A. Signal fading due to Doppler shift in the channel
B. Temporary failure of message transfer
C. Large coherence time of the channel as compared to the delay constraints
D. All of the mentioned
I had been asked this question by my college director while I was bunking the class.
This interesting question is from Modulation Performance in Fading and Multipath Channels in division Modulation Techniques for Mobile Radio of Wireless/Mobile
Explanation: Doppler spread refers to signal fading due to Doppler shift in the channel. It is a measure of spectral broadening caused by time rate of change of the mobile radio channel.