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Vehicular Technology, IEEE Transactions on

Issue 1 • Date Feb. 1998

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Displaying Results 1 - 25 of 37
  • Comments on "Overview of cellular CDMA

    Page(s): 369 - 371
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (88 KB)  

    The author comments that the radio capacity of the cellular code-division multiple-access (CDMA) system and a methodology of solving the problems have been introduced with a clear concept in the paper of Lee (see ibid., vol.40, no.2, p.291-302, 1991). In this paper, a more accurate approach is presented with the equations found and the results plotted. View full abstract»

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  • On the statistical properties of deterministic simulation models for mobile fading channels

    Page(s): 254 - 269
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    Rice's (9144, 1945) sum of sinusoids can be used for an efficient approximation of colored Gaussian noise processes and is therefore of great importance to the software and hardware realization of mobile fading channel models. Although several methods can be found in the literature for the computation of the parameters characterizing a proper set of sinusoids, less is reported about the statistical properties of the resulting (deterministic) simulation model. In this paper, not only is the simulation model's amplitude and phase probability density function (PDF) investigated, but also higher order statistics [e.g., level-crossing rate (LCR) and average duration of fades (ADFs)]. It is shown that due to the deterministic nature of the simulation model, analytical expressions for the PDF of the amplitude and phase, autocorrelation function (ACF), crosscorrelation function (CCF), LCR, and ADFs can be derived. We also propose a new procedure for the determination of an optimal set of sinusoids, i.e., the method results for a given number of sinusoids in an optimal approximation of Gaussian, Rayleigh, and Rice processes with given Doppler power spectral density (PSD) properties. It is shown that the new method can easily be applied to the approximation of various other kinds of distribution functions, such as the Nakagami (1960) and Weibull distributions. Moreover, a quasi-optimal parameter computation method is presented View full abstract»

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  • On the correlation and scattering functions of the WSSUS channel for mobile communications

    Page(s): 270 - 282
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    The wide-sense stationary-uncorrelated scattering (WSSUS) channel model is a commonly employed model for the multipath channel experienced in mobile communications. The second order statistics of these channels are described by the delay cross-power density φh(τ;Δt) or by its Δt-Fourier transform, the scattering function Sh(τ;λ). This paper presents an analysis of the delay cross-power density and scattering functions for mobile communications channels. We assume an arbitrary spatially uncorrelated scattering (US) field with arbitrary propagation-loss factors. Our first result is a general integral expression for φh(τ;Δt) that holds with both transmitter and receiver being mobile. We then derive more detailed results for the case of a stationary base station. We derive an infinite Bessel series for φh(τ;Δt) and a closed-form expression for Sh(τ; λ). These results generalize the well-known classical approximation for the time-correlation function φ¯h(Δt)=def∫φh (τ;Δt)dτ≈ J0(2πλmΔt), which corresponds to the zeroth term of our Bessel series View full abstract»

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  • Characterization of UHF radio propagation channels in tunnel environments for microcellular and personal communications

    Page(s): 283 - 296
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    Narrowband and wideband propagation measurements have been conducted in five tunnels. The effects of pedestrians, vehicles, and curvature on propagation are included in the characterization. The narrowband propagation is characterized in terms of power distance law, slow fading, and fast fading statistics: wideband propagation, rms delay spread, and its statistics. The results show that the power distance law is insensitive to the location of the transmit antenna in the cross section of a tunnel, but not to the antenna insertion loss. The lognormal distribution basically fits the slow variation of the received signals, whereas the Rician distribution, the fast fading in the straight empty sections of the tunnels. In the curved tunnel sections, the Rayleigh distribution does not fit the fast fading variation as is expected. Tunnel radio propagation channels are dependent strongly upon frequency. Higher frequency signals exhibit more severe fluctuations and larger rms delay spread. The rms delay spreads are found to be generally less than 25 and 103 ns for the emptied and occupied tunnel conditions, respectively. One can conclude that the tunnel channels have a broad coherent bandwidth and can support the data rate up to 1 Mb per second without equalization View full abstract»

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  • Performance of switched-beam smart antennas for cellular radio systems

    Page(s): 10 - 19
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    The performance and feasibility of switched-beam smart antennas for cellular radio systems is investigated. Switched-beam smart antenna systems are shown to either increase the capacity or extend the radio coverage by increasing the carrier-to-interference ratio (CIR). The trunking efficiency degradation caused by narrow-beam sectoring can be recovered or even improved by using a variety of trunkpool techniques. One drawback of switched-beam smart antennas is that the improvement in reverse-channel performance is not uniform over the entire cell area, and this presents a limiting factor on the achievable gains, practical considerations such as power control and the limited deployment of smart antenna cells are also addressed View full abstract»

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  • A vision sensor having an expanded dynamic range for autonomous vehicles

    Page(s): 332 - 341
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    Insufficiency of dynamic range of conventional video cameras is an important problem in realizing a robust vision system for autonomous vehicles because road scenes have a very wide dynamic range of brightness. To solve the problem, a method for expanding the dynamic range of video cameras by combining the images taken under different exposure conditions has been developed. Using this method, an experimental vision sensor with a wide dynamic range has been manufactured. The developed sensor has a dynamic range of 10 000, which is approximately 30 times as wide as that of a conventional video camera. The effectiveness of the developed vision sensor in comparison with a conventional video camera was confirmed from the experiments on a highway under various lighting conditions View full abstract»

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  • A radio-over-fiber network for microcellular system application

    Page(s): 84 - 94
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    This paper investigates the feasibility of a radio-over-fiber network, which employs a single high-power Nd:YAG laser shared among many microcells. External amplitude modulators are employed at both base station (BS) and radio ports (RPs) to form an optical fiber distribution network. The distortions induced by the uplink remodulation are analyzed. The optimal preamplifier gain in the uplink is estimated for given sensitivity and dynamic range (DR). Appropriate modulator linearization and thermal-noise suppression schemes are utilized together to improve the DR. The clipping distortion for the predistortion-linearized modulator is also considered. The result shows that the effects of clipping and higher order distortions have little impact on the estimation of the system performance. A numerical example shows that a 100-mW Nd:YAG laser can provide for a macrocell of 5-km radius up to 16 microcells and 1600 channels when a 20-dB modulator linearization and 10-dB thermal-noise suppression are employed. The experiment setup uses a two-tone test to verify the theoretical calculation. The measurement agrees with the theoretical estimation very well View full abstract»

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  • Performance analysis of a DS/CDMA system with noncoherent M-ary orthogonal modulation in Nakagami fading

    Page(s): 20 - 29
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    The probability of error performance of a direct sequence code-division multiple-access (DS/CDMA) system employing noncoherent M-ary orthogonal signaling in a Nakagami multipath fading channel is analyzed. A RAKE receiver structure with square-law demodulation is used at the receiver. The multiple-access interference are modeled as Gaussian and expressions derived for the exact probability of error. The performance is also evaluated in terms of the number of users that can be supported by the system at a given probability of error. The effect of correlated fading on system performance is also investigated by considering two correlation models, which can be characterized by a single correlation coefficient ρ. In the first model, the correlation coefficient between any two diversity branches is constant. In the second model, it is assumed that the correlation coefficient between any two diversity branches decreases exponentially as the separation between them increases. For both models, it is found that the presence of correlation deteriorates system performance. The use of larger signal alphabets than binary modulation in conjunction with diversity reception provides a considerable performance improvement even in the presence of correlated fading View full abstract»

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  • Modulation and coding for mobile radio communications: channels with correlated Rice fading and Doppler frequency shift

    Page(s): 133 - 141
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    We discuss the relative performance of coherent phase-shift keying (PSK), differential PSK (DPSK), and double differential PSK (DDPSK) modulation schemes over a mobile radio channel in which transmission is affected by additive noise, a constant carrier phase offset, a constant Doppler frequency shift, and correlated Rice fading. We first compare the performance of these schemes to assess the amount of degradation caused on each one of them by fading. Among our findings, we observe that DDPSK turns out to be less sensitive to the effects of correlated fading than the other two schemes and that in these conditions interleaving may not be beneficial. We then consider the introduction of trellis-coded modulation (TCM). The system we advocate as offering the best tradeoff between performance and complexity with the channel model assumed here includes double-differential encoding, differential detection, an open-loop Doppler phase tracking circuit, and differential decoding in addition to a simple TCM scheme View full abstract»

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  • The use of coding and diversity combining for mitigating fading effects in a DS/CDMA system

    Page(s): 95 - 102
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    Spatial diversity is an attractive technology to cope with the fading channel encountered in mobile communications. This paper presents novel closed analytical expressions of the bit-error rate (BER) achievable in a coherent binary phase-shift-keying (CBPSK) direct-sequence code-division multiple-access (DS/CDMA) system for any power delay profile and for either postdetection selection or maximal ratio combining (MRC). In particular, expressions for the cutoff rate R o and for its related parameter D are also formulated in order to assess the system performance under the consideration of some channel coding schemes. Finally, an exemplary study is carried out in order to illustrate the behavior of a realistic space-diversity code-division multiple-access (CDMA) system according to the analytical expressions that have been derived View full abstract»

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  • Matched frequency-hopping (MFH) signals for slowly fading dispersive channels

    Page(s): 365 - 369
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    The design of channel-matched frequency-hopping (MFH) spread-spectrum signals that overcome the performance degradation caused by the channel dispersion is described. In MFH systems, the used frequency slots are selected such as to correspond to maximum transmission through the communication channel. This is affected by adapting the MFH signals so that the probability density function (PDF) of hopped frequencies matches the transfer function of the communication channel. The performance of MFH signals in multipath slowly fading dispersive channels is evaluated, using a generalized bandpass two-path transfer function model. The performance is compared with that of frequency-hopping (FH) signals with uniformly distributed frequencies for different scenarios of channel parameters. The results clearly show the advantages of MFH transmission View full abstract»

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  • A hybrid analytical-simulation procedure for performance evaluation in M-QAM-OFDM schemes in presence of nonlinear distortions

    Page(s): 142 - 151
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    Presents a hybrid analytical-simulation procedure for performance evaluation in M-ary quadrature amplitude modulation (M-QAM) orthogonal frequency-division multiplexing (OFDM) digital radio systems in the presence of nonlinear distortions caused by high-power amplifiers (HPAs). The present analysis is carried out considering an additive white Gaussian noise (AWGN) transmission channel. It is shown that, in the case of an OFDM system with a large number of subcarriers, the distortion on the received symbol caused by the amplifier can be modeled, with good approximation, as a “Gaussian nonlinear noise” added to the received symbol. This important result allows a hybrid analytical-simulation approach to solve the problem of performance evaluation. In practice, the simulation aspect is only used to estimate means and variances of the “nonlinear noise”. Such estimated parameters are subsequently used to evaluate analytically the system bit-error rate (BER) using an expression, which takes into account both AWGN and “nonlinear noise” effects. The advantage of the proposed method lies in the strongly reduced computational time. In fact, an accurate estimate of the “nonlinear noise” parameters requires only few iterations when compared with a classical semianalytical approach. This is especially true when low BER values (<10-4) have to be estimated. The proposed procedure is applied to evaluate M-QAM-OFDM performance in the presence of nonlinear distortions caused by traveling-wave tube (TWT) and solid-state-power (SSP) amplifiers View full abstract»

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  • Microcell prediction in dense urban area

    Page(s): 246 - 253
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    The use of microcell to increase the capacity of cellular mobile communication, especially in the dense urban areas, is an attractive possibility. A number of experimental and theoretical studies have been undertaken regarding propagation in the urban microcellular system. A microcell prediction model based on building thickness is developed to predict the statistical properties of the cell site. The model is validated based on several drive tests performed in different countries/cities with different transmitter heights, frequencies, cell-site parameters, and mobile environments. The first finding is that this empirical-based microcell model performed well in all these areas with a combination of various parameters. Second, the terrain does have a major impact on microcell prediction. This paper addresses the sufficient requirement of having only a two-dimensional (2-D) microcell prediction model. The impact of terrain contour on the microcell prediction is not included View full abstract»

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  • Signal recognition and signature code acquisition in CDMA mobile packet communications

    Page(s): 196 - 208
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    Fast and reliable signal sense and signature code synchronization for direct-sequence spread-spectrum (DS-SS) signals are key issues in the design of the receiver for modern packet code-division multiple-access (CDMA) radio networks for mobile communications; this motivates the study of the signal recognition and code-acquisition (SR/CA) scheme we describe in this paper. Specifically, starting from elementary estimation and detection theory criteria, we work out a noncoherent parallel SR/CA algorithm that is suited to a full-digital implementation in a single application-specific integrated circuit (ASIC). The results of a theoretical analysis of such a scheme, encompassing additive white Gaussian noise (AWGN) and multiple-access interference (MAI), are integrated and validated by an overall time-domain system simulation. We also evaluate through a simplified approach the impact of some degradation factors on the overall circuit performance, namely, sampling epoch and carrier frequency offset and 1-b signal quantization, to allow optimization of the design parameters as a function of the characteristics of the received signal View full abstract»

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  • Amplifier linearization using RF feedback and feedforward techniques

    Page(s): 209 - 215
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    The performance of feedback as a distortion reduction technique is highly dependent on the integrity of the feedback path. Any error or noise generated in this path is directly reflected into the output of the amplifier. Linearized RF power amplifiers (PAs) using Cartesian feedback require a demodulator in the feedback loop, and this is a potential source of linear errors, nonlinear errors, and noise. RF feedback with Cartesian compensation is proposed as a technique for overcoming some of these problems. The scheme is most suited to systems requiring an RF input. In addition, the RF nature of the input, feedback, and error signals enables the addition of a feedforward loop to further improve the linearization capability while still maintaining good efficiency. Design equations and simulation results are given for such a system. Disadvantages include the limited bandwidth (estimated at 1 MHz) and the need for additional circuits to generate the RF input signal when included in an integrated transmitter View full abstract»

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  • A unified performance model for reservation-type multiple-access schemes

    Page(s): 173 - 189
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    This paper presents a unified performance model for an integrated voice/data wireless system using reservation type multiple-access (MA) schemes. It is observed that although these schemes are different in the frame structure and resource assignment procedure, all of them can be described by several common state variables whose evolvement exhibits the Markovian property. Based on this observation, a general Markovian model is developed in this paper. Three performance measures, namely, voice-packet-loss probability, data throughput, and data delay are defined. As a special case, the performance evaluation model for the voice-only system is also presented. Numerical results are given and verified by simulation under both voice-only and integrated scenarios using packet-reservation MA (PRMA), dynamic time-division multiple access (D-TDMA), and resource auction multiple access (RAMA) as examples. It is found that our analytical model is quite accurate, especially in the region of interest. The impact of system parameters (such as the voice-permission probability, data-retransmission probability, maximum number of voice slots per frame, etc.) on the integrated system performance is also investigated for these three example systems View full abstract»

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  • A study of a land mobile satellite channel model with asymmetrical Doppler power spectrum and lognormally distributed line-of-sight component

    Page(s): 297 - 310
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    In satellite to mobile communications, there is generally, in addition to the diffuse multipath component, a strong line-of-sight (LOS) component present. The spectral and statistical properties of both components are influenced by shadowing caused by obstacles such as trees, houses, or small buildings. In this paper, an analytical model for a land mobile satellite channel is analyzed that takes into consideration various kinds of shadowing situations. For the LOS component, it is assumed that, first, the received frequency shows a Doppler shift. Second, the amplitude variations coincide with a lognormal distribution. Moreover, it is also assumed that shadowing influences the diffuse scattered component, with the consequence that its Doppler power spectrum gets an asymmetrical shape. The resulting spectral and statistical properties of the analytical model are investigated. Exact solutions for the probability density function (pdf) of the amplitude and phase are given, and approximative solutions for the level-crossing rate (LCR) and average duration of fades (ADFs) are derived. Finally, an efficient deterministic simulation model is presented that enables the implementation of the proposed analytical model on a digital computer View full abstract»

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  • Optimum diversity combining and equalization over interference-limited cellular radio channel

    Page(s): 103 - 118
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    This paper presents the comparative analysis of Nth-order diversity combining and equalization over an interference-limited cellular radio channel. The method of combining diversity and equalization has been analyzed previously. However, cochannel interference (CCI) was not considered, and the number of equalization taps was assumed to be infinite. A quadrature amplitude modulation (QAM) is used in our signal analysis. In modeling the multipath radio, we take into account CCI generated by frequency reuse and additive white Gaussian noise (AWGN). The performance evaluations are made of average error probability and outage probability. The average error rate is determined by using a Monte Carlo simulation for a set of channel parameters such as signal-to-noise ratio (SNR), signal-to-interference ratio (SIR), and equalization coefficients determined for this channel. In the error-rate estimation, we analyze and compare the results of system performance obtained by the upper bound approach and the moment estimation method. We also investigate the tradeoff of the performance improvement in terms of average error probability and equalizer complexity (the number of equalization taps) View full abstract»

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  • Low-complexity cochannel interference cancellation and macroscopic diversity for high-capacity PCS

    Page(s): 124 - 132
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    More than a factor of three increase in overall personal communication system (PCS) capacity can be achieved in small handheld communication devices with limited battery power or in small low-complexity base stations when incorporating simple interference cancellation techniques without training sequences in the channel-access algorithm that realizes macroscopic selection diversity based on signal quality measurement. The comparison is done with respect to microscopic selection diversity and macroscopic selection diversity based on channel power measurement. Results were obtained by computer simulations View full abstract»

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  • A real-time traffic simulation system

    Page(s): 321 - 331
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    This article studies the usefulness of parallel processing in real-time traffic-flow simulation based on continuum modeling of traffic dynamics. Computational fluid dynamics (CFDs) methods for solving simple macroscopic traffic-flow continuum models have been studied and efficiently implemented in traffic simulation codes (on serial computers) in the past. We designed a traffic-flow simulation code and mapped it onto a parallel computer architecture. This traffic simulation system is capable of simulating freeway traffic flow in real time. Tests with real traffic data collected from the freeway network in the metropolitan area of Minneapolis, MN, were used to validate the accuracy and computational rate of the parallel simulation system. The execution time for a 2-h traffic-flow simulation of about 200 619 vehicles in an 18-mi freeway, which takes 2.35 min of computer time (on a single-processor computer simulator), took only 5.25 s on the parallel traffic simulation system. This parallel system has a lot of potential for real-time traffic engineering applications View full abstract»

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  • Hot-spot traffic relief with a tilted antenna in CDMA cellular networks

    Page(s): 1 - 9
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    Direct-sequence code division multiple-access (DS-CDMA) cellular networks are highly promising in terms of their potential to provide more capacity than an advanced mobile phone system (AMPS). However, heterogeneous traffic loading causes traffic congestion in a CDMA hot-spot. This paper presents a tilted antenna mechanism for sectored cells in CDMA cellular networks to relieve the congestion in a hot-spot sector. The fixed antenna-tilted mechanism, which only tilts the hot-spot antenna, can provide the merit of traffic balancing. Besides, we design a dynamic antenna-tilted mechanism in which tilting the antennas of the hot spot and its adjacent cell sectors is based on varying the signal-to-noise ratio (SNR). The dynamic mechanism can automatically tilt the antenna corresponding to the variation of traffic. Consequently, more capacity can be provided than in a fixed tilting mechanism, which only tilts the hot-spot antenna. Another benefit is the traffic-balancing effect with a tilted-antenna mechanism that reduces the transceivers of a hot-spot base station. Therefore, extra facilities are unnecessary for the hot spot than for a normal or light traffic sector View full abstract»

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  • Propagation considerations for the design of an indoor broad-band communications system at EHF

    Page(s): 235 - 245
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    This paper reports the measurement and analysis of wideband propagation data for indoor radio channels at 40 GHz. Propagation characteristics are reported for two open-concept office areas of different sizes in two different buildings. Also, the results of measurements in one building are compared for system configurations in which either an omnidirectional or a narrowbeam antenna is employed at a base station for communications to multiple work stations with omnidirectional antennas. It is reported that, on a statistical basis, at the 90th percentile, multipath dispersion is the same for the two base-station antenna radiation patterns. Dispersion was, however, found to be lower in the smaller of the two measurement areas, where transmit/receive ranges were shorter. The 90th percentile of static RMS delay spread for this area was 19 ns compared with 45 ns for the larger area. Multipath spreads at the -25 dB relative power level were about 370 ns, compared with 140 ns in the larger area. In the larger area, global propagation loss was found to be well modeled by the one-way propagation equation with different range exponents (1.5 and 4) before and after a breakpoint at a range of 25 m. In the smaller area, the range exponent was found to be greater, being equal to 3.5. This is considered to be a result of reduced multipath infill, which would accompany the reduced dispersion. Temporal fading on fixed links with omnidirectional antennas was found to have depths such that a 14-dB fade margin is required for 99% reliability. Finally, spatial variations in received power at a given range indicated the requirement for a power margin between 4-7 dB for 99% reliability. These results are used in a link budget example for a broad-band indoor extremely high frequency (EHF) digital communications system View full abstract»

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  • An integrated services MAC protocol for local wireless communications

    Page(s): 352 - 364
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    This paper proposes a medium-access control (MAC) protocol for integrated voice/data services in local wireless communications. The proposed protocol is a hybrid of R-Aloha and Aloha reservation adapted to local wireless environment. In the proposed hybrid Aloha-reservation/R-Aloha (HAR) protocol, data messages are transmitted using Aloha-reservation protocol, whereas voice packets are transmitted according to R-Aloha on the channel assigned using Aloha reservation. The performance of the HAR protocol is analyzed by computer simulation. Simulation results prove that the HAR protocol is appropriate as a protocol for integrated services wireless networks in which computer data is major traffic and voice traffic coexists View full abstract»

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  • Characteristics' prediction in urban and suburban environments

    Page(s): 225 - 234
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    The characteristics of the propagation in the microcellular urban and suburban environments in the 902-928-MHz frequency band in line-of-sight (LOS) conditions is investigated both theoretically and experimentally for the purpose of wireless radio local loop (WRLL) prediction. The path-loss characteristics and the range of a break point, at which the polynomial character of field intensity decay along the street level is changed, are analyzed for various parameters of street widths, for different average building heights, and for the actual electrical impedance properties of building walls. A multislit waveguide with randomly distributed gaps between the sides of buildings is considered as a model of straight streets. Results of experiments for VHF/UHF wave propagation along the straight streets in urban environment in the conditions of direct visibility between receiver and transmitter are compared with theoretical analysis of field intensity decay, path-loss distribution, and dependence of the break point on street topography in LOS conditions View full abstract»

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  • A method for estimating local traffic load in a simulcast radio system

    Page(s): 30 - 37
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    This paper presents a simple method for estimating the average local traffic load in a simulcast radio system. Such estimation is crucial to achieving efficient resource sharing and dynamic reconfiguration of the simulcast areas. The proposed method is based only on relative power measurements at each radio port (or distributed antenna element) and is applicable to both code-division multiple-access (CDMA) and time-division multiple-access (TDMA) systems. Simulation results are derived to test the method over various system conditions and assumptions. The proposed method is shown to provide excellent results, giving estimates to within ±15% of the actual Erlang traffic, while requiring only an approximate knowledge of the radio propagation environment 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