## What is/are Pilot Decontamination?

Pilot Decontamination - Then, the pilot assignment optimization is mapped to the Max k-Cut problem, and a heuristic algorithm is exploited to realize pilot decontamination.^{[1]}In order to achieve the capacity results, spatial (de)spreading based on the second-order channel statistics plays a pivotal role in terms of pilot decontamination and interference suppression.

^{[2]}The more pilot slots available in superimposed pilot (SIP) arrangement compared to the conventional time-multiplexed pilot (TMP) arrangement allows higher amount of generatable orthogonal pilots; therefore, SIP arrangement have recently gained significant attentions for pilot decontamination.

^{[3]}By exploiting the pilot decontamination feature of R-TDD, the achievable rates of primary/secondary systems can be significantly boosted, compared to the underlay spectrum sharing with C-TDD.

^{[4]}In this paper, we propose a pilot decontamination method based on a spatial filter, which exploits the spatial sparsity of massive MIMO channels.

^{[5]}Aiming at the drawbacks of the weighted graph coloring based pilot decontamination (WGC-PD) algorithm, the pilot assignment ignores the users of lower potential pilot contamination, which allocates the pilot of lower interference for the user of higher potential pilot contamination sequentially, and a joint power control and pilot assignment algorithm is proposed.

^{[6]}The second algorithm for pilot decontamination utilizes the idea of pseudo-random codes in which orthogonal pilot are assigned to different cells.

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