I need to know the origin/root cause of the CEE.
e.g. We know that one of the causes is imperfect channel estimation. But I want to know what are the factors that lead to this imperfect channel estimation.
In the case of Massive MIMO where the number of a base station (BS) large than the number of single-antenna users.To estimate the channels, TDD operation with the reverse-link pilots are used.However, due to the limited coherence interval ,we use the same orthogonal pilot sequences in all cells.
the error occurs in channel estimation when the terminals in the cell transmit their pilot sequences to its BS but also their other terminals in other cells use the same pilot sequences transmit it in the same time cause what is called pilot contamination that affects the channel estimation.
In addition to Carlos' answer, I would add:
- channel frequecny offset,
- Doppler effect,
- time synchronization mismatch
among other sources of distortion. More specifically to channel estimation in multicarrier systems, in the case of scattered pilots, interpolation along time and frequency axes is required to estimate the channel over all the carriers/symbols. Most of interpolation methods induce estimation errors as well.
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