数据通信

扩频

2019-03-21 08:00 CST
2019-03-21 08:00 CST
CC BY-NC 4.0
在扩频码(伪随机数)下调制使带宽增加

Spread Spectrum

Frequency Hopping(FHSS)

  • signal is broadcast over seemingly random series of frequencies
  • receiver hops between frequencies in sync with transmitter
  • Slow $T_{\text{shift}}\geq T_{\text{symbol}}$
  • Fast $T_{\text{shift}}< T_{\text{symbol}}$
  • 信号带宽远大于数据信号带宽
  • 提高抗人为干扰能力

直接序列扩频(DSSS)

  • each bit is represented by multiple bits using a spreading code

Code Division Multiple Access

  • break each bit into k chips according to a fixed chipping code specific to each user
  • 用户码
  • 码片率:新信道码片数据率
  • 接收器解码:用相同用户码做乘积,若为 $\pm N$ 则接受,否则拒绝