Showing papers by "Theodore S. Rappaport published in 1992"

914 MHz path loss prediction models for indoor wireless communications in multifloored buildings

Abstract: Qualitative models are presented that predict the effects of walls, office partitions, floors, and building layout on the path loss at 914 MHz. The site-specific models have been developed based on the number of floors, partitions, and concrete walls between the transmitter and receiver, and provide simple prediction rules which relate signal strength to the log of distance. The standard deviation between measured and predicted path loss is 5.8 dB for the entire data set, and can be as small as 4 dB for specific areas within a building. Average floor attenuation factors, which describe the additional path loss (in decibels) caused by floors between transmitter and receiver, are found for as many as four floors in a typical office building. Path loss contour plots for measured data are presented. In addition, contour plots for the path loss prediction error indicate that the prediction models presented are accurate to within 6 dB for a majority of locations in a building. >

A ray tracing method for predicting path loss and delay spread in microcellular environments

Abstract: The ability to predict path loss and delay spread is crucial for determining coverage and for planning interference reduction strategies in wireless radio system design. A promising theoretical method to accurately predict these channel characteristics in microcells is presented. The method uses modified geometrical optics to evaluate average path loss and delay spread. Quantitative building data, such as location, height, and electrical properties, are used to determine the individual multipath component amplitudes and delays. Preliminary verification of the technique against measured data has been conducted. The results illustrate that accurate path loss prediction is possible, with predicted values being within 5 dB of the measured values. As a result of this study, a computer program is being developed to automate the prediction process. The technical issues required for automated propagation prediction are presented. The ray optics model, computer ray tracing techniques, and building data requirements are also described. Comparisons between simulations and measurements are provided. >

A ray tracing technique to predict path loss and delay spread inside buildings

Abstract: A ray tracing technique for predicting path loss and delay spread in buildings is described. A novel approach is used to determine the ray directions from the source in three dimensions. Line-of-sight, specular, and nonspecular transmissions and reflections are included in the propagation model. This method shows that accurate impulse response, path loss, and delay spread prediction in buildings is possible using site-specific information, although modeling refinements are still needed. With such a propagation prediction tool, personal communications systems (PCSs) could be designed and installed more rapidly and economically than if measurements were required for each building. >

Performance evaluation for cellular CDMA

Abstract: The authors consider the performance of a cellular radio, direct-sequence code-division multiple access, (CDMA) system. The base-to-mobile link is modeled as a flat Rayleigh fading channel, with all signals transmitted from a given base station fading in unison. For the mobile-to-base link, the authors use a similar model, except that the waveforms from all users are assumed to experience independent fading. The effects of imperfect power control are shown. >

Effects of radio propagation path loss on DS-CDMA cellular frequency reuse efficiency for the reverse channel

Abstract: Analysis techniques for quantitatively describing the impact of propagation path loss and user distribution on wireless direct-sequence code-division multiple-access (DS-CDMA) spread spectrum systems are presented. Conventional terrestrial propagation models which assume a d/sup 4/ path loss law are shown to describe modern cellular and personal communication system channels, poorly. A two-ray propagation model and path loss model derived from field measurements are used to analyze the impact of path loss on the frequency reuse efficiency of DS-CDMA cellular radio systems. The analysis shows that the frequency reuse efficiency (F) of the reverse channel with a single ring of adjacent cells can vary from a maximum of 71% in d/sup 4/ channels with a favorable distribution of users, to a minimum of 33% in d/sup 2/ channels with a worst-case user distribution. For three rings of adjacent users, F drops to 58% and 16%, respectively. Using the two-ray model, it is shown that F can vary over a wide range of values due to the fine structure of propagation path loss. >

Wide-band microwave propagation parameters using circular and linear polarized antennas for indoor wireless channels

Abstract: Results of experiments using a variety of antennas inside several buildings are presented. Path loss models for the 1.3 GHz and 4.0 GHz bands that show little difference in indoor path loss throughout the low-microwave region are discussed. Results show that line-of-sight (LOS) channels offer significantly more cross-polarization discrimination than obstructed channels. A profound result is that directional circularly polarized (CP) antennas always reduce RMS delay spread when compared to omnidirectional and directional linearly polarized (LP) antennas in LOS. The variation of RMS delay spread as a mobile moves over several wavelengths is also greatly reduced when CP antennas are used. >

The impact of surrounding buildings on propagation for wireless in-building personal communications system design

Abstract: The impact of surrounding buildings on path loss and multipath delay spread for personal communication services (PCS) operating inside buildings is studied. Measurements concluded inside three large office buildings in the San Francisco Bay are provide an extensive database for propagation models at 915 MHz and 1900 MHz, and show variability in path loss and delay spread caused by multiple floors between communication terminals, and multipath scattering from surrounding buildings. Quantitative models provide prediction of the propagation effects caused by surrounding buildings for wireless personal communications system design. >

Statistics of shadowing in indoor radio channels at 900 and 1900 MHz

Abstract: The authors describe measurements which were performed to characterize shadowing in indoor radio environments. They investigated the suitability of the log-normal shadowing model for indoor mobile and portable radio channels and determined how the parameters of the log-normal shadowing model are dependent on frequency and topography. They show that the correlation coefficient can be completely independent of wavelength over a frequency octave; however, it is highly dependent on the specific topography of the building. Furthermore, they discuss mechanisms for shadowing which explain why the shadowing component is nearly identical for two frequencies in one environment, while in other environments, the shadowing components at two frequencies are virtually independent. >

Path loss and delay spread models as functions of antenna height for microcellular system design

Abstract: Results of wideband path loss and delay spread measurements for two representative microcellular environments in the San Francisco Bay area in the 1900 MHz band are presented. The results 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 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 radius. >

Effects of antenna polarization and beam pattern on multipath delay spread and path loss in indoor obstructed wireless channels

Abstract: The effects of different combinations of antenna patterns and polarizations on path loss and RMS delay spread in indoor obstructed channels at 245 GHz are treated Based on measurement results, and assuming the main beams of the antennas are lined up on boresight, it appears that using vertically polarized (VP) antennas at both the transmitter and the receiver can provide smaller delay spread and smaller path loss compared to those of other antenna combinations The correlation between path loss and RMS delay spread of different antenna combinations is presented It is found that path loss is uncorrelated with RMS delay spread when the antennas are omnidirectional However, strong correlations are found when the antennas are directional and both polarizations of the transmitter and receiver are vertically polarized (VP) or horizontally polarized (HP) >

Simulation of bit error performance and outage probability of pi /4 DQPSK in frequency-selective indoor radio channels using a measurement-based channel model

Abstract: A real-time simulation tool called BERSIM is developed and used to study bit-by-bit errors, average bit error rate and block outage probabilities for pi /4 differential quadrature phase-shift keying (DQPSK) at megabit rates with raised-cosine pulse shaping. Simulation results show that when the ratio of RMS delay spread to bit duration is greater than about 0.02, the irreducible average BER is not only a function of RMS delay spread, but is also a function of the temporal and spatial distribution of individual multipath components in the complex channel impulse response. The results show that fading caused by multipath cancellation is the major error mechanism over a local area for RMS delay spreads smaller than 0.02-b duration. An example of BERSIM's real time output is shown for the transmission of a video image through a mobile radio system. The simulation methods are suited for evaluation and design of indoor wireless LANs, as well as paging and cellular systems. >

Use of a building database in prediction of three-dimensional diffraction

Abstract: The use of a building database and a three-dimensional formulation of the Fresnel-Kirchoff diffraction theory to compute the shadowing by buildings in the general situation where diffraction can occur by building edges of both horizontal and vertical orientation is described. The storage format of buildings in a geographic information system database is described. An algorithm for identifying the nearest diffracting building and deriving the necessary information for the evaluation of the diffraction integral is presented. Example results are presented to show the utility of this approach. >

The effects of antenna gains and polarization on multipath delay spread and path loss at 918 MHz on cross-campus radio links

Abstract: Results of delay spread and path loss measurements across a large college campus are presented. Two line-of-sight links were used with three different types of antennas to determine best polarizations and pointing angles. Measurements show multipath is most severe when antennas of different polarizations are used on each end of the link. Minimum delay spreads are encountered when antennas of the same polarization are used and pointed directly toward each other. As long as polarizations are matched on each side of the link, polarization does not have significant impact on delay spread or path loss. However, circularly polarized helical antennas offer multipath reduction over a wide range of pointing angles. This suggests that on point-to-point cross-campus links where a single antenna is desired to serve a broad coverage area, circular polarization could be used in lieu of channel equalization to improve bit error rates in high-speed data networks. >

Site specific propagation prediction models for PCS design and installation

Abstract: The authors present novel site-specific propagation prediction methods for emerging personal communication system (PCS) services which will offer high capacity in urban settings. The propagation prediction models, composed of 3-D diffraction and ray tracing, are being implemented as software tools on SUN computer workstations. A geographical information system software package is being used to interface building and terrain data with the propagation prediction programs. Early work at Virginia Tech's Mobile and Portable Radio Research Group shows that the predicted signal strengths are within a few decibels of average measured signal strengths for some test cases. >

Performance of decision feedback equalizers in urban and indoor mobile channels

Abstract: An idealized computer simulation of an equalizer using two-ray and measurement-based channel impulse response models is presented. A decision feedback equalizer (DFE) with a recursive least squares (RLS) algorithm is used as the equalization scheme. The results show that adaptive equalization can significantly improve the bit-error-rate (BER) of a mobile system if the channel does not change too rapidly. The simulation shows that in a two-ray Rayleigh fading channel, if the delay of the second ray is too small, then adaptive equalization will degrade the BER performance. The value of the delay at which the adaptive equalizer can improve the BER depends on the normalized Doppler frequency. A mobile channel simulator is used to show how much the equalizer can improve the BER in real-world urban channels. The performance of adaptive equalization for indoor high-data-rate systems is evaluated. An equalization structure for pi /4 DQPSK modulation is developed, and simulation results are presented. >

Analysis of the mobile-to-base link in cellular CDMA

Abstract: The authors have evaluated the performance of the mobile-to-base link of a cellular code-division multiple access (CDMA) system. The analysis incorporates the effects of flat Rayleigh fading, and it is found, for example, that using a rate 1/2 block code and a processing gain of 511 allows somewhere between 80 and 150 simultaneously active users at a decoded bit error rate (BER) of 10/sup -3/. The lower number arises from a propagation exponent of two, and the higher number results when the exponent is four. These numbers, of course, will roughly double when voice activity effects are included. >

Application of GRASS in mobile and portable communications

Abstract: This paper discusses the application of GRASS iil the area of mobile and portable radio communications. The growing interest in wireless personal communications has fueled efforts to produce systems with better performance and increased capacity. A brief view of mobile communications is presented along with the motivation for this research. The role of GRASS in radio propagation prediction is discussed. GRASS is used to analyze spatial information as well as display the results graphically. The work done in interfacing and applying GRASS toward the development of an integrated radio propagation prediction tool is presented. Finally, directions for future work are noted, including tessellation algorithms and enhanced_ attribute storage facilities. The adaptability of GRASS combined with the technical capabilities of propagation prediction software promise an effective software tool for mobile communication system design. ·

The effect of diversity on cellular CDMA

Abstract: It is desired to determine the effect ·of second order diversity on a cellular code division multiple access (CDMA) system. Toward that end, we consider somewhat of a worst-case situation for the base-to-mobile link, namely one where a mobile is straddling the boundary between two cells. We analyze the performance of the system when space diversity is employed, and show that a substantial improvement in performance is indeed possible.