Dear Rayi,

The attached file discusses in detail the following techniques:

AR Reddy

Dear Rayi,

Here is my personal picture on pilot decontamination. I generally divide the works on pilot mitigation/decontamination to the following 6 main groups:

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1. Pilot Reuse-less aggressive approaches

 This is in fact nothing new do not achieve a good performance.

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2. Architecture Based Solution 

2.1. Pilot Assignment protocol: a simple subcategory of this approach is the pilot assignment approach. Examples are:

Exploiting All Pilots for Interference Suppression" that benefits a network wide pilot assignment.

2.2. Protocol Redesign

Like  in the following papers where they use a modified TDD protocol where users from different cells transmit pilot sequences asynchronously according to a time-shifted protocol proposed.

• F. Fernandes, A. Ashikhmin, T. L. Marzetta, “Interfernce Reductionon Cellular Networks with Large Antenna Arrays,” IEEE InternationalConference on Communicaions (ICC), Ottawa, Canada, 2012.
• F. Fernandes, A. Ashikhmin, T. L. Marzetta, “Inter-Cell Interference inNoncooperative TDD Large Scale Antenna Systems,” IEEE Journal onSelected Areas in Communications, 31, pp. 192–201, 2013.

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3. Precoding Based Approaches

It is one of major directions and can be further classified to:

3.1. Multicell Precoding:

This is on of the interesting approaches that you can find plenty of work. An example would be the work of Ashikhmin and Marzetta where they proposed massive MIMO systems with limited collaboration between base stations and an outer multi-cellular precoding. This outer-cellular precoding

is based only on the use of large-scale fading coefficients in their papers

• A. Ashikhmin and T. L. Marzetta, “Pilot contamination precoding in multi-cell large scale antenna systems,” Proceedings of 2012 IEEE International Symposium on Information Theory (ISIT), pp. 1137–1141,2012.
• Interference Reduction in Multi-Cell Massive MIMO Systems I: Large-Scale Fading Precoding and Decoding
• and many others

3.2. Multi Layer Precoding

Here the authors use two or more layers of precoding to cancel both intra and inter cell interference. Again there are many papers.

3.3. Designing  the precoder for pilot decontamination

It has some overlap with multicell precoding in some sense like the work of Jubin Jose at

• Pilot Contamination and Precoding in Multi-Cell TDD Systems

But there other work, I also have a beautiful paper that comes by the next year.

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4. RMT base approaches:

The main idea is to use RMT to remove the pilot contamination or mitigate its effect like the work of Ralf R. Muller

• Blind Pilot Decontamination

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5. Combinatorial Approaches

They combine some of the above methods, also some techniques outside the domain to fight against the contamination. Like using 3D MIMO to remove pilot contamination.

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6. Other Approaches

There are other approaches to follow that I did not talked about them.

thank you Meysam Sadeghi sir for your valuable refrence