Point-to-point optical and millimeter wave communication has recently been of interest, especially in urban areas. Its benefits include simpler and easier installation compared with a land-based line. However, this technology suffers when adverse weather conditions are present, such as rain, fog and clouds, which induce scattering and absorption of the optical wave. The effects of scattering and absorption degrade the quality of the communication link resulting in increase of bit-error-rate. Therefore, there exists a need for accurate channel characterization in order to understand and mitigate the problem. In this paper, radiative transfer theory is employed to study the behavior of amplitude modulated signal propagating through a random medium. We show the effect of the medium to a modulated signal and relate the outcome on the quality of the communication link.

Analysis of electromagnetic wave propagation and scattering in a random medium is a field of great interest. This research field becomes more important if we consider the study of phsyical effects on wave propagation and scattering from targets in random media. Curvature of the targets' cross-sections plays an important parameter in the radar detection problem. In previous study, analysis of scattering data from nonconvex conducting targets has pointed out to the effect of target configuration together with both effects of the spatial coherence length of incident waves around the target and the double passage on the backscattering enhancement. Here, we make sure this fact by considering targets with relatively large sizes in continuous random media for H-wave incidence. We assume the cross-section of targets to be smoothly deformed contour comprising concave and convex portions.

We study the electromagnetic wave propagation in three-dimensional (3-D) dense random discrete media containing dielectric spheroidal scatterers. We employ a Monte Carlo method in conjunction with the Method of Moments to solve the volume integral equation for the electric field. We calculate the effective permittivity of the random medium through a coherent-field approach and compare our results with a classical mixing formula. A parametric study on the dependence of the effective permittivity on particle elongation and fractional volume is included.

Experiment is reported of enhanced backscattering of light in binary and ternary suspensions of rutile and/or alumina particles. With a conventional CCD camera system for observing the phenomena, the angular line shape and the enhancement factor were agreed with the theoretically predicted curve and value. Observation of the angular distribution scattered at the backscattered direction supported the hypothesis proposed by Pine et al. , in which the transport mean free path of the polydisperse mixture can be expressed in terms of summing its reciprocal values weighted over the particle sizes.

There has been an increasing interest in multiple scattering phenomena in recent years. This is primarily due to the discovery of new multiple scattering phenomena and an increasing awareness that a common thread underlies the work of many researchers in such diverse fields as atmospheric optics, ocean acoustics, radio physics, astrophysics, condensed matter physics, plasma physics, geophysics, bioengineering, etc. In addition, waves in random media is one of the most challenging problems to theoreticians. Thus the field of wave propagation and scattering encompasses the most practical as well as the most theoretical questions. The strong interest in this subject is reflected in the launch of a new journal, Waves in Random Media, by the Institute of Physics, United Kingdom in 1991. This paper reviews some of the most recent developments and discoveries in the field of wave propagation and scattering in turbulence and volume and surface scattering. Included are new discoveries of backscattering enhancement and memory effects which may be applicable to tissue optics, ultrasound imaging, ocean acoustics and geophysical remote sensing. Also indicated are recent developments of numerical Monte-Carlo techniques and experimental studies on this subject.

A piece of information on the polarization effects on the effective dielectric constant εeff of a medium whose dielectric circular cylinders are randomly distributed is obtained by analyzing εeff for both E-wave and H-wave incidences. Our numerical analysis shows clearly the difference of εeff between E-wave and H-wave incidences and also shows the difference of εeff between our method and the Foldy's approximation.

This paper investigates the problems which inhibits the use of today's WDM networks. These are propagation delay, packet processing overhead, bit & frame synchronization, and tuning latency. So far, these problems, especially propagation delay, have been ignored in most performance analysis papers. They have always hindered network designers, but they are magnified by the order of magnitude increase in speed of optical communications systems as compared to previous media. This paper examines the impact of the propagation delay on the performance of WDM protocols with variations in the number of channels, packet length and system size, specifically in two reservation based protocols with control channels and two pre-allocation protocols without the control channels. Also the impact of three delay factors (packet processing overhead, bit & frame synchronization and tuning latency) are studied with different propagation delay parameters. In reservation protocols, each node has one agile transmitter and two receivers; one of them is fixed and the other one is agile. The fixed receiver continuously monitors the control channel, receives all control packets, and updates their own status tables in order to track the availability of the other nodes as a target and data channels to avoid the destination collisions and the data channel collisions, respectively. In pre-allocation protocols, each node has a tunable transmitter, a fixed or slow tunable receiver, and its own home channel to receive the packets. The performance of this protocol is evaluated through the discrete-event simulation in terms of the average packet delay and network throughput.

Coherent and incoherent electromagnetic (EM) waves scattered by many particles are approximately expressed as solutions of integral equations by unconventional multiple scattering method. The particles are randomly displaced from a uniformly ordered distribution, and hence the distribution of particles can change from total uniformity to complete randomness. The approximate expressions of the EM waves are systematically given, independent of the distributions of particles, on the following assumptions. First the particles are identical in material, shape, size and orientation. Second each random displacement of particles from the ordered positions is statistically independent of each other and homogeneous in space. These assumptions may be extended to more general ones but have been used here to make clear the derivation process of the coherent and incoherent EM waves. The approximate expressions of the EM waves are reduced to known ones for both limiting cases: a periodic distribution and a very sparse random distribution. The effective dielectric constant of a random medium containing randomly distributed dielectric spheres can be calculated from the coherent EM wave and compared with those given by conventional methods such as the quasi-crystalline approximation, using the previous results. The comparison indicates the advantage of the method presented here. The present method is expected to be useful for the study of interaction of EM waves with many particles.

The effective dielectric constant εeff of discrete random medium composed of many dielectric spheres has been analyzed by EFA (Effective Field Approximation), QCA (Quasicrystalline Approximation) and QCA-CP (Quasicrystalline Approximation and Coherent Potential) in the case where the optical path length is very large in the medium. These methods lead to a reasonable K for non-large dielectric constants of spheres, while their methods yield an unphysical dependence of εeff on large dielectric constants of spheres: that is, the εeff does not become large for increasing the dielectric constant. In this paper, we remove the unphysical dependence and present new results for εeff of our method, comparing with the results for εeff of EFA, QCA and QCA-CP.

A method is presented for analyzing the scalar wave scattering from a conducting target of arbitrary shape in random media for both the Dirichlet and Neumann problems. The current generators on the target are introduced and expressed generally by the Yasuura method. When using the current generators, the scattering problem is reduced to the wave propagation problem in random media.