We present Roomify, a spatially-grounded transformation system that generates themed virtual environments anchored to users’ physical rooms while maintaining spatial structure and functional semantics. Current VR approaches face a fundamental trade-off: full immersion sacrifices spatial awareness, while passthrough solutions break presence. Roomify addresses this through spatially-grounded transformation—treating physical spaces as “spatial containers” that preserve key functional and geometric properties of furniture while enabling radical stylistic changes. Our pipeline combines in-situ 3D scene understanding, AI-driven spatial reasoning, and style-aware generation to create personalized virtual environments grounded in physical reality. We introduce a cross-reality authoring tool enabling fine-grained user control through MR editing and VR preview workflows. Two user studies validate our approach: one with 18 VR users demonstrates a 63% improvement in presence over passthrough and 26% over fully virtual baselines while maintaining spatial awareness; another with 8 design professionals confirms the system’s creative expressiveness (scene quality: 5.95/7; creativity support: 6.08/7) and professional workflow value across diverse environments.

Camera glasses create fundamental privacy tensions between wearers seeking recording functionality and bystanders concerned about unauthorized surveillance. We present a systematic multi-stakeholder evaluation of privacy mechanisms through surveys (N=525) and paired interviews (N=20) in China. Study 1 quantifies expectation-willingness gaps: bystanders consistently demand stronger information transparency and protective measures than wearers will provide, with disparities intensifying in sensitive contexts where 65–90% of bystanders would take defensive action. Study 2 evaluates twelve privacy-enhancing technologies, revealing four fundamental trade-offs that undermine current approaches: visibility versus disruption, empowerment versus burden, protection versus agency, and accountability versus exposure. These gaps reflect structural incompatibilities rather than inadequate goodwill, with context emerging as the primary determinant of privacy acceptability. We propose context-adaptive pathways that dynamically adjust protection strategies: minimal-friction visibility in public spaces, structured negotiation in semi-public environments, and automatic protection in sensitive contexts. Our findings contribute a diagnostic framework for evaluating privacy mechanisms and implications for context-aware design in ubiquitous sensing.

The integration of LLMs into GUI agents promises to revolutionize web browsing automation, yet the practical user experience remains challenging. This paper systematically characterizes user-reported issues with GUI agents by focusing on three dimensions: phenomena, influences, and user-centric mitigation. We adopted a two-phase method combining social media analysis (N=221 posts) and semi-structured interviews (N=21). Our findings reveal a taxonomy of complaints unique to GUI agents, including deficits in grounding abstract intent into concrete interface affordances, the inability to adapt to dynamic visual states, and the execution of erroneous actions. These lead to influences distinct from text-based hallucinations, ranging from task abandonment to security risks like uncontrolled file system access. In response, users are forced to employ ad-hoc mitigation strategies, including ecological sandboxing, and cursor shadowing to correct GUI agents behaviors. We contribute: (1) a comprehensive characterization of complaints specific to GUI agents interaction, (2) an analysis of how these phenomena degrade interaction integrity, and (3) design implications for creating consequence-aware agents.

Privacy Policies are a cornerstone of informed consent, yet a persistent gap exists between their legal intent and practical efficacy. Despite decades of research proposing various visualizations, user comprehension remains low, and designs rarely see widespread adoption. To understand this landscape and chart a path forward, we synthesized 65 top-tier papers using a framework adapted from user-centered design lifecycles. Our analysis presented four findings of the field’s evolution: (1) trade-off between information load and decision efficacy, which shows a shift from augmenting disclosures to cognitive load management, (2) co-evolutionary dynamic of design and automation, revealing that designs such as context-awareness drove automation needs, while LLM breakthroughs enable the semantic interpretation required to realize those designs, (3) tension between generality and specificity, highlighting the divergence between standardized solutions and the increasing necessity for specialized interaction in IoT and immersive environments, and (4) balancing stakeholder opinions, where visualization efficacy is constrained by the interplay of regulatory mandates, developer capabilities and provider incentives.

While web agents gained popularity by automating web interactions, their requirement for interface access introduces privacy risks that are understudied, particularly from users’ perspective. Through a formative study (N=15), we found that users frequently misunderstand agent data practices, and desire unobtrusive, transparent data management. To achieve this, we developed PrivWeb, a trusted add-on on web agents that utilizes a localized LLM to anonymize private information on interfaces based on user preferences. It employs a tiered delegation to balance automation and intrusiveness, using ambient notifications for low-sensitivity data and enforces a mandatory pause for high-sensitivity data. The user study (N=14) across travel, information retrieval, shopping, and entertainment tasks showed that PrivWeb enhances perceived privacy protection and trust compared to transparency-only baselines, without increasing cognitive load. Crucially, we identified user delegation strategies: they prefer to manually execute sensitive steps for high-sensitivity data, while granting agent access to low-sensitivity data.

As Smart Home Personal Assistants (SPAs) evolve into social agents, understanding user privacy necessitates interpersonal communication frameworks, such as Privacy Boundary Theory (PBT). To ground our investigation, our three-phase preliminary study (1) identified transmission and sharing ranges as key boundary-related risk factors, (2) categorized relevant SPA functions and data types, and (3) analyzed commercial practices, revealing widespread data sharing and non-transparent safeguards. A subsequent mixed-methods study (N=412 survey, N=40 interviews among the survey participants) assessed users’ perceived privacy risks across data types, transmission ranges and sharing ranges. Results demonstrate a significant, non-linear escalation in perceived risk when data crosses two critical boundaries: the ‘public network’ (transmission) and ‘third parties’ (sharing). This boundary effect holds robustly across data types and demographics. Furthermore, risk perception is modulated by data attributes (e.g., social relational data), and contextual privacy calculus. Conversely, anonymization safeguards show limited efficacy especially for third-party sharing, a finding attributed to user distrust. These findings empirically ground PBT in the SPA context and inform design of boundary-aware privacy protection.

Always-on sensing of AI applications on AR glasses makes traditional permission techniques inefficient for context-dependent private visual data within home environments. Home presents a challenging privacy context due to massive sensitive objects and the intimate nature of daily routines. We propose VisGuardian, a fine-grained content-based visual permission technique for AR glasses. VisGuardian features a group-based control mechanism that enables users to efficiently manage permissions for multiple private objects. VisGuardian detects objects using YOLO and adopts a pre-classified schema to group them. By selecting a single object, users can obscure groups of related objects based on criteria including privacy sensitivity, object category, or spatial proximity. A technical evaluation shows VisGuardian achieves mAP50 of 0.6704 with only 14.0 ms latency and a 1.7% increase in battery consumption per hour. Furthermore, a user study (N=24) comparing VisGuardian to slider-based and object-based baselines found it to be significantly faster for setting permissions and was preferred by users for its efficiency, effectiveness, and ease of use.

Qingjie Zhang, Di Wang, Haoting Qian, Yiming Li, Tianwei Zhang, Minlie Huang, Ke Xu, Hewu Li, Liu Yan, Han Qiu. Proceedings of the 63rd Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers). 2025.

Driver decision quality in take-overs is critical for effective human-Autonomous Driving System (ADS) collaboration.However, current research lacks detailed analysis of its variations.This paper

Figure 1: Interaction flow of PrivCAP: (a) PrivCAP automatically extracts key information from the app's privacy policy, grouping them into information categories and presents them as a CAPTCHA during app registration.(b) Users click on orange chunks that represent personal information collection.As they interact, new chunks appear, allowing users to simultaneously learn about the app's privacy policy.(c) Once all orange chunks are clicked, the interaction on the current page is complete, directing users to a new page featuring the next information category.

The deployment of commercial-off-the-shelf (COTS) GPUs in space has emerged as a promising approach for supporting inorbit deep neural network (DNN) inference. However, unlike terrestrial environments, understanding the impact of space radiation on COTS GPU-enabled DNNs is critical. This is challenging because existing methods, such as real-world radiation testing and software emulation, fail to link radiation-induced memory errors to runtime DNN behaviors. In this paper, we propose REMU, a memory-aware Radiation EMUlator to fill this gap. REMU introduces a dual addressing mechanism across virtual, physical, and DRAM memory spaces, enabling precise mapping and efficient injection of radiation-induced errors from DRAM to runtime DNN inference. Extensive evaluations across 10 well-known DNN models and 2 typical in-orbit computing tasks demonstrate the effectiveness of REMU, providing valuable insights for understanding the resilience of runtime DNN inferences on space radiations.

Qingjie Zhang, Di Wang, Haoting Qian, Liu Yan, Tianwei Zhang, Ke Xu, Qi Li, Minlie Huang, Hewu Li, Han Qiu. Proceedings of the 2025 Conference on Empirical Methods in Natural Language Processing. 2025.

Low-earth-orbit (LEO) satellite mega-constellations enable universal Internet access from space. To ensure mission safety, LEO satellites conduct orbital maneuvers to prevent physical collisions with other space objects. These maneuvers challenge the performance of predictive TCP congestion control, which mitigates unnecessary throughput reductions caused by handover-induced data loss/delay. Our empirical study shows that these maneuvers can downgrade predictive TCP congestion control’s throughput by 17.63% due to the maneuvering satellite’s cumulative position deviations. The root cause is that end users rely on coarse-grained Two-Line Elements (TLEs) to predict satellites’ orbits, thus suffering from inaccurate predictions. Although these negative impacts seem unsolvable, fine-grained ephemeris can help end users enhance the accuracy of predicting handover events and effectively manage the durations of freezing congestion windows to a more affordable level. We then propose MATCP, a Maneuver-Aware TCP congestion control scheme to enhance the performance of TCP transport in maneuverable satellite networks. Compared to existing predictive congestion control, MATCP leverages ephemeris to achieve more accurate predictions of satellite handovers, and freezes the congestion window at predicted handover timing with a shorter freezing duration, thus improving the throughput of predictive congestion control. Our evaluations, driven by Starlink’s space situational awareness (SSA) dataset, validate that MATCP can safely prevent 94.21% of maneuver-induced throughput reductions in predictive TCP congestion control and increase throughput by 3.83× compared to TCP CUBIC and 20.07% compared to existing predictive satellite congestion control (SATCP).

Auto-regressive large language models (LLMs) have yielded impressive performance in many real-world tasks. However, the new paradigm of these LLMs also exposes novel threats. In this paper, we explore their vulnerability to inference cost attacks, where a malicious user crafts Engorgio prompts to intentionally increase the computation cost and latency of the inference process. We design Engorgio, a novel methodology, to efficiently generate adversarial Engorgio prompts to affect the target LLM's service availability. Engorgio has the following two technical contributions. (1) We employ a parameterized distribution to track LLMs' prediction trajectory. (2) Targeting the auto-regressive nature of LLMs' inference process, we propose novel loss functions to stably suppress the appearance of the <EOS> token, whose occurrence will interrupt the LLM's generation process. We conduct extensive experiments on 13 open-sourced LLMs with parameters ranging from 125M to 30B. The results show that Engorgio prompts can successfully induce LLMs to generate abnormally long outputs (i.e., roughly 2-13$\times$ longer to reach 90\%+ of the output length limit) in a white-box scenario and our real-world experiment demonstrates Engergio's threat to LLM service with limited computing resources. The code is released at https://github.com/jianshuod/Engorgio-prompt.

As Virtual Reality (VR) devices become increasingly shared among users, there is a pressing need for authentication methods that balance security, usability, and privacy while accommodating VR's unique interaction constraints. This paper presents cLock, a novel single-handed two-factor authentication technique in VR that allows users to enter PINs with multiple cursors on a virtual circular numpad through wrist rotation and finger tapping. We first optimized the UI design of cLock by comparing participants' input performance with different UI parameters. We then extracted spatiotemporal behavioral features of both fingers and palm during PIN entry, which facilitated cLock's authentication algorithm. In the usability evaluation with four input postures, cLock achieved significantly faster authentication speed than laser and touch-based baselines, without sacrificing accuracy. Meanwhile, it was most preferred by participants in terms of privacy, social acceptance and physical effort. A following evaluation of security demonstrated that cLock achieved a deciphering rate of only$1 / 8$of the baselines against shoulder-surfing within 1 m. Even in scenarios of password leakage, cLock could still achieve an FAR of 2.3% and FRR of 3.2% with 20 registered users. A final 11-day study verified the longitudinal stability of cLock.

Direct-to-cell satellites enable global network services for our regular phones/IoTs via 4G, 5G, and beyond. To enforce highly available, trustworthy, and roaming policy-compliant network services, they heavily rely on user geolocation and timing information from external global navigation satellite systems (GNSS) to assist with their radio access, authentication, and authorization. Our analysis and field tests reveal that, this cross-technology over-reliance propagates satellite navigation's defects to direct-to-cell satellite networks, leading to diverse issues such as intermittent connectivity, over/under-billing, unauthorized services, and service denials even when direct-to-cell satellites are accessible. Our solution, SN2, adopts the "fate-sharing" principle to reuse direct-to-cell satellites themselves for self-navigating networks. By exploiting the flexible tradeoffs between satellite network availability and navigation accuracy, it enables "good enough" built-in navigation for highly available and functionally correct network services at a negligible cost of hardware or communication resources. Our evaluations with commodity satellite phones and 3GPP NTN protocol stacks demonstrate SN2's 4.4–23.5× network availability boost and 1.9–12.3× access latency reduction over legacy solutions.

The recent renaissance of low Earth orbit (LEO) satellite networks expands the boundaries of global Internet access, but also introduces substantial new challenges for existing end-to-end congestion control algorithms (CCAs). The rapid and continuous movement of LEO satellites leads to infrastructure-level dynamics, resulting in frequent, LEO-dynamics-induced changes in link capacity, delay, and packet loss rate, which can further mislead the rate control in existing CCAs and cause self-limited performance.

Do we really need 10,000s of Low Earth Orbit (LEO) satellites to meet huge global Internet demands? While proven feasible and valuable, such LEO mega-constellation networks have raised concerns about their prohibitive capital expenditures, market monopoly, and unsustainable use of space. Instead, our analysis reveals that most of their satellites can be wasted due to their mismatch with physically uneven demands. We thus propose TinyLEO, a software-defined solution to shrink LEO network size for enormous global demands via dynamic spatiotemporal supply-demand matching. TinyLEO sparsifies satellite supplies on demand by combining diverse yet sparse orbits, hides complexities of this sparse LEO network via orbital model predictive control, and shifts the responsibility for handling these complexities to its geographic segment anycast for higher network usability, lower resource wastes, faster failovers, simpler satellites, and more flexible network orchestration. We have prototyped TinyLEO as a community toolkit for open research. Our evaluation using this toolkit shows that TinyLEO can compress the existing LEO mega-constellation network size by 2.0–7.9×, cut control plane costs by 1–3 orders of magnitude, and maintain the same demands and comparable data plane performance.

Leveraging direct-to-cell (DTC) satellites in low-earth orbits (LEO) to directly provide communication services for terrestrial cellphones is gaining popularity in recent years. However, the unique characteristics of the wireless medium in space-ground communication, combined with the dynamic behavior of LEO satellites, raise a new privacy leakage risk that an adversary eavesdropping on DTC broadcasts could steal the physical locations of active users. In this paper, we investigate new techniques to analyze the location leakage risks in emerging LEO direct-to-cell satellite networks (DCSN). We present DCATOR1DCATOR indicates the abbreviation of DCSN terminal locator. , a novel location leakage analyzer which continuously monitors DTC signaling messages in broadcast channels, extracts various location clues and combines them with the time-varying satellite trajectories to infer the physical locations of active users. We use DCATOR to analyze the consequences if an adversary is able to continuously monitor and process broadcast DTC signaling to deduce the locations of other users within the same satellite coverage area, in three representative DCSNs: (i) the operational Iridium; (ii) the developing Starlink DTC; and (iii) a DCSN based on the latest 3GPP NTN standards. Our extensive experiments demonstrate the existence of location leakages in real DCSNs, and in the worst case an adversary can precisely track the locations of other users within hundreds of meters. Finally, we propose privacy-enhancing countermeasures for DCSNs.

We present CoordAuth, a gaze-based two-factor authentication technique in VR utilizing implicit head-eye motion features to offer a more secure and natural alternative to traditional pattern-based authentication. Users authenticate by performing gestures across 3×3 grid points using their eyes. We first optimized CoordAuth’s UI by evaluating participants’ input performance and experiences across different grid sizes. Then we extracted the head-eye coordination features during pattern entering to construct CoordAuth’s authentication algorithm, which ensembles Random Forest classifiers across saccade and fixations segments. CoordAuth demonstrated strong security with a 1.6% FAR and 1.5% FRR across 24 registered users in the password collision scenarios. A subsequent study demonstrated that CoordAuth achieved an 0.6% Attack Success Rate (ASR) against shoulder-surfing attack from a 1-meter distance. Usability evaluations in standing, sitting, and moving postures showed that CoordAuth achieved significantly faster authentication speed and lower rejection rate than laser and touch-based baselines. Meanwhile, it was the most preferred by the participants in terms of social acceptance and physical effort.

In this paper, we perform a systematic study to explore a pivotal problem facing the web community: is current distributed web cache ready for future satellite Internet? First, through a worldwide performance measurement based on the RIPE Atlas platform and Starlink, the largest low-earth orbit (LEO) satellite network (LSN) today, we identify that the uneven deployment of current distributed cache servers, inter-ISP meandering routes and the last-mile congestion on LEO links jointly prevent existing terrestrial web cache from providing low-latency web access for users in emerging LSNs. Second, we propose Spache, a novel web caching system which addresses the limitations of existing ground-only cache by exploiting a bold idea: integrating web cache into LEO satellites to achieve ubiquitous and low-latency web services. Specifically, Spache leverages a key feature of LSNs called communication schedule to efficiently prefetch web contents on satellites, and adopts a schedule-driven partitioning strategy to avoid cache pollution involved by LEO mobility. Finally, we implement a prototype of Spache, and evaluate it based on real-world HTTP traces and data-driven LSN simulation. Extensive evaluations demonstrate that as compared to existing distributed caching solutions, Spache can improve cache hit ratio by 19.8% on average, reduce latency by up to 17.7%, and maintains consistently low web browsing latency for global LSN users.

User-perceived latency is important for the quality of experience (QoE) of wide-area real-time communications (RTC). With the rapid development of low Earth orbit (LEO) mega-constellations, this paper explores a futuristic yet important problem facing the RTC community:can we exploit emerging mega-constellations to facilitate low-latency RTC globally?We carry out our quest in three steps. First, through a measurement study associated with a large number of geo-distributed RTC users, we quantitatively expose that themeandering routesin theclient-to-cloudandinter-cloud-sitesegment of existing cloud-based RTC architecture are critical culprits for the high latency issue suffered by wide-area RTC sessions. Second, we proposeSpaceRTC, a satellite-cloud cooperative framework that dynamically selectsrelay serversupon satellites and cloud sites to build an overlay network which enables diverse close-to-optimal paths.SpaceRTCjudiciously allocates RTC flows of different sessions upon the network to facilitate low-latency interactions and adaptively selects bitrates to offer high user-perceived QoE in energy-limited space circumstance. Finally, we implement a testbed based on public constellation information and real-world RTC traces. Extensive experiments demonstrate thatSpaceRTCcan deliver near-optimal interactive latency, with up to 53.3% average latency reduction and 103.6% average bitrate improvement as compared to other state-of-the-art cloud-based solutions.

Private conversations in social Virtual Reality (VR) environments lack the nuanced cues of physical interactions, potentially diminishing the sense of privacy and social presence. This paper introduces Whisper, a novel multisensory interaction technique designed to enhance private conversations for social VR applications. We first conducted a formative study (N=20) to understand private conversation demands, limitations of existing methods, and user expectations in social VR. Informed by these insights, Whisper incorporates visual (avatar proximity, gestures and illumination), auditory (voice conversation), and tactile (simulated airflow) elements to simulate the act of whispering, providing users with an intuitive and immersive method of private communication. The technique also features a contextual record to maintain conversation continuity. We evaluated Whisper through a comparative user study (N=24) in party and classroom scenarios. Results demonstrate that Whisper significantly outperforms existing methods in sense of privacy, mode distinguishability, intimacy, perceptual realism, and social presence.

Low Earth Orbit (LEO) satellite network is undergoing an explosive expansion to enable high-speed Internet for numerous users anywhere on Earth. However, as a cyber-physical network, the LEO network's sustainable expansion is constrained by its harsh, crowded, and imbalanced physical environment. This position paper dives into two physical constraints for the LEO network scalability: the scale-out limit by satellite safety distances in crowded outer space, and the scale-up limit by the mismatch between the uniform LEO network capacity supply and geographically non-uniform global distribution of user demands. Traditional networking research pays less attention to these physical scaling limits, which may imply a call for a cyber-physical co-design to help the LEO network grow in the challenged space environment.

End-to-end congestion control algorithms (CCAs) are expected to perform well in any Internet path, including those paths with low-earth orbit (LEO) satellite links. In this paper, we conduct a performance study on various CCAs in an operational LEO satellite network. We find that existing CCAs struggle to deal with the drastic network variations caused by the mobility of LEO satellites, resulting in poor link utilization or high latency. Further, through an in-depth analysis, we identify the fundamental challenge is that existing end-to-end CCAs detect network congestion based on performance changes observed on the sender, but the unique LEO mobility can involve massive non-congestion performance changes which seriously mislead CCA behaviors. Finally, we explore and discuss possible solutions to mitigate the misleading effects of LEO mobility.

Emerging satellite Internet constellations such as SpaceX's Starlink will deploy thousands of broadband satellites and construct Low-Earth Orbit (LEO) satellite networks (LSNs) in space, significantly expanding the boundaries of today's terrestrial Internet. However, due to the unique global LEO dynamics, satellite routers will inevitably pass through uncontrolled areas, suffering from security threats. It should be important for satellite network operators (SNOs) to enable verifiable riskavoidance routing to identify path anomalies. In this paper, we present STARVERI, a novel network path verification framework tailored for emerging LSNs. STARVERI addresses the limitations of existing crypto-based and delay-based verification approaches and accomplishes efficient and accurate path verification by: (i) adopting a dynamic relay selection mechanism deployed in SNO's operation center to judiciously select verifiable relays for each communication pair over LSNs; and (ii) incorporating a lightweight path verification algorithm to dynamically verify each segment path split by distributed relays. We build an LSN simulator based on real constellation information and the results demonstrate that STARVERI can significantly improve the path verification accuracy and achieve lower router overhead compared with existing approaches.

Recently we have witnessed the active deployment of mega-constellations with hundreds to thousands of low-earth orbit (LEO) satellites, targeting at constructing LEO satellite networks (LSN) to provide ubiquitous Internet services globally. However, while the massive deployment of LEO satellites can improve the network survivability and performance of an LSN, it also involves additional sustainable challenges such as higher deployment cost, risk of satellite conjunction and space debris.In this paper, we investigate an important research problem facing the upcoming satellite Internet: from a network perspective, how many satellites exactly do we need to construct a survivable and performant LSN? To answer this question, we first formulate the survivable and performant LSN design (SPLD) problem, which aims to find the minimum number of needed satellites to construct an LSN that can provide sufficient amount of redundant paths, required link capacity and acceptable latency for traffic carried by the LSN. Second, to efficiently solve the tricky SPLD problem, we propose MegaReduce, a requirement-driven constellation optimization mechanism, which can calculate feasible solutions for SPLD in polynomial time. Finally, we conduct extensive trace-driven simulations to verify MegaReduce’s cost-effectiveness in constructing survivable and performant LSNs on demand, and showcase how MegaReduce can help optimize the incremental deployment and long-term maintenance of future satellite Internet.

Emerging integrated space and terrestrial networks (ISTN) built upon low earth orbit (LEO) satellite constellations aim at providing planet-wide Internet services, not only for residential users, but also for mobile users (e.g., in airplane and cruise scenarios). Efficiently managing global mobility and keeping connections active for mobile users is critical for ISTN operators. However, our quantitative analysis identifies that existing mobility management (MM) schemes suffer from frequent connection interruptions and long latency in ISTN scenarios. The fundamental challenge stems from a unique characteristic of ISTNs: not only users are mobile, but also core network infrastructures (i.e., LEO satellites) are frequently changing their locations in the network.To facilitate seamless and low-latency satellite Internet services, this paper presents SkyCastle, a novel network-based global mobility management mechanism. SkyCastle incorporates two key techniques to address frequent connection interruptions in ISTNs. First, to reduce the interruption time, SkyCastle adopts distributed satellite anchors to track the location changes of mobile nodes, manage handovers and avoid routing convergence. Second, SkyCastle leverages an anchor manager to schedule MM functionalities at satellites to reduce deployment costs while guaranteeing low latency. Extensive evaluations combining real constellation information and mobile user trajectories show that: SkyCastle can improve up to 55.8% uninterrupted time and reduce 47.8% latency as compared to other existing MM solutions.

With the rapid evolution of space-borne capabilities, space edge computing (SEC) is becoming a new computation paradigm for future integrated space and terrestrial networks. Satellite edges adopt advanced on-board hardware, which not only enables new opportunities to perform complex intelligent tasks in orbit, but also involves new challenges due to the additional energy consumption in power-constrained space environment.In this paper, we present Phoenix, an energy-efficient task scheduling framework for emerging SEC networks. Phoenix exploits a key insight that in the SEC network, there always exist a number of sunlit edges which are illuminated during the entire orbital period and have sufficient energy supplement from the sun. Phoenix accomplishes energy-efficient in-orbit computing by judiciously offloading space tasks to "sunlight-sufficient" edges or to the ground. Specifically, Phoenix first formulates the SEC battery energy optimizing (SBEO) problem which aims at minimizing the average battery energy consumption while satisfying various task completion constraints. Then Phoenix incorporates a sunlight-aware scheduling mechanism to solve the SBEO problem and schedule SEC tasks efficiently. Finally, we implement a Phoenix prototype and build an SEC testbed. Extensive data-driven evaluations demonstrate that as compared to other state-of-the-art solutions, Phoenix can effectively reduce up to 54.8% SEC battery energy consumption and prolong battery lifetime to 2.9× while still completing tasks on time.

In recent years, the rapid proliferation of satellite Internet constellations (SICs) operating in low-earth orbit (LEO) has attracted attention due to their charming merits. Despite the potential of LEO satellite networks, the security aspects of their operation have largely been neglected.Composed by a large number of satellites, these mega-constellation networks are considered to be performant and resilient. In this paper, however, we challenge this intuitive notion by proposing STARMAZE, an impactful ring-based attack which could lead to severe consequences such as network service disruption or causing routing detours. Unlike other existing attack methods, STARMAZE removes the extra assumptions of specific routing algorithms and has the periodicity which contribute to lower-cost yet long-lasting launch of attack. Simultaneously, we also introduce the concept of intentional gaps to emphasize our consideration of real-world attacks, where attackers may not always succeed in precisely targeting all links. Comprehensive evaluations, grounded in practical constellation insights, show that impairing just 2.5% of Inter-Satellite Links (ISLs) can markedly amplify the average propagation delay of chosen long-distance communication pairs by over 63%. Moreover, during more than 47% of the observation time, the value can even reach over 312%.

Low Earth Orbit (LEO) satellite mega-constellations promise ubiquitous network services to "unconnected" users. But their upcoming global routing for Earth will be unstable due to exhaustive topology updates between satellites and Earth, inside an orbital shell, and across heterogeneous orbital shells. In real LEO networks, these multi-dimensional dynamics are interleaved and complicated by chaotic orbital maneuvers and random failures. They are less predictable than most satellite routing proposals expect and threaten these proposals' availability, efficiency, or resiliency at scale.

With the rapidly increasing number of satellites in space and their enhanced capabilities, the amount of earth observation images collected by satellites is exceeding the transmission limits of satellite-to-ground links. Although existing learned image compression solutions achieve remarkable performance by using a sophisticated encoder to extract fruitful features as compression and using a decoder to reconstruct. It is still hard to directly deploy those complex encoders on current satellites' embedded GPUs with limited computing capability and power supply to compress images in orbit. In this paper, we propose COSMIC, a simple yet effective learned compression solution to transmit satellite images. We first design a lightweight encoder (i.e. reducing FLOPs by 2.5~5X) on satellite to achieve a high image compression ratio to save satellite-to-ground links. Then, for reconstructions on the ground, to deal with the feature extraction ability degradation due to simplifying encoders, we propose a diffusion-based model to compensate image details when decoding. Our insight is that satellite's earth observation photos are not just images but indeed multi-modal data with a nature of Text-to-Image pairing since they are collected with rich sensor data (e.g. coordinates, timestep, etc.) that can be used as the condition for diffusion generation. Extensive experiments show that COSMIC outperforms state-of-the-art baselines on both perceptual and distortion metrics.

The emergent direct-to-cell Low-Earth Orbit (LEO) satellite mega-constellations promise ubiquitous LTE/5G access for our commodity phones and IoTs without terrestrial base stations. While their extreme scale and mobility help tolerate diverse attacks, we show that both new features are exploitable to amplify signaling protocol vulnerabilities inherited from LTE/5G and obfuscate attacks to threaten satellite services. We showcase this with SatOver, a control-plane cross-layer attack that lets a greedy terrestrial operator or a man-in-the-middle attacker block all direct-to-cell satellites in urban areas. SatOver can reuse terrestrial LTE/5G base stations or deploy commodity software-defined radios as false satellites, stealthily hijack victim devices, delay their satellite access, stop them from probing other satellites, and block the entire mega-constellation. Our real-world satellite tests, lab tests with commodity 3GPP NR/IoT-NTN stacks, and operational trace-driven emulation validate SatOver’s viability for attacking COTS and upcoming NTN phones/IoTs. We discuss potential defenses against SatOver’s attack amplification/obfuscation.

The integration of Mobile Edge Computing (MEC) and Low Earth Orbit (LEO) satellite networks holds the potential to offer ubiquitous computing services for ground users and has garnered significant attention recently. While there has been extensive research conducted in the field of Satellite Mobile Edge Computing (SMEC), research on edge server deployment in mega-constellation is overlooked. Edge servers require an appropriate quantification and placement before the implementation of computation offloading. The improper deployment strategy can result in high access latency and imbalance workload. In this paper, we propose a two-stage approach, called cluster-based small-scale server deloyment (CSSD), for small-scale placing and dynamic allocating edge servers that enable low access latency and workload balancing. Specifically, the offline stage is employed to determine the optimal placement of edge servers and the initial offloading mapping from access satellites to service satellites. The online stage, building dynamically adjusts the offloading mapping based on the spatiotemporal positions and workload of the satellites to balance system workload. Evaluation results show that CSSD outperforms other approaches with up to 16.37% and 35.38% enhancements in terms of workload standard deviation and user service rate while maintaining low access latency.

Delay-sensitive Web services are crucial applications in emerging low-earth orbit (LEO) satellite networks (LSNs). However, our real-world measurement study based on SpaceX's Starlink, the most widely used commercial LSN today, reveals that the endless and bursty packet losses over unstable LEO satellite links impose significant challenges on guaranteeing the quality of experience (QoE) of Web applications. We propose SatGuard, a distributed in-orbit loss recovery mechanism that can reduce user-perceived delay by completely concealing packet losses in the unstable and lossy LSN environment from endpoints. Specifically, SatGuard adopts a series of techniques to: (i) correctly migrate on-board packet buffer to support link-local retransmission under LEO dynamics; (ii) efficiently detect packet losses on satellite links; and (iii) ensure packet ordering for endpoints. We implement a SatGuard prototype, and conduct extensive trace-driven evaluations guided by public constellation information and real-world measurements. Our experiments demonstrate that, in comparison with other state-of-the-art approaches, SatGuard can significantly improve Web-based QoE, by reducing: (i) up to 48.3% of page load time for Web browsing; and (ii) up to 57.4% end-to-end communication delay for WebRTC.

Deep Neural Networks are well-known to be vulnerable to Adversarial Examples. Recently, advanced gradient-based attacks were proposed (e.g., BPDA and EOT), which can significantly increase the difficulty and complexity of designing effective defenses. In this paper, we present a study towards the opportunity of mitigating those powerful attacks with only pre-processing operations. We make the following two contributions. First, we perform an in-depth analysis of those attacks and summarize three fundamental properties that a good defense solution should have. Second, we design a lightweight preprocessing function with these properties and the capability of preserving the model's usability and robustness against these threats. Extensive evaluations indicate that our solutions can effectively mitigate all existing standard and advanced attack techniques, and beat 11 state-of-the-art defense solutions published in top-tier conferences over the past 2 years.

In this paper, we proposed Squeez’In, a technique on smartphones that enabled private authentication by holding and squeezing the phone with a unique pattern. We first explored the design space of practical squeezing gestures for authentication by analyzing the participants’ self-designed gestures and squeezing behavior. Results showed that varying-length gestures with two levels of touch pressure and duration were the most natural and unambiguous. We then implemented Squeez’In on an off-the-shelf capacitive sensing smartphone, and employed an SVM-GBDT model for recognizing gestures and user-specific behavioral patterns, achieving 99.3% accuracy and 0.93 F1-score when tested on 21 users. A following 14-day study validated the memorability and long-term stability of Squeez’In. During usability evaluation, compared with gesture and pin code, Squeez’In achieved significantly faster authentication speed and higher user preference in terms of privacy and security.

Exploiting a constellation of small satellites to realize continuous earth observations (EO) is gaining popularity. Large-volume EO data acquired from space needs to be transferred to the ground. However, existing EO delivery approaches are either: (a) efficiency-limited, suffering from long delivery completion time due to the intermittent ground-space communication, or (b) scalability-limited since they fail to support concurrent delivery for multiple satellites in an EO constellation.To make big data delivery for emerging EO constellations fast and scalable, we propose Falcon, a multi-path EO delivery framework that wisely exploits diverse paths in broadband constellations to collaboratively deliver EO data effectively. In particular, we formulate the constellation-wide EO data multi-path download (CEOMD) problem, which aims at minimizing the delivery completion time of requested data for all EO sources. We prove the hardness of solving CEOMD, and further present a heuristic multipath routing and bandwidth allocation mechanism to tackle the technical challenges caused by time-varying satellite dynamics and flow contention, and solve the CEOMD problem efficiently. Evaluation results based on public orbital data of real EO constellations show that as compared to other state-of-the-art approaches, Falcon can reduce at least 51% delivery completion time for various data requests in large EO constellations.

The emerging satellite internet constellation aims to deploy hundreds of low-orbit satellites to provide high-speed broadband internet services to global ground terminals. However, this poses a significant challenge for large-scale and highly dynamic satellite networking due to the traditional satellite constellations’ uniform structure. This structure is limited by four laser links per low-orbit satellite, using default connections of two intra-orbit links and two inter-orbit links, and is difficult to match with the uneven population distribution and user traffic on the ground, resulting in unnecessary overheads in propagation delay and transmission hops. In recent years, researchers have developed methods for matching structure and traffic distribution that overcome the limitations of traditional connection methods, reducing transmission delay and hops. Despite this progress, these methods still maintain the characteristics of uniform configuration. To address this issue, a new link connection design for large-scale low-orbit satellite network driven by user distribution has been proposed. This mechanism enables the dynamic matching of satellite structure and users, facilitating elastic networking under dynamic topology conditions, improving the overall capacity and utilization of satellite networks. Through simulation, this user-driven link connection design has been verified to reduce the average hop count by at least 41% in many scenarios, demonstrating its effectiveness for a variety of new large-scale low-orbit satellite networks.

Entering the “NewSpace” era, satellite Internet constellation (SIC) is expanding rapidly. However, while operating a large number of broadband satellites in free space enables great opportunities for ubiquitous and low-latency Internet services, it also involves new threats that were previously ignored to the energy-limited satellite systems. In this paper, we investigate the feasibility and impact of a new class of real risk in emerging SICs: energy drain attack. To this end, we play the role of an attacker and propose Starmelt,an energy drain attack mechanism that persistently injects malicious traffic that goes through the victim satellite from various geo-distributed locations, preventing the victim from hibernating and overusing the satellite battery to cut its lifetime. Further, we design a series of techniques to: (i) handle the path ambiguity challenge caused by various access selection and routing schemes to guarantee that the deliberately crafted traffic can precisely pass through the victim; (ii) leverage the tail energy consumption characteristics to reduce the detectability as well as the traffic cost of an attack. Extensive simulations based on real constellation knowledge demonstrate that Starmeltcan substantially increase on-board energy consumption, reducing up to 76% lifetime of the victim satellite under various power models and traffic patterns.

Low-earth-orbit (LEO) satellite mega-constellations, such as SpaceX Starlink, are under rocket-fast deployments and promise broadband Internet to remote areas that terrestrial networks cannot reach. For mission safety and sustainable uses of space, Starlink has adopted a proprietary onboard autonomous driving system for its extremely mobile LEO satellites. This paper demystifies and diagnoses its impacts on the LEO mega-constellation and satellite networks. We design a domain-specific method to characterize key components in Starlink's autonomous driving from various public space situational awareness datasets, including continuous orbit maintenance, collision avoidance, and maneuvers between orbital shells. Our analysis shows that, these operations have mixed impacts on the stability and performance of the entire mega-constellation, inter-satellite links, topology, and upper-layer network functions. To this end, we investigate and empirically assess the potential of networking-autonomous driving co-designs for the upcoming satellite networks.

Linear hand movement in mid-air is one of the most fundamental interactions in virtual reality (e.g., when dragging/scaling/manipulating objects and drawing shapes). However, the lack of tactile feedback makes it difficult to precisely control the direction and amplitude of hand movement. In this paper, we conducted three user studies to progressively examine users' ability of fine motor control in 3D linear hand movement tasks. In Study 1, we examined participants' behavioural patterns when drawing straight lines in various directions and lengths, using both the hand and the controller. Results showed that the exhibited stroke length tended to be longer than perceived, regardless of the interaction tool. While displaying the trajectory could help reduce directional and length errors. In Study 2, we further tested the effect of different visual references and found that, compared with an empty room or cluttered scenarios, providing only a virtual table yielded higher input precision and user preference. In Study 3, we repeated Study 2 in real dragging and scaling tasks and verified the generalizability of the findings in terms of input error. Our core finding is that the user's hand moves significantly longer than the task length due to the underestimation of stroke length, yet the error of the Z-axis movement is smaller than that of the X-axis and the Y-axis, and a simple virtual desktop can effectively reduce errors.

Internet content providers (ICPs) typically exploit content distribution networks (CDNs) to provide wide-area data access with high availability and low latency. However, our analysis on a large-scale trace collected from seven major CDN operators has revealed that: from a global perspective, there are still a large portion of users suffering from high user-perceived latency due to the insufficient deployment of terrestrial cloud infrastructures, especially in remote or rural areas where even the closest available cache server is too far away. This paper presents STAR FRONT, a cost-effective content distribution framework to optimize global CDNs and enable low content access latency anywhere. STAR FRONT collaboratively builds CDNs upon emerging low earth orbit (LEO) constellations and existing cloud platforms to satisfy the low latency requirements while minimizing the operational cost. Specifically, STAR FRONT exploits a key insight that emerging mega-constellations will consist of thousands of LEO satellites which can be equipped with high-speed data links and storage, and thus can potentially work as “cache in space” to enable pervasive and low-latency data access. STAR FRONT judiciously places replicas on either LEO satellite caches or terrestrial cloud caches, and dynamically assigns user requests to proper cache servers based on different constellation parameters, cloud/user distributions and pricing policies. We have implemented a STAR FRONT prototype in our testbed, and extensive trace-driven evaluations covering multiple geo-distributed vantage points have demonstrated that STAR FRONT can effectively reduce the global content access latency with acceptable operational cost under representative CDN traffic.

Emerging low earth orbit (LEO) satellites and geo-distributed ground station networks can assist pervasive and efficient Internet data delivery on a global scale. However, while promising, the improper integration of ingress satellite selection (ISS) and inter-satellite routing (ISR) can result in significantly high propagation latency and low network utilization. In this paper, we propose AeroPath, a ground-station-driven data delivery architecture that enables high-throughput data transmission while maintaining low latency. Specifically, to accomplish transmission efficiency, geo-distributed ground stations independently schedule flows over ground-satellite links in collaboration with ISR and cooperatively select inter-satellite paths to avoid bandwidth competition between different ground stations. Finally, we evaluate the effectiveness of AeroPath via extensive simulations driven by realistic constellation information. Evaluation results show that AeroPath can outperform other approaches with up to 24.1% and 18.5% improvement in terms of average system throughput and ground station utilization respectively under state-of-the-art constellation patterns.

The emergence of mega-constellations is the most promising satellite network trend in recent years, which brings new security challenges to the network layer and higher layers, such as DDoS, worm, and DNS pollution. Source address validation is one of the effective solutions in terrestrial networks, by filtering the invalid address and resisting the source address spoofing. Because of the time-vary topology in mega-constellations, the source address validation mechanism faces the severe problem of the anchor mobility, which leads to a sharp decline in SAVI (Source Address Validation Improvements) performance and increases the cost to maintain the user status. In this paper, we develop a source address spoofing avoidance mechanism under high movement (SASA) for mega-constellations. Specifically, we propose that the user and the satellite both maintain the user status. After the satellite signed the binding information by the private key, it forms the mapping between the authenticity of the user address and the initial access satellite on the user side. Moreover, when the handover occurs, the user safely transmits the authentication information to the new access satellite through asymmetric encryption to complete rebinding. Simulation results show that SASA can greatly reduce the rebinding cost of mega-constellations by 95.04% in Starlink and 81.84% in Kuiper.

User-perceived latency is important for the quality of experience (QoE) of wide-area real-time communications (RTC). This paper explores a futuristic yet important problem facing the RTC community: can we exploit emerging mega-constellations to facilitate low-latency RTC globally? We carry out our quest in three steps. First, through a measurement study associated with a large number of geo-distributed RTC users, we quantitatively expose that the meandering routes in the client-cloud and inter-cloud-site segment of existing cloud-based RTC architecture are critical culprits for the high latency issue suffered by wide-area RTC sessions. Second, we propose SPACERTC, a satellite-cloud cooperative framework that adaptively selects relay servers upon satellites and cloud sites to build an overlay network which enables diverse close-to-optimal paths, and then judiciously allocates RTC flows upon the network to facilitate low-latency interactions. Finally, we implement our SPACERTC prototype on an experimental environment based on public constellation information and RTC trace, and extensive experiments demonstrate that SPACERTC can deliver near-optimal interactive latency, with up to 64.9% latency reduction as compared to other state-of-the-art cloud-based solutions under representative videoconferencing traffic.

The network topology design is critical for achieving low latency and high capacity in future integrated satellite and terrestrial networks (ISTN). However, existing studies mainly focus on the design of inter-satellite topology of ISTN, and very little is known about the design of satellite-ground topology, as well as its impact on the attainable network performance.In this paper, we conduct a quantitative study on the impact of various satellite-ground designs on the network performance of ISTN. We identify that the high-density and high-dynamicity characteristics of emerging mega-constellations have jointly imposed big challenges, such as significant routing instability, low network reachability, high latency and jitter on the ISTN paths. To alleviate the above challenges, we formulate the Low-latency Satellite-Ground Interconnecting (LSGI) problem, targeting at the integration of space and ground segment in the ISTN, while minimizing the maximum transmission latency and keeping routing stable. We further design algorithms to solve the LSGI problem through wisely coordinating the establishment of ground-to-satellite links among distributed ground stations. Comprehensive experiment results demonstrate that our solution can outperform existing related schemes by about 19% reduction of the latency and 70% reduction of the jitter on average, while sustaining the highest network reachability.

The low-earth-orbit (LEO) satellite networks promise low-latency broadband network services to remote areas. LEO networks require deploying many satellites to serve numerous users in crowded terrestrial areas, thus forming a satellite mega-constellation. It is well known that this practice would lower network utilization, which may be exacerbated with recent LEO satellite mega-constellations. For LEO satellite mega-constellation networks with complex and dynamic structures, multiple functions, and diversified user demands, this paper presents a methodology for systematically analyzing utilization. Our study shows that operational mega-constellations today suffer from < 10% low network utilization. The root cause is twofold. First, today's evenly distributed satellites do not match the unevenly distributed terrestrial users, and the law of satellite movement keeps a satellite above sparsely populated areas most of the time. Second, a uniform LEO mega-constellation cannot simultaneously meet the heterogeneous demands from local satellite access (requiring more satellites to serve the enormous population in hotspots) and global satellite routing (requiring fewer satellites for shorter paths). Based on these findings, we analyze how to improve utilization from angles of constellation structure and network architecture design. We showcase it can increase the utilization with fewer and divergent satellites while retaining comparable performance to state-of-the-art.

Low-earth-orbit (LEO) satellite mega-constellations promise broadband, low-latency network infrastructure from space for terrestrial users in remote areas. However, they face new QoS bottlenecks from infrastructure mobility due to the fast-moving LEO satellites and earth’s rotations. Both cause frequent space-ground link churns and challenge the network latency, bandwidth, and availability at the global scale. Today’s LEO networks mask infrastructure mobility with fixed anchors (ground stations) but cause single-point bandwidth/latency bottlenecks. Instead, we design LBP to remove the LEO network’s QoS bottlenecks from infrastructure mobility. LBP removes remote terrestrial fixed anchors via geographic addressing for shorter latencies and more bandwidth. It adopts local, orbit direction-aware geographic routing to avoid global routing updates for high network availability. LBP further shortens the routing paths by refining handover policies by satellites’ orbital directions. Our experiments in controlled testbeds and trace-driven emulations validate LBP’s 1.64× network latency reduction, 9.66× more bandwidth, and improve network availability to 100%.

Is it worth and feasible to push mobile core network functions to low-earth-orbit (LEO) satellite mega-constellations? While this paradigm is being tested in space and promises new values, it also raises scalability, performance, and security concerns based on our study with datasets from operational satellites and 5G. A major challenge is today's stateful mobile core, which suffers from signaling storms in satellites' extreme mobility, intermittent failures in outer space, and attacks when unavoidably exposed to untrusted foreign locations. To this end, we make a case for a stateless mobile core in space. Our solution, SpaceCore, decouples states from orbital core functions, simplifies location states via geospatial addressing, eliminates unnecessary state migrations in satellite mobility by shifting to geospatial service areas, and localizes state retrievals with device-as-the-repository. Our evaluation with datasets from operational satellites and 5G shows SpaceCore's 17.5× over existing solutions signaling reductions and resiliency to failures/attacks.

Gaze-based target suffers from low input precision and target occlusion. In this paper, we explored to leverage the continuous eyelid movement to support high-efficient and occlusion-robust dwell-based gaze pointing in virtual reality. We first conducted two user studies to examine the users’ eyelid movement pattern both in unintentional and intentional conditions. The results proved the feasibility of leveraging intentional eyelid movement that was distinguishable with natural movements for input. We also tested the participants’ dwelling pattern for targets with different sizes and locations. Based on these results, we propose DEEP, a novel technique that enables the users to see through occlusions by controlling the aperture angle of their eyelids and dwell to select the targets with the help of a probabilistic input prediction model. Evaluation results showed that DEEP with dynamic depth and location selection incorporation significantly outperformed its static variants, as well as a naive dwelling baseline technique. Even for 100% occluded targets, it could achieve an average selection speed of 2.5s with an error rate of 2.3%.

We devise a simple, provably effective, and readily usable deterrence against intelligent, unknown DDoS threats: Demotivate adversaries to launch attacks via multi-hop traffic divergence. This new strategy is motivated by the fact that existing defenses almost always lag behind numerous emerging DDoS threats and evolving intelligent attack strategies. The root cause is if adversaries are smart and adaptive, no single-hop defenses (including optimal ones) can perfectly differentiate unknown DDoS and legitimate traffic. Instead, we formulate intelligent DDoS as a game between attackers and defenders, and prove how multi-hop traffic divergence helps bypass this dilemma by reversing the asymmetry between attackers and defenders. This insight results in EID, an Economical Intelligent DDoS Demotivation protocol. EID combines local weak (yet divergent) filters to provably null attack gains without knowing exploited vulnerabilities or attack strategies. It incentivizes multi-hop defenders to cooperate with boosted local service availability. EID is resilient to traffic dynamics and manipulations. It is readily deployable with random-drop filters in real networks today. Our experiments over a 49.8 TB dataset from a department at the Tsinghua campus network validate EID's viability against rational and irrational DDoS with negligible costs.

We study a new design objective for "Internet in space" for terrestrial users: To align logical network topology, address, and route in the virtual cyberspace with movements of satellite mega-constellations and earth's rotations in the real physical world. We explain why this is particularly desirable by the recent low-earth-orbit (LEO) mega-constellations, and how it welcomes mobility to streamline the network design for stability, efficiency, and scalability in an unstable space-ground environment. We showcase its feasibility with the common fixed satellite sub-point trajectory in mega-constellations. We describe how it permits stable recursive topology, unifies cyber-physical locations in the address, and naturally embeds the geographical routing into the topological routing.

Internet content providers typically exploit cloud-based content delivery/distribution networks (CDNs) to provide wide-area data access with high availability and low latency. However, from a global perspective, a large portion of users still suffer from high content access latency due to the insufficient deployment of terrestrial cloud infrastructures.This paper presents StarFront, a cost-effective content distribution framework to optimize global CDNs and enable low content access latency anywhere. StarFront builds CDNs upon emerging low Earth orbit (LEO) constellations and existing cloud platforms to satisfy the low-latency requirements while minimizing the operational cost. Specifically, StarFront exploits a key insight that emerging mega-constellations will consist of thousands of LEO satellites equipped with high-speed data links and storage, and thus can potentially work as "cache in space" to enable pervasive and low-latency data access. StarFront judiciously places replicas on either LEO satellites or clouds, and dynamically assigns user requests to proper cache servers based on constellation parameters, cloud/user distributions and pricing policies. Extensive trace-driven evaluations covering geo-distributed vantage points have demonstrated that: StarFront can effectively reduce the global content access latency with acceptable operational cost under representative CDN traffic.

Satellite-based Earth Observation (EO) systems are gaining popularity and widely used in many time-sensitive scenarios, including disaster monitoring, emergency response, forecasting and defense. Existing efforts for gathering EO data mainly rely on either ground station networks or geostationary (GEO) satellites. However, our quantitative analysis reveals that existing approaches are either limited as their achievable latency is far away from the desired value due to the insufficient coverage of ground stations, or hard to scale as the number of sensing satellites increases because of the high cost of GEO satellite relays.This paper explores the feasibility and performance of a novel approach that leverages emerging low Earth orbit (LEO) constellations to enable low-latency and scalable EO data delivery from space. We present OrbitCast, a hybrid EO data delivery architecture upon LEO constellations and geo-distributed ground stations to forward EO data from the source remote sensing satellite to a collection of end users. To handle the network dynamicity caused by LEO satellite movements and achieve stable communication over the satellite network, we propose a geo-location driven scheme to forward and deliver data packets. To demonstrate the effectiveness of OrbitCast, we build a testbed driven by public constellation information and implement the OrbitCast prototype on top of the testbed. Extensive realistic-data-driven simulations demonstrate that OrbitCast can significantly reduce the latency as compared to other state-of-the-art approaches, and complete the data delivery within five minutes for representative EO data traffic.

The booming of satellite mega-constellations to provide Internet access around the Earth is attracting more attention recently. To provide broadband Internet globally, satellites will be responsible to undertake IP address management of ground terminals. However, the movement of the LEO (Low Earth Orbit) satellite will cause difficulties to IP address management, because every LEO satellite can just stay in sight of a ground terminal for several minutes. On one hand, stateful IP address management faces a short lifetime, signal storm, and unstable address space problems. On the other hand, stateless IP address management cannot avoid high overhead in DAD (Duplicate Address Detection). This paper proposes GAMS, Geographical Addressing Management for Satellite, an efficient IP address management mechanism for mega-constellations networks. By embedding both satellites' feature information and geographical location into IPv6 addresses, GAMS enables efficient DAD with assigned address tables ONLY on respective satellite routers. Theoretical proof and simulation results validate that GAMS could effectively provide unique and long-lifetime IPv6 addresses to ground terminals with negligible cost.

The rapid development of high-speed rails (HSRs) has brought great convenience to people's travel. But related scholars found that the network status on the train is very inefficient. In order to solve that, some scholars proposed to use multipath TCP (MPTCP). However, MPTCP suffers when different paths have heterogeneous quality. In HSR scenarios, frequent handover (less than 10 seconds) occurs when devices connect to cellular network base stations. If MPTCP is used, each sub-flow has to go through handover and packets will be heavily garbled. In turn, it occupies a large amount of the receiver's buffer, even up to 100%. The latency of data submission to application will also be higher (10ms or more). It will affect the overall transfer performance. The reason for the above problem is that MPTCP does not react quickly enough to link changes and cannot accurately schedule packets between sub-flows. After consulting the measurement data of relevant scholars, we found that the trains in HSR have some recurring phenomena. For example, base station handover always occurs in the same place for devices in HSR. Based on relevant recurring information, this paper proposes Hysteresis Optimized Multipath TCP Data Scheduling Algorithm (HoMPTCP) in Predictable Networks. Combined with the prediction information formed by using historical trajectories in HSR, HoMPTCP can more accurately schedule packets between sub-flows and control the congestion window of sub-flows. After the experiments of HSR scenario, HoMPTCP can improve throughput performance by 5%-15% while increasing sequential arrival rate by 10%-15%.

With low latency and wide coverage, Low Earth Orbit (LEO) satellite networks can provide network services for places that cannot be reached by the terrestrial network and become a critical supplement to the traditional network, playing an increasingly important role. While the wide coverage and broadcasting enable LEO satellite networks (LSNs) accessible to more devices, this also raises the risk of being attacked by potential adversaries. Previous research on secure routing is either mainly based on the design of encryption-based algorithms or is only suitable for the relative static topology of the traditional terrestrial networks. However, given limited computational resources and the highly dynamic changes of the LEO satellite, encryption-based algorithms can hardly meet the demands of LSNs. Unlike these works, this paper proposes a lightweight risk-avoidance routing algorithm (LRAR). It allows users' data packets to be forwarded by avoiding specified high-risk areas to reduce the risk of user data being attacked. As can be seen in extensive simulation experiments, the LRAR implements results close to the optimal path with little overhead. Also, it enhances security and flexible extensibility.

This paper reports our five-year lessons of developing and using MobileInsight, an open-source community tool to enable software-defined full-stack, runtime mobile network analytics inside our phones. We present how MobileInsight evolves from a simple monitor to a community toolset with cross-layer analytics, energy-efficient real-time user-plane analytics, and extensible user-friendly analytics at the control and user planes. These features are enabled by various novel techniques, including cross-layer state machine tracking, missing data inference, and domain-specific cross-layer sampling. Their powerfulness is exemplified with a 5-year longitudinal study of operational mobile network latency using a 6.4TB dataset with 6.1 billion over-the-air messages. We further share lessons and insights of using MobileInsight by the community, as well as our visions of MobileInsight's past, present, and future.

Due to the simplification of path selection in traditional IP routing schemes and the uneven distribution of traffic, problems such as congestion and low system performance are still unavoidable in satellite networks. Compared with terrestrial networks, satellite networks have much more equal-cost paths between any two points. So, this paper uses path diversity to solve the above problems. Researchers have proposed many traffic engineering algorithms to solve similar problems, but high-dynamics and high-latency of the satellite network make these algorithms ineffective. This paper proposed a Multi-routing-plane based Flow Scheduling Strategy (MFSS), using different routing schemes in different routing planes. It can make full use of path diversity to solve simplification of path selection and solve the high-dynamics problem through cooperation between satellites and the terrestrial networks. The simulation result on the topology of Starlink shows that, in our scenarios, MFSS can increase the system throughput by 60.9% while the delay growth does not exceed 3%.

With the rapid evolution of space communication technologies, satellite networks have entered a booming period. In recent years, Integrated Satellite and Terrestrial Network (ISTN) has been recognized as the trend of future networks. In order to adapt the existing routing technology to the network with high dynamic characteristics, a large number of research have tried to divide the timeslot in the satellite network and regard the network as static in a timeslot. However, The existing methods do not consider the existence of network convergence process in ISTN. With the massive increase in satellite handoff and the consensus of running distributed routing protocol, the network availability drops sharply in the timeslot divided by the existing methods. This paper proposes Handoff Synchronization to reduce the long convergence time. Moreover, STARSLOT is proposed to divide timeslots and improve the ISTN's availability. Extensive simulation show that for the typical ISTN architecture, STARSLOT can improve the network availability by 52.63% as compared to other existing methods. Moreover, STARSLOT is much less affected by the increase in network scale.

"Newspace" mega-constellations, such as Starlink and OneWeb are gaining tremendous popularity, with the promising potential to provide high-capacity and low-latency communication globally. However, very little is known about the architecture and performance of such emerging systems, the workload they have to face, as well as the impact of topological options on the attainable network performance. This paper presents StarPerf, a mega-constellation performance simulation platform that enables constellation manufacturers and content providers to estimate and understand the achievable performance under a variety of constellation options. The proposed platform integrates two key techniques: (1) performance simulation for mega-constellation, which captures the impact of the inherent high mobility in satellite networks and profiles the area-to-area attainable network performance; (2) constellation scaling, which synthesizes various topological options by scaling the space resource and enables exploration on multiple operating conditions that can not be easily reproduced. To demonstrate the effectiveness of StarPerf on understanding and optimizing satellite networks, we leverage StarPerf to evaluate and compare the performance of several state-of-the-art low earth orbit (LEO) constellations and obtain insights on optimizing the architectural design to improve area-to-area network performance. Finally, to further show how applications can benefit from the proposed simulator, we propose an adaptive relay selection algorithm that can intelligently choose the optimal relay on cloud platforms and LEO satellites to achieve reduced latency. Evaluation results show that by properly selecting a relay in the satellite-cloud integrated infrastructure, end-to-end communication latency can be reduced by up to 62% for typical interactive traffic.

This paper provides a new perspective for IP mobility support in LEO satellite network, that the network mobility should be solved via network driving rather than terminal driving methods. Terminal driving methods comes from terrestrial network which ones are typically reactive to the moving of users and improve the predictability of the terminals’ motion behaviors to enhance the performance. However, the mobility in LEO satellite network most comes from network(satellites) rather than terminals. It is inefficient to solve the continuous, high-speed, global and regular network mobility via terminal driving solutions who are designed for intermittent, low-speed, local and irregular user mobility. After modeling the satellite mobility behavior for single and multiple orbit plane, a network driving mobility management solution, namely NDM, is proposed in this paper, including 1) trigger and selection 2) proxy group handover 3) silent and explicit resource release. NDM utilizes the benefit of network driving and cooperate with terminal driving methods for robust consideration. Evaluations are conducted to proof the feasibility of mechanism to improve performance and apportion cost.

A trusted network path is a desired property of the Internet. Previous works introduced new protocol headers based on source routing for source authentication and path verification. It is obvious that any extra protocol headers will increase the network burden, and network path privacy deserves attention, especially when we use source routing. The emergence of IPv6 Segment Routing (SRv6) may bring the opportunity to assemble trusted network paths with a lightweight header. In this paper, we propose SR-TPP, a novel mechanism based on SRv6 to support network path verification meanwhile hides both-end and path information. Different from existing works, SR-TPP extends SRv6 function instead of introducing a new protocol header to meet the requirement of path compliance. Path information is sequentially encoded into the segment list in SR-TPP so that path information is partially visible to each intermediate router. The distributed verification of SR-TPP also makes it easier to locate faults. Finally, the security analysis and evaluation show that SR-TPP can assemble private and trusted network paths with acceptable performance.

The integrated satellite and terrestrial network(ISTN) is considered one of the most promising trend to provide global low-delay high-bandwidth Internet access service. For the mobility issue in ISTN, both of the satellites and terminals are moving. The motion of satellites is continuous, high-speed, global and regular, while the motion of terminals is intermittent, low-speed, local and irregular. The complete different characteristics make the classical methods based on the passive reaction of motion terminals ineffective in ISTN. The dealing with the motion of satellites and the motion of terminals are two indispensable terms in ISTN mobility management. Thus, filling the blank of dealing satellite motion is urgently needed. This paper demonstrates one solution integrated with Mobile IP for IP mobility support in ISTN. The flexible agent and aggregated handover are two essential novel points in our method. Flexible agent aims at relaxing the burden of fixed home satellite which moves faraway, relaying the home agent like functionality to a closer satellite in a flexible manner. Aggregated handover do the pre-handover together for users under the same satellite, which is in view of the regularity of passive motion caused by the satellite mobility. Evaluations are conducted to proof the necessity of supplementing the ability to handle the network motion in ISTN.

Edge caching in 5G networks shortens latency and alleviates the backhaul. Bringing content from the core network to the caches is a critical issue. When the satellite is integrated with the terrestrial 5G system, an overlay can be formed for cost-efficient content delivery. Multicast delivery over satellite is a promising scheme due to the broadcast nature of the wireless medium and wide coverage. Requests for popular content at nearby times can be aggregated through a multicast stream for bandwidth efficiency. However, directly multicast to a large audience from the satellite suffers from the problems led by fading channels and the flat topologies. The overlay architecture provides new solutions to handle the drawbacks of satellite multicast, e.g., channel and reception diversity, the difficulty of loss recovery and feedback explosion. We explicitly introduce the overlay architecture based on the configuration of multiple multicast groups and the merging of base station clusters for each communication session. The operation of this overlay is further explained. Besides, we also apply network coding to the multicast and cache networks to improve data recovery and bandwidth efficiency. Both theoretical analysis and numerical experiments demonstrate the optimization of network performance.

The rapid development of high-speed railway (HSR) system draws great attention and challenges the current broadband Internet access with high mobility. Though LTE-A networks can provide 100 Mbps throughput within a cell for a train speeding up to 350 km/h, the frequent handovers and service disruptions remain to be handled. This problem is particularly prominent for the delivery of a large volume of contents which demands high throughput and continuous connections. Besides the terrestrial cellular system, a satellite can also provide wireless broadband access with less frequent handovers. Recent advances in low earth orbit (LEO) satellite networks also prove to be practical for content delivery with acceptable delay. Therefore, we present a solution based on the integrated terrestrial-satellite network (ITSN) for high throughput and continuous connectivity. Multipath TCP (MPTCP) protocol is adopted to support multi-bearer communications and we apply network coding to further optimize the performance of MPTCP. Considering the mobility patterns of the HSR and satellite, we propose a scheduling and resource allocation mechanism with the prediction of the handovers and channel situation information (CSI). Cache assisted femto cells are implemented to aggregate the traffic demands and proactively cache the requested contents. Numerical results demonstrate that our solution well resists to the dynamic network conditions and improves the network performance and content delivery efficiency.

This article proposes a general and lightweight PHY-layer authentication framework for the Internet of Things (IoT) devices in smart cities, based on tag embedding and tag verification. More specifically, a tag signal carefully designed to be independent of the message signal of a transmitter [i.e., an IoT device (IoTD)] is encrypted and embedded into the signal of the device, and the tag signal is then retrieved at a receiver based on signal detection techniques to verify if it is from the legitimate IoTD or from an illegitimate adversary. With the help of matrix analysis and composite hypothesis testing theories, analytical models are further developed to depict the authentication performance of the proposed authentication framework under various tag signal models. We then provide numerical results to validate these analytical models and to illustrate how authentication performance against the typical impersonation attack varies with system parameters. Finally, we include discussions to demonstrate the effectiveness of the proposed authentication solution in resisting against other various attacks like replay, unauthorized detection, tampering, and man-in-the-middle.

Network attacks have become a growing threat to the current Internet. For the enhancement of network security and accountability, it is urgent to find the origin and identity of the adversary who misbehaves in the network. Some studies focus on embedding users' identities into IPv6 addresses, but such design cannot support the Stateless Address Autoconfiguration (SLAAC) protocol which is widely deployed nowadays. In this paper, we propose SDN-Ti, a general solution to traceback and identification for attackers in IPv6 networks based on Software Defined Network (SDN). In our proposal, the SDN switch performs a translation between the source IPv6 address of the packet and its trusted ID-encoded address generated by the SDN controller. The network administrator can effectively identify the attacker by parsing the malicious packets when the attack incident happens. Our solution not only avoids the heavy storage overhead and time synchronism problems, but also supports multiple IPv6 address assignment scenarios. What's more, SDN-Ti does not require any modification on the end device, hence can be easily deployed. We implement SDN-Ti prototype and evaluate it in a real IPv6 testbed. Experiment results show that our solution only brings very little extra performance cost, and it shows considerable performance in terms of latency, CPU consumption and packet loss compared to the normal forwarding method. The results indicate that SDN-Ti is feasible to be deployed in practice with a large number of users.

Wireless services have been extended from connection-centric to content-centric and this brings rapid increasing data traffic. Considering the concurrent multiple requests for popular contents, multicast is a promising delivery scheme to exploit content reuse. Satellite multicast is superior to others due to the coverage. When terrestrial base stations (BSs) are integrated with the satellite, cooperative transmission is then enabled to handle the fading satellite channels as well as maximize data throughput. Therefore, this paper proposes a co-operative multicast scheme for content delivery in the integrated terrestrial-satellite networks (ITSN) which is further enhanced by network coding. To exploit bandwidth of both terrestrial base stations (BSs) and the satellite, this cooperative multicast scheme uses two-phase transmission. The satellite multicast contents to subscribers in an opportunistic manner with real-time data rate adaptation. Then terrestrial BSs retransmit the lost packets for reliable transmission. Ground users are allocated to subgroups for the channel diversities while network coding is applied to packet loss recovery with fewer retransmissions. Sufficient numerical results demonstrate the enhancement on network throughput brought by the cooperative multicast scheme.

The rapid growth in multimedia applications over cellular networks calls for multicast services. Multicast is an efficient means of delivering contents to multiple users while efficiently utilizing network resources. Layered streaming, e.g., scalable video coding (SVC) provides an excellent solution to handle channel diversities in wireless multicast. This paper presents a cooperative multicast scheme for scalable video content delivery in D2D-enabled heterogeneous cellular networks (HetNets). To extend the multicast service beyond base stations (BSs), D2D links are used to help relay content for cellular multicast. Network coding (NC), implemented through random linear network coding (RLNC) with unequal error protection (UEP) is incorporated in layered contents to enhance reliability and throughput. This paper tries to optimize the multicast scheduling procedures, aiming to assign the optimal modulation and coding schemes (MCSs) for transmissions. The constraints on cache size, backhaul capacity and channel fading are comprehensively considered. Besides, this paper also presents a interference-aware approach for D2D link selection in order to further improve the cooperative multicast. Sufficient numerical results have demonstrated the improvement brought by the proposed scheme significantly on the content delivery efficiency as well as quality of experience (QoE).

The integration of satellite and terrestrial network(ISTN) is an ongoing trend in prospect. Recently many commercial companies such as SpaceX, OneWeb plan to launch tens of thousands satellites which promotes the scale of satellite networks rapidly. While the scale of the satellite network is still small relatively compared with the terrestrial network. IP-routing ability in satellite network is becoming more and more important for ISTN. Suffering from high topology dynamics, long propagation delay, and onboard processing limitations on satellite networks, routing in ISTN faces many challenges worth analyzing in-depth. This paper builds an IP-based routing usability theoretical analytical model with calculable formula, which formulates different types of networks under a unified framework that accommodates various configurations and characteristics of multiple networks. Moreover, massive experiments based on real satellite motion data are designed and conducted to analyze the routing performance and challenges in ISTN deeply, combining various ground stations, satellite processing ability, number of satellites per orbit, etc. At last, with the analysis of routing usability for ISTN, some instructive conclusions are drawn. Although the number of routing nodes in satellite networks is relatively small compared with terrestrial networks, but the influence is big. With the network scale extending, high topology dynamics makes the IP-based routing performance of ISTN decrease dramatically. Routing usable time in one day period decreases from 23.36h to 2.99h when the number of satellites grows from 60 to 960. To keep routing usability, the number of satellites in space is not the more the better in ISTN. The scale of network and the onboard processing ability should do trade off.

The introduction of adaptive coding and modulation (ACM) in DVB-S2 improves system capacity. Transmission mode is adapted to receiving conditions which are fed back through return link supported in DVB-RCS2. A big challenge is that ACM scheme has to follow channel variations which are faster than the delay between channel measurement and feedback reception. Channel state information (CSI) for next transmission often differs profoundly from current estimated result. This causes the mismatch between transmission mode and channel quality. To resolve this problem, this paper deploys a CSI prediction framework and implements machine learning (ML) algorithms for accuracy. Compared with conventional prediction algorithms, ML algorithms have advantage on handling the complicate and changeable time series. In ACM scheme, MODCOD selection is based on channel SNR and MODCOD SNR threshold. Therefore, this prediction work takes channel SNR for next transmission as the prediction target and past SNR plus other correlated information as the prediction basis. To verify prediction accuracy, this paper discusses major factors impacting channel situation in detail and proposes a synthesis channel fading model. Numerical experiment results demonstrate the improvement on system performance while the efficiency and complexity of different commonly-used ML algorithms are also included.

Lack of effective accountability mechanisms brings a series of security problems for Internet today. In Next Generation Internet based on IPv6, the system of identity authentication and IP verification is the key to accounting ability. Source Address Validation Improvement (SAVI) can protect IP source addresses from being faked. But without identity authentication mechanism and certain relationship between IP and accountable identity, the accountability is still unreliable. To solve this problem, most research focus on embedding accountable identity into IP address which need either changing DHCP client or twice DHCP request process due to the separate process of user authentication and address assignment. Different from previous research, this paper first analyzes the problems and requirements of combining Web Portal or 802.1X, two main identity authentication mechanism (AAA), with the accountable address assignment in SAVI frame-work. Then a novel Cooperative mechanism for Accountable IP address assignment (CAIP) is proposed based on 802.1X and SAVI, which takes into account the validation of IP address, the authenticity and accountability of identity at the same time. Finally, we build up prototype system for both Fat AP and Thin AP wireless scenarios and simulate the performance of CAIP through large-scale campus networks' data logs. The experiment result shows that the IP addresses and identities in CAIP are protective and accountable. Compared with other previous research, CAIP is not only transparent to the terminals and networks, but also low impact on network equipment, which makes CAIP easy deployment with high compatibility and low cost.

Nowadays, many solutions have been provided to reduce the bandwidth usage of living streaming in the wired part of the Internet, like CDN, P2P, etc. However, it is often overlooked that the capacity of wireless network is inherently limited due to the restriction of wireless spectrum resources. Wireless multicast is a native way to reduce wireless bandwidth usage for living streaming, but it is difficult to deploy due to several problems, like low link data rate, absence of retransmission and lackof multicast support on the Internet. This paper proposes Wi-Live an adaptive wireless multicast solution based on SDN. With the global perspective of SDN, Wi-Live detects potential wireless multicast scenarios where multiple users who associate with the same AP are watching the same live video simultaneously. Then multicast service is adaptively initialized according to the scenarios by Wi-Live. Users watching the same live video are assigned to the same multicast group. A unicast-to-multicast conversion is deployed to generate multicast live video streams. To overcome the shortcoming of traditional wire less multicast, Wi-Live accomplishes a rate adaption scheme to support high rate wireless multicast and adopts FEC for recovery of lost packets. Then we conduct a measurement study based on the real data collected from the campus IPTV platform and the campus wireless network of Tsinghua University. The results indicate that potential wireless multicast scenarios account for a considerable proportion during live video traffic bursts and that high rate multicast is feasible in the campus wireless network. Next, a theoretical analysis on the performance improvement and the overhead of the proposed mechanism is carried out based on the real data as well.

IP based satellite network will become an important component of Internet in the future. Due to the shared medium, it is more efficient to build transmission by using multicast than unicast. But how to run a reliable multicast in space Internet becomes a great challenge because satellite has limited resource to deal with massive feedback packages to ensure reliable transmission. Compared with ground Internet, the continuously dynamic topology of space Internet is also a big challenge to provide continuous multicast transmission. The terminals with multiple interface is more and more common, and terminals will have satellite access ability in future. How to make more efficient use of the advantages of satellite networks and terrestrial networks will become the focus of future research. In this paper, we extend current content delivery network architecture to support satellite networks at first. Then we propose a mechanism based on integrating multicast in satellite network and unicast using this architecture to take advantage of terrestrial and satellite networks. We use terrestrial network to aggregate the feedback information and retransmit loss packages to ensure reliable transmission in satellite multicast. We also propose a greedy algorithm and a zero-one linear programing model to select satellite when there are more than one satellites can connect with the terminal. We use STK to set up a simulation environment to evaluate our mechanism and algorithm. The result shows that the mechanism achieves efficient to reduce feedback information and the algorithm can balance handoff times and the numbers of selected satellite.

In consideration of future significant number of network satellites orbiting in various heights and trajectories, there is a new trend that network protocols designed for current satellites might give way to protocols that dominate terrestrial networks for better adaption in scale as well as integration of future Internet. QUIC, a novel and experimental transport layer protocol, implemented by Google and designed for a quicker HTTP service has proved itself in the market and QUIC outperformed TCP most in environment with a long latency and high packet loss, which is the main feature in space. However, there is a lack of research that studies QUIC's performance in space networks. This paper focuses on QUIC's performance in space-terrestrial integrated networks compared with TCP and its modification. For this purpose, we design a concise space network with both LEO and GEO satellites involved, covering different kinds of transmission scenarios. Simulation of the network is divided into several parts, decision of different satellites' orbit parameters, real-time visibility data calculated through Satellite Tool Kit(STK), communication modeling in MATLAB and finally network conditions converted. Related data were then input in a real testbed for transport performance comparison among QUIC, TCP(Cubic Reno) and TCP with ECN enabled. The semi-physical experiment demonstrates that QUIC outperforms TCP in all experiment cases through the analysis of page load time (PLT), which shows the potential that network issues in space settled with terrestrial solutions.

In 802.11 based WLAN networks, using MPTCP (Multipath TCP) to transmit over multiple APs simultaneously has the benefits of aggregating the access bandwidth, increasing transmission robustness and balancing the load among APs. However, as WLAN is multirate and shared medium, we perform thorough analysis and verify through simulation that in some 802.11 multirate network environments, the total system fairness and efficiency of transmitting over multiple APs can be lower than simply transmitting over the best AP by using TCP. We find the reasons mainly lie in two aspects: Firstly, when the bottleneck is wireless link, 802.11 CSMA/CA is the main resource allocation mechanism, but 802.11 CSMA/CA does not couple with each other, this results in the reduction of proportional fairness. Secondly, 802.11 CSMA/CA is proved to realize max-min fairness, which will allocate relatively more transmission time to low rate users, and make the total system throughput drop rapidly. We solve this problem by designing a cross layer multipath utility maximization model which combines both MPTCP coupled congestion control (MPTCP-CC) and 802.11 CSMA/CA. Based on the decomposition of our model, we proposed clmCSMA (cross layer multipath CSMA), which is a fully distributed algorithm that operates only on end host and does not require any AP modifications. Finally, the performance improvement is validated through simulation.

Future Space-Based Internet (FSBI) aims to provide global Internet access by interconnecting geosynchronous orbit (GEO), Medium Earth Orbit (MEO), Low Earth Orbit (LEO) satellites, and gateways on the ground. Border Gateway Protocol (BGP) is considered as a feasible routing protocol for interconnecting these independent facilities in FSBI. However, the vast Mobility-Related Topology Changes (MRTCs) in FSBI will put great stress on the BGP stability. We carry out a deep analysis on it and find that the routing updates of BGP will be triggered frequently. Many BGP routing updates will occur even before the accomplishment of previous updates and then the network will be instable for most of the time. To solve this problem, we build a Discrete-Time Topology Changes Aggregation (DT-TCA) scheme to improve BGP stability by making as many MRTCs as possible be triggered at the same time. Using a high-fidelity testbed and a virtualization-based emulator of FSBI, we show that DT-TCA dramatically improves the BGP stability in small-scale and large-scale scenarios.

As the rapid growth of smart phones, dense and large-scale 802.11-based WLANs have become an important infrastructure to the Mobile Internet. Usually, mobile devices perform periodic scan to collect the information of surrounding APs for awareness of wireless environment. However, this kind of frequent scan severely degrades both the performance of network and client. In this paper, we first collect a real-world WLAN dataset which contains handoff information and related client state in two weeks from about 3500 mobile devices. Based on the analysis of this dataset, we observe that such kind of frequent scan for mobility is unnecessary for stationary client to pursue better performance, which will result in a large number of invalid scans and even the ping-pong. To address this issue, we propose an efficient WiFi scanning scheme called iScan, which triggers scan based on client and network behavior learning. The network behavior is represented by the change of network load, while the client behavior is detected by an accelerometer. In iScan scheme, when the client is moving, scans will be triggered if the RSSI is below the specific thresholds for different speeds. When the client keeps stationary, iScan adjusts the scanning intervals adaptively based on the law of network load change. We conduct experiments by both case study and simulation in campus WLAN. The case study shows that iScan can trigger scan more accurately without missing necessary handoffs when the client is moving. And the simulation shows that iScan reduces 95.8% of invalid scans while ensuring the stationary client discoveries the change of network load timely.

As the rapid growth of Wireless Local Area Network (WLAN), the densities of both Access Points (APs) and clients have dramatically increased. In the dense and crowded WLANs, the challenges of load balance become non-negligible due to the problems raised by traditional AP selection mechanism based on signal strength. To address this issue, many existing works consider the load metrics and conduct dynamic topology adjustment for the AP selection. In these literatures, a specific server and trick communications between client and network are always introduced, but they are not general. In this paper, we propose a novel load balancing mechanism, which is implemented on a client-network collaborative architecture based on Software Defined Network (SDN) and 802.11u. In our architecture, we implement several SDN applications to collect and maintain the information of load and topology, and design Network Resource Query Protocol (NRQP) to exchange the metrics of AP selection between client and network based on 802.11u. With the help of this architecture, we propose a novel load aware algorithm which can take the comprehensive consideration of the link state, client traffic and AP load. It can not only work when first association or moving handoff, but also conduct topology adjustment at proper time. We evaluate our mechanism on a real SDN prototype testbed and the results show the competitive performance.

As 802.11 network has become an important infrastructure for the Mobile Internet, the performance of WLAN handoff is critical to the quality of user's experience. Although it has shown that there are a large number of invalid handoffs in large-scale 802.11 networks with dense AP, the reason and seriousness still remain unclear. In this paper, we propose HandoffAnalyser, a client-network collaborative framework, to deeply measure and analyze the handoffs. Then, we give a clear explanation of invalid handoffs by defining two patterns termed Loose Ping-Pong (LPP) and Strict Ping-Pong (SPP) based on association history. The experimental results of real campus WLAN with about 2,700 APs and 220,000 mobile devices show that 22.1% and 31.3% of handoffs are SPP and LPP respectively. We even observe that several clients experience more than 280 LPP and 220 SPP per day respectively. Such a large number of ping-pong will seriously affect the performance of both client and network. We carry out in-depth analysis and find that ping-pong has relationship to some wireless metrics such as channel utilization, network configuration such as AP with Multi-SSID, and hardware defect such as poor 5 GHz chip. These findings and conclusions can help us to better optimize the WLAN.

With the rapid growth of Mobile Internet, supporting different Qos for a variety of mobile applications becomes a great challenge in wireless network more and more. SDN providing huge flexibility on IP stream management in wired networks motivates considerable works on extending SDN to wireless network, but most of them are mainly focused on wireless resource abstraction and management. Different from wired networks, there are lots of complex parameters of wireless resource, which influences the performance of not only one IP stream but also the whole mobile terminal. How to make SDN supporting IP-stream Oriented Management in wireless environment is still far from research. This paper proposes a mechanism of decoupling wireless resource allocation from mobile terminal by mapping different IP flows to different virtual wireless cards, which makes it possible to support integrated management in wired and wireless network. By extending SDN framework to support virtual network interface, the traditional controller has a global view of network and calculates the IP stream policy for the mobile terminal with multiple virtual network interface. Local agent and flow manager are extended on mobile terminal to maintain the state of virtual interfaces and allocate the data-flows to different virtual interfaces. A real SDN testbed is built to evaluate the performance of our mechanism, and the result shows the mechanism achieves efficient IP flow- level management in both wired and wireless network.

Today's Internet mobility management is facing great challenges to satisfy the requirement of scalability and flexibility, such as heavy signaling overhead, data traffic centralization, etc. In this paper, some mobility management design principles concerning the trend of large-scale and high-density wireless network are given. A mobility management scheme is proposed according to these principles by taking advantage of the separated control plane and flexible programmability in software defined network. In this scheme the switches lying in the core of the network are stateless. Flow rules in the core switches are not correlated with the mobile hosts in the network, which simplifies the flow rules in the core switches sharply. The implementation on a real SDN testbed shows that this scheme gets less cost and more efficient than other solutions based on SDN.

DHCP is one of most intensively used and researched Internet Protocol since its standardization, whose dynamic use of IP address matched perfectly the requirement of PC dominant times for the past years. However, the explosive growth of mobile terminal and application makes mobile becoming dominated in recent years. The use case and manner between PC and mobile devices is quite difference, does dynamic of DHCP still work for today's mobile Internet? Work on this problem with large-scale real mobile wireless network is scarce. Based on 4-month real data collected from Tsinghua University campus wireless network, which including 2,500+ Wifi access points and 15,000+ concurrent users, this paper found that there is a close relationship between DHCP performance and users' online patterns, the immutable lease time would lead to quite low efficiency of IP distribution. Moreover, according to our analysis on factors such as terminal type, location type and network access time, users' online patterns can be divided into different categories. Therefore, we could distribute different lease time to the different online patterns for optimization. The simulation results show that our mechanism could save 39% IPv4 addresses (43C) and improve the IP usage efficiency from 19.8% to 69.7% without increasing much DHCP payload.

Using unlicensed spectrums is a key factor in popularity of WLANs. Meanwhile, the interference is becoming severer in coming time because of network expansion. Assigning channels for AP in distributed way only reduce interference around single AP rather than reducing system interference. However systematic optimizations usually require real-time information which increase complexity for applying. This paper identifies a idea for optimizing system interference from the view of several sub-areas. Actually, interferences spread regionally depending on signal propagation. Conflict-areas are divided according to the interfering range. We define an index to present interference in conflict-areas and the goal is to minimize maximum index of the areas. It means that interferences of the whole network are comparatively low and distributed evenly. Both the theoretical evaluation and experiments in real network show that the conflict-area method is reasonable. Average interferences in most conflict-areas under experiments are reduced (about 50%) or remain unchanged (about 40%).

By using the prevalent smart phone embedded with different kinds of sensors, we build a practical indoor localization system which takes low labor-cost and is large-scaly applied. In this paper we discuss the challenges in building such a system and how we handle them. Our indoor localization system is based on the radio frequency (RF) heard from the surrounding Access Points (APs). The Received Signal Strength Indicators (RSSIs) heard by APs from each other are used to build the propagation models of different environments. We propose a novel method to use the sensors embedded in smart phone to amend the locating result of a RF-based system, and successfully decrease the discrepancy of original result. The accuracy of our system reaches 70% within 2m and 95% within 3m, which can meet the needs of most indoor applications.

Recently, cooperative retransmissions have exhibited great potentials in enhancing the reliability and efficiency of wireless communications by exploring spatial diversity. With cooperative retransmissions, a cooperative node helps retransmit an overheard frame if the frame from a sender fails to reach the destination. Several cooperative retransmission schemes have been proposed for wireless local area networks (WLANs) in the literature. However, most of them require explicit coordination between the sender and the cooperative node before each retransmission, which results in a non-negligible overhead. Moreover, these schemes are not designed for the latest IEEE 802.11n standard, and are incompatible with the frame aggregation and block ACK mechanisms of 802.11n. In this paper, we propose an efficient cooperative retransmission MAC (CAR-MAC) protocol that utilizes new features of 802.11n and is compatible with standard 802.11n transmissions. In CAR-MAC, all nodes periodically broadcast a C-Beacon message to release their retransmitting capability, and each node selects a cooperative node based on received CBeacon messages. If some sub-frames in the aggregated frame from the sender fail to reach the destination, the cooperative node retransmits the failed sub-frames together with its own new sub frames, such that overhead from cooperative retransmissions is amortized by normal frame transmissions. We have theoretically analyzed the improvement on network throughput brought by CAR-MAC protocol. In addition, we have conducted extensive simulations to evaluate CAR-MAC protocol under various channel conditions. Both theoretical and simulation results show that the proposed protocol can greatly improve network throughput and reduce packet delay, compared with the 802.11n standard and existing cooperative retransmission schemes.

In wireless local area networks (WLANs), link-layer multicast is a promising technology for many multimedia applications, e.g., video conference, as multicast frames can reach multiple clients simultaneously. However, the efficiency of multicast in WLANs is unsatisfactory since multicast frames are transmitted at low data rates to reach clients with poor channel quality. Moreover, the reliability of multicast cannot be guaranteed either, as multicast transmissions are not acknowledged. Some recent works have utilized smart antennas to improve multicast performance. But most of them require customized hardware and are not designed for the latest IEEE 802.11 standard, 802.11n WLANs. In this paper, we consider link-layer multicast in 802.11n WLANs with smart antennas. We partition clients into several groups, then select an antenna pattern from smart antennas and a multicast rate for each group, and transmit the same frame to each group. We first examine the gain of smart antennas and reliability of various 802.11n data rates for multicast in indoor WLANs via experiments. We then present the system model for multicast over smart antennas and formulate the problem into a mixed integer program. After that, we propose an optimal algorithm for the mixed integer program, under the condition that the packet reception ratio (PRR) of all antenna patterns and data rates is known for every client. As clients join and leave the network frequently and the wireless channel is time varying, we also propose an on-line algorithm that is able to adapt the partition of clients, antenna pattern and multicast rate for each group dynamically, based on PRR reports from clients. We have implemented the on-line algorithm on off-the-shelf WLAN products and conducted extensive experiments to evaluate the performance. The results show that the proposed algorithm can significantly improve multicast throughput compared to other strategies, and at the same time guarantee high PRR for all clients.

Multiple MIMO (Multiple Input Multiple Output) modes are the salient characteristics of 802.11n wireless networks. An efficient MIMO mode switching scheme is highly desirable for rate adaptation, which can optimize combination of MIMO mode and MCS (Modulation Coding Scheme) to achieve the maximum system throughput. In this paper, we have proposed and verified three design guidelines for the MIMO mode switching through real experiments. Based on these guidelines, we then present a simple and efficient MImo mode Switching Scheme, called MISS, and implement it into the Atheros-based device driver. MISS uses a crossover step-based searching algorithm to find the appropriate MIMO mode for rate adaptation. The efficiency of MISS has been evaluated through real experiments conducted in the indoor environments.

In wireless local area networks (WLANs), collision-free channel access is desirable for real-time services that require guaranteed bandwidth and bounded delay. In WLANs with a single access point (AP), collision-free access can be achieved by applying the point coordination function (PCF), where the AP polls all associated clients for data transmissions. However, in larger WLANs with multiple APs, if there is no inter-AP coordination mechanism, concurrent transmissions from nearby basic service sets (BSSs) may collide and thus degrade service performance even if all APs operate on the PCF mode. So far only few schemes have been proposed to resolve this problem, and the client throughput in these schemes is quite limited due to the inaccurate modeling of polling conflicts. In this paper, we study client polling in multi-AP WLANs, with the objective of providing high-throughput, collision-free channel access for each client, and maximizing network capacity. We first give a WLAN framework in which the PCF of all APs is coordinated and clients are polled in a time slotted manner.We then formulate client polling into a time slot allocation problem and propose a collision-free polling scheme consisting of three procedures: (1) a basic polling procedure that determines the minimum number of time slots required to poll every client once to obtain the polling frequencies of all clients; (2) a complementary polling procedure that makes extra polls for APs that have idle time slots without causing collisions, to improve spatial reuse of the network; (3) a backup poll selecting procedure that finds backup clients to poll in case the current polled client has no data to transmit, to utilize the otherwise wasted bandwidth. We have conducted extensive simulations and compared it with two existing schemes. The simulation results show that the proposed scheme can provide high throughput and uniform channel access time for all clients, while boosting spatial reuse 2 to 3 times compared to other schemes.

Base stations (BSes) in the 3G cellular network are not energy proportional with respect to their carried traffic load. Our mea- surements show that 3G traffic exhibits high fluctuations both in time and over space, thus incurring energy waste. In this paper, we propose a profile-based approach to green cellular infrastruc- ture. We profile BS traffic and approximate network-wide energy proportionality using non-load-adaptive BSes. The instrument is to leverage temporal-spatial traffic diversity and node deployment heterogeneity, and power off under-utilized BSes under light traf- fic. Our evaluation on four regional 3G networks shows that this simple scheme yields up to 53% energy savings in a dense large city and 23% in a sparse, mid-sized city.

Throughput of Concurrent Multipath Transfer varies with different path selection schemes. As the number of path increases, the path selection solution space increases exponentially while receiving buffer efficiency decreases. To solve this problem, we model the throughput of Concurrent Multipath Transfer and find that it may be limited by the receiving buffer size and the round trip time of the slowest path. By analyzing the throughput modeling, this paper proposes a range-based path selection method, which is also validated by the simulation result.

The number of competing stations has great influence on the performance of IEEE 802.11 MAC protocol based on the distributed coordination function (DCF), which utilizes Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). Some researchers try to use performance modeling to analyze and optimize the protocol, but the strict assumptions of the modeling often lead to research results that could not be adaptive to the dynamic change of competing station number, which is extremely prevalent in today's IEEE 802.11 networks. Some other researchers try to use filters, based on accurate measurement, to estimate the number of competing stations, and improve system performance by dynamically tuning the protocol parameters. However, such mechanisms are too complex to apply in real environment. Base on our discovery, we propose a simple adaptive optimization mechanism, DOOR (Dynamic Optimization on Range), for the IEEE 802.11 DCF, which is based on the subrange of competing station number. The reason, principle and method for partitioning subranges are introduced. Moreover, the detailed system model and performance evaluation for the new mechanism are given. The elaborate numerical results show that this mechanism could achieve much higher throughput and shorter delay than the standard IEEE 802.11 DCF in almost all the different competing stations numbers.

The dynamic character of complex and variable network environment, the key problem, puzzles the corresponding protocols design for wireless LANs. However, the distributed coordination function (DCF) of IEEE 802.11 MAC protocol, which is carrier sense multiple access with collision avoidance (CSMA/CA) using constant parameters, could not perform well when network environment changes. Thus many researchers try to optimize IEEE 802.11 DCF. However early dynamic optimization mechanisms for the protocol mostly depend on measuring the number of "competing" stations accurately. The problem of them is that the algorithms are too complex to apply in reality. In our research, we find that system performance approaches optimization with the same protocol parameters, when the number of competing stations changes within a certain range dynamically. Therefore, we propose a self-adaptive optimization mechanism, DOOR (dynamic optimization on range), for the IEEE 802.11 DCF. DOOR uses filter to estimate the range of competing station number and adjusts the protocol parameters to optimize system performance effectively. The detailed analytical model and performance evaluation for the new mechanism are given. Moreover, the measurement method and parameters of filter are introduced. At last, the elaborate numerical results show that our mechanism could not only achieve much higher throughput and lower delay than the standard IEEE 802.11 DCF along with the change of competing stations, but also improve the stability of system performance based on reasonably partitioned ranges.