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The platoon control for vehicles can efficiently reduce traffic pressure. Current control schemes are able to achieve stable platoon control, but cannot guarantee collision avoidance, connectivity preservation and convergence time at the same time. In this paper, we propose a novel control scheme that can simultaneously guarantee the safe distance and communication connectivity, which is called flexible safe distance constraint, and also can guarantee the specified convergence time. A dynamic gain based distributed control law is first designed for the vehicle with single-integral model. Using the prescribed transient and steady-state performance control approach, the flexible safe distance constraint can be satisfied. Using the time transformation method and Lyapunov stability theory, the closed-loop systems under the proposed protocols can achieve stable platoon within the specified time. Compared with some existing results, the novelty of this work is that the proposed approaches allow a vehicle to converge with the platoon within any preset time without dependence on the initial conditions or system parameters. Another contribution of this work is to propose specified-time platoon control protocols for the vehicle with double-integral model under a flexible safe distance constraint. Furthermore, in order to get closer to the actual system, the controller is extended to the triple-integral system, and some special cases are also discussed. Finally, some simulations are presented to show the effectiveness of the proposed protocols.

We develop a new location spoofing detection algorithm for geo-spatial tagging and location-based services in the Internet of Things (IoT), called Enhanced Location Spoofing Detection using Audibility (ELSA) which can be implemented at the backend server without modifying existing legacy IoT systems. ELSA is based on a statistical decision theory framework and uses two-way time-of-arrival (TW-TOA) information between the user's device and the anchors. In addition to the TW-TOA information, ELSA exploits the implicit available audibility information to improve detection rates of location spoofing attacks. Given TW-TOA and audibility information, we derive the decision rule for the verification of the device's location, based on the generalized likelihood ratio test. We develop a practical threat model for delay measurements spoofing scenarios, and investigate in detail the performance of ELSA in terms of detection and false alarm rates. Our extensive simulation results on both synthetic and real-world datasets demonstrate the superior performance of ELSA compared to conventional non-audibility-aware approaches., Comment: A shorten version of this work has been accepted to the IEEE IoT Journal (IoT-J) on 08-Feb-2016

This paper uses a spatial Aloha model to describe a distributed autonomous wireless network in which a group of transmit-receive pairs (users) shares a common collision channel via slotted-Aloha-like random access. The objective of this study is to develop an intelligent algorithm to be embedded into the transceivers so that all users know how to self-tune their medium access probability (MAP) to achieve overall Pareto optimality in terms of network throughput under spatial reuse while maintaining network stability. While the optimal solution requires each user to have complete information about the network, our proposed algorithm only requires users to have local information. The fundamental of our algorithm is that the users will first self-organize into a number of non-overlapping neighborhoods, and the user with the maximum node degree in each neighborhood is elected as the local leader (LL). Each LL then adjusts its MAP according to a parameter R which indicates the radio intensity level in its neighboring region, whereas the remaining users in the neighborhood simply follow the same MAP value. We show that by ensuring R less than or equal to 2 at the LLs, the stability of the entire network can be assured even when each user only has partial network information. For practical implementation, we propose each LL to use R=2 as the constant reference signal to its built-in proportional and integral controller. The settings of the control parameters are discussed and we validate through simulations that the proposed method is able to achieve close-to-Pareto-front throughput., 32 pages, 10 figures, accepted for publication in IEEE Transactions on Vehicular Technology

Inter-user interference occurs when multiple body sensor networks (BSNs) are transmitting simultaneously in close proximity to each other. Interference analysis in BSNs is challenging due to the hybrid medium access control (MAC) and the specific channel characteristics of BSNs. This paper presents a stochastic geometry analysis framework for inter-user interference in IEEE 802.15.6 BSNs. An extended Matern point process is proposed to model the complex spatial distribution of the interfering BSNs caused by the hybrid MAC defined in IEEE 802.15.6. We employ stochastic geometry approach to evaluate the performance of BSNs, considering the specific channel characteristics of BSNs in the vicinity of human body. Performance metrics are derived in terms of outage probability and spatial throughput in the presence of inter-user interference. We conduct performance evaluation through extensive simulations and show that the simulation results fit well with the analytic results. Insights are provided on the determination of the interference detection range, the BSN density, and the design of MAC for BSNs.

The wireless multihop backhaul is a unique feature of wireless mesh networks (WMNs), which necessitates redesign of association control algorithms. In this paper, we formulate and propose approximation algorithms for the problem of optimal joint association and bandwidth allocation in WMNs, considering max–min fairness (MM) and proportional fairness (PF) objectives. We first relax the integral association constraint and get an optimal fractional association solution. Then, we propose two rounding algorithms, namely, largest fraction rounding and bipartite graph rounding, to get an integral solution and analyze their theoretical approximation ratios. Finally, we propose two approximation ratio improvement algorithms so that the improved approximation ratio can more accurately reflect the true performance gap between the produced solution and the optimal one. Our simulation results show that the proposed algorithms achieve performance that is close to the optimal and outperform popular heuristic algorithms. We also compare the performance of PF and MM in WMNs in terms of network throughput and fairness in user bandwidth. Finally, we compare the performances of the proposed rounding algorithms and show that the approximation ratio can be reduced to 1–2 by the proposed ratio improvement algorithms. Therefore, our proposed algorithm is able to achieve nearly optimal association control, as well as bandwidth allocation, considering MM or PF, with small approximation ratios, in WMNs.

Network coding techniques are usually applied upon network-layer protocols to improve throughput in wireless networks. In scenarios with multiple unicast sessions, fairness is also an important factor. Therefore, a network coding-aware packet-scheduling algorithm is required. A packet-scheduling algorithm determines which packet to send next from a node’s packet backlog. Existing protocols mostly employ a basic round-robin scheduling algorithm to give “equal” opportunities to different packet flows. In fact, this “equal”-opportunity scheduling is neither fair, nor efficient. This paper intends to accentuate the importance of a coding-aware scheduling scheme. With a good scheduling scheme, we can gain more control over the per-flow throughput and fairness. Specifically, we first formulate a static scheduling problem and propose an algorithm to find the optimal scheduling scheme. We then extend the technique to a dynamic setting and, later, to practical routing protocols. Results show that the algorithm is comparatively scalable, and it can improve the throughput gain when the network is not severely saturated. The fairness among flows is drastically improved as a result of this scheduling scheme.

This paper proposes a novel self-contained pedestrian tracking method using a foot-mounted inertial and magnetic sensor module, which not only uses the traditional zero velocity updates, but also applies the stride information to further correct the acceleration double integration drifts and thus improves the tracking accuracy. In our method, a velocity control variable is designed in the process model, which is set to the average velocity derived from stride information in the swing (nonzero velocity) phases or zero in the stance (zero-velocity) phases. Stride-based position information is also derived as the pseudomeasurements to further improve the accuracy of the position estimates. An adaptive Kalman filter is then designed to fuse all the sensor information and pseudomeasurements. The proposed pedestrian tracking method has been extensively evaluated using experiments, including both short distance walking with different patterns and long distance walking performed indoors and outdoors, and have been shown to perform effectively for pedestrian tracking.

There have been researchers working on the design of coding-aware routing protocols to exploit the power of network coding in static wireless ad hoc networks. However, most of them have overlooked the fact that routing decisions for multiple flows need to be coordinated in order to achieve maximum throughput. A mechanism to alter prior routing decisions is mandatory for this purpose. In this paper, we propose Self-recommendation coding-aware routing (SCAR), to provide such a mechanism. With intermediate nodes sensing the arrival of new flows, they can send self-recommendations to source nodes, triggering a route-change procedure. In the route-change procedure, adjustments are applied to the route metrics so that the newly recommended route can be fairly weighed without bias. A thorough analysis of coding structures is carried out, and a series of indicators are devised to predict how much throughput benefits we can gain from the mere knowledge of the topology. The rationale behind the protocol design and the effectiveness of the indicators are further justified by a series of simulations. Results show that SCAR can exploit coding opportunities better and provide higher throughput than other coding-aware routing protocols. It is also shown that the opportunity of throughput gain is ubiquitous and it is tested on many typical topologies.

This paper presents a novel hierarchical information fusion algorithm to obtain human global displacement for different gait patterns, including walking, running, and hopping based on seven body-worn inertial and magnetic measurement units. In the first-level sensor fusion, the orientation for each segment is achieved by a complementary Kalman filter (CKF) which compensates for the orientation error of the inertial navigation system solution through its error state vector. For each foot segment, the displacement is also estimated by the CKF, and zero velocity update is included for the drift reduction in foot displacement estimation. Based on the segment orientations and left/right foot locations, two global displacement estimates can be acquired from left/right lower limb separately using a linked biomechanical model. In the second-level geometric fusion, another Kalman filter is deployed to compensate for the difference between the two estimates from the sensor fusion and get more accurate overall global displacement estimation. The updated global displacement will be transmitted to left/right foot based on the human lower biomechanical model to restrict the drifts in both feet displacements. The experimental results have shown that our proposed method can accurately estimate human locomotion for the three different gait patterns with regard to the optical motion tracker.

Context awareness, as one of the key techniques applied in ubiquitous computing, makes information technology invisible and seamless to people's daily living. As a result, numerous context frameworks have been developed for simplifying the development of context-aware applications by providing low-level context data operations such as acquisitions and simple aggregations in terms of APIs or toolkits. These frameworks are still falling short in requiring developers to explicitly deal with context-related tasks such as constraint enforcement in the application code. In this article, we present a framework to bridge the gap. More specifically, an application context model (ACM) is proposed for developers to specify their requirements on the context-related tasks. At application runtime, the ACM is instantiated for automatic context realization by the application context engine (ACE), which supports the full life cycle of each ACM instance (initialization, execution, and termination). We validate the concept of the framework through a case study, and present the experimental results based on the system prototype.

In this paper, we consider medium access control (MAC) protocol design for random-access cognitive radio (CR) networks. A two-level opportunistic spectrum access strategy is proposed to optimize the system performance of the secondary network and to adequately protect the operation of the primary network. At the first level, secondary users (SUs) maintain a sufficient detection probability to avoid interference with primary users (PUs), and the spectrum sensing time is optimized to control the total traffic rate of the secondary network allowed for random access when the channel is detected to be available. At the second level, two MAC protocols called the slotted cognitive radio ALOHA (CR-ALOHA) and cognitive-radio-based carrier-sensing multiple access (CR-CSMA) are developed to deal with the packet scheduling of the secondary network. We employ normalized throughput and average packet delay as the network metrics and derive closed-form expressions to evaluate the performance of the secondary network for our proposed protocols. Moreover, we use the interference and agility factors as the performance parameters to measure the protection effects on the primary network. For various frame lengths and numbers of SUs, the optimal performance of throughput and delay can be achieved at the same spectrum sensing time, and there also exists a tradeoff between the achievable performance of the secondary network and the effects of protection on the primary network. Simulation results show that the CR-CSMA protocol outperforms the slotted CR-ALOHA protocol and that the PUs' activities have an influence on the performance of SUs for both the slotted CR-ALOHA and CR-CSMA.

Advances in ubiquitous sensing and computing technologies, combined with the well developed theories in cognitive science, present major opportunities for the future Internet. We argue that the future Internet should be a usercentric and context-aware communication network, which goes far beyond today's host-centric and store-forward Internet. In this article we propose to explicitly introduce the end-user's context information into the future Internet framework. We, therefore, define a new functional module called the User-Context Module, and describe its architecture and key design principles. We also present two User-Context Module applications to aid gaining an understanding of its operation and impacts.

When a Body Sensor Network (BSN) that is linked to the backbone via a wireless network interface roams from one coverage zone to another, a handover is required to maintain network connectivity. This paper proposes an optimized BSN handover strategy which utilizes the movement trend of the BSN wearer and makes handover decisions based on the estimated future position of the user. Simulation results indicate that outage probability can be reduced by the proposed approach while unnecessary handover rate remains similar compared to that of the conventional methods. In addition, no extra equipment is needed for the proposed method.

This paper presents the generalized butterfly graph (GBG) and its application to video stream authentication. Compared with the original butterfly graph, the proposed GBG provides significantly increased flexibility, which is necessary for streaming applications, including supporting arbitrary bit-rate budget for authentication and arbitrary number of video packets. Within the GBG design, the problem of constructing an authentication graph is defined as follows: given the total number of packets to protect, the expected packet loss rate for the network, and the available overhead budget, how should one design the authentication graph to maximize the probability that the received packets are verifiable? Furthermore, given the fact that media packets are typically of unequal importance, we explore two variants of the GBG authentication, packet sorting and unequal authentication protection, which apply unequal treatment to different packets based on their importance. Lastly, we examine how the proposed GBG authentication can be applied within the context of rate-distortion-authentication (R-D-A) optimized streaming: given a media stream protected by GBG authentication, the R-D-A optimized streaming technique computes an optimized transmission schedule by recognizing and accounting for the authentication dependencies in the GBG authentication graph.

In this paper, we present a system model for multiuser multicode code-division multiple access (CDMA) in a multipath fading channel and propose a hybrid receiver scheme for the system. Conventional receivers for CDMA systems utilized interference cancellation (IC) schemes, with the RAKE receiver as an initial data estimator. However, the RAKE receiver generates inaccurate data estimates due the interference that is caused by the cross correlation between the spreading codes. This inaccurate data estimate leads to significant error propagation to the subsequent stages and thus degrades the bit error rate (BER) performance. Our proposed scheme overcomes the problem by using a more accurate initial data estimator. It consists of an equalizer for obtaining initial data estimation, followed by several stages of parallel IC (PIC). Computer simulation results show that the BER curves of our proposed scheme do not encounter an error floor under all channel conditions; in contrast, the BER curves of the conventional RAKE-PIC receiver are constrained by an irreducible error floor. In addition, in an uplink four-path channel and at a BER of 10-3, our simulation results show that a one-stage PIC achieves a 2.5-dB gain over the first stage equalization receiver.

We define authenticated video as decoded video that results from those received packets whose authenticities have been verified. Generic data stream authentication methods usually impose overhead and dependency among packets for verification. Therefore, the conventional rate-distortion (R-D) optimized video streaming techniques produce highly sub-optimal R-D performance for authenticated video, since they do not account for the overhead and additional dependencies for authentication. In this paper, we study this practical problem and propose an Rate-Distortion-Authentication (R-D-A) optimized streaming technique for authenticated video. Based on packets' importance in terms of both video quality and authentication dependencies, the proposed technique computes a packet transmission schedule that minimizes the expected end-to-end distortion of the authenticated video at the receiver subject to a constraint on the average transmission rate. Simulation results based on H.264 JM 10.2 and NS-2 demonstrate that our proposed R-D-A optimized streaming technique substantially outperforms both prior (authentication-unaware) R-D optimized streaming techniques and data stream authentication techniques. In particular, when the channel capacity is below the source rate, the PSNR of authenticated video quickly drops to unacceptable levels using conventional R-D optimized streaming techniques, while the proposed R-D-A Optimization technique still maintains optimized video quality. Furthermore, we examine a low-complexity version of the proposed algorithm, and also an enhanced version which accounts for the multiple deadlines associated with each packet, which is introduced by stream authentication

Energy awareness is a crucial component in the design of wireless sensor networks at all layers. This paper looks into efficient energy utilization of a target-tracking sensor network by predicting a target's trajectory through experience. While this is not new, the chief novelty comes in conserving energy through both dynamic spatial and temporal management of sensors while assuming minimal locality information. We adapted our target trajectory model from the Gauss-Markov mobility model, formulated the tracking problem as a hierarchical Markov decision process (HMDP), and solved it through neurodynamic programming. Our HMDP for target-tracking (HMTT) algorithm conserves energy by reducing the rate of sensing (temporal management) but maintains an acceptable tracking accuracy through trajectory prediction (spatial management) of multiple targets. We derived some theoretical bounds on accuracy and energy utilization of HMTT. Simulation results demonstrated the effectiveness of HMTT in energy conservation and tracking accuracy against two other predictive tracking algorithms, with accuracy of up to 47% higher and energy savings of up to 200%

This paper proposes an optimized content-aware authentication scheme for JPEG-2000 streams over lossy networks, where a received packet is consumed only when it is both decodable and authenticated. In a JPEG-2000 codestream, some packets are more important than others in terms of coding dependency and image quality. This naturally motivates allocating more redundant authentication information for the more important packets in order to maximize their probability of authentication and thereby minimize the distortion at the receiver. Towards this goal, with the awareness of its corresponding image content, we formulate an optimization framework to compute an authentication graph to maximize the expected media quality at the receiver, given specific authentication overhead and knowledge of network loss rate. System analysis and experimental results demonstrate that the proposed scheme achieves our design goal in that the rate-distortion (R-D) curve of the authenticated image is very close to the R-D curve when no authentication is required

This paper studies the performance of overlay device-to-device (D2D) communication links via carrier sense multiple access (CSMA) protocols. We assume that the D2D links have heterogeneous rate requirements and different willingness to pay, and each of them acts non-altruistically to achieve its target rate while maximizing its own payoff. Spatial reuse is allowed if the links are not interfering with each other. A non-cooperative game model is used to address the resource allocation among the D2D links, at the same time leveraging on the ideal CSMA network (ICN) model to address the physical channel access issue. We propose a Stackelberg game in which the base station in the cellular network acts as a Stackelberg leader to regulate the individual payoff by modifying the unit service price so that the total D2D throughput is maximized. The problem is shown to be quasi-convex and can be solved by a sequence of equivalent convex optimization problems. The pricing strategies are designed so that the network always operates within the feasible throughput region. The results are verified by simulations., 32 pages, 11 figures, accepted for publication in IEEE Transactions on Vehicular Technology, Dec 11, 2015

A wearable sensor system enables continuous and remote health monitoring and is widely considered as the next generation of healthcare technology. The performance, the packet error rate (PER) in particular, of a wearable sensor system may deteriorate due to a number of factors, particularly the interference from the other wearable sensor systems in the vicinity. We systematically evaluate the performance of the wearable sensor system in terms of PER in the presence of such interference in this paper. The factors that affect the performance of the wearable sensor system, such as density, traffic load, and transmission power in a realistic moderate-scale deployment case in hospital are all considered. Simulation results show that with 20% duty cycle, only 68.5% of data transmission can achieve the targeted reliability requirement (PER is less than 0.05) even in the off-peak period in hospital. We then suggest some interference mitigation schemes based on the performance evaluation results in the case study.

In this brief, we present an image entropy coder, context-based bit-plane Golomb coder (CB-BPGC), for wavelet-based scalable image coding. CB-BPGC follows the idea of the state-of-the-art image coding standard JPEG2000 entropy coding to apply the rate-distortion optimization algorithm after block coding. However, it explores a more efficient block coding where statistical properties of the block coefficients are considered. Compression ratio and error resilience performances of the proposed coder are evaluated, and the experimental results show that, compared with the JPEG2000, it achieves better lossless and lossy coding performance with lower complexity and greater resilience to transmission errors when simulated on the wireless Rayleigh fading channel

Our analysis and simulations show that in a practical ATM network environment consisting of a mix of low cost ABR binary switches and higher cost ABR ERICA (explicit rate) switches, partially compliant ABR sources can illegally grab more bandwidth from the network without being detected. Consequently, fully compliant ABR sources lose their available fair share. At the same time, congestion conditions are experienced at the binary switches. Three schemes are contributed, namely SDP (partial-behaving user detection and punishment), DFC (Direct Fairness Control) and IFC (Instantaneous Fairness Control), all of which can be implemented in any ERICA switches with negligible increase in complexity, to overcome ABR source misbehaviour. Of the three, the IFC scheme is the most promising in terms of restoring fair share and reducing congestion in the binary switches.

Dynamic spectrum access in the form of cognitive radio (CR) has gained traction in wireless sensor networks (WSN) because of a) scarcity caused by the proliferation of wireless devices and service and b) it provides spectrum efficient communication for the resource constrained WSNs. However, proper means have to be devised to satisfy the requirements of both WSNs and CRs and to enjoy the benefits of cognition in sensor networks. In this paper, we propose a novel energy-efficient and spectrum aware multi-channel medium access control (MAC) protocol for the underlying cognitive radio enabled sensor network. We designed a spectrum aware asynchronous duty cycle approach which caters to the requirements of both the domains. The performance of the proposed MAC is evaluated via simulations and analytical methods. The simulation results are also compared with a multi-channel MAC (MCMAC) for WSNs. The comparative results show that the proposed approach outperforms the multi-channel scheme for WSN.

When a body sensor network (BSN) that is linked to the backbone via a wireless network interface moves from one coverage zone to another, a handover is required to maintain network connectivity. This paper presents an optimized handover scheme with movement trend awareness for BSNs. The proposed scheme predicts the future position of a BSN user using the movement trend extracted from the historical position, and adjusts the handover decision accordingly. Handover initiation time is optimized when the unnecessary handover rate is estimated to meet the requirement and the outage probability is minimized. The proposed handover scheme is simulated in a BSN deployment area in a hospital environment in UK. Simulation results show that the proposed scheme reduces the outage probability by 22% as compared with the existing hysteresis-based handover scheme under the constraint of acceptable handover rate.

Aloha games study the transmission probabilities of a group of non-cooperative users which share a channel to transmit via the slotted Aloha protocol. This paper extends the Aloha games to spatial reuse scenarios, and studies the system equilibrium and performance. Specifically, fixed point theory and order theory are used to prove the existence of a least fixed point as the unique Nash equilibrium (NE) of the game and the optimal choice of all players. The Krasovskii's method is used to construct a Lyapunov function and obtain the conditions to examine the stability of the NE. Simulations show that the theories derived are applicable to large-scale distributed systems of complicated network topologies. An empirical relationship between the network connectivity and the achievable total throughput is finally obtained through simulations., 26 pages, 9 figures, 1 table, accepted by IEEE Transactions on Wireless Communications, June 15, 2013

The greatest single factor in enhancing spectral efficiency of a network is the mass deployment of microcells. By this simple technique we can repeatedly and efficiently reuse the precious spectrum. The number of users a network can support is fundamentally dependent on the common air interface (CAI) over which users communicate. User capacity is dependent on many factors, but the cardinal ones are the amount of spectrum the regulators allocate, the size of the radio coverage area from a base station (BS), and the amount of interference a particular radio link can tolerate. In this article we are primarily concerned with the system aspects associated with the CAI. We focus on the critical importance of BS siting. Starting with existing large cells, we deliberate on the problems that might arise in siting BSs in three dimensional microcells, in order to consider suitable multiple access methods for future cellular environments. >

Various strategies to provide low-delay high-quality digital speech communications in a high-capacity wireless network are examined. Various multiple access schemes based on time-division and packet reservation are compared in terms of their statistical multiplexing capabilities, sensitivity to speech packet dropping, delay, robustness to lossy packet environments, and overhead efficiency. In particular, a low-delay multiple access scheme, called shared time-division duplexing (STDD) is proposed. This scheme allows both the uplink and downlink traffic to share a common channel, thereby achieving high statistical multiplexing gain even with a low population of simultaneous conversations. The authors also propose a choice of low delay, high quality speech coding and digital modulation systems based on adaptive DPCM, with QDPSK or pseudo-analog transmission (skewed DPSK), for use in conjunction with the STDD multiple access protocol. The choice of the alternative systems depends on required end-to-end delay, recovered speech quality and bandwidth efficiency. Typically, with a total capacity of 1 MBaud, 2 ms frame and 8 kBaud speech coding rate, low delay STDD is able to support 48 pairs of users compared to 38, 35, and 16 for TDMA with speech activity detection, basic TDMA and PRMA respectively. This corresponds to respective gains of 26%, 37% and 200%. >

The author studies the performance of a high capacity metropolitan microcellular radio network using computer simulation. Packet reservation multiple access carriers are dynamically assigned or released depending on current teletraffic loading conditions. Significant performance improvements are obtained using a 2-stage costing strategy which attempts to balance call blocking probabilities against packet dropping rate, thereby leading to more efficient utilisation of channel resources. The author achieves 40 to 50% improvements over a fixed allocation scheme in terms of the blocking probability performance, by soft assigning carriers to the microcells and performing a 2-stage dynamic carrier allocation procedure based on a simple costing algorithm which attempts to pack co-carrier cells as closely as possible. >

In a metropolitan microcellular environment, the cell coverage zone can be highly irregular. Thus highly overlapping areas can result due to an attempt to achieve ubiquitous coverage. The authors propose a predictive load sharing (PLS) scheme to alleviate localised congestion by using the knowledge of users potentially entering and leaving a cell. They study the system in a linear bidirectional highway environment. Results show that load carried is increased and the handoff failure rate is lowered compared to the fixed channel assignment (FCA) scheme. A lower handoff failure rate is a desirable feature since the forced termination of an existing call can be very annoying to a user. >

The authors propose an ordered dynamic channel assignment with reassignment (ODCAR) scheme and study its performance in a highway microcellular radio environment where the microcells are shaped to segments of the highway. Channels are assigned on an ordered basis in conjunction with a minimax algorithm to provide high capacity and to alleviate worst case channel congestion in each microcell. Simulation results show significant performance improvements in terms of channel utilization and probability of call failure. The load sharing feature of this improved scheme is demonstrated in a highway microcellular radio network with an asymmetrical teletraffic load condition. The authors examine how load sharing is accomplished under such circumstances. >

The problem of jointly optimizing the transmitter and receiver beamforming weights in the downlink of a cyclic prefix-free MC-CDMA system over multipath fading channels is addressed in this paper. Both the base station and user terminals are equipped with antenna arrays to leverage on the spatial information provided by the antenna arrays. The precoding and equalization matrices are designed with the aim of minimizing the overall mean-squared-error (MSE) of the system subject to a power constraint for each transmitter antenna, which has the additional benefit of reducing the probability of clipping of the transmitted signals from the transmitter. This is highly favorable for a MC-CDMA system due to the multi-carrier modulation involved. The performance of the optimization process is supported by simulation results.

Video streaming with authentication is practically important, where a packet is decoded only when it is both received and authenticated. Recent work examined the problem of rate-distortion-authentication (R-D-A) optimized streaming of authenticated video. The original R-D-A technique assumes that each packet has only one deadline, its display deadline, and that a packet is not considered for transmission after its deadline. However, for video protected with an inter-packet graph-based authentication technique, a video packet can still be useful for verification of other packets even if it misses its own display deadline. We formulate the problem of multiple-deadline R-D-A optimized streaming and also propose ways to reduce the complexity. Simulation results using H.264 and NS-2 demonstrate that multiple-deadline R-D-A optimization achieves performance improvements of up to 4 dB over single-deadline R-D-A optimization.

This paper proposes a stream authentication method based on the generalized butterfly graph (GBG) framework. Compared with the original Butterfly graph, the proposed GBG graph supports an arbitrary overhead budget and number of packets. Within the GBG framework, the problem of constructing an authentication graph is considered as a design problem: Given total number of packets, packet loss rate, and overhead budget, we show how to design the graph (number of rows and columns and edge allocation among nodes) to maximize the expected number of verified packets. In addition, we also propose a new evaluation metric called loss-amplification-factor (LAF), which measures the extent to which the authentication method exacerbates the effective packet loss rate. Experimental results demonstrate significant performance improvements over existing authentication methods like EMSS, augmented chain, and the original Butterfly.

In this paper, we propose an optimized content-aware authentication scheme for JPEG-2000 streams over lossy networks, where a received packet is consumed only when it is both decodable and authentic. In a JPEG-2000 codestream some packets are more important than others in terms of coding dependency and visual quality. This inspires us to allocate more redundant authentication information for the more important packets to minimize the distortion of the authenticated image at the receiver. In other words, with the awareness of image content, we formulate an optimization framework, which is able to build an authentication graph yielding the best visual quality at the receiver, given a specific authentication overhead and network condition. Experimental results demonstrate that the proposed scheme achieved our design goals in that the R-D curve of an authenticated image is very close to its original one where no authentication is applied.

This paper proposes a content-aware authentication scheme optimized to account for distortion and overhead for media streaming. When authenticated media is streamed over a lossy network, a received packet is consumed only when it is both decodable and authenticated. In most media formats, some packets are more important than others. This naturally motivates allocating more redundant authentication information for the more important packets in order to maximize their probability of authentication and thereby minimize distortion at the receiver. Toward this goal, with awareness of the media content, we formulate an optimization framework to compute an authentication graph to maximize the expected media quality at the receiver, given specific authentication overhead and knowledge of network loss rates. Experimental results with JPEG-2000 coded images demonstrate that the proposed method achieves our design goal in that the R-D curve of the authenticated image is very close to the R-D curve when no authentication is required.

In this paper, we propose a butterfly-graph based stream authentication scheme for lossy networks where the streaming packets could be lost in both random and burst ways. Due to the nice properties of butterfly graph, the proposed scheme is quite robust and efficient. Theoretical analysis and simulation results show that the proposed scheme outperforms existing schemes in terms of overhead and authentication probability while maintaining the same levels of sender/receiver delay and robustness.

In this paper, we present a new entropy coder, context-based bit plane Golomb coder (CB-BPGC) for scalable image coding, which achieves better coding performance with lower complexity compared to the state-of-the-art JPEG 2000 entropy coder EBCOT. Because of the direct output lazy bit planes, applying the partial decoding on the corrupted bit planes, and the better compression ratio which may lead to corruption to the less important codestream, CB-BPGC appears more resilient to errors when simulated on the wireless channel based on Rayleigh fading model.

An analytical model to describe the statistical multiplexing performance in a variable partition duplexing (VPD) multiple access scheme is described. The analytical and simulation results are shown to agree closely for a variety of conditions.

The effect of queuing on an ordered dynamic channel assignment with reassignment (QODCAR) scheme in a highway microcellular environment are studied. Results show that queuing improves channel use by approximately 9-43%, and significantly lowers the probability of call failure. >

A hybrid approach in determining the excitation vector in a low-delay code excited linear predictive coder is proposed. By a judicious division of the composite excitation vector into long-term and short-term components, and the use of switched quantisation, substantial improvement in coding quality is obtained.

In a highway microcellular structure, accidents and road works result in localised congestions contributing to asymmetrical teletraffic load situations. A dynamic load-sharing scheme based on a reconfigurable overlapped cellular coverage is investigated for various teletraffic conditions. System performance in terms of the probabilities of new calls blocked and handoff failure are improved significantly with this scheme.