Prerequisites & Notation

Before You Begin

This chapter analyzes the design of distributed MIMO systems under finite-capacity fronthaul links. The material builds on the cell-free architecture from Chapters 11--13 and requires familiarity with rate-distortion theory and quantization from information theory.

Cell-free massive MIMO architecture and user-centric clustering(Review ch11, ch12)
Self-check: Can you describe the difference between full cell-free and user-centric cell-free?
Distributed processing levels 1--4 and local MMSE combining(Review ch13)
Self-check: Can you explain the fronthaul overhead difference between Level 1 and Level 4 cooperation?
Linear precoding and achievable rates: MRT, ZF, MMSE(Review ch06)
Self-check: Can you write the ZF precoder $\mathbf{W} = \mathbf{H}(\mathbf{H}^{H} \mathbf{H})^{-1}$ and explain its rate expression?
Rate-distortion theory and source coding(Review ch09)
Self-check: Can you state the rate-distortion function for a Gaussian source?
Achievable rate analysis with the UatF bound(Review ch04)
Self-check: Can you explain why the use-and-then-forget bound is tractable for imperfect CSI?

Notation for This Chapter

Symbols introduced in this chapter. See also the global notation table.

Symbol	Meaning	Introduced
$C_{\text{fh}}$	Fronthaul capacity per access point (bits/s or bits/symbol)	s01
$\hat{\mathbf{y}}_l$	Quantized received signal at AP $l$	s02
$\mathbf{q}_l$	Quantization noise at AP $l$	s02
$\mathbf{R}_q$	Quantization noise covariance matrix	s02
$\hat{s}_k$	Compressed precoded signal for user $k$	s03
$L$	Number of access points (APs)	s01
$K$	Number of users	s01
$\mathbf{H}_{lk}$	Channel vector from user $k$ to AP $l$	s01
$\eta_l$	Fronthaul load factor at AP $l$ (fraction of capacity used)	s04
$f_l$	Computation resource allocated to AP $l$ (FLOPS)	s04

← Ch 13 Limited-Capacity Fronthaul