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Vehicular Technology, IEEE Transactions on

Issue 3 • Date May 2002

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Displaying Results 1 - 20 of 20
  • A parametric model for the distribution of the angle of arrival and the associated correlation function and power spectrum at the mobile station

    Page(s): 425 - 434
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    One of the main assumptions in Clarke's classic channel model is isotropic scattering, i.e., uniform distribution for the angle of arrival (AOA) of multipath components at the mobile station. However, in many mobile radio channels we encounter nonisotropic scattering, which strongly affects the correlation function and power spectrum of the complex envelope at the mobile receiver. We propose the use of the versatile von Mises (1918) angular distribution, which includes and/or closely approximates important distributions like uniform, impulse, cardioid, Gaussian, and wrapped Gaussian, for modeling the nonuniform AOAs at the mobile. Based on this distribution, the associated correlation function and. power spectrum of the complex envelope at the mobile receiver are derived. The utility of the new results is demonstrated by comparison with the correlation function estimates of measured data View full abstract»

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  • A real-time traffic simulation using a communication latency hiding parallelization

    Page(s): 498 - 510
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (443 KB) |  | HTML iconHTML  

    This paper implements and analyzes a highway traffic-flow simulation based on continuum modeling of traffic dynamics. A traffic-flow simulation was developed and mapped onto a parallel computer architecture. Two algorithms (the one-step and two-step algorithms) to solve the simulation equations were developed and implemented. Tests with real traffic data collected from the freeway network in the metropolitan area of Minneapolis, MN, were used to validate the accuracy and computation rate of the parallel simulation system (with 256 processors): The execution time for a 24-h traffic-flow simulation over a 15.5-mi freeway, which takes 65.7 min on a typical single-processor computer, took only 88.51 s on the nCUBE2 and only 2.39 s on the CRAY T3E. The two-step algorithm, whose goal is to trade off extra computation for fewer interprocessor communications, was shown to save significantly on the communication time on both parallel computers View full abstract»

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  • Nonlinear distortion-tolerant filters for detection of road signs in background noise

    Page(s): 567 - 576
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (595 KB)  

    In a road sign recognition task, many distortions of targets can occur at the same time. Scale invariance, tolerance to both in-plane and out-of-plane rotations and illumination invariance are examples of features that a road sign recognition system must possess. We propose a nonlinear correlator that performs several correlations between an input scene and different reference targets. Postprocessing of nonlinear correlation results permits attainment of a single output for the recognition system. The nonlinear filters provide invariance to. distortions of the target, noise robustness, and rejection of background noise. We combine a bank of nonlinear composite correlation filters to design a more versatile road sign recognition system. The bank of filters allows tolerance to changes in scale and tolerance to a certain degree of input-plane rotation. The synthesized nonlinear composite correlation filter permits tolerance to out-of-plane rotation of the target. The system is tested by analysis of real images, which include different distorted versions of stop signs. The processor can be designed for a variety of road signs in background scenes. The recognition results obtained for the proposed system show its robustness against the aforementioned distortions, any varying illumination conditions and partially occluded objects View full abstract»

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  • Variable forgetting factor linear least squares algorithm for frequency selective fading channel estimation

    Page(s): 613 - 616
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (251 KB) |  | HTML iconHTML  

    In this article, the variable forgetting factor linear least squares algorithm is presented to improve the tracking capability of channel estimation. A linear channel model with respect to time change describes a time-varying channel more accurately than a conventional stationary channel model. To reduce the estimation error due to model mismatch, we incorporate the modified variable forgetting factor into the proposed algorithm. Compared to the existing algorithms-exponentially windowed recursive least squares algorithm with the optimal forgetting factor and linear least squares algorithm-the proposed method makes a remarkable improvement in a fast fading environment. The effects of channel parameters such as signal-to-noise ratio and fading rate are investigated by computer simulations View full abstract»

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  • An architecture for a nondeterministic distributed simulator

    Page(s): 453 - 471
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB) |  | HTML iconHTML  

    A computer architecture for an accelerated, parallel, nondeterministic, discrete event simulator is described. The machine is evaluated for accelerating: road traffic simulation. The architecture employs reconfigurable logic, systolic arrays, and a reduction bus to perform microscopic discrete event simulation. The simulator, which achieves a speedup factor of at least 91 over its traffic software counterpart, is fast enough to be practical to municipal traffic management engineers handling road incidents in large metropolitan traffic networks View full abstract»

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  • Iterative interference cancellation for DS-CDMA systems with high system loads using reliability-dependent feedback

    Page(s): 445 - 452
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (383 KB) |  | HTML iconHTML  

    In this paper, coded transmission over time-variant multipath Rayleigh-fading channels employing direct-sequence code division multiple access (DS-CDMA) is considered. Assuming ideal knowledge of the actual channel state and randomly chosen spreading sequences, we show that iterative multi-user interference suppression based on adapted minimum mean-squared error (MMSE) filters combined with serial successive cancellation and single user decoding can reach near optimum performance within a few iteration cycles. This holds even for doubly loaded systems, i.e., when the number of users K in the system is two times as large as the spreading factor N. Further, we evidence that for sufficiently reliable symbol estimates soft decision feedback can be replaced by hard decision feedback without any performance degradation but with significant savings in complexity View full abstract»

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  • Evaluation of relative merits/demerits of different signaling schemes used at a railway station for an approaching train in Indian Railways today

    Page(s): 561 - 566
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    Indian Railways, one of the largest railway networks in the world today, has a peculiarity that a station exists almost every 5-7 km. Most trains do not stop at all stations and run through more stations than they stop at. The speed at which the trains run through the stations, therefore, is a crucial parameter that determines the run time of a train through a section and, hence, the total throughput (or carrying capacity of the railways). Indian Railways uses several signaling schemes to enable movement of trains in a safe manner. The signaling schemes play an important role in determining the action of the driver in terms of slowing down of trains and, consequently, on the throughput of the railway system. This paper examines the different signaling schemes used currently and in the recent past by Indian Railways from the point of view of information that they present to the train driver and the impact that it has on total throughput. The signaling schemes are compared using total signal entropy presented to the driver at each stage. Apart from theoretical computation of signal entropy, results of some experiments conducted to obtain the impact of signaling schemes on run time of trains are also presented View full abstract»

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  • Performance analysis of adaptive interleaving for OFDM systems

    Page(s): 435 - 444
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB) |  | HTML iconHTML  

    We proposed a novel interleaving technique for orthogonal frequency division multiplexing (OFDM), namely adaptive interleaving, which can break the bursty channel errors more effectively than traditional block interleaving. The technique rearranges the symbols according to instantaneous channel state information of the OFDM subcarriers so as to reduce or minimize the bit error rate (BER) of each OFDM frame. It is well suited to OFDM systems because the channel state information (CSI) values of the whole frame could be estimated at once when transmitted symbols are framed in the frequency dimension. Extensive simulations show that the proposed scheme can greatly improve the performance of the coded modulation systems utilizing block interleaving. Furthermore, we show that the adaptive interleaving out performs any other static interleaving schemes, even in the fast fading channel (with independent fading between symbols). We derived a semi-analytical bound for the BER of the adaptive interleaving scheme under correlated Rayleigh fading channels. Furthermore, we discussed the transmitter-receiver (interleaving pattern) synchronization problem View full abstract»

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  • Performance analysis of slotted random access channels for W-CDMA systems in Nakagami fading channels

    Page(s): 411 - 424
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (521 KB) |  | HTML iconHTML  

    We perform a new analysis of the performance of the wideband code-division multiple access (W-CDMA) randomized slotted-offset random access channel (RAC) with Nakagami-m fading and compare it with that of a comparable randomized slotted-ALOHA-based RAC. Previously, it was shown that the W-CDMA RAC is fast, robust and simple to implement (see Esmailzadeh, R. and Gustafsson, M., Proc. 1997 IEEE ICUPC Conf, p.43-7, 1997). However, it was assumed that any random access packet arrival events involving multiple packets from cochannel mobile stations would result in lost packets. Closed-form equations are developed for the collision process of the arriving random access packets in slotted-offset and slotted-ALOHA RACs. An analysis is developed of the signal-to-interference-and-noise ratio of a packet involved in a multipacket DS-CDMA collision with a generalized Nakagami fading channel and diversity reception at the base station. A closed-form equation is developed for the bit error rate and packet throughput of the slotted-offset- and slotted-ALOHA-based RACs. The results of the analysis show that considerable improvement in the RAC performance can be achieved when multiple arrival collisions, on the same timeslot and with the same signature code, are partially resolved. The results also show the RAC's sensitivity to fading severity, packet Eb/N 0, spreading gain and number of base station receive selection diversity antennas. Compared to the randomized slotted-ALOHA designs, W-CDMA RAC performs as well in light fading conditions and slightly worse in severe fading conditions View full abstract»

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  • Measurement of the impulsive noise environment for satellite-mobile radio systems at 1.5 GHz

    Page(s): 551 - 560
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (302 KB) |  | HTML iconHTML  

    Noise amplitude distribution measurements relevant to satellite-mobile radio systems are reported. The rationale for the measurements is outlined and the choice of measurement parameters justified. The measurement equipment and measurement methodology are described in detail. Results characterizing the elevation angle distribution of impulsive noise are presented for rural, suburban and urban environments and also for an arterial road (U.K. motorway) carrying high density, fast moving traffic. Measurements of the levels of impulsive noise to be expected in each environment for high- and low-elevation satellite scenarios using appropriate antenna configurations are also presented View full abstract»

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  • Global versus distance-based local mobility tracking strategies: a unified approach

    Page(s): 472 - 485
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (643 KB) |  | HTML iconHTML  

    We have considered fixed location areas for personal communication systems with hysteresis effect in the location update process. Our scheme can be seen as a hybrid between the global (static) and the distance-based local (dynamic), location update strategies, and clearly improves the performance when compared with previous proposals. Selective paging with delay constraint has also been considered. It can be implemented in standard cellular systems View full abstract»

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  • Principles of space-time array processing for ultrawide-band impulse radar and radio communications

    Page(s): 393 - 403
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (518 KB) |  | HTML iconHTML  

    The emerging ultrawide-band (UWB) impulse technology has found numerous applications in the commercial as well as the military sector. The rapid technological advances have made it possible to implement (cost-effective, short-range) impulse radar and impulse-radio communication and localization systems. Array beamforming and space-time processing techniques promise further advancement in the operational capabilities of impulse radar and impulse-radio communications to achieve long-range coverage, high capacity and interference-free quality of reception. We introduce a realistic signal model for UWB impulse waveforms and develop the principles of space-time array processing based on the signal model. A space-time resolution function (STRF), a space-frequency distribution function (SFDF) and a monopulse-tracking signal are derived for impulse waveforms received by a self-steering array beamforming system. The directivity peak-power pattern and energy pattern of the beamformer are also derived. Computer plots of the STRF, SFDF and the beam patterns are obtained. The directivity beam patterns of impulse waveforms are sidelobe-free and, therefore, there is no need for sidelobe suppression via amplitude weighting of the array elements. Also, the resolution angle for the beam patterns is derived as a decreasing function of array size and frequency bandwidth. Electronic beamsteering based on slope processing of monopulse waveforms is described View full abstract»

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  • Performance of service-node-based mobile prepaid service

    Page(s): 597 - 612
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (699 KB) |  | HTML iconHTML  

    The mobile prepaid service has become an important mobile application with rapid growth of subscription rate. The most widely deployed prepaid solution today is the service node approach that deducts and updates the prepaid credit during a phone call. Implementation of the service-node approach may generate a large number of credit checks that significantly degrades the performance of a service node. We investigate how the number of credit checks affects the workload of the service node and the bad debt that a service provider may bear. We propose an analytic model to derive the optimal credit checking/updating frequency for the service node approach: The analytic analysis is validated against simulation experiments. Our study indicates that the number of credit checks increases rapidly when the call pattern is irregular. We also observe that in order to reduce the checking cost of the service node, the prepaid service provider should encourage the customer to make long calls by giving them discounts View full abstract»

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  • A CDMA network architecture using optimized sectoring

    Page(s): 404 - 410
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (282 KB) |  | HTML iconHTML  

    We propose a network architecture for code-division multiple-access (CDMA) cellular systems based on adaptive sector coverage. We show that there is a capacity limit for a CDMA system, which for a soft limit is fairly hard. We also show that for nonhomogeneous traffic, changing the area of coverage for each sector in a sectored-cell can absorb the dynamics of the traffic. For a cell of a fixed radius, divided into n sectors, it is possible to select the angles of coverage of each sector in order to avoid excessive blocking due to temporary nonuniformity of traffic across the cell. This result is based on the fact that for a given set of system parameters (bandwidth, bit rates, Eb/N0 etc.), a certain amount of area is covered. Hence, the exact shape of the cell/sector is not important. The idea presented is shown to be applicable to overlapping sectors View full abstract»

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  • Performance analysis of variable rate: symbol-by-symbol adaptive bit interleaved coded modulation for Rayleigh fading channels

    Page(s): 537 - 550
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (478 KB) |  | HTML iconHTML  

    A challenging problem for a high-speed data service over wireless is to protect data over the error-prone fading channel in an effective way (high-bandwidth efficiency). We propose a bandwidth-efficient error correction scheme, namely variable rate adaptive bit interleaved coded modulation (ABICM), for the wireless mobile channel. The code rate and modulation level are varied according to the current channel state to exploit the time-varying nature of the wireless channel. Design challenges to achieve symbol-by-symbol adaptation are addressed. In particular, we address the criteria for choosing the family of component codes for the ABICM system. We propose a multilevel puncturing scheme that solves the problem of symbol-by-symbol adaptive puncturing and interleaving. The equivalent distance spectrum for variable rate symbol-by-symbol adaptive codes is introduced and analytical bounds on adaptive codes are derived that enable us to determine the optimal adaptation thresholds. Two operation modes, namely constant throughput and constant bit error rate (BER) controls, are proposed. It is found that there are significant gains relative to fixed-rate coding in terms of signal-to-noise ratio (SNR) and throughput. It is also found that the ABICM scheme is essentially not degraded when used with small interleaving depths. This makes the ABICM very suitable for real-time applications View full abstract»

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  • Design and analysis of dynamic mobility tracking in wireless personal communication networks

    Page(s): 486 - 497
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (460 KB) |  | HTML iconHTML  

    In personal communication networks (PCN), mobility tracking provides the function of locating a mobile user within the service area. We propose an intersection-oriented dynamic location update (LU) strategy, which is designed to minimize the cost of mobility tracking by optimally partitioning the service area into location registration (LR) areas on a per-user basis. A realistic mobility model is proposed in which we consider not only the mobility behavior of the individual subscriber, but also the street layout. Based on this model, a transient Markov process is developed to analyze the tracking cost. To reduce the implementation cost and to make the proposed strategy feasible, the concept of mobile subscriber (MS) grouping, and equivalent quadrangular LR area are also adopted View full abstract»

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  • Maximum-likelihood block-size detection for MPSK signaling

    Page(s): 511 - 525
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    In some communications systems, it is required to estimate the size of the received frame or block blindly; that is, using only the received frame. An example where such a problem arises is third-generation wideband code division multiple access universal mobile terrestrial systems (WCDMA UMTS), where it is sometimes required to perform a blind transport format detection. We propose and evaluate a novel method for block-size detection for M-ary phase-shift keying (MPSK) signaling based on the maximum-likelihood principle. Either the method we propose can be used to estimate the block size directly when the operating signal-to-noise ratio (SNR) yields a satisfactory "one-shot" detection error probability or it can be used as a good "coarse" estimate of the block size. In the latter, a good initial guess of only few potential block-size candidates is obtained instead of scanning all possible candidates and then a more accurate detection technique, however more complex, is used to narrow down the number of potential candidates to only one successful candidate View full abstract»

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  • Performance of multicarrier CDMA with DPSK modulation and differential detection in fading multipath channels

    Page(s): 526 - 536
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (510 KB)  

    Multicarrier (MC) direct sequence (DS) code division multiple access (CDMA) with differential phase-shift keying (DPSK) modulation and differential detection is proposed. Transmitted data bits are differentially encoded after serial-to-parallel conversion to a number of parallel streams. On each branch, encoded bits are direct sequence spread spectrum (SS) modulated and transmitted using different carriers. The system is analyzed with a differential detector in static Rayleigh fading multipath channel, in fast Rayleigh fading multipath channel and for variable overlapping between carrier spectra in static fading channel. Closed-form expressions are derived for the error probability and evaluated for many cases. The performance is compared to that of a system using phase-shift keying (PSK) with conventional matched filter (CMF) coherent receiver. For static fading channel, the error probability performance of the differential detector is close to that of CMF receiver. For fast fading, the performance degrades slightly with increasing fading rate. Finally; successive carriers of the system are allowed to overlap with various overlapping percentages. The condition of a single path can be achieved by increasing both the number of carriers and the separation between successive carriers. Also, for each number of carriers, there exists an optimum overlapping percentage at which the system performance is optimized. The performance of the proposed DPSK with differential detection system is close to that of PSK with CMF receiver, but the former is simpler to implement View full abstract»

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  • Analysis of the priority stack random-access protocol in W-CDMA systems

    Page(s): 588 - 596
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    The use of the stack protocol (also called tree protocol) to introduce a priority mechanism on the random access stage in wideband code-division multiple access (W-CDMA) seems more robust when compared with slotted ALOHA. In fact, the protocol stability in infinite population and the guaranteed low-contention delay appear very attractive for a random-access system proposal. Also, for third-generation networks, defining and offering priorities in wireless communication systems appears to be more important for operators and system users. Indeed, after voice only 2G networks, 3G systems (UMTS) should offer more services with quality and priority. However, all priorities in the UMTS system are based on the dedicated channel, which is offered after the random-access mechanism that uses the weak access protocol, slotted ALOHA. We analyze theoretically the possibility of applying the tree random-access protocol for the W-CDMA part of the UTRA radio interface proposition. We also study a priority system applied for random access directly. This seems to be very useful to propose priority for some applications, especially emergency applications. The analytical model uses generating functions and an algebraic method in order to show the stack protocol performance. Also, numerical and simulation results are presented and show the predominance of this protocol compared with the slotted-ALOHA mechanism View full abstract»

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  • Compensation of axle-generator errors due to wheel slip and slide

    Page(s): 577 - 587
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB) |  | HTML iconHTML  

    Significant errors of train axle generators (tachometers) are due to wheel slip and slide. An algorithm is designed to compensate for these errors. The algorithm identifies the wheel slip and slide by examining the variation of the processed vehicle longitudinal acceleration. Whenever wheel slip/slide is identified, then the vehicle speed is adjusted if a certain condition is met. The adjustment is a simple linear interpolation between the two speed values recorded before and after wheel slip/slide detection. In addition, a speed and acceleration observer using a Kalman filter is implemented. Experimental results using three different axle encoders aboard a freight train are provided to illustrate the performance of the proposed algorithm 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.

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Meet Our Editors

Editor-in-Chief
Yuguang Michael Fang
University of Florida