As the handset travels from one edge of a cell to another edge at a speed , the receiver carrier frequency shift occurs. This degrades BER compared to fixed handset (non-moving handset). The performance of mobile handset can be improved Doppler effect is compensated or nullified.
How to mitigate the Doppler effect? What are the methods used in 4G LTE ?
Mobility is simply more difficult to support. To mitigate the effects of Doppler shift, a requirement when your system is optimized for mobility, LTE keeps the number of OFDM subcarriers relatively low. This spreads the subcarrier frequencies apart as much as possible, increasing the tolerance to Doppler shift.
But you pay a price. So for instance, in 2K mode, for a given guard interval, say 1/4, the cyclic prefix duration will only be 1/8 as long as a 1/4 GI in 16K mode. A very short duration GI means that you'll begin experiencing intersymbol interference more readily, in the presence of multipath distortion.
That's why, in multicast/broadcast single frequency network (SFN) mode, tower spacing has to be so tight, in LTE-A.
This is an interesting paper which describes the use of LTE for TV broadcasting. While I disagree strongly with some of its points, especially when it comes to spectrum requirement comparisons, it does show the outcome when a scheme has to be optimized for mobility. As the economist Milton Friedman famously said, "There's no free lunch."
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5936211&tag=1
Here's another paper you might find interesting, using the active pilots more effectively than in conventional receivers. (It covers OFDM but not specifically LTE, although the same techniques ought to be applicable to LTE.) Their results seem convincing, at least with the Doppler shift they tested. The scheme might have limits in how fast channel conditions can change. I would need more study time.
Basically, the Doppler effect is caused by the user mobility, thus unavoidable in dynamic systems. Nonetheless, increasing the frequency interval between the subcarriers, e.g., in OFDM, allows a higher overall system performance for given Doppler shifts.
@AR Reddy
Data rate is same as ofdm..but ofdm/oqam allows the use of pulse shape other than rectangular having very good stop band attenuation. Hence more robust to frequency offset.
Considering these methods to mitigate the Doppler effect, for LTE terminal moving at high speed. Do these methods cater for the situation that the LTE terminal is moving (at high speed) in a straigh line towards the eNodeB? You may consider that to be the extreme Doppler effect.
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