  User-centric cell-free (UCCF) wireless networks have a range of distinguished
characteristics, which can be exploited for meeting some challenges that the
conventional cellular systems are hard to. This chapter is devoted to
delivering the fundamentals of wireless communications in UCCF systems,
including channel modeling and estimation, uplink (UL) detection, downlink (DL)
transmission, and resource optimization. Specifically, the advantages of
cell-free networking are examined in contrast to the conventional celluar
systems. The global and location-aware distributed UL detection are explored in
the principles of minimum mean-square error (MMSE) and brief propagation.
Correspondingly, the global and distributed DL transmission schemes are
designed based on the MMSE precoding. The optimization of both UL and DL is
analyzed with respect to system design and resource-allocation. Furthermore,
some challenges for the implementation of UCCF systems in practice are
identified and analyzed.
