Herein, we focus on convergent 6G communication, localization and sensing systems by identifying key technology enablers, discussing their underlying challenges, implementation issues, and recommending potential solutions. Moreover, we discuss exciting new opportunities for integrated localization and sensing applications, which will disrupt traditional design principles and revolutionize the way we live, interact with our environment, and do business. Regarding potential enabling technologies, 6G will continue to develop towards even higher frequency ranges, wider bandwidths, and massive antenna arrays. In turn, this will enable sensing solutions with very fine range, Doppler, and angular resolutions, as well as localization to cm-level degree of accuracy. Besides, new materials, device types, and reconfigurable surfaces will allow network operators to reshape and control the electromagnetic response of the environment. At the same time, machine learning and artificial intelligence will leverage the unprecedented availability of data and computing resources to tackle the biggest and hardest problems in wireless communication systems. As a result, 6G will be truly intelligent wireless systems that will provide not only ubiquitous communication but also empower high accuracy localization and high-resolution sensing services. They will become the catalyst for this revolution by bringing about a unique new set of features and service capabilities, where localization and sensing will coexist with communication, continuously sharing the available resources in time, frequency, and space. This work concludes by highlighting foundational research challenges, as well as implications and opportunities related to privacy, security, and trust.The associate editor coordinating the review of this manuscript and approving it for publication was Ahmed Farouk .

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This paper proposes a novel approach to extracting the narrowband propagation channel from the communication link by de-embedding the impact of the antennas. In the proposed approach, the mode-to-mode mapping matrix M which is the expression of the propagation channel in the spherical vector wave domain, is estimated by applying pseudo-inverse computation to the channel transfer functions with dedicated spherical arrays. The estimated M is truncated and only the dominant modes within the spatial bandwidth of the fields radiated from the finite volume of the spherical array are considered. Two types of spherical array are investigated: an ideal array using tangential dipoles and a virtual array using dielectric resonator antenna (DRA). The ideal array is used for parameter investigation including the array radius and the spacing with regard to the size of M and the condition number of the excitation coefficient matrix, while the virtual DRA array is proposed as a practical implementation of the ideal array. The accuracy of the proposed approach has been validated numerically. The uncertainties of spherical array in practice, such as the influence of non-ideally embedded array elements, cables and fixtures, are considered in the validation. Moreover, the channel transfer functions reproduced by the deembedded M are analyzed given different target antennas at link ends. The gain and phase discrepancies as well as the antenna correlations of the reproduced channel transfer function are compared with the generated reference.

This paper explores the feasibility of using the multiple-input multiple-output (MIMO) radio channel properties to passively detect and localize multiple humans in indoor environments. We propose to utilize the unique reverberation characteristics of indoor channels for the purpose of detecting, and the power angular delay profile (PADP) for localizing humans. On the one hand, the reverberation time corresponds with the decay rate of multipath in a closed or partially closed cavity, and varies with the change of the number of humans or the moving of humans relative to the antennas at link ends. On the other hand, the PADP is proposed to be calculated by the Multiple Signal Classification (MUSIC) super resolution algorithm with frequency smoothing preprocessing. The proposed approach is evaluated based on real-world MIMO radio channel measurements obtained from a meeting room. Measurements with and without the presence of humans have been conducted, where the maximum number of humans considered is four. Humans facing different directions, either in parallel or orthogonal to the direct line between the transmit and the receive antennas have been taken into account. In term of the detection feasibility, it is found that the change of the number of humans as well as the change of their facing/moving directions inside the partial reverberant region can be reflected on the change of the reverberation time estimated from the power delay profile of channel. In term of the localization feasibility, it is found that single human location can be well associated to the peak of the variation of the PADP during his/her movement, while multiple humans' movements result in obvious power variation in the very vicinity of some of them, and also in the vicinity of some background objects that is far from target humans. INDEX TERMS Indoor radio channel, MIMO, reverberation time, power delay angular profile, passive detection and localization of humans.

This paper proposes a hybrid modeling approach for prediction of the room-to-room radio propagation channel. The model combines ray tracing with propagation graph. The propagation graph vertices are obtained at each room by ray tracing with the assumption that the receive antenna (or transmit antenna) virtually locates on the surface of the separating wall between two rooms. Rays transmitted from one room to the other through the separating wall are deterministically calculated by Snell's law of refraction. Predictions by the proposed model are compared with measurement data from an office-to-office scenario. The results show that the proposed modeling works with the simplest parameter settings, i.e. assuming no propagation from the room containing receive antenna to the room containing transmit antenna, ray tracing applied separately in each room only involves mechanism of line-of-sight and first order specular reflection.