Beam tracking is a core issue in 5G vehicle-to-everything (V2X) networks. Specifically, higher beamforming gain is required to compensate for the path loss at higher frequencies, e.g., 5G FR2, to realize high data rate vehicle-toinfrastructure (V2I) communications. However, shorter time slots at higher frequencies, high velocity of vehicles, and unpredictable localization errors make this problem more challenging. Under these circumstances, wider beams can lead to higher beam tracking accuracy. Bear in mind that wider beams mean lower beamforming gain, which cannot compensate for high path loss at high frequencies and would further influence the data rate of V2I communications. Thus, there exists a trade-off between tracking accuracy and data rate in V2I communications. Furthermore, this problem needs to be solved within an extremely short time slot according to the high transmission frequency. To solve this problem, we propose a reinforcement learning (RL) assisted, high-resolution codebook-based beam tracking method. By comparing several different RL frameworks, we found that the twin delayed deep deterministic policy gradient (TD3) framework can help the roadside infrastructure (RSI) determine a proper beam pattern within a short duration. Moreover, according to the Hurst exponent analysis, recurrent neural networks (RNNs) are selected to improve the performance of the RL framework. The simulation results show that the proposed method performs well in tracking accuracy, data rate, and temporal efficiency.

The papers in this special section focus on the use of artificial intelligence (AI)-enabled technologies to address human wellness. As the COVID-19 pandemic took hold over the last several years, there was an urgent demand to pay more attention to psychological health for human wellness by providing methods and means of sensing psychological parameters, emotional care and mental disorder patient monitoring, especially during these difficult times. With the aid of wearable computing technology and artificial intelligence, emotion and mental disorder detections are available through sensing and analyzing psychological parameters. Discusses the use of AI-based patient monitoring and the ability to monitor human wellness via remote sensing technologies. The papers in this issue provide a snapshot of some of the latest research advances on the research and application of Small Things and Big Data, knowledge discovery and knowledge representation for the combination towards biomedical and health informatics.

Future industrial cyber-physical system (CPS) devices are expected to request a large amount of delay-sensitive services that need to be processed at the edge of a network. Due to limited resources, service placement at the edge of the cloud has attracted significant attention. Although there are many methods of design schemes, the service placement problem in industrial CPS has not been well studied. Furthermore, none of existing schemes can optimize service placement, workload scheduling, and resource allocation under uncertain service demands. To address these issues, we first formulate a joint optimization problem of service placement, workload scheduling, and resource allocation in order to minimize service response delay. We then propose an improved deep Q-network (DQN)-based service placement algorithm. The proposed algorithm can achieve an optimal resource allocation by means of convex optimization where the service placement and workload scheduling decisions are assisted by means of DQN technology. The experimental results verify that the proposed algorithm, compared with existing algorithms, can reduce the average service response time by 8-10%.

One of the biggest problems facing future mobile systems beyond 5G (B5G) is the energy dissipation of mobile devices at high data rates. The heat generated by these devices can impact the performance as a result of a new type of outage called power-consumption outage. In this article, we propose a general definition of the power-consumption outage and describe its three features. Based on the heat transfer model in smartphones, the power-consumption outage probability is analyzed. Specifically, we derive the joint outage probability of channel and power-consumption outages in relation to the signal-to-noise ratio (SNR), communication duration, and initial temperature of the smartphone-back-plate. The joint outage probability is then used to obtain the upper bound of the maximum receiving rate of a typical smartphone. Furthermore, we propose and analyze the impact on the capacity of the power-consumption outage. Simulation results show that the power-consumption outage probability increases with an increase of SNR and with extension of the communication duration. The upper bound of the maximum receiving rate of a smartphone decreases with an extension of communication duration. Considering the joint outage probability, simulation results show that the outage capacities, i.e., channel and power-consumption outages, decrease with an increase of SNR after reaching a given capacity threshold.

As we power through to the future, in-vehicle communications' reliance on speed is becoming a challenging predicament. This is mainly due to the ever-increasing number of electronic control units (ECUs), which will continue to drain network capacity, hence further increasing bandwidth demand. For a wired network, a tradeoff between bandwidth requirement, reliability, and cost-effectiveness has been our main motivation in developing a high-speed network architecture that is based on the integration of two time-triggered protocols namely; Time Triggered Ethernet (TT-E) and Time Triggered Controller Area Network (TT-CAN). Therefore, as a visible example of an Internet of Vehicles technology, we present a time triggered communication-based network architecture. The new architecture can provide scalable integration of advanced functionalities, while maintaining safety and high reliability. To comply with the bandwidth requirement, we consider high-speed TT-Ethernet as the main bus (i.e., backbone network) where sub-networks can use more cost-effective and lower bandwidth TT-CAN to communicate with other entities in the network via a gateway. The main challenge in the proposed network architecture has been to resolve interoperability between two entirely different time-triggered protocols, especially in terms of timing and synchronization. In this paper, we first explore the main key drivers of the proposed architecture, which are bandwidth, reliability, and timeliness. We then demonstrate the effectiveness of our gateway design in providing full interoperability between the two time-triggered protocols.

The Smart Grid represents an unprecedented opportunity to move the electric grid into a new era of reliability, availability, and efficiency. It uses two-way communications, digital technologies, advanced sensing and computing infrastructure, and software abilities to provide improved monitoring, protection and optimization of all the grids’ components including generation, transmission, distribution and consumers.

In this paper, we propose an analytical framework to derive all positive integer moments of MIMO mutual information in high-SNR regime. The approach is based on efficient use of the underlying matrix integrals of the high-SNR mutual information. As an example, the framework is applied to the study of Jacobi MIMO channel model relevant to fiber optical and interference-limited multiuser MIMO communications. For such a channel model, we obtain explicit expressions for the exact moments of the mutual information in the high-SNR regime. The derived moments are utilized to construct approximations to the corresponding outage probability. Simulation shows the usefulness of the results in a crucial scenario of low outage probability with finite number of antennas.

With the remarkable progress of cooperative communication technology in recent years, its transformation to vehicular networking is gaining momentum. Such a transformation has brought a new research challenge in facing the realization of cooperative vehicular networking (CVN). This paper presents a comprehensive survey of recent advances in the field of CVN. We cover important aspects of CVN research, including physical, medium access control, and routing protocols, as well as link scheduling and security. We also classify these research efforts in a taxonomy of cooperative vehicular networks. A set of key requirements for realizing the vision of cooperative vehicular networks is then identified and discussed. We also discuss open research challenges in enabling CVN. Lastly, the paper concludes by highlighting key points of research and future directions in the domain of CVN.

With the growing interest in the deployment of massive multiple-input-multiple-output (MIMO) systems and millimeter wave technology for fifth generation (5G) wireless systems, the computation power to the total power consumption ratio is expected to increase rapidly due to high data traffic processing at the baseband unit. Therefore in this paper, a joint optimization problem of computation and communication power is formulated for multi-user massive MIMO systems with partially-connected structures of radio frequency (RF) transmission systems. When the computation power is considered for massiv MIMO systems, the results of this paper reveal that the energy efficiency of massive MIMO systems decreases with increasing the number of antennas and RF chains, which is contrary with the conventional energy efficiency analysis results of massive MIMO systems, i.e., only communication power is considered. To optimize the energy efficiency of multi-user massive MIMO systems, an upper bound on energy efficiency is derived. Considering the constraints on partially-connected structures, a suboptimal solution consisting of baseband and RF precoding matrices is proposed to approach the upper bound on energy efficiency of multi-user massive MIMO systems. Furthermore, an oPtimized Hybrid precOding with computation and commuNication powEr (PHONE) algorithm is developed to realize the joint optimization of computation and communication power. Simulation results indicate that the proposed algorithm improves energy and cost efficiencies and the maximum power saving is achieved by 76.59% for multi-user massive MIMO systems with partially-connected structures.

This paper focuses primarily on leveraging synchronized current/voltage amplitudes and phase angle measurements to foster new categories of applications, such as improving the effectiveness of grid protection and minimizing outage duration for distributed grid systems. The motivation for such an application arises from the fact that with the support of communication, synchronized measurements from multiple sites in a grid network can greatly enhance the accuracy and timeliness of identifying the source of instabilities. The paper first provides an overview of synchrophasor networks and then presents techniques for power quality assessment, including fault detection and protection. To achieve this we present a new synchrophasor data partitioning scheme that is based on the formation of a joint space and time observation vector. Since communication is an integral part of synchrophasor networks, the newly adopted wireless standard for machine-to-machine (M2M) communication, known as IEEE 802.11ah, has been investigated. The paper also presents a novel implementation of a hardware in the loop testbed for real-time performance evaluation. The purpose is to illustrate the use of both hardware and software tools to verify the performance of synchrophasor networks under more realistic environments. The testbed is a combination of grid network modeling, and an Emulab-based communication network. The combined grid and communication network is then used to assess power quality for fault detection and location using the IEEE 39-bus and 390-bus systems.

Hurricane Sandy and other recent extreme weather events, which have caused significant service interruptions including power outages, have revealed that our power grid is not sufficiently planned and operated to be resilient to large-scale events. Power grid resilience is a generic term that covers many aspects of power grid planning and operation. A resilient power grid should be capable of executing preventive measures, mitigating the impact of extreme events, responding optimally by automated control procedures, reducing the time needed to restore service to consumers, and potentially leading to significant economic savings. In addition, due to the growing usage of information and communication technologies (ICT), power grids are being increasingly exposed to cyber attacks. The recent blackout in Ukraine serves as a good example to illustrate the severe consequence that cyber attacks on the power grid can entail. Extensive reports and media coverage indicate the urgency to improve our power grid resilience. Maintaining resilience of the power grid is crucial to our nation’s energy security and sustainability.

A major problem of the grid system is identifying the source of abnormal behaviors. It is particularly important to identify the areas in which the grid system suffers from power deficiencies due to fault or voltage instability. Phasor Measurement Units (PMUs) are capable of measuring current and voltage amplitudes and phase angles, which can then be effectively used to monitor the power quality. This would require the support of a communication network to detect regions in the grid that may suffer from voltage instability. In this paper we present a distributed mapping technique that is based on a hierarchical network structure to identify the proximity of the grid instability for any possible remedial control action at the local level. For voltage monitoring, we also develop an average standard deviation measurement technique to access the power quality. We use the IEEE 34 bus grid distribution model and the IEEE 39 bus transmission model to assess the performance of the proposed techniques.

Linear dispersion codes (LDC) can support arbitrary configurations of transmit and receive antennas in multi-input multi-output (MIMO) systems. In this paper, we investigate two transmit diversity applications of LDC for orthogonal frequency division multiplexing (OFDM) systems in order to achieve space-time/frequency (ST/SF) diversity gains when transmitting over time-/frequency-selective fading channels. LDC-aided ST/SF-OFDM is flexible in configuring various numbers of transmit antennas and time-slots or frequency-tones. Our results show that the ST-OFDM scheme is sensitive to exploiting diversity gains, subject to the impact of varying channel Doppler spreads; while the performance of SF-OFDM is mainly subject to delay spread. Particularly, when the transmitter employs more than two antennas, the LDC-aided ST/SF-OFDM outperforms the orthogonal block codes (e.g. Tarokh's codes) aided ST/SF-OFDM, when communicating over higher Doppler/delay spread.

With a growth of surveillance cameras, the amount of captured videos expands. Manually analyzing and retrieving surveillance video is labor intensive and expensive. It would be much more convenient to generate a video digest, with which we can view the video in a fast and motion-preserving way. In this paper, we propose a novel video synopsis approach to generate condensed video, which uses an object tracking method for extracting important objects. This method will generate video tubes and a seam carving method to condense the original video. Experimental results demonstrate that our proposed method can achieve a high condensation rate while preserving all the important objects of interest. Therefore, this approach can enable users to view the surveillance video with great efficiency.

There has been a growing interest in the deployment of Phasor Measurement Units (PMUs) in a Distributed Generation (DG) grid system. A major obstacle is the lack of a communication network infrastructure that can support phasor measurements for distribution area monitoring as well as providing sensing capabilities for protection against undesirable grid dynamics. In the absence of such a network, the most cost-effective solution would be to consider a wireless network to support centralized control for situational awareness in a DG environment. Therefore, the main objective in this paper is to design and implement a synchrophasor network testbed using Wireless LAN (WLAN) technology. Based on a hierarchical network architecture, we propose an efficient method to reduce the synchrophasor data bandwidth, as well as provide capabilities for control and management at each hierarchical level. This testbed is then used to evaluate different network configurations under various test conditions.

Image retargeting attempts to adapt images to different devices while preserving the salient contents. Most existing methods address retargeting of a single image. In this paper, we propose a novel image retargeting method for resizing a pair of stereo images. Naively retargeting each image independently will distort the geometric structure and will impair the perception of the 3-D structure of the scene. We introduce an extension to the 2-D image retargeting method that works on a pair of stereo images. We demonstrate the performance of our method on a number of challenging indoor and outdoor stereo images. Experimental results show that our method is able to provide visually comfortable resized images when the resizing ratio is relatively high.

In this paper, a greedy backpressure routing protocol is proposed for multigate mesh networks. This protocol evaluates the greedy backpressure metric (GBM) value of mesh points and routes packets in the direction of the steepest gradient. The GBM value is calculated using a combination of traffic load and the mesh point's hop count to the closest gateway. The proposed routing algorithm can realize the effect of traffic load from all the nodes along the path to each gateway by iteratively updating information from neighbors through periodic beacon exchange. The consideration of incorporating traffic load helps to route packets around congested area. The results indicate that the greedy backpressure multigate mesh routing is capable of achieving significant improvement in the network reliability, latency, and throughput performance.

Wireless mesh/sensor networks offer various unique features such as self-configuration, ease of installation, scalability, and self-healing, which make them very attractive for deployment in various smart grid domains, such as Home Area Networks (HAN), Neighborhood Area Networks (NAN), and substation/plant-generation local area networks for real-time monitoring and control. Their main drawback is that they are more exposed to cyber-attack as data packets have to be relayed on a hop-by-hop basis. This paper presents a dynamically updating key distribution strategy, together with a message protection scheme in support of 4-way handshaking. For the 4-way handshaking, we propose a hash based encryption scheme to secure the unprotected message exchanges during the handshaking process. This is aimed at improving the resiliency of the network in the situation where an intruder carries a denial of service attack. We then evaluate the security of the proposed scheme against cyber-attack, as well as network performance in terms of delay and overhead.

In this paper we firstly propose a general model to combat the Inter-Symbol Interference (ISI) caused by frequency selective channels in a Multi-InputMulti-Output (MIMO) system and/or by asynchronous cooperative transmissions. The general model is not only exemplified by the Asynchronous Cooperative Liner Dispersion Codes (ACLDC) scheme, but also by the Time-Reversed Space-Time Block Code (TR-STBC) scheme. In these schemes a guard interval of various lengths has to be inserted to help mitigate the effect of ISI. Consequently, this could impact the effective symbol rate for a small block-size. A larger block size however, could substantially increase the decoding complexity. We present a novel low-complexity breadth-adjustable tree-search algorithm in the proposed general model. We will discuss the difference between our algorithm and the Sphere Decoding (SD)-based algorithms. With simulation results, we will illustrate that our algorithm will achieve the optimal Bit-Error-Rate (BER) performance with a complexity that is lower than the SD-based algorithms, whether the system employs the ACLDC scheme or the TR-STBC scheme.

In order to contain a differential propagation delay in a block based cooperative Multiple-Input-Multiple-Output (MIMO) system, a guard interval can be inserted to mitigate the effect of inter-symbol interference. A larger block size could substantially increase the effective symbol rate, although at the expense of decoding complexity. In this paper, we propose a novel low-complexity breadth-adjustable tree-search algorithm, which, as an example, has been applied to decode Asynchronous Cooperative Liner Dispersion Codes (ACLDC). With simulation we demonstrate that when the blocksize is equivalent to 20, the complexity of the proposed algorithm is only a fraction of 10-8of that of the Maximum Likelihood (ML) algorithm. This would allow us to practically enhance the effective symbol rate without any performance degradation.

In this paper, we present a multi-gate mesh network architecture that has been developed to ensure high performance and reliability under emergency conditions when a system expects to receive power outage notifications and exchanges. In order to handle the metering traffic, under time varying outage conditions we introduce a multi-gate and single-class back-pressure based scheduling algorithm, which takes into account both the hop-count, as well as the queue length of each mesh node. An important requirement of this algorithm is that all the meter nodes should always maintain a separate path to each gateway. We first quantify the stability region of the network when our novel algorithm is applied to schedule the packets. We then present a numeric analysis to prove that the overall network delay is reduced as a result of employing the proposed scheduling algorithm. Moreover, we also theoretically prove that the network is always able to remain stable as long as the arrival rate vector lies inside the stability region provided by our scheduling algorithm. Finally, we derive a distributed objective function that is adopted by the practical implementation of the packet-scheduling scheme. The simulation results indicate that under the context of the multi-gate network, our packet-scheduling scheme can indeed significantly improve the network's reliability and delay performance, which are important factors under outage conditions.

With the emergence of the HEVC project, TCSVT published the first special section of its kind in December 2010. The special section consisted of a number of video coding proposals that were submitted to the ISO/IEC SC29/WG11 (MPEG) and ITU-T SG16/Q6 (VCEG). Now, on the eve of its ratification of formally becoming a new video coding standard, we are very pleased to dedicate the entire issue to the topic of HEVC. The first part will be the special section on HEVC standard and is edited by J.-R. Ohm, G.J. Sullivan, and T. Wiegand. It consists of three invited papers. These excellent papers provide a comprehensive overview of the important aspects of the new standard. The second part is the special issue that was initiated by the Editor-in-Chief in 2012, and the Guest Editors were carefully selected from the members of our regular editorial team. Seventy two submissions were received in response to our call for papers, and unfortunately, we could only accommodate 18 due to our limited space.

In this paper we first propose a block-code based general model to combat the Inter-Symbol Interference (ISI) caused by frequency selective channels in a Multi-Input Multi-Output (MIMO) system and/or by asynchronous cooperative transmissions. The general model is not only exemplified by the Time-Reversed Space-Time Block Code (TR-STBC) scheme, but also by the Asynchronous Cooperative Liner Dispersion Codes (ACLDC) scheme. In these schemes a guard interval has to be inserted between adjacent transmission blocks to mitigate the effect of ISI. Consequently, this could degrade the effective symbol rate for a small block size. A larger block size would enhance the effective symbol rate and also substantially increase the decoding complexity. In the general model proposed in this paper, we further present a novel low-complexity breadth-adjustable tree-search algorithm and compare it with Sphere-Decoding (SD) based algorithms. With simulation results we will illustrate that our algorithm is able to achieve the optimal performance in terms of Bit Error Rate (BER) with a complexity much lower than the SD-based algorithms, whether the ACLDC or TR-STBC scheme is employed. Through simulations we further demonstrate that when the block size of the ACLDC is equivalent to 20, the complexity of the proposed algorithm is only a fraction of 10-8that of the Maximum Likelihood (ML) algorithm. This would allow us to practically enhance the effective symbol rate without any performance degradation.

In this paper, we present a multi-gate mesh network architecture that has been developed to ensure high performance and reliability under emergency conditions when a system expects to receive power outage notifications and exchanges. In order to handle the metering traffic, we introduce a back-pressure based scheduling algorithm, which takes into account both the hop-count, as well as the queue length of each mesh node. We first present the objective function of the scheduling algorithm in a centralized manner. We then present a practical implementation of the packet-scheduling scheme. The simulation results indicate that under the context of the multi-gateway network, our novel packet-scheduling scheme can indeed signi-ficantly improve the network's reliability, self-healing, through-put and delay performance.

In this treatise, we propose a novel family of Asynchronous Cooperative Linear Dispersion Codes (ACLDCs), which is capable of maintaining full diversity in cooperative scenarios even at the presence of asynchronous reception. The linear dispersion structure is employed in order to accommodate the dynamic topology of cooperative networks, as well as to achieve higher throughput than conventional space time codes based on orthogonal designs. By introducing guard intervals and block encoding/decoding techniques, the interference signals caused by asynchronous reception can be exploited rather than discarded.

The linear dispersion structure is employed to accommodate the dynamic topology of cooperative networks, as well as to achieve higher throughput than conventional space-time codes based on orthogonal designs. Asynchronous Cooperative Liner Dispersion Codes (ACLDC) are applied to achieve full diversity in the presence of asynchronous reception. To achieve a near ML performance with much lower decoding complexity, we present an Ant-Colony Optimization (ACO) based decoder. We demonstrate that the proposed decoder is able to provide the system with a near-ML performance at a significantly reduced complexity.

This paper proposes an effective algorithm for spatial error concealment with accurate edge detection and partitioning interpolation. Firstly, a new method is used for detecting possible edge pixels and their matching pixels around the lost block. Then, the true edge lines can be determined, with which the lost block is partitioned. Finally, based on the partition result, each lost pixel can be interpolated with correct reference pixels, which are in the same region with the lost pixel. Experimental results show that the proposed spatial error concealment method is obviously superior to the previous methods for different sequences by up to 4.04 dB.

One of the most important issues in Smart Grid is to provide consumers with the knowledge of their energy usage, as well as allowing the utility to monitor and control the electric system components with real time status. This would require the design of a network architecture that is capable of providing secure and reliable two-way communication from meters to other Smart Grid domains. While networking technologies and systems have been greatly enhanced, in wireless communication environments the smart grid faces new challenges in terms of reliability. In this paper we are mainly concerned with assessing the performance of wireless mesh networks for the last mile communication. We consider a tree-based mesh routing scheme based on a multigate mesh network architecture. The multigate mesh routing scheme is based on a flexible mesh network architecture that expands on the hybrid tree routing of the IEEE 802.11s. The network is specifically designed to operate in a multi gateway structure in order to meet the smart grid requirements in terms of reliability, self-healing, and throughput performance. To further exploit the multigate network structure, a timer-based multipath routing diversity scheme is proposed in order to enhance the network reliability. The network is then used to measure the performance in terms of throughput and reliability.

It is envisioned that one of the most important issues in smart grid will be to design a network architecture that is capable of providing secure and reliable two-way communication from meters to other Smart Grid domains. While networking technologies and systems have been greatly enhanced, in wireless communication environments the smart grid faces new challenges in terms of reliability and efficiency. In this paper we present a multigate mesh network architecture to handle real-time traffic for the last mile communication. The paper consists of three parts; multigate routing, real-time traffic scheduling, and multichannel (MC) aided wireless mesh routing. The multigate routing is based on a flexible mesh network architecture that expands on the hybrid tree routing of the IEEE 802.11s. The network is specifically designed to operate in a multi gateway structure in order to meet the smart grid requirements in terms of reliability, self-healing, and throughput performance. This includes developing a timer-based multiple-path diversity scheme that takes advantage of the multi gateway network structure. With respect to packet scheduling, we introduce a novel and efficient scheme that is capable of balancing the traffic load among multiple gateways. The proposed scheme, which is based on the backpressure concept due to its simplicity, is suitable for practical implementation. We also present an MC aided wireless mesh routing protocol which is specifically designed for multigate smart grid networks. The results indicate that a combination of multipath routing and the backpressure-based packet-scheduling scheme can show a significant improvement in the network reliability, latency, and throughput performance. We also show an improvement in the order of magnitude can be achieved via the proposed multichannel aided routing protocol.

In this paper, we present a systematic design structure for high-density ad hoc networks aimed at achieving full cooperative diversity, based on which the PHY, MAC and Network layers of the system are specifically tailored. For the latter in particular, we present a cooperative routing protocol that is capable of exploiting full transmit diversity in adhoc networks. Simulation results are provided to demonstrate the substantial performance gain in terms of increased packet delivery reliability over high-throughput scenarios and reduced system delay, achieved by the cooperative diversity attained using a virtual MIMO system architecture.

Image inpainting is a useful and powerful technique for automatically restoring or removing objects in films and damaged pictures. In the last ten years, many excellent inpainting algorithms have been proposed after Bertalmio et al. [1]. However, no paper systematically and theoretically analyzes the factors, which limit the performances of existing algorithms. Based on extensive experiments, we firstly construct a universal framework for image inpainting, which contains three crucial factors—Area, Shape, and Perimeter (ASP). Then we propose a Pyramid model based Down-sampling Inpainting (PDI) model according to the ASP principles. Experimental results show that the performances of existing methods can be tremendously improved after incorporating the PDI model.

In packet-based video transmissions, packets loss due to channel errors may result in the loss of the whole video frame. Recently, many error concealment algorithms have been proposed in order to combat channel errors; however, most of the existing algorithms can only deal with the loss of macroblocks and are not able to conceal the whole missing frame. In order to resolve this problem, in this paper, we have proposed a new hybrid motion vector extrapolation (HMVE) algorithm to recover the whole missing frame, and it is able to provide more accurate estimation for the motion vectors of the missing frame than other conventional methods. Simulation results show that it is highly effective and significantly outperforms other existing frame recovery methods.

Multipath routing can be effectively used to maximize the utilization of network resources for real-time traffic. In mobile ad-hoc network environments, this approach can suffer from co-channel interference due to the simultaneous transmission of packets via multiple routes. In this paper, by exploiting the directionality of directional antennas, a Directional Dynamic Source Routing (DDSR)-based Multipath routing protocol is proposed for mobile wireless ad hoc networks. Three metrics are considered in the route discovery process in order to select the best multiple routes. These are hop count, beam overlaps, and the number of joint nodes between the different routes. The proposed directional routing protocol has shown to be capable of minimizing inter-path and intra-path interference, hence significantly improving the system throughput performance for simultaneous transmission of multimedia information over multiple routes.

In this paper, we propose a new spatial interpolation algorithm for Intra-Frame error concealment. The method aims at interpolating areas in the image, which have been affected by packet loss. We have proposed an edge detection technique to aid the bilinear interpolation. The edge-detection scheme is based on designing a robust Hough transform-based technique that is capable of systematically connecting edges irrespective of the number of edge points surrounding missing areas. The connected edges are used to divide the missing areas into different regions for interpolation along the directions of each detected line. Simulation results demonstrate that the proposed algorithm can recover the missing areas with a greater accuracy, when compared with the bilinear interpolation technique.

For low bitrate video communications, each video frame usually fills the payload of a single network packet. In this situation, the loss of a packet may result in loosing the entire video frame. Currently, most existing error concealment algorithms can only deal with the loss of macroblocks and are not able to conceal the whole missing frame. In this paper, we have proposed a new hybrid motion vector extrapolation (HMVE) algorithm to recover the whole missing frame. The proposed algorithm is capable of estimating the missing motion vectors with much greater accuracy than other existing methods. Experimental results show that it is highly effective and significantly outperforms other existing frame recovery methods.

A directional routing approach for multihop ad-hoc networks, is presented which has been applied to two on-demand routing protocols: namely dynamic source routing (DSR) and ad-hoc on-demand distance vector routing (AODV). Both DSR-based and AODV-based directional routing protocols are designed to balance the trade-off between co-channel interferences from nodes hops away and the total power consumed by all the nodes. In order to select the best route, three metrics are considered in the route discovery process. They consist of hop count, power budget and overlaps between adjacent beams. By exploiting the direction of directional antennas, both routing protocols are capable of reducing overlaps between beams of the nodes along the route, thus eliminating interference. Arbitrary networks and random networks are considered in the simulations. The results show considerable performance gains for transmission of real-time traffic over ad hoc networks.

This paper is mainly concerned with multichannel transmission of real-time information such as video over multihop ad hoc links. We propose two multichannel routing protocols. The first is based on single-path routing and aims at suppressing the intrapath interference in a carrier sense multiple access/collision avoidance network. This is achieved by developing a link-partitioning scheme where nodes in the neighboring partitions operate at different nonoverlapping frequency bands. For this approach, we present a systematic channel assignment technique that has been specifically developed for the ad hoc on-demand distance vector routing protocol. It is shown that this partitioning scheme can considerably enhance the throughput performance of a multihop link.

In this paper, a Dynamic Source Routing (DSR)- based directional routing protocol is invoked for wireless ad hoc networks using directional antennas. This is designed to balance the trade-off between co-channel interferences from nodes hops away, and the total power consumed by all the nodes. Three metrics are considered in the route discovery process in order to select the best route: hop count, power budget and overlaps between adjacent beams. By exploiting the directionality of directional antennas, the proposed DSR-based directional routing protocol is capable of reducing the overlaps between beams of the nodes along the route, hence eliminating the interference. Arbitrary networks and random networks are considered in our simulations. The results show considerable performance gains for transmission of real-time traffic over ad hoc networks.

In this paper, we present an innovative recursive motion estimation technique that can take advantage of the in-depth resolution (range) to perform an accurate estimation of objects that have undergone 3-D translational and rotational movements. This approach iteratively aims at minimizing the error between the object in the current frame and its compensated object using estimated motion displacement from the previous range measurements. In addition, in order to use the range data on the non-rectangular grid in the Cartesian coordinate, we consider a combination of derivative filters and the transformation between the Cartesian coordinates and the sensor-centered coordinates. For sequences of moving range images we demonstrate the effectiveness of the proposed scheme.

This introductory article overviews the progress of electrical, electronics, software, and other relevant technologies that shape the modern automobile. Some of these technologies are described in more detail in the articles that comprise this special issue.

Advanced vehicle-based safety and warning systems use laser scanners to measure road geometry (position and curvature) and range to obstacles in order to warn a driver of an impending crash and/or to activate safety devices (air bags, brakes, and steering). In order to objectively quantify the performance of such a system, the reference system must be an order of magnitude more accurate than the sensors used by the warning system. This can be achieved by using high-resolution range images that can accurately perform object tracking and velocity estimation. Currently, this is very difficult to achieve when the measurements are taken from fast moving vehicles. Thus, the main objective is to improve motion estimation, which involves both the rotational and translation movements of objects. In this respect, an innovative recursive motion-estimation technique that can take advantage of the in-depth resolution (range) to perform accurate estimation of objects that have undergone three-dimensional (3-D) translational and rotational movements is presented. This approach iteratively aims at minimizing the error between the object in the current frame and its compensated object using estimated-motion displacement from the previous range measurements. In addition, in order to use the range data on the nonrectangular grid in the Cartesian coordinate, two approaches have been considered: 1) membrane fit, which interpolates the nonrectangular grid to the rectangular grid, and 2) the nonrectangular-grid range data by employing derivative filters and the proposed transformation between the Cartesian coordinates and the sensor-centered coordinates. The effectiveness of the proposed scheme is demonstrated for sequences of moving-range images

In this paper we present a DSR-based multi-path routing protocol, which has been developed for transmission of multiple description coded (MDC) packets in wireless ad-hoc network environments. The protocol is designed to eliminate co-channel interference between multiple routes from source to destination by assigning a different frequency band to each route. In the route discovery process we use three metrics to select the best multiple routes. These are hop count, power budget, and the number of joint nodes between the different routes. For continuous media communications we show that in order to effectively benefit from the advantages associated with multipath diversity routing, it is important to use a multi-channel protocol such as the one developed here

This paper aims at improving the power efficiency of the CSMA/CA protocol for transmission of multimedia information over multihop wireless channels. Using a distance dependent propagation model, we present a power control scheme, which is based on the receiver sensitivity adjustment mechanism. The receiver sensitivity approach aims at exploiting a tradeoff between the interference and the contention in accessing the shared medium. For real-time traffic, we show that by controlling the receiver sensitivity threshold we can significantly improve the multihop link performance.

This paper is concerned with evaluating ad-hoc networks for group-oriented tactical operations. For such operations, a cellular-based ad-hoc network architecture has been constructed for real-time multimedia communications. To assess the suitability of this network, its performance has been compared with conventional peer-to-peer ad-hoc network architectures under various test scenarios using IEEE 802.11 WLAN technology. We have shown that the cellular network, which operates in two modes: infrastructure for intracell and ad-hoc for intercell communications, is more suitable for group-based tactical missions

This paper is concerned with transporting video information via multihop mobile ad-hoc channels. The major problem with transmitting real-time video information over these channels is the issue of link reliability. To improve the quality of the video reception we propose a cross layer feedback control mechanism that can allow the application layer to adapt itself to a dynamically changing network topology. We also present packet transmission strategies capable of recovering video signals under long bursts of packet drops, typical of a route change condition. This feedback control scheme has been developed for transmission of RTP/UDP/IP packets using the emerging H.264/AVC video-coding standard.

This paper presents a packet-loss feedback tracking scheme for the transmission of video signals over mobile channels. The proposed feedback scheme is based on the real time transport control protocol (RTCP), which is designed to provide an end-to-end feedback assessment of transmitted packets on a frame-by-frame basis (video frame). In addition, the frame synchronized RTCP-based feedback scheme is designed to take care of losses of RTCP packets due to bad channels. The video encoder, upon receiving its feedback report, can identify the exact location of the missing packets in the transmitted video frame. The feedback scheme is then applied to transport H.264/RTP/UDP/IP packets in real-time. A packet-loss compensation strategy has been used to assess the quality of the received signal under multipath fading channel conditions.

This paper presents a master/slave cellular-based mobile ad hoc network architecture for multihop multimedia communications. The proposed network is based on a new paradigm for solving the problem of cluster-based ad hoc routing when utilizing existing wireless local area network (WLAN) technologies. The network architecture is a mixture of two different types of networks: infrastructure (master-and-slave) and ad hoc. In this architecture, the participating slave nodes (SNs) in each cluster communicate with each other via their respective master nodes (MNs) in an infrastructure network. In contrast to traditional cellular networks where the base stations are fixed (e.g., interconnected via a wired backbone), in this network the MNs (e.g., base stations) are mobile; thus, interconnection is accomplished dynamically and in an ad hoc manner. For network implementation, the IEEE 802.11 WLAN has been deployed. Since there is no stationary node in this network, all the nodes in a cluster may have to move together as a group. However, in order to allow a mobile node to move to another cluster, which requires changing its point of attachment, a handoff process utilizing Mobile IP version 6 (IPv6) has been considered. For ad hoc routing between the master nodes (i.e., MNs), the Ad hoc On-demand Distance Vector (AODV) Routing protocol has been deployed. In assessing the network performance, field test trials have been carried out to measure the proposed network performance. These measurements include packet loss, delays under various test conditions such as a change of ad hoc route, handoffs, etc.

In many applications, such as construction, manufacturing, ground robotic vehicles, and rescue operations, there are many issues that necessitate the capability of transmitting digital video and that such transmissions should be performed wirelessly and in an ad-hoc manner. Recently, we proposed an ad-hoc, cluster-based, multi-hop network architecture for video communications (see Gharavi, H. and Ban, K., 3G Wireless Conference, 2002). For implementation, the IEEE 802.11 FHSS wireless LAN system using 2GFSK modulation was employed. To enhance the overall throughput rate for higher quality video communications, we present a performance evaluation of the IEEE 802.11 FHSS when 4GFSK modulation option is selected. Unfortunately, the 2 Mb/s system utilizing 4GFSK modulation is not very efficient in terms of RF range. Therefore, to improve its performance for multi-hop applications, a combination of diversity and non-coherent Viterbi based receiver is considered. For the video transmission part, we have considered a bitstream. splitting technique together with a packet-based error protection strategy to combat packet drops under multipath fading conditions. Finally, the paper presents simulation results, including the effects of receiver design and diversity on the quality of the received video signals.

This paper presents a twin-class transmission system for narrowband radio access channels suitable for handheld video phone and multimedia portable PC applications. The transmission system is comprised of a hierarchical 16-QAM modulation technique and a channel-coding scheme. The formation of dual-priority transmission is due to differing error resiliencies of the bits that make up a given symbol in a Gray-coded 16-QAM. On this basis, a twin-class pilot-assisted fade-estimation technique that can gracefully reduce the power loss caused by the transmission of pilot overhead is developed. The twin-class 16-QAM system is then used to transport a compressed video bitstream, which is partitioned to match the bit-error sensitivity of the transmitted symbol. The partitioning scheme is based on a separation of the variable-length (VL) coded discrete cosine transform (DCT) coefficients within each DCT block. This partitioning scheme is then applied to split the ITU-T H.263-coded bitstream. The scheme is suitable for constant bit-rate transmission (CBR), where the fraction of bits assigned to each of the two partitions can be adjusted according to the requirements of the unequal error protection scheme employed. The distribution of the VL-coded (VLC) information amongst the two partitions is performed adaptively. Finally, the performance of the partitioning scheme for transmission of video signals using our twin-class 16-QAM transmission system is evaluated under multipath fading conditions.

Abstract Recently, we proposed an ad hoc, cluster‐based, multihop network architecture for video communications using IEEE 802.11 FHSS (Frequency Hopping Spread Spectrum) wireless LAN (WLAN) technology with 2GFSK (2‐level Gaussian Frequency Shift Keying) modulation capable of 1 Mb s−1 transmission. To increase the transmission rate to 2 Mb s−1 for higher‐quality video communications, we evaluated the performance of the IEEE 802.11 FHSS system when a 4GFSK modulation option is selected. Since the 2 Mb s−1 system utilizing 4GFSK modulation is not very efficient in terms of Radio Frequency (RF) range, to improve its performance for multihop applications a combination of diversity and noncoherent Viterbi equalizer are considered. For video transmission, we employed a bitstream‐splitting technique together with a packet‐based error‐protection strategy to combat packet drops under multipath fading conditions. The real‐time transport protocol (RTP), user datagram protocol (UDP), and Internet protocol (IP) are used for video streaming. This includes an RTP packetization scheme to control the packet size and to improve the error‐resilient decoding of the partitioned video signal. The paper includes the simulation results showing the effects of the receiver design and diversity on the quality of the received video signals. Copyright © 2002 John Wiley & Sons, Ltd.

This paper presents a robust dual-priority video partitioning method suitable for twin-class unequal protected video transmission over wireless channels. The partitioning is based on a separation of the variable-length (VL) coded discrete cosine transform (DCT) coefficients within each block. The scheme is suitable for constant bit-rate transmission (CBR), where the fraction of bits assigned to each of the two partitions can be adjusted according to the requirements of the unequal error-protection scheme employed. The distribution of the VL-coded (VLC) information between the two partitions is performed adaptively. Subsequently, the partitioning method was applied to the ITU-T H.263 coding standard. It was shown that, for the input video with quarter common intermediate format (QCIF) spatial resolution (or less), the partitioning overhead can be embedded in the B-bit code word representing the group number (GN), thus avoiding transmission of additional bits. As a transport vehicle, we have considered one of the leading third generation cellular radio standards known as wide-band code division multiple access (W-CDMA). A dual-priority transmission system is then invoked on the W-CDMA system where the video data, after being broken into two streams, are unequally protected. We use a very simple error-correction coding scheme for illustration and then propose more sophisticated forms of unequal protection of the digitized video signals. We show that this strategy results in a significantly higher quality of the reconstructed video data when they are transmitted over time-varying multipath fading channels.

This paper introduces an efficient technique for dividing a preceded Moving Pictures Expert Group-2 (MPEG-2) bitstream into an arbitrary number of partitions in decreasing order of visual importance. For a fixed partition size ratio, this has been achieved by variable-length code (VLC) interleaving within a macroblock or group of macroblocks. The algorithm is capable of recreating a syntactically correct bitstream, regardless of the error rate on secondary partitions. This renders it applicable to many efficient transmission schemes, particularly over wireless channels.

There is a renewed interest in video-based communications. The expected proliferation of various video communication applications has in turn resulted in a need for scalable and efficient digital video encoding schemes which would enable the dissemination of video signals at differing spatial resolution, depending on end-user needs and limitations. Also, along with this is the need for a universal broadband in which the same transmitted signal is efficiently distributed to various end-user applications, allowing them to communicate at differing grades of video quality. As a first step, this paper presents an efficient and scalable video coding scheme. The scheme is capable of encoding and decoding video signals in a hierarchical, multilayer fashion to provide video at differing quality grades, e.g., NTSC, extended quality (EQTV), high definition (HDTV). Since the lower levels in such a scheme can be encoded independently of the upper levels, compatibility with some of the standard codecs can be directly imposed. In addition, strategies to control quantization noise for independent transmission by means of residual layering are also discussed. This paper also discusses the utilization of this coding scheme to enable efficient bit rate sharing and robust distribution of video communication signals at three distinct quality grades in multicasting, as well as multipoint communication applications for multiparty video-conferencing. Two special distribution architectures are considered which involve the use of SMDS and ATM as the transport and delivery vehicles.

The feasibility of a mobile video handset is investigated for Rayleigh-fading channels, where transmissions must be confined to the channel's coherence bandwidth to avoid the deployment of complex high-power-consumption channel equalizers. This necessitates the utilization of a low-bit-rate image codec error-protected by embedded low-complexity BCH codecs and spectrally efficient 16-level quadrature amplitude modulation (16 QAM). Motion-compensated nonuniform seven-band subband coding with subband-specific scanning, adaptive quantization, runlength coding, and adaptive buffering to equalize bit-rate fluctuations offer good objective and subjective image quality at moderate complexity and a bit-rate of 55 kb/s. Using a twin-class embedded-BCH error protection as well as pilot symbol 16 QAM and diversity assisted, the 22 kBd candidate system yields unimpaired image quality for average channel signal-to-noise ratios (SNRs) in excess of about 16-18 dB, when the mobile speed is 4 miles/h.>

A motion compensated interframe subband coding algorithm suitable for a wide range of video coding applications is described. In this approach the spectrum of each frame of video signal is first decomposed into smaller frequency bands where each can then be coded accordingly. For the best performance a combination of hybrid DCT/DPCM (discrete cosine transform/differential pulse code modulation), interframe DPCM, and intraframe PCM was considered. To preserve its hierarchical structure each band is coded independently of higher frequency bands but can share information with the lower bands. A simulation was carried out for HDTV sequences.>

Various subband coding schemes are developed for high compression video coding applications. These schemes are based on two distinct interframe subband models. Both models are compared and show that they perform equally under certain conditions. The first model, which is relatively less complex but operates at full speed, was considered for video conferencing applications at lower rates. The second model, however, due to its generic structure which operates at a reduced speed, was found to be suitable for high quality video applications. As a result, a CCITT compatible video coding scheme for HDTV conferencing is developed. For the best performance, the higher frequency bands were coded with a combination of interframe differential pulse code modulation (DPCM) and direct PCM.>

The author presents a method for subband coding of video signals. In this method, the difference between the input signal and the motion-compensated interframe prediction signal is decomposed into several narrow bands using separable two-dimensional quadrature mirror filtering (QMF). Each subband is then quantized by a symmetric uniform quantizer with a center dead zone. The nonzero quantized values are variable-word-length coded and transmitted together with their run-length-coded positional information. For interframe motion-compensated prediction, block matching motion estimation is used. Simulation results showing the efficiency of the method and the quality of the consecutive coded frames are presented. It is concluded that the method has potential for a wide range of high-compression video applications.>

In this paper an efficient method for subband coding of color images is presented. The basic approach is to transfer an RGB picture into YIQ components where each component is decomposed separately into several narrow bands. The higher band signals corresponding to the Y component are retained and coded separately, while the higher bands associated with I, and Q components are discarded. Furthermore, the low band signals are coded using a DPCM coding scheme. Our simulation results show that, by using such a coding scheme, good quality pictures can be reconstructed at low transmission rates.

In earlier publications, we have presented two coding schemes which take into account the conditional statistics of input signals. In the first scheme, the codewords are assigned in such a way as to provide a signal with long runs of zeros and ones. In the second scheme, each picture element is coded by variable-length codewords according to the values of previously transmitted PEL's. In this paper, by providing further results, we examine these coding schemes in greater detail. The performance of both schemes in terms of entropy and bit rate are compared with an optimum predictive coder. The simulation results indicate that these schemes have a significant advantage over standard predictive encoders. Methods to reduce the storage requirement for the encoder and decoder codebooks are also discussed.