In most modern CDMA, OFDM communication systems, there are means of helping their receivers to track and compensate Doppler effects, such as AGC resetting, etc.
My question is, what would happen if the receiver cannot track and compensate the Dopplers?
Dear,
The occurrence of Doppler shift makes the wireless channel fast-time variant and frequency selective. As well as affecting synchronization, channel estimation and data recovery. This destroys the orthogonally in data transmission making ICI appear again between the sub-carriers. The Doppler Effect is tremendously important and one of the most distinct phenomena when dealing with multicarrier access communication systems where a small amount of frequency variation can cause a significant degradation in overall performance.
I agree with Khalid. The papers which address Doppler shift correction would be your best bet to determine what might happen without Doppler shift accommodation. There's a lot available on the subject. For instance,
http://www.wirelesscommunication.nl/reference/chaptr05/ofdm/doppler/doppler.htm
for OFDM and a weird sort of hybrid CDMA, or
https://www.researchgate.net/publication/224724031_Space-Doppler_parameter_estimation_for_space-time-Doppler_reception_in_time-varying_multipath_DS-CDMA_systems
for direct sequence CDMA.
The problem should be more acute in OFDM, especially in the higher modes of OFDM (such as 8K on up), simply because the subcarriers are so close to one another. Intuitively, you can see that even relatively minor Doppler shift would result in ambiguity of the subcarrier, if Doppler were not compensated. This is why, for mobile applications, you will see OFDM used in 4K or 2K modes. It's a tradeoff. Faster mobility, but less tolerance of ghost images.
Conference Paper Space-Doppler parameter estimation for space-time-Doppler re...
Doppler shift is simply a frequency shift of the received signal due to the relative TX and RX platform motion. It is no different than a LO offset and can be compensated/corrected in the same manner as an LO offset or LO drift is handled. Analytically determined the expected relative velocity range between the transmitter and the receiver. and the expected accelerations of the same to determine the expected Doppler induced frequency shift and add that to the LO frequency drifts and errors.
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