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Vehicular Technology, IEEE Transactions on

Issue 1 • Date Jan. 2009

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Displaying Results 1 - 25 of 51
  • Table of contents

    Publication Year: 2009 , Page(s): C1 - C4
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    Freely Available from IEEE
  • IEEE Transactions on Vehicular Technology publication information

    Publication Year: 2009 , Page(s): C2
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    Freely Available from IEEE
  • Editorial

    Publication Year: 2009 , Page(s): 2
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    Freely Available from IEEE
  • Millimeter-Wave Propagation Channel Characterization for Short-Range Wireless Communications

    Publication Year: 2009 , Page(s): 3 - 13
    Cited by:  Papers (49)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1939 KB) |  | HTML iconHTML  

    This paper presents and analyzes the results of millimeter-wave 60-GHz frequency range propagation channel measurements that are performed in various indoor environments for continuous-route and direction-of-arrival (DOA) measurement campaigns. The statistical parameters of the propagation channel, such as the number of paths, the RMS delay spread, the path loss, and the shadowing, are inspected. Moreover, the interdependencies of different characteristics of the multipath channel are also investigated. A linear relationship between the number of paths and the delay spread is found, negative cross correlation between the shadow fading and the delay spread can be established, and an upper bound exponential model of the delay spread and the path loss is developed to estimate the worst case of the RMS delay spread at given path loss. Based on the DOA measurements that are carried out in a room [line of sight (LOS)] and in a corridor with both LOS and nonline-of-sight (NLOS) scenarios, radio-wave propagation mechanisms are studied. It is found that considering the direct wave and the first-order reflected waves from smooth surfaces is sufficient in the LOS cases. Transmission loss is very high; however, diffraction is found to be a significant propagation mechanism in NLOS propagation environments. The results can be used for the design of 60-GHz radio systems in short-range wireless applications. View full abstract»

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  • An Empirical Model for Nonstationary Ricean Fading

    Publication Year: 2009 , Page(s): 14 - 20
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB) |  | HTML iconHTML  

    Ricean fading is common in dense urban cellular networks and, as a mobile moves through that environment, the K-factor of the Ricean fading will change. This paper presents a statistical model for dense urban vehicular nonstationary Ricean fading, where the K-factor gradually changes due to movement through changing surroundings. This model is empirical and is based on K-factor fluctuations that are observed in dense urban cellular radio channel measurements. The K -factor is modeled using a random process with a distribution that is fit to the measured K-factor values. An autoregressive (AR) model is also used to ensure that the autocorrelation of the simulated K-factor process matches the empirical data. The nonstationary Ricean fading envelope that is generated using this model is verified by comparing it with the fading envelope that is observed in the measurements. View full abstract»

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  • Aggregated Renewal Markov Processes With Applications in Simulating Mobile Broadcast Systems

    Publication Year: 2009 , Page(s): 21 - 31
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (693 KB) |  | HTML iconHTML  

    For purposes of simulating contemporary communication systems, it is, in many cases, useful to apply error models for specific levels of abstraction. Such models should approximate the packet error behavior of a given system at a specific protocol layer, thus incorporating the possible detrimental effects of lower protocol layers. Packet error models can efficiently be realized using finite-state models; for example, there exists a wide range of studies on using Markov models to simulate communication channels. In this paper, we consider aggregated Markov processes, which are a subclass of hidden Markov models (HMMs). Artificial limitations are set on the state transition probabilities of the models to find efficient methods of parameter estimation. We apply these models to the simulation of the performance of digital video broadcasting-handheld (DVB-H). The parameters of the packet error models are approximated as functions of the time-variant received signal strength and speed of a mobile vehicular DVB-H receiver, and it is shown that useful results may be achieved with the described packet error models, particularly when simulating mobile reception in field conditions. View full abstract»

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  • Statistical Analysis of a Mobile-to-Mobile Rician Fading Channel Model

    Publication Year: 2009 , Page(s): 32 - 38
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (474 KB) |  | HTML iconHTML  

    Mobile-to-mobile communication is an important application for intelligent transport systems and mobile ad hoc networks. In these systems, both the transmitter and receiver are in motion, subjecting the signals to Rician fading and different scattering effects. In this paper, we present a double-ring with a line-of-sight (LOS) component scattering model and a sum-of-sinusoids simulation method to characterize the mobile-to-mobile Rician fading channel. The developed model can facilitate the physical-layer simulation for mobile ad hoc communication systems. We also derive the autocorrelation function, level crossing rate (LCR), and average fade duration (AFD) of the mobile-to-mobile Rician fading channel and verify the accuracy by simulations. View full abstract»

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  • Application of the “Contact Convoy” Concept to Hybrid Electric Vehicles

    Publication Year: 2009 , Page(s): 39 - 47
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (521 KB) |  | HTML iconHTML  

    This paper applies an intelligent intervehicle device (termed a ldquobridging damperrdquo) to a convoy of in-contact vehicles. The field of application is backup for future automated highways and operation of novel guided systems using vehicle-following control. The vehicle represented in computer simulations is a parallel hybrid electric automobile. Using the advanced vehicle simulator (ADVISOR) model, the vehicle representation is tuned to achieve matching of the overall force and power characteristics and the same performance over an urban driving cycle. The model for which a dedicated Matlab Toolbox was constructed is described. Simulation results compare the vehicle-following control on its own with a passive damper and a ldquoquasi-activerdquo damper that is controlled in collaboration with the vehicle's drivetrain. Using transient disturbances in the form of wind gusts and short gradients, power peaks and longitudinal ride quality (vibration dose value) are used to evaluate the performance. View full abstract»

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  • Generator Operation of a Switched Reluctance Starter/Generator at Extended Speeds

    Publication Year: 2009 , Page(s): 48 - 56
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1099 KB) |  | HTML iconHTML  

    Switched reluctance (SR) drive systems are a candidate technology for electric vehicle applications, particularly where a high degree of component integration is required within a thermally demanding environment-typical of engine-mounted power-assist solutions. This paper discusses the design, prototype realization, and test validation of an SR machine for a mild-hybrid power-assist starter/alternator application that has performance requirements of both high starting torque and a wide speed range at full power. While a number of papers on SR machine design for automotive starter/alternator applications have been published, a comprehensive case study discussing the design and application issues has not been published. This paper focuses on the impact of the performance requirements and volumetric and environmental constraints on the machine design. It is shown that a higher number of stator and rotor poles is more appropriate for the utilization of the available active volume. While various operation and fault scenarios have been presented for SR drive systems, this paper also discusses test observations that suggest the potential for the transient self-excitation of the SR generator via residual magnetization of the machine rotor-a fault scenario that has only been briefly reported on. View full abstract»

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  • Comparison of Submarine Drive Topologies Using Multiobjective Genetic Algorithms

    Publication Year: 2009 , Page(s): 57 - 68
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1824 KB) |  | HTML iconHTML  

    A multiobjective genetic algorithm (MOGA) is used to compare submarine propulsion concepts and seek out tradeoffs in their design. Concepts include the novel integrated electric propulsion (IEP) concept and hybrid steam turbine and electric motor drive. System design and supervisory controllers are optimized under multiple operating conditions to give maximum propulsive efficiency. The advantages of each propulsive topology are compared, along with tradeoffs in their design. The hybrid steam turbine/electric motor drive is found to give superior propulsive efficiency compared with pure mechanical and pure electrical drive topologies. The optimal hybrid drive system design favors a large steam turbine and smaller electric motor, which is utilized during slow cruise speeds and top speed cruising only. Optimization of the supervisory controller simultaneously with the system design is found to give improvements in overall propulsive system efficiency. View full abstract»

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  • Fuzzy Gain-Scheduling Proportional–Integral Control for Improving Engine Power and Speed Behavior in a Hybrid Electric Vehicle

    Publication Year: 2009 , Page(s): 69 - 84
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2156 KB) |  | HTML iconHTML  

    With the increased emphasis on improving fuel economy and reducing emissions, hybrid electric vehicles (HEVs) have emerged as very strong candidates to achieve these goals. The power-split hybrid system, which is a complex hybrid powertrain, exhibits great potential to improve fuel economy by determining the most efficient regions for engine operation and thereby high-voltage (HV) battery operation to achieve overall vehicle efficiency optimization. To control and maintain the actual HV battery power, a sophisticated control system is essential, which controls engine power and thereby engine speed to achieve the desired HV battery maintenance power. Conventional approaches use proportional-integral (PI) control systems to control the actual HV battery power in power-split HEV, which can sometimes result in either overshoots of engine speed and power or degraded response and settling times due to the nonlinearity of the power-split hybrid system. We have developed a novel approach to intelligently controlling engine power and speed behavior in a power-split HEV using the fuzzy control paradigm for better performances. To the best of our knowledge, this is the first reported use of the fuzzy control method to control engine power and speed of a power-split HEV in the applied automotive field. Our approach uses fuzzy gain scheduling to determine appropriate gains for the PI controller based on the system's operating conditions. The improvements include elimination of the overshoots as well as approximate 50% faster response and settling times in comparison with the conventional linear PI control approach. The improved performances are demonstrated through simulations and field experiments using a ford escape hybrid vehicle. View full abstract»

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  • Image Processing-Based Methodology for Optimizing Automotive Ignition Timing

    Publication Year: 2009 , Page(s): 85 - 92
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (809 KB) |  | HTML iconHTML  

    Modern fuel-injected automobiles use an electronic engine control unit (ECU) that is programmed to ignite the air-fuel mixture in a way that maximizes the torque (TQ) and power output of the engine without compromising its reliability. The ECU achieves this by reading a base value from the primary ignition map (PIM) and then manipulating various other parameters to come up with the final solution. Each input into the final solution comes from a so-called map, which is a 3-D image that represents a set of all the possible values that each parameter can take on. In this paper, we develop a robust methodology using image processing techniques to optimize the PIM for automobiles. The techniques are used to compare, combine, manipulate, and reconstruct various maps. Experiments show that the process yields a gain of about 7 hp and a TQ of 15 ft middotlb measured at the wheels. View full abstract»

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  • Wireless Location Estimation With the Assistance of Virtual Base Stations

    Publication Year: 2009 , Page(s): 93 - 106
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1305 KB) |  | HTML iconHTML  

    In recent years, wireless location estimation has attracted a significant amount of attention in different areas. Various types of radio signals are applied for the development of location-estimation algorithms. In this paper, the range measurements acquired from the received time-based information are adopted, and the modified least square (LS) method is utilized to process the raw data and to finally locate the target object. Practical issues, such as the nonline-of-sight (NLOS) errors and the geometric dilution of precision (GDOP) effect, are of concern. The NLOS error will cause a large nonnegative bias while measuring the propagation delay, which will lead to an unreliable result for location estimation. On the other hand, a large GDOP value corresponds to a poor geometric topology, which will result in inferior performance by adopting most of the existing location algorithms. The proposed location-estimation algorithms with virtual base stations (VBSs) will both mitigate the influence from the NLOS errors by imposing the geometric constraints and reduce the GDOP effect by incorporating the assisted VBSs. Two iterative schemes are proposed, including the center-of-gravity-based VBS (VBS-CG) and the minimal GDOP-based VBS (VBS-MG) algorithms, to determine the required number and the locations of the assisted VBSs. The proposed VBS algorithms are compared with other existing location-estimation schemes via simulations. The performance of the VBS-MG algorithm is observed to outperform the other schemes, particularly under the environments with larger NLOS errors and poor geometric layouts. View full abstract»

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  • Multiuser Detection Using Hidden Markov Model

    Publication Year: 2009 , Page(s): 107 - 115
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (567 KB) |  | HTML iconHTML  

    Many existing multiuser detection algorithms assume that the user sequences are independent and identically distributed (i.i.d.). These algorithms, however, may not be efficient when the user sequences sent to a multiuser system are time correlated due to signal processing procedures such as channel coding. In this paper, we assume that the user sequences are time correlated and can be modeled as first-order, finite-state Markov chains. The proposed algorithm applies the decision feedback framework in which a linear filter based on the maximum target likelihood (MTL) criterion is derived to remove the interferences. A hidden Markov model (HMM) estimator is applied to the output of the MTL filter to estimate the user data, noise variance, and state transition probabilities. The estimated user data in turn are applied to update the parameters of the MTL filter. By exploiting the transmission of training symbols, the proposed algorithm requires neither knowledge of the user codes nor the timing information. Simulation results show the performance improvement of the proposed algorithm by exploiting the time-correlated redundancy of the Markov sources. View full abstract»

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  • Joint Channel and DOA Estimation for Multicarrier CDMA Uplink Transmissions

    Publication Year: 2009 , Page(s): 116 - 125
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (297 KB) |  | HTML iconHTML  

    The use of antenna arrays in wireless communications makes it possible to estimate the directions of arrival (DOAs) of impinging waveforms. The latter can be exploited to enhance channel estimation accuracy or as an input for advanced mobile positioning systems. In this paper, we consider the uplink of a multicarrier code-division multiple-access (MC-CDMA) network in which the base station is endowed with multiple receiving antennas arranged in a uniform linear array. Transmission takes place over a multipath channel, and the goal is the joint estimation of the channel responses and DOAs of the uplink signals. In doing so, we follow a maximum-likelihood (ML) approach and assume that users transmit orthogonal training sequences to facilitate the task of separating the signals. This way, all unknown parameters are estimated independently of each other with affordable complexity. Theoretical analysis and computer simulations are used to assess the performance of the proposed scheme and make comparisons with existing alternatives. View full abstract»

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  • Collaborative Uplink Transmit Beamforming With Robustness Against Channel Estimation Errors

    Publication Year: 2009 , Page(s): 126 - 139
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (450 KB) |  | HTML iconHTML  

    We consider the uplink of collaborative wireless communication systems, where multiple relay terminals decode the signal of a nearby user and forward it to a distant single-antenna base station. We present a collaborative uplink transmit beamforming strategy that can be employed at the relay terminals to provide robustness against uncertainties in the channel state information. The proposed beamforming scheme is obtained using the available knowledge about the second-order statistics of the channel and the possibly erroneous channel state information. The beamforming weight vector is derived by minimizing the total transmitted power subject to a constraint that preserves the received signal at the base station for all the channel realizations within a prescribed uncertainty set. We present two beamforming algorithms based on different mathematical descriptions of the uncertainty set. Both algorithms can be applied to line-of-sight (LOS) propagation and flat-fading channels. In the first algorithm, the robust beamforming vector is computed at the base station using the uplink data and fed back to the cooperating relay terminals. This centralized processing scheme allows any additional convex constraint to be easily incorporated into the beamforming strategy. In the second algorithm, the beamforming vector of each terminal is locally computed using the available knowledge about the terminal's channel and a single parameter (Lagrange multiplier) that is broadcast from the base station to all the cooperating terminals. Simulation results are presented, showing the superior performance of our proposed algorithms compared with classical transmit beamforming techniques in both LOS propagation and flat-fading channels. View full abstract»

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  • Polynomial Estimation of Time-Varying Multipath Gains With Intercarrier Interference Mitigation in OFDM Systems

    Publication Year: 2009 , Page(s): 140 - 151
    Cited by:  Papers (29)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2363 KB) |  | HTML iconHTML  

    In this paper, we consider the case of a high-speed mobile receiver operating in an orthogonal frequency-division multiplexing (OFDM) communication system. We present an iterative algorithm for estimating multipath complex gains with intersubcarrier interference (ICI) mitigation (using comb-type pilots). Each complex gain variation is approximated by a polynomial representation within several OFDM symbols. Assuming knowledge of delay-related information, polynomial coefficients are obtained from time-averaged gain values, which are estimated using the least-square (LS) criterion. The channel matrix is easily computed, and the ICI is reduced by using successive interference suppression (SIS) during data symbol detection. The algorithm's performance is further enhanced by an iterative procedure, performing channel estimation and ICI mitigation at each iteration. Theoretical analysis and simulation results for a Rayleigh fading channel show that the proposed algorithm has low computational complexity and good performance in the presence of high normalized Doppler spread. View full abstract»

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  • Performance of Orthogonal Beamforming for SDMA With Limited Feedback

    Publication Year: 2009 , Page(s): 152 - 164
    Cited by:  Papers (86)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1170 KB) |  | HTML iconHTML  

    On the multiantenna broadcast channel, the spatial degrees of freedom support simultaneous transmission to multiple users. The optimal multiuser transmission, which is known as dirty paper coding, is not directly realizable. Moreover, close-to-optimal solutions such as Tomlinson-Harashima precoding are sensitive to channel state information (CSI) inaccuracy. This paper considers a more practical design called per user unitary and rate control (PU2RC), which has been proposed for emerging cellular standards. PU2RC supports multiuser simultaneous transmission, enables limited feedback, and is capable of exploiting multiuser diversity. Its key feature is an orthogonal beamforming (or precoding) constraint, where each user selects a beamformer (or precoder) from a codebook of multiple orthonormal bases. In this paper, the asymptotic throughput scaling laws for PU2RC with a large user pool are derived for different regimes of the signal-to-noise ratio (SNR). In the multiuser interference-limited regime, the throughput of PU2RC is shown to logarithmically scale with the number of users. In the normal SNR and noise-limited regimes, the throughput is found to scale double logarithmically with the number of users and linearly with the number of antennas at the base station. In addition, numerical results show that PU2RC achieves higher throughput and is more robust against CSI quantization errors than the popular alternative of zero-forcing beamforming if the number of users is sufficiently large. View full abstract»

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  • A Comparison of Frequency-Domain Block MIMO Transmission Systems

    Publication Year: 2009 , Page(s): 165 - 175
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (997 KB) |  | HTML iconHTML  

    Block transmission techniques, with appropriate cyclic prefix and frequency-domain processing schemes, have been shown to be excellent candidates for digital transmission over severely time-dispersive channels, allowing good performance with implementation complexity that is much lower than traditional time-domain processing schemes. Orthogonal frequency-division multiplexing (OFDM) modulation is the most popular block transmission technique. Single-carrier (SC) modulation using frequency-domain equalization (FDE) is an attractive alternative approach based on this principle. In this paper, we propose two new receiver structures for multiple-input-multiple-output (MIMO) channels employing SC (MIMO-SC) modulation and FDE schemes. These receivers have a hybrid structure with frequency-domain feedforward and time-domain feedback filters for intersymbol interference (ISI) and interference cancellation. The proposed schemes are compared with different MIMO systems employing OFDM modulation (MIMO-OFDM) receivers in terms of performance [bit error rate (BER) and throughput] and complexity. Our performance results show the superiority of MIMO-SC approaches relative to MIMO-OFDM in terms of the BER performance for the simulated scenarios. Also, the simulation results show that the proposed hybrid MIMO-SC receivers yield a higher throughput than a MIMO-OFDM system. View full abstract»

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  • Reduced Data Rates for Energy-Efficient Reed–Solomon FEC on Fading Channels

    Publication Year: 2009 , Page(s): 176 - 187
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (497 KB) |  | HTML iconHTML  

    In the CDMA2000 1xEV-DO broadcast service, Reed-Solomon (RS) coding is applied at the medium access control (MAC) layer. Long bursts of errors are corrected by an additional block interleaving mechanism, which improves the performance of RS coding by increasing the time diversity. This is achieved by increasing the width of the error control block (ECB) to convert error bursts into sparse patterns. On the assumption that the number of ECBs transmitted over the air channel in a given interval of time remains constant, we propose performance and energy models of RS decoding under varying conditions of Rayleigh fading on the broadcast channel, which allows for varying levels of block interleaving. Evaluation of this model shows that a higher data rate for the MAC payload and more efficient recovery from bursty errors can be achieved by increasing the level of block interleaving, although it increases the energy consumption. We therefore make the ECB as small as we can without incurring significant performance reduction by sacrificing the data rate to an extent that depends on the channel conditions. We suggest a way of choosing an adequate but energy-efficient level of ECB interleaving and, thus, determine the data rate. Our approach is effective for energy-constrained mobile devices running multimedia applications, which benefit from an increase in energy efficiency, and can tolerate a certain level of packet errors and a reduction in data rate. View full abstract»

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  • Improved Error Control for Real-Time Video Broadcasting Over CDMA2000 Networks

    Publication Year: 2009 , Page(s): 188 - 197
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (583 KB) |  | HTML iconHTML  

    The broadcast and multicast services (BCMCS) protocol is designed for real-time applications such as MPEG-4 video streaming, which requires successive frames to arrive within a specific time interval. We analyze the execution time of Reed-Solomon (RS) decoding, which is the medium access control (MAC)-layer forward error-correction (FEC) scheme used in CDMA2000 1xEV-DO BCMCS, under various air channel conditions. The results show that the timing constraints of MPEG-4 cannot always be met by RS decoding when the packet loss rate (PLR) is high, due to the limited processing power of current hardware. We therefore propose three error control schemes: First, we have our static scheme, which bypasses RS decoding at the mobile node to satisfy the MPEG-4 timing constraint when the PLR exceeds a given level. Second, we have the dynamic scheme, which corrects as many errors as possible within the timing constraint, instead of giving up altogether when the PLR is high; this improves quality. Third, we have the video-aware dynamic scheme, which fixes errors in a similar way to the dynamic scheme but in a priority-driven manner, yielding a further increment in video quality at mobile terminals. Extensive simulation results show the effectiveness of our schemes compared with the original FEC scheme. View full abstract»

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  • A RAKE Receiver With an ICI/ISI Equalizer for a CCK Modem

    Publication Year: 2009 , Page(s): 198 - 206
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (327 KB) |  | HTML iconHTML  

    In this paper, we first derive the theoretical performance of a complementary code keying (CCK) code on an additive white Gaussian noise (AWGN) channel and over a multipath channel. To derive the error performance, we use the weight and cross-correlation distributions of the CCK code for optimal and suboptimal decoding, respectively, based on union bound. In addition, we propose a RAKE receiver for a CCK modem, which is suitable for a multipath environment with a large delay spread. The RAKE receiver principle is acceptable for modest multipath because it can coherently combine multipath components to provide signal-to-noise ratio (SNR) enhancement. However, as the delay spread is larger and the data rate of systems goes higher, intersymbol interference (ISI) generated due to multipath environments are increased. To handle the increasing ISI, the CCK modem needs an equalization technique to remove the ISI, together with RAKE processing. Thus, our proposed system is based on a channel matched filter (CMF) with a decision feedback equalizer (DFE). The CMF is applied for RAKE processing, whereas the DFE structure is used for ISI cancellation. In our system, ISI is calculated and removed by using a decoded CCK codeword. View full abstract»

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  • Distributive High-Rate Space–Frequency Codes Achieving Full Cooperative and Multipath Diversities for Asynchronous Cooperative Communications

    Publication Year: 2009 , Page(s): 207 - 217
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (422 KB) |  | HTML iconHTML  

    In user-cooperative communications, relay nodes are usually asynchronous. By realizing that the processing in the frequency domain is insensitive to the errors in the time domain, Mei and Shin recently applied the space-time-coded orthogonal frequency-division multiplexing (OFDM) technique to achieve full cooperative diversity for asynchronous cooperative communications, where orthogonal space-time block codes (particularly the Alamouti code) were used for relay nodes. In this paper, we consider asynchronous cooperative communications, and the channels from one node to another node are frequency-selective fading. We propose a high-rate space-frequency coding method and prove that it can achieve both cooperative and multipath diversities. Simulation results are shown to verify the performance of the constructed codes. View full abstract»

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  • A Comparative Analysis of Spatial Multiplexing Techniques for Outdoor MIMO-OFDM Systems with a Limited Feedback Constraint

    Publication Year: 2009 , Page(s): 218 - 230
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (755 KB) |  | HTML iconHTML  

    In this paper, we analyze spatial multiplexing techniques for the downlink of a multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) system. Our study is focused on outdoor environments characterized by a moderate angular spread. We consider two techniques that are able to separate the downlink data streams associated with different users and to guarantee a fixed error probability by exploiting limited feedback from each user. The grid of beams (GoBs) and the proposed adaptive GoB (AGoB) differ in the way the precoders are designed (by adaptive or fixed processing) and in their scheduling policy. The new AGoB is able to harness partial knowledge of the downlink channel spatial structure to better select the users and adjust their precoders for downlink transmission. The performances of GoB and AGoB are compared in this paper in terms of throughput and cell coverage capability. The radio interface is adapted to fit the requirements for the adaptive modulation and coding with advanced antenna system (AMC-AAS) mode of the IEEE 802.16-2005 standard. Numerical results show that, as long as the channel exhibits a limited angular spread at the base station, the AGoB technique is able to provide significant throughput gains compared with the fixed GoB approach. On the other hand, large angular spreads are proved to have a substantial impact on system performance as the benefits of adaptation are significantly reduced. View full abstract»

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  • Ant-Colony-Optimization-Based Scheduling Algorithm for Uplink CDMA Nonreal-Time Data

    Publication Year: 2009 , Page(s): 231 - 241
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (892 KB) |  | HTML iconHTML  

    Scheduling plays an important role in determining the overall performance of code-division multiple-access (CDMA) systems. This paper is focused on the uplink scheduling of CDMA nonreal-time data. In practical CDMA systems, data can only be transmitted with a few fixed transmission rates. Moreover, to guarantee receiving accuracy, the actual received signal-power-to-interference-plus-noise-power ratio (SINR) is expected to be no less than the target SINR value. Using Heaviside unit step functions, the relationship between the actual SINR value and the actual available maximum transmission rate is described in the proposed system model. Based on the proposed system model, an integer optimization problem is formulated to simultaneously maximize the throughput and the scheduling efficiency. Particularly, an ant-colony-optimization (ACO)-based scheduling algorithm is proposed to solve the proposed optimization problem. The computational complexity analysis indicates that the proposed ACO-based scheduling algorithm is computationally efficient in terms of both running time and storage space. In addition, the numerical results show that the proposed optimization problem is more efficient at guiding the development of scheduling algorithms for uplink CDMA nonreal-time data. Moreover, the proposed ACO-based scheduling algorithm performs quite well in terms of quality, running time, and stability. 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