Can pilot contamination be neglected, with orthogonal sequences allocated (feasible since there are only tens of active users)?

Or does it still need to be considered as an inter-user interference? ]]>

1. Inter-cell interference

2. Noise in the channel

Does it also mean there is no way to know which pilot signal arrives first at the BS?

Just thinking about it.

]]>Is it possible for each pilot signal to have a unique signature…..

]]>You can find examples of how to compute the coherence time and coherence bandwidth in Fundamentals of Wireless Communications, which is freely available here: https://web.stanford.edu/~dntse/wireless_book.html

You can also find a detailed explanation in the book “Fundamentals of Massive MIMO” and a short description in the book “Massive MIMO Networks”.

]]>http://www.diva-portal.org/smash/get/diva2:1049059/FULLTEXT02.pdf

Its dimensionality is the product of the coherence time and the coherence bandwidth. You can check out Chapter 2 in “Fundamentals “Fundamentals of Massive MIMO” or “Massive MIMO Networks” for details on how to compute these parameters in different scenarios. I think Fundamentals of Wireless Communications also contain discussions about this.

The covariance matrix of a random channel h is E{(h-E{h})(h-E{h})^H}, where E{} stands for expectation.

]]>The number of antennas does not affect the required number of pilots, if we use TDD and channel reciprocity.

]]>I would only like to inquire what is specific for Massive MIMO systems? Pilot contamination can occur in any cellular system. So, is the only difference the limited number of orthogonal pilot signal due to the massive antenna array?

Thank you ]]>

The potential benefit of having random pilots is that you can “share” the pilot contamination between the users, so that everyone get an equal share on average. However, since cell-edge users are more sensitive to pilot contamination than cell-center users, you might want to coordinate the pilot allocation across cells instead of randomize it. In that sense, random pilots is the baseline scheme that any “smart” scheme should be able to beat.

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