Showing papers in "IEEE Transactions on Vehicular Technology in 2000"
TL;DR: The pilot-symbol-aided parameter estimation for orthogonal frequency division multiplexing (OFDM) systems is highly robust to Doppler frequency for dispersive fading channels with noise impairment even though it has some performance degradation for systems with lower Dopple frequencies.
Abstract: In this paper, we investigate pilot-symbol-aided parameter estimation for orthogonal frequency division multiplexing (OFDM) systems. We first derive a minimum mean-square error (MMSE) pilot-symbol-aided parameter estimator. Then, we discuss a robust implementation of the pilot-symbol-aided estimator that is insensitive to channel statistics. From the simulation results, the required signal-to-noise ratios (SNRs) for a 10% word error rate (WER) are 6.8 dB and 7.3 dB for the typical urban (TU) channels with 40 Hz and 200 Hz Doppler frequencies, respectively, and they are 8 dB and 8.3 dB for the hilly-terrain (HT) channels with 40 Hz and 200 Hz Doppler frequencies, respectively. Compared with the decision-directed parameter estimator, the pilot-symbol-aided estimator is highly robust to Doppler frequency for dispersive fading channels with noise impairment even though it has some performance degradation for systems with lower Doppler frequencies.
671 citations
TL;DR: It is found that in typical urban environments the power azimuth spectrum (PAS) is accurately described by a Laplacian function, while a Gaussian PDF matches the Azimuth PDF.
Abstract: A simple statistical model of azimuthal and temporal dispersion in mobile radio channels is proposed. The model includes the probability density function (PDF) of the delay and azimuth of the impinging waves as well as their expected power conditioned on the delay and azimuth. The statistical properties are extracted from macrocellular measurements conducted in a variety of urban environments. It is found that in typical urban environments the power azimuth spectrum (PAS) is accurately described by a Laplacian function, while a Gaussian PDF matches the azimuth PDF. Moreover, the power delay spectrum (PDS) and the delay PDF are accurately modeled by an exponential decaying function. In bad urban environments, channel dispersion is better characterized by a multicluster model, where the PAS and PDS are modeled as a sum of Laplacian functions and exponential decaying functions, respectively.
647 citations
TL;DR: The design tradeoffs of turbo-coded burst-by-burst adaptive orthogonal frequency division multiplex (OFDM) wideband transceivers are analyzed and AOFDM provides a convenient framework for adjusting the required target integrity and throughput both with and without turbo channel coding.
Abstract: The design tradeoffs of turbo-coded burst-by-burst adaptive orthogonal frequency division multiplex (OFDM) wideband transceivers are analyzed. We demonstrate that upon aiming for a higher throughput a higher proportion of low-quality OFDM subcarriers has to be used for the transmission of inherently vulnerable high-order modem modes, transmitting several bits per subcarrier. Upon invoking turbo coding and adjusting the modem mode switching regime near-error-free performance can be achieved at the cost of a reduced throughput. Various blind modem mode detection techniques have also been investigated and the most complex channel coding trellis-based detection algorithm was found to be the most powerful. Last, the design tradeoffs of spectral pre-equalization have been explored and quantified. We concluded that AOFDM provides a convenient framework for adjusting the required target integrity and throughput both with and without turbo channel coding.
342 citations
TL;DR: An overview of the novel class of channel codes referred to as turbo codes, which have been shown to be capable of performing close to the Shannon limit, is provided.
Abstract: We provide an overview of the novel class of channel codes referred to as turbo codes, which have been shown to be capable of performing close to the Shannon limit. We commence with a discussion on turbo encoding, and then move on to describing the form of the iterative decoder most commonly used to decode turbo codes. We then elaborate on various decoding algorithms that can be used in an iterative decoder, and give an example of the operation of such a decoder using the so-called soft output Viterbi (1996) algorithm (SOVA). Lastly, the effect of a range of system parameters is investigated in a systematic fashion, in order to gauge their performance ramifications.
342 citations
TL;DR: The analysis accounts for fading of the signal of interest (SOI) as well as the cochannel interference (CCI) in BPSK signalling in flat, quasi-static channels and a limited analysis of the equal gain combiner is presented.
Abstract: The performance of maximal ratio combining for space diversity reception in digital cellular mobile radio systems is studied for communications in the presence of multiple cochannel interference (CCI) sources and is compared to optimum combining. The main contribution of the paper is that the analysis accounts for fading of the signal of interest (SOI) as well as the cochannel interference (CCI). The paper considers BPSK signalling in flat, quasi-static channels. Rayleigh or Rice fading is assumed for the SOI, while CCI is assumed subject to Rayleigh fading. Channels associated with interference sources are assumed independent and identically distributed. Using a multivariate statistical analysis approach and assuming equal-power interference sources, analytical expressions are derived for the density function of the array output signal-to-interference ratio (SIR), the outage probability, and the average probability of bit error with maximal ratio combining. Earlier results obtained for optimum combining and Rayleigh fading are extended to the case when the SOI is subject to Rice fading. A limited analysis of the equal gain combiner is also presented.
275 citations
TL;DR: The minimum longitudinal spacing which the vehicles involved in a lane changing/merging maneuver should initially have so that no collision, of any type, takes place during the maneuver.
Abstract: One of the riskiest maneuvers that a driver has to perform in a conventional highway system is to merge into the traffic and/or to perform a lane changing maneuver. Lane changing/merging collisions are responsible for one-tenth of all crash-caused traffic delays often resulting in congestion. Traffic delays and congestion, in general, increase travel time and have a negative economic impart. We analyze the kinematics of the vehicles involved in a lane changing/merging maneuver, and study the conditions under which lane changing/merging crashes can be avoided. That is, given a particular lane change/merge scenario, we calculate the minimum longitudinal spacing which the vehicles involved should initially have so that no collision, of any type, takes place during the maneuver. Simulations of a number of examples of lane changing maneuvers are used to demonstrate the results. The results of this paper could be used to assess the safety of lane changing maneuvers and provide warnings or take evasive actions to avoid collision when combined with appropriate hardware on board of vehicles.
238 citations
TL;DR: The performance of recognizing registration numbers on license plates has been investigated on real images of about 1000 vehicles captured under various illumination conditions and showed that the developed system is quite effective for license-plate recognition.
Abstract: Novel methods to recognize license plates robustly are presented. A sensing system with a wide dynamic range has been developed to acquire fine images of vehicles under varied illumination conditions. The developed sensing system can expand the dynamic range of the image by combining a pair of images taken under different exposure conditions. In order to avert blurring of images against fast passing vehicles, a prism beam splitter installed a multilayered filter, and two charge-coupled devices are utilized to capture those images simultaneously. Furthermore, to extend the flexibility of camera placement, a recognition algorithm that can be applied to inclined plates has been developed. The performance of recognizing registration numbers on license plates has been investigated on real images of about 1000 vehicles captured under various illumination conditions. Recognition rates of over 99% (conventional plates) and over 97% (highly inclined plates) showed that the developed system is quite effective for license-plate recognition.
237 citations
TL;DR: In this paper, the authors formulated the cell planning problem with capacity expansion in wireless communications as an integer linear programming problem and solved by a tabu search algorithm to minimize the cost of new base stations.
Abstract: The cell planning problem with capacity expansion is examined in wireless communications. The problem decides the location and capacity of each new base station to cover expanded and increased traffic demand. The objective is to minimize the cost of new base stations. The coverage by the new and existing base stations is constrained to satisfy a proper portion of traffic demands. The received signal power at the base station also has to meet the receiver sensitivity. The cell planning is formulated as an integer linear programming problem and solved by a tabu search algorithm. In the tabu search intensification by add and drop move is implemented by short-term memory embodied by two tabu lists. Diversification is designed to investigate proper capacities of new base stations and to restart the tabu search from new base station locations. Computational results show that the proposed tabu search is highly effective. A 10% cost reduction is obtained by the diversification strategies. The gap from the optimal solutions is approximately 1/spl sim/5% in problems that can be handled in appropriate time limits. The proposed tabu search also outperforms the parallel genetic algorithm. The cost reduction by the tabu search approaches 10/spl sim/20% in problems: with 2500 traffic demand areas (TDAs) in code division multiple access (CDMA).
212 citations
TL;DR: Simple techniques are presented for performing digital predistortion by use of look-up tables and adaptive indexing is introduced which allow the various techniques to adapt to changing signal and power amplifier characteristics.
Abstract: Simple techniques are presented for performing digital predistortion by use of look-up tables. Performance is measured by the traditional spectral regrowth analysis which quantifies the out-of-band distortion. Also included in the performance evaluation is constellation distortion which quantifies the in-band distortion which is important for bit error rate (BER) performance. As an added performance measure, predistortion is also analyzed with respect to its effect on amplifier efficiency. A nonuniform spacing technique is described which is simple to implement and has a performance very close to the cited optimum approach. In addition, scaling the gain of these tables provides further improvement in terms of correction and efficiency performance. Finally, adaptive indexing is introduced. These algorithms allow the various techniques to adapt to changing signal and power amplifier characteristics.
207 citations
TL;DR: The presented results offer a simple, generic, and useful analytical tool for the accurate performance evaluation and optimization of switched diversity systems.
Abstract: We evaluate and optimize the performance of switch and stay diversity systems which have the advantage of offering one of the least complex solutions to mitigating the effect of fading. We study the impact of fading type and severity, unbalanced branches, fading correlation, and imperfect channel estimation on the performance of these systems, and compare this performance with that of more complex diversity schemes such as maximal-ratio combining and selection combining. We also propose, analyze, and optimize the performance of a generalized switched diversity scheme. In summary, the presented results offer a simple, generic, and useful analytical tool for the accurate performance evaluation and optimization of switched diversity systems.
187 citations
TL;DR: An analysis of the effects of gain decorrelation and of the number of antennas are provided, and an assessment of the effect of fading when the method supports multiple users is assessed.
Abstract: In maximal ratio transmission, the base station adjusts the complex weights of its transmit antennas to compensate for downlink channel gains in order to produce signal reinforcement-diversity-at a desired mobile that may have only a single antenna. To make the method adaptive, the complex weights are obtained from the instantaneous complex gains in the uplink; however, delay and frequency offset between uplink measurements and downlink transmission reduce the correlation between the gains in the two directions. This paper provides an analysis of the effects of gain decorrelation and of the number of antennas, and an assessment of the effect of fading when the method supports multiple users. It demonstrates that large reductions in downlink transmit power are achievable, and it examines simple transmission models to see how well they support the technique.
TL;DR: An analytic expression for the probability that a portable moves across K registration areas (RAs) is obtained and is very useful for cost analysis for location updating and paging.
Abstract: In this paper, we propose a new model for the portable movement in personal communications services (PCSs) networks. Based on this model with general interservice time and registration area residence time distributions, an analytic expression for the probability that a portable moves across K registration areas (RAs) is obtained. The busy-line effect on this quantity is also studied and an analytic expression is presented. The result given in this paper is very useful for cost analysis for location updating and paging.
TL;DR: A ray tracing technique to predict the propagation channel parameters in indoor scenarios is presented and some comparisons between predicted results and measurements are presented to validate the method.
Abstract: A ray tracing technique to predict the propagation channel parameters in indoor scenarios is presented. It is a deterministic technique, fully three-dimensional, based on geometrical optics (GO) and the uniform theory of diffraction (UTD). A model of plane facets is used for the geometrical description of the environment. The ray tracing is accelerated considerably by using the angular Z-buffer algorithm. Some comparisons between predicted results and measurements are presented to validate the method.
TL;DR: A comparison of five of the most discussed receiver structures: the decorrelator, the minimum mean square error (MMSE) receiver, the multistage parallel interference cancellation receivers, the successive interference cancellation receiver, and the decor Relating decision feedback receiver.
Abstract: Multiuser detection has gained significant notoriety as a potential advanced enabling technology for the next generation of CDMA systems. Due to the limitations of the conventional correlation receiver, the capacity of a single cell using CDMA is limited by self-interference and is subject to the near-far problem. To overcome these drawbacks, several advanced receiver structures have been proposed. Unlike the conventional receiver which treats multiple access interference (MAI) as if it were AWGN, multiuser receivers treat MAI as additional information to aid in detection. Although each of the multiuser types have been the subject of much literature, there is little published work comparing all structures on the basis of common assumptions. We present a comparison of five of the most discussed receiver structures: the decorrelator, the minimum mean square error (MMSE) receiver, the multistage parallel interference cancellation receiver, the successive interference cancellation receiver, and the decorrelating decision feedback receiver. Comparisons are based on both theoretical analysis and simulation results, examining bit error rate (BER) performance in AWGN, Rayleigh fading, and near/far channels. Additionally, receiver structures are compared on the basis of computational complexity as well as robustness to code phase misalignment. Finally, we present simulation results for noncoherent architectures of the aforementioned receivers.
TL;DR: An efficient ray-path search algorithm is presented, and the software tool Radio Tracer using such techniques is briefly described, and some comparisons between experimental results and computed predictions for indoor and outdoor scenarios are shown.
Abstract: Ray-tracing and uniform theory of diffraction techniques are already widely applied to site-specific radio propagation modeling for wireless applications. Software tools using such techniques may take considerable computation time in the analysis of the propagation conditions in a given environment even for a short mobile terminal route. Efficient acceleration techniques are required to make such analysis tools practical for the design of modern radio systems. To reduce computation time, ray-tracing routines must be applied only to those areas where rays are likely to exist. This is achieved by using ray-path search algorithms prior to performing any actual ray tracing. An efficient ray-path search algorithm is presented. First, a two-dimensional version is described, which is valid for indoor and microcell studies. Then, an extension to the three-dimensional case is explained in detail. Finally, the software tool Radio Tracer using such techniques is briefly described, and some comparisons between experimental results and computed predictions for indoor and outdoor scenarios are shown.
TL;DR: Numerical examples are presented which illustrate, the increase in the two-dimensional (2-D) capacity region achievable by optimizing the assignment of powers and processing gains to each class.
Abstract: We consider a packet data direct-sequence code-division multiple-access (DS-CDMA) system which supports integrated services. The services are partitioned into different traffic classes according to information rate (bandwidth) and quality of service (QoS) requirements. Given sufficient bandwidth, QoS requirements can be satisfied by an appropriate assignment of transmitted power and processing gain to users in each class. The effect of this assignment is analyzed for both a single class of data users and two classes of voice and data users. For a single class of data users, we examine the relationship between average delay and processing gain, assuming that ARQ with forward error correction is used to guarantee reliability. The only channel impairment considered is interference, which is modeled as Gaussian noise. A fixed user population is assumed and two models for generation of data packets are considered: (1) each user generates a new packet as soon as the preceding packet is successfully delivered and (2) each user generates packets according to a Poisson process. In each case, the packets enter a buffer which is emptied at the symbol rate. For the second traffic model, lowering the processing gain below a threshold can produce multiple operating points, one of which corresponds to infinite delay. The choice of processing gain which minimizes average delay in that case is the smallest processing gain at which multiple operating points are avoided. Two classes of users (voice/data and two data classes) are then considered. Numerical examples are presented which illustrate, the increase in the two-dimensional (2-D) capacity region achievable by optimizing the assignment of powers and processing gains to each class.
TL;DR: Equations are developed that relate the prefix extension to the guard-band given the required subchannel signal-to-noise ratio (SNR) and the total loss reduces as the inverse fast Fourier transform (IFFT) size N increases and the required SNR reduces.
Abstract: Filtering is required in the practical implementation of orthogonal frequency division multiplex (OFDM) systems operating at radio frequencies. These filters smear the transmitted waveform, and cause inter-symbol interference (ISI) between the blocks, forcing a further extension to the cyclic prefix. The tighter the filtering, the smaller the frequency bandwidth (guard-band) needed between adjacent channel users and the longer the prefix extension. Equations are developed that relate the prefix extension to the guard-band given the required subchannel signal-to-noise ratio (SNR). Numerical evaluation is then used to show the trade off between time domain and frequency domain capacity loss. There is an optimum guard-band loss, that will minimize the total (time+frequency) capacity loss. The total loss reduces as the inverse fast Fourier transform (IFFT) size N increases and the required SNR reduces. The capacity loss exceeds 40% when N=32 and SNR is 33 dB (needed for 8DPSK with an symbol error rate (SER) of 3% and a margin of 10 dB). Some of the loss can be reduced by using better filters (Chebyshev II), but the general trend of the results imply that schemes with a low number of subchannels (N<16) will not work well with high order modulations.
TL;DR: The proposed beamforming algorithm is applied to the base station of a code-division-multiple access (CDMA) mobile communication system and the performance is shown in multipath fading communication channels in terms of the signal-to-interference+noise ratio, the bit error rate, and the achievable capacity of a given CDMA cell/sector.
Abstract: An alternative way of adaptive beamforming is presented. The main contribution of the new technique is in its simplicity with a minimal loss of accuracy. The total computational load for computing a suboptimal weight vector from each new signal vector is about O(2N/sup 2/+5N). It can further be reduced down to O(3N) by approximating the autocorrelation matrix with the instantaneous signal vector at each snapshot. The required condition on the adaptive gain for the proposed algorithm to converge is derived analytically. The proposed beamforming algorithm is applied to the base station of a code-division-multiple access (CDMA) mobile communication system. The performance of the proposed method is shown in multipath fading communication channels in terms of the signal-to-interference+noise ratio (SINR), the bit error rate (BER), and the achievable capacity of a given CDMA cell/sector.
TL;DR: A finite-state Markov model is fitted to the mobile propagation channel by the use of contingency tables and functional dependence between the transition probabilities and the steady-state probabilities is found in the slow fading case.
Abstract: A finite-state Markov model is fitted to the mobile propagation channel by the use of contingency tables. Narrow-band Rayleigh and Ricean fading are considered in detail, but the techniques extend to other types of fading. Several criteria may indicate that a first-order finite-state Markov model sufficiently characterizes the channel behavior. The parameters of the model are obtained both from theoretical analysis and simulation. Functional dependence between the transition probabilities and the steady-state probabilities is found in the slow fading case.
TL;DR: An analytical model is proposed to investigate the performance of an integrated voice/data mobile network with finite data buffer in terms of voice-call blocking probability, data loss probability, and mean data delay, based on the movable-boundary scheme that dynamically adjusts the number of channels for voice and data traffic.
Abstract: Personal communication service (PCS) networks offer mobile users diverse telecommunication applications, such as voice, data, and image, with different bandwidth and quality-of-service (QoS) requirements. This paper proposes an analytical model to investigate the performance of an integrated voice/data mobile network with finite data buffer in terms of voice-call blocking probability, data loss probability, and mean data delay. The model is based on the movable-boundary scheme that dynamically adjusts the number of channels for voice and data traffic. With the movable-boundary scheme, the bandwidth can be utilized efficiently while satisfying the QoS requirements for voice and data traffic. Using our model, the impact of hot-spot traffic in the heterogeneous PCS networks, in which the parameters (e.g., number of channels, voice, and data arrival rates) of cells can be varied, can be effectively analyzed. In addition, an iterative algorithm based on our model is proposed to determine the handoff traffic, which computes the system performance in polynomial-bounded time. The analytical model is validated by simulation.
TL;DR: A novel three-dimensional (3-D) ray-tracing model capable of supporting detailed representation of the indoor environment, as well as external building structures, is presented and provides an insight into the real and the modeled radio channel.
Abstract: A novel three-dimensional (3-D) ray-tracing model capable of supporting detailed representation of the indoor environment, as well as external building structures, is presented in this paper. The developed algorithm uses a hybrid imaging technique where the two-dimensional (2-D) image generations in vertical and horizontal planes are combined to produce 3-D paths. It also employs the concept of "illumination zones" of the images which greatly simplifies the image map and allows the evaluation of complex indoor scenarios. In order to investigate the accuracy of the presented model, comparisons of predictions with narrow-band and wide-band measurements are performed in line-of-sight (LOS), non-LOS (NLOS), and deep shadow areas, both for co- and cross-polarized antennas. The analysis shows that accurate power predictions can be achieved for both antenna polarizations with rms errors less than 7 dB, even when long sections of the test route are in deep shadow areas. There is a trend agreement between the simulated and measured channel impulse responses, while the rms delay spread in NLOS areas is predicted with less than 5-ns rms error (or better than 13% normalized mean error). The paper provides an insight into the real and the modeled radio channel.
TL;DR: An analysis method is developed that determines the efficiency of the LINC power amplifier as a function of the amplitude modulation statistics and can be employed to design the RF communication system amplitude modulation characteristics and to tradeoff and optimize the RF transmitter PAE.
Abstract: Linear amplification using nonlinear components (LINC) is a method of vector summing two constant amplitude phase-modulated signals to achieve power amplification. The theoretical efficiency of the LINC power amplifier has been reported as 100% since highly efficient nonlinear constant amplitude amplifiers can be used. However, the 100% efficiency performance is only possible at one or two loads along the power output curve. The bulk of the papers regarding LINC has focused on clever implementations of the signal vector decomposition as well as methods to achieve highly linear signal separation. There has been little regard in the literature to the signal combiner implementation necessary to achieve the high power-added efficiency (PAE) of the LINC radio frequency (RF) power amplifier. Efficiency is not an intrinsic property of the combiner implementations, however, the combiner method is the single biggest contributor to efficient performance of a LINC RF power amplifier. This paper develops an analysis method that determines the efficiency of the LINC power amplifier as a function of the amplitude modulation statistics. This can be employed to design the RF communication system amplitude modulation characteristics and to tradeoff and optimize the RF transmitter PAE.
TL;DR: It is shown that because of significant burstiness in RLP frame errors in highly correlated Rayleigh fading, longer persistence at the RLP layer to recover lost RLP frames is beneficial at low-link fading margins.
Abstract: In this paper, we present the throughput performance of the transport control protocol/radio link protocol (TCP/RLP) stack on correlated fading direct-sequence code-division multiple-access (DS-CDMA) wireless links. It is shown that because of significant burstiness in RLP frame errors in highly correlated Rayleigh fading, longer persistence at the RLP layer to recover lost RLP frames (more than the IS-99 specified three retransmission attempts at the RCP layer) is beneficial at low-link fading margins.
TL;DR: Simulation results demonstrate that when the magnitude and phase of the received signal components are properly accounted for, the ray-tracing solution may be accurate down to a fraction of a wavelength.
Abstract: Problems with the use of ray-tracing techniques in indoor propagation environments are identified, and a new set of widely applicable diffraction coefficients is developed. The limitations on the accuracy of the ray-tracing method in indoor propagation environments are first assessed. The effects of scatterers with dimensions approaching the wavelength of operation and of scatterers with finite conductivity are considered. The accuracy of ray tracing is quantified by comparison to a full-wave simulation technique, which combines the finite-difference time-domain method with a spatial transformation technique, the Kirchhoff surface integral formulation. Simulation results demonstrate that when the magnitude and phase of the received signal components are properly accounted for, the ray-tracing solution may be accurate down to a fraction of a wavelength. A new set of diffraction coefficients is presented for calculations involving obstacles with finite conductivity. The new coefficients eliminate an artificial dip in the diffracted field strength, which is often encountered when currently available techniques are used. Validation is provided by comparison with full-wave simulations and measurements. Improved accuracy in both the illuminated and shadowed regions is demonstrated.
TL;DR: This paper analyzes this ideal approach in terms of the power consumption of the A/D converter, based on a theoretical analysis of its minimum possible value, to indicate that for the number of bits required to cope with the slow and fast fading environments and consequent large dynamic range encountered in a mobile radio system, the power consume is a fundamental limitation.
Abstract: An "ideal" software radio receiver is often considered as an analog/digital (A/D) converter connected directly to an antenna. This paper analyzes this ideal approach in terms of the power consumption of the A/D converter, based on a theoretical analysis of its minimum possible value. The results indicate that for the number of bits required to cope with the slow and fast fading environments and consequent large dynamic range encountered in a mobile radio system, the power consumption of the A/D converter is a fundamental limitation.
TL;DR: It is shown that ignoring the autocorrelations in the arrival process or the time-varying nature of the channel state can lead to significant underestimation of the delay performance, particularly at high channel error rates.
Abstract: In this paper, we analyze the mean delay experienced by a Markovian source over a wireless channel with time-varying error characteristics. The wireless link implements the selective-repeat automatic repeat request (ARQ) scheme for retransmission of erroneous packets. We obtain good approximations of the total delay, which consists of transport and resequencing delays. The transport delay, in turn, consists of queueing and transmission delays. In contrast to previous studies, our analysis accommodates both the inherent correlations between packet interarrival times (i.e., traffic burstiness) and the time-varying nature of the channel error rate. The probability generating function (PGF) of the queue length under the "ideal" SR ARQ scheme is obtained and combined with the retransmission delay to obtain the mean transport delay. For the resequencing delay, the analysis is performed under the assumptions of heavy traffic and small window sizes (relative to the channel sojourn times). The inaccuracy due to these assumptions is observed to be negligible. We show that ignoring the autocorrelations in the arrival process or the time-varying nature of the channel state can lead to significant underestimation of the delay performance, particularly at high channel error rates. Some interesting effects of key system parameters on the delay performance are observed.
TL;DR: A multimedia communication system based on direct sequence code-division multiple-access (DS/CDMA) techniques aims at ensuring secure and noise-robust wireless transmission links between the guarded stations and the remote control center where the processing results are displayed to the human operator.
Abstract: In this paper, a distributed video-surveillance system for the detection of dangerous situations related to the presence of abandoned objects in the waiting rooms of unattended railway stations is presented. The image sequences, acquired with a monochromatic camera placed in each guarded room, are processed by a local PC-based image-processing system, devoted to detecting the presence of abandoned objects. When an abandoned object is recognized, an alarm issue is transmitted to a remote control center located a few miles from the guarded stations. A multimedia communication system based on direct sequence code-division multiple-access (DS/CDMA) techniques aims at ensuring secure and noise-robust wireless transmission links between the guarded stations and the remote control center where the processing results are displayed to the human operator. Results concern: 1) the performances of each local image processing system in terms of false-alarm and misdetection probabilities, and 2) the performances of the CDMA multimedia transmission system in terms of bit error rates (BERs) and quality of service (QoS).
TL;DR: An adaptive QoS handoff priority scheme is described which reduces the probability of call handoff failures in a mobile multimedia network with a micro/picocellular architecture and exploits the ability of most multimedia traffic types to adapt and trade off QoS with changes in the amount of bandwidth used.
Abstract: For various advantages including better utilization of radio spectrum (through frequency reuse), lower mobile transmit power requirements, and smaller and cheaper base station equipment, future wireless mobile multimedia networks are likely to adopt micro/picocellular architectures. A consequence of using small cell sizes is the increased rate of call handoffs as mobiles move between cells during the holding times of calls. In a network supporting multimedia services, the increased rate of call handoffs not only increases the signaling load on the network, but makes it very difficult for the network to guarantee the quality of service (QoS) promised to a call at setup or admission time. This paper describes an adaptive QoS handoff priority scheme which reduces the probability of call handoff failures in a mobile multimedia network with a micro/picocellular architecture. The scheme exploits the ability of most multimedia traffic types to adapt and trade off QoS with changes in the amount of bandwidth used. In this way, calls can trade QoS received for fewer handoff failures. The call level and packet level performance of the handoff scheme are studied analytically for a homogeneous network supporting a mix of wide-band and narrow-band calls. Comparisons are made to the performance of the nonpriority handoff scheme and the well-known guard-channel handoff scheme.
TL;DR: The results achieved through this approach capture effects that others overlook and enrich the existing literature on the subject, and should be useful for teletraffic engineering mobile systems.
Abstract: This paper examines the channel holding time probability distribution in different public telephony systems. The systems analyzed are public access mobile radio under its two possible operation modes (message and transmission trunking) and personal communications systems. The three statistical studies are based on a fully empirical approach and make use of data acquired from actual working systems that the authors considered to be sufficiently representative. Although this empirical approach is obviously highly dependent on the environment, it eliminates the need to assume a number of hypotheses present in all analytical and simulation studies. The results achieved through this approach capture effects that others overlook and enrich the existing literature on the subject, and should be useful for teletraffic engineering mobile systems.
TL;DR: Analysis results and simulations demonstrate that this new correction technique for linear amplification with nonlinear component transmitters is sufficient to suppress the out-of-band spectrum for mobile communications.
Abstract: This paper presents a new correction technique for linear amplification with nonlinear component transmitters. During the transmit mode, the algorithm modulates and filters the baseband signal as a normal signal component separator, while during the correction mode, by use of a downconversion mixer, the gain and phase imbalance are measured and compensated by introducing a correction. This system is free of adjacent channel interference during the correction period. Analytical results and simulations demonstrate that this system is sufficient to suppress the out-of-band spectrum for mobile communications.