0122229现代数字通信与编码理论 December 16,2008 XDU,Winter 2008 Lecture Notes Chapter 7 Coding and Modulation for Fading Channels physical channels may be characterized as time-varying fading channels.In this chapter,we will study communications over fading channels from an information-theoretic point of view. Many state-of-the-art coding and modulation schemes,including space-time codes,will be introduced. 7.1 Wireless Cha nne 1 Models 无线通信中，由于电波的反射、散射和绕射等，使得发射机和接收机之间有 在多条传播路径，并且每条路径的传播时延和衰耗因子都是时变的：在接收端，从不同 路径到达的信号分量叠加在一起，导致接收信号的强度随时间变化，我们通常用“衰落” 来描述这种现象。多径时变衰落是移动通信信道的主要特点。Many channel models arise or fading.Fi7.I depicts an overview of fading manifestations Fading channel manifestations Large-scale fading due to Small-scale fading due to motion over large areas small changes in position Variations about the mean Time spread Time-varying of the signal of the channel Frequence-selective fading ading ading Figure 7.1 7.1.1 Large-Scale Fading:Path loss and Shadowing Let s()=Rex()e be the transmitted signal,where x(t)x()e=R(e) is the complex baseband equivalent signal.In a fading environment,the magnitude of the received baseband waveform()can be expressed as |()Fa()R0=m)-()R() 1 0122229 现代数字通信与编码理论 December 16, 2008 XDU, Winter 2008 Lecture Notes Chapter 7 Coding and Modulation for Fading Channels The research on wireless communications has received many attentions. The underlying physical channels may be characterized as time-varying fading channels. In this chapter, we will study communications over fading channels from an information-theoretic point of view. Many state-of-the-art coding and modulation schemes, including space-time codes, will be introduced. 7.1 Wireless Channel Models 在许多无线通信中，由于电波的反射、散射和绕射等，使得发射机和接收机之间存 在多条传播路径，并且每条路径的传播时延和衰耗因子都是时变的；在接收端，从不同 路径到达的信号分量叠加在一起，导致接收信号的强度随时间变化，我们通常用“衰落” 来描述这种现象。多径时变衰落是移动通信信道的主要特点。Many channel models arise according to different fading characteristics. Fig. 7.1 depicts an overview of fading channel manifestations. Figure 7.1 7.1.1 Large-Scale Fading: Path loss and Shadowing Let   2 ( ) Re ( ) c j ft st xte   be the transmitted signal, where () () ( ) | ( )| ( ) jt jt x t xt e Rte     is the complex baseband equivalent signal. In a fading environment, the magnitude of the received baseband waveform y(t) can be expressed as 0 | ( )| ( ) ( ) ( ) ( ) ( ) y t tRt mt r t Rt     , Fading channel manifestations Large-scale fading due to motion over large areas Small-scale fading due to small changes in position Variations about the mean Time spread of the signal Time-varying of the channel Frequence-selective fading Flat fading Fast fading Slow fading