频道模型是通信信道的效果的数学表示，无线信号传播。频道模型可以表示通过无线介质行进时信号产生的功率损耗。在更常规的情况下，信道模型是频域中时域或其傅里叶变换中的信道介质的脉冲响应。无线通信系统的信道脉冲响应通常随时间随机变化。
By using channel models with your wireless system design in MATLAB®and Simulink®, you can optimize link performance, perform system architecture tradeoffs, and provide a realistic assessment of the overall system performance.
Channel models can be classified in four categories:
- 路径损失
- Purely stochastic
- 空间
- 雷追踪
路径损失
路径损耗信道模型表示其遍历无线介质的发送信号的功率降低。它们不会对信号执行任何过滤。这些信道模型基于信号传播的介质，例如自由空间，雨，雾或气体。你可以使用FSPL.function in MATLAB to calculate the free space path loss for a communications link.
Purely Stochastic
纯粹的随机信道模型地址热噪声发电和多径衰落通道。它们不需要任何知识所建模链路的几何形状。一种添加性白色高斯噪声（AWGN）信道在接收器前端中的电子噪声模拟。这种噪声是光谱平坦的，并且其幅度遵循高斯PDF。您可以使用Communications Toolbox™AWGN.模拟将此噪声添加到信号的功能。
A multipath fading channel exhibits delay spread, in which multiple copies of the transmitted signal arrive at the receiver. These copies typically are attenuated and phase shifted relative to the original. This channel can be modeled with an impulse response. The figure below shows a MATLAB time domain plot of a representative impulse response.
MATLAB impulse response plot.
The delay spread of a channel is the time duration between the first and last multipath components with significant energy. If the reciprocal of the delay spread is much greater than the signal bandwidth, then the fading is called frequency flat. If that reciprocal is comparable to or less than the signal bandwidth, then the fading is called frequency selective. The MATLAB figure below shows the response of a frequency selective channel with the impulse response above.
频率选择频道频率响应。
空间
Modern wireless systems typically use beamforming to direct energy toward desired receivers and away from interferers. Beamforming requires a transceiver to use antenna arrays, giving rise to multiple-input multiple-output (MIMO) systems. Spatial channel models were developed to better represent MIMO links, since previously developed channel models did not account for array geometries and array responses. As the name suggests, these channel models enable the prediction of the angles of departure (AoD) and arrival (AoA) of signals in a wireless system. These models typically define scatterers that reflect transmitted signals to a receiver. The diagram below depicts these scatterers, also known as clusters, with two circles.
Scatterers between a transmitter and receiver.
The获奖者II频道模型是一种这样的空间频道模型（SCM），它利用集群延迟线（CDL）来模拟各个链路和多链路系统。
雷追踪
Where spatial channel models do not explicitly specify the locations of scatterers, ray tracing channel models do. They use precise building location information to generate outdoor channel models, and precise room information to generate indoor models. One output of a ray tracing analysis is an impulse response that can be used to filter an input signal.
下图显示了由通信工具箱生成的实际城市环境中的发射器和接收器之间的代表性点对点分析raytrace.function.
Urban point-to-point analysis.
为什么频道模型重要？
- They are essential to predict link performance (e.g., BER) in a single-user scenario.
- 它们对于预测多用户场景中的系统性能（例如，吞吐量，延迟）至关重要。
- 他们减少了对昂贵的渠道测量项目的需求。
Communications Toolbox,5G Toolbox™,WLAN Toolbox™,LTE Toolbox™，和相控阵系统工具箱™在所有上述类别中提供众多通道模型，适用于基于通用和基于标准的应用程序。
