Radar cross section (RCS) plays a critical role in modeling target scattering characteristics and enhancing the precision of target detection and localization in integrated sensing and communication (ISAC) systems. This paper investigates the human body RCS at 26 GHz via multi-angle channel measurements under different clothing conditions. Based on calibrated electromagnetic (EM) parameters, the RCS characteristics of the human body in far-field conditions are analyzed using ray-tracing (RT) simulations. Some suggestions for the design of ISAC systems are also discussed. The results provide a solid theoretical foundation and practical reference for the modeling of target scattering characteristics for ISAC channels.

As a complement of terrestrial networks, non-terrestrial networks (NTN) have advantages of wide-area coverage and service continuity. The NTN is potential to play an important role in the 5G new radio (NR) and beyond. To enable the massive machine type communications (mMTC), the low earth orbit (LEO) satellite is preferred due to its lower transmission delay and path loss. However, the LEO satellite may generate notable Doppler shifts to degrade the system performance. Recently, orthogonal time frequency space (OTFS) modulation has been proposed. It provides the opportunity to allocate delay Doppler (DD) domain resources, which is promising for mitigating the effect of high mobility. Besides, as the LEO satellite constellation systems such as Starlink are thriving, the space spectrum resources have become increasingly scarce. Therefore, non-orthogonal multiple access (NOMA) is considered as a candidate technology to realize mMTC with limited spectrum resources. In this paper, the application of OTFS enabled NOMA for mMTC over the LEO satellite is investigated. The LEO satellite based mMTC system and the OTFS-NOMA schemes are described. Subsequently, the challenges of applying OTFS and NOMA into LEO satellite mMTC systems are discussed. Finally, the potential technologies for the systems are investigated.

Wireless communication technologies play an essential role in supporting railway operation and control. The current Global System for Mobile Communications-Railway (GSM-R) system offers a rich set of voice services and data services related with train control, but it has very limited multimedia service bearer capability. With the development of commercial wireless industry, Long-Term Evolution (LTE) mobile broadband technology is becoming the prevalent technology in most of commercial mobile networks. LTE is also a promising technology of future railway mobile communication systems. The 3rd Generation Partner Project (3GPP) and China Communications Standards Association (CCSA) have proposed two feasible LTE based broadband trunking communication solutions: the 3GPP Mission Critical Push to Talk (MCPTT) solution and B-TrunC solution. In this paper, we first introduce the development of railway mobile communications and LTE technology. The user requirements of future railway mobile communication system (FRMCS) are then discussed. We also analyze the suitability of the two LTE-based solutions for LTE based Next-Generation Railway Mobile Communication System (LTE-R) from different aspects.

In the new era of railways, infrastructure, trains and travelers will be interconnected. In order to realize a seamless high-data rate wireless connectivity, up to dozens of GHz bandwidth is required. This motivates the exploration of the underutilized millimeter wave (mmWave) as well as the largely unexplored THz band. In this paper, we first identify relevant communication scenarios for railway applications. Then the specific challenges and estimates of the bandwidth requirements for high-data rate railway connectivity in these communication scenarios are described. Finally, we outline the major challenges on propagation channel modeling and provide a technical route for further studies.