  Integrating sensing functions into future mobile equipment has become an
important trend. Realizing different types of sensing and achieving mutual
enhancement under the existing communication hardware architecture is a crucial
challenge in realizing the deep integration of sensing and communication. In
the 5G New Radio context, active sensing can be performed through uplink beam
sweeping on the user equipment (UE) side to observe the surrounding
environment. In addition, the UE can perform passive sensing through downlink
channel estimation to measure the multipath component (MPC) information. This
study is the first to develop a hybrid simultaneous localization and mapping
(SLAM) mechanism that combines active and passive sensing, in which mutual
enhancement between the two sensing modes is realized in communication systems.
Specifically, we first establish a common feature associated with the
reflective surface to bridge active and passive sensing, thus enabling
information fusion. Based on the common feature, we can attain physical anchor
initialization through MPC with the assistance of active sensing. Then, we
extend the classic probabilistic data association SLAM mechanism to achieve UE
localization and continuously refine the physical anchor and target reflections
through the subsequent passive sensing. Numerical results show that the
proposed hybrid active and passive sensing-based SLAM mechanism can work
successfully in tricky scenarios without any prior information on the floor
plan, anchors, or agents. Moreover, the proposed algorithm demonstrates
significant performance gains compared with active or passive sensing only
mechanisms.
