A Rayleigh fading channel
1, the concept of
After passing through the wireless channel signal, an amplitude of the signal is random, i.e., "fading" and the envelope Rayleigh distribution, such a channel is called "Rayleigh channel."
2, the applicable conditions
Rayleigh channel is only applicable to the absence of the direct signal from the transmitter to the receiver, that is to say after the emission, refractive or diffractive reach the receiver.
This channel model can describe the ionospheric and tropospheric emitted HF channel, and building dense urban environments.
If the transmitter and receiver is present direct channel, then the channel model is used to describe the Rice fading channel.
Rayleigh fading effect of small scale fading belongs, as it is always superimposed on the shadow, the attenuation effects of large-scale fading.
3, Rayleigh distribution
When the two components form a two-dimensional vector of random independent, when a normal distribution with the same variance, the magnitude of a vector was a Rayleigh distribution.
Rayleigh distribution probability density function is:
Figure 1: a probability density function of the Rayleigh distribution
4, Doppler shift
Size of the channel fading speed and the relative velocity of the transmitter and the receiver about the relative movement caused by the Doppler frequency shift of the received signal. In considering the channel model must consider the relative velocity of the sender and receiver side.
5, the magnitude through rate (LCR, levelcrossing rate)
A measure of how fast fading. LCR amplitude signal fading is given how often a certain threshold crossing, usually calculated in the forward direction crossing. Rayleigh fading as LCR
Which is the maximum Doppler shift, normalized rms signal threshold for signals:
Second, the Rice fading channel
1, the concept of
If the signal received in addition to the signal scattered by the catadioptric the like, there reaches the receiver directly from the transmitter (e.g., directly from the satellite receiver reaches the ground), then the total signal strength points obey Bryce, so Rice called fading.
Rice channel when the direct wave signal exists between the mobile station and the base station, i.e. there is a main path, the received signal transmitted by the main path of a stable amplitude Ak and a phase phi] [kappa, remaining multipath propagation over the signal remains as " Rayleigh fading probability model "the.
2, Rice distribution
Rice distribution (Ricedistribution or Rician distribution) is a continuous probability distribution, the probability density function is:
Where I0 is the modified Bessel function of the first kind of order zero (Bessel function). At that time, Rice distribution reduces to a Rayleigh distribution.
Third, the Gaussian channel
1, the concept of
Channel is a Gaussian channel parameters constant, means a signal superimposed a Gaussian white noise after passing through the channel, the channel such as: satellite communications, fiber channel, a coaxial cable.
