A Review of Millimeter Wave Device-Based Localization and Device-Free Sensing Technologies and Applications

The commercial availability of low-cost millimeterwave (mmWave) communication and radar devices is starting to improve the adoption such technologies in consumer markets, paving way for large-scale dense deployments fifthgeneration (5G)-and-beyond as well 6G networks. At same time, pervasive mmWave access will enable device localization device-free sensing with unprecedented accuracy, especially respect sub-6 GHz commercial-grade devices. This paper surveys state art device-based using devices, a focus on indoor deployments. We overview key concepts about signal propagation system design, detailing approaches, algorithms applications sensing. Several dimensions are considered, including main objectives, techniques, performance each work, whether they reached an implementation stage, which hardware platforms or software tools were used. analyze theoretical (including processing machine learning), technological, (hardware prototyping) aspects, exposing under-performing missing techniques items towards enabling highly effective human parameters, position, movement, activity vital signs. Among many interesting findings, we observe that systems would greatly benefit from exposes channel information, better integration between standardcompliant initial algorithms, multiple points (APs). Moreover, more advanced requiring zero-initial knowledge environment help simultaneous mapping (SLAM). Machine learning (ML)-based gaining momentum, but still require collection extensive training datasets, do not yet generalize any environment, limiting their applicability. Device-free (i.e., radar-based) have be improved terms of: accuracy detection signs (respiration heart rate) enhanced robustness/generalization capabilities across different environments; moreover, support needed tracking users, automatic creation networks largescale applications. Finally, integrated performing joint communications infancy: practical advancements required add functionalities mmWave-based protocols based orthogonal frequency-division multiplexing (OFDM) multi-antenna technologies.