Prerequisites & Notation

Before You Begin

Cell-free massive MIMO is a network architecture: instead of a single base station covering a cell, a dense set of distributed access points (APs) jointly serve UEs with no predetermined cell assignment. The combination with OTFS is the CommIT contribution of Mohammadi-Ngo-Matthaiou-Caire (2023) — a first quantitative evaluation showing $\sim 35\%$ gain in 95%-likely per-user throughput under high mobility. This chapter develops the architecture, the distributed OTFS channel estimation, and the DD-domain conjugate beamforming that deliver this gain.

OTFS modulation and detection(Review OTFS Ch. 6, 8)
Self-check: Can you derive the DD input-output relation and state MP detection convergence?
Embedded-pilot channel estimation(Review OTFS Ch. 7)
Self-check: Can you explain how DD pilots recover path parameters?
MIMO-OTFS tensor channel(Review OTFS Ch. 16)
Self-check: Do you recall the 3D MIMO-OTFS tensor structure?
Cell-free massive MIMO fundamentals(Review MIMO Ch. 11)
Self-check: Can you explain why cell-free beats classical cellular at cell edges?
Fronthaul and backhaul networks(Review Telecom Ch. 23)
Self-check: Are you familiar with CPRI / eCPRI / O-RAN fronthaul?

Notation for This Chapter

Cell-free OTFS symbols introduced here.

Symbol	Meaning	Introduced
$L$	Number of distributed access points (APs)	s01
$K$	Number of user equipments (UEs)	s01
$N_a$	Antennas per AP (typical: $N_a = 4$ - $8$ )	s01
$\mathbf{H}^{(l, k)}$	DD channel from UE $k$ to AP $l$	s01
$\mathbf{v}^{(l, k)}$	Conjugate beamforming vector at AP $l$ for UE $k$	s03
$R_k^{95\%}$	95%-likely per-user throughput of UE $k$	s04
$\tau_p$	Pilot duration (in DD cells)	s02

← Ch 16 Cell-Free Architecture and the DD Channel