26th February 2006, 21:49 #1
Member level 4
doppler shift in ofdm
i have question if the mobile channel cause a frequency modulation of the subacarriers in an OFDM based syste?
And i want to know what is the physical explanation of the Doppler shift from the communications point of view?
26th February 2006, 21:49
28th February 2006, 07:53 #2
Advanced Member level 3
doppler shift ofdm
It makes a frequency shift of the subcarriers. If OFDM is used that is normally corrected within the frequency/phase adjustment. There is only minor effect that the frequency shift is very little less for the lower subcarrier numbers than for the higher numbers.
I remember that a connection to a spacecraft was lost because these difference was not taken into account.
For OFDMA this effect is more important. Then the frequency shifts of interleaved subcarriers from different mobile stations are different. This shifts violate the orthogonality of the subcarriers and the interstation noise increases. I expect that the base stations for 802.16e have mobile station individual frequency corrections.