Near-Field Communications with Block-Dominant Compressed Sensing: Fundamentals, Approaches, and Future Directions

In the context of extremely large-scale antenna arrays deployed in sixth-generation (6G) mobile networks, near-field (NF) communications have gained considerable attention. Unlike the planar waves formulated in the far-field, electromagnetic radiation propagates as spherical waves in the NF. This alteration affects the NF channel characteristics, particularly resulting in weak sparsity in angular-domain NF channels, which poses tricky challenges to the application of compressed sensing (CS). Motivated by these facts, we propose the block-dominant compressed sensing (BD-CS) techniques to assist NF communications. This article begins with an introduction on why block sparsity exists in the distance-limited NF region. Then, block-dominant side-information (BD-SI) is exploited to facilitate the actual NF communication implementation. While BD-CS shows promise in providing exceptional channel estimation accuracy and high spectral efficiency, several key challenges, opportunities, and practical implementation issues in NF communications need careful consideration.