In: Electrical Engineering
WHAT DO YOU MEAN BY DOPPLER SPREAD AND CHOREANCE TIME?
Dopler spread Bd is a measure of spectral broadening caused by the time rate of change of the mobile radio channel and is defined as the range of frequencies over which the received Doppler spectrum is essentially nonzero. When the bandwidth of the transmitted signal is much larger than the Doppler spread, the effects of the Doppler spread are negligible at the receiver.
Cohreance Time Tc is a statistical measure of the time duration over which the channel impulse response essentially remains unchanged (i.e., highly correlated). If the time interval between the signal transmissions is much greater than the coherence time, the channel will likely affect the two signal transmissions differently; otherwise, they will be affected similarly. The Doppler spread is inversely proportional to the coherence time, and we thus have the following:
Bd=1/Tc