Path loss (or path attenuation) is the reduction in power density (attenuation) of an electromagnetic wave as it propagates through space. In Physics, attenuation (in some context also called extinction) is the gradual loss in intensity of any kind of Flux through a medium Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Path loss is a major component in the analysis and design of the link budget of a telecommunication system. A link budget is the accounting of all of the gains and losses from the transmitter through the medium (free space cable waveguide fiber etc
This term is commonly used in wireless communications and signal propagation. Wave propagation is any of the ways in which waves travel through a Waveguide. Path loss may be due to many effects, such as free-space loss, refraction, diffraction, reflection, aperture-medium coupling loss, and absorption. In Telecommunication, free-space path loss ( FSPL) is the loss in Signal strength of an Electromagnetic wave that would result from a line-of-sight Refraction is the change in direction of a Wave due to a change in its Speed. Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle Reflection is the change in direction of a Wave front at an interface between two different media so that the wave front returns into the medium from which As a receiver, antenna aperture can be visualised as the Area of a Circle constructed broadside to incoming Radiation where all radiation passing A transmission medium' (plural transmission media) is a material substance ( Solid, Liquid or Gas) which can propagate Coupling loss also known as connection loss is the loss that occurs when Energy is transferred from one circuit, circuit element or medium to another In Physics, absorption of electromagnetic radiation is the process by which the Energy of a Photon is taken up by matter typically the electrons of an Path loss is also influenced by terrain contours, environment (urban or rural, vegetation and foliage), propagation medium (dry or moist air), the distance between the transmitter and the receiver, and the height and location of antennas.
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Causes
Path loss normally includes propagation losses caused by the natural expansion of the radio wave front in free space (which usually takes the shape of an ever-increasing sphere), absorption losses (sometimes called penetration losses), when the signal passes through media not transparent to electromagnetic waves, diffraction losses when part of the radiowave front is obstructed by an opaque obstacle, and losses caused by other phenomena. Radio waves are electromagnetic waves occurring on the Radio frequency portion of the Electromagnetic spectrum. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle
The signal radiated by a transmitter may also travel along many and different paths to a receiver simultaneously; this effect is called multipath. In Wireless Telecommunications multipath is the propagation phenomenon that results in Radio signals reaching the receiving Multipath can either increase or decrease received signal strength, depending on whether the individual multipath wavefronts interfere constructively or destructively. The total power of interfering waves in a Rayleigh fading scenario vary quickly as a function of space (which is known as small scale fading), resulting in fast fades which are very sensitive to receiver position. Rayleigh fading is a statistical model for the effect of a propagation environment on a Radio signal such as that used by Wireless This is about the phenomenon of loss of signal in telecommunications
Loss exponent
In the study of wireless communications, path loss can be represented by the path loss exponent, whose value is normally in the range of 2 to 4 (where 2 is for propagation in free space, 4 is for relatively lossy environments and for the case of full specular reflection from the earth surface -- the so-called flat-earth model). In Classical physics, free space is a concept of Electromagnetic theory, corresponding to a theoretically "perfect" Vacuum, and sometimes In some environments, such as buildings, stadiums and other indoor environments, the path loss exponent can reach values in the range of 4 to 6. On the other hand, a tunnel may act as a waveguide, resulting in a path loss exponent less than 2. A waveguide is a structure which guides waves such as Electromagnetic waves Light, or Sound waves
Path loss is usually expressed in dB. The decibel ( dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity relative to In its simplest form, the path loss can be calculated using the formula
where L is the path loss in decibels, n is the path loss exponent, d is the distance between the transmitter and the receiver, usually measured in meters, and C is a constant which accounts for system losses.
Prediction
Calculation of the path loss is usually called prediction. Exact prediction is possible only for simpler cases, such as the above-mentioned free space propagation or the flat-earth model. For practical cases the path loss is calculated using a variety of approximations.
Statistical methods (also called stochastic or empirical) are based on measured and averaged losses along typical classes of radio links. Among the most commonly used such methods are COST-231, Okumura-Hata, W. C. Y. Lee, etc. These are also known as radio wave propagation models and are typically used in the design of cellular networks and PLMN. A cellular network is a Radio network made up of a number of radio cells (or just cells) each served by a fixed transmitter known as a Cell In Telecommunication, a public land mobile network (PLMN is a network that is established and operated by an administration or by a Recognized For wireless communications in the VHF and UHF frequency band (the bands used walkie-talkies, police, taxis and cellular phones), one of the most commonly used methods is that of Okumura-Hata as refined by the COST-231 project. Very high frequency (VHF is the Radio frequency range from 30 MHz to 300 MHz. Other well-known models are those of Walfisch-Ikegami, W. Walfisch is an uninhabited German Island, in the Bay of Mecklenburg in the Baltic Sea. C. Y. Lee, and Erceg. Erceg is a Croatian and Serbian surname and may refer to Jason Erceg (born c For FM radio and TV broadcasting the path loss is most commonly predicted using the ITU model as described in P. 1546 (former P. 370) recommendation.
Deterministic methods based on the physical laws of wave propagation are also used; ray tracing is one such method. In physics ray tracing is a method for calculating the path of Waves or Particles through a system with regions of varying propagation Velocity, absorption These methods are expected to produce more accurate and reliable predictions of the path loss than the empirical methods; however, they are significantly more expensive in computational effort and depend on the detailed and accurate description of all objects in the propagation space, such as buildings, roofs, windows, doors, and walls. For these reasons they are used predominantly for short propagation paths. Among the most commonly used methods in the design of radio equipment such as antennas and feeds is the finite-difference time-domain method. Finite-difference time-domain (FDTD is a popular computational electrodynamics modeling technique
The path loss in other frequency bands (MW, SW/HF) is predicted with similar methods, though the concrete algorithms and formulas may be very different from those for VHF/UHF. Reliable prediction of the path loss in the SW/HF band is particularly difficult, and its accuracy is comparable to weather predictions.
Some easy to remember approximations for calculating the path loss over distances significantly shorter than the distance to the radio horizon:
- In free space the path loss increases with 20 dB per decade (one decade is when the distance between the transmitter and the receiver increases ten times) or 6 dB per octave (one octave is when the distance between the transmitter and the receiver doubles). In Telecommunication, radio horizon is the locus of points at which direct rays from an antenna are tangential to the surface of the Earth This can be used as a very rough first-order approximation for SHF (microwave) communication links;
- For signals in the UHF/VHF band propagating over the surface of the Earth the path loss increases with roughly 35 -- 40 dB per decade (10 -- 12 dB per octave). Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 This can be used in cellular networks as a first guess.
Examples
In cellular networks, such as UMTS and GSM, which operate in the UHF band, the value of the path loss in built-up areas can reach 110 -- 140 dB for the first kilometer of the link between the BTS and the mobile. GSM ( Global System for Mobile communications: originally from Groupe Spécial Mobile) is the most popular standard for Mobile phones in the The path loss for the first ten kilometers may be 150 -- 190 dB (Note: These values are very approximate and are given here only as an illustration of the range in which the numbers used to express the path loss values can eventually be, these are not definitive or binding figures -- the path loss may be very different for the same distance along two different paths and it can be different even along the same path if measured at different times. )
See also
- Radio propagation model
- Professional Path Analysis Using a Spreadsheet: http://www.narte.org/n/212/Summer03Page10_13.pdf
References
A radio propagation model, also known as the Radio Wave Propagation Model or the Radio Frequency Propagation Model, is an Empirical Mathematical Federal Standard 1037C, entitled Telecommunications Glossary of Telecommunication Terms is a United States Federal Standard issued by the General Services Administration MIL-STD-188 is a series of US military standards relating to Telecommunications Purpose Faced with “past technical deficiencies in telecommunicationsDapyx Software network: MP3 Explorer | Ebook Manager | Zenithic