Multipath Propagation Model Research Articles

Characterisation of mobile radio signals: model description

Following a brief review of multipath propagation models, the major characteristics of mobile radio signals are determined using an adaptation of the generic three-dimensional model proposed by Aulin. The various multipath component waves, which have equal amplitude and random, uniformly-distributed phase are allowed to have spatial angles of arrival with both vertical and horizontal components. The spatial angle of arrival in the horizontal plane is assumed to be uniformly distributed in the interval (0, 2π) but a new PDF is proposed for the vertical angle of arrival, β. The effective scatterers are assumed to form a cyclinder around the mobile with a radius and height that depends on the maximum value βm of the vertical angle of arrival. Suitable values for βm are estimated from published experimental results. The limitations of two-dimensional scattering models are illustrated by considering not only the power spectral density, but also the cross correlation between antennas spatially separated in the vertical plane.

A New Class of Adaptive Cross-Polarization Interference Cancellers for Digital Radio Systems

Frequency reuse is an attractive way for increasing transmission capacity of digital radio systems. Propagation impairments such as multipath fading or antenna imperfections require the introduction of new techniques to fight against the degradation of crosspolarization discrimination. This paper presents the performance of new kinds of cross-polarization interference cancellers for a dual 16 QAM system over dispersive radio channels. The structure of the studied cancellers is a decision feedback one. Topics include a multipath propagation model, canceller description, and the theoretical and dynamic simulated performance of the receiver. For asynchronous clocks for the horizontally and vertically polarized channels, the results show that the receiver performance is critically sensitive to the timing delay between the main and the interfering signals.

A Multipath RF Propagation Model for Computer Simulation of Complex Impulse Responses of Broadcast Teletext Channels

To accurately predict the performance of broadcast teletext systems, one must know the characteristics of typical over-the-air broadcast television channels. Consequently, ensembles of typical complex impulse responses of broadcast teletext channels in the VHF and UHF frequency ranges are required for computer performance simulations. To circumvent the lack of comprehensive measured channel data, a theoretical multipath propagation model for suburban and urban environments was developed to gain insight into the nature of typical television multipath channels. In this model, both the direct and scatter paths consist of a line-of-sight and ground-reflected component. The basis of the propagation model is an expression for the ratio of the scattered path to direct path field strength caused by vertically oriented dielectric slabs of specified thickness, height, and width. The reflector location, orientation, width, height, and thickness are randomized for each Monte Carlo simulation cycle. A scatter table of relative amplitude versus multipath delay is maintained for subsequent analysis and formation of typical multipath channel impulse responses. A perceived desired-to-undesired ratio (PDUR), which is essentially a signal-to-clutter ratio, is computed to eliminate channels of unacceptable video quality, as these would be of no interest to the teletext application. A modification to account for near-field scattering is described. Finally, mobile channel applications are discussed.

Time division adaptive retransmission for reducing signal impairments in portable radiotelephones

Multiple-antenna receiving diversity was shown previously to be effective in mitigating the effects of random angular orientation and multipath radio propagation for portable radiotelephones. It is shown that time-division adaptive retransmission used with appropriate antenna configurations can also mitigate these effects. The retransmission configurations require fewer antennas than the receiving diversity configurations for a given improvement in relative signal-to-noise ratio (S/N). Cumulative distributions of S/N were determined for adaptive retransmission and diversity using random orientation and multipath propagation models. Distributions of S/N for systems with two antennas at the portable set and two appropriately polarized antennas at the portable radiotelephone terminal (PORT) are similar to distributions for two-branch selection diversity in the fixed-orientation mobile radio environment. Systems with one portable antenna and two PORT antennas have distributions with slopes similiar to two-branch mobile radio distributions but the distributions for the portables range from 3 to 7 dB worse.

Antenna Diversity Performance in Mitigating the Effects of Portable Radiotelephone Orientation and Multipath Propagation

Antenna diversity can mitigate signal impairments caused by random angular orientation and multipath radio propagation when using portable radiotelephones. Cumulative distributions of signal-to-noise ratio ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S/N</tex> ) were determined for antenna diversity using realistic orientation and multipath propagation models. In a random orientation and multipath propagation environment with -6 dB average crosspolarization coupling, two-branch selection diversity with two perpendicular antennas yields an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S/N</tex> distribution with the same slope as two-branch selection diversity in the fixed-oriented mobile radio environment. The distribution for random orientation is about 4.5 dB worse, however, than the mobile radio distribution.

First-order statistics for finite bandwidth multipath signals with and without frequency or phase modulation

The phase-random model of multipath acoustic propagation is used to derive the first-order probability densities for the time rate-of-change of the short time average mean-square pressure ?, and the time rate-of-change of the level in decibels of the short time average mean-square pressure ?. It is shown that the probability densities for the signal amplitude, and amplitude rate are insensitive to frequency or phase modulation of the signal by the source, but that the density for the time rate-of-change of the multipath phase ?, is sensitive to such modulation. Because the finite bandwidths of acoustic signals can be modeled by uniform frequency modulation, the analysis presented applies to this problem as well. It is shown that bandwidth effects can be neglected only if B≪2ν, where B is the signal bandwidth, and ν2 is the single path mean-square phase rate. This inequality provides a useful definition of what is meant by ’’narrow band’’ as it applies to phase-random multipath propagation. It is also shown that the density for ? depends only on ν, while the density for ? depends on ν and parameters of the modulation. A potentially powerful technique is developed for determining source bandwidth and parameters of the source modulation, minus the effects of oceanic fluctuations, from the received multipath signal. The analytical results are compared with a computer simulation, and data from experiments in the ocean with extremely favorable results.

Acoustic transfer function of the ocean for a motional source

The motional-source transfer characteristics of long-range acoustic propagations are derived based on the discrete multipath propagation model predicted by geometrical acoustics. Parameters are those associated with the characteristic solutions of the eikonal equation. A modified transfer function is formulated which relates the received signal to a particularly useful transformation of the source signal. The modified transfer function shows that a remotely received signal consists of the weighted superposition of a number of modified source signals both slightly compressed (or expanded) and translated in time. The time variable compression factor is a stochastic process which reflects the fluctuations inherent in both the medium and the source motion. Application of the model transfer function to a specific ocean profile exemplifies the ocean filter characteristics and the complex nature of the received signal from a CW source in motion. It is concluded that the model transfer function will be a useful tool for signal processing applications in underwater acoustics.

A statistical model of urban multipath propagation

An urban multipath propagation experiment, involving the simultaneous transmission from a fixed site of 100-ns pulses at 488, 1280, and 2920 MHz and their reception at a mobile van, is described. A statistical analysis of the data in the resulting multipath responses is given and used as a basis for a statistical model of urban multipath propagation.

Tropospheric effects on design of line-of-sight space-diversity system

The successful application of space diversity to achieve a high propagation reliability over line-of-sight microwave links requires proper separation between diversity antennas, whereby the signals received at the antennas are sufficiently decorrelated. The multipath-propagation model is examined, and en expression is derived for the envelope correlation coefficient which is a function of antenna spacing and is dependent on the parameters of the troposphere.