Showing papers in "IEEE Transactions on Vehicular Technology in 1994"
TL;DR: Some information-theoretic considerations used to determine upper bounds on the information rates that can be reliably transmitted over a two-ray propagation path mobile radio channel model, operating in a time division multiplex access (TDMA) regime, under given decoding delay constraints are presented.
Abstract: We present some information-theoretic considerations used to determine upper bounds on the information rates that can be reliably transmitted over a two-ray propagation path mobile radio channel model, operating in a time division multiplex access (TDMA) regime, under given decoding delay constraints. The sense in which reliability is measured is addressed, and in the interesting eases where the decoding delay constraint plays a significant role, the maximal achievable rate (capacity), is specified in terms of capacity versus outage. In this case, no coding capacity in the strict Shannon sense exists. Simple schemes for time and space diversity are examined, and their potential benefits are illuminated from an information-theoretic stand point. In our presentation, we chose to specialize to the TDMA protocol for the sake of clarity and convenience. Our main arguments and results extend directly to certain variants of other multiple access protocols such as code division multiple access (CDMA) and frequency division multiple access (FDMA), provided that no fast feedback from the receiver to the transmitter is available. >
1,216 citations
TL;DR: Results show that the degradation in performance with correlation in an adaptive array that combats fading and suppresses interference is only slightly larger than that for combating fading alone, i.e., with maximal ratio combining.
Abstract: In this paper, we investigate the effect of correlations among the fading signals at the antenna elements of an adaptive array in a digital wireless communication system. With an adaptive array, the signals received by multiple antennas are optimally weighted and combined to suppress interference and combat desired signal fading. Previous results for flat and frequency-selective fading assumed independent fading at each antenna. Here, we present a model of local scattering around a mobile where the received multipath signals arrive at the base station within a given beamwidth, and derive a closed-form expression for the correlation as a function of antenna spacing. Results show that the degradation in performance with correlation in an adaptive array that combats fading and suppresses interference is only slightly larger than that for combating fading alone, i.e., with maximal ratio combining. This degradation is small even with correlation as high as 0.5. >
635 citations
TL;DR: Time delay comparison shows that the amplitudes of many significant multipath components are accurately predicted by this model, and the effective building material properties are derived for two dissimilar buildings based upon comparison of measured and predicted power delay profiles.
Abstract: The paper describes a geometrical optics based model to predict propagation within buildings for personal communication system (PCS) design. A ray tracing model for predicting propagation based on a building blueprint representation is presented for a transmitter and receiver located on the same floor inside a building. Measured and predicted propagation data are presented as power delay profiles that contain the amplitude and arrival time of individual multipath components. Measured and predicted power delay profiles are compared on a location-by-location basis to provide both a qualitative and a quantitative measure of the model accuracy. The concept of effective building material properties is developed, and the effective building material properties are derived for two dissimilar buildings based upon comparison of measured and predicted power delay profiles. Time delay comparison shows that the amplitudes of many significant multipath components are accurately predicted by this model. Path loss between a transmitter and receiver is predicted with a standard deviation of less than 5 dB over 45 locations in two different buildings. >
610 citations
TL;DR: The authors model the effects of path loss, Rayleigh fading, log-normal shadowing, multiple access interference, and thermal noise, and show that by using an antenna array at the base-station, one can increase system capacity several fold.
Abstract: The use of an antenna array at a base-station for cellular CDMA is studied The authors present a performance analysis for a multicell CDMA network with an antenna array at the base-station for use in both base-station to mobile (downlink) and mobile to base-station (uplink) links They model the effects of path loss, Rayleigh fading, log-normal shadowing, multiple access interference, and thermal noise, and show that by using an antenna array at the base-station, both in receive and transmit, one can increase system capacity several fold Simulation results are presented to support the claims >
568 citations
TL;DR: The authors observe that giving priority to hand-off attempts over initial access attempts would dramatically improve the forced termination probability of the system without seriously degrading the number of failedInitial access attempts.
Abstract: The forced termination probability (the probability that a hand-off call is blocked) is an important criterion in the performance evaluation of personal communication service (PCS) networks. The forced termination of an ongoing call is considered less desirable than blocking the initial access of a new call. The paper proposes analytic and simulation models to study the performance of different channel assignment strategies for hand-off and initial access. The authors observe that giving priority to hand-off attempts over initial access attempts would dramatically improve the forced termination probability of the system without seriously degrading the number of failed initial access attempts. Some of the results are different from previously published results because the present models capture features not considered in those studies. >
426 citations
TL;DR: A statistical channel model which is a combination of Rice and lognormal statistics, and is suitable in principle to all types of environment (rural, suburban, urban) simply by tuning the model parameters, is introduced.
Abstract: The paper introduces a statistical channel model which is a combination of Rice and lognormal statistics, and is suitable in principle to all types of environment (rural, suburban, urban) simply by tuning the model parameters. The model validity is confirmed by comparisons with measurement data collected in the literature. Empirical formulas are derived for the model parameters to fit measured data over a wide range of elevation angles. In particular, the model is applied to nongeostationary satellite channels, such as low-Earth orbit and medium-Earth orbit channels, in which for a given user located in a generic site the elevation angle changes continuously. Finally, examples of average bit error probability evaluations in the channel are provided. >
352 citations
TL;DR: The results presented in this paper provide insight into the statistical distributions of measured path loss by showing the validity of a double regression model with a break point at a distance that has first Fresnel zone clearance for line-of-sight topographies.
Abstract: This paper presents results of wide-band path loss and delay spread measurements for five representative microcellular environments in the San Francisco Bay area at 1900 MHz. Measurements were made with a wide-band channel sounder using a 100-ns probing pulse. Base station antenna heights of 3.7 m, 8.5 m, and 13.3 m were tested with a mobile receiver antenna height of 1.7 m to emulate a typical microcellular scenario. The results presented in this paper provide insight into the statistical distributions of measured path loss by showing the validity of a double regression model with a break point at a distance that has first Fresnel zone clearance for line-of-sight topographies. The variation of delay spread as a function of path loss is also investigated, and a simple exponential overbound model is developed. The path loss and delay spread models are then applied to communication system design allowing outage probabilities, based on path loss or delay spread, to be estimated for a given microcell size. >
308 citations
TL;DR: In this paper, the outage probability of a desired lognormal shadowed signal in the presence of multiple correlated Lognormal cochannel interferers is investigated, and the outage results are presented as a function of the reuse factor, defined as the distance between the centers of two nearest cells using the same frequencies divided by the cell radius.
Abstract: Several approaches that can be used to compute the distribution of a sum of correlated lognormal random variables (RVs) are investigated. Specifically, Wilkinson's approach (Schwartz and Yeh, 1982), an extension to Schwartz and Yeh's (1982) approach, and a cumulants matching approach (Schleher, 1977) are studied. The aim is to determine which method is best for computing the complementary distribution function (CDF) of a sum of correlated lognormal RVs considering both accuracy and computational effort. Then, using these techniques, the authors compute the outage probability of a desired lognormal shadowed signal in the presence of multiple correlated lognormal cochannel interferers. The outage results are presented as a function of the reuse factor. The reuse factor is defined as the distance between the centers of the two nearest cells using the same frequencies divided by the cell radius. It is a key parameter in the design of any frequency reuse system. Simulation results are used for verification and comparison. Overall, the results obtained show that among the three methods considered Wilkinson's approach may be the best method to compute the CDF of sums of correlated lognormal RVs (and hence the outage probability in correlated lognormal shadowed mobile radio environments). This is due to both its accuracy and computational simplicity over the range of parameters valid for practical applications. >
287 citations
TL;DR: Three different velocity estimators are introduced and compared with respect to their sensitivity to Rice factors, non-isotropic scattering, additive Gaussian noise, and performance in a adaptive handoff algorithm.
Abstract: Fast velocity adaptive handoff algorithms for microcellular systems capable of providing consistent and near optimal performance are presented and characterized. Guidelines are first developed for the amount of spatial averaging required for local mean estimation in microcellular systems. Afterwards, three different velocity estimators are introduced and compared with respect to their sensitivity to Rice factors, non-isotropic scattering, additive Gaussian noise, and performance in a adaptive handoff algorithm. >
277 citations
TL;DR: A prediction algorithm is presented such that propagation characteristics can be estimated for small-cell high-data-rate systems and demonstrates the model's ability to predict typical rms delay spread values.
Abstract: Propagation characteristics play a fundamental role in the design and implementation of radio systems. The application of broadband digital data services within the cordless environment requires close consideration of the dispersive nature of radio channels. A prediction algorithm is presented such that propagation characteristics can be estimated for small-cell high-data-rate systems. Through the use of geometric optics and geometric theory of diffraction the algorithm performs ray launching techniques in order to evaluate reflected, transmitted, and diffracted rays from a simplified description of a given environment. Both modeled and measured results are presented demonstrating the model's ability to predict typical rms delay spread values. >
219 citations
TL;DR: Statistical properties of mobile-to-mobile land communication channels have been developed, including the level-crossing rate and duration of fades of the envelope, the probability distribution of random FM, and the expected number of crossings of the random phase and random FM of the channel.
Abstract: Statistical properties of mobile-to-mobile land communication channels have been developed. In particular, the level-crossing rate and duration of fades of the envelope, the probability distribution of random FM, the expected number of crossings of the random phase and random FM of the channel, and the power spectrum of random FM of the channel have been considered. >
TL;DR: In this paper, the authors present control schemes that perform the major longitudinal tasks that will be required from the lead vehicle of a platoon moving on an automated highway, such as maintaining safe spacing, tracking an optimal velocity and performing various maneuvers (forming, breaking up platoons and changing lanes).
Abstract: Presents longitudinal control laws for vehicles moving in an intelligent vehicle highway system (IVHS). In particular, the scenario where cars move along the highway in tightly spaced platoons is considered. The authors present control schemes that perform the major longitudinal tasks that will be required from the lead vehicle of a platoon moving on an automated highway. More specifically, schemes that maintain safe spacing, track an optimal velocity and perform various maneuvers (forming, breaking up platoons and changing lanes) are described. Simulation results are given. >
TL;DR: It seems that the long delay (high selectivity) problem has been somewhat overemphasized in the past, at least for areas like Toronto, and problems associated with short delays (flat fading), on the contrary, appear to have been underestimated in the case of dense urban environments.
Abstract: The paper describes a set of measurements performed in the Toronto area, in order to assess the impact of multipath propagation on the performance of the TIA IS-54 digital standard. Five existing cells were systematically surveyed: two in downtown Toronto, two in the suburbs, and one in a suburban/rural area. A sweeping correlator apparatus with a 0.1 /spl mu/s resolution and 910 MHz carrier frequency, and an omnidirectional antenna was used. In one of the cells, the measurements were repeated with a 60 degree beamwidth directional antenna. A fairly sophisticated thresholding technique was applied in order to reduce the impact of noise. Generally, the measurements with the omnidirectional antenna exhibit multipath propagation with considerably smaller excess delays than some reported, but are consistent with earlier results obtained in the U.S. and Europe. Sectorization was found to considerably reduce the multipath effects. Very large delay components appear to be due mostly to the combination of large transmitter-receiver distances and a large degree of shadowing, and could probably be avoided to a large extent by standard cellular engineering techniques. In view of these results, it seems that the long delay (high selectivity) problem has been somewhat overemphasized in the past, at least for areas like Toronto. Problems associated with short delays (flat fading), on the contrary, appear to have been underestimated in the case of dense urban environments. >
TL;DR: Simulations and analytical results are presented which demonstrate that steerable direction antennas at the base station can dramatically improve the reverse channel performance of multicell mobile radio systems, and new analytical techniques for characterizing mobileRadio systems which employ frequency reuse are described using the wedge-cell geometry of Rappaport and Milstein (1992).
Abstract: Examines the performance enhancements that can be achieved by employing spatial filtering in code division multiple access (CDMA) cellular radio systems. The goal is to estimate what improvements are possible using narrow-beam adaptive antenna techniques, assuming that adaptive algorithms and the associated hardware to implement these systems can be realized. Simulations and analytical results are presented which demonstrate that steerable direction antennas at the base station can dramatically improve the reverse channel performance of multicell mobile radio systems, and new analytical techniques for characterizing mobile radio systems which employ frequency reuse are described using the wedge-cell geometry of Rappaport and Milstein (1992). The authors also discuss the effects of using directional antennas at the portable unit. Throughout the paper the authors use phased arrays and steerable, fixed pattern antennas to approximate the performance of adaptive antennas in multipath-free environments. >
TL;DR: A new scheme that allows cell gateways (base stations) to borrow channels from adjacent gateways in a cellular communication system is presented and results indicate that significantly increased traffic capacity can be achieved in comparison with nonborrowing schemes.
Abstract: A new scheme that allows cell gateways (base stations) to borrow channels from adjacent gateways in a cellular communication system is presented. Borrowed channels are used with reduced transmitted power to limit interference with cochannel cells. No channel locking is needed. The scheme, which can be used with various multiple access techniques, permits simple channel control management without requiring global information about channel usage throughout the system. It provides enhanced traffic performance in homogeneous environments and also can be used to relieve spatially localized traffic overloads (tele-traffic 'hot spots'). Co-channel interference analysis shows that the scheme can maintain the same SIR as nonborrowing schemes. Analytical models using multidimensional birth-death processes and decomposition methods are devised to characterize performance. The results which are also validated by simulation indicate that significantly increased traffic capacity can be achieved in comparison with nonborrowing schemes. >
TL;DR: An adaptive predistortion system to linearize class B and class C radio frequency high power amplifiers using a digital signal processing microprocessor and memory look-up tables to predistort the baseband drive signals.
Abstract: This paper describes an adaptive predistortion system to linearize class B and class C radio frequency high power amplifiers. The system, which can handle a 30 dB power control range, uses a digital signal processing microprocessor and memory look-up tables to predistort the baseband drive signals. Low data rate services such as are found in mobile satellite applications ( >
TL;DR: In this article, the authors considered two measurement methods (filtering the squared envelope, and filtering the logarithm of squared envelope), and two filter types (integrate-and-dump and RC) and showed that the dB measurement error tends to be Gauss-distributed, and can readily be made unbiased (zero mean) by proper amplitude calibration.
Abstract: Real-time power measurements performed by cellular receivers are essential for power control, handoff, and dynamic channel allocation. For best results, the measurement filter bandwidth must be sufficiently narrow to average out multipath fluctuations, yet sufficiently wide to follow shadow fading fluctuations. Our study considers two measurement methods (filtering the squared envelope, and filtering the logarithm of the squared envelope), and two filter types (integrate-and-dump and RC). We show, using standard models for the multipath and shadow fadings, that the dB measurement error tends to be Gauss-distributed, and can readily be made unbiased (zero mean) by proper amplitude calibration. The performance metric then becomes the standard deviation (/spl Delta/) of the dB error, which can be minimized by proper choice of the filter bandwidth. We find that /spl Delta/ can be kept to values of 3 dB or lower over a wide range of mobile velocities and shadow fading characteristics. Also, we discuss the potential gains in measurement accuracy associated with diversity reception and broad-band channels. >
TL;DR: The authors present a class of Viterbi algorithms for tailbiting convolutional codes used in blockwise transmission to save the overhead of a known tail and conclude that for noisy channels the CVA decodes in a much shorter time with better performance than previously published iterative algorithms.
Abstract: Viterbi decoding algorithms for convolutional codes are being considered for a number of applications in cellular mobile radio systems. There are three classes of Viterbi decoders depending on the nature of the formatting of the data: continuous decoding with a finite path memory, blockwise decoding with a terminating tail (known to the decoder), and blockwise decoding without a known tail. The latter class is also known as decoding of tailbiting convolutional codes. In this case, a coded message begins and ends in the same state which is unknown to the receiver. The authors present a class of Viterbi algorithms for tailbiting convolutional codes. These algorithms are used in blockwise transmission to save the overhead of a known tail. They call the new algorithm the circular Viterbi algorithm (CVA). The basic ideas are: (1) continue conventional seamless continuous Viterbi decoding beyond the block boundary by recording and repeating the received block of (soft) symbols; (2) start the decoding process in all states; and (3) end the decoding process either adaptively or with a fixed length. Three robust adaptive stopping rules are constructed and evaluated. Simulation results and comparison to previously known algorithms as well as the optimum algorithm are presented. The amount of computation required for previously reported iterative algorithms tends to increase dramatically as the channel bit error rate (BER) increases. In one reported instance, computation increased by over 900% while decoded BER increased from 8/spl times/10/sup /spl minus/6/ to 8/spl times/10/sup /spl minus/3/. For the same example, the CVA increase in computation was 11.4% and the worst case decoded BER was 4/spl times/10/sup /spl minus/3/. The authors conclude that for noisy channels the CVA decodes in a much shorter time with better performance than previously published iterative algorithms. >
TL;DR: In this article, the authors present a method of automatic vehicle location (AVL) based on the assumption that the base stations are separated from each other by 5 km and the point-to-area terrain configuration has a 3 dB standard deviation of a normal signal strength distribution.
Abstract: The paper presents a method of automatic vehicle location (AVL). Signals are transmitted from base stations in a cellular communications system. A device is embedded into a cellular phone installed in a vehicle. When this vehicle is traveling through a cellular territory, the device receives those signals and calculates the attenuation of those signals to locate the current vehicle position. A preliminary study by using computer simulation shows that the error between the exact position and the estimated position is in the range from 0 to 575 m. This result is based on the assumptions that the base stations are separated from each other by 5 km and the point-to-area terrain configuration has a 3 dB standard deviation of a normal signal strength distribution. A further modification by employing fuzzy logic is under development. The goal is to keep the location accuracy within 200 m. >
TL;DR: In this article, the authors discuss the parameters involved in the engineering of a heterogeneous CDMA network, including factors that determine the size of the cell, the soft handoff zone, and the capacity of cell clusters, and engineering techniques for overlay-underlay cell clustering.
Abstract: The demand for cellular radio services is growing rapidly, and in heavily populated areas the need arises to shrink the cell sizes and "scale" the clustering pattern. The extension of the service into the PCN domain, mostly in-buildings and in pedestrian areas, further enhances this trend. The vision of the "third generation" cellular systems incorporates micro- and picocells for pedestrian use, with macrocells for roaming mobiles. Connectivity between all these cells, while maximizing total system capacity, is the main challenge facing the "third generation architects." The CDMA cellular system, which shares the same frequency channel across the system (reuse pattern of one) and applies soft handoff between the cells, has already shown, both by analysis and by tests, to have full connectivity between the microcells and the overlaying macrocells without capacity degradation. The parameters involved in the engineering of a heterogeneous CDMA network are discussed in the paper. Factors that determine the size of the cell, the soft handoff zone, and the capacity of the cell clusters are analyzed, and engineering techniques for overlay-underlay cell clustering are outlined. >
TL;DR: Using a large empirical data base of 12000 impulse response estimates collected in two office buildings the root mean square (rms) delay spread for the individual impulse responses have been calculated and analyzed and a simulation model capable of generating a set of /spl tau//sub rms/ values for spatially-adjacent points has been developed.
Abstract: Using a large empirical data base of 12000 impulse response estimates collected in two office buildings the root mean square (rms) delay spread for the individual impulse responses have been calculated and analyzed. Statistical modeling of /spl tau//sub rms/ includes investigation of the local and global distributions, correlations in space, dependence on transmitter-receiver antenna separation, correlations with large scale path losses, and dependence on the dynamic range of measurements. Using the results of the statistical analysis, a simulation model capable of generating a set of /spl tau//sub rms/ values for spatially-adjacent points has been developed. >
TL;DR: In this article, the results of extensive measurements and analysis of an indoor radio propagation channel's temporal variations are reported. But the results can be used in fixed wireless computer communication applications, and in supplementing the available spatial variation models of the indoor Radio propagation channel.
Abstract: The paper reports the results of extensive measurements and analysis of an indoor radio propagation channel's temporal variations. The empirical data base consists of 192 one-min recordings of CW envelope fading waveforms with both antennas stationary. Measurements were carried out in an office environment at 1100 MHz with four transmitter-receiver antenna separations of 5, 10, 20, and 30 m. Effects of controlled degrees of motion with 0, 1, 2, 3, or 4 individuals walking around the high antenna only, around the low antenna only, and around both antennas were investigated. The reported results include amplitude fading distributions, correlation properties, level crossing rates, duration of fades statistics, and spectrum widths of the frequency domain data, The results can be used in fixed wireless computer communication applications, and in supplementing the available spatial variation models of the indoor radio propagation channel. >
TL;DR: In this paper, the performance of switched dual-diversity systems operating on independent and correlated Ricean fading channels is analyzed using a discrete time model and the average bit error rate (BER) of the discrete time switched diversity system using binary non-coherent frequency shift keying (NCFSK) on slow, nonselective Ricean channels is derived.
Abstract: The performances of switched dual diversity systems operating on independent and correlated Ricean fading channels are analyzed using a discrete time model. The average bit error rate (BER) of the discrete time switched diversity system using binary noncoherent frequency shift keying (NCFSK) on slow, nonselective Ricean fading channels is derived. A closed form expression that gives the optimum switching threshold in a minimum error rate sense is derived for the case of independent branch signals. Results for the optimum switching threshold for the case of correlated branch signals, obtained numerically, are also presented. Results using selection diversity combining are obtained for comparison. The effects of fading severity on both the BER and on the optimum switching threshold are investigated. The Ricean fading model may be used to model both the microcellular radio environment and the mobile satellite fading channel. Hence, the results of the paper are useful for both of these areas. >
TL;DR: The author proposes a simple location tracking scheme called the T-threshold location cache scheme, which adaptively modifies the threshold to yield the best performance when the incoming call frequency changes.
Abstract: In a personal communications services system, it is required to locate the destination portable when an incoming call arrives. The author proposes a simple location tracking scheme called the T-threshold location cache scheme. In the scheme, a threshold T is used to determine whether a cached location record is obsolete. When the incoming call frequency changes, this scheme adaptively modifies the threshold to yield the best performance. An analytical model is proposed to study the T-threshold scheme. The analysis indicates that the T-threshold scheme effectively reduces the network traffic compared to the IS-41 scheme. >
TL;DR: A toll quality speech codec at 8 kb/s suitable for the future personal communications system and can support a frame erasure rate up to 3% with a degradation in its performance that is still worse than the ITU-T requirements.
Abstract: A toll quality speech codec at 8 kb/s suitable for the future personal communications system is presented. The codec is currently under standardization by the ITU-T (successor of CCITT) where the codec terms of reference were mainly determined considering PCS application. The encoding algorithm is based on algebraic code-excited linear prediction (ACELP) and has a speech frame of 10 ms. Efficient pitch and codebook search strategies, along with efficient quantization procedures, have been developed to achieve toll quality encoded speech with a complexity implementable on current fixed-point DSP chips. Formal subjective listening tests, performed by ITU-T SG 12, showed that the codec quality is equivalent to that of G.726 ADPCM at 32 kb/s in error-free conditions and it outperforms G.726 under error conditions. The codec performs adequately under tandeming conditions, and can support a frame erasure rate up to 3% with a degradation in its performance that is still worse than the ITU-T requirements, and this is one subject of study for the next phase. The algorithm has been implemented on a single fixed-point DSP for the ITU-T subjective rest, and required about 29 MIPS. An optimized version, however, requires 24 MIPS without any speech quality degradation. >
TL;DR: The paper reports the path loss measurements made in urban and suburban areas where the receiving mobile was driven along preselected line-of-sight, zig-zag, and staircase routes to gather information about direct propagation along streets, as well as diffraction over the roofs in suburban areas, and diffraction around the corners in urban areas.
Abstract: New microcellular systems have been proposed to operate over short radio paths by using low-base station antennas, and transmitting at low power. In order to study radio propagation in the microcellular environments for future personal communications services (PCS), comprehensive radio propagation measurements were conducted by Telesis Technologies Laboratory (TTL) in the San Francisco Bay area using three transmitting antenna heights of 3.2, 8.7, and 13.4 m and two frequencies in the 900 and 1900 MHz bands. The paper reports the path loss measurements made in urban and suburban areas where the receiving mobile was driven along preselected line-of-sight (LOS), zig-zag, and staircase routes to gather information about direct propagation along streets, as well as diffraction over the roofs in suburban areas, and diffraction around the corners in urban areas. The results obtained for the three antenna heights are studied, and show the height gain that can be expected for microcells in different environments. >
TL;DR: The outage probability in a mobile communications environment, where the interferers are randomly distributed on the ground, taking into account the background noise, the cochannel interference and the random effects of propagation is evaluated.
Abstract: The outage probability in a mobile communications environment, where the interferers are randomly distributed on the ground, taking into account the background noise, the cochannel interference and the random effects of propagation (log-normal shadowing and Rayleigh fading), is evaluated. Although not feasible in closed form, the computation can be performed numerically in a very fast and accurate manner. A comparison to the results reported in the recent literature is presented, along with a sensitivity analysis and an example of application. >
TL;DR: P(/spl ges/m,n) denotes the probability that at least m errors will occur in a block of n bits in the mobile VHF environments mentioned, and should give some indication of the performance to be expected from block error-correcting schemes.
Abstract: We apply techniques for the modeling of error sequences on digital communication channels to results of experiments undertaken on mobile VHF channels. The experiments were carried out using four different modulation schemes at some of the different standardized signaling rates. The modulation schemes used were: FSK @ 300 baud, DPSK @ 1200 baud, QPSK @ 1200 baud, and 8-ary PSK @ 1600 baud, and in each case, subcarrier modulation was used. The experiments were undertaken for urban as well as freeway environments. Fritchman-partitioned Markov chain models were derived throughout, and from the models, block error probability distributions were derived. These block error probability distributions or P(m,n) give the probability that a block of n bits will contain exactly m errors. We present P(/spl ges/m,n) for 7-, 15-, 31-, 63-, 127-, and 255-b blocks, for the above-mentioned modulation schemes, in the mobile VHF environments mentioned. P(/spl ges/m,n) denotes the probability that at least m errors will occur in a block of n bits. Furthermore, the P(/spl ges/m,n) information presented here, should give some indication of the performance to be expected from block error-correcting schemes. >
TL;DR: In this article, a combination tutorial and research paper on the propagation aspects of transmission at infrared (IR) frequencies for wireless in-building communications are explored, where basic principles of propagation at IR, a comparison with indoor radio propagation, and derivation of the channel's baseband model are explored.
Abstract: In a combination tutorial and research paper, propagation aspects of transmission at infrared (IR) frequencies for wireless in-building communications are explored. The tutorial section of the paper presents basic principles of propagation at IR, a comparison with indoor radio propagation, and the derivation of the channel's baseband model. The research aspect of the paper reports on the results of recent frequency response measurements at eight different sites in a university building. A major result shows that the indoor wireless optical channel is very dynamic, with great variations in the channel's characteristics for data collected in different rooms, in different locations within the same room, and for different orientations of the optical receiver at the same location of the same room. Numerical values of the channel's relative path loss and 3 dB bandwidth, along with frequency response plots covering a wide range of conditions, are presented and discussed. Finally, on the basis of the results of measurements, schemes for improving the performance of future wireless in-building optical transceivers are proposed. >
TL;DR: In this paper, the theoretical principles of the elementary process of scattering from a 2D surface, such as a wall, are described and a ray-tracing algorithm based on this is employed to describe propagation in 3D structures, like rectangular rooms or street canyons.
Abstract: For the investigation of propagation mechanisms in microcell and indoor environments, theoretical model calculations are compared to wide-band measurements. The theoretical principles of the elementary process of scattering from a 2-D surface, such as a wall, are described. A ray-tracing algorithm based on this is employed to describe propagation in 3-D structures, like rectangular rooms or street canyons. Space-dependent complex impulse responses are calculated. These are compared to the results of high resolution measurements of the space-dependent complex impulse response in the same environments. If conducted in an appropriate manner, the measurements yield very dense information about the propagation in the measured environment. It is demonstrated that the concept of the scattering function is useful for microcell and indoor environments. Comparisons between the theoretical and measured wide-band results show a high degree of agreement. >