RF Propagation Pathloss Model

RF elongation Path spill stumperIntroductionWhat is the need of RF Propagation Model?In piano tuner confabulation the transmitted maneuver propagates in space i.e the radio receiver signal. Wireless conversation carcass is the most wide used communication system now a days and communication took place in such system with the help of radiowave in space. Thus a fine analysis and study of radiowave propagation is wantd and it is a very important aspect before we finally design and implement a wireless communication system.When we talk about the communication through a wired line medium such as RF Coaxial cable or twisted pair cable or optical fiber provides reliable communication with minimum pathloss as signal is well secured in it from the atmospheric distortions. though the laying and maintaining of the wired medium takes time and is cost effective as well but it is reliable means of communication. on the other hand communication in such medium i.e. in wireless communication is quite unreliable and unsecured. In wireless communication a limited operating oftenness bandwidth is available for communication as it has many other applications of radiowave propagation in space.Every communication system is intentional with some specific objectives of providing continuous communication services to expeditious subscribers that argon present in the service rural area i.e. the area upto which the operator will provide communication services. But as we study earlier a good quality service contribute save be obtained if loss of transmitted signal will be minimum and maximum signal will reach at receiver end.The design can be optimized only when the parameters under which a system has to operate are fully understood whether the absolute frequency band allocated or the height of barbel, distance amidst transmitter and receiver, and the most important is the pathloss and an estimation of received signal level at the receiver end. If proper radio analysis is done than it will be of great use to design a ne twork and implement it in computer hardware level with proper and desired results which are expected from a system.The most important design parameter in mobile communication system is to hit the desired signal coverage as the basic purpose of operator is to serve the subscribers in a specified service area. Whenever a system is designed it is designed for some specific aims and that is to provide a better service to subscribers with in the range for which the services are introduced but if we directly implement the system without checking it whether the system is giving desired output or not and directly implement it than if it is not coiffeing according to ones expectation the system will be wasted and soon our efforts so it is the most important promoter to check and calculate the pathloss.Classification of RF Propagation Pathloss modelDifferent models were developed which are empirical in nature that means they are developed based on the collection of information in specific areas. Data must be sufficient enough so as to study the losses that may happen in any specific area, so that on the basis of that data one can come to a conclusion as propagation models does not see the exact pathloss that may happen but it will tell the most likely behavior of the link under some defined conditions.Mainly RF Propagation Models can be classified as at a lower placeBasically RF Propagation models can be classified into three main categories which can be classified as above defined.Empirical modelsSemi-deterministic modelsdeterministic modelsThe Basic classification of RF Propagation Pathloss Models can be seen in the above enroll 3.1. Three kinds of modelsFigure 3.1 Classification of RF Propagation Pathloss ModelEmpirical models based on measurement data, simple (few parameters),use statistical properties, not very accurate.Semi-deterministic models based on empirical models + deterministic aspectsDeterminist ic models site-specific, require enormous number of geometry information about the cite, very important computational effort, accurate.Every Model is defined for a diverse and a specific environs and for different cells. Cells in a mobile communication is nothing but a geographical area covered by a telephone transmitter. cells can also be divided into three main types and they are as followsMacrocellMicrocellPicocellMacrocell The area of largest coverage. Macrocells are used to described the widest range of cell sizes.Example An stallion City.It covers the area upto 1-5 km long.Microcell The area of intermediate coverage. Mainly the range of microcell is less than two kilometers.It covers the area upto 100- 1 kilo meters.Pico cell A picocell is a exquisite cellular base station which covers a small station such as in buildings, offices, shopping malls etc.It covers the area upto euchre meters.From the above figure we can understand the concept and coverage area covered by a macrocell, microcell and picocell.Representation of macrocell, microcell, picocellA table is shown where different cells and the area covered by those cells i.e Macrocell, Microcell, and picocell is shown in table 3.1.3.Table 3.1.3 Different cell sites and area they covered.Different RF Propagation Pathloss models are defined for different cells which can better perform on different cells and better results can be obtained. Now the cells and the models defined for it will be described.Okumura-Hata modelIt is the most popular model which is based on the empirical information obtained from measurements in japan.(okumura 1965). The okumura Hata predicts the Pathloss L between the transmitter and receiver taking into considering the frequency, the distance between transmitter and receiver, height of antenna, terrain type.this model fits best for urban and suburban areas.General formulaThe general formula for the path loss L according to the Okumura-Hata model isL = a0 + a4logf a2logh b ahm + a1 a3loghblogd Lc,where a0, a1, a2, a3, and a4 are adjustable parametersSpecific formulasThe path loss L can be found by the standard path loss formulas for GSM-900, GSM-1800, and GSM-1900 according to the Okumara-Hata model.GSM900 formulaThe path loss formula for GSM-900 isL = 69.55 + 26.16logf 13.82loght ahm + 44.9 6.55loghtlogd Lc.GSM1800/1900 formulaThe path loss formula for GSM-1800/1900 isL = 46.3 + 33.9logf 13.82loght ahm + 44.9 6.55loghtlogd -LcWhere,L= Pathlossfc=frequency of transmissionht=antenna heightar=correction factor for effective mobile antenna height which depends on the size of the in areaLc=correction factor for different terrains.Correction factor for different clutter classes is determined according to okumura hata model and following is the table 3.1.4 which shows the clutter classes and correction factor for it.Table 3.1.4 Correction factor defined according to okumura Hata ModelCost 231 Hata Propagation ModelA Model that is widely used for predicting pathloss in wireless system operating from 500 MHz to 2000 MHz is the cost 231 Hata Model. It contains correction factor for Urban, suburban and open rural environment. The general expression for calculating pathloss in the urban area as given by COST 231 Hata model isLpch(urban)db)=46.3 + 33.9logfc 13.82loght ar + (44.9-6.55loght)logr + Cmwhere, fc=frequency of transmissionht=antenna heightar=correction factor for effective mobile antenna height which depends on the size of the coverage area.Cm =3db for urban environments and 0db for suburban or open environmentWalfisch-Ikegami modelThe Walfisch-Ikegami model is more novel than the Okumura-Hata model. It is based upon the deterministic models of Walfisch, Ikegami, and Bertoni.It works in 2 cases LOS and NLOSLOS (Line of sight)LLOS dB = 42.6 + 26 log10 dkm + 20 log10 f MHzNLOS (Non line of sight)LNLOS dB = LFS + Lrts (wr, f, hMobile , ) + LMSD (hBase, hBase, d, f, bS )LFS = free space path loss = 32.4 + 20 log10 dkm + 20 log10 f MHzLrts= roof-to-street lossLMSD= multi-diffraction lossBut it has some restrictions which are as followsFrequency f between 800 MHz and 2000 MhzTX height hBase between 4 and 50 mRX height hMobile between 1 and 3 mTX RX distance d between 0.02 and 5 kmLongley Rice Propagation ModelThe Longley Rice Propagation model also known as irregular terrain model. It basically calculates large scale median propagation loss sexual intercourse to free space loss propagation loss over irregular terrain. It is mainly applicable for evince to point wireless communication system.It operates in the frequency range from 40 MHz to 100 GHz.It is mainly used for frequency planning in television broadcasting.The modified model can also be used for radio wave propagation in urban areas for mobile communication.The Longley Rice propagation models has two parts modelArea to area expectation model.Point to point prediction model.The area to area is used when path profile is not given but point ot point is used when detailed path profile is given. But, the main drawback of this model is that it doesnot consider the effect of multipath, foliage, buildings and other environment factors.Two Ray Point to Point Propagation modelThe point to point propagation model is a basic system design tool that is used to generate a signal coverage map, an interference area map, or a handoff occurrence map. In many mobile communication system the maximum distance between the cellsite and the mobile is at the most only a few tens of kilometers and surface is assumed flat. A simple two ray model can be used to predict pathloss and received signal strength.Lpch = 40 log r 20 log ht 20 log hrThus it implies that the propagation pathloss in a mobile communication Lpch increases by 40dB for every increase in distance by 10 times. If the cellsite antenna height is doubled, there will be reduction in pathloss by 6dB.The two ray model is found to be reasonably accurate for predicting the l arge scale received signal strength over distances of several kilometers for mobile radio communication system that use tall cellsite towers and los microcell application in urban area.