Industrial Internet of Things (IIoT) devices often rely on public communication channels for authentication, which makes them particularly susceptible to a variety of security threats. Physically Unclonable Function (PUF) provides a lightweight cryptographic method to address authentication challenges in resource-constrained devices. However, some PUF-based authentication frameworks store challenge-response pairs (CRPs) centrally on a server, posing risks of single point failure and performance bottlenecks in the authentication process. Although blockchain (BC) can mitigate this through decentralized storage, they still suffer from high computational overhead, large CRPs storage requirements, limited authentication efficiency, and ledger synchronization latency challenges. Therefore, we propose a novel direct mutual authentication framework for IIoT devices and peer nodes in consortium BCs, called PUF-D2PB. It enables peer nodes and IIoT devices to authenticate each other without involving BC-clients, and simultaneously supports CRP updates without requiring extra operations. In addition, we introduce a competition-based mechanism and a distributed encryption method to enhance CRP synchronization and prevent CRP leakage. Security analysis and a prototype implementation using a real PUF circuit demonstrate that our framework provides strong security guarantees and efficient authentication. Compared with existing BC-assisted PUF schemes, PUF-D2PB effectively reduces authentication latency and resource overhead while preventing CRP leakage.

In this paper, we explore the fine-grained channel state information (CSI) obtained through the sensing function in an reconfigurable intelligent surface (RIS)-assisted integrated sensing and communication (ISAC) system to support the efficient covert communications in the system. We first construct a new fine-grained CSI model for the RIS-assisted ISAC system and propose a novel covert communication scheme based on the new CSI model. We then develop theoretical models for the detection error probability, Cramér-Rao Bound and covert rate to depict the covertness, sensing and covert communication performances under the proposed scheme. Based on these theoretical models, we further formulate an optimization problem for covert rate maximization through optimizing the reflection coefficient in RIS and the transmit powers for covert/probing signals. With the help of the homogenization for quadratic constrained quadratic programming, semi-definite relaxation and Dinkelbach transform, an efficient alternating optimization (AO) algorithm is devised to tackle this complex optimization problem. Finally, extensive numerical results are presented to demonstrate the performance enhancement for covert communication in the RIS-assisted ISAC system from exploring the fine-grained CSI and AO-based parameter optimization therein.

This paper addresses the spoofing detection issue for the Global Positioning System (GPS) based on radio frequency fingerprinting (RFF). We first introduce a new RFF feature in the post-despreading domain of GPS signal processing to better capture the hardware characteristics of GPS satellites. We model the new RFF feature as grayscale constellation images (GCIs) and provide in-depth analysis to show the hardware characteristics that can be captured by GCIs. Using this feature, we develop a deep-learning based spoofing detection framework named GCI-GANomaly, which applies a generative adversarial network (GAN) with a cosine latent anomaly scoring strategy for robust detection. We evaluate the detection accuracy and false positive rate (FPR) of the proposed method based on the open-source Texas Spoofing Test Battery (TEXBAT) dataset. The results showed that GCI-GANomaly improves the detection accuracy of traditional signal quality monitoring (SQM)-based methods by up to 30.8% and reduces the average FPR of existing RFF-based methods by 4.2% with much less training data while achieving slightly better average detection accuracy. We further evaluate the robustness (against spoofing power and time) of GCI-GANomaly based on a specific GPS signal dataset that we collected from the real-world constellation. The results showed that GCI-GANomaly achieves robust detection performance under varying spoofing power and shows acceptable stability as time elapses.

Space-Terrestrial Integrated Networks (STINs) serve as the crucial infrastructure for future 6G Networks, while network failures in STINs pose serious threats to the services provided by such networks. This paper focuses on the service request recovery in STINs against a satellite failure. For the uplink requests, downlink requests, and relay requests disrupted by a satellite failure, we explore both independent recovery and joint recovery. In independent recovery where each type of requests is recovered independently and sequentially, an Integer Linear Programming (ILP) model and related heuristic are proposed to identify the optimal recovery solution for each type of requests. We further explore the joint recovery where all requests are recovered jointly and simultaneously to achieve a high recovery efficiency. The ILP formulation and time-efficient heuristic are developed as well for the joint recovery. Finally, extensive numerical results are provided to demonstrate the effectiveness of the joint recovery and proposed heuristics in service recovery under a satellite failure.

Beam alignment (BA) is a crucial process in millimeter-wave (mmWave) communications for precise directional transmission and efficient link establishment, but its open nature makes it vulnerable to eavesdropping and identity impersonation attacks. To this end, we propose a novel security framework named CovertAuth, designed to provide a unified defense against both threats. For eavesdropping attacks, we advance the existing covert communication design by extending its joint optimization of the beam training budget and transmission power to a more practical BA scenario that incorporates the mutual coupling (MC) effect in antenna array impairments and imperfect eavesdropper channel state information. For impersonation attacks, the MC effect is explored as a device feature to design a novel adaptive weight-based physical layer authentication mechanism. Theoretical models for authentication metrics like detection and false alarm probabilities are first provided to conduct performance analysis. Based on these models, an optimization problem is constructed to determine the optimal weight value that maximizes authentication accuracy. With these optimal weights, a weighted-sum energy detector is employed to achieve identity validation. The resulting adaptive authentication scheme is then integrated with the covert communication to enhance the security of the BA phase. Finally, simulation results demonstrate that CovertAuth achieves high detection accuracy while satisfying the covertness requirement, offering a comprehensive security solution for the mmWave BA stage.

In this paper, we propose BiTDB, a built-in Trusted Execution Environment (TEE) database for embedded systems, to realize higher system availability while ensuring data confidentiality. With BiTDB, dilemmas that the state-of-the-art research work on secure embedded databases has to face can be significantly reduced and eliminated, including (i) complicated research and realization on searchable encryption algorithms (SEA), (ii) limited support to all database operations, and (iii) almost none of specific design and optimizations toward built-in TEE embedded databases. Through BiTDB, all database operations can process plaintext in TEE instead of retrieving ciphertext by developing complicated SEAs. To enable BiTDB to handle database files in Rich Execution Environment (REE) as local ones, we extend the TEE OS with generic file I/O libraries. Then, we contribute three critical optimizations to significantly reduce redundant memory and file operations between TEE and REE, and BiTDB achieve better system performance and availability in embedded systems. Finally, we have implemented the prototype system based on OP-TEE and SQLite for several typical platforms, including virtualization and hardware environments. The TPC-H test shows BiTDB can achieve 85% (on average) of the original database performance while guaranteeing data confidentiality and integrity.

Wireless systems are of paramount importance in enabling ubiquitous data transmission for various Internet of Things (IoT) applications. However, due to the broadcast nature and openness of wireless channels, such systems face inherent security challenges. Covert communication is an enabling technology for secure wireless communications while the Unmanned Aerial Vehicle (UAV)-assisted covert communication is particularly promising for enhancing covert performance. This paper investigates joint covert and secure communications in a two-hop UAV-assisted wireless system, where a source S transmits a covert message to a destination D with the help of an untrusted UAV, while being subject to detection by a warden W. We first design a covert transmission scheme for the proposed system with the considerations of both covert and secure constraints. We then develop theoretical models for the warden1detection error probability and the covert-and-secure rate (CSR) from S to D. Based on these models, we further explore the optimal power control for CSR maximization under both covertness and security constraints. Finally, numerical results are presented to validate the theoretical models and demonstrate the performance of covert and secure communications in the UAV-assisted system.

This article investigates the covert communication in a D2D underlaying cellular network consisting of a cellular transmitter, a base station, a cellular receiver, multiple colluding wardens, and an underlaid D2D pair with a transmitter and a receiver. For multiple colluding wardens, they fuse their observations to a fusion center (FC) with the maximum ratio combining (MRC) scheme and the equal gain combining (EGC) scheme. To protect the covert communication between the cellular transmitter and the base station from being detected by multiple colluding wardens, the underlaid D2D transmitter reuses the spectrum of the cellular user to transmit its signal to the D2D receiver with a random power to deliberately confuse multiple colluding wardens. We first provide the basic theoretical results for the detection performance of FC under MRC and EGC, respectively, i.e., the optimal detection threshold, the minimum detection error probability and its average value. We then explore the modeling of the average covert rate as well as the optimal power control for average covert rate maximization to enhance the covert performance under MRC and EGC. Finally, extensive numerical and simulation results are presented to validate theoretical analysis and also to illustrate the effects of some important system parameters on the average minimum detection error probability, the average covert rate, and the maximum average covert rate under MRC and EGC, respectively. We can find that the detection performance of multiple colluding wardens under the MRC scheme is better than that under the EGC scheme.

The entropy source is the most critical component of a true random number generator (TRNG), which determines the quality of the random numbers. Current TRNGs mainly utilize a specific source of physical randomness as the entropy source, but it is difficult for this method to achieve a balance between low resource overhead and high throughput. This paper explores the self-feedback multiplexer (SFMUX) structure to obtain a novel dynamic hybrid entropy source for TRNGs. Unlike other MUX-based entropy source circuits, our SFMUX cross-connects the outputs of four independent high-frequency ring oscillators (ROs) as the input signals of four MUXs, and the output of each MUX is self-fed back to serve as a selection signal. Thus, the SFMUX can not only output jitter, but also update the selection signal rapidly and randomly, which increases the probability that the SFMUX outputs unstable signals. When using a D-flip-flop (DFF) to sample this signal, the DFF may become metastable. Modeling the entropy source shows that connecting 1-stage ROs and 2-stage ROs to each SFMUX can achieve higher minimum entropy than using ROs with other numbers of stages. The proposed TRNG design is implemented on Xilinx Virtex-6, Artix-7 and Kintex-7 FPGAs. The experimental results demonstrate that our TRNG achieves a maximum throughput of 550 Mbps while using only 6 slices, and it passes the NIST, AIS-31 and Dieharder tests without postprocessing.

This paper investigates the joint relay and transmission mode selection for covert communication in a wireless relay system with amplify-and-forward (AF) forwarding mode, which consists of one source, multiple AF relays, one destination, one friendly jammer and one warden, and each relay can switch between the half-duplex (HD) and full-duplex (FD) transmission modes. We first explore the fundamental covert performance of the system when it works in either the fixed HD or fixed FD mode. Based on this result, we then investigate the covert performance of the system with optimal (resp. random) relay selection and random (resp. optimal) mode selection, so as to reveal the achievable covert performance in the system with solely the relay selection or mode selection. Building upon above results, we further design the optimal joint relay and mode selection scheme, and develop related theoretical models for performance analysis. Finally, we provide extensive numerical results to conduct a comprehensive comparison between the relay selection and mode selection on their achievable covert performance and to illustrate the performance enhancement from adopting the joint relay and mode selection in the relay system.

Authentication is a crucial method for ensuring the security of the unmanned aerial vehicle (UAV)-assisted communication systems; however, it also raises concerns about the leakage of private data. To address this problem, this paper focuses on the problem of identity authentication with privacy-preserving consideration. We propose a two-way privacy-preserving physical layer (PHY-Layer) authentication framework in a UAV-assisted multiple-input multiple-output (MIMO) communication system, by exploiting the carrier frequency offset (CFO) characterizing UAV identity and CFO-based session keys constructed by elliptic curve cryptography (ECC) to encrypt data frames. In particular, we first employ a MOOSE algorithm to extract the hardware fingerprint feature related to UAV, and based on the extracted CFO feature parameters, we devise an ECC-based algorithm for a session key negotiation. To achieve identity validation for the network parties, we establish a two-way authentication framework based on the resulting CFO feature parameters, and apply the CFO-based session key to encrypt data frames for avoiding the leakage of private data. Moreover, we derive the closed-form analytical expressions for the probabilities of the detection and false alarm for the rigorous performance analysis. Finally, we provide extensive numerical results to validate the proposed theoretical model and demonstrate its effectiveness in both identity authentication and privacy preservation. In comparison with the prior scheme, the proposed framework has a better robustness and privacy.

The super-directive arrays in millimeter wave (mmWave) multiple-input multiple-output (MIMO) systems possess some intrinsic beam pattern features like amplitude and phase errors of element excitations. We first show experiment results to illustrate the uniqueness and stability properties of the amplitude and phase error features, and apply the Rician probability density function to efficiently approximate the distributions of these features under hardware impairments. By utilizing such beam pattern features and the hypothesis testing theory, we then develop a new physical layer authentication protocol for transmitter authentication in the mmWave MIMO communication systems. Based on the theories of statistical signal processing and composite hypothesis testing, a related theoretical framework is also developed for the analytical performance modeling of the new authentication protocol under both fixed and random beam pattern scenarios. Finally, we provide simulation and theoretical results to evaluate the reliability and security of the new authentication protocol against the identity-based spoofing attack.

The fifth-generation mobile communication technology (5G) supports wireless data transmission across civil, commercial, industrial, and even military networks, where vast amounts of privacy data are constantly transmitted. However, the open nature of the air interface in 5G systems makes them vulnerable to various attacks. Physical-layer key generation (PKG) has been recognized as a highly promising technology for ensuring data security in 5G systems, while existing PKG schemes achieve low key entropy (i.e., low key randomness) due to poor channel probing and quantization. In this paper, we propose a PKG scheme with high key entropy, tailored to the unique characteristics of 5G systems. First, we design a channel probing method based on the demodulation reference signal in accordance with 5G standards, enhancing the similarity between channel measurements. Next, we introduce a quantization method based on local increment and monotonicity, which effectively leverages channel characteristics to achieve high-speed key generation and improve key entropy. Finally, we use both MATLAB simulation and real-world channel measurements to achieve comprehensive verification of the proposed scheme. The simulation results showed that the proposed scheme increases the key entropy by at least 25% with nearly the same key generation rate compared with existing PKG schemes for 5G systems. The experiment using real-world channel measurements also confirmed that the proposed scheme has higher key entropy.

This paper focuses on developing a reliable physical layer authentication (PLA) scheme in an millimeter wave (mmWave) communication system. To this end, we first derive the statistical quantities of the radiation pattern with random array errors in terms of gain, phase and position, and demonstrate that both Beckmann distribution and Rice distribution can effectively characterize the distorted radiation pattern. We then design a highly reliable PLA scheme, which combines three array error features to increase the distinguishability of the radiation pattern fused these array errors, as well as creates constructive two-beam pattern transmission that can not only resist to occasional blockages of few constituent beams but also enhance the reliability of the PLA. Applying the principles of statistical signal processing and composite hypothesis testing, a theoretical framework modeling of the typical performance metrics is also established to assess the performance of the proposed novel authentication scheme, under Rice distribution approximation model for radiation pattern statistics. Finally, performance evaluation is verified the reliability, effectiveness of the proposed authentication scheme with various settings in the presence of the identity-based impersonate attack, and performance comparison is also provided to highlight performance gain using the three array errors and two-beam pattern transmission.

Warden collusion represents a hazardous threat to wireless covert communication, where wardens can combine their observations to perform a more aggressive detection attack. This paper investigates the impact of warden collusion on covert communication in a multi-antenna wireless network consisting of one source, one destination, multiple wardens and interferers. By employing the techniques of Laplace Transform and Cauchy Integral Theorem, we first establish a framework to model the aggregate interference distribution (AID) for covert communication in the network under the typical additive white Gaussian noise (AWGN) and Rayleigh fading channels. Based on the AID results, we then develop theoretical models to reveal the inherent relationship between the collusion intensity and fundamental communication metrics in terms of the covert outage probability, connection outage probability and covert throughput. With the help of these models, we further explore the covert throughput optimization problems and present extensive numerical results to illustrate the impact of warden collusion on the covert throughput under both channel models.

This paper explores the joint covert and secure communications in a device-to-device (D2D)-enabled cellular system (DCS) consisting of a base station BS, an eavesdropper Eve, and two user equipments UE and UR. To conduct secure communications with UE against Eve, BS works either under the cellular mode using direct transmission or under the D2D mode replying through UR, while UR is greedy since it opportunistically transmits its own covert message to UE against the detection from BS. To understand the fundamental performance of secrecy rate and covert rate in DCS, we first develop theoretical models to depict the detection probability/secrecy rate of BS and covert rate of UR under different modes (i.e., underlay, overlay, or cellular). Based on these models, we further explore the secrecy rate maximization (SRM) for BS subject to the constraints of detection probability at BS and transmit power at both BS and UR, as well as the covert rate maximization (CRM) for UR subject to the constraints of covertness requirement and covert transmit power. Finally, we employ the Newton-based searching method to solve the SRM/CRM problems and illustrate via numerical results the achievable secrecy rate and covert rate of BS and UR under various DCS scenarios.

In this paper, we explore covert communications in a device-to-device (D2D) network consisting of an intelligent reflecting surface (IRS), a base station, a cellular user, a D2D pair, and an adversary warden. With the help of the IRS, the D2D pair attempts to perform covert communication, while the warden also tries to detect the very existence of such a transmission. To investigate the covert performance under the scenario, we derive the detection error probability at Warden, the optimal detection threshold for minimizing the probability, and the transmission outage probabilities for D2D and cellular communications, respectively. We further jointly optimize the transmission powers of the cellular user and the D2D transmitter, the reflection phase shifts, and the amplitudes of the IRS reflecting elements to improve covert communication performance. Finally, we provide numerical results to reveal the impact of system parameters on the covert performance and also to exhibit the merits of IRS-enabled D2D networks for achieving covert communications.

Authentication in millimeter-Wave (mmWave) Multiple-Input Multiple-Output (MIMO) systems is a critical issue due to the unique characteristics of mmWave communication, such as highly directional beamforming and the ability to support massive device connectivity. To address this challenge, this paper proposes a novel low-complexity decision-level-based Distributed Physical Layer Authentication (DPLA) framework to combat identity-based impersonation attacks in mmWave MIMO systems. The DPLA framework leverages Beam Pattern (BP) deviation, which arises from hardware-specific gain errors, as a key authentication feature. A fusion center is introduced to make the final authentication decision by aggregating local decisions from multiple collaborative nodes, enabling multi-directional perception. Specifically, a low-complexity hybrid combining fusion rule is carefully designed to accommodate the fully connected structure of mmWave MIMO systems, balancing computational efficiency and authentication performance. A rigorous performance analysis is conducted by deriving closed-form analytical expressions for the probabilities of correct detection and false alarm. Furthermore, the asymptotic detection and discrimination performance are systematically analyzed in the large-scale antenna regime. To further enhance authentication accuracy, digital signaling matrices are designed using the deflection coefficient maximization principle. The feasibility of the proposed framework is validated through a comprehensive evaluation, demonstrating its superior robustness and efficiency compared to benchmark methods.

Commercial SRAM-based field-programmable gate arrays (FPGAs) are extremely susceptible to failures caused by external ionizing radiation or prolonged internal overloading in harsh applications, such as single event effects (SEEs) and aging failure. Existing methods utilize the triple modular redundancy (TMR) architecture to shield against the effects of radiation on FPGA systems. However, these solutions are resource-costly and practically unnecessary. Additionally, hard faults caused by the aging effects of long-term usage of FPGA systems is not effectively alleviated. To address these issues, we present a comprehensive framework for ensuring adaptive fault tolerance and aging mitigation in FPGAs, i.e., Ada-FA. Ada-FA is a cross-layer-aware reliability framework that includes two phases: 1) offline and 2) online. (1) In the offline phase, a task criticality evaluation strategy supporting fine-grained fault tolerance is proposed to reduce the hardware resource overhead. Specifically, we improve the integer linear programming (ILP) formula, which considers both fault tolerance and aging mitigation, to obtain the optimal reliability-aware layout, thus maximizing the mean time to failure (MTTF). (2) In the online phase, we propose a runtime management architecture to further ensure the reliable operation of FPGA systems. The experimental results show that the resource usage (RU) of the proposed Ada-FA framework is reduced by 15.8% on average compared to that of existing fault-tolerant layout/scheduling methods. Moreover, our method provides a higher reliability and task accomplishment rate (TAR) than the state-of-the-art offline aging mitigation methods.

This article investigates sum-rate maximization while achieving seamless coverage with the minimum number of unmanned aerial vehicles (UAVs) in a device-to-device (D2D)-enabled UAV network. Toward this end, we formulate it as a nonlinear and nonconvex optimization problem, and then propose a max-rate-min-number (MRMN) scheme to solve this optimization problem. First, we derive UAV’s coverage radius which can depict the maximum coverage for user equipments, and then implement the optimal deployment for UAV swarm by exploiting the disk covering theory. Furthermore, we apply the coalitional game theory to design the cooperative strategy between UAV swarm and ground equipments. Finally, a coalition formation algorithm is presented for achieving maximum system sum-rate while reducing the number of UAVs under seamless coverage constraint. Extensive simulation results are provided to validate the effectiveness of our proposed MRMN scheme, and also illustrate that the scheme can improve the system sum-rate and reduce the number of deployed UAVs. Meanwhile, we further conduct a performance comparison between our scheme and the existing benchmark schemes.

This paper explores a new secure wireless communication scenario for the data collection in the Internet of Things (IoT) where the physical layer security technology is applied to counteract both the detection and eavesdropping attacks, such that the critical covertness and secrecy properties of the communication are jointly guaranteed. We first provide theoretical modeling for covertness outage probability (COP), secrecy outage probability (SOP) and transmission probability (TP) to depict the covertness, secrecy and transmission performances of the wireless communication system. To understand the fundamental security performance under the wireless communication system, we then define a new metric -covert secrecy rate (CSR), which characterizes the maximum transmission rate subject to the constraints of COP, SOP and TP. We further conduct detailed theoretical analysis to identify the CSR under various scenarios determined by the detector-eavesdropper relationships and the secure transmission schemes adopted by transmitters. Finally, numerical results are provided to illustrate the achievable performances under the secure wireless communication system.

This paper investigates the covert communications via cooperative jamming and relay selection in a wireless relay system, where a source intends to transmit a message to its destination with the help of a selected relay, and a warden attempts to detect the existence of wireless transmissions from both the source and relay, while friendly jammers send jamming signals to prevent warden from detecting the transmission process. To this end, we first propose two relay selection schemes, namely random relay selection (RRS) and max-min relay selection (MMRS), as well as their corresponding cooperative jamming (CJ) schemes for ensuring covertness in the system. We then provide theoretical modeling for the covert rate performance under each relay selection scheme and its CJ scheme and further explore the optimal transmit power controls of both the source and relay for covert rate maximization. Finally, extensive simulation/numerical results are presented to validate our theoretical models and also to illustrate the covert rate performance of the relay system under cooperative jamming and relay selection.

This paper exploits the efficient channel modeling and channel sparsity to propose a novel Physical (PHY)-layer authentication framework for a Millimeter Wave (mmWave) Multiple-Input Multiple-Output (MIMO) Unmanned Aerial Vehicle (UAV)-ground system. Inspired by the Image Processing theory, we first explore a new Laplace prior approach for the efficient modeling of angular-domain mmWave MIMO channels. With the help of the new channel model, we then reveal the channel sparsity in the concerned system exhibiting a nice spatial correlation property. By a joint use of channel sparsity correlation, efficient sparsity feature extraction with Expectation Maximization (EM)/Generalized Approximate Message Passing (GAMP) algorithms and hypothesis testing, we thus devise a new authentication framework for the concerned system. Theoretical performance analysis is also carried out by deriving the closed-form expressions for false alarm and detection probabilities. Finally, extensive numerical results are provided to validate the feasibility of the proposed channel model and the theoretical analysis, as well as to demonstrate the efficiency of the new authentication framework under various scenarios.

This paper studies the possible physical layer security (PLS) enhancement in a wiretapped two-way relay system from utilizing the reconfigurable intelligent surface (RIS) and beamforming techniques. We first jointly apply the RIS and beamforming (RIS-B) to develop an advanced secure transmission scheme for the system, and conduct related theoretical modeling for the system secrecy sum rate (SSR) under the RIS-B scheme. We then apply the theories of alternating optimization, successive convex approximation, augmented Lagrange method and the quasi-Newton method to devise both the optimal and low-complexity sub-optimal frameworks to identify the optimal settings of RIS phase shifts and beamforming matrix of the RIS-B scheme for SSR maximization. We further investigate a special case when solely the RIS technique is applied for SSR performance enhancement. With the help of Charnes-Cooper transformation, semidefinite programming and Gaussian randomization, we devise an optimization framework to identify the optimal settings of RIS phase shifts for SSR maximization. Finally, extensive numerical results are provided to illustrate the efficiency of the RIS and RIS-B schemes in PLS enhancement in comparison with the conventional channel-capacity-based secure transmission.

This article exploits the spatial–temporal features of user screen-touch trajectory (STT) to develop a user authentication framework for Industrial Internet of Things (IIoT) systems. We first model the STT as a trajectory image and apply the speeded-up robust features (SURF) algorithm for STT spatial feature characterization. We then model the STT as a time series and employ the hidden Markov model (HMM) for the STT temporal feature extraction. We further design a classifier based on HMM for the above temporal feature and also a classifier based on eXtreme Gradient Boosting for the spatial feature. By combining the two classifiers and assigning each classifier an appropriate weight, we develop a passive user authentication framework. The new framework has the potential to significantly impact the IIoT security practices by offering a flexible and efficient authentication method for IIoT systems, and it also can serve as a complementary solution or an enhancement for the traditional authentication mechanism of such systems.

In this paper, we propose BiTDB, a built-in Trusted Execution Environment (TEE) database for embedded systems, to realize higher system availability while ensuring data confidentiality. With BiTDB, dilemmas that the state-of-the-art research work on secure embedded databases has to face can be significantly reduced and eliminated, including (i) complicated research and realization on searchable encryption algorithms (SEA), (ii) limited support to all database operations, and (iii) almost none of specific design and optimizations toward build-in TEE embedded databases. Through BiTDB, all database operations can process plaintext in TEE instead of retrieving ciphertext by developing complicated SEAs. To enable BiTDB to handle database files in Rich Execution Environment (REE) as local ones, we extend the TEE OS with generic file I/O libraries. Then, we contribute three critical optimizations to significantly reduce redundant memory and file operations between TEE and REE, and BiTDB achieve better system performance and availability in embedded systems. Finally, we have implemented the prototype system based on OP-TEE and SQLite for several typical platforms, including virtualization and hardware environments. The TPC-H test shows BiTDB can achieve 85% (on average) of the original database performance while guaranteeing data confidentiality and integrity. Our project repository is athttps://github.com/CharlieMCY/BiTDB.

This paper demonstrates that thefractal dimension of frame preambleserves as a new radiometric feature that can be used together with other known radiometric features to enhance the identification accuracy in wireless device identification. We first propose a fractal dimension estimation scheme for direct-sequence spread spectrum (DSSS) frame preamble, then provide theoretical analysis to reveal how the fractal dimension is primarily determined by the device hardware imperfections, and thus prove that the fractal dimension serves as an intrinsic radiometric feature. We further show simulation results to verify our theoretical modeling of the fractal dimension and also numerically evaluate the effects of device hardware imperfections and wireless channels on the fractal dimension. Finally, by jointly applying the fractal dimension and the five features reported in the literature, we conduct extensive experiments to demonstrate that the fractal dimension can lead to a further improvement of the state-of-the-art result in the radiometric feature-based device identification.

This paper investigates the fundamental covert rate performance in a D2D-enabled cellular network consisting of a cellular user Alice, a base station BS, an active warden Willie, and a D2D pair with a transmitter$D_{t}$and a full-duplex receiver$D_{r}$. To conduct covert communication between Alice and BS, the full-duplex$D_{r}$transmits jamming signal to confuse the active Willie and also receives signal from$D_{t}$simultaneously. With spectrum sharing,$D_{t}$can operate over either an underlay mode reusing cellular spectrum or an overlay mode using dedicated spectrum. With power control,$D_{r}$can send jamming signal to confuse Willie's detection of the transmission from Alice. We first provide theoretical results for the outage probabilities of the cellular and D2D transmissions, the average minimum detection error probability at Willie, and the achievable covert rate from Alice to BS. We then explore the power control for covert rate maximization (CRM) under the underlay mode as well as the joint designs of power control and spectrum partition for CRM under the overlay mode. We further consider a mode selection that flexibly switches between these two modes with a probability, and also investigate the covert rate modeling and joint designs of power control, spectrum partition and mode selection probability for CRM. Finally, numerical results are presented to illustrate the covert rate performances of the network under the underlay mode, overlay mode and mode selection.

Abstract The privacy-preserving data publishing (PPDP) problem has gained substantial attention from research communities, industries, and governments due to the increasing requirements for data publishing and concerns about data privacy. However, achieving a balance between preserving privacy and maintaining data quality remains a challenging task in PPDP. This paper presents an information-driven distributed genetic algorithm (ID-DGA) that aims to achieve optimal anonymization through attribute generalization and record suppression. The proposed algorithm incorporates various components, including an information-driven crossover operator, an information-driven mutation operator, an information-driven improvement operator, and a two-dimensional selection operator. Furthermore, a distributed population model is utilized to improve population diversity while reducing the running time. Experimental results confirm the superiority of ID-DGA in terms of solution accuracy, convergence speed, and the effectiveness of all the proposed components.

Satellites serve as a key component for the upcoming space-air-ground integrated networks, while their signals are susceptible to spoofing attacks. Radio frequency fingerprinting (RFF) has been recognized as a highly promising authentication approach to counteracting spoofing attacks. Despite extensive RFF schemes proposed for terrestrial networks, RFF for satellites remains largely unexplored except for a recently reported scheme named PAST-AI, which exploits the spatial property of the IQ imbalance of downlink signals to authenticate Iridium satellites. Although PAST-AI demonstrates the potential of RFF for satellite authentication, its authentication accuracy and time are unsatisfactory. To address this issue, this paper proposes a novel 3D convolution-based RFF scheme for Iridium satellite authentication, which exploits not only the spatial property but also the temporal property of the IQ imbalance. The proposed RFF scheme transforms short-period sequences of successive IQ samples into 3D data samples and uses a 3D convolutional neural network (CNN) to train an RFF model. To evaluate the authentication accuracy, we collected over 198000000 IQ samples from all 66 Iridium satellites and generated 1000 3D data samples for each satellite. The results showed that the proposed RFF scheme achieves more accurate authentication than PAST-AI using fewer IQ samples (i.e., shorter time).

This paper investigates the joint secrecy and covert communication in a two-hop relaying system consisting of a transmitter Alice, a receiver Bob, an eavesdropper Eve and a Relay. Eve always overhears the secret message from Alice. Meanwhile, Alice transmits covert message on top of secret message without being detected by Relay. First, we propose a covert transmission scheme that Alice will transmit covert message only when the signal-to-interference-plus-noise-ratio (SINR) of the secret message is greater than a threshold. Then, we provide the closed-form expressions of covert performance, i.e., the optimal detection threshold of Relay and the corresponding minimal detection error probability as well as the average minimum detection error probability. Finally, extensive numerical results are presented to illustrate the impacts of the system parameters on covert performances. Remarkably, the corresponding theoretical results well match with the simulation ones indicating that our theoretical analysis can accurately model the covert performance of the considered system.

Satellite internet serves as an indispensable component of the upcoming sixth‐generation networks for providing global broadband internet access service. Due to the open nature of satellite‐ground communication, security issue in satellite internet has always been an important concern for both industry and academia. Although many researchers focus on secure communications in satellite internet, the literature is surprisingly sparse, with no comprehensive overview of the state‐of‐the‐art security techniques. This paper provides an in‐depth survey of secure communications for various satellite internet scenarios. Based on different security mechanisms, we first categorize the existing works of secure communications in satellite internet into two categories: cryptography‐based and physical layer security‐based. The former includes classical encryption‐based and quantum encryption‐based secure communication, and the latter is further divided into precoding‐based, cooperative jamming‐based, relay selection‐based, and physical‐layer authentication‐based secure communication depending on the applied techniques. Finally, we provide some future research directions.

This article investigates the covertness and secrecy of wireless communications in an untrusted relay-assisted device-to-device (D2D) network consisting of a full-duplex base station (BS), a user equipment (UE), and an untrusted relay${R}$. For the covertness, we attempt to prevent Willie from detecting the very existence of communications via a D2D link from UE to R and cellular link from R to BS, while for the secrecy, we aim to prevent the untrusted relay from eavesdropping the UE message. To explore the fundamental covertness and secrecy in such a network, we first provide theoretical modelings for the average minimum detection error rate of Willie, and the average covert/secrecy rate from UE to BS under the underlay and overlay modes, respectively. Based on these models, th we further explore the optimal power control at UE, R, and BS to achieve the average covert rate maximization (MCR) for UE with the constraints of covertness and security requirements under the underlay mode. We also identify the optimal transmit powers and the optimal spectrum partition factor for MCR under the overlay mode. Finally, the exhaust searching method is adopted to solve the MCR problems, and extensive numerical and simulation results are presented to validate our theoretical analysis and to illustrate the average covert rate and secrecy rate of UE under various scenarios.

Passive user authentication is critical for the secure operation of Industrial Internet of Things (IIoT) systems. By jointly utilizing both the time-varying characteristics of the user sequential operation actions and spatial variation characteristics of channel state information (CSI) caused by these actions, this paper proposes a novel two-dimensional passive authentication framework for IIoT systems. In particular, we construct the time-varying operation action sequences from the routine work process of a user and apply the Hidden Markov Model to characterize behavioral biometric characteristics of the user, and also employ the eXtreme Gradient Boosting model to depict the spatial variation characteristics of CSI related to the user. By designing two classifiers corresponding these two characteristics and assigning each classifier an appropriate weight, we propose a two-dimensional user authentication framework for continuous and non-intrusive user authentication in IIoT scenarios. Extensive experiments are conducted to illustrate the authentication performance of the proposed authentication framework in terms of false acceptance rate, false rejection rate and equal-error rate. We further investigate the related authentication efficiency issues like the sensitivity to the weights for classifiers, the sensitivity to authentication time and the capability of resisting against impersonation attacks.

This article proposes a tag-based approach for physical (PHY)-layer authentication in a reconfigurable intelligent surface (RIS) communication system. We first extract the intrinsic PHY-layer features of RIS communication systems in terms of channel gain and background noise, and then apply these PHY-layer features, a random signal as well as the private key of the transmitter to construct a robust cover tag signal against the impersonation attack. We adopt an asymmetric cryptography technique to encrypt tagged signals and to resist against unauthorized detection and tampering attacks during the transmission process. The receiver then applies the maximum a-posteriori (MAP) ratio test to conduct authentication based on the received tag signal, a reference tag signal transmitted in training phase and the knowledge of distributions of the channel gain, background noise and the random signal. We also provide security analysis to demonstrate how the proposed scheme can resist unauthorized detection, tampering attacks, etc. With the help of tools of the MAP ratio test, maximum likelihood estimation, we further analyze the distribution of the test statistics and derive analytical models for the false alarm and detection probabilities. Finally, extensive simulations are conducted to verify the theoretical results and to illustrate the performance of the proposed scheme.

The communication channels in millimeter wave (mmWave) multiple-input multiple-output (MIMO) systems possess some unique fine-grained angle domain features such as channel gain, azimuth angle of arrival (AAoA), and elevation angle of arrival (EAoA). This paper combines AAoA, EAoA, channel gain as well as phase noise features to propose a novel physical layer authentication scheme for mmWave MIMO communication systems. Based on the limit posterior Bayesian Cramér-Rao bound (LPBCRB) and maximum-likelihood (ML) estimation theories, we first develop an efficient approach for the evaluation of hardware phase noise and mmWave channel features. To depict the authentication performance of the new scheme, we then apply the statistical signal processing and hypothesis testing theories to derive the closed-form expressions for false alarm and detection probabilities under the scheme. Finally, extensive numerical results are provided to validate our theoretical models and to demonstrate the capability of the proposed authentication scheme against impersonation attacks.

While the millimeter-wave (mmWave) communication is less susceptible against the conventional wiretapping attack due to its short transmission range and directivity, this paper proposes a new opportunistic wiretapping and jamming (OWJ) attack model in mmWave wireless networks. With OWJ, an attacker can opportunistically conduct wiretapping or jamming to initiate a more hazardous attack based on the instantaneous costs of wiretapping and jamming. We also provide three realizations of the OWJ attack, which are mainly determined by the cost models relevant to distance, path loss and received power, respectively. To understand the impact of the new attack on mmWave network security, we first develop novel approximation techniques to characterize the irregular distributions of wiretappers, jammers and interferers under three OWJ realizations. With the help of the results of node distributions, we then derive analytical expressions for the secrecy transmission capacity to depict the network security performance under OWJ. Finally, we provide extensive numerical results to illustrate the effect of OWJ and to demonstrate that the new attack can more significantly degrade the network security performance than the pure wiretapping or jamming attack.

The efficient buffer space management in intermittently connected Internet of Things (IC-IoT) is of great importance for data delivery performance guarantee in such networks. This article considers two typical buffer space management policies for IC-IoT, i.e., buffer-space sharing (BS) and buffer-space allocation (BA). The BS policy allows the buffer space of each device to be fully shared by the exogenous packets and the packets from other devices, while the BA policy divides the buffer space into the source buffer and relay buffer for storing the two kinds of packets separately. With the help of the queueing theory and Markov chain theory, we develop a theoretical framework to capture the sophisticated queueing processes for the buffer space under either BS or BA policy, which enables the limiting distribution of the buffer occupation state to be determined. We then provide theoretical modeling for throughput and expected end-to-end delay to evaluate the fundamental performance of the IC-IoT under the BS and BA policies. Finally, extensive simulation and numerical results are presented to validate theoretical models and to demonstrate the effects of BS and BA policies on the IC-IoT performance.

Passive authentication is of great importance for security guarantee in industrial Internet of Things (IIoT) systems. Based on the behavioral biometrics from sequential operation actions in IIoT, this article proposes a nonintrusive and passive authentication framework for continuous user authentication against the impersonation attack. We first provide experimental results to demonstrate the discriminability and stability for the intrinsic features of sequential operation actions, and then leverage the Kalman filtering and wavelet techniques for noise elimination and the singular value decomposition method for the dimensionality reduction of feature space. We further exploit the one-class classification technique to formulate the authentication decision process as a hidden Markov model (HMM). Extensive experiments are conducted to illustrate the authentication performance of the passive authentication framework in terms of the false acceptance rate, false rejection rate, and equal-error rate. We also investigate the related authentication efficiency issues in terms of the usability to the operation-action sequence length, the scalability to the number of features and user space, and the sensitivity to the operation action features.

This paper explores the joint secrecy and delay guarantees based on opportunistic jamming and link selection in a wireless relay system consisting of a source, a destination, multiple buffer-aided relays and a passive eavesdropper wiretapping over both hops. Based on the information of link state and buffer status, we design a novel transmission scheme based on link selection and jammer selection, which dynamically grants transmission links different priorities for packet delivery, such that the constraints on both secrecy outage probability and packet delay are jointly satisfied. To understand the performance of the new scheme, we then apply the bitmap technique and Markov chain theory to develop a complete theoretical framework for the modelling of three fundamental metrics, namely reliability outage probability, packet discarding probability and secrecy/delay constrained throughput (SDT). Finally, we provide extensive simulation and numerical results to validate our theoretical modelling, as well as to demonstrate that the proposed scheme is superior to the benchmarks in terms of SDT.

Communication performance relies largely on the availability of channel state information (CSI). This paper investigates the impact of outdated CSI on the achievable covert communication performance in a two-hop wireless relay system under two typical covert transmission schemes of rate-control transmission (RCT) and power-control transmission (PCT). We first apply the typical channel feedback delay model to determine the statistical distribution of outdated CSI, based on which we then develop theoretical models to depict the inherent relationship between outdated CSI and the fundamental covert performance metrics in terms of detection error probability (DEP) and covert rate (CR). With the help of these models, we further explore the optimization of DEP subject to the CR constraint as well as the optimization of CR subject to the DEP constraint to reveal the max-min DEP performance and the maximal CR performance with the outdated CSI. Finally, extensive numerical results are provided to illustrate the impact of outdated CSI on the covert communication performance.

Millimeter-wave (mmWave) communications are highly promising to improve the capacity of modern wireless networks, while the physical layer security (PLS) techniques hold great potential to enhance the critical secrecy performance therein. By carefully exploiting the significant signal difference between the Non-Light-of-Sight (NLoS) and Line-of-Sight (LoS) mmWave links, this paper proposes a Sight-based Cooperative Jamming (SCJ) scheme to improve the PLS performance of mmWave ad hoc communications. In this scheme, each potential jammer that has no LoS link to its nearest receiver but may have LoS links to eavesdroppers is selected with a certain probability to generate artificial noise such that channel advantages at legitimate receivers can be achieved. For performance modeling of the new jamming scheme, novel and efficient theoretical approximation approaches are firstly developed to enable the challenging issue of interference distribution modeling to be tackled, and then a theoretical framework based on stochastic geometry is proposed to capture the secrecy transmission capacity behavior under the SCJ scheme. Finally, extensive numerical results are provided to illustrate the SCJ scheme under various network scenarios.

As important network infrastructures to support data storage and service delivery for worldwide users, cloud data centers are facing great threaten by frequent disasters around the world and thus the survivability of cloud data centers becomes a critical issue. Since both data and service evacuations are desired at the same time under a real disaster scenario, this paper studies a joint design of them to fight against disasters. We consider a disaster that can present an early warning time before it really affects cloud data centers, and by exploiting the intrinsic interplay between data and service evacuations and efficiently utilizing the early warning time we propose a joint data and service evacuation scheme for emergency protection. We first formulate the joint design as two optimal Integer Linear Program (ILP) models. Notice that the protection process is highly time-sensitive due to the early warning time constraint, two time-efficient heuristics are then designed by carefully selecting evacuated services and candidate evacuation nodes to achieve a better sharing of network resources between data backup and service migration. Extensive numerical results demonstrate the efficiency of the proposed scheme on improving survivability of data and services in cloud data centers. With a set of given resource and early warning time constraints, this work can guide data center operators to achieve a tradeoff between data backup and service migration.

Internet of Things (IoT) systems are of paramount importance to provide ubiquitous wireless connectivity for smart cities. However, such systems are facing security challenges due to the broadcast and openness nature of wireless channels. This article studies the performance of covert communication under a scenario consisted of a source-destination pair, a passive warden, and multiple relays. We first propose two relay selection schemes, one is random selection and another is superior-link selection. Based on these two schemes, we then examine the transmission strategy design for the source and thus define the necessary condition that the source can transmit covert messages. We further derive the detection error probability of warden and covert capacity based on two relay selection schemes and also explore the covert capacity maximization through efficient numerical searches. Finally, numerical results are provided to illustrate our theoretical findings and the performance of covert communication in such systems. Remarkably, the superior-link selection scheme has 108% improved to the random selection scheme for the maximum covert capacity performance under the same transmission power at the source.

This article focuses on the secure routing problem in the decentralized Internet of Things (IoT). We consider a typical decentralized IoT scenario composed of peer legitimate devices, unauthorized devices (eavesdroppers), and selfish helper jamming devices (jammers), and propose a novel incentive jamming-based secure routing scheme. For a pair of source and destination, we first provide theoretical modeling to reveal how the transmission security performance of a given route is related to the jamming power of jammers in the IoT. Then, we design an incentive mechanism with which the source pays some rewards to stimulate the artificial jamming among selfish jammers, and also develop a two-stage Stackelberg game framework to determine the optimal source rewards and jamming power. Finally, with the help of the theoretical modeling as well as the source rewards and jamming power setting results, we formulate a shortest weighted path-finding problem to identify the optimal route for secure data delivery between the source-destination pair, which can be solved by employing the Dijkstra's or Bellman-Ford algorithm. We prove that the proposed routing scheme is individually rational, stable, distributed, and computationally efficient. Simulation and numerical results are provided to demonstrate the performance of our routing scheme.

The k-nearest neighbors (k-NN) query is a fundamental primitive in spatial and multimedia databases. It has extensive applications in location-based services, classification & clustering and so on. With the promise of confidentiality and privacy, massive data are increasingly outsourced to cloud in the encrypted form for enjoying the advantages of cloud computing (e.g., reduce storage and query processing costs). Recently, many schemes have been proposed to support k-NN query on encrypted cloud data. However, prior works have all assumed that the query users (QUs) are fully-trusted and know the key of the data owner (DO), which is used to encrypt and decrypt outsourced data. The assumptions are unrealistic in many situations, since many users are neither trusted nor knowing the key. In this paper, we propose a novel scheme for secure k-NN query on encrypted cloud data with multiple keys, in which the DO and each QU all hold their own different keys, and do not share them with each other; meanwhile, the DO encrypts and decrypts outsourced data using the key of his own. Our scheme is constructed by a distributed two trapdoors public-key cryptosystem (DT-PKC) and a set of protocols of secure two-party computation, which not only preserves the data confidentiality and query privacy but also supports the offline data owner. Our extensive theoretical and experimental evaluations demonstrate the effectiveness of our scheme in terms of security and performance.

This paper investigates the fundamental covert rate performance in a wireless relaying system consisting of a source-destination pair, a full-duplex (FD) relay and a warden, where the relay can work at either the FD mode or the half-duplex (HD) mode. We first provide theoretical modeling for the instantaneous/average covert rate when the system works solely under the FD mode or HD mode, and then explore the corresponding optimal transmit power control of relay for the covert rate maximization. For an improvement of covert rate, we further propose a joint FD/HD mode that flexibly switches between the FD and HD modes depending on channel state of the relay self-interference channel. Under the joint FD/HD mode, we also examine the related problems of theoretical modeling for covert rate and optimal transmit power control of relay for covert rate maximization. Finally, extensive numerical results are provided to illustrate the covert rate performances of the relaying system under the FD, HD and joint FD/HD modes.

By exploiting two intrinsic physical (PHY)-layer features in terms of location-specific channel gain and transmitter-specific phase noise, this paper proposes a new PHY-layer authentication scheme for massive multiple-input multiple-output (MIMO) systems. In particular, we apply the linear minimum mean square error technique to estimate the time-varying channel gain and adopt extended Kalman filtering to track the time-varying phase noise. Based on the estimation error covariance matrices of channel gain and phase noise, we then formulate the PHY-layer authentication as a composite hypothesis testing problem. With the help of tools from statistical signal processing, matrix analysis, and composite hypothesis testing, we develop theoretical models to capture the false alarm and detection probability performances of the proposed scheme. Finally, we provide extensive numerical results to validate these theoretical models and to illustrate the efficiency of the proposed authentication scheme.

This paper focuses on the multiple-input-multiple-output (MIMO) two-way relay system with an untrusted relay and investigates its secure and energy-efficient precoding design issue based on the physical layer security technology. We first provide theoretical modeling for the index of secrecy energy efficiency (SEE) and formulate the optimal precoding design for SEE maximization (SEEM) as a high-dimensional non-convex programming problem. By exploring the techniques like fractional programming, alternate optimization and semi-definite programming, we then develop a hierarchical theoretical framework to solve the SEEM problem and thus to identify the optimal precoding designs for the source and relay. Furthermore, we demonstrate the proposed theoretical framework is also applicable to the problem of precoding design for secrecy sum rate maximization. Finally, with the help of generalized singular value decomposition, we propose a sub-optimal relay precoding design scheme with significantly lower computational complexity. Extensive numerical results provided in the paper indicate that the proposed schemes can remarkably improve the SEE performance in MIMO two-way untrusted relay systems.

This paper focuses on the QoS-aware secure routing design based on the physical layer security technology for a multi-hop wireless network consisting of legitimate nodes, malicious eavesdroppers, and selfish jammers. We first provide theoretical modeling for a given route to reveal how its end-to-end security/QoS performance is related to the transmitting power of legitimate nodes along the route and the jamming power of jammers in the network. We then design an incentive mechanism that stimulates jammers to generate artificial jamming for security enhancement, and also develop a non-cooperative game framework to resolve the jamming power setting issue here. Based on the security/QoS performance modeling of the route and jamming power setting, we further propose a theoretical framework to determine the optimal transmitting power of nodes along the route such that its optimal transmission security can be achieved under a QoS constraint. Finally, with the help of the power setting results of the given route, we formulate a shortest weighted path-finding problem to identify the optimal route for data delivery in the network, which can be solved by employing the Bellman-Ford or Dijkstra's algorithm. It is demonstrated that the proposed routing scheme is individually rational, stable, distributed and computationally efficient.

Unmanned aerial vehicle (UAV) swarm connected to millimeter wave (mmWave) cellular networks is emerging as a new promising solution to provide ubiquitous high-speed and long distance wireless communication services for supporting various applications. To satisfy different quality of service (QoS) requirements in future large-scale applications of such networks, this article investigates the rate performance, fairness and their tradeoff in the networks with directional antennas in terms of sum-rate maximization, fairness index maximization, max-min fair rate and proportional fairness. We first consider a more realistic mmWave 3D directional antenna array model for UAVs and base station (BS), where the antenna gain depends on the radiation angle of the antenna array. Based on this antenna array model, we formulate the performance, fairness and their tradeoff as four constrained optimization problems, and propose corresponding iterative algorithm to solve these problems by jointly optimizing elevation angle, azimuth angle and height of antenna array at BS in the downlink transmission scenario. Furthermore, we also explore them in uplink transmission scenario, where the interference issue among links is carefully considered. Finally, according to the sum rate, minimum rate and fairness index under each optimization problem, numerical results are provided to illustrate the impacts of network parameters on the performance, fairness and their tradeoff, and also to reveal new findings under both downlink and uplink transmission scenarios, respectively.

Mobile ad hoc networks (MANETs) represent a class of important network models for supporting various critical applications, while the security breach due to eavesdropping attacks has been a critical issue. This study investigates the security issue of MANETs from the perspective of physical layer security (PLS). In particular, by combining PLS techniques [e.g. artificial noise (AN) injection and Secrecy Guard zoNe (SGN)] and the conventional Aloha protocol, the authors first propose an AN‐based Aloha protocol and a SGN‐based Aloha protocol to ensure secure medium access for legitimate transmitters. In the AN‐based Aloha protocol, all potential transmitters are allowed to be active and each active transmitter injects AN into its transmitted signals to confuse eavesdroppers. In the SGN‐based protocol, each potential transmitter has an SGN, a circle centred at itself, and only the potential transmitters whose SGN contains no eavesdroppers are allowed to be active. To understand the security performances of the proposed security‐aware Aloha protocols, the authors then apply tools from Stochastic Geometry to analyse the secrecy transmission capacity (STC) performances of MANETs under both protocols. Finally, the authors provide simulation/numerical results to corroborate the proposed theoretical analysis and also to show the impacts of network parameters on the STC performances.

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.

In this paper, we propose a physical layer authentication scheme in heterogeneous coexist multiple-input-multiple-output (MIMO) systems. This scheme utilizes two physical layer features in terms of location-specific channel gains and transmitter-specific phase noise caused by imperfect oscillators to identify transmitters. Three properties of the proposed scheme: covertness, robustness, and security, are analyzed in detail. By using a maximum-likelihood estimator (MLE) and extended Kalman filter (EKF), we estimate channel gains and phase noise, and formulate variances of estimation errors. We also quantize the temporal variations of channel gains and phase noise through the developed quantizers. Based on quantization results and theories of hypothesis testing and stochastic process, we then derive the closed-form expressions for false alarm and detection probabilities with the consideration of quantization errors. Simulations are carried out to validate the theoretical results of the two probabilities. Based on theoretical models, we further demonstrate that the proposed scheme makes it possible for us to flexibly control authentication performance by adjusting thresholds (for channel gain, phase noise, and decision, respectively) to achieve a required authentication performance in specific MIMO applications.

This article investigates the secure communication in a two-hop cooperative wireless network, where a buffer-aided relay helps forward data from the source to destination, and a passive eavesdropper attempts to intercept data transmission from both the source and relay. To ensure the transmission security and communication quality of service (QoS) of the system, we design novel link selection policies for two cases that the instantaneous channel state information is available or unavailable at the source node. For evaluating the system performance, we then derive the closed-form expressions of end-to-end secrecy outage probability, system throughput and secrecy throughput, respectively. Based on the theoretical performance analysis, we further explore the performance optimization issues, revealing the insightful tradeoffs between the transmission security and QoS. An iterative algorithm is developed to identify the optimal setting of link selection parameters, which is helpful for the practical configuration of link selection policies to satisfy various system performance requirements. Finally, we conduct simulations to validate our theoretical performance analysis, and also provide extensive numerical results to illustrate the efficiency of the proposed link selection policies for ensuring the secure communication in a two-hop cooperative network.

This paper focuses on a full-duplex multiple-input multiple-output two-way untrusted relay system, and investigates the optimal beamforming design of such system to maximize its secrecy sum rate (SSR) based on the physical layer security technology. We first provide the modeling of SSR under a general beamforming setting as well as the theoretical formulation of the optimal beamforming design problem. Based on the ideal assumption that the full channel state information is available, we then develop a novel theoretical framework to solve the optimal design problem and thus establish an upper bound on SSR, where the techniques of alternate optimization, fractional programming, semi-definite programming and barrier function method are jointly employed. With the consideration of the constraints in practical implementations, we further propose two sub-optimal beamforming design solutions based on either Wiener prediction or asymptotic approximation. The issue of how to reduce the computational complexity in the optimal relay beamforming design is also discussed in this paper. Finally, we present extensive numerical results to illustrate our theoretical findings and to demonstrate the performance of the proposed sub-optimal beamforming design solutions.

We study transmitter authentication in massive multiple-input multiple-output (MIMO) systems with non-ideal hardware for the fifth generation (5G) and beyond networks. A new channel-based authentication scheme is proposed by taking hardware impairments into account. Based on signal processing theory, we first formulate channel estimation under hardware impairments and determine error covariance matrix to assess the quantity caused by hardware impairments on authentication performance. With the help of hypothesis testing and matrix transformation theories, we are then able to derive exact expressions for the probabilities of false alarm and detection under different channel covariance matrix models. Extensive simulations are carried out to validate theoretical results and illustrate the efficiency of the proposed scheme. Impacts of system parameters on performance are revealed as well.

In Japan, early warnings such as the earthquake early warning and the tsunami warning are broadcast to cellular phones by using the Earthquake and Tsunami Warning System (ETWS) [1]. The connectivity of a LTE device (UE: user equipment) depends on the LTE base station (evolved Node B: eNB) which acts as a relay with the Internet. Therefore it is difficult to broadcast early warnings during large-scale disasters.

A lot of works have been done to demonstrate that buffer-aided relaying can achieve a significant performance gain in cooperative wireless networks. However, the additional delay introduced by buffer has been largely neglected in available works, which is of significant importance for delay-sensitive networks. In this paper, we consider a two-hop buffer-aided relaying system suffering from eavesdropping, where every packet owns a limited lifetime. In order to satisfy a specific secrecy rate of the system, this paper proposes a novel security and lifetime (SELI)-aware relay selection scheme by balancing the security and lifetime constraints. Furthermore, to address the problem of the heterogeneous packets queuing in the buffer, the approach of Markov chain is embedded to model the packet occupancy process. With the help of this complete framework, we derive the exact expressions of performance metrics, including reliable outage probability, packet discarding probability and secrecy throughput. Finally, extensive simulation and numerical results are provided to validate our analysis and illustrate the proposed scheme can efficiently reduce the packet discarding ratio.

Internet of Things (IoT), an significant support for strategic emerging industries, is re-building industrial systems, such as transportation, healthcare and energy, while a number of new features and requirements like data cross-industry sharding appear in recent years. The emerging Blockchain technology has provided a promising opportunity to break information island and single-domain management in multi-domain IoT systems by leveraging distributed storage. On the other hand, the transaction consensus throughput in the mainstream blockchain systems, such as Ethereum and Fabric, is far from meeting the demand for massive data storage in time in multi-domain IoT systems. In this paper, we design a sharding protocol called MDIoTSP. The protocol first partitions the overall blockchains into many small shards, each of which generally recognized as a micro-blockchain according to the multiple domains, and then make the final consensus by merging the hash digests of the sub-blocks which generated from the shards for the multi-domain IoT blockchains ecosystem specifically. We also develop MicrothingsChains to run MDIoTSP in multi-domain IoT blockchains to prove our assumption that MDIoTSP scales up the transaction consensus throughput near linearly with the number of shards.

In this paper, we investigate energy-efficient secure communications in an untrusted two-way relay network, where two source nodes exchange messages via an untrusted relay. Considering both security threats and energy limitation, the performance metric secure energy efficiency is defined as the ratio of the secrecy sum rate to the total power consumption. Our objective is to maximize the secure energy efficiency by jointly designing the source and relay beamformers. We first derive the expression of secure energy efficiency under a general beamforming configuration. Then, an iterative algorithm based on the techniques of alternate optimization, fractional programming, barrier function method and semi-definite programming, is proposed to find the optimal solutions of the source and relay beamformers. Our analysis shows that the proposed scheme can not only solve the problem of secure energy efficiency maximization but also be applicable for solving the problem of secrecy sum rate maximization. Simulation results demonstrate that the proposed scheme achieves a good gain in terms of secure energy efficiency.

This paper investigates a critical access control issue in the Internet of Things (IoT). In particular, we propose a smart contract-based framework, which consists of multiple access control contracts (ACCs), one judge contract (JC), and one register contract (RC), to achieve distributed and trustworthy access control for IoT systems. Each ACC provides one access control method for a subject-object pair, and implements both static access right validation based on predefined policies and dynamic access right validation by checking the behavior of the subject. The JC implements a misbehavior-judging method to facilitate the dynamic validation of the ACCs by receiving misbehavior reports from the ACCs, judging the misbehavior and returning the corresponding penalty. The RC registers the information of the access control and misbehavior-judging methods as well as their smart contracts, and also provides functions (e.g., register, update, and delete) to manage these methods. To demonstrate the application of the framework, we provide a case study in an IoT system with one desktop computer, one laptop and two Raspberry Pi single-board computers, where the ACCs, JC, and RC are implemented based on the Ethereum smart contract platform to achieve the access control.

This paper investigates the fundamental issues of mode selection and spectrum partition in cellular networks with in-band device-to-device (D2D) communication from the physical-layer security (PLS) perspective. We consider a mode selection scheme allowing each D2D pair to probabilistically switch between the underlay and overlay modes, and also a spectrum partition scheme where the system spectrum is orthogonally partitioned between cellular and overlay D2D communications. We first develop a general theoretical framework to model the secrecy outage and secrecy capacity performance of cellular users as well as the outage and capacity performance of D2D pairs. Optimization problems are also solved to identify the optimal mode selection and spectrum partition for secrecy capacity maximization and secrecy outage probability minimization. A case study is then provided to demonstrate the application of our theoretical framework for performance modeling and optimization, and also to illustrate the impacts of mode selection and spectrum partition on the PLS performances of in-band D2D communications.

To enable the network softwarization, network function virtualization (NFV) and software defined networking (SDN) are integrated to jointly manage and utilize the network resource and virtualized network functions (VNFs). For a network flow resulting from any NFV application, an associated switch would send a routing request to the controller in SDN. The controller then generates and configures a routing path to dynamically steer the flow across appropriate VNFs or service function chains. This process, however, exhibits a skew distribution of response latency with a long tail. Cutting the long-tail latency of response is critical to enable the network softwarization, yet difficult to achieve due to many factors, such as the limited capacities and the load imbalance among controllers. In this paper, we reveal that such flow requests still experience the long-tail response latency, even using the up-to-date controller-to-switch assignment mechanism. To tackle this essential problem, we first propose a light-weight and load-aware switch-to-controller selection scheme to cut the long-tail response latency under the simple scenario of homogeneous controllers, and then design a general delay-aware switch-to-controller selection scheme to fundamentally cut the long-tail response latency for the more complicated heterogeneous controller scenario with performance fluctuations. The comprehensive evaluations indicate that our two new switch-to-controller selection schemes can significantly reduce the long-tail latency and provide higher system throughput.

Big data applications have made significant impacts in recent years thanks to the fast growth of cloud computing and big data infrastructures. However, public cloud is still not widely accepted to perform big data computing, due to the concern with the public cloud's security. Result integrity is one of the most significant security problems that exists in the cloud-based big data computing scenario. In this paper, we propose MtMR, a Merkle tree-based verification method that assures high result integrity of MapReduce jobs. MtMR overlays MapReduce on a hybrid cloud environment and applies two rounds of Merkle tree-based verifications on the prereduce phase (i.e., the map phase and the shuffle phase) and the reduce phase, respectively. In each round, MtMR samples a small portion of reduce task input/output records on the private cloud and performs Merkle tree-based verification on all the task input/output records. Based on the design of MtMR, we perform a series of theoretical studies to analyze its security and performance overhead. Our results indicate that MtMR is a promising method in terms of high result integrity and low performance overhead. For example, by setting the sampled record ratio as an optimal value, MtMR can guarantee no more than 10 incorrect records in each reduce task by sampling only 4 percent of records in that task.

Highly fault-tolerant optical switch is becoming a critical network element for large wavelength division multiplexing mesh networks. Optical nodes built on replicated banyan network (RBN) structures are attractive for serving as optical switching systems due to the nice properties of banyan network structures. Furthermore it is expected that an optical RBN structure also has a good fault-tolerant capability because it consists of multiple identical banyan networks. Previous analytical models have been developed to understand the blocking behaviors of optical RBN networks without taking into account the link failure in optical RBN networks. In this paper, we conduct the link failure-tolerant analysis of optical RBN networks and present an analytical model for the blocking probability of optical RBN networks when link failures are taken into account. The model is significant because it provides network developers a quantitative guidance to determine the effects of network failure on the overall blocking behaviors of optical RBN networks and enables a desirable tradeoff to be made between blocking probability and hardware cost in a faulty optical RBN network.

Public cloud vendors have been offering a variety of big data computing services on their clouds. However, runtime integrity is one of the major security concerns that hinder the wide adoption of those services. In this paper, we focus on MapReduce, a popular big data computing framework, and propose the runtime integrity audition (RIA), a solution that remotely verifies the runtime integrity of MapReduce applications. RIA records the runtime variable values of the MapReduce application on the public cloud and checks those values against the application's code on the private cloud. By doing so, RIA protects the runtime integrity of MapReduce applications. Based on the idea of RIA, we developed a prototype system, called MR Auditor, and tested its applicability and performance with several Hadoop applications. Our experimental results showed that MR Auditor is a general tool that can efficiently audit the runtime integrity of all the MapReduce applications that we tested. In addition, MR Auditor incurs a moderate performance overhead. For example, when verifying the Word Count application, a proper parameter setting of MR Auditor incurs 1% of extra execution time on the public cloud and 14% of extra execution time on the private cloud.

Service Oriented Computing (SOC) has initially developed for the Internet, but also identified as an appealing computing paradigm for developing applications in distributed wireless environments. The open nature of wireless medium may expose services to a variety of unauthorized third parties (eavesdroppers), resulting in insecure service interactions, while cooperative jamming is promising to provide a strong form of security. This paper focuses on security performance study of wireless communications for service interactions among different parties in SOC. More specifically, this paper establishes a theoretical framework for the study of eavesdropper-tolerance capability (i.e., the maximum number of eavesdroppers that can be tolerated) in a two-hop wireless network, where the cooperative jamming is adopted to ensure security defined by secrecy outage probability (SOP) and opportunistic relaying is adopted to guarantee reliability defined by transmission outage probability (TOP). For the concerned network, exact modeling for SOP and fine approximation for TOP are first conducted based on the Central Limit Theorem. With the help of SOP and TOP models and also the Stochastic Ordering Theory, the model for eavesdropper-tolerance capability analysis is then developed. Finally, extensive simulation and numerical results are provided to illustrate the efficiency of our theoretical framework as well as the eavesdropper-tolerance capability of the concerned network from adopting cooperative jamming and opportunistic relaying.

This paper investigates the security-delay trade-off of the buffer-aided relay selection scheme in a two-hop wireless system, which consists of a source-destination pair, one eavesdropper, and multiple relays each having a finite buffer. To evaluate the security and delay performances of the system, we derive analytical expressions for the end-to-end (E2E) secure transmission probability (STP) and the expected E2E delay under both perfect and partial eavesdropper channel state information (CSI) cases. These analytical expressions help us to explore the inherent trade-off between the security and delay performances of the concerned system. In particular, the results in this paper indicate that: 1) the maximum E2E STP increases as the constraint on the expected E2E delay becomes less strict, and such trend is more sensitive to the variation of the number of relays than that of the relay buffer size; 2) on the other hand, the minimum expected E2E delay tends to decrease when a less strict constraint on E2E STP is imposed, and this trend is more sensitive to the variation of the relay buffer size than that of the number of relays.

This paper investigates the secrecy and reliability of a communication where the user is assisting an Intrusion Detection System (IDS) in detecting the adversary’s attack. The adversary is assumed to be sophisticated such that it can conduct eavesdropping and jamming attacks. The IDS is equipped with the capability of detecting both of those attacks. Two scenarios were considered; the first scenario is that the user is trying to detect the adversary by assisting the IDS, and the second scenario is that the user is equipped with a silent time slot in its communication protocol besides assisting the IDS, in order to provoke the adversary into jamming the channel, thus detecting it with a higher probability. Interestingly, adding the capability of detecting eavesdropping attacks pushed the adversary into conducting jamming attacks much more, thus aiding in detecting the adversary earlier. All of that was modeled by means of stochastic game theory, in order to analyze and study the behavior and the interactions between the user and the adversary. Results show a major improvement in the first scenario by 188% and an improvement by 294% in the second scenario in the game value when the probability of detecting eavesdropping attacks was 0.3, which represents the payoff that the user gains in terms of secrecy and reliability.

Device-to-device (D2D) content sharing holds great promise to alleviate the growing strain on cellular networks, as it offloads popular content data onto direct peer-to-peer links. However, it is still largely unexplored how content sharing could benefit from utilizing multi-hop rather than conventional single-hop D2D communications. As a step towards this end, this paper proposes a generalized two-level Stackelberg game theoretic framework to enable content sharing with multi-hop D2D communication capabilities. At the lower level, a Nash bargaining subgame is proposed to provide the routing and pricing graphs, where a novel incentive mechanism is adopted to stimulate cooperation. At the upper level, the set of participants is decided to ensure all participants contribute to the content sharing. An additional pricing plan is introduced to make sure that the final pricing is practical and feasible. Numerical results are presented to demonstrate that the proposed game theoretic framework could not only jointly deal with participants selection, routing and pricing in D2D content sharing, but also effectively restrict utilities and transmission resources to only contributive participants.

This paper study the secure optimal QoS routing (SOQR) in wireless ad hoc networks (WANETs) based on the physical layer security techniques. Specifically, we consider a multi-hop WANET with malicious eavesdroppers and cooperative jammers, and formulate the SOQR as an optimization problem. To deal with this problem, we first derive the closed-form expressions of connection outage probability (COP) and secrecy outage probability (SOP) for any given end-to-end path, which serve as the performance metrics of communication QoS and transmission security, respectively. Then, we explore the minimum COP conditioned on that SOP is below a pre-specified threshold and obtain the corresponding achievable power allocation strategy. With the help of analysis of a given path, we further propose the SOQR algorithm which selects the secure path between a pair of source and destination nodes in a distributed manner to achieve the optimal QoS performance. Finally, numerical simulations are conducted to validate the efficiency of our theoretical results, as well as to illustrate the QoS-security tradeoffs.

Banyan networks serve as a class of important switching network architecture, whose multicast capability is critical for future high-performance switches to support multicast-intensive applications. The available literature indicates that, in order to construct optical multicast banyan networks based on the directional coupler (DC) technology, a high-hardware cost is usually involved to ensure the nonblocking property. In this paper, we conduct blocking probability analysis for such networks to explore the inherent tradeoff between blocking probability and hardware cost. In particular, we focus on a class of DC-based optical networks built on the replicated banyan network (RBN) architecture, and develop a theoretical upper bound on blocking probability for such networks under the general f-cast traffic, which covers the unicast and multicast as special cases. This bound captures the overall blocking behavior of f-cast optical RBN networks and agrees with the conditions of strictly nonblocking f-cast optical RBN networks. The proposed bound is significant because it provides a fundamental guideline to achieve the desirable tradeoff between blocking probability and hardware cost. This paper shows that the hardware cost of an f-cast optical RBN network can be dramatically reduced if a small blocking probability is allowed.

Data backup in data center networks (DCNs) is critical to minimize the data loss under disaster. This paper considers the cost-efficient data backup for DCNs against a disaster with ε early warning time. Given geo-distributed DCNs and such a ε-time early warning disaster, we investigate the issue of how to back up the data in DCN nodes under risk to other safe DCN nodes within the ε early warning time constraint, which is significant because it is an emergency scheme for data protection against a predictable disaster and also help DCN operators to build a complete backup scheme, i.e., regular backup and emergency backup. Specifically, an Integer Linear Program (ILP)-based theoretical framework is proposed to identify the optimal selections of backup DCN nodes and data transmission paths, such that the overall data backup cost is minimized. Extensive numerical results are also provided to illustrate the proposed framework for DCN data backup.

Recently extensive works have been devoted to the performance analysis of physical layer security in wireless communication systems. However, the combination of physical layer security and quality of service (QoS) for route selection in multi-hop wireless ad hoc networks (WANETs) still remains an open technical challenge. As an initial step towards this end, this paper focuses on a multi-hop WANET with two typical transmission schemes amplify-and-forward (AF) and decode-and-forward (DF), and explores the route selection with the consideration of both security and QoS. We first derive the closed-form expressions of secrecy outage probability (SOP) and connection outage probability (COP) for a single hop link, and further extend the results to an end-to-end route. Then we conduct the performance comparison between the AF scheme and DF scheme. Finally, based on both the SOP and COP of a route, we formulate the route metric and propose a flexible route selection algorithm which enables us to select the suitable route for message delivery according to different security and QoS requirements.

Wireless communication is one of the key technologies that actualize the Internet of Things (IoT) concept into the real world. Understanding the security performance of wireless communications lays the foundation for the security management of IoT. Eavesdropper collusion represents a significant threat to wireless communication security, while physical-layer security serves as a promising approach to providing a strong form of security guarantee. This paper studies the important secrecy outage performance of wireless communications under eavesdropper collusion, where the physical layer security is adopted to counteract such attack. Based on the classical Probability Theory, we first conduct analysis on the secrecy outage of the simple noncolluding case in which eavesdroppers do not collude and operate independently. For the secrecy outage analysis of the more hazardous M-colluding scenario, where any M eavesdroppers can combine their observations to decode the message, the techniques of Laplace transform, keyhole contour integral, and Cauchy Integral Theorem are jointly adopted to work around the highly cumbersome multifold convolution problem involved in such analysis, such that the related signal-to-interference ratio modeling for all colluding eavesdroppers can be conducted and thus the corresponding secrecy outage probability can be analytically determined. Finally, simulation and numerical results are provided to illustrate our theoretical achievements. An interesting observation suggests that the SOP increases first superlinearly and then sublinearly with M.

Despite extensive efforts on exploring the asymptotic capacity bounds for mobile ad hoc networks (MANETs), the general exact capacity study of such networks remains a challenge. As one step to go further in this direction, this paper considers two classes of Aloha MANETs (A-MANETs) NAand NCthat adopt an aggressive traffic-independent Aloha and the conventional traffic-dependent Aloha, respectively. We first define a notation of successful transmission probability (STP) in NA, and apply queuing theory analysis to derive a general formula for the capacity evaluation of NA. We also prove that NCactually leads to the same throughput capacity as NA, indicating that the throughput capacity of NCcan be evaluated based on the STP of NA as well. With the help of the capacity formula and stochastic geometry analysis on STP, we then derive closed-form expressions for the throughput capacity of an infinite A-MANET under the nearest neighbor/receiver transmission policies. Our further analysis reveals that although it is highly cumbersome to determine the exact throughput capacity expression for a finite A-MANET, it is possible to have an efficient and closed-form approximation to its throughput capacity. Finally, we explore the capacity maximization and provide extensive simulation/numerical results.

This paper focuses on a class of important two-hop relay mobile ad hoc networks (MANETs) with limited-buffer constraint and any mobility model that leads to the uniform distribution of the locations of nodes in steady state, and develops a general theoretical framework for the end-to-end (E2E) delay modeling there. We first combine the theories of fixed-point (FP), quasi-birth-and-death process, and embedded Markov chain to model the limiting distribution of the occupancy states of a relay buffer, and then apply the absorbing Markov chain theory to characterize the packet delivery process, such that a complete theoretical framework is developed for the E2E delay analysis. With the help of this framework, we derive a general and exact expression for the E2E delay based on the modeling of both packet queuing delay and delivery delay. To demonstrate the application of our framework, case studies are further provided under two network scenarios with different MAC protocols to show how the E2E delay can be analytically determined for a given network scenario. Finally, we present extensive simulation and numerical results to illustrate the efficiency of our delay analysis as well as the impacts of network parameters on delay performance.

Data center network (DCN) placement with the consideration of potential large-scale region failures is critical to ensure its functionality under such catastrophic scenarios. This paper considers the optimal DCN placement for DCN failure risk minimization against such region failures. We first apply a general probabilistic region failure model to determine the failure probability of a node/link, and then propose a general grid partition-based scheme to flexibly define the global distribution of a region failure in terms of its occurring probability and intensity. Such grid partition scheme also helps us to evaluate the vulnerability under a region failure. With the help of the vulnerability information, we further propose an Integer Linear Program-based theoretical framework to identify the optimal DCN placement to lead to the minimum DCN failure risk under a region failure. An example and extensive numerical results are also provided to illustrate the proposed framework for DCN placement.

Heterogeneous networks (HetNets), where multiple low power small cell eNodeBs (SeNBs) are overlaid on the coverage of a high power macrocell eNodeB (MeNB), serve as promising paradigm to enhance spectral efficiency of future cellular wireless networks. To capture the complicated interference interaction and also the coordination behavior among MeNB and SeNBs, this paper proposes a bargaining cooperative game (BCG) framework for interference-aware power coordination in a HetNet. In particular, a new adjustable utility function is employed in the BCG framework to jointly address the spectral and energy efficiencies as well as to achieve the optimal tradeoff between them. We then derive the closed-form power coordination solutions and further propose an interference-aware power coordination scheme with the considerations of both interference mitigation and energy saving. Finally, the numerical results are provided to illustrate the convergence property and efficiency of the proposed power coordination scheme.

Vertical stacking of banyan networks has been an attractive architecture to construct optical switching networks due to its small depth, absolute signal loss uniformity and good fault tolerance property. Recently, F.K. Hwang extended the study of banyan-based networks to the general f-cast case, which covers the unicast (f = 1) and multicast (f = N) as special cases. In this paper, we study the blocking probability of f-cast optical banyan networks under crosstalk-free constraint. It is expected that the proposed probability model can be used to dimension such an f-cast network and achieve a graceful tradeoff between hardware cost and blocking probability.

Reference Point Group Mobility (RPGM) has been a practical mobility model used to efficiently capture the potential correlation among mobile nodes in many important applications. In this paper, we explore the throughput-delay tradeoff in a mobile ad hoc network (MANET) operating under the RPGM model and also a general setting of node moving speed. In particular, we consider a MANET with unit area and n nodes being divided evenly into Θ(nα) groups, a Є [0,1], where the center of each group moves according to a random direction model with speed no more than v e [0,1]. We determine the regions of per node throughput, average delay and their tradeoffs that can be achieved (in order sense) in such a network. For the regime of v =0, we first prove that the per node throughput capacity is Θ(n−α/2), and then develop a routing scheme to achieve this capacity, resulting an average delay of Θ (max1/2, n1-α) for any α Є [0,1]. Regarding the regime of v > 0, we prove that the per node throughput capacity there can be improved to Θ(1), which is achievable by adopting a new routing scheme with an average delay of Θ(max{n1-α, na/2/v}) for v = o(l) and Θ(n) for v = Θ(1). The results in this paper help us to have a deep understanding on the fundamental performance scaling laws and also enable an efficient throughput-delay tradeoff to be achieved in MANETs with correlated mobility.

Since the seminal work of Grossglauser and Tse [1], the two-hop relay algorithm and its variants have been attractive for mobile ad hoc networks (MANETs) due to their simplicity and efficiency. However, most literature assumed an infinite buffer size for each node, which is obviously not applicable to a realistic MANET. In this paper, we focus on the exact throughput capacity study of two-hop relay MANETs under the practical finite relay buffer scenario. The arrival process and departure process of the relay queue are fully characterized, and an ergodic Markov chain-based framework is also provided. With this framework, we obtain the limiting distribution of the relay queue and derive the throughput capacity under any relay buffer size. Extensive simulation results are provided to validate our theoretical framework and explore the relationship among the throughput capacity, the relay buffer size and the number of nodes.

The explosion of Internet traffic calls for quality of service (QoS)-guaranteed packet transmission in wavelength division multiplexing (WDM) networks with high energy and bandwidth efficiency. Conventional routing and wavelength assignment (RWA) algorithms focus on circuit switching, which does not well meet this requirement due to the bursty nature of IP traffic. Based on a novel traffic matrix decomposition technique, we study the joint design of traffic scheduling and routing in a reconfigurable WDM optical network to improve energy and bandwidth efficiency. Specifically, every node in the network is equipped with a set of parallel tunable lasers, each with a reconfiguration overhead. A dynamic matrix is adopted to model the traffic among the nodes and is decomposed into a set of transmission configurations (i.e., traffic scheduling). The configurations are then fulfilled by tuning the parallel lasers and routing the scheduled traffic under the topology constraint, to achieve loss-free packet transmissions with bounded delay (i.e., QoS guarantee). We reveal that a tradeoff exists between the packet delay and the required number of tunable lasers. The latter is then minimized under a given packet delay to save energy. As far as we know, this is the first work to adopt traffic matrix decomposition in WDM networks to save energy. The proposed framework is validated by extensive simulation studies.

Cloud services based on data center networks (DCNs) require a transmission infrastructure with high-capacity, low-latency, low-cost and high-availability, which can be offered by survivable optical networks. DCN placement is a fundamental issue in supporting cloud services in optical networks. It concerns not only the cost of providing cloud services, but also the service availability against failures via proper service replicas. In this paper, we jointly optimize DCN placement with service routing and protection to minimize the network cost, while ensuring fast protection of all services against any single link failure or service failure at a particular DCN. An ILP (Integer Linear Program) is first formulated to achieve optimal joint design. It integrates p-cycle (preconfigured protection cycle) for fast protection against a single link failure, and DCN replicas and fast service rerouting against a service failure. To make the design more scalable, a two-step heuristic is then proposed for large-size network scenarios. The first step separately solves the DCN placement and service routing problem in the failure-free scenario, and the second step takes fast service protection into account. The proposed design is validated by extensive numerical experiments.

Wireless nano-sensor networks (WNSNs), which consist of nano-sensors a few hundred nanometers in size with the capability to detect and sense new types of events in nano-scale, are promising for many unique applications such as air pollution surveillance. The nano-sensors of WNSNs are highly energy-constrained, which makes it essential to develop energy-efficient communication techniques in such networks. In this paper, we focus on WNSNs employing on-off keying (OOK) modulation, whereby transmission energy minimization corresponds to the minimization of average codeword weight (ACW). We formulate an integer nonlinear programming problem to construct prefix-free codes with minimum ACW under the constraint of average codeword length (ACL) so as to minimize the transmission energy consumption while guaranteeing the throughput larger than a preset desired value. In addition, two efficient algorithms, called binary tree based weight decreasing (BT-WD) algorithm and binary tree based length decreasing (BT-LD) algorithm, are presented for constructing low-ACW prefix-free codes. The effectiveness of the proposed algorithms is verified through simulations and comparisons with the exhaustive search method. Compared with the available fixed-length low-weight codes, the designed prefix-free variable-length codes allow us to not only control the throughput more flexibly but also achieve lower transmission energy consumption in the scenarios with low or medium bit error rates.

Data center networks (DCNs) generally adopt Clos network with crossbar middle switches to achieve non-blocking data switching among the servers, and the number of middle switches is proportional to the number of ports of the aggregation switches in a fixed manner. Besides, reconfiguration overhead of the switches is generally ignored, which may contradict the engineering practice. In this paper, we consider batch scheduling based packet switching in DCNs with reconfiguration overhead at each middle switch, which inevitably leads to packet delay. With existing state-of-the-art traffic matrix decomposition algorithms, we can generate a set of permutations, each of which stands for the configuration of a middle switch. By reconfiguring each middle switch to fulfill multiple configurations in parallel with others, we reveal that a tradeoff exists between packet delay and switch cost (denoted by the number of middle switches), while performance guaranteed switching with bounded packet delay can be achieved without any packet loss. Based on the tradeoff, we can minimize the number of middle switches (under a given packet delay bound) and an overall cost metric (by translating delay into a comparable cost factor), as well as formulating criterions for choosing a matrix decomposition algorithm. This provides a flexible way to reduce the number of middle switches by slightly enlarging the packet delay bound.

Available works either explore the order sense capacity scaling laws or derive closed-form throughput results for mobile ad hoc networks (MANETs) where a transmitter randomly probes only once a neighboring node for possible transmission. Obviously, such single probing strategy may result in a significant waste of the precious transmission opportunities in highly dynamic MANETs since the randomly selected node may already get the packets that the transmitter hopes to deliver. In this paper, we consider a two-hop relay MANET where each transmitter may conduct multiple rounds of probing so as to identify a possible receiver. We first develop closed-form expressions for per node throughput capacity in such probing-based network, with a careful consideration of the time cost taken to probe for an eligible receiver in each time slot. Extensive numerical results are further presented to explore the possible maximum per node throughput capacity, the corresponding optimum setting of probing round limit, and also their relationships with the network control parameters, like the probing time limit, the redundancy limit and the number of users, etc.

Wireless nanosensor networks (WNSNs), which consist of a lot of nanosensors with size of just a few hundred nanometers and are able to detect and sense new types of events at the nanoscale, are promising for a lot of unique applications like intrabody drug delivery systems, air pollution surveillance, etc. One important feature of WNSNs is that the nanosensors are highly energy-constrained, which makes it essential to develop energy efficient protocols for different layers of such networks. This paper focuses on a WNSN with on-off keying (OOK) modulation and explores the problem of transmission energy minimization in it. We first propose a general minimum transmission energy (MTE) coding scheme, which maps m-bit symbols into n-bit codewords with the least number of high-bits and thus results in the lowest energy consumption per symbol for any given m and n. We further determine the optimal setting of symbol length m and codeword length n in the MTE coding scheme so as to achieve the minimum energy consumption per data bit, which serves as the lower bound of transmission energy consumption in such WNSNs. Numerical results are provided to demonstrate the efficiency of the MTE coding scheme.

This paper focuses on the delivery probability performance in a two-hop relay mobile ad hoc network (MANET) with erasure coding. Available works in this line either considered a simple extreme case of achieving the delivery probability 1, or assumed a simple traffic pattern with only one source-destination pair, or studied a very special MANET scenario (i.e., the sparsely distributed MANET) by assuming that whenever two nodes meet together they can transmit to each other. Obviously, such models cannot be applied for an accurate delivery probability analysis in the general MANETs where the interference, medium contention and traffic contention issues are of significant importance. In this paper, a general finite-state absorbing Markov chain theoretical framework is first developed to model the complicated message spreading process in the challenging MANETs. Based on the theoretical framework, closed-form expressions are further derived for the corresponding message delivery probability under any given message lifetime and message size, where all the above important issues in MANETs are carefully incorporated into analysis. As verified through extensive simulation studies, the new framework can be used to accurately predict the message delivery probability behavior and characterize its relationship with the message size, replication factor and node density there.

This paper studies the exact per node throughput capacity of a MANET, where the transmission power of each node can be controlled to adapt to a specified transmission range υ and a generalized two-hop relay with limited packet redundancy f is adopted for packet routing. Based on the concept of automatic feedback control and the Markov chain model, we first develop a general theoretical framework to fully depict the complicated packet delivery process in the challenging MANET. With the help of the framework, we are then able to derive the exact per node throughput capacity for a fixed setting of both υ and f. Based on the new throughput result, we further explore the optimal throughput capacity for any f but a fixed υ and also determine the corresponding optimum setting of f to achieve it. This result helps us to understand how such optimal capacity varies with υ (and thus transmission power) and to find the maximum possible throughput capacity of such a network for any f and υ. Interestingly, our results show that increasing the transmission power of the nodes improves the capacity, which is the same as that proved in fixed networks.

A major obstacle stunting the application of mobile ad hoc networks (MANETs) is the lack of a general throughput capacity theory for such networks. Available works in this area mainly focused on exploring the order sense scaling laws of throughput capacity in MANETs with omnidirectional antennas or that of static ad hoc networks with directional antennas. Although the order sense results can help us to understand the general scaling behaviors, it tells us little about the exact throughput capacity. Another limitation of available works is that the impact of transmission power constraint on the throughput capacity is largely neglected. In most MANET applications, however, the mobile nodes are usually powered by batteries and have limited transmission power. In this paper, we study the exact throughput capacity of MANETs with directional antenna and transmission power constraint, where a generalized twohop relay algorithm with limited packet redundancy is adopted for packet routing. For given transmission power constraint, we first develop a model to map the omnidirectional transmission range to that of the directional one. We then explore the exact throughput capacity under directional transmission and group-based scheduling. Finally, numerical studies are provided to demonstrate the efficiency of these models and validate our theoretical results.

We consider the secure transmission of information over Rayleigh fading wiretap channel when the main and eavesdropper channels are correlated there. Assuming that before transmission the transmitter knows the full channel state information (CSI) of both the main and eavesdropper channels, we analyze the average secrecy capacity with limited signal-to-noise ratio (SNR), for which a simple closed-form expression is derived based on the typical Marcum Q function. This is achieved by exploring the symmetry property between the main channel and eavesdropper channel to avoid a complicated integration involved in the secrecy capacity analysis, such that the secrecy capacity derivation can be significantly simplified. Numerical results are also provided to confirm our analytical ones.

This paper considers the transmission of confidential data over a quasi-static fading wiretap channel where the main and eavesdropper channels are correlated. Assuming that before transmission the transmitter knows the channel state information (CSI) of the main channel, we derive the secrecy outage probability in a closed-form expression based on a new secrecy outage probability formula, which gives a more explicit measure on the level of security compared with the previous one. Remarkably, our results, which cover the corresponding results when the main channel and eavesdropper channels are independent as special cases, reveal that channel correlation has a significant impact on secrecy outage probability and such impact can be helpful or harmful depending on the relative channel conditions and transmission SNR threshold.

This paper focuses on the per node throughput capacity in mobile ad hoc networks (MANETs) with the general group-based two-hop relay algorithm. Under such an algorithm with packet redundancy limit f and group size g (2HR-(f, g) for short), each packet is delivered to at most f distinct relay nodes and can be accepted by its destination if it is a fresh packet to the destination and also it is among g packets of the group the destination is currently requesting. A general Markov chain-based theoretical framework is first developed to characterize the complicated packet delivery process in the challenging MANET environment. With the help of the new theoretical framework, closed-form expressions are further derived for the throughput capacity of the 2HR-(f, g) algorithm, from which one can easily recover the available throughput capacity results by proper settings of the redundancy limit f and group size g.

Due to their simplicity and efficiency, the two-hop relay algorithm and its variants serve as a class of attractive routing schemes for mobile ad hoc networks (MANETs). With the available two-hop relay schemes, a node, whenever getting an opportunity for transmission, randomly probes only once a neighbor node for the possible transmission. It is notable that such single probing strategy, although simple, may result in a significant waste of the precious transmission opportunities in highly dynamic MANETs. To alleviate such limitation for a more efficient utilization of limited wireless bandwidth, this paper explores a more general probing-based two-hop relay algorithm with limited packet redundancy. In such an algorithm with probing round limit τ and packet redundancy limit f, each transmitter node is allowed to conduct up to τ rounds of probing for identifying a possible receiver and each packet can be delivered to at most f distinct relays. A general theoretical framework is further developed to help us understand that under different setting of τ and f, how we can benefit from multiple probings in terms of the per node throughput capacity.

The communication network is now one of the critical infrastructures in our society. However, the current communication networks are facing more and more large-scale region failure threats, such as natural disasters (e.g. earthquake, tornado) and physical attacks (e.g. dragging anchors or EMP attack). Therefore, a deep understanding of network behaviors under region failure is essential for the design and maintenance of future highly survivable networks. In this paper, we focus on the network vulnerability assessment under the geographically correlated region failure(s) caused by a random “line-segment” cut, an important region failure model that can efficiently capture the behaviors of some region failures like earthquake, tornado and anchor cutting. To facilitate such vulnerability assessment, we apply the geometrical probability theory to design a grid partition-based estimation scheme for Disrupted Link Capacity, Pairwise Traffic Reduction and Pairwise Disconnection Probability, three commonly used metrics for statistical vulnerability assessment. A theoretical framework is also established to determine a suitable grid partition such that a specified estimation error requirement is satisfied.

A lot of works have been dedicated towards understanding the relationship between throughput capacity and packet delay in mobile ad hoc networks (MANETs). However, nearly all these works either assume a localized transmission range, or report the relationship between throughput capacity and packet delay only in terms of the number of users. It remains largely unknown for such a fundamental relationship in terms of other network parameters, like the packet redundancy and node transmission range. As a first step towards this end, in this paper we derive closed-from expressions for throughput capacity and delivery delay under a general setting of node transmission range and also a generalized two-hop relay with limited packet redundancy. Extensive numerical results are further provided to explore how throughput capacity varies with delivery delay in terms of various network parameters, such as the number of users, the packet redundancy limit, and the node transmission range, etc.

A lot of work has been done to model and analyze the performances of two-hop relay algorithm and its variants. However, the delivery ratio, especially under limited message lifetime, has been largely neglected in literature, which is not only of significant importance for delay sensitive applications (where a message beyond some delay limit will typically be dropped) but also of practical interests for general MANET scenarios (where mobile nodes are usually both energy-constrained and buffer storage-limited). In this paper, we study the delivery ratio of a generalized two-hop relay with limited message lifetime and redundancy. In particular, a finite-state absorbing Markov chain-based theoretical framework is first developed to model the complicated message delivery process under the considered relay algorithm. Closed-form expressions are then derived for the message delivery ratio under any given message lifetime, where the important interference, medium contention and traffic contention issues are carefully incorporated into analysis. Finally, extensive simulations are conducted to validate the theoretical framework and corresponding delivery ratio results.

The lack of a general capacity theory on mobile ad hoc networks (MANETs) is still a challenging roadblock stunting the application of such networks. The available works on this line mainly focus on deriving order sense results, which are helpful for us to explore the general scaling laws of throughput capacity but tell us little about the exact achievable throughput. This paper studies the exact per node throughput capacity of a MANET, where the transmission power of each node can be controlled to adapt to a specified transmission range v and a generalized two-hop relay with limited packet redundancy f is adopted for packet routing. Based on the concept of automatic feedback control and the Markov chain model, we first develop a general theoretical framework to fully depict the complicated packet delivery process in the challenging MANET environment. With the help of the framework, we are then able to derive the exact per node throughput capacity for a fixed setting of both v and f. Based on the new throughput result, we further explore the optimal throughput capacity for any f but a fixed v and also determine the corresponding optimum setting of f to achieve it. This result helps us to understand how such optimal capacity varies with v (and thus transmission power) and to find the maximum possible throughput capacity of such a network for any f and v. Surprisingly, our results here indicate that usually such maximum throughput capacity can not be achieved through the local transmission, a fact different from what is generally believed in literature.

Many important real networks can be modeled as intermittently connected mobile networks (ICMNs), like the vehicular ad hoc networks, wildlife tracking and habitat monitoring sensor networks, military networks, etc. However, the fundamental performance limits of ICMNs are still largely unknown so far. This paper explores the capability of these networks to support multicast traffic, where each source node desires to send packets to k distinct destinations and all nodes move according to the generalized hybrid random walk mobility model. We show how the network capacity and related delay/delay jitter for supporting multicast in such ICMNs are scaling with the basic network parameters under three transmission protocols: one-hop relay, two-hop relay without packet redundancy and two-hop relay with packet redundancy.

One of the challenging roadblocks stunting the development and commercialization of mobile ad hoc networks (MANETs), is the lack of a thorough understanding of the fundamental performance limits in MANETs. Distinguished from available works which mainly focused on deriving order sense scaling laws of the delay performance in MANETs and usually assumed a localized transmission range, this paper examines the MANET packet delay from a much more detailed perspective. Specifically, we assume for each node a general transmission power control such that the transmission range can be flexibly adapted and adopt a generalized two-hop relay with limited packet redundancy for packet routing. For a tagged traffic flow in the MANET, we first develop a theoretical framework based on two correlated FIFO queues to fully characterize the complicated packet delivery process. Then for any feasible traffic input rate there, we derive closed-form expressions for the corresponding expected end-to-end packet delay. Extensive simulations are further conducted to validate our theoretical results.

This paper examines the optimal forwarding problem in mobile ad hoc networks (MANETs) based on a generalized two-hop relay with limited packet redundancy f (f-cast) for packet routing. We formulate such problem as a forwarding game, where each node i individually decides a probability τi(i.e., a strategy) to deliver out its own traffic and helps to forward other traffic with probability 1-τi, τi∈[0,1], while its payoff is the achievable throughput capacity of its own traffic. We derive closed-form result for the per node throughput capacity (i.e., payoff function) when all nodes play the symmetric strategy profiles, identify all the possible Nash equilibria of the forwarding game, and prove that there exists a Nash equilibrium strategy profile that is strictly Pareto optimal. Finally, for any symmetric profile, we explore the possible maximum per node throughput capacity and determine the corresponding optimal setting of f to achieve it.

All-optical router has been considered as a natural choice to keep pace with growing fiber link capacity. One main research issue of all-optical router is the design of optical queues with the same flexibility as their electronic counterparts, and some recent works have proved the feasibility of using optical switches and fiber delay lines (SDL) to emulate the electronic queues. In this paper, we focus on the SDL-based construction of N -to- N shared optical queue, a more efficient queue structure in comparison with the dedicated input and output queues. The construction we consider consists of a crossbar switch of size (N + M) × (N + M), where N inputs (outputs) are reserved for external arrivals (departures), and M fiber delay lines are connected from the remaining M outputs back to the remaining M inputs. We first show that by setting the length riof fiber delay line i as ri= 1 + [(1 - 1) mod N], i = 1, . . . M, and scheduling packets properly among these delay lines, such a construction can work as a non- idling first in first out (FIFO) shared queue of size B = Σi=1Mri. We further extend our work to the design of more general shared buffer, where the packets can be stored for an arbitrary time and may depart in a non-FIFO order.

The available two-hop relay protocols with out-of-order or strictly in-order reception cannot provide a flexible control for the packet delivery delay, which may significantly limit their applications to the future mobile ad hoc networks (MANETs) with different delay requirements. This paper extends the conventional two-hop relay and proposes a general group-based two-hop relay algorithm with packet redundancy. In such an algorithm with packet redundancy limit$f$and group size$g$(2HR-$(f,g)$for short), each packet is delivered to at most$f$distinct relay nodes and can be accepted by its destination if it is a fresh packet to the destination and also it is among$g$packets of the group the destination is currently requesting. The 2HR-$(f,g)$covers the available two-hop relay protocols as special cases, like the in-order reception ones$(f\geq 1,g=1)$, the out-of-order reception ones with redundancy$(f>1,g=\infty)$, or without redundancy$(f=1,g=\infty)$. A Markov chain-based theoretical framework is further developed to analyze how the mean value and variance of packet delivery delay vary with the parameters$f$and$g$, where the important medium contention, interference, and traffic contention issues are carefully incorporated into the analysis. Extensive simulation and theoretical results are provided to illustrate the performance of the 2HR-$(f,g)$algorithm and the corresponding theoretical framework, which indicate that the theoretical framework is efficient in delay analysis and the new 2HR-$(f,g)$algorithm actually enables both the mean value and variance of packet delivery delay to be flexibly controlled in a large region.

Due to their simplicity and efficiency, the two-hop relay algorithm and its variants serve as a class of attractive routing schemes for mobile ad hoc networks (MANETs). With the available two-hop relay schemes, a node, whenever getting an opportunity for transmission, randomly probes only once a neighbor node for the possible transmission. It is notable that such single probing strategy, although simple, may result in a significant waste of the precious transmission opportunities in highly dynamic MANETs. To alleviate such limitation for a more efficient utilization of limited wireless bandwidth, this paper proposes a more general probing-based two-hop relay algorithm with limited packet redundancy. In such an algorithm with probing round limit τ and packet redundancy limit f, each transmitter is allowed to conduct up to τ rounds of probing for identifying a possible receiver and each packet can be delivered to at most f distinct relays. A general theoretical framework is further developed to help us understand that under different setting of τ and f, how we can benefit from multiple probings in terms of the per node throughput capacity and the expected end-to-end packet delay.

Among the "store-carry-forward" kind of protocols, the two-hop relay and its variants have become a class of attractive routing protocols for the mobile ad hoc networks (MANETs) due to its efficiency and simplicity. This paper focuses on the performance modeling for two-hop relay with erasure coding, a promising technique for improving the delay performance of conventional two-hop relay with simple replication. A general Markov chain-based theoretical framework is first developed to model the complicated message delivery process in such a network, based on which not only the mean value but also the variance of message delivery delay are derived analytically. The important medium contention, interference and traffic contention issues are carefully incorporated into our analysis, so the new theoretical framework can be used to precisely predicate the message delivery delay performance of two-hop relay with erasure coding, as verified by extensive simulation results.

Two-hop relay is a class of attractive routing protocols for mobile ad hoc networks (MANETs) due to its efficiency and simplicity. This paper extends the conventional two-hop relay and proposes a more general group-based two-hop relay algorithm with redundancy. In such an algorithm with redundancy f and group size g (2HR-(f, g) for short), each packet is delivered to at most f distinct relay nodes and can be accepted by its destination if it is among the group of g packets the destination is currently requesting. The 2HR-(f, g) covers the available two-hop relay protocols as special cases, like the in-order protocols (f ≥ 1, g = 1), the out-of-order protocols with redundancy (f >; 1, g = ∞) or without redundancy (f = 1, g = ∞), and it enables a more flexible control of packet delivery process to be made in the challenging MANET environment. A general theoretical framework is further developed to explore how the control parameters f and g affect the expected packet delivery delay in an 2HR-(f, g) MANET, where the important medium contention, interference and traffic contention issues are carefully incorporated into the analysis. Finally, extensive simulation and theoretical results are provided to demonstrate the efficiency of the 2HR-(f, g) scheme and the corresponding theoretical framework.

The lack of optical buffer is still one of the main problems that hinder the development of all optical networks. One approach to this problem is to emulate the behavior of optical buffers by using optical switches and fiber delay lines (SDL). Current works on this topic have demonstrated the feasibility of constructing SDL-based First In First Out (FIFO) buffer, Priority buffer, etc. The Last In First Out (LIFO) buffer is another important network component for congestion control and QoS guarantee, and parallel and cascade architectures have been peoposed for the efficient design of such optical buffer. The recent work in showed that it is possible to use M fiber delay lines (FDLs) to construct a LIFO buffer of size B = (3/2) · 2M/2- 1 and B = 2(M+1)/2- 1 when M is even and odd, respectively. In this paper, we improve the work in [3] by providing a more efficient construction of SDL-based optical LIFO buffer. We first show that with a single stage feedback structure consisted of one (M + 1) × (M + 1) crossbar switch and M FDLs connecting M outputs of the crossbar back to M its inputs, we are able to construct a LIFO buffer of size B = 2 · 2M/2- 2 and B = (3/2) · 2(M+1)/2- 2 when M is even and odd, respectively. This is achieved through adopting a properly delay length setting for each FDL and a careful packets scheduling among FDLs, as well as exploiting the nice function of simultaneous packet reading and witting a FDL can support. We further show that if we adopt a cascade of smaller switches rather than a single (M+1)×(M+1) big switch, the new LIFO design can be implemented with much lower complexity in terms of the total number of basic 2 × 2 switch elements.

The mission critical network infrastructures are facing potential large region threats, both intentional (like EMP attack, bomb explosion) and natural (like earthquake, flooding). The available research on region failure related vulnerability studies generally adopt a kind of simple “deterministic” region failure models, which can not capture some important features of real region failure scenarios, where a network component in the region only fails with certain probability, and more importantly, such failure probability tends to vary with both its dimension and its distance to failure center. In this paper, we provide a more general “probabilistic” region failure model to capture the key features of a region failure and apply it for the network vulnerability assessment. To facilitate such assessment, we adopt a grid partition-based scheme to estimate various statistical network metrics under a random region failure. A theoretical framework is also established to determine a suitable grid partition such that a specified estimation error requirement is satisfied. The grid partition technique is also useful for identifying the vulnerable zones of a network, which can guide network designers to initiate proper network protection against such failures. The work in this paper helps us more deeply understand the network vulnerability behavior under region failure and facilitates the design and maintenance of future highly survivable mission critical networks.

The 2-hop relay algorithm and its variants have been attractive for ad hoc mobile networks, because they are simple yet efficient, and more importantly, they enable the capacity and delay to be studied analytically. This paper considers the 2-hop relay with f-cast (2HR-f) under i.i.d. mobility model, a general 2-hop relay algorithm that allows one packet to be delivered to at most f distinct relay nodes. The 2HR-f algorithm covers the available 2-hop relay algorithms (f = 1,√n) as special cases. Closed-form analytical models rather than order sense ones are developed for the 2HR-f algorithm with a careful consideration of important medium contention and queuing delay issues, which enable an accurate delay and capacity analysis to be performed for ad hoc mobile networks employing 2HR-f. Based on our models and some typical settings of f (say, f = 1,√n), one can easily derive the corresponding order sense results.

The simple and cheap memory-less RFID tag systems have found many diverse applications. The available singulation algorithms for such systems adopt either single-slot or multi-slot frames with a fixed frame size, independent of tag population. A single-slot scheme has good performance in terms of the number of overall slots N, but it can cause a very large number of requests R. A multi-slot scheme, on the other hand, achieves good performance of R, but it may introduce an unacceptable large N. In this paper, we propose an adaptive frame size singulation scheme for memory-less RFID systems. Our basic idea is to adaptively choose a suitable frame size based on tag population information collected during the singulation, such that the number of unnecessary collision and idle slots can be reduced. Analytical models are also derived for the performance analysis of the new scheme. Surprisingly, our theoretical and simulation studies indicated that through adopting such adaptive frame size, the new singulation scheme can achieve a performance of N as good as the single-slot scheme, and at same time, guarantees a performance of R similar to the available multi-slot schemes.

The simple and cheap passive RFID tag systems have recently been used for efficient localization of indoor mobile robots, where each RFID tag stores its own absolute position and the mobile robot carrying an RFID reader scans the RFID tags to localize itself. The available localization schemes using passive RFID systems do not consider the scanning delay which may cause location estimation error especially when the robot moves with a high speed. In this paper, a new Non-Blocking scanning (reading) scheme is proposed to avoid collisions such that the scanning delay and consequently the localization error can be reduced. This scheme avoids collision among tags replies by assigning tags IDs based on the FCA coloring scheme. Theoretical and simulation studies indicate that the new Non-Blocking scheme combined with the new tag arrangement pattern can achieve a good RFID localization performance in terms of both estimation error and scanning delay.

The lack of optical buffer is still one of the main problems that hinder the development of all optical networks. Current works on this topic mainly focus on the emulation of optical buffers based on a combination of fiber delay line (FDL) and switch. These works have demonstrated the feasibility of FDL-based emulation for many kinds of optical buffers, like the First In First Out (FIFO) buffer, Priority buffer, etc. The Last In First Out (LIFO) buffer is another basic network component for congestion control and QoS guarantee. Recently, Huang et al. introduced a recursive construction for the LIFO buffer, which requires no less than 9 log2B FDLs to build such a buffer of size B. In this paper, we first show that by a proper FDL grouping and a suitable FDL length assignment for each FDL-group, we need approximately 3 log2B FDLs to emulate a LIFO buffer of size B. We then demonstrate that if a careful packet scheduling among FDL-groups is adopted, this number of FDLs can be further reduced to 2 log2B.

The two-hop relay algorithm and its variants have been attractive for ad hoc mobile networks, because they are simple yet efficient, and more importantly, they enable the capacity and delay to be studied analytically. This paper considers a general two-hop relay with f-cast (2HR-f), where each packet is delivered to at most f distinct relay nodes and should be received in order at its destination. We derive the closed-form theoretical models rather than order sense ones for the 2HR-f algorithm with a careful consideration of the important interference, medium contention, traffic contention and queuing delay issues, which enable an accurate delay and capacity analysis to be performed for an ad hoc mobile network employing the 2HR-f. Based on our models, one can directly get the corresponding order sense results. Extensive simulation studies are also conducted to demonstrate the efficiency of these new models.

Mobile Ad Hoc networks (MANETs) is composed of mobile wireless nodes that are self-organized. The infrastructureless and dynamic nature of these networks demand very efficient routing strategies to be implemented in order to provide reliable end-to-end communication. Different routing protocols have been proposed in literature, but all of them are restricted to certain topology and scale assumptions or applicable only in presence of low mobility. However, as in Ad Hoc networks the network is set up on the fly, and as it might be applied to high mobility scenarios such as vehicular communication the need of a topology and mobility independent routing scheme is crucial. In this paper, we introduce a new routing scheme for MANETs, which has the ability to work efficiently under different network topology: nodes-density and coverage area size under a high nodes-mobility unlike all the available routing schemes that assume a limited setting of those factors. Instead of broadcasting extensive control packets for network topology discovery, the proposed scheme reuses the already allocated feedback information carried in unicast packets for the routing process without introducing any extra overhead. The conducted simulations-based analysis demonstrate that the proposed scheme can significantly enhance the routing process.

The integration of Ethernet Passive Optical Networks (EPONs) and IEEE 802.16 (WiMAX) has been lately presented as a promising fiber-wireless (FiWi) broadband access network. Conversely, lightweight layer-2 virtual private networks (VPNs) over FiWi, which can provide bandwidth guarantee to the respective users, were only recently addressed by Dhaini et. al. In this paper, WiMAX-VPON, the framework proposed by Dhaini et. al to support layer-2 VPNs over EPON-WiMAX, is improved to take into account the polling control overhead when distributing the VPN bandwidth. A new generic analytical model is also presented to evaluate the performance of each registered VPN service. Our proposed model, which can also be used to analyze any polling-based FiWi network, applies for wireless and optical domains and provides performance measurements such as packet queuing delay, end-to-end (from wireless user to optical server) packet delay and average queue size. Numerical results are compared with simulation experiments, and show consistency between both outcomes.

This paper analyzes the loss process distribution of a finite buffer queue. In contrast to the previous work that assumed the buffer can merely store finite number of packets, our model adopts the bounded delay policy where only the packet arrival finding its delay not exceeding a preset value is admitted into the buffer. The quantity of interest is the probability distribution of the number of lost packets within a block of n consecutive packet arrivals, which is an important measure for the design of communication networks, e.g., the forward error correction (FEC). We derive a set of recursive equations to compute the above quantity for various packet size distributions. We then focus on the influence of adding redundant packets on loss probability of message block and FEC efficiency. The impacts of bounded delay, packet size distribution and traffic load are also evaluated. We demonstrate a unique property of the finite queue with bounded delay, which is different from that of the conventional finite queue (e.g., M/G/1/K queue).

The trade-off between resource efficiency and Quality of Service (QoS) is always a vital issue for communication networks, and link overbooking is a common technique used to improve resource efficiency. How to properly overbook a link and analytically determine its overbooking factor under QoS constraints are still problems, especially when achieving advanced QoS by per-flow queueing, as urged by the emerging mobilized applications in the access networks. This paper first proposes an Opportunistic Link Overbooking (OLO) scheme for an edge gateway to improve its link efficiency, and then develops an integrated analytical framework for determining the suitable link overbooking factor with service guarantee on flow level. In our scheme, once the idle time of a high priority flow's quasi-dedicated link is larger than a specified threshold, the link is temporarily overbooked to a low priority flow; and then when the high priority flow's subsequent packets start arriving, the link can be recovered at the expense of a setup delay. To explore the balance between link efficiency and the flow's QoS in the proposed scheme, we develop the corresponding queueing model under either bounded packet delay (relevant to delaysensitive flow) or finite buffer size (relevant to loss-sensitive flow). Our queueing analysis reveals the inherent trade-offs among the link overbooking factor, packet loss rate and delay/jitter under different traffic patterns.

We consider the lifetime optimization problem for multicasting in wireless ad hoc networks, in which each node is equipped with a directional antenna and has limited energy supplies. Several distributed algorithms proposed recently are especially beneficial to a resource-constrained wireless ad hoc network. In this paper, we propose a new distributed algorithm and investigate its theoretical performance compared to existing distributed algorithms. We use a graph theoretic approach to obtain the upper bound of the approximation ratio for a group of distributed algorithms. In particular, the derived upper bound in a closed form for each algorithm provides a sufficient condition to determine if the obtained solutions can reach optimum. Both theoretical and experimental performance analysis show that the new algorithm outperforms other proposals in terms of providing long-lived multicast tree.

Reliable multicast, the lossless dissemination of data from one sender to a group of receivers, has a wide range of important applications like software update and dissemination of stock quotes. Recently, network coding has been applied to the reliable multicast in wireless networks, where the sender encodes multiple lost packets together into one packet and uses a single retransmission to potentially recover multiple packet losses, resulting in a significant reduction of band-width consumption. In this paper, we provide a review of recent research works in this area, examine their advantages and limitations, and also present some open research challenges need to be addressed in the future.

The complexity of an interconnection network often determines the size of the parallel computer and thus the attainable performance of a parallel computer is limited by the characteristics of the interconnection network. Pruning technique reduces the complexity and hence increases the performance. In this paper, we apply the pruning technique on hierarchical torus network (HTN) and study the architectural details of the pruned HTN. We have explored the network diameter, average distance, bisection width, peak number of vertical links, and VLSI layout area of different HTN. It is shown that the pruned HTN possesses several attractive features including small diameter, small average distance, small number of wires, a particularly small number of vertical links, and economic layout area as compared to its non-pruned counterpart.

Optical buffering is fundamental to contention resolution in optical networks. The current works on this line mainly focus on the emulation of dedicated input/output buffer queue by using switched fiber delay lines (SDL). It is notable that the shared buffer queue, where a common buffer pool is shared by all the input/output ports of a switch, has the potential to significantly reduce the overall buffer capacity requirement. As far as we know, however, no related work is available yet on the exact emulation of a shared optical buffer queue with SDLs. In this paper, we focus on the design of first in first out (FIFO) shared optical buffer queue based on the optical feedback SDL construction. The construction considered consists of an (M + 2) x (M + 2) switch fabric and M fiber delay lines FDL1, . . ., FDLM, where FDLiconnects the ithoutput of the switch fabric with its ithinput. We show that by setting the length of FDL1as min(M + 1 - i, i), i = 1, . . . , M, such a construction can actually work as an 1-to-2 shared buffer queue. We then extend this emulation to the more general N-to-2 case.

Volunteer computing is very promising to build large scale parallel computing systems from enormous number of computers over the Internet. In a volunteer computing system, sabotage-tolerance is an important issue because there may be malicious users on the Internet who sabotage system by intentionally submitting erroneous results. In this paper, we consider the task scheduling problem of volunteer computing systems which implement sabotage-tolerance mechanism. Although existing sabotage-tolerance mechanisms can guarantee the requirement of credibility for computing results, however, such mechanisms always cause a high performance slowdown in terms of overall execution time. In this paper, we propose an efficient scheduling mechanism called Priority Round Robin (PRR) that takes into account the computing capacity of each volunteer computer. By grouping volunteer computers that have similar computing capacity, the PRR scheduling mechanism can help to reduce overall execution time in comparision with the conventional Round Robin (RR) scheduling, as shown by our extensive simulation results.

Shared-memory optical packet (SMOP) switch architecture is very promising for significantly reducing the amount of required optical memory, which is typically constructed from fiber delay lines (FDLs). The current reservation-based scheduling algorithms for SMOP switches can effectively utilize the FDLs and achieve a low packet loss rate by simply reserving the departure time for each arrival packet. It is notable, however, that such a simple scheduling scheme may introduce a significant packets out of order problem. In this paper, we first identify the two main sources of packets out of order in the current reservation-based SMOP switches. We then show that by introducing a "last-timestamp " variable and modifying the corresponding FDLs arrangement as well as the scheduling process in the current reservation-based SMOP switches, it is possible to keep packets in-sequence while still maintaining a similar delay and packet loss performance as the previous design.

We derive conditions which are both necessary and sufficient for the d-ary multi-log switching networks to be f-cast strictly nonblocking under all combinations of fanout and crosstalk constraints. The fanout constraint tells us which stage(s) of the networks has fanout capability. The crosstalk constraint tells us whether or not two routes are allowed to share a link, or are allowed to share a switching element (crosstalk-free or not). The most novel contribution of this paper is the analytical technique, which combines an algebraic view of the d-ary multi-log network with the max-flow min-cut theorem. Our results are more general than previously known results on several fronts: (a) d-ary networks are more general than binary networks, (b) f-cast covers both unicast (f = 1) and broadcast (f = N), (c) both link-blocking and node-blocking are considered in a unified manner, and (d) all combinations of fanout constraints are considered.

Effective support of VoIP over Wireless LAN (WLAN) remains a crucial challenge for the last-mile wireless coverage of IP networks with mobility support. Due to the limited bandwidth available in a WLAN, an accurate analysis of voice capacity in such a network is critical for the efficient usage of WLAN's resources. The available upper or lower bound models on voice capacity may significantly overestimate or underestimate a WLAN's capacity to support VoIP, thus they are not suitable for above purpose. In this paper, we focus on the voice capacity analysis of a single wireless 802.11(a/b) network cell running the distributed coordination function (DCF). In particular, by taking into account the spatial distribution of clients, we propose a more accurate analytical model to estimate the average voice capacity of such a network cell. We further show that by properly exploring the clients' spatial distribution information in allocating the access points, we may be able to increase the overall voice capacity. The efficiency of our new voice capacity model and new access point allocation scheme is validated through simulation and comparisons with available ones.

A new packet-forwarding architecture, COPE [1], was proposed recently to demonstrate that by properly exploiting the network coding and physical-layer broadcast properties, the throughput of multihop wireless networks may be significantly improved. However, the theoretical framework is not available yet for a rigorous throughput study of COPE. As the first step toward this direction, in this paper we conduct an analytical analysis on coding opportunities that COPE can create in a multihop wireless network. For a given node, we first derive the probability density function (pdf) of overhearing probability between its two neighbor nodes. Then, based on the pdf of overhearing probability we further analyze the probability of encoding multiple packets together at the node. This work not only provides a framework for the node-level performance analysis of COPE but also lays a foundation for the further network-level performance analysis of COPE.

Multi-log2N networks (or vertically stacked banyan networks) have been an attractive class of switching networks due to their small depth O(log N), absolute signal loss uniformity and good fault tolerance property. Recently, F.K.Hwang extended the study of multi-log2N networks to the general f-cast case, which covers the unicast case (f = 1) and multicast case (f = N) as special cases, and determined the conditions for these networks to be f-cast strictly nonblocking when the fan-out capability is available at both the input stage and middle banyan stage. In this paper, we study the rearrangeable f-cast multilog2N networks under both node-blocking scenario (relevant to photonic switches) and link-blocking scenario (relevant to electronic switches). In particular, we consider the following three fan-out cases in our study: (1) no restriction on fan-out capability; (2) input stage has no fan-out capability; (3) middle banyan stage has no fan-out capability. We determine the necessary conditions for the first two cases while obtaining the necessary and also sufficient condition for the third one.

It is anticipated that a large amount of multicast traffic needs to be supported in future communication networks. The network coding technique proposed recently is promising for establishing multicast connections with a significantly lower bandwidth requirement than that of traditional Steiner-tree-based multicast connections. How to design multicast network topologies with the consideration of efficiently supporting multicast by the network coding technique becomes an important issue now. It is notable, however, that the conventional algorithms for network topology design are mainly unicast-oriented, and they cannot be adopted directly for the efficient topology design of network-coding-based multicast networks by simply treating each multicast as multiple unicasts. In this paper, we consider for the first time the novel topology design problem of network-coding-based multicast networks. Based on the characteristics of multicast and network coding, we first formulate this problem as a mixed-integer nonlinear programming problem, which is NP-hard, and then propose two heuristic algorithms for it. The effectiveness of our heuristics is verified through simulation and comparison with the exhaustive search method. We demonstrate in this paper that, in the topology design of multicast networks, adopting the network coding technique to support multicast transmissions can significantly reduce the overall topology cost as compared to conventional unicast-oriented design and the Steiner-tree-based design.

Current implementations of multi-hop wireless networks suffer from a severe throughput limitation and do not scale well with an increasing number of nodes. A promising architecture COPE [12], which exploits the physical-layer broadcast property and network coding technique, was recently proposed to significantly improve the throughput of multi-hop wireless networks. In this paper, we will improve the packet coding scheme in COPE to further reduce the number of bytes transmitted by a network node for forwarding its incoming packets to the respective neighbors. We first propose a more general packet coding framework, which covers the one in COPE as a special case and can offer us more coding opportunities. We then formulate the optimal packet coding problem under this general coding framework as an integer programming problem, and prove that it is NP-complete. Finally, we present an efficient algorithm to find the optimal coding solution for the proposed general packet coding framework.

Future communication networks should be designed with the consideration of efficiently supporting intensive multicast applications. Network coding technique proposed recently is promising for implementing multicast transmissions with low bandwidth requirement. This paper concerns the novel topology design problem of network coding-based multicast networks, and proposes an improved heuristic algorithm for it by adopting a new cost efficiency (CE) metric for link removal and introducing a local optimization in the design process. The effectiveness of the new heuristic is demonstrated through extensive simulations and comparisons with both the available heuristic and the exhaustive search method. The results in this paper also clearly indicate that applying the novel network coding technique in a multicast network can significantly reduce the overall topology cost.

Load balance (LB) switch architecture is attractive for building high speed switches since it does not require a centralized scheduler and still can guarantee 100% throughput under any admissible traffic. It is notable, however, that due to the multi-path property of LB switches, the packet out-of-sequence problem may happen in such switches. Several schemes have been proposed to tackle the above problem, but these schemes either require infinite central buffer or introduce a high average packet delay. In this paper, we propose a new LB switch architecture - central buffer one-packet-crosspoint (CBX-1). The key idea ofCBX-1 is to introduce a VIOQ (virtual input output queue) with capacity one (i.e., it can store only one packet) after the first stage of a LB switch to emulate a CIXB-1 switch (combined input-one-packet-crosspoint buffered switch). We show through both analysis and simulation that although our architecture requires only finite central buffer to tackle the packet out-of-sequence problem, it still guarantees 100% throughput and achieves a good delay performance.

Active restoration (AR) is a novel lightpath restoration scheme proposed recently to guarantee a certain degree of survivability in wavelength-division multiplexing (WDM) optical networks with a reasonable trade-off between capacity requirement and restoration time. In this paper, we conduct a comprehensive performance analysis for AR-based optical networks. In particular, we propose a novel analytical framework for modeling the restoration probability of a connection (the probability that the connection can be successfully restored in case of a failure) when the possible correlation among its multiple backup routes is incorporated. Although theoretically, we need to consider all the possible correlations between as many as Q) pairs of backup routes to analyze the restoration probability in a network with N nodes, and this high computation complexity may obscure the practicality of an approach, considering all the possible correlations among backup routes, our analysis in this paper indicates that by considering at most the possible correlations among any three successive backup routes of a connection, we can achieve a very good approximation to the simulated restoration probability of the connection, as verified by extensive simulation results upon two typical network topologies under various workloads. We find that the proposed framework can deeply investigate into the inherent relationship among restoration probability, wavelength channel utilization ratio, number of wavelengths per fiber, routes hop length, and wavelength conversion capability. As a result, the framework significantly contributes to the related areas by providing network designers with a quantitative tool to evaluate the restoration probability and, thus, the survivability of AR-based optical networks.

The future communication networks should have a good capability to support the rapidly growing multicast applications. It is notable, however, that the conventional algorithms for network design are mainly unicast-oriented, and they can not be adopted directly for the efficient topology design of multicast-capable networks by simply treating each multicast as multiple unicasts. The network coding technique proposed recently has the potential to efficiently support multicast transmissions with lower bandwidth requirement. In this paper we study the network-coding based network topology design problem with the consideration of efficiently supporting multicast traffic. Based on the characteristics of multicast and network coding, we first formulate this problem as a nonlinear integer programming problem, which is NP-hard. We then propose a heuristic algorithm for it. The efficiency of our algorithm is demonstrated by extensive simulation results under different traffic patterns. We conclude that our network-coding based topology design algorithm can be used to design multicast-capable networks with significantly lower cost than that of conventional unicast-oriented algorithms.

The evolution of VLSI chips towards larger die size, smaller feature size and faster clock speed makes the clock distribution an increasingly important issue. In this paper, we propose a new clock distribution network (CDN), namely Variant X-Tree, based on the idea of X-Architecture proposed recently for efficient wiring within VLSI chips. The Variant X-Tree CDN keeps the nice properties of equal-clock-path and symmetric structure of the typical H-tree CDN, but results in both a lower maximal clock delay and a lower clock skew than its H-tree counterpart, as verified by an extensive simulation study that incorporates simultaneously the effects of process variations and on-chip inductance.

Active restoration (AR) is a novel lightpath restoration scheme proposed recently for guaranteeing a certain degree of survivability in WDM optical networks with a reasonable tradeoff between capacity requirement and restoration time. An analytical model has been proposed to understand the restoration probability behavior of a connection request in optical networks employing AR based on the assumption that all the backup routes of the connection are independent. In a real AR-based optical network, however, the backup paths of a connection are likely correlated since they may share some common links along their routes. As the first step toward the restoration probability analysis incorporating the correlation among backup paths of a connection in AR-based networks, we propose in this paper an analytical approach to modeling the restoration probability of the connection by considering all the possible correlation between any two of its successive backup paths. Compared to the old restoration models without considering the correlation among backup paths, the proposed new model can significantly improve the accuracy in estimating the restoration probability for AR-based networks, as verified by extensive simulation results based on two typical backbone network topologies.

Additive Increase Multiplicative Decrease (AIMD) window adjustment mechanism has been embedded in TCP in order to regulate the transmission rate in modern communication networks. In recent years, the AIMD (1,0.5) traffic regulation mechanism along with possibly additional enhancements, such as false timeout detection and explicit notification, has been considered in the carriers with Optical Burst Switching (OBS) as the underlying transmission technology. This paper introduces a novel rate control mechanism based on Generalized AIMD (α,β), called Burst AIMD (BAIMD), for tuning the rate control parameters (α, β) at each sender. BAIMD is designed to improve throughput while maintaining friendliness with co-existing AIMD (1,0.5) flows, and is characterized in the following two folds: (1) no burst window is required in the TCP sender's level; (2) no explicit notifications are required. The above characteristics make the proposed scheme distinguished from all the past reported counterparts by minimizing the signalling efforts and control complexity. The simulation result shows that BAIMD can solidly outperform the past reported AIMD-based (1,0.5) rate control schemes under a wide range of traffic loads. We also suggest that BAIMD rate control mechanism may serve as a better choice than AIMD (1,0.5) in the bufferless OBS networks due to its dynamic and flexible (α,β) parameter pair.

Banyan networks are attractive for serving as the optical switch architectures due to their nice properties of small depth and absolutely signal loss uniformity. Combining the horizontal expansion and vertical stacking of optical banyan networks is a general scheme for constructing banyan-based optical switching networks. The resulting horizontally expanded and vertically stacked optical banyan (HVOB) networks usually take either a high hardware cost or a large network depth to guarantee the nonblocking property. Blocking behavior analysis is an effective approach to studying network performance and finding a graceful compromise among hardware cost, network depth, and blocking probability; however, little has been done to analyze the blocking behavior of general HVOB networks. In this paper, we study the overall blocking behavior of general HVOB networks, where an upper bound on the blocking probability of a HVOB network is developed with respect to the number of planes (stacked copies) and the number of stages. The upper bound accurately depicts the overall blocking behavior of a HVOB network as verified by an extensive simulation study, and it agrees with the strictly nonblocking condition of the network. The derived upper bound is significant because it reveals the inherent relationship among blocking probability, network depth, and network hardware cost, so that a desirable tradeoff can be made among them. In particular, our bound gives network developers an effective tool to estimate the maximum blocking probability of a HVOB network, in which different routing strategies can be applied with a guaranteed performance in terms of blocking probability, hardware cost and network depth. Our upper bound model predicts some unobvious qualitative behaviors of HVOB networks, and it draws an important conclusion that a very low blocking probability (e.g., less than 0.001 percent) can be achieved in a HVOB network without introducing either a significantly high hardware cost or a large network depth.

It is observed that the singular value decomposition (SVD) transformation based on min-plus algebra (or called tropical semi-rings) leads to a very good characteristic in zero underestimating the reconstructed matrix. This paper introduces a novel distributed control framework for shared protection in optical networks with reduced routing information based on the tropical semi-rings technique, called sharing with reduced information with tropical semi-rings (SRI-TROP). The design of the proposed framework aims to initiate a compromise between the amount of link-state dissemination and the performance impairment due to the incompleteness of routing information, such that the precision in the link-state matrix reconstruction can efficiently map to the reduction in blocking probability. Based on the framework, a series of novel schemes are proposed, which are verified and compared with the reported counterparts in a simulation. The simulation results show that the performance in terms of the precision in the reconstructed link-state and the resultant blocking probability can be significantly improved.

This paper proposes a novel framework of bandwidth provisioning based on optical burst switching (OBS), called optical flooding cluster switching (OFCS), which is developed to achieve a better resource allocation and efficiency by fully exploiting the potential characteristics of data-dominated traffic with a high self-similarity and burstiness in the modern communication networks. The concept of flooding clusters is first defined, which serves as basis of the study. The design objectives and the working principles of the OFCS scheme are introduced, where the corresponding advantages against the pure OBS, pure OCS (optical circuit switching), and the hybrid OBS/OCS architectures, are discussed. A comprehensive analytical model on the burst drop rate is formulated for the proposed scheme. To verify the analytical model and compare with the other counterparts, extensive simulation efforts have been addressed. The results reveal that OFCS can overcome the non-predictiveness of traffic self-similarity, where the flooding clusters are set up for a partial prediction of the burst arrival. We conclude that the flooding effect of data-dominated traffic can be successfully smoothed out by the proposed OFCS scheme

Horizontally expanded and vertically stacked optical banyan (HVOB) is a general architecture for constructing banyan-based optical switches. Blocking analysis is an effective approach to studying network performance and finding a graceful compromise among hardware cost, network depth and blocking probability; however, little has been done on analyzing the blocking behavior of general HVOB networks. In this paper, we study the overall blocking behavior of a HVOB network, where an upper bound on the blocking probability of the network is developed. The upper bound depicts accurately the overall performance behavior of a HVOB network as verified by extensive simulation results and it agrees with the strictly nonblocking condition of the network. The derived upper bound is significant because it reveals the inherent relationship among blocking probability, network depth, and network hardware cost, by which a desirable tradeoff can be made among them. In particular, our bound provides network developers an effective tool to estimate the maximum blocking probability of a HVOB network in which different routing algorithms can be applied with a guaranteed performance in terms of blocking probability, hardware cost and network depth. An important conclusion drawn from our work is that the hardware cost of HVOB networks can be reduced dramatically without introducing either significantly high blocking probability or a large network depth.

The scheme of vertical stacking has caught much interest in the design of ultra high-speed communication switches for the past a few years. In particular, the scheme can greatly facilitate the effort of constructing all-optical photonic switches in the event that a banyan network structure is adopted. A vertically stacked photonic banyan (VSPB) network can preserve the good properties of the banyan network structures, such as the small depth and absolute loss uniformity; on the other hand, it introduces a significant increase in the hardware cost. Extensive research efforts have been addressed in determining the minimum number of stacked copies (planes) required for a nonblocking VSPB network. However, very few of them focused on the performance of the VSPB networks in terms of blocking probability. Therefore, in this paper, we study the blocking behavior of the VSPB networks and propose a corresponding analytical model under the random routing strategy. The proposed analytical model is designed to fully explore the property of symmetry in banyan network structures, and can calculate the blocking probability of a VSPB network stage by stage in a recursive manner such that the combinatorial explosion problem is avoided. To verify the proposed model, we conduct extensive simulations, in which the results indicate that our model can accurately describe the blocking behavior of VSPB networks under the random routing strategy and it agrees with the conditions of strictly nonblocking VSPB networks. We find that the proposed analytical model can deeply investigate into the inherent relationship between blocking probability and network hardware cost in terms of the number of planes; as a result, a quantitative guidance for initiating a graceful compromise between blocking probability and hardware cost can be developed based on the analytical model. Our analysis results also show that the hardware cost of a VSPB network can be dramatically reduced by simply allowing a negligible nonzero blocking probability in most of the practical cases. This fact will solidly contribute to the network switch architecture design and enable more practical applications of VSPB networks.

The paper proposes a novel distributed control architecture for shared protection with reduced complete routing information, which aims to initiate a graceful compromise between the amount of link-state dissemination and the performance impairment due to the incompleteness of routing information. We first give explicit and comprehensive descriptions on a number of reported routing information dissemination scenarios for shared protection. A novel framework of link-state dissemination for facilitating shared protection, called reduced complete routing scenario, is introduced, in which the singular value decomposition (SVD) transformation is adopted to deal with the information reduction. We show, through simulation, that the proposed scheme can achieve a higher throughput and a better estimation in reconstruction of the spare provision matrix than the other schemes taking the same complexity of link-state dissemination.

Vertical stacking of optical banyan networks is an attractive scheme for building nonblocking (crosstalk-free) optical switching networks. The resulting networks, namely vertically stacked optical banyan (VSOB) networks, preserve all the good properties of banyan networks, but increase the hardware cost significantly. In this paper, we study the blocking probabilities of VSOB networks under random routing strategy, and develop a model to compute the blocking probabilities with respect to the number of planes in the networks. Our model calculates the blocking probabilities stage by stage recursively, and it depicts accurately the blocking behaviors of VSOB networks under random routing. The proposed model is significant because it reveals the inherent relationships between blocking probability and network hardware cost in terms of the number of planes, and provides network developers a quantitative guidance to find a desirable tradeoff between blocking probability and hardware cost. An important conclusion drawn from our work that has practical applications is that the hardware cost of a VSOB network can be reduced dramatically if a predictable and almost negligible non-zero blocking probability is allowed.

Banyan networks are attractive for constructing directional coupler (DC)-based optical switching networks for their small depth and self-routing capability. Crosstalk between optical signals passing through the same DC is an intrinsic drawback in DC-based optical networks. Vertical stacking of multiple copies of an optical banyan network is a novel scheme for building nonblocking (crosstalk-free) optical switching networks. The resulting network, namely vertically stacked optical banyan (VSOB) network, preserves all the properties of the banyan network, but increases the hardware cost significantly. Though much work has been done for determining the minimum number of stacked copies (planes) required for a nonblocking VSOB network, little is known on analyzing the blocking probabilities of VSOB networks that do not meet the nonblocking condition (i.e., with fewer stacked copies than required by the nonblocking condition). In this paper, we analyze the blocking probabilities of VSOB networks and develop their upper and lower bounds with respect to the number of planes in the networks. These bounds depict accurately the overall blocking behaviors of VSOB networks and agree with the conditions of strictly nonblocking and rearrangeably nonblocking VSOB networks respectively. Extensive simulation on a network simulator with both random routing and packing strategy has shown that the blocking probabilities of both strategies fall nicely within our bounds, and the blocking probability of packing strategy actually matches the lower bound. The proposed bounds are significant because they reveal the inherent relationships between blocking probability and network hardware cost in terms of the number of planes, and provide network developers a quantitative guidance to trade blocking probability for hardware cost. In particular, our bounds provide network designers an effective tool to estimate the minimum and maximum blocking probabilities of VSOB networks in which different routing strategies may be applied. An interesting conclusion drawn from our work that has practical applications is that the hardware cost of a VSOB network can be reduced dramatically if a predictable and almost negligible nonzero blocking probability is allowed.

Crosstalk in optical switching elements (SEs) is one of the major shortcomings in optical switching networks, and avoiding crosstalk is an important issue for proper optical network operation. We propose a new class of optical multistage interconnection networks (MINs)-vertically stacked Benes networks VSB(N, K) that have N inputs (outputs) and consist of K vertically stacked Benes networks. The VSB(N, K) network can support any permutation of an N-element set {0, 1, ..., N-1}. Complete algorithms to realize crosstalk-free permutation in a VSB(N, K) network are the main contributions of this paper.

Clock skew modeling is important in the performance evaluation and prediction of clock distribution networks. This paper addresses the problem of statistical skew modeling for general clock distribution networks in the presence of process variations. The only available statistical skew model is not suitable for modeling the clock skews of general clock distribution networks in which clock paths are not identical. The old model is also too conservative for estimating the clock skew of a well-balanced clock network that has identical but strongly correlated clock paths (for instance, a well-balanced H-tree). In order to provide a more accurate and more general statistical skew model for general clock distributions, we propose a new approach to estimating the mean values and variances of both clock skews and the maximal clock delay of general clock distribution networks. Based on the new approach, a closed-form model is also obtained for well-balanced H-tree clock distribution networks. The paths delay correlation caused by the overlapped parts of path lengths is considered in the new approach, so the mean values and the variances of both clock skews and the maximal clock delay are accurately estimated for general clock distribution networks. This enables an accurate estimate of yields of both clock skew and maximal clock delay to be made for a general clock distribution network.