Chapter 18: XL-MIMO Channel Estimation

Learning Objectives

• Define a visibility region (VR) as the subset of array elements illuminated by a user and explain why XL-MIMO arrays induce spatial non-stationarity
• Model the VR binary mask with a 2D Markov random field prior and connect the MRF parameters to physical cluster sizes
• Derive a message-passing / variational inference procedure for MAP VR detection from noisy pilot observations
• Decompose XL-MIMO channel estimation into subarray-level operations and analyze the complexity reduction
• Exploit the spherical wavefront structure to build a polar-domain dictionary for near-field sparse channel estimation
• Combine VR detection and channel estimation into a joint EM procedure and quantify performance vs pilot overhead
• Relate VR mismatch penalties to classical pilot contamination (Ch. 3) and contrast with far-field stationary models