Topic 4: RF Engineering.

Sub-topic 4: Channel Modelling.

The 3 most important aspects:
Channel modelling definition in time domain, channel modelling in frequency domain, and classification of channel modelling.

Summary:

A. Introduction Channel Modelling

Wireless signal propagates in the air from transmitter to receiver and depending on various situation. The transmission media is called channel model. It is a mathematical representation of the effect of a communication channel. It can represent power loss while the signal travels through wireless medium. The channel model is represented mathematically in frequency domain or time domain.

• Time domain
  In time domain, channel model is impulse response of channel medium. The calculation receiver signal is y(t) is measured by the result of convolution between transmitted signal x(t) and channel response impulse h(t) plus noise z(t).

Fig.1

• Frequency domain
  In frequency domain, channel model is Fourier transform of channel medium. The calculation receiver signal is Y(n) is measured by the result of multiplication between transmitted signal X(n) and channel response impulse H(t) plus noise Z(t).

Fig.2

B. Classification of Channel Model

1. Path loss
   Represent the power reduction of a transmitted signal through wireless medium. This channel based on the medium through free space, gas, fog, or rain.

2. Purely stochastic
   This channel models overcome the thermal noise generation and multipath fading channel that disturb the wireless travel.

• AWGN or Additive White Gaussian Noise is cannot be eliminated on the communication channel.
  

Fig. 3

• Multipath fading channel is condition when multiple signal copies of the transmitted signal up to the receiver.

Fig. 4

• Delay spread and delay profile.
  

  
  Fig. 5

• Coherence bandwidth.
  

Fig. 6

3. Spatial
   The wireless system uses beamforming to direct energy to desired receiver and away from interference and it’s using antenna arrays (MIMO).

Fig. 7

Fig. 8

4. Ray tracing
   It’s explicitly specified the location of scatters.

Fig. 9