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Vehicular Technology, IEEE Transactions on

Issue 8 • Date Oct. 2010

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  • Table of contents

    Page(s): C1 - C4
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    Freely Available from IEEE
  • IEEE Transactions on Vehicular Technology publication information

    Page(s): C2
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  • A Polarized Clustered Channel Model for Indoor Multiantenna Systems at 3.6 GHz

    Page(s): 3685 - 3693
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (870 KB) |  | HTML iconHTML  

    Multiple-input-multiple-output (MIMO) technologies allow high data rates to be obtained, but they suffer from interantenna correlation caused by the limits in interantenna spacing. Polarized MIMO systems resolve this problem by using colocated perpendicularly polarized antennas that have low interantenna correlation. In this paper, a polarized single-directional channel model for 2×N MIMO systems at 3.6 GHz in an indoor environment is presented. The wireless channel is modeled as a sum of clusters, where each cluster has specular and diffuse components. The polarization of the specular component of the clusters is included by considering a per-path polarization. The diffuse component of the clusters is modeled with a Fisher-Bingham (FB5) spectrum in the azimuth-coelevation domain and with an exponential power delay profile. Polarization is analyzed by introducing the cross-polar discrimination of the exponential power delay profile parameters. All of the parameters in the model are extracted from an experimental measurement campaign performed in an indoor environment at 3.6 GHz. Individual paths are extracted from the measurements with the space-alternating generalized expectation-maximization (SAGE) algorithm. These paths are grouped in clusters within the azimuth of arrival-elevation of arrival-delay domains at the receiver side using automatic clustering algorithms. The specular component properties of the clusters are then determined. Finally, the diffuse components of the clusters are investigated and parameterized by applying a beamforming algorithm on the diffuse part of the impulse response. View full abstract»

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  • An Enhanced Background Estimation Algorithm for Vehicle Detection in Urban Traffic Scenes

    Page(s): 3694 - 3709
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3739 KB) |  | HTML iconHTML  

    This paper proposes a new background subtraction algorithm based on the sigma-delta filter, which is intended to be used in urban traffic scenes. The original sigma-delta algorithm is a very interesting alternative due to its high computational efficiency. However, the background model quickly degrades in complex urban scenes because it is easily “contaminated” by slow-moving or temporarily stopped vehicles. Then, subsequent foreground validation steps are needed to refine the foreground detection mask. Instead of requiring any subsequent processing steps or resorting to algorithms with higher computational cost, the proposed algorithm tries to achieve a more stable background model by introducing a confidence measurement for each pixel. This confidence measurement assists in a selective background-model updating mechanism at the pixel level. Experimental comparative tests and a quantitative performance evaluation over typical urban traffic sequences corroborate the benefits of the proposed algorithm. View full abstract»

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  • Statistical Development of a Duty Cycle for Plug-in Vehicles in a North American Urban Setting Using Fleet Information

    Page(s): 3710 - 3719
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (898 KB) |  | HTML iconHTML  

    Development of a daily duty cycle based on real-world driving behavior and parking times is a critical requirement in the optimal design of power-train components of a plug-in vehicle. Standard driving cycles cannot completely emulate the real-world power demand of a vehicle and its downtimes in particular. To address these shortcomings, a large database of one year of measured data collected from a fleet of 76 cars in the city of Winnipeg, MB, Canada, is obtained and is then used to develop a new duty cycle. This paper describes a methodology for statistical analysis of the fleet data, including while a vehicle is parked. Due to the intrinsic differences in vehicle usage profiles during weekdays and weekends, two 24-h duty cycles with suitable windows of opportunity for charging are developed for weekday and weekend driving patterns. The uniqueness of the proposed statistical methodology and the resulting duty cycles contribute to addressing the present shortcomings of standard driving cycles. View full abstract»

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  • Beacon-Aided Adaptive Localization of Noise Sources Aboard a Pass-By Railcar Using a Trackside Microphone Array

    Page(s): 3720 - 3727
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (690 KB) |  | HTML iconHTML  

    A new adaptive “beamforming” signal-processing algorithm is developed to locate the loudest noise sources aboard a railcar that passes by a trackside immobile microphone array. This proposed microphone-array beamformer tracks the railcar's spatial movement with the aid of two inaudible acoustic beacons placed aboard the railcar. The proposed scheme then localizes the noise sources with reference to the railcar's coordinates. No auxiliary infrastructure (e.g., no radar or video camera) is needed besides the onboard beacons. Monte Carlo simulations and anechoic chamber experiments verify the efficacy of the proposed scheme. View full abstract»

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  • Estimation of Engine Rotational Dynamics Using Kalman Filter Based on a Kinematic Model

    Page(s): 3728 - 3735
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1516 KB) |  | HTML iconHTML  

    For a conventional scooter engine with a four-plus-one-tooth crankshaft wheel, not only is the crankshaft position estimation insufficient due to poor angle resolution, but the speed measurement might also be easily contaminated by the sensor noise. We proposed a Kalman filter with stroke identification to estimate the engine rotational dynamics. The design of the Kalman filter is based on a kinematic model that requires no engine parameters. A nonlinear engine model is used to evaluate the estimation performance of the conventional algorithm using a low-pass filter and the proposed algorithm at various operating conditions. Preliminary simulation and experimental results show that the proposed algorithm can mitigate the noise impact and result in estimations closer to the actual engine responses. View full abstract»

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  • Asymmetrical Multilevel Inverter for Traction Drives Using Only One DC Supply

    Page(s): 3736 - 3743
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1347 KB) |  | HTML iconHTML  

    The main advantage of asymmetrical multilevel inverters is the optimization of levels with a minimum number of power supplies. However, this optimized multilevel system still needs a large number of isolated and floating dc supplies, which makes these converters complicated to implement in electric vehicles (EVs), because the system will require many independent battery packs. In this paper, a very simple scheme, based on a small and cheap high-frequency link (HFL), allows the utilization of only one power supply for the complete multilevel inverter drive, with an inherent regulation of the voltages supplied among the H-bridges. It also allows voltage control with the full number of levels if the dc source is of a variable voltage characteristic. This paper is focused on a 27-level asymmetric inverter, but the strategy, using only one power supply, can be applied to converters with any number of levels. In particular, an asymmetrical 27-level converter needs nine isolated power supplies, and the proposed system reduces these nine sources to only one: the battery car. The topology also permits full regenerative braking working as a three-level converter. The proposed system is intended for application in EVs from power ratings up to 150 kW. Simulations and experimental results show the feasibility to implement this “one-source” multilevel system. View full abstract»

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  • Anti-Temporal-Aliasing Constraints for Image-Based Feature Tracking Applications With and Without Inertial Aiding

    Page(s): 3744 - 3756
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (723 KB) |  | HTML iconHTML  

    Image-aided navigation techniques can determine the navigation solution (position, velocity, and attitude) by observing a sequence of images from an optical sensor over time. This operation is based on tracking the location of stationary objects in multiple images, which requires solving the correspondence problem. This paper enhances previous research efforts to characterize the correspondence problem using fundamental optical principles and statistical temporal sampling theory by including a rigorous derivation of the Nyquist constraint in pixel space. This development results in a general temporal sampling constraint and reveals the essential connection between the deleterious effects of temporal aliasing and the ambiguities that plague the correspondence search problem. This temporal image sampling constraint is expressed as a function of the navigation trajectory for elementary camera motions. The predicted temporal sampling (also known as frame) rates are on the order of those needed for adaptive optics control systems and require very large bandwidths. The temporal image sampling constraint is then reevaluated by incorporating inertial measurements. The incorporation of inertial measurements is shown to reduce the required temporal sampling rate to practical levels, which evidences the fundamental synergy between image and inertial sensors for navigation and serves as the basis for a real-time adaptive antialiasing strategy. View full abstract»

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  • Neural Network Based Self-Learning Control Strategy for Electronic Throttle Valve

    Page(s): 3757 - 3765
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (467 KB) |  | HTML iconHTML  

    Recently, the application of the electronic throttle has been very popular in the automotive industry. However, difficulties in the control of electronic throttle valves exist due to multiple nonlinearities and plant parameter variations. A neural-network-based self-learning control (SLC) strategy that consists of a fuzzy neural network (FNN) controller and a recurrent neural network (RNN) identifier is proposed for electronic throttle valves in this paper. The FNN controller, which combines the semantic transparency of rule-based fuzzy systems with the learning capability of a neural network, is utilized as an SLC scheme and will be robust to plant parameter variations. An RNN identifier is employed to model the plant and provides plant information for the learning of the FNN controller. Both the structure and the learning algorithm of the control system are presented. The proposed controller is verified by computer simulations and experiments. View full abstract»

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  • Fast Link Adaptation for MIMO OFDM

    Page(s): 3766 - 3778
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (493 KB) |  | HTML iconHTML  

    We investigate link-quality metrics (LQMs) based on raw bit-error-rate, effective signal-to-interference-plus-noise ratio, and mutual information (MI) for the purpose of fast link adaptation (LA) in communication systems employing orthogonal frequency-division multiplexing and multiple-input-multiple-output (MIMO) antenna technology. From these LQMs, the packet error rate (PER) can be estimated and exploited to select the modulation and coding scheme (MCS) among a class of candidate MCSs that achieves the maximum throughput for the current channel state under a specified target PER objective. We propose a novel MI-based LQM and compare the PER-estimation accuracy obtained with this LQM with that resulting from using other LQMs by means of comprehensive Monte Carlo simulations. Search methods for the MCS in the class that is most suitable for a given channel state are presented. An algorithm for obtaining a practical upper bound on the throughput of any LA scheme is proposed. The investigated LQMs are applied to the IEEE 802.11n standard with a 2 × 2 MIMO configuration and practical channel estimation. The proposed MI-based LQM yields the highest PER estimation accuracy, and its throughput shows only 1.7 dB signal-to-noise-ratio (SNR) loss with respect to the upper bound but up to 9.5 dB SNR gain, compared to the MCS maximizing the throughput for the current noise variance. View full abstract»

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  • Using Fountain Codes to Control the Peak-to-Average Power Ratio of OFDM Signals

    Page(s): 3779 - 3785
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB) |  | HTML iconHTML  

    In this paper, we apply fountain codes to control the peak-to-average power ratio (PAPR) of orthogonal frequency-division multiplexing (OFDM) signals. The main key idea of the proposed scheme is based on the fact that the best fountain-coded OFDM packets can be generated with a low PAPR. Both theoretical analysis and simulation results prove that the proposed scheme can effectively obtain the desirable PAPR and good throughput with rateless codes. Moreover, the flexibility of controlling PAPR makes the proposed scheme more suitable for implementing random frame sizes and providing effective error detection. View full abstract»

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  • Joint Transmitter–Receiver Frequency-Domain Equalization in Generalized Multicarrier Code-Division Multiplexing Systems

    Page(s): 3786 - 3797
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (399 KB) |  | HTML iconHTML  

    Joint transmitter-receiver optimization in generalized multicarrier code-division multiplexing (GMC-CDM) systems is investigated in this paper. The optimization consists of a one-tap post-frequency-domain equalizer (post-FDE) and a one-tap pre-FDE. While the one-tap post-FDE is optimized under the criterion of minimum mean square error (MMSE), the one-tap pre-FDE is achieved through three stages of optimization, which are operated at different levels and motivated to achieve, possibly, different objectives, including maximum throughput and maximum reliability. Specifically, in our three-stage pre-FDE, the first-stage pre-FDE is operated at the symbol level, concerning only the symbols within a group. The second-stage pre-FDE is carried out at the group level for harmonization among the groups. Finally, the third-stage pre-FDE handles group partition. In this paper, the error and throughput performance of the GMC-CDM systems is investigated when assuming communications over frequency-selective Rayleigh fading channels. It can be shown that the reliability or throughput of the GMC-CDM systems can be significantly improved by employment of the proposed pre- and post-FDE schemes. Furthermore, the pre- and post-FDE algorithms obtained can be implemented with high flexibility, which facilitates a GMC-CDM system to achieve a good tradeoff between its throughput and reliability. View full abstract»

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  • Preequalizer Design for Spatial Multiplexing SIMO-UWB TR Systems

    Page(s): 3798 - 3805
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (767 KB) |  | HTML iconHTML  

    A spatial multiplexing single-input-multiple-output (SM-SIMO) ultrawideband (UWB) communication system using the time-reversal (TR) technique is proposed in this paper. The system with only one transmit antenna, using a spatial multiplexing scheme, can transmit several independent data streams to achieve a very high data rate. To cope with the long delay spread of the UWB channel, the TR technique is adopted. TR can mitigate not only the intersymbol interference (ISI) but the multistream interference (MSI) caused by multiplexing several data streams simultaneously as well. Preequalization using the channel state information (CSI), which is already available at the transmitter in TR systems, is proposed to further eliminate the ISI and MSI. Simulation results show that the preequalization based on shortened equivalent channels can considerably improve the bit error rate (BER) performance of the system. View full abstract»

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  • Blind Spectrum Sensing by Information Theoretic Criteria for Cognitive Radios

    Page(s): 3806 - 3817
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB) |  | HTML iconHTML  

    Spectrum sensing is a fundamental and critical issue for opportunistic spectrum access in cognitive radio networks. Among the many spectrum-sensing methods, the information theoretic criteria (ITC)-based method is a promising blind method that can reliably detect the primary users while requiring little prior information. In this paper, we provide an intensive treatment on the ITC sensing method. To this end, we first introduce a new overdetermined channel model constructed by applying multiple antennas or oversampling at the secondary user to make ITC applicable. Then, a simplified ITC sensing algorithm is introduced, which needs to compute and compare only two decision values. Compared with the original ITC sensing algorithm, the simplified algorithm significantly reduces the computational complexity with no loss in performance. Applying the recent advances in random matrix theory, we then derive closed-form expressions to tightly approximate both the probability of false alarm and the probability of detection. Based on the insight derived from the analytical study, we further present a generalized ITC sensing algorithm that can provide a flexible tradeoff between the probability of detection and the probability of false alarm. Finally, comprehensive simulations are carried out to evaluate the performance of the proposed ITC sensing algorithms. Results show that they considerably outperform other blind spectrum-sensing methods in certain cases. View full abstract»

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  • Partial Equalization for MC–CDMA Systems in Non-Ideally Estimated Correlated Fading

    Page(s): 3818 - 3830
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (735 KB) |  | HTML iconHTML  

    Multicarrier code-division multiple access (MC-CDMA) can support high data rates in next-generation multiuser wireless communication systems. Partial equalization (PE) is a low-complexity technique for combining the signals of subcarriers to improve the achievable performance of MC-CDMA systems in terms of their bit error probability (BEP) and bit error outage (BEO) in comparison with maximal ratio combining, orthogonality restoring combining, and equal-gain combining techniques. We analyze the performance of the multiuser MC-CDMA downlink and derive the optimal PE parameter expression, which minimizes the BEP. Realistic imperfect channel estimation and frequency-domain (FD) block-fading channels are considered. More explicitly, the analytical expression of the optimum PE parameter is derived as a function of the number of subcarriers, number of active users (i.e., the system load), mean signal-to-noise ratio (SNR), and variance of the channel-estimation errors for the aforementioned FD block-fading channel. We show that the choice of the optimal PE technique significantly increases the achievable system load for the given target BEP and BEO. View full abstract»

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  • Secure Transmission With Artificial Noise Over Fading Channels: Achievable Rate and Optimal Power Allocation

    Page(s): 3831 - 3842
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1197 KB) |  | HTML iconHTML  

    We consider the problem of secure communication with multiantenna transmission in fading channels. The transmitter simultaneously transmits an information-bearing signal to the intended receiver and artificial noise to the eavesdroppers. We obtain an analytical closed-form expression of an achievable secrecy rate and use it as the objective function to optimize the transmit power allocation between the information signal and the artificial noise. Our analytical and numerical results show that equal power allocation is a simple yet near-optimal strategy for the case of noncolluding eavesdroppers. When the number of colluding eavesdroppers increases, more power should be used to generate the artificial noise. We also provide an upper bound on the SNR, above which, the achievable secrecy rate is positive and shows that the bound is tight at low SNR. Furthermore, we consider the impact of imperfect channel state information (CSI) at both the transmitter and the receiver and find that it is wise to create more artificial noise to confuse the eavesdroppers than to increase the signal strength for the intended receiver if the CSI is not accurately obtained. View full abstract»

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  • Location-Aided Gateway Advertisement and Discovery Protocol for VANets

    Page(s): 3843 - 3858
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1032 KB) |  | HTML iconHTML  

    Intelligent transportation systems (ITSs) are gaining momentum among researchers. ITS encompasses several technologies, including wireless communications, sensor networks, voice and data communication, real-time driving-assistant systems, etc. These state-of-the-art technologies are expected to pave the way for a plethora of vehicular network applications. However, ITS faces difficult issues when trying to widely deploy such networks and applications. The interconnection of different networks, even in the case of the Internet, is one of the main difficulties that is delaying the wide spread of vehicular networks. In this paper, we present a novel gateway discovery technique for vehicular ad hoc networks (VANets). Our protocol aims to provide an efficient hybrid adaptive Location-Aided Gateway Advertisement and Discovery (LAGAD) mechanism for VANets. First, it permits gateway clients to discover nearby gateways; then, gateways keep advertising themselves to their clients to permit client information about the route toward the discovered gateway without having to resort to reactive route discovery. We discuss the implementation of our algorithm and present its proof of correctness, in addition to the performance evaluation demonstrated through an extensive set of simulation experiments using a Manhattan mobility model. Our results indicate that our LAGAD scheme is scalable and that a significant success rate could be achieved using our algorithm while guaranteeing low response time (on the order of milliseconds) and low bandwidth usage when compared with other gateway discovery approaches. Moreover, our results indicate that LAGAD achieves a high delivery ratio of data packets, as well as a low end-to-end delay, and permits duplicate and ordered data packet reception at the destination gateway. View full abstract»

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  • Energy Provisioning in Solar-Powered Wireless Mesh Networks

    Page(s): 3859 - 3871
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (600 KB) |  | HTML iconHTML  

    Solar-powered wireless mesh nodes must be provisioned with a solar panel and battery combination that is sufficient to prevent node outage. This is normally done using historical solar insolation data for the desired deployment location and based on a temporal bandwidth usage profile (BUP) for each deployed node. Unfortunately, conventional methodologies do not take into account the use of energy-aware routing, and therefore, the deployed system may be overprovisioned and unnecessarily expensive. In this paper, we consider this resource assignment problem with the objective of minimizing the network deployment cost for a given energy source assignment. We first propose a resource-provisioning algorithm based on the use of temporal shortest-path routing and taking into account the node energy flow for the target deployment time period. We then introduce a methodology that incorporates energy-aware routing into the resource-assignment procedure. A genetic algorithm (GA) has been developed for this purpose. Our results show the large cost savings that an energy-aware resource assignment can achieve when compared with that done using the conventional methodology. To evaluate the quality of the resource assignments, we also develop a linear programming formulation that gives a lower bound on the total network resource assignment. Our results show that significant resource savings are possible using the proposed algorithms and the potential resource assignment benefits of energy-aware routing. View full abstract»

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  • A Service/Device Differentiation Scheme for Contention-Tone-Based Wireless LAN Protocol

    Page(s): 3872 - 3885
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (402 KB) |  | HTML iconHTML  

    A contention-tone-based wireless local area network (WLAN) protocol uses out-of-band signaling for contention resolution to achieve efficient medium access. It is shown that such a protocol can operate at near-optimal channel utilization in the medium access control (MAC) layer. This paper addresses the service differentiation design aspect of a contention-tone-based WLAN protocol. In particular, service and device differentiation schemes are proposed to fulfill a particular quality of service (QoS) for data packet transmissions for contention-tone-based WLANs. Our analysis shows that our design not only provides bandwidth differentiation that matches that specified in the IEEE 802.11e standard but operates at near-optimal channel utilization as well. Our design also incorporates device differentiation to eliminate the access-point bottleneck problem in WLANs. Analytical and simulation results confirm the performance advantages of our design. View full abstract»

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  • QoS and Channel-Aware Packet Bundling for Capacity Improvement in Cellular Networks

    Page(s): 3886 - 3901
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (864 KB) |  | HTML iconHTML  

    We study the problem of multiple-packet bundling to improve spectral efficiency in cellular networks. The packet size of real-time data, such as voice over Internet Protocol (VoIP), is often very small. However, the common use of time-division multiplexing (TDM) limits the number of VoIP users supported because a packet has to wait until it receives a time slot, and if only one small VoIP packet is placed in a time slot, capacity is wasted. Packet bundling can alleviate such a problem by sharing a time slot among multiple users. A recent revision of cdma2000 1xEV-DO has introduced the concept of the multiuser packet (MUP) in the downlink to overcome limitations on the number of time slots. However, the efficacy of packet bundling is not well understood, particularly in the presence of time-varying channels. We propose a novel quality-of-service (QoS) and channel-aware packet bundling algorithm that takes advantage of adaptive modulation and coding. We show that optimal algorithms are nondeterministic polynomial time (NP)-complete, recommend heuristic approaches, and use analytical performance modeling to show the gains in capacity that can be achieved from our packet bundling algorithms. We show that channel utilization can be significantly increased by slightly delaying some real-time packets within their QoS requirements while bundling those packets with like channel conditions. We validate this paper through extensive OPNET simulations with a complete evolution-data optimized (EV-DO) implementation. View full abstract»

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  • A Hierarchical AF Protocol for Distributed Orthogonalization in Multiuser Relay Networks

    Page(s): 3902 - 3916
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1096 KB) |  | HTML iconHTML  

    We consider distributed orthogonalization of multiple source-destination terminal pairs through coherent amplify-and-forward (AF) relaying. When an excess number of relays are available in the network, additional gains of diversity and sum rates are known to be attained through efficient gain-allocation schemes. The common requirement of these schemes is global dissemination of local channel state information (CSI) of each relay. Consequently, as the number of relays grows, the CSI dissemination overhead may diminish the aforementioned gains in practice. We propose a novel hierarchical relaying protocol where relays with different amounts of CSI knowledge can coexist within the same network. In the lower level of hierarchy, each relay employs only local CSI to compute its gain factor and, hence, is cost-free in terms of CSI dissemination overhead. However, the relays in the higher level of hierarchy have further channel information that allows them to determine the gain factors enabling distributed orthogonalization of multiple pairs. We study sufficient conditions to achieve full spatial multiplexing, the required channel knowledge per hierarchical level, the corresponding relay gain allocations, and power-allocation strategies among hierarchical levels. We finally identify relay selection for different hierarchical levels as an efficient means to recover outage (diversity) and sum-rate gains. It is shown that with drastically reduced CSI dissemination overhead, the hierarchical protocol combined with relay selection approaches the performance of conventional multiuser relaying that requires global CSI at all relay nodes. View full abstract»

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  • Comprehensive Evaluation of the IEEE 802.15.4 MAC Layer Performance With Retransmissions

    Page(s): 3917 - 3932
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1381 KB) |  | HTML iconHTML  

    Supported by IEEE 802.15.4 standardization activities, embedded networks have been gaining popularity in recent years. The focus of this paper is to quantify the behavior of key networking metrics of IEEE 802.15.4 beacon-enabled nodes under typical operating conditions, with the inclusion of packet retransmissions. We corrected and extended previous analyses by scrutinizing the assumptions on which the prevalent Markovian modeling is generally based. By means of a comparative study, we singled out which of the assumptions impact each of the performance metrics (throughput, delay, power consumption, collision probability, and packet-discard probability). In particular, we showed that - unlike what is usually assumed - the probability that a node senses the channel busy is not constant for all the stages of the backoff procedure and that these differences have a noticeable impact on backoff delay, packet-discard probability, and power consumption. Similarly, we showed that - again contrary to common assumption - the probability of obtaining transmission access to the channel depends on the number of nodes that is simultaneously sensing it. We evidenced that ignoring this dependence has a significant impact on the calculated values of throughput and collision probability. Circumventing these and other assumptions, we rigorously characterize, through a semianalytical approach, the key metrics in a beacon-enabled IEEE 802.15.4 system with retransmissions. View full abstract»

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  • Cross-Layer Joint Rate Control and Scheduling for OFDMA Wireless Mesh Networks

    Page(s): 3933 - 3941
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (498 KB) |  | HTML iconHTML  

    We consider the utility-maximization problem in the downlink of wireless mesh networks with orthogonal frequency-division multiple access (OFDMA). We formulate this problem as a cross-layer design of joint rate control and OFDMA scheduling to efficiently utilize the scarce radio resources. The problem is decoupled into a rate-control problem at the transport layer and a channel-aware and queue-aware scheduling problem at the Media Access Control/physical layer (MAC/PHY). The rate-control problem adjusts arrival rates to the base station (BS) queues, and the scheduling problem determines link rates, i.e., departure rates from the BS and other network nodes, through subcarrier and modulation rate assignment. Although the rate-control problem is locally solved at the BS, we propose a greedy algorithm that solves the scheduling problem in a distributed manner, at network nodes. Furthermore, we propose a heuristic algorithm for fast execution of the scheduling scheme at individual nodes. Numerical results show that the heuristic algorithm performs comparably with the greedy algorithm, whereas it has lower computational complexity. In addition, our proposed scheduling scheme, when it cooperates with the rate-control mechanism, improves the network performance in terms of end-to-end delay, aggregate utility, and fairness. View full abstract»

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  • An Open-System Transportation Security Sensor Network: Field-Trial Experiences

    Page(s): 3942 - 3955
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1328 KB) |  | HTML iconHTML  

    Cargo shipments are subject to hijack, theft, or tampering. Furthermore, cargo shipments are at risk of being used to transport contraband, potentially resulting in fines to shippers. The Transportation Security Sensor Network (TSSN), which is based on open software systems and service-oriented architecture principles, has been developed to mitigate these risks. Using commercial off-the-shelf hardware, the TSSN can detect and report events that are relevant to appropriate decision makers. However, field testing is required to validate the system architecture and to determine if the system can provide timely event notification. Field experiments were conducted to assess the TSSN's suitability to monitor rail-borne cargo. Log files were collected from these experiments and were postprocessed. We present the TSSN architecture and results of field experiments, including the time taken to report events using the TSSN and the interaction between various components of the TSSN. These results show that the TSSN architecture can be used to monitor rail-borne cargo. View full abstract»

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Aims & Scope

IEEE Transactions on Vehicular Technology covers land, airborne, and maritime mobile services, vehicular electrotechnology, equipment, and systems identified with the automotive industry.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Yuguang Michael Fang
University of Florida