多径多普勒效应讲义含matlab程序 2005.pdfVIP

Multipath and Doppler Effects and Models There are two parts in this lecture. • In Part I, we will first introduce the mutipath propagation effects and Doppler frequency shift/spread effects. • In Part II, we will briefly introduce multipath and Doppler channel models. 1 Background: Overviews on Wireless Channel Modeling We need to ask the following three important questions while designing a wireless communication link: 1. Fading Power Loss: Is the signal to interference plus noise ratio (SINR) large enough for the receiver to detect the transmitted signal? 2. Signal Distortion: Can the signal distortion be ignored, predicted or removed so that we know how to recover the transmitted information at the receiver? 3. Time Variation: Can the receiver adapt faster enough to the variations of the above two features (SINR signal distortion)? A complete wireless channel model should provide quantitative measures of SINR, signal distortion and time variation. For SINR (referred in question 1), we need only to consider the time invariant transmission loss at a single frequency (that is the RF carrier frequency). The frequency and time dependent properties of signal can be addressed in answering questions 2 and 3. Signal distortion (referred in question 2) is caused by the frequency dependent variations of the received signal strength and phase. The primary source of frequency dependent variations is multipath propagation. Here, we need only to consider time invariant situations and leave the time varying features to question 3. Motions of receivers, transmitters or wireless environments generate Doppler effects. With Doppler effects, signal frequencies shift and spread. These Doppler effects will cause ti