Comparison of Orthogonal vs. Union of Subspace Based Pilots for Multi-Cell Massive MIMO Systems

Chowdhury, A and Sasmal, P and Murthy, CR (2020) Comparison of Orthogonal vs. Union of Subspace Based Pilots for Multi-Cell Massive MIMO Systems. In: 21st IEEE International Workshop on Signal Processing Advances in Wireless Communications, SPAWC 2020, 26-29 May 2020, Atlanta; United States.

PDF iee_int_wor_sig_pro_adv_wir_com_2020_2020.pdf - Published Version Restricted to Registered users only Download (882kB) | Request a copy

Abstract

In this paper, we analytically compare orthogonal pilot reuse (OPR) with union of subspace based pilots in terms of channel estimation error and achievable throughput. In OPR, due to the repetition of the same pilot sequences across all cells, inter-cell interference (ICI) leads to pilot contamination, which can severely degrade the performance of cell-edge users. In our proposed union of subspace based method of pilot sequence design, pilots of adjacent cells belong to distinct sets of orthonormal bases. Therefore, each user experiences a lower level of ICI, but from all users of neighboring cells. However, when the pilots are chosen from mutually unbiased orthonormal bases (MUOB), the ICI power scales down exactly as the inverse of the pilot length, leading to low ICI. Further, as the number of users increases, it may no longer be feasible to allot orthogonal pilots to all users within a cell. We find that, with limited number of pilot sequences, MUOB is significantly more resilient to intra-cell interference, yielding better channel estimates compared to OPR. On the other hand, when the pilot length is larger than the number of users, while OPR achieves channel estimates with very high accuracy for some of the users, MUOB is able to provide a more uniform quality of channel estimation across all users in the cell. We evaluate the fairness of OPR vis-�-vis MUOB using the Jain's fairness metric and max-min index. Via numerical simulations, we observe that the average fairness as well as convergence rates of utility metrics measured using MUOB pilots outperform the conventional OPR scheme. © 2020 IEEE.

Item Type:	Conference Paper
Publication:	IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC
Publisher:	Institute of Electrical and Electronics Engineers Inc.
Additional Information:	The copyright of this article belongs to Institute of Electrical and Electronics Engineers Inc.
Keywords:	Cells; Channel estimation; MIMO systems; Signal processing, Achievable throughputs; Channel estimation errors; Convergence rates; Intercell interference; Intra-cell interference; Orthonormal basis; Pilot contaminations; Union of subspaces, User experience
Department/Centre:	Division of Electrical Sciences > Electrical Communication Engineering
Date Deposited:	11 Nov 2020 09:52
Last Modified:	11 Nov 2020 09:52
URI:	http://eprints.iisc.ac.in/id/eprint/66621

Actions (login required)

View Item