Wenchao Xu

• PhD Student at University of Waterloo

In densely deployed IEEE 802.11 wireless networks, the transmission delay experienced by a user depends not only on the traffic load of the associated AP, but also the contention level of other APs operating on the same channel. However, due to the random distribution of users and inappropriate allocation of AP channels, the traffic loads of differ...

In the multi-cell IEEE 802.11 wireless networks, the traffic loads of access points(APs) are often uneven, which leads to inefficient use of network resources and unfair service to users. To alleviate such imbalance, different user association schemes have been proposed that use different metrics for measuring the congestion level of APs. In this p...

Hallucination remains a significant challenge in Large Vision-Language Models (LVLMs). To alleviate this issue, some methods, known as contrastive decoding, induce hallucinations by manually disturbing the raw vision or instruction inputs and then mitigate them by contrasting the outputs of the original and disturbed LVLMs. However, these holistic...

In Automatic Modulation Classification (AMC), deep learning methods have shown remarkable performance, offering significant advantages over traditional approaches and demonstrating their vast potential. Nevertheless, notable drawbacks, particularly in their high demands for storage, computational resources, and large-scale labeled data, which limit...

Sequential recommendation is an advanced recommendation technique that utilizes the sequence of user behaviors to generate personalized suggestions by modeling the temporal dependencies and patterns in user preferences. However, it requires a server to centrally collect users' data, which poses a threat to the data privacy of different users. In re...

The Fully Decoupled Radio Access Network (FD-RAN) divides the base station (BS) into three components: the Uplink Data Base Station (UBS), the Downlink Data Base Station (DBS), and the Control Base Station (CBS) to achieve an ultra flexible network. FD-RAN can easily realize dynamic multi-BS cooperation to boost throughput and guarantee users’ qual...

Hyperparameter optimization (HPO) is crucial for federated learning (FL) performance. Given the inherent data heterogeneity across clients, recent research has focused on providing personalized hyperparameters for individual clients. However, such personalized approaches introduce exponential search complexity as the number of clients increases, si...

Non-Centralized Continual Learning (NCCL) has become an emerging paradigm for enabling distributed devices such as vehicles and servers to handle streaming data from a joint non-stationary environment. To achieve high reliability and scalability in deploying this paradigm in distributed systems, it is essential to conquer challenges stemming from b...

Foundation model (FM) powered agent services are regarded as a promising solution to develop intelligent and personalized applications for advancing toward Artificial General Intelligence (AGI). To achieve high reliability and scalability in deploying these agent services, it is essential to collaboratively optimize computational and communication...

Unmanned aerial vehicles (UAVs), due to their low cost and high flexibility, have been widely used in various scenarios to enhance network performance. However, the optimization of UAV trajectories in unknown areas or areas without sufficient prior information still faces challenges related to poor planning performance and low distributed execution...

Unmanned Aerial Vehicles (UAVs), due to their low cost and high flexibility, have been widely used in various scenarios to enhance network performance. However, the optimization of UAV trajectories in unknown areas or areas without sufficient prior information, still faces challenges related to poor planning performance and low distributed executio...

Radio Frequency (RF) fingerprinting is to identify a wireless device from its uniqueness of the analog circuitry or hardware imperfections. However, unlike the MAC address which can be modified, such hardware feature is inevitable for the signal emitted to air, which can possibly reveal device whereabouts, e.g., a sniffer can use a pre-trained mode...

This paper investigates an intelligent reflecting surfaces (IRS) aided anti-jamming communication strategy in the integrated terrestrial-satellite network (ITSN), where the IRS is exploited to mitigate jamming interference and enhance the integrated system communication performance. In such a network, the terrestrial network and satellite network a...

Personalized Federated Learning (pFL) can improve the accuracy of local models and provide enhanced edge intelligence without exposing the raw data in Mobile Edge Computing (MEC). However, in the MEC environment with constrained communication resources, transmitting the entire model between the server and the clients in traditional pFL methods impo...

The integrated terrestrial satellite networks (ITSNs) have been deemed as a promising solution to ubiquitous Internet access anytime and anywhere. In this paper, we investigate the spectrum sharing problem in ITSN, in particular focusing on the downlink transmission of the satellite network, which adopts the framing structure for the satellite user...

p>Federated learning (FL) has gained increasing attention due to its ability to collaboratively train while protecting client data privacy. However, vanilla FL cannot adapt to client heterogeneity, leading to a degradation in training efficiency due to stragglers, and is still vulnerable to privacy leakage. To address these issues, this paper propo...

p>Federated learning (FL) has gained increasing attention due to its ability to collaboratively train while protecting client data privacy. However, vanilla FL cannot adapt to client heterogeneity, leading to a degradation in training efficiency due to stragglers, and is still vulnerable to privacy leakage. To address these issues, this paper propo...

Blockchain has been deemed as a promising solution for providing security and privacy protection in the next-generation wireless networks. Large-scale concurrent access for massive wireless devices to accomplish the consensus procedure may consume prohibitive communication and computing resources, and thus may limit the application of blockchain in...

Federated learning (FL) has gained increasing attention due to its ability to collaboratively train while protecting client data privacy. However, vanilla FL cannot adapt to client heterogeneity, leading to a degradation in training efficiency due to stragglers, and is still vulnerable to privacy leakage. To address these issues, this paper propose...

Over-the-air computation (AirComp) is a novel technology that utilizes the superposition characteristic of the wireless multiple-access channel to accomplish communication and computation tasks simultaneously, which can be used to achieve efficient data fusion in wireless networks. However, the performance of AirComp can be compromised due to non-i...

Blockchain has been deemed as a promising solution for providing security and privacy protection in the next-generation wireless networks. Large-scale concurrent access for massive wireless devices to accomplish the consensus procedure may consume prohibitive communication and computing resources, and thus may limit the application of blockchain in...

The 6G wireless network is promising to build bridges toward smart society in the digital world, which calls for innovative architectures and new solutions. The future 6G network should be sensing-based and data-driven for near-instant and massive connectivity with distributed intelligence. With a majority of intelligent applications being deployed...

Intelligent reflecting surface (IRS) is a novel technology to manipulate wireless propagation channels via smart and controllable signal reflection. In this paper, we investigate an IRS-aided integrated terrestrial-satellite network (ITSN) system, where the IRS is deployed to assist the co-existing transmissions of the terrestrial small base statio...

Dual connectivity (DC) has been emphasized in both LTE and 5G networks to utilize a secondary evolved NodeB (SeNB) connected to the master evolved NodeB (MeNB) that can simultaneously serve the user equipment (UE) to improve the per-user throughput as well as the mobility support. However, the non-ideal X2 link between the MeNB and SeNB and the dyn...

With its potential versatility and reliability, the space-air-ground integrated vehicular network (SAGVN) is envisioned as a promising solution to deliver quality vehicular services anywhere at any time. This article proposes a software defined framework for SAGVN to achieve flexible, reliable, and scalable network resource management. First, key a...

The upcoming development of 5G network is envisioned to offer various types of services like virtual reality/augmented reality and autonomous vehicles applications with low latency requirements in Internet of Things (IoT) networks. Mobile edge computing (MEC) has become a promising solution for enhancing the computation capacity of mobile devices a...

To enable ever-increasing vehicular applications, heterogeneous vehicular networks (HetVNets) are recently emerged to provide enhanced and cost-effective wireless network access. Meanwhile, edge caching is imperative to future vehicular content delivery to reduce the delivery delay and alleviate the unprecedented backhaul pressure. This work invest...

In this study, the authors adopt the non‐orthogonal multiple access (NOMA) technique to improve the spectrum efficiency in the wireless backhaul networks, whereby the downlink and uplink NOMA techniques are applied for the backhaul and access links, respectively. Due to the coupling between the backhaul and access transmission stages, the transmiss...

With the emerging of automated driving technology, wireless demand for secure information exchange among automated vehicles has increased dramatically. To this end, we design a security-aware dynamic device-to-device (D2D) spectrum resource sharing mechanism to enhance the security of vehicular D2D communications with the improved spectrum efficien...

In vehicular networks, Radio frequency (RF) jamming attacks are considered as a major threat to the availability of control channel. In particular, vehicles may not be able to receive control messages from roadside units (RSUs) due to persistent interference in the control channel, which may claim human lives and result in significant economic loss...

To enable large-scale and ubiquitous automotive network access, traditional vehicle-to-everything (V2X) technologies are evolving to the Internet of Vehicles (IoV) for increasing demands on emerging advanced vehicular applications, such as intelligent transportation systems (ITS) and autonomous vehicles. In recent years, IoV technologies have been...

Connected vehicles have been considered as an effective solution to enhance driving safety as they can be well aware of nearby environments by exchanging safety beacons periodically. However, under dynamic traffic conditions, especially for dense-vehicle scenarios, the naive beaconing scheme where vehicles broadcast beacons at a fixed rate with a f...

Drive-thru Internet has been considered as an effective Internet access method for Internet of vehicles (IoV). Through the opportunistic vehicle-to-roadside WiFi connection, it can provide high throughput performance with low communication cost for IoV applications, such as intelligent transportation system, automotive infotainment, etc. However, i...

Enabling connected vehicles is becoming an essen-tial demand for modern mobility world. To envision the Internet of Vehicles (IoVs) and better support the transmission of the explosive vehicular data, the Ultra High Frequency(UHF) spec-trum resource in TV White Space (TVWS) band is re-utilized to provide cognitively wireless access for vehicle user...

The IEEE 802.11p-based dedicated short range communication (DSRC) is essential to enhance driving safety and improve road efficiency by enabling rapid cooperative message exchanging. However, there is a lack of good understanding on the DSRC performance in urban environments for vehicle-to-vehicle (V2V) communications, which impedes its reliable an...

By providing effective wireless vehicle-to-everything (V2X) communication, it is expected that the Internet of Vehicles will be provisioned, whereby various automotive service requirements could be satisfied (enhanced road safety, improved transportation efficiency, etc.). Despite the successful standardization of 802.11-based communication protoco...

Roadside WiFi network has been widely considered for the drive-thru Internet access. However, the data throughput is significantly affected by the access procedure which includes the steps of association, user authentication and assignment of network parameters such as Internet Protocol (IP) address. In this paper, we investigate the throughput per...

IoVs have been envisioned to improve road safety and efficiency, and provide Internet access on the move, by providing a myriad of safety and infotainment applications to drivers and passengers. However, with limited spectrum resource, harsh wireless channel, and variable vehicle density, IoV communication faces severe challenges to achieve scalabi...

Time-division multiple access (TDMA) based medium access control (MAC) protocol provides a promising solution to well support delay-sensitive safety applications in vehicular ad hoc networks, since a time-slotted access scheme ensures the transmission within the ultra-low delays. However, due to the varying vehicle mobility, existing TDMA-based MAC...

WiFi networks can offload data traffic from congested cellular networks in a cost-effective way. However, it is difficult to perform WiFi offloading in mobile environments due to the complicated and time consuming access procedure of WiFi networks. In this article, we first investigate mobile traffic offloading by leveraging the HS-2.0 technique, w...

Under IEEE 802.11p based Dedicated Short Range Communication (DSRC) modules, vehicular safety applications rely on periodical broadcasts of safety beacons by each vehicle. However, the channel can be easily congested by high-frequency periodic beacons when the vehicle density becomes heavy. In this paper, through real-trace based empirical study on...

The ever-increasing mobile data demands have posed significant challenges in the current radio access networks, while the emerging computation-heavy Internet of things (IoT) applications with varied requirements demand more flexibility and resilience from the cloud/edge computing architecture. In this article, to address the issues, we propose a no...

The ever-increasing mobile data demands have posed significant challenges in the current radio access networks, while the emerging computation-heavy Internet of things (IoT) applications with varied requirements demand more flexibility and resilience from the cloud/edge computing architecture. In this article, to address the issues, we propose a no...

Vehicular communications networks (VANETs) enable information exchange among vehicles, other end devices and public networks, which plays a key role in road safety/infotainment, intelligent transportation system, and self-driving system. As the vehicular connectivity soars, and new on-road mobile applications and technologies emerge, VANETs are gen...

Vehicular communications networks (VANETs) enable information exchange among vehicles, other end devices and public networks, which plays a key role in road safety/infotainment, intelligent transportation system, and self-driving system. As the vehicular connectivity soars, and new on-road mobile applications and technologies emerge, VANETs are gen...

In this paper, we propose a Drone Assisted Radio Access Networks (DA-RAN) architecture in which drone-cells are leveraged to relay data between base stations and users. Based on the state-of-the-art Drone-to-User (D2U) and Droneto- BS (D2B) channel models, we first analyze the user coverage and the D2B backhaul connection features of drone-cells. W...

This article introduces the DAVN, which provides ubiquitous connections for vehicles by efficiently integrating the communication and networking technologies of drones and connected vehicles. Specifically, we first propose a comprehensive architecture of the DAVN and outline its potential services. By cooperating with vehicles and infrastructures,...

As the rapid development of automotive telematics, modern vehicles are expected to be connected through heterogeneous radio access technologies and are able to exchange massive information with their surrounding environment. By significantly expanding the network scale and conducting both real time and long term information processing, the traditio...

Efficient and scalable media access control (MAC) protocol design is crucial to guarantee the reliable broadcast of safety messages in vehicular ad hoc networks (VANETs). To devise a MAC for safety message broadcasting with reliability and minimum delay, in this paper, we propose a novel time slot-sharing MAC, referred to as SS-MAC, which can suppo...

Dynamic sharing of 5G and the DSRC spectrum has been considered as an attainable paradigm to provide VANETs with massive system capacity, reduced latency, and lowered cost. It can meet the ever growing expectations of tailor- made vehicular services. However, due to the high mobility of vehicles and heterogeneity of 5G spectrum, how to achieve effi...

Internet of vehicles (IoV) is an emerging paradigm for accommodating the requirements of future intelligent transportation systems (ITSs) with the overwhelming trend of equipping vehicles with versatile sensors and communications modules, and facilitating drivers and passengers with a variety of innovative ITS applications. However, the implementat...

Providing cost-effective and high throughput WiFi access for vehicle drivers and passengers is a promising solution to support the increasing demand for in-vehicle Internet applications. Prior to accessing Internet services via an on-road WiFi access point (AP), a vehicle user has to wait for a certain time duration, referred to as access delay, un...

Wi-Fi is a cost-effective way to offload the increasing data traffic from cellular networks. However, users can only associate to one access point (AP) at a time, which limits the offloading performance in multiple hotspots scenario. In order to enhance the offloading performance and improve the utilization of Wi-Fi capacity as well, we propose a t...

In urban vehicular networks, traveling users can enjoy Internet multimedia services through various mobile devices, such as smart phones and laptops. To maintain seamless and ubiquitous Internet connectivity, an efficient handoff scheme has to be employed when mobile users travel across different access networks. However, in the urban vehicular env...

Wireless channels are inherently time-varying due to many different factors, such as fading, shadowing, multipath effects, etc. In practice, it is too complicated to completely capture these factors in a single theoretical framework. Therefore, many simplified channel models have been proposed and widely used in theoretical analysis, protocol desig...