Over the past few years, massive penetrations targeting an Industrial Control System (ICS) network intend to compromise its core industrial processes. So far, numerous advanced methods have been proposed to detect anomalous patterns in the numeric data streams with respect to the heterogeneous field devices involved in the industrial processes. These methods, despite reporting decent results, usually conduct system-wise detection instead of fine-grained anomalous pattern recognition at the device level. Furthermore, lacking explicit consideration of the exclusive process-related features with respect to each differentiated device, the fitness of their application in specified industrial processes is undermined. To tackle these issues, a GNN-based Attributed Heterogeneous Graph Analyzer (the AHGA) is designed to perform device-wise anomalous pattern detection via in-depth process-oriented associativity learning. The AHGA’s framework is constructed with four building blocks : a graph processor, a feature analyzer, a link inference decoder, and an anomaly detector . Its performance is assessed and compared against multiple link inference and anomaly detection baselines over 2 popular ICS datasets (SWaT and WADI). Comparative results demonstrate the AHGA’s reliability in capturing sophisticated process-oriented relations among heterogeneous devices as well as its effectiveness in boosting the performance of anomalous pattern recognition at device-level granularity .

Intelligent Transport System (ITS) shall be able to incorporate transparently and seamlessly a large number of different and heterogeneous traffic system, while providing communication access to vehicles with various Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communication for the development of a safety commuting service. Building a route forecasting system is a complex task, mainly because of the changing traffic conditions. This paper presents a new route guidance algorithm and presents a compact road traffic model with real time updating. The algorithm enables to select a shortest path between source to destination by estimating the histogram model which captures the higher order distribution function using ITS. The data entity collection through sensors used for histogram modelling is presented in detail. A microscopic simulation model is utilized to evaluate the effectiveness of the proposed traffic model against the existing algorithm. Average travel time and overall network productivity are measured using the simulation. Various scenarios were created to study the impact of the proposed model in the traffic modelling.

In this paper, a novel synthetic aperture radar (SAR) ground moving target imaging (GMTIm) algorithm is presented within a parametric and dynamic sparse Bayesian learning (SBL) framework. A new time-frequency representation, which is known as Lv's distribution (LVD), is employed on the moving targets to determine the parametric dictionary used in the SBL framework. To combat the inherent accuracy limitations of the LVD and extrinsic perturbation errors, a dynamical refinement process is further developed and incorporated into the SBL framework to obtain highly focused SAR image of multiple moving targets. An emerging inference technique, which is known as variational Bayesian expectation-maximization, is applied to achieve an efficient Bayesian inference for the focused SAR moving target image. A remarkable advantage of the proposed algorithm is to provide a fully posterior distribution (Bayesian inference) for the SAR moving target image, rather than a poor point estimate used in conventional methods. Because of utilizing high-order statistical information, the error propagation problem is desirably ameliorated in an iterative manner. The perturbations, known as the multiplicative phase error and additive clutter and noise, are both well adjusted for further improving the image quality. Experimental results by using simulated spotlight-SAR data and real Gotcha data have demonstrated the superiority of the proposed algorithm over other reported ones.

This paper presents a new ground moving target imaging (GMTIm) algorithm for airborne synthetic aperture radar (SAR) based on a novel time-frequency representation (TFR), Lv's distribution (LVD). We first analyze generic moving target signatures for a multichannel SAR and then derive the analytical spectrum of a point target moving at a constant velocity by a polar format algorithm for SAR image formation. SAR motion deviation from a predetermined flight track is considered to facilitate airborne SAR applications. LVD, as a recently developed TFR for the analysis of multicomponent linear-frequency-modulated signal, is adopted to represent the target kinematic spectrum in the Doppler centroid frequency and chirp rate domain. As a result, the proposed SAR-GMTIm algorithm is capable of imaging multiple moving targets even when they are located at the same range resolution cell. Some practical issues such as imaging maneuvering targets and small/weak targets are discussed to enhance the applicability of the proposed algorithm. Simulation results with isotropic point moving targets are presented to validate the effectiveness and superiority of the proposed algorithm. Raw data collected by an airborne multichannel SAR are also used to verify the performance improvement made by the proposed algorithm.

This paper considers the problem of estimating multiple frequency hopping signals with unknown hopping pattern. By segmenting the received signals into overlapped measurements and leveraging the property that frequency content at each time instant is intrinsically parsimonious, a sparsity-inspired high-resolution time-frequency representation (TFR) is developed to achieve robust estimation. Inspired by the sparse Bayesian learning algorithm, the problem is formulated hierarchically to induce sparsity. In addition to the sparsity, the hopping pattern is exploited via temporal-aware clustering by exerting a dependent Dirichlet process prior over the latent parametric space. The estimation accuracy of the parameters can be greatly improved by this particular information-sharing scheme and sharp boundary of the hopping time estimation is manifested. Moreover, the proposed algorithm is further extended to multi-channel cases, where task-relation is utilized to obtain robust clustering of the latent parameters for better estimation performance. Since the problem is formulated in a full Bayesian framework, labor-intensive parameter tuning process can be avoided. Another superiority of the approach is that high-resolution instantaneous frequency estimation can be directly obtained without further refinement of the TFR. Results of numerical experiments show that the proposed algorithm can achieve superior performance particularly in low signal-to-noise ratio scenarios compared with other recently reported ones.

Compressive sensing (CS) based Inverse Synthetic Aperture Radar (ISAR) imaging exploits the sparsity of the target scene to achieve high resolution and effective denoising with limited measurements. This paper extends the CS based ISAR imaging to further include the continuity structure of the target scene within a Bayesian framework. A correlated prior is imposed to statistically encourage the continuity structures in both the cross-range and range domains of the target region and the Gibbs sampling strategy is used for Bayesian inference. Because the resulted method requires to recover the whole target scene at a time with heavy computational complexity, an approximate strategy is proposed to alleviate the computational burden. Experimental results demonstrate that the proposed algorithm can achieve substantial improvements in terms of preserving the weak scatterers and removing noise over other reported CS based ISAR imaging algorithms.

A novel approach is presented to improve firewall packet filtering through optimising the order of firewall rules for early packet acceptance as well as the order of rule‐fields for early packet rejection. The proposed approach is based on the calculation of the histograms of packet matching rules and of packet not matching rule‐fields. These histograms are able to effectively monitor firewall performance in real‐time and to predict the patterns of packet filtering in terms of rules order and rule‐fields order. Furthermore, the proposed approach becomes even more significant when firewall is heavily loaded with burst traffic. A comparison of the proposed approach and the other conventional approaches, including static rule order approach and dynamic rule order approach is presented. The numerical results obtained by simulations demonstrate that the proposed approach is able to significantly improve the firewall efficiency in terms of cumulative processing time compared to other conventional approaches. Furthermore, the proposed scheme also has the capability to significantly reduce the effect of many common network attacks on firewall performance.

Equal-Cost Multipath (ECMP) routing has been widely adopted to perform load balancing. With ECMP, a router can maintain multiple next hops for a destination IP prefix. The most common method used by such routers is to split traffic with per-flow basis evenly among those next hops. This approach, although simple, cannot achieve optimal load balancing. In this paper we study the optimal configuration of weighted ECMP, where traffic splitting among the available paths is based on a set of pre-determined ratios. The contribution of this paper is two-fold. First, we develop a model to obtain the split ratios such that the overall network end-to-end delay is optimized. This is important because better delay performance is a result of better bandwidth allocation and has a direct impact on application, while most existing work tries to minimize the traffic load on the most utilized link. Second, we prove that the problem can be first solved by using a simple flow-based routing model and then converting the results to apply to IP networks, where destination-based forwarding is used. We present a heuristic algorithm to find the near-optimal weight configurations and demonstrate the effectiveness of the algorithm using computer simulations.

Sensor networks can be used to monitor and control pipeline infrastructures. This paper discusses and compares different sensor network architectures that can be used for monitoring underwater pipelines infrastructures. These architectures are underwater wired sensor networks, underwater acoustic wireless sensor networks, RF (Radio Frequency) wireless sensor networks, integrated wired/acoustic wireless sensor network, and integrated wired/RF wireless sensor networks. The reliability characteristics, advantages, and disadvantages among these architectures are discussed and compared. Three reliability factors are used for the discussion and comparison: the network connectivity, the continuity of power supply for the network, and the physical network security.

Inter-vehicular communication is an important research area that is rapidly growing due to considerable advances in mobile and wireless communication technologies, as well as the growth of microprocessing capabilities inside today's cars, and other moving vehicles. A good amount of research has been done to exploit the different services that can be provided to enhance the safety and comfort of the driver. Additional functions provide the car electronics and the passengers with access to the Internet and other core network resources. This paper provides a survey of the latest advances in the area of inter-vehicular communication (IVC) including vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) functions and services. In addition, the paper presents the most important projects and protocols that are involved in IVC systems as well as the different issues and challenges that exist at each layer of the networking model.

This paper focuses on the characterization of vehicle mobility in vehicular ad hoc networks (VANETs). The performance of vehicle mobility in terms of link available time and the number of inter-vehicle link changes for maintaining active links in VANET is analyzed using both the handover and random moving models. The theoretical analysis is verified by simulation experiments. The numerical results indicate that the vehicle random moving analytical model is able to provide a more accurate description of the complicated vehicle moving behavior than the conventional random way point mobility model, especially when vehicles are moving relatively fast.

This paper presents a novel k-hop compound metric based clustering (KCMBC) scheme, which uses the host connectivity and host mobility jointly to select cluster-heads. KCMBC is a fast convergent and load balancing clustering approach that is able to offer significant improvement on scalability for large-scale ad hoc networks. On the other hand, since host mobility has been taken into account in terms of the average link expiration time, the clusters constructed by KCMBC are more stable than many other schemes. Simulation results show that the clusters created by using the KCMBC approach retain modest but more uniform cluster size, and cluster-head life-time can be increased by KCMBC up to 50%. Moreover, the control overheads for cluster formation using the KCMBC scheme are kept relatively low if compared to other clustering schemes.

Abstract A new algorithm of adaptive subcarrier allocation and bit loading (A‐SABL) is proposed for simultaneous voice and data transmission in multiuser OFDM systems. The algorithm takes advantage of the frequency diversity and the voice/data transmission requirements to dynamically assign the number of subcarriers and bits/per symbol on each subcarrier for each user in a single cell. Due to the strict delay requirement of voice service, the subcarriers with low channel gains are assigned for voice transmission with a small number of bits per symbol to guarantee its required bit‐error‐rate (BER) and transmission rate. Based on the remaining subcarriers with high channel gains and the transmission power, the throughput of data transmission is then maximized by loading as many bits as possible on each subcarrier to achieve the required transmission bit rate and BER. Theoretical analysis and simulation on the proposed algorithm show that a better performance is obtained than previously reported schemes. Copyright © 2008 John Wiley & Sons, Ltd.

This paper presents a novel video scheduling algorithm for streaming MPEG video over multi-user shared wireless link, in which video sessions are scheduled based on both location-dependent channel condition and instantaneous frame delay. This algorithm also employs a pro-active frame discard mechanism to discard potential problematic frames. The numerical results show that the proposed algorithm is able to significantly improve link throughput and guarantee long-term fairness.

The IEEE 802.11 working group is currently working on the support of quality of service (QoS) in a new standard called IEEE 802.lie which introduces the so-called hybrid coordination function (HCF). A simple admission control unit has already been developed as a reference for HCF controlled channel access (HCCA) in a recent TGe draft. However, this reference scheme is inefficient because it is implemented based on the minimum physical rate from which the mobile stations' actual physical rates deviate greatly at most of the time. In this paper, we propose a physical rate based admission control scheme (PRBAC) which enhances the reference scheme by taking account of both the wireless channel characteristics and the stations' mobility. Numerical analysis and simulation results show the significant improvement of the proposed admission control scheme.

Two novel MAC schemes are proposed to solve the hidden terminal problem and the exposed problem in ad hoc networks with large interference range. With the aid of dual busy tones, one scheme is a simple enhancement to IEEE 802.11, and the other is to exactly signify the interference range by adjusting the transmission power of busy tones. Both of the two schemes are able to prevent the collisions of data/ACK packets. The numerical results show that the two proposed schemes are able to enhance the saturation throughput of IEEE 802.11 significantly. The proposed VPDBT MAC can balance the trade off between spatial reuse and collision avoidance.

This paper focuses on the design of a novel approach for dynamic k-hop clustering architecture, which is called k-hop compound metric based clustering (KCMBC). KCMBC is a fast convergent and load balancing clustering approach that is able to demonstrate significant improvement on the network performance, in terms of scalability and stability for large-scale ad hoc networks. On the other hand, since KCMBC has taken into account the host mobility, the clusters constructed by KCMBC are more stable than the other schemes. Simulation results show that the clusters created by using the KCMBC approach have modest but more uniform cluster size. Moreover, cluster-head duration can be increased by KCMBC significantly.

This paper presents the application of sequential Monte Carlo (SMC) methodology for blind detection in wireless DS-CDMA systems over fading channels. A novel blind Cholesky-SMC receiver based on the techniques of Cholesky factorization and sequential importance sampling is developed for differentially encoded DS-CDMA systems. With simulated results, the promising performance of the proposed receiver is demonstrated for the both the systems over the flat fading channels and frequency-selective fading channels.

Traditional bandwidth smoothing techniques can be naturally supported by the renegotiated constant bit rate (RCBR) service model, but renegotiation failure in RCBR may cause buffer underflow and interrupt the playback of video. To address this concern, a novel dual-plan bandwidth smoothing (DBS) scheme is proposed in this paper by taking advantage of the SNR scalability of layer-encoded video. Upon renegotiation failure, the proposed scheme can adaptively discard certain enhancement layers to guarantee continuous video playback at the original frame rate. Experiments are carried out to demonstrate the validity of the proposed scheme. The impacts of renegotiation interval, granularity of enhancement layers, and playback buffer size on resulted video quality are also studied. From the simulation results, it is shown that the performance of the RCBR-based DBS scheme can be improved by 1) reducing the minimum time gap of renegotiation interval; 2) employing multilayer video encoding with finer granularity; and/or 3) increasing the playback buffer size.

Group-blind multiuser detectors for uplink code-division multiple-access (CDMA) were recently developed by Wang and Host-Madsen. These detectors make use of the spreading sequences of known users to construct a group constraint to suppress the intracell interference. However, such techniques demand the estimation of the multipath channels and the delays of the known users. In this paper, several improved blind linear detectors are developed for CDMA in fading multipath channels. The proposed detectors utilize the correlation information between consecutively received signals to generate the corresponding group constraint. It is shown that by incorporating this group constraint, the proposed detectors can provide different performance gains in both uplink and downlink environments. Compared with the previously reported group-blind detectors, our new methods only need to estimate the multipath channel of the desired user and do not require the channel estimation of other users. Simulation results demonstrate that the proposed detectors outperform the conventional blind linear multiuser detectors.

Traditional bandwidth smoothing techniques can be supported naturally by the renegotiated constant bit rate (RCBR) service model, but renegotiation failure in RCBR may cause buffer underflow and interrupt the playback of video. To address this concern, a novel dual-plan bandwidth smoothing scheme is proposed by taking advantage of layer-encoded video. Upon renegotiation failure, the proposed scheme can adaptively discard enhancement layers to guarantee continuous video playback at the original frame rate. Experimental results are provided to demonstrate the validity of the proposed scheme and the impact of playback buffer size on the resulting video quality degradation.

Voice over IP is a hot topic for the networking technologies. Delay and delay jitter are the important measures of QoS particularly for the voice traffic in the network environment with bursty background traffic. This paper studies the performance behavior of delay and delay jitter at the IP packet level by using the transient queuing solution. The analysis focuses on the voice over IP traffic going through a IP router with the bursty background traffic over network. We study the individual effects of various traffic parameters on the jitter behavior of packet voice stream multiplexing background traffic with different bursty characteristics in the IP router. The numerical results for the investigation of the effects of delay and delay jitter to a speech sample are presented.

Based on an assumption that a steady state exists in the full-memory multidestination automatic repeat request (ARQ) scheme, we propose a novel analytical method called steady-state function method (SSFM), to evaluate the performance of the scheme with any size of receiver buffer. For a wide range of system parameters, SSFM has higher accuracy on throughput estimation as compared to the conventional analytical methods.

Point-to-multipoint connections for available bit rate (ABR) services are not merely extensions of unicast ABR services. The feedback implosion problem must be solved in the case of multicast connections and hence consolidation of the feedback information at branch points becomes necessary. A new feedback consolidation algorithm for point-to-multipoint ABR services in ATM networks is proposed in this paper, aiming to achieve fast transient response and low consolidation noise. Simulation indicates that the proposed algorithm gives satisfactory results in different network configurations.

This paper presents our study on the effects of cell loss on QoS for the MPEG video transmission in ATM networks. A new evaluation method for the cell loss behavior of ATM networks due to congestion is proposed. The method uses a real MPEG video sequence as the input source and the MPEG video data is packetized into ATM cells. A cell discard process model called the Gilbert model is used to generate a cell discard pattern. The pattern represents the occurrences of ATM lost cells due to buffer overflow in multiplexers, Finally, the effects of cell loss on QoS is evaluated by de-packetizing (assembling) the resultant ATM cells back into MPEG video data, The QoS evaluations presented in this paper include subjective and objective evaluations of video quality under different network conditions. The evaluation results show that the effects of cell loss on QoS for MPEG video transmission in ATM networks depend on factors such as the burst cell loss length and the MPEG coding modes used.

An effective method to support multiple QoS classes in IPv6 over ATM networks is implemented by mapping of the priority field in IPv6 to the ATM cell. Such a scheme might not be necessary for simple congestion control in a network of equal capacity links; however, it might be important for multicasting to destinations reachable through a very diverse capacity network. When network congestion occurs, the cell loss requirements for different services can be satisfied by selectively discarding low priority cells. The results obtained show how the QoS can be affected by this field and how priority can be given for more important traffic in times of network congestion.

One of the key issues related to deadline guarantees of synchronous messages in FDDI networks is the feasibility test of synchronous bandwidth allocation (SBA). Much work has been done on how to allocate synchronous bandwidth properly in order to guarantee synchronous messages transmission before their deadlines, and as a result quite a few SBA schemes have been proposed. In contrast, limited research has been done on how to effectively test the feasibility of a given allocation of synchronous bandwidths (i.e., whether or not a given allocation can guarantee the synchronous message set considered), and the existing approach cannot always give an effective test and may even produce wrong testing results. This paper presents an algorithm of polynomial time worst-case complexity which ensures the correctness and effectiveness of the testing for any given synchronous message set with message deadlines equal to periods.