Contents
12.3. Doppler spread and coherence time are parameters that describe the frequency-dispersion nature of the mobile channel, and their values with respect to the transmitted signal bandwidth Bs and the symbol duration (period) Ts can help determine if the channel is experiencing fast fading or slow fading.
How does Doppler shift cause fading?
In the case of the Doppler shift effect, fading is due to multipath propagation. In multipath propagation, the signal reaches the receiver by two or more paths. A potential effect is fading due to destructive interference between phase-shifted signals arriving from different directions.
What are the causes of fast and slow fading?
Wireless Communications Fast fading and slow fading are considered as small-scale fading. Frequency dispersion due to Doppler spreading causes the transmitted signal to undergo either fast fading or slow fading, where the high Doppler spread gives rise to fast fading and the low Doppler spread brings about slow fading.
How do I fix my Doppler shift?
The Doppler effect can be corrected for a given sky direction by resampling the detected signal with an average frequency equal to the source one, but phase modulated so to compensate for phase modulation due to observer motion.
Which needs re sending of signal?
1. Which needs re-sending of signal? Explanation: Error detection needs re-sending of data.
What causes the fading effect of Doppler spread?
Explain fading effects due to Doppler spread. Depending on how rapidly the transmitted baseband signal changes as compared to the rate of change of the channel, a channel may be classified either as a fast fading or slow fading channel.
How is Doppler spread and coherence time related?
• Doppler spread is expressed in the following formula. As mentioned, doppler spread is defined as maximum doppler shift (fm). • The coherence time of the channel is the inverse of the Doppler spread. • It is the measure of the speed at which channel characteristics change.
Is the coherence time of a slow fading channel long?
In the previous sections, we have dealt with the ergodic capacity to analyze the transmission capability of MIMO fast fading channels. In slow fading channels, the coherence time of the channel is long and encoding can be performed only over a single or a few fading states (e.g., time diversity).
Why does a fast fading signal cause dispersion?
Fast Fading: In a fast fading channel, the channel impulse response changes rapidly within the symbol duration. That is, the coherence time of the channel is smaller than the symbol period of the transmitted signal. This causes frequency dispersion due to Doppler spreading, which leads to signal distortion.