By Topic

Vehicular Technology, IEEE Transactions on

Issue 1 • Date Jan. 2010

Filter Results

Displaying Results 1 - 25 of 53
  • Table of contents

    Page(s): C1 - C4
    Save to Project icon | Request Permissions | PDF file iconPDF (55 KB)  
    Freely Available from IEEE
  • IEEE Transactions on Vehicular Technology publication information

    Page(s): C2
    Save to Project icon | Request Permissions | PDF file iconPDF (42 KB)  
    Freely Available from IEEE
  • Special Section on Channel Modeling and Estimation

    Page(s): 2
    Save to Project icon | Request Permissions | PDF file iconPDF (29 KB)  
    Freely Available from IEEE
  • Observation-Based Time-Varying MIMO Channel Model

    Page(s): 3 - 15
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1144 KB) |  | HTML iconHTML  

    This paper presents a method to model and simulate time-varying narrowband multiple-input-multiple-out (MIMO) channels based on observations from measured data. The data were obtained in a vehicular urban environment, with a fixed transmitter array and a mobile receiver array. The measured channel response matrices were decomposed to isolate the coupling from the transmitter eigenbasis to the received eigenbasis, as in the Weichselberger model. These complex coupling elements have been characterized and seen to comprise directional components that may be Ricean or Rayleigh fading. The Rayleigh fading directional components can be well modeled using the von Mises probability density function, which is parameterized for the time-varying model using the measured data. The model has been validated by comparing the mutual information and eigenstructure autocorrelation characteristics of its output with those of the measured data. The statistical nature of the model means that different realizations can be generated, each representative of the originating data. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Time-Varying Path-Shadowing Model for Indoor Populated Environments

    Page(s): 16 - 28
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2597 KB) |  | HTML iconHTML  

    This paper presents a path-shadowing model for indoor populated environments that has been developed based on computer simulations. The propagation paths between the transmitting and receiving points in an empty rectangular space are determined using the ray-tracing method, in which moving quasi-human bodies that are modeled as cylinders with a finite height are generated in the space, and intersections of the paths with the bodies are counted. From the results, the shadowing probabilities, durations, and intervals are evaluated for each propagation path, and this shadowing process is characterized as a Markov process. This paper proposes a method that individually generates the shadowing effects on each propagation path. The measurement results of the path-shadowing characteristics using a 5.2-GHz high-resolution channel sounder are presented, and the validity of this model is confirmed. Similar measurement results using a photoelectric sensor are also presented to reinforce the channel-sounding measurement results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Method for Simulating Complex Nakagami Fading Time Series With Nonuniform Phase and Prescribed Autocorrelation Characteristics

    Page(s): 29 - 35
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (223 KB) |  | HTML iconHTML  

    The availability of an accurate and systematic channel simulation technique is critical for the verification of the performance of digital radio transceivers designed for use on wireless channels. Despite the abundant results on channel simulation techniques available in the literature, an accurate technique for simulating Nakagami- m fading signals that have nonuniform phase distributions and any prespecified temporal autocorrelation function is not yet available. Such a technique is reported for the first time in this paper. We develop new cumulative distribution function (cdf) mapping methods to generate complex Nakagami sequences from complex Gaussian sequences, based on the independent transformation of their real and imaginary parts. Additionally, we analyze the relationships between the autocorrelation functions of Rayleigh and Nakagami fading signals to determine the autocorrelation function of Rayleigh input that is required to produce a specified autocorrelation function for the Nakagami output. Then, we implement the mapping algorithm to transform Rayleigh sequences with the so-determined autocorrelation functions into Nakagami sequences with the desired prespecified autocorrelation functions. Simulation results verify that our approaches can lead to the accurate simulation of Nakagami fading signals with prespecified autocorrelation functions and nonuniform phase distributions. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Novel Inversion Method for Outdoor Coverage Prediction in Wireless Cellular Network

    Page(s): 36 - 47
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2441 KB) |  | HTML iconHTML  

    A novel coverage-prediction method for outdoor radio propagation based on the inversion theory is proposed here. Coverage prediction in a wireless cellular network is treated as an inverse problem instead of using high-precision geometric modeling. More precisely, the problem is solved by an inversion of the measured data under some a priori constraints, and the complicated propagation-prediction problem is reduced to solving a system of large-scale ill-condition equations. The effectiveness of the proposed method is demonstrated by using experiments under various radio environments in Guangdong, China. The prediction results are approximately consistent with independent checking samples, and the proposed strategy is compared with other existing approaches. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multipath Parameter Estimation for Radio Propagation Channel Measurements With a Vector Network Analyzer

    Page(s): 48 - 52
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (175 KB) |  | HTML iconHTML  

    This paper proposes a new approach to estimating multipath parameters such as time delays and attenuation factors for channel measurements using a vector network analyzer. In the proposed scheme, we introduce a coarse-and-fine time-delay-estimation scheme and attenuation-factor-estimation schemes. The coarse time-delay estimation employs a superresolution technique based on the generalized eigenvalues utilizing signal subspace eigenvectors (GEESE) algorithm, and the fine time-delay estimation is derived to exploit real-valued attenuation factors. For attenuation-factor estimation, we focus on the least squares estimator (LSE) and the simplified estimator (SE). Numerical results show that the proposed time-delay-estimation scheme outperforms the multiple-signal classification (MUSIC)-based time-delay-estimation scheme. Theoretical analysis and computer simulations are used in the comparisons of the LSE and the SE. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Semiblind Channel Estimation for MIMO Single Carrier With Frequency-Domain Equalization Systems

    Page(s): 53 - 62
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (646 KB) |  | HTML iconHTML  

    We propose a semiblind channel-estimation method for multiple-input multiple-output (MIMO) single carrier with frequency-domain equalization systems. By taking advantage of periodic precoding and the block circulant channel model after cyclic prefix removal, we obtain the channel-product matrices by solving a series of decoupled linear systems, which is gained from the covariance matrix of the received data. Then, the channel-impulse-response matrix is obtained by computing the positive eigenvalues and eigenvectors of a Hermitian matrix formed from the channel-product matrices. We also propose an optimal design of the precoding sequence, which minimizes the noise effect and numerical error in covariance matrix estimation, and discuss the impact of the optimal sequence on channel equalization. With the proposed framework, the method is shown to be robust with respect to channel-order overestimation, and the identifiability condition is simply that the channel-impulse-response matrix has full column rank. Due to the identifiability condition, the method is applicable to MIMO channels with more transmitters or more receivers. Simulations are used to demonstrate the performance of the proposed method. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optical Wireless Systems Employing Adaptive Collaborative Transmitters in an Indoor Channel

    Page(s): 63 - 74
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1221 KB) |  | HTML iconHTML  

    We propose a novel optical wireless (OW) system based on a power adaptive multibeam spot-diffusing transmitter serving multiple seven-segment maximum ratio combining (MRC) angle diversity receivers. A feedback link is assumed between the transceivers so that each receiver conveys to the multibeam transmitter the new beams transmit power weights to be used to achieve the best signal quality at a given receiver location. Two cases involving three and five receivers are considered. Four different configurations for the placement of the three-receiver case in the room are also examined. The system's performance in each case is evaluated in terms of signal-to-noise ratio (SNR) and is compared with the single receiver scenario with and without power adaptation. In the presence of one receiver, the transmit spot powers can be adjusted for optimum performance at that receiver location. For multiple receivers, there is conflict, and we propose spot power adaptation based on the average requirements (power distribution in spots), i.e., transmit equal gain combining (EGC) of spot power or MRC of transmit spot powers. The results show that the three receivers benefit most from an adaptive transmitter when each is placed at a corner of the room. In this case, an SNR increase of as much as 2.6 dB is achieved for all three receivers at the corners by both MRC and EGC. Moreover, when all receivers are placed away from the line of diffusing spots, our proposed MRC collaborative approach is 1 dB better than the noncollaborative system. This gain reduces the difference from the upper bound set by the single receiver adaptation, which is 3 dB. For a mobile transmitter, MRC also significantly improved the SNR for the farthest receivers at the opposite end from the transmitter located near one room corner. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Implementation and Development of an Adaptive Steering-Control System

    Page(s): 75 - 83
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (830 KB) |  | HTML iconHTML  

    In this paper, an adaptive steering-control system for a steer-by-wire system, which consists of a vehicle directional-control unit and a driver-interaction unit, is developed. The adaptive online estimation method is used to identify the dynamic parameters of the vehicle directional-control and driver-interaction units. A nonlinear 4-degree-of-freedom (DOF) vehicle model, including the longitudinal, lateral, yaw, and quasi-static roll motions, is derived using Newtonian mechanics to simulate and test the adaptive steering-control system. Experimental results are performed to demonstrate the efficacy of the proposed adaptive steering-control system. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Transmission-Actuated Energy-Management Strategy

    Page(s): 84 - 92
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB) |  | HTML iconHTML  

    In this paper, we analyze a hybrid electric vehicle structure and propose a simple and computationally cheap yet close-to-optimal energy-management strategy. The underlying hybrid configuration is of parallel type. Furthermore, the parallel hybrid does not include a clutch between the electric motor and the engine. The considered vehicle uses a six-speed dual-clutch transmission (DCT). The proposed supervisory controller considers both the torque split management and the gear-shifting strategy. Results show that the proposed approach achieves fuel consumption (FC) within 1% of the global optimum for most driving cycles. In addition, using the proposed controller, the number of gears in the gearbox can be reduced to three while maintaining the FC within 2% of what is achieved with a six-speed gearbox. Moreover, the results shown in this paper are not sensitive to limitations and energy losses associated with gear shifting. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance Analysis of TDMA Relay Protocols Over Nakagami- m Fading

    Page(s): 93 - 104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (359 KB) |  | HTML iconHTML  

    Several time-division multiple-access (TDMA) cooperative wireless relay protocols and their performances have recently been developed by Nabar, Bolcskei, and Kneubuhler. Their work, however, is limited to an upper bound-based performance analysis for Rayleigh fading. We thus provide an exact analysis of two of their protocols in single-relay and multiple-relay networks over independent identically distributed (i.i.d.) Nakagami-m fading channels. Our analysis is focused on an Alamouti-coded system with two-stage protocols, fixed-gain amplify-and-forward (AF) relays, and maximal ratio combiner (MRC) reception. The performance metrics are the capacity, the diversity order, and the symbol error rate (SER). The closed-form moment-generating function (MGF) of the total end-to-end signal-to-noise ratio (SNR) is derived. The MGF is then used to derive the diversity order and the SER of M-ary phase-shift keying (M-PSK) and M-ary quadrature amplitude modulation (M -QAM). It is found that the end-to-end SNR for relaying with orthogonal channels is higher than that of nonorthogonal relay channels. The diversity order of a multiple-relay network (n relays) in a Nakagami-m environment is shown to be (n + 1)m. The closed-form SER expressions for relay-destination links with high SNRs and static relay-destination links are derived. Numerical and simulation results are provided to verify the analysis. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance Analysis of OSTBC Transmission in Amplify-and-Forward Cooperative Relay Networks

    Page(s): 105 - 113
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (602 KB) |  | HTML iconHTML  

    A performance analysis is presented for amplify-and-forward (AF) cooperative relay networks employing transmit antenna diversity with orthogonal space-time block codes (OSTBCs), where multiple antennas are equipped at the transmitter. We develop a symbol-error-rate (SER) and outage performance analysis for OSTBC transmissions with and without cooperative diversity over flat Rayleigh fading channels. We first derive exact probability density functions (pdf's) and cumulative distribution functions (cdf's) for the system SNR without direct transmission with an arbitrary number of transmit antennas and then present the exact closed-form SER and outage probability expressions. Next, we derive the moment-generating function (MGF) for the overall system SNR with direct transmission and present the exact SER and outage probability with joint transmit antenna diversity and cooperative diversity. The theoretical analysis is validated by simulations, which indicate an exact match between them. The results also show how the transmit antenna diversity and the cooperative diversity affect the overall system performance. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Adaptation in Convolutionally Coded MIMO-OFDM Wireless Systems Through Supervised Learning and SNR Ordering

    Page(s): 114 - 126
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (791 KB) |  | HTML iconHTML  

    Multiple-input-multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) wireless systems use link adaptation to exploit the dynamic nature of wireless environments. Link adaptation maximizes throughput while maintaining target reliability by adaptively selecting the modulation order and coding rate. Link adaptation is extremely challenging, however, due to the difficulty in predicting error rates in OFDM with binary convolutional codes, bit interleaving, MIMO processing, and real channel impairments. This paper proposes a new machine-learning framework that exploits past observations of the error rate and the associated channel-state information to predict the best modulation order and coding rate for new realizations of the channel state without modeling the input-output relationship of the wireless transceiver. Our approach is enabled through our new error-rate expression that is only parameterized by postprocessing signal-to-noise ratios (SNRs), ordered over subcarriers and spatial streams. Using ordered SNRs, we propose a low-dimensional feature set that enables machine learning to increase the accuracy of link adaptation. An IEEE 802.11n simulation study validates the application of this machine-learning framework in real channels and demonstrates the improved performance of SNR ordering as it compares with competing link-quality metrics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Channel Capacity Over Generalized Fading Channels: A Novel MGF-Based Approach for Performance Analysis and Design of Wireless Communication Systems

    Page(s): 127 - 149
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1396 KB) |  | HTML iconHTML  

    Since the trail-blazing paper of C. Shannon in 1948, channel capacity has been regarded as the fundamental information-theoretic performance measure to predict the maximum information rate of a communication system. However, in contrast with the analysis of other important performance measures of wireless communication systems, a unified and general approach for computing the channel capacity over fading channels has yet to be proposed. Motivated by this consideration, we propose a novel and unified communication-theoretic framework for the analysis of channel capacity over fading channels. It is shown that the framework can handle various fading channel models, communication types, and adaptation transmission policies. In particular, the specific contributions of this paper are as follows: (1) We introduce a transform operator, called the E i-transform, which is shown to provide a unified tool to compute the channel capacity with either side information at the receiver or side information at the transmitter and the receiver, directly from the moment-generating function (MGF) or the MGF and the truncated MGF of the Signal-to-Noise-Ratio (SNR) at the receiver, respectively; (2) we show that when either a channel inversion or a truncated channel inversion adaptation policy is considered, the channel capacity can readily be computed from the Mellin or the Hankel transform of the MGF of the received SNR, respectively; (3) a simple yet effective numerical method for the analysis of higher order statistics (HOS) of the channel capacity with side information at the receiver is introduced; and (4) some efficient and ad hoc numerical methods are explicitly introduced to allow the efficient computation of the proposed frameworks. Numerical and simulation results are also shown and compared to substantiate the analytical derivation. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Pilot-Based LMMSE Channel Estimation for OFDM Systems With Power–Delay Profile Approximation

    Page(s): 150 - 159
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1373 KB) |  | HTML iconHTML  

    In linear-minimum-mean-square-error (LMMSE) channel estimation for multicarrier systems, one needs to know the channel correlation function. This poses a problem for systems with a small number of pilots operating in time-varying channels. We propose to approximate the channel power-delay profile (PDP) with a shape that can completely be described in two parameters, namely, the mean delay and the root-mean-square (RMS) delay spread. Furthermore, we develop a simple technique to estimate these delay parameters. The approximate PDP is then used to generate the LMMSE filter coefficients for data-subcarrier channel estimation. Mathematical expressions are derived that can be used to predict the accuracy of the various estimates, and they are verified by simulation. The proposed technique is applicable to both point-to-point communication and multiaccess communication where different users may experience different channel conditions. As a practical application, we also specialize the proposed technique to Mobile WiMAX signals and investigate the resulting performance. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Feedback Reduction for Multiuser OFDM Systems

    Page(s): 160 - 169
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (602 KB) |  | HTML iconHTML  

    Feedback reduction in multiuser orthogonal frequency-division multiplexing (OFDM) systems has become an important issue due to the excessive amount of feedback required to use opportunistic scheduling, particularly when the number of users and carriers is large. In this paper, we propose a novel feedback-reduction scheme for efficient downlink scheduling. In the proposed scheme, each user determines the amount of feedback based on the so-called feedback efficiency in a distributed manner. The key idea is to give more of an opportunity for feedback to users who are more often scheduled. Simulation results demonstrate that the proposed scheme can substantially decrease the feedback load while achieving almost the same scheduling performance as in the case of full feedback. In addition, the proposed scheme offers unique advantages over existing ones. First, it is not tailored to a specific scheduling policy; thus, it has adaptability to the change of the underlying scheduling policy. Second, the total feedback load can be maintained below a target level, regardless of the number of users in the system. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Efficient MIMO Scheduling Algorithms With a Fixed-Time Allocation Ratio

    Page(s): 170 - 181
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (902 KB) |  | HTML iconHTML  

    A scheduling problem that maximizes the system throughput under a constraint on the time-slot allocation ratio of users is considered in the systems having Gaussian-distributed performance metrics, which include multiple-input-multiple-output (MIMO) systems. Two schedulers, which are denoted by the control variance (CV) scheduler and the control mean (CM) scheduler, are proposed in this paper. The proposed schedulers have a beneficial characteristic wherein parameters of the schedulers are independent of channel statistics. Due to this characteristic, the parameters can be precalculated and then applied in the systems where only a limited number of desired ratios exist. For the systems that include an infinitely or extremely large number of desired ratios, parameter computation for the CV scheduler is greatly simplified by eliminating integral calculations. An approximation of the complementary error function is applied for simplification. Simulation results show that the proposed schedulers achieve nearly the maximum system throughput, and the Gaussian assumption and the approximation of the complementary error function cause a negligible error on the time-slot allocation ratio, even in MIMO systems equipped with a small number of antennas. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On Clock Synchronization Algorithms for Wireless Sensor Networks Under Unknown Delay

    Page(s): 182 - 190
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB) |  | HTML iconHTML  

    In this paper, three clock-synchronization algorithms for wireless sensor networks (WSNs) under unknown delay are derived. They include the maximum-likelihood estimator (MLE), a generalization of the estimator of Noh , and a novel low-complexity estimator. Their corresponding performance bounds are derived and compared, and complexities are also analyzed. It is found that the MLE achieves the best performance with the price of high complexity. For the generalized version of the estimator of Noh , although it has low complexity, its performance is degraded with respect to the MLE. On the other hand, the newly proposed estimator achieves the same performance as the MLE, and the complexity is at the same level as that of the generalized version of the estimator of Noh et al. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Zero Forcing in General Two-Hop Relay Networks

    Page(s): 191 - 202
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (342 KB) |  | HTML iconHTML  

    In this paper, we investigate four different two-hop amplify and forward relay networks, which differ on the processing capabilities at the source, relay, and destination nodes. We derive new exact outage probability expressions where zero-forcing processing is performed at the following four areas: (1) source and relay; (2) relay; (3) relay and destination; and (4) destination nodes only. We show that, depending on the particular scheme, adding source, relay, and/or destination nodes can be either beneficial or detrimental to the outage probability. We confirm our results through comparison with Monte Carlo simulations. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Soft Linear Precoding for the Downlink of DS/CDMA Communication Systems

    Page(s): 203 - 215
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1314 KB) |  | HTML iconHTML  

    In this paper, we propose a transmitter-based linear-precoding scheme that outperforms conventional precoding by making use of a portion of the interference between the users in a code-division multiple-access (CDMA) system downlink. The utilization of part of the interference is achieved by selectively orthogonalizing the desired symbols to destructive interference by means of precoding while allowing interference that constructively contributes to the useful signal's energy. The existence and exploitation of constructive interference effectively spreads the signal constellation and enhances the signal-to-interference-plus-noise ratio (SINR) at the receiver. SINR improvement is attained with no need for additional power-per-user investment at the transmitter since energy that is inherent in the CDMA system is utilized. The scheme introduced in this paper applies to the downlink of cellular phase-shift keying (PSK)-based CDMA systems. Theoretical analysis and comparative simulations show that significant performance improvement can be attained with the proposed technique. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Iterative Decoding Convergence and Termination of Serially Concatenated Codes

    Page(s): 216 - 224
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    In this paper, we demonstrate that the previously proposed arrangements of serially concatenated codes have extrinsic-information-transfer (EXIT) functions that intersect each other at points that are near but not at the (1, 1) point in the top-right-hand corner of the EXIT chart, which is typically associated with elevated error floors. We propose a novel arrangement having EXIT functions that do not intersect before the (1, 1) point, which is typically associated with approaching the maximum-likelihood (ML) bit-error-ratio (BER) performance. Our method employs an inner recursive code that is terminated using specifically designed termination sequences, which have a minimum Hamming distance of at least two between each other. Additionally, we provide optimal termination sequences for a range of inner code designs. Finally, we demonstrate that our novel approach can facilitate useful BER reductions in the challenging application scenario when employing short frame lengths on the order of 100 bits, which are typical in wireless sensor networks, for example. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Low-Rate-Feedback-Assisted Beamforming and Power Control for MIMO-OFDM Systems

    Page(s): 225 - 234
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (369 KB) |  | HTML iconHTML  

    This paper proposes a novel solution to the problem of beamforming and power control in the downlink of a multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) system. This solution is developed in two steps. First, we describe an adaptive beamforming technique that, using a stochastic gradient method, maximizes the power delivered to a mobile terminal. In the proposed solution, perturbed precoding matrices are time multiplexed in the information signal transmitted to a mobile terminal; then, the mobile terminal informs the transmitter, via a single feedback bit, about the perturbation delivering the larger power. This approach does not need pilot symbols and uses quasi-Monte Carlo methods to generate the required perturbations with the relevant advantages of improving the downlink spectral efficiency and reducing the system complexity with respect to other competing solutions. Then, we propose a novel power-control algorithm that, selecting a proper transmission energy level from a set of possible values, aims to minimize the average bit error rate. This set of levels is generated on the basis of the channel statistics and a long-term constraint on the average transmission power. Numerical results evidence the robustness of the proposed algorithms in a dynamic fading environment. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Spatial Transmission Mode Switching in Multiuser MIMO-OFDM Systems With User Fairness

    Page(s): 235 - 247
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (937 KB) |  | HTML iconHTML  

    Multiantenna radio systems allow accessing the channel in diversity or spatial multiplexing (SMUX) mode. Adequate switching between these modes according to current channel conditions was shown to yield significant performance improvements while requiring little feedback from the receiving side. We present a transmission concept for the downlink of a multiuser multiple-input-multiple-output orthogonal frequency-division-multiplexing (MU-MIMO-OFDM) system aiming at high user rates with limited feedback demands. An extended score-based scheduling (SB) approach ensures fair-resource allocation to the users, whereas transmission mode switching is used to guarantee high user rates. The degree of fairness of the scheduler can be adapted by adequately configuring a weighting function for the scores. Comparison with single-mode schemes reveals substantial throughput gains of the adaptive switching concept. Furthermore, targeting maximum throughput, we show that a considerable proportion of the capacity of the MIMO broadcast channel (BC) can be achieved with a comparatively low amount of required feedback. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

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