications, where there exist both near- and far-field users in the
network. For this scenario, we first obtain a closed-form expression for the
inter-user interference at the near-field user caused by the far-field beam by
using Fresnel functions, based on which the effects of the number of BS
antennas, far-field user (FU) angle, near-field user (NU) angle and distance
are analyzed. We show that the strong interference exists when the number of
the BS antennas and the NU distance are relatively small, and/or the NU and FU
angle-difference is small. Then, we further obtain the achievable rate of the
NU as well as its rate loss caused by the FU interference. Last, numerical
results are provided to corroborate our analytical results.
