=== Physics-Based Propagation Channel Modeling Using SBR Ray Tracing ===
Every wireless communication system involves a transmitter that transmits some sort of signal (voice, video, data, etc.), a receiver that receives and detects the transmitted signal, and a channel in which the signal is transmitted into the air and travels from the location of the transmitter to the location of the receiver. The channel is the physical medium in which the electromagnetic waves propagate. The successful design of a communication system depends on an accurate link budget analysis that determines whether the receiver receives adequate signal power to detect it against the background noise. The simplest channel is the free space. Real communication channels, however, are more complicated and involve In a large number free-space line-of wave scatterers. For example, in an urban environment-sight (LOS) communication system, the obstructing buildings, vehicles and vegetation reflect, diffract or attenuate signal propagates directly from the propagating radio waves. As a result, transmitter to the receiver receives a distorted signal without encountering any obstacles (scatterers). Free-space line-of-sight channels are ideal scenarios that contains several components with different power levels and different time delays arriving from different anglescan typically be used to model aerial or space communication system applications.
The rapid growth of wireless communications along with the high costs associated with the design and deployment of effective wireless infrastructures underline a persistent need for computer aided communication network planning tools[[Image:Info_icon. The different rays arriving at a receiver location create constructive and destructive interference patterns. This is known as png|40px]] Click here to learn more about the multipath effect. This together with the shadowing effects caused by building obstructions lead to channel fading. The use theory of statistical models for prediction of fading effects is widely popular among communication system designers. These models are either based on measurement data or derived from simplistic analytical frameworks. The statistical models often exhibit considerable errors especially in areas having mixed building sizes. In such cases, one needs to perform a physics'''[[SBR_Method#Free-based, siteSpace_Wave_Propagation | Free-specific analysis of the propagation environment to accurately identify and establish all the possible signal paths from the transmitter to the receiver. This involves an electromagnetic analysis of the scene with all of its geometrical and physical detailsSpace Propagation Channel]]'''.
In Real communication channels, however, are more complicated and involve a free-space line-large number of-sight (LOS) communication systemwave scatterers. For example, in an urban environment, the obstructing buildings, vehicles and vegetation reflect, diffract or attenuate the propagating radio waves. As a result, the receiver receives a distorted signal propagates directly that contains several components with different power levels and different time delays arriving from different angles. The different rays arriving at a receiver location create constructive and destructive interference patterns. This is known as the transmitter to multipath effect. This together with the receiver without encountering any obstacles (scatterers)shadowing effects caused by building obstructions lead to channel fading. Free-space line-The use of-sight channels are ideal scenarios that can typically be used to model aerial or space statistical models for prediction of fading effects is widely popular among communication system applicationsdesigners. [[Image:Info_iconThese models are either based on measurement data or derived from simplistic analytical frameworks.png|40px]] Click here The statistical models often exhibit considerable errors especially in areas having mixed building sizes. In such cases, one needs to learn more about the theory of perform a '''[[SBR_Method#Freephysics-Space_Wave_Propagation | Freebased, site-Space Propagation Channel]]'''specific analysis of the propagation environment to accurately identify and establish all the possible signal paths from the transmitter to the receiver. This involves an electromagnetic analysis of the scene with all of its geometrical and physical details.
[[Image:multi1_tn.png|thumb|500px|A multipath propagation scene showing all the rays arriving at a particular receiver.]]
In ground-based systems, the presence of the ground as a very large reflecting surface affects the signal propagation to a large extent. Along the path from a transmitter to a receiver, the signal may also encounter many obstacles and scatterers such as buildings, vegetation, etc. In an urban canyon environment with many buildings of different heights and other scatterers, a line of sight between the transmitter and receiver can hardly be established. In such cases, the propagating signals bounce back and forth among the building surfaces. It is these reflected or diffracted signals that are often received and detected by the receiver. Such environments are referred to as âmultipathâ. The group of rays arriving at a specific receiver location experience different attenuations and different time delays. This gives rise to constructive and destructive interference patterns that cause fast fading. As a receiver moves locally, the receiver power level fluctuates sizably due to these fading effects.
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Link budget analysis for a multipath channel is a challenging task due to the large size of the computational domains involved. Typical propagation scenes usually involve length scales on the order of thousands of wavelengths. To calculate the path loss between the transmitter and receiver, one must solve [[Maxwell's Equations|Maxwell's equations]] in an extremely large space. Full-wave numerical techniques like the Finite Difference Time Domain (FDTD) method, which require a fine discretization of the computational domain, are therefore impractical for solving large-scale propagation problems. The practical solution is to use asymptotic techniques such as SBR, which utilize analytical techniques over large distances rather than a brute force discretization of the entire computational domain. Such asymptotic techniques, of course, have to compromise modeling accuracy for computational efficiency.