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Showing papers by "Theodore S. Rappaport published in 1991"


Journal ArticleDOI
TL;DR: Statistical radio channel impulse response models are presented for the analysis and design of wireless factory and open plan office communication systems and large-scale models for path loss are implicitly included in this work.
Abstract: Statistical radio channel impulse response models are presented for the analysis and design of wireless factory and open plan office communication systems. The models incorporate first- and second-order statistics to characterize the discrete impulse responses of indoor radio channels for both line-of-sight (LOS) and obstructed (OBS) topographies. The effects of large-scale transmitter-receiver separation distance, small-scale receiver movement, and models for the correlation of multipath component amplitudes over 1 m local areas are developed from 1.3 GHz measurements. SIRCIM, a computer simulator based on the models presented, has recreated multipath power delay profiles and CW fading profiles that are representative of measured data. Large-scale models for path loss are implicitly included in this work. >

455 citations


Journal ArticleDOI
TL;DR: The authors present typical and worst-case root mean square (RMS) delay spreads and excess delay spreads (10 dB) and mean channel path loss at 900 MHz in four European cities using typical cellular and microcellular antenna locations to form the basis for statistical models which can be used to predict the percentages of locations or the percentage of time in which channels will possess particular values of RMS delay spread.
Abstract: The authors present typical and worst-case root mean square (RMS) delay spreads and excess delay spreads (10 dB) and mean channel path loss at 900 MHz in four European cities using typical cellular and microcellular antenna locations. Several thousand power delay profile measurements were made at six typical cellular and microcellular base station locations in the four cities. The data were obtained at local worst-case time-dispersion locations over hundreds of kilometers of typical operating routes, such as highways, bridges, and city streets, and form the basis for statistical models which can be used to predict the percentage of locations or the percentage of time in which channels will possess particular values of RMS delay spread and excess delay spread. The effect of reference distance on wideband path loss and the propagation path loss laws for cellular and microcellular radio channels are given. Radar cross sections computed from the data for typical scatterers in cellular and microcellular radio channels are given. >

181 citations


Journal ArticleDOI
TL;DR: Current demand for and recent developments in wireless communication are described and funding for wireless worldwide is examined.
Abstract: Current demand for and recent developments in wireless communication are described. Funding for wireless worldwide is examined. Tools and techniques used to characterize radio propagation are discussed, and some research results are presented. >

125 citations


Journal ArticleDOI
TL;DR: A number of antenna and propagation research problems which need to be solved to improve the spectral efficiency, and thus the system capacity, of emerging high-density personal-communication systems are discussed.
Abstract: The rapid expansion of the field of wireless personal communication services is described, focusing on statistics showing demands and on recent events on the industry. Some propagation research results that should have an impact on the design and implementation of future cellular and personal communication services are surveyed. A number of antenna and propagation research problems which need to be solved to improve the spectral efficiency, and thus the system capacity, of emerging high-density personal-communication systems are discussed. >

67 citations


Patent
29 May 1991
TL;DR: In this paper, the authors present a system that combines computer software and hardware that computes a convolution, in the time domain, of a sequence of binary digits or data symbols (i.e., the data stream) with a computer model of a radio transmitter, a propagation channel or channels and a receiver.
Abstract: A communications stimulation system allows a user to perform a quantitative or subjective test of digital baseband devices over wireless channels using actual measured or modeled propagation data. The digital wireless communication simulation system is capable of simulating the transient nature of channels and radio hardware so that loss of synchronization can be included in the simulation. The simulator is a combination of computer software and hardware that computes a convolution, in the time domain, of a sequence of binary digits or data symbols (i.e., the data stream) with a computer model of a radio transmitter, a propagation channel or channels and a receiver. The transmitter typically comprises a coder, a pulse shaper, a modulator, and a spreader. The propagation channel or channels may include impulsive and average noise levels, co-channel interference and adjacent interference levels, fading and multipath propagation events, and non-linear channel and radio system effects. The receiver system typically comprises at least a filter bank, a demodulator, a despreader, a synchronizer, a detector, and a decoder. The data stream may either be random or applied by the user. The software computes the bit-by-bit sequence for replay at a later time. Once stored, the bit-by-bit error sequence can be clocked through a hardware data port and compared with an applied data stream in real time. The output of the hardware data port is a real time sequence of bits that has errors due to the bit-by-bit simulation computed earlier by the software.

42 citations


Proceedings ArticleDOI
19 May 1991
TL;DR: Preliminary evaluation of techniques to predict signal strength based on site-specific geometry are presented and average floor attenuation factors which describe the additional path loss caused by floors between the transmitter and receiver are found.
Abstract: The effects of walls, floors, and building type on path loss in four different buildings are considered. Using a simple d/sup n/ model, average path loss falls off to the n=3.14 power with a standard deviation of 16.3 dB for the entire data set. However, when the effects of building type and number of floors between the transmitter and receiver are considered, standard deviations are reduced to 5 dB about a mean d/sup n/ power law. Average floor attenuation factors which describe the additional path loss caused by floors between the transmitter and receiver are found for as many as four floors in a typical office building. Preliminary evaluation of techniques to predict signal strength based on site-specific geometry are presented. >

41 citations


Journal ArticleDOI
TL;DR: In this paper, the authors presented a model that predicts the effect of walls, office partitions, floors, and building layout on path loss at 914 MHz in a typical office building, and found that average floor attenuation factors (FAF) are 12.9 dB and 16.2 dB for one floor between the transmission and receiver.
Abstract: Quantitative models are presented that predict the effect of walls, office partitions, floors, and building layout on path loss at 914 MHz. Average floor attenuation factors (FAF), which describe the additional path loss (in dB) caused by floors between transmitter and receiver are found for up to four floors in a typical office building. Average FAFs are 12.9 dB and 16.2 dB for one floor between the transmission and receiver in two different office buildings. For same floor measurements, attenuation factors (AF) are found to be 1.4 dB for each cloth-covered office partition and 2.4 dB for each concrete wall between transmitter and receiver.

38 citations


Proceedings ArticleDOI
23 Jun 1991
TL;DR: Analysis of noise level distributions, amplitude probability distributions, pulse duration distributions, and interarrival time distributions indicate that photocopiers, printers, elevators, and microwave ovens are significant sources of impulsive noise in office and retail environments.
Abstract: The authors describe average and impulsive noise measurements inside several office buildings and retail stores The receiver had a 70 dB dynamic range and operated at 918 MHz, 244 GHz, and 40 GHz with a nominal 40 MHz 3 dB RF bandwidth Omni-directional and directional antennas were used to investigate the characteristics and sources of RF noise in indoor channels Statistical analyses of the measurements are presented in the form of noise level distributions, amplitude probability distributions, pulse duration distributions, and interarrival time distributions These analyses indicate that photocopiers, printers (line printers and cash register receipt printers), elevators, and microwave ovens are significant sources of impulsive noise in office and retail environments >

23 citations


Proceedings ArticleDOI
19 May 1991
TL;DR: The authors investigate several adaptive noise-cancellation algorithms and their effectiveness in improving the quality of speech degraded by additive acoustic noise in mobile communications and find the FTF algorithm demonstrated excellent convergence qualities compared to the LMS algorithm.
Abstract: The authors investigate several adaptive noise-cancellation algorithms and their effectiveness in improving the quality of speech degraded by additive acoustic noise in mobile communications. A personal-computer system which was used to acquire test data and implement the algorithms is described. The algorithms studied include least mean squares (LMS), recursive least squares (RLS), a fast transversal filter (FTF) implementation of RLS, direct solution of the normal equation, and an adaptive notch filter. The results of a comparison of the algorithms based on various criteria are presented. The results of applying each of the algorithms to adaptive noise cancellation in mobile environments are described and evaluated. The FTF algorithm demonstrated excellent convergence qualities compared to the LMS algorithm. >

19 citations


Proceedings ArticleDOI
02 Dec 1991
TL;DR: Results are presented from an experiment that used a variety of antennas inside two buildings and found that directional circularly polarized (CP) antennas reduce RMS delay spreads when compared with omnidirectional and directional linearly polarized antennas at identical locations.
Abstract: Results are presented from an experiment that used a variety of antennas inside two buildings. An important result is that directional circularly polarized (CP) antennas reduce RMS delay spreads when compared with omnidirectional and directional linearly polarized (LP) antennas at identical locations. The variation of RMS delay spread over distances of several wavelengths is also greatly reduced when CP antennas are used in place of LP antennas with similar gains. >

13 citations


Proceedings ArticleDOI
19 May 1991
TL;DR: In this paper, the adaptive lattice decision feedback equalizer (L-DFE) and maximum-likelihood sequence estimation (MLSE) algorithms are used to update the equalizers.
Abstract: Adaptive equalization techniques designed to improve bit error rates (BERs) degraded by multipath propagation in mobile communication systems are addressed. Two kinds of equalizers are used in a simulation: the adaptive lattice decision feedback equalizer (L-DFE) and maximum-likelihood sequence estimation (MLSE). RLS (recursive-least-squares) algorithms are used to update the equalizers. The choices are based on the fact that a DFE has little noise enhancement and a RLS algorithm converges fast and has good tracking capability. The sensitivities of these equalizers to receiver velocity and signal-to-noise ratio are tested for a two-ray multipath channel where the ratio of powers of the rays can vary. Results show that these two kinds of equalizers have similar performances. >