Ruisi He

• PhD
• Professor at Beijing Jiaotong University

With the advancement of sixth-generation (6G) wireless communication systems, integrated sensing and communication (ISAC) is crucial for perceiving and interacting with the environment via electromagnetic propagation, termed channel semantics, to support tasks like decision-making. However, channel models focusing on physical characteristics face c...

Time-varying non-stationary channels, with complex dynamic variations and temporal evolution characteristics, have significant challenges in channel modeling and communication system performance evaluation. Most existing methods of time-varying channel modeling focus on predicting channel state at a given moment or simulating short-term channel flu...

Intelligent vehicular communication with vehicle road collaboration capability is a key technology enabled by 6G, and the integration of various visual sensors on vehicles and infrastructures plays a crucial role. Moreover, accurate channel prediction is foundational to realizing intelligent vehicular communication. Traditional methods are still li...

5G for Railways (5G-R) is globally recognized as a promising next-generation railway communication system designed to meet increasing demands. Channel modeling serves as foundation for communication system design, with tapped delay line (TDL) models widely utilized in system simulations due to their simplicity and practicality and serves as a cruci...

The communication scenarios and channel characteristics of 6G will be more complex and difficult to characterize. Conventional methods for channel prediction face challenges in achieving an optimal balance between accuracy, practicality, and generalizability. Additionally, they often fail to effectively leverage environmental features. Within the f...

Integrated sensing and communication (ISAC) has become a promising technology in current sixth-generation (6G) wireless communications due to its ability to support both communication and sensing. Existing works regarding ISAC channels mainly focus on far-field propagation conditions based on plane wave assumption. However, with the deployment of u...

Integrated Sensing and Communication (ISAC) is a promising technology for 6G, with the goal of providing end-to-end information processing and inherent perception capabilities for future communication systems. Within ISAC emerging application scenarios, vehicular ISAC technologies have the potential to enhance traffic efficiency and safety through...

Integrated sensing and communications (ISAC) is a potential technology of 6G, aiming to enable end-to-end information processing ability and native perception capability for future communication systems. As an important part of the ISAC application scenarios, ISAC aided vehicle-to-everything (V2X) can improve the traffic efficiency and safety throu...

In the upcoming 6 G communications, radar sensing will be integrated with communication to support a wide range of application scenarios. However, in complex Integrated Sensing and Communication (ISAC) channels, radar targets and communication scatterers may overlap, leading to similar sparse distributions of the sensing and communication channels...

5 G for Railways (5G-R) is globally recognized as a promising next-generation railway communication system designed to meet increasing demands. Channel modeling serves as foundation for communication system design, with tapped delay line (TDL) models widely utilized in system simulations due to their simplicity and practicality and serves as a cruc...

Millimeter-wave channel prediction requires detailed and accurate environmental information due to challenges of non-line-of-sight transmission and severe reflection and scattering. Image information conveniently reflects real-time changes of physical environment and provides a promising solution for millimeter-wave channel modeling. However, resea...

The mode mismatch between active and passive fibers directly determines transmission and gain characteristics. Due to the significant difference in doping profiles between the two fiber types, modal dynamics probably happen in fiber connections. Precise observation of the mode evolution enables us to clarify the tiny fluctuation mechanism and find...

Please check and confirm whether the author affiliations in the first footnote are correct as set."?>Ray-tracing (RT) channel simulation has been widely used for simulating and analyzing propagation of electromagnetic waves in complex environments. The electrical properties of materials play a critical role in RT simulation accuracy and calibration...

With the development of high-speed railways, 5G for Railways (5G-R) is gradually replacing Global System for the Mobile Communications for Railway (GSM-R) worldwide to meet increasing demands. The large bandwidth, array antennas, and non-stationarity caused by high mobility has made 5G-R channel characterization more complex. Therefore, it is essen...

Utilizing unmanned aerial vehicles (UAVs) to provide reliable and effective wireless communication services for ground users has become a promising solution in emergency scenarios. However, energy consumption limitations lead to new challenges to timeliness of UAV communications. In this paper, we propose a service time optimization strategy using...

The characterization and modeling of wireless channels are crucial prerequisites for designing and deploying communication systems, which have been widely recognized. It must be measured and investigated, especially for vehicle-to-vehicle (V2V) channels, because it differs from the general cellular network in propagation environment, transceiver he...

In this paper, a 3D geometry-based reconfigurable intelligent surface (RIS)-aided channel model is proposed with directional antenna at base station (BS) side. Different from traditional RIS-assisted channel model, visible area (i.e., range of observed scatters) and radiated power of directional antenna with uniform, cos and Gaussian patterns are c...

The space-air-ground integrated network (SAGIN) greatly improves coverage and reliability for millimeter-wave (mmWave) communication in high-speed railway (HSR) scenarios. However, a significant challenge arises in the transmission scheduling due to the rapid changes in channel state, link selection for train mobile relays (MRs), and order of the f...

Reconfigurable intelligent surface (RIS)-aided terahertz (THz) cell-free massive multiple-input-multiple-output (mMIMO) networks have been envisioned as a prospective technology for future 6G networks. However, due to the ultra-wide bandwidth and the frequency-dependent characteristics of RISs, beam-split effect has become an unavoidable obstacle....

Millimeter wave (mmWave) has been considered as an enabler to alleviate the spectrum shortage problem while providing high data rates in high speed railway (HSR) communications. However, a mmWave channel has a larger path loss, and therefore is sensitive to blockage. In such a high speed mobile environment with fast-changing channels, considering t...

High-speed train (HST) has garnered significant attention from both academia and industry due to the rapid development of railways worldwide. Millimeter wave (mmWave) communication, known for its large bandwidth is an effective way to address performance bottlenecks in cellular network based HST wireless communication systems. However, mmWave signa...

The emerging 6G network envisions integrated sensing and communication (ISAC) as a promising solution to meet growing demand for native perception ability. To optimize and evaluate ISAC systems and techniques, it is crucial to have an accurate and realistic wireless channel model. However, some important features of ISAC channels have not been well...

Railway wireless communications play an increasingly significant role in train control and signal transmission. Communication-based train control system (CBTC) can improve the safety, efficiency and reliability of train operations, and is widely used in subway wireless communication system. Therefore, radio propagation characterization and channel...

In the sixth-generation wireless communication, integrated sensing and communication (ISAC) stands out as a key emerging technology. This letter proposes a novel geometry-based stochastic multiple-input multiple-output channel model for ISAC scenarios. We differentiate between communication channel and sensing channel, and investigate impacts of ef...

Deploying reconfigurable intelligent surfaces (RIS) near source and destination is of practical interest for improving the link quality of vehicle-to-vehicle (V2V) wireless systems. However, the accurate channel modeling and RIS tile deployment constitute a pair of challenges to evaluate the system performance such as error performance, capacity, e...

Reconfigurable intelligent surface (RIS) is considered to be a promising technology for future terahertz (THz) communications. However, due to ultra bandwidth and large scale of antenna arrays at base station and RIS, RIS-assisted THz communication would suffer from severe beam split effect, which poses significant challenges in channel estimation....

Millimeter-wave (MmWave) channel characteristics are quite different from sub-6 GHz frequency bands. The major differences include higher path loss and sparser multipath components (MPCs), resulting in more significant time-varying characteristics in mmWave channels. It is difficult to characterize the time-varying characteristics of mmWave channel...

With the advancement of communication technology, there is a higher demand for high-precision and high-generalization channel path loss models as it is fundamental to communication systems. For traditional stochastic and deterministic models, it is difficult to strike a balance between prediction accuracy and generalizability. This paper proposes a...

High-speed train (HST) has garnered significant attention from both academia and industry due to the rapid development of railways worldwide. Millimeter wave (mmWave) communication, known for its large bandwidth is an effective way to address performance bottlenecks in cellular network based HST wireless communication systems. However, mmWave signa...

Accurate wireless channel models are essential in design and optimization of wireless communication systems. Deep learning provides a promising approach for wireless channel modeling with the help of environmental information. One important application is satellite image-based path loss prediction, which has attracted much attention recently. For p...

The space-air-ground integrated network (SAGIN) greatly improves coverage and reliability for millimeter-wave (mmWave) communication in high-speed railway (HSR) scenarios. However, a significant challenge arises in the transmission scheduling due to the rapid changes in channel state, link selection for train mobile relays (MRs), and order of the f...

Wireless channels typically exhibit a sparse structure, with sparsity regarded as an inherent characteristics. A deeper understanding and accurate representation of channel sparsity contribute to a more comprehensive revelation of channel features and structure, thereby enhancing the performance of communication systems. However, current research o...

Demands for data traffic in high-speed railway (HSR) has increased drastically. The increasing entertainment needs of passengers, safety control information exchanges of trains, etc., make train-to-train (T2T) communications face the challenge of achieving high-capacity and high-quality data transmissions. In order to greatly increase the communica...

As a crucial technology for 6G wireless network, integrated sensing and communication (ISAC) can significantly improve system performance, and characterization of correlation between communication and sensing channels is important for modeling ISAC channel. In this paper, shared multipath components (SMC) for ISAC scenarios are investigated and its...

With the rapid growth of mobile data traffic, the shortage of radio spectrum resource has become increasingly prominent. Millimeter wave (mmWave) small cells can be densely deployed in macro cells to improve network capacity and spectrum utilization. Such a network architecture is referred to as mmWave heterogeneous cellular networks (HetNets). Com...

Recently, reconfigurable intelligent surface (RIS) is regarded as a potential technology in future communication networks, and design of RIS phase shift is important for performance and should be carefully considered in channel modeling of RIS-aided communications. However, most existing researches only use a discrete or continuous phase shift to i...

Pump selection plays an important role in an FM-EDFA when the active fiber is determined in an MDM system. In this paper, a hybrid-pumped FM-EDFA was proposed for low differential modal gain (DMG), combining both cladding pumping and forward LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> c...

With the rapid development of railways, especially high-speed railways, there is an increasingly urgent demand for new wireless communication system for railways. Taking the mature 5G technology as an opportunity, 5G-railways (5G-R) have been widely regarded as a solution to meet the diversified demands of railway wireless communications. For the d...

Demands for data traffic in high-speed railway (HSR) has increased drastically. The increasing entertainment needs of passengers, safety control information exchanges of trains, etc., make train-to-train (T2T) communications face the challenge of achieving high-capacity and high-quality data transmissions. In order to greatly increase the communica...

Due to the development of communication technology and the rise of user network demand, a reasonable resource allocation for wireless networks is the key to guaranteeing regular operation and improving system performance. Various frequency bands exist in the natural network environment, and heterogeneous cellular network (HCN) has become a hot topi...

With the rapid growth of mobile data traffic, the shortage of radio spectrum resource has become increasingly prominent. Millimeter wave (mmWave) small cells can be densely deployed in macro cells to improve network capacity and spectrum utilization. Such a network architecture is referred to as mmWave heterogeneous cellular networks (HetNets). Com...

Smart warehouses are revolutionizing traditional logistics operations by incorporating advanced technologies such as Internet of Things, robotics, and artificial intelligence. In these complex and dynamic environments, control and operation instructions need to be transmitted through wireless networks. Therefore, wireless communication plays a cruc...

Integration of digital twin (DT) and wireless channel provides new solution of channel modeling and simulation, and can assist to design, optimize and evaluate intelligent wireless communication system and networks. With DT channel modeling, the generated channel data can be closer to realistic channel measurements without requiring a prior channel...

The emerging intelligent transparent surface (ITS), unlike the intelligent reflection surface (IRS), allows incident signals to penetrate it instead of being reflected, which enables the ITS to combat the severe signal penetration loss for high-speed railway (HSR) wireless communications. This paper thus investigates the channel estimation problem...

Vehicular communication has been widely concerned by academia and industry. Wireless channel characterization and modeling are the foundation of communication systems. Compared with typical road scenarios such as urban and suburban areas, wireless channel characterization in intersections is a challenging task. In this paper, channel measurements a...

In a few-mode fiber-based mode division multiplexing system, the different modes as distinct channels suffer from discrepant mode-dependent loss, leading to an intensive channel power imbalance and large bit error. The few-mode erbium-doped fiber amplifier (FM-EDFA) enables mode power regulation to ensure high-quality long-distance transmission. In...

To deal with the explosive growth of mobile traffic, millimeter-wave (mmWave) communications with abundant bandwidth resources have been applied to vehicular networks. As mmWave signal is sensitive to blockage, we introduce the unmanned aerial vehicle (UAV)-aided two-way relaying system for vehicular connection enhancement and coverage expansion. H...

The internet of things (IoT) has been widely considered to be integrated with high-speed railways to improve safety and service. It is important to achieve reliable communication in IoT for railways (IoT-R) under high mobility scenarios and strict energy constraints. Orthogonal time frequency space (OTFS) modulation is a two-dimensional modulation...

Wireless channel modeling plays an essential role in the design of wireless communication networks. Especially the future integrated network with various applications and extended-spectrum needs an accurate channel model as the cornerstone. However, with the expansion of scenarios, frequencies, and user requirements, classical channel modeling meth...

Due to the development of communication technology and the rise of user network demand, a reasonable resource allocation for wireless networks is the key to guaranteeing regular operation and improving system performance. Various frequency bands exist in the natural network environment, and heterogeneous cellular network (HCN) has become a hot topi...

In this paper, a 3D geometry-based millimeter-wave channel model is proposed for reconfigurable intelligent surface (RIS)-assisted high-speed train communications. Remarkably, the RIS is attached to surface of train window to guarantee the channel between RIS and receiver is quasi-static, and radiation pattern of RIS element and penetration loss ca...

Reconfigurable intelligent surface (RIS) emerges as an efficient and promising technology for the next wireless generation networks and has attracted a lot of attention owing to the capability of extending wireless coverage by reflecting signals toward targeted receivers. In this paper, we consider a RIS-assisted high-speed train (HST) communicatio...

With the increasing demands from passengers for data-intensive services, millimeter-wave (mmWave) communication is considered as an effective technique to release the transmission pressure on high speed train (HST) networks. However, mmWave signals encounter severe losses when passing through the carriage, which decreases the quality of services on...

In this letter, UAV-assisted localization of terrestrial nodes based on identification is investigated. The proposed algorithm is intended to alleviate adverse effects of non-line-of-sight (NLOS) propagation and considers air-to-ground channel model, which is mainly divided into two parts: identification and localization. First, UAV is used as an a...

To overcome increasing traffic, provide various new services, further ensure safety and security, significantly improve travel comfort, a new communication system for railways is required. Since 2019, public networks have been evolving to the fifth generation communication (5G) worldwide, whereas the main communication system of railway is still ba...

Recently, unmanned aerial vehicle (UAV)-assisted ground targets localization is widely used in search and rescue (SAR) scenes. In this article, we propose a UAV search and localization strategy, which can search and locate unknown number of victims. The proposed strategy uses the UAV as a mobile anchor to measure time of arrival (TOA) and can effec...

Relying on direct and converse piezoelectric effects, piezo-acoustic backscatter (PAB) technology reflects ambient acoustic signals to enable underwater backscatter communications at near-zero power, which was first realized through a prototype. In this paper, we propose a mathematical model of the PAB assisted underwater acoustic (UWA) communicati...

Recently, intelligent reflecting surface (IRS) has become a research focus for its capability of controlling the radio propagation environments. Compared to the conventional terrestrial IRS, aerial IRS (AIRS) exploiting unmanned aerial vehicle (UAV)/high-altitude platform (HAP) can provide better deployment flexibility. To this end, a three-dimensi...

Recently, reconfigurable intelligent surface (RIS) has drawn much attention due to its capability of improving coverage and communication performance. The development of RIS-assisted communication technology relies on deep understanding of RIS channel characteristics. However, most of the existing investigations focus on the impact of RIS, ignoring...

Reconfigurable intelligent surfaces (RISs) and cell-free (CF) massive multiple-input multiple-output (MIMO) are two promising technologies for realizing beyond-fifth generation (5G) networks. In this paper, we study the uplink spectral efficiency (SE) of a practical spatially correlated RISs-aided CF massive MIMO system over Rician fading channels....

The critical distinction between the emerging intelligent transparent surface (ITS) and intelligent reflection surface (IRS) is that the incident signals can penetrate the ITS instead of being reflected, which enables the ITS to combat the severe signal penetration loss for high-speed railway (HSR) wireless communications. This paper thus investiga...

To overcome increasing traffic, provide various new services, further ensure safety and security, significantly improve travel comfort, a new communication system for railways is required. Since 2019, public networks have been evolving to the fifth generation communication (5G) worldwide, whereas the main communication system of railway is still ba...

This two-part paper investigates the application of artificial intelligence (AI) and, in particular, machine learning (ML) to the study of wireless propagation channels. In Part I of this article, we introduced AI and ML and provided a comprehensive survey on ML-enabled channel characterization and antenna-channel optimization, and in this part (Pa...

To provide higher data rates, as well as better coverage, cost efficiency, security, adaptability, and scalability, the 5G and beyond 5G networks are developed with various artificial intelligence (AI) techniques. In this two-part article, we investigate the application of AI and, in particular, machine learning (ML) to the study of wireless propag...

With the explosive growth of vehicle applications, vehicular networks based on millimeter wave (mmWave) bands have attracted interests from both academia and industry. mmWave communications are able to utilize the huge available bandwidth to provide multiple Gbps transmission rates among vehicles. In this paper, we address the content distribution...

The era of wireless communications began at the turn of the 20th century, when Guglielmo Marconi used electromagnetic waves to transmit telegraph signals from ships to stations onshore [1] . To understand how radio signals propagate is critical for wireless communication system design. With the development of wireless communications, much effort...

Reconfigurable intelligent surface (RIS) has received increasing attention due to its capability of extending cell coverage by reflecting signals toward receivers. This paper considers a RIS-assisted high-speed train (HST) communication system to improve the coverage probability. We derive the closed-form expression of coverage probability. Moreove...

In this paper, a 3D geometry-based double-spherical terahertz (THz) channel model is proposed for ultra massive multiple-input multiple-output (MIMO) communications. To reflect real THz ultra massive MIMO communications, the characteristic of nano-material array antenna and the high loss of THz bands are considered in channel modeling. Based on the...

Different from the traditional terrestrial intelligent reflecting surface (IRS), aerial IRS (AIRS) can provide some unique advantages, such as flexible deployment and wider-view signal reflection. In this paper, a three-dimensional (3D) single cylinder simulation channel model is proposed for AIRS-aided multiple-input multiple-output (MIMO) communi...

With the explosive growth of vehicle applications, vehicular networks based on millimeter wave (mmWave) bands have attracted intensive interests from both academia and industry. mmWave communications are able to utilize the huge available bandwidth to provide multiple Gbps transmission rates among vehicles. In this paper, we address the content dis...

Radio propagation characteristics in subway tunnels are significant for designing reliable wireless communications. To obtain large scale channel characteristics, extensive propagation measurements are conducted in a straight subway tunnel at 1.8 GHz and 5.8 GHz, respectively. Based on the measurements, some typical large-scale channel parameters a...

Aiming to the vision of 6G, integrated sensing and communication (ISAC), as the potential techniques to deal with the increasing demands of native perception ability, has recently attracted a lot of attention. In order to guide system optimization and evaluate novel ISAC techniques, accurate and realistic wireless channel model for ISAC is essentia...

With the emerging demands of new communication services, the contradiction between capacity demand and spectrum shortage of railway communication systems becomes more severe. How to provide broadband communication services has become the key goal of future smart high-speed railway (HSR) systems. Millimeter wave (mm-wave) frequency band has abundant...

A three-dimensional (3D) printed Luneburg lens with nearly isotropic properties is presented. The cubical-lattice-type and the rod-type gradient-index materials are employed together to construct the novel printable spherical lens geometry, whose nearly isotropic properties improve the antenna radiation characteristics significantly. The dual-polar...

Recently, vehicle-to-vehicle (V2V) based localization has attracted much attention due to its potential to achieve high accuracy. However, the error caused by non-line-of-sight (NLOS) propagation significantly affects the localization performance. In this paper, a novel method combining V2V communication and NLOS identification is proposed to impro...