Does lteDLPerfectChannelEstimate command in LTE toolbox yields the true channel response or just an estimate?
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Yes, you've captured it well, lteDLPerfectChannelEstimate should serve as an upper bound. Doppler effects deemed "negligible" to the OFDM link performance will degrade the perfect channel estimate, but the degree of degradation should be similarly negligible.
More Answers (2)
Iain Stirling on 31 Jul 2018
lteDLPerfectChannelEstimate operates by generating an impulse train (one impulse for each OFDM symbol), passing the impulse train through the channel and performing OFDM demodulation. Therefore it yields the true channel up to any limitations imposed by OFDM:
- if the channel varies (non-zero Doppler frequency) then orthogonality is lost and inter carrier interference (ICI) results, adding noise to the channel estimate
- if the channel delay spread exceeds the length of the cyclic prefix, then this also manifests as a varying channel, again introducing ICI
The degree of "imperfection" therefore depends on the exact operating conditions. Note that the waveform of interest being passed through the same channel will also suffer the same degree of ICI.
lteFadingChannel operates solely in the time domain, combining the path gains with time-domain filters that delay the inputs according to the path delays. Therefore the channel frequency response needs to derived by performing some kind of transformation from the time to frequency domain. This has theoretical limitations when the signal is varying over time.
Do you have a specific scenario where the channel estimate from lteDLPerfectChannelEstimate is not a good fit?