Explain me the Time Diversity concept

[urwelcome]

Mobile user moving with speed of 30km/h have more time Diversity as compared to one moving with 3km/h.

I don't understand how this is analytically,I mean how does this relate with coherence time or coherence bandwidth.

Thanks a lot!

 

[amihomo]

Re: Time Diversity

coherence time is related to the doppler frequency, which is related to the relative speed of the TX and RX.

(Δt)c = 1/fD

where (Δt)c and fD denote the coherence time and maximum doppler frequency , respectively.

fD is directly related to the speed of vehicle with the following formula (if i remember correctly):

fD=f0.v/C≈1080×f0(MHz) / v(Km/h)
So if a mobile user moves faster , the doppler freq. is greater and the coherence time will be smaller , which means that it has more time diversity.

for more information refer to Proakis's Digital Communications 4th ed. book


i hope it helps you

regards

 

[farzad_m]

Time Diversity

channel impulse response for the faster one varies faster so you have lower coherence time and consequently more diversity