Content1. Introduction2.Channel model2.1.Lee model2.1.1. outdoor model2.1.2. The Philosophy of Forming Lee' Model2.1.2.1 Caused by the human-made structures only2.1.2.2 Adding the cause of terrain contour2.1.3. A Normal-cell Model2.1.4. Microcell Model2.2.Ray Tracing2.2.1. Indoor channel2.2.2. Physical phenomena involved2.2.3. General equation2.2.3.1 Reflection2.2.3.2 The transmission2.2.3.3 The diffraction2.2.3.4 The diffusion on a surface2.2.3.5 The divergence2.2.4. Ray tracing model in a forested environment2.2.5. Building Definition2.3.JTC(Joint Technical Committee)2.3.1. History2.3.2. wide band multipath propagation models2.3.3 Physical Environments2.3.4 General Channel Model2.3.5. Doppler Spectrum2.3.6. The Wide band Tapped Delay-Line Model2.3.6.1 Indoor2.3.6.2 Outdoor-Low antenna2.3.6.3 Outdoor-High Antenna2.3.7. Implementation2.3.7.1 Simulation Block Diagram2.3.7.2 Simulation Algorithm and Result3.Trend and issues on channel model4, References1.IntroductionThe increasing demandistics over distance.(1) Lee model is used to predict the local-mean of a receive signal along a mobile path where the mobile unit travels. The standard derivation of prediction error by comparing the predicted values with the measured data is approximately 2-3 dB. the model is simple 鯵 implement and has a theory to back it.(4)Most prediction models are used to predict the pathloss along the radio path is the basestation antenna to the mobile-station antenna. The pathloss curve is generated from the measured data received along the mobile path and plotted along the radio path. the standard deviation is about 6-8dB. Since a large standard deviation from the prediction is hard to used to design a cellular system, Lee model is used to predict the local mean along the mobile path.(4)Secondly we check the Ray tracing model.The study of the propagation in indoor environments has increased enormously in recent years, the main reason begin the large amount of competition that exists in mobile Tap spacing and Doppler spectra vary fir the different environments in which PC is expected to operate. Three tapped delay lines are specified for each environment. This model was developed to accommodate wide band digital mobile radio systems.(3)Transmission loss is characterized by both average path loss and shadow fading statistics. The transmission loss problem is divided into macrocell and microcell groupings. Macrocell models apply for antenna heights above rooftop level. Microcell models apply for antenna heights near or below rooftop level. Formulas for mean path loss and shadow fading ststistics are provided for each of the expected environments.2.Channel model2.1.Lee model2.1.1. outdoor modelLee's Model is used to predict the local-mean of a received signal along a mobile path where the mobile unit travels. The standard derivation of prediction error by comparing the predicted values with the measured data is approximately 2-3 dB.Most prediction models are used to predict thel to predict the signal in more or less deterministic conditions where the propagation distance is short.2.2.Ray Tracing2.2.1. Indoor channelRay Tracing model is the indoor model. So I think ray tracing's physical environment is the inside of a building or a house. So when I read this paragraph "Ray Tracing techniques are used to simulate the propagation of radio waves in a geometrical urban environment composed of terrain buildings, forest, and vegetation.(10)", I can't under -stand the paragraph. To tell the truth the reason that we differentiate indoor model from outdoor model is the jamming of a radio wave because a building consists of a reinforcing rod. But forest have the jamming of a radio wave, too. Beause leaves of the tree interfere a radio wave. If a radio wave doesn't go out of the forest, the forest is like the inside of a building. In the same manner, buildings is the same.2.2.2. Physical phenomena involvedTo simulate the radio channel, classical optical phenomena are toh depends on the very nature of the ray. For a direct pathC_i =1; if only reflections occurC_iwill be the product of reflection coefficients.D_iviis the divergence of the wave i, and has a dependance on the diffracting points, and the distance between the base and the mobile.(12)2.2.3.1 ReflectionReflection is considered as perfectly specular. Indeed experiments show that the distribution of the reflected wave due to surface roughness could be neglected at GSM frequencies (from 900 MHz to 2 GHz). The reflection coefficient Cr is deduced from a complex Fresnel coefficient computed for 2 polarizations : vertical and horizontal, and roughness fading given by Beckmann(11). It uses four main physical parameters: ュ's the real part of the relative permittivity of the material, ヲ its permeability (or penetrability), ヱ ts roughness and R0 a constant empitical factor taking wall appertures into account (real number=1). Theoretically ュ' is dependant on frequency in the vicinity of the material reS
