A novel approach to enhancing spectral efficiency in massive MIMO using optimal pilot reuse factor and receive combining techniques
Nirav D. Patel1 and Vijay K. Patel2
Assistant Professor, Department of Electronics and Communication Engineering,Government Engineering College, Modasa, Gujarat Technological University, Ahmedabad, Gujarat,India1
Professor, Department of Electronics and Communication Engineering,Ganpat University, Mehsana, Gujarat,India2
Professor, Department of Electronics and Communication Engineering,Ganpat University, Mehsana, Gujarat,India2
Corresponding Author : Nirav D. Patel
Recieved : 20-May-2024; Revised : 23-June-2025; Accepted : 25-June-2025
Abstract
Current and future wireless applications demand high data rates, which can be achieved through wider bandwidths. However, the available bandwidth is inherently limited and cannot be expanded beyond physical constraints. Therefore, improving the efficiency of the available spectrum—referred to as spectral efficiency (SE)—is essential. Massive multiple input multiple output (MIMO) systems operating with time division duplexing (TDD) are considered a promising solution for enhancing SE. A critical factor influencing SE is the accuracy of channel state information (CSI), which can be obtained through pilot-based channel estimation methods. While assigning orthogonal pilots to each mobile station (MS) is theoretically ideal for improving CSI accuracy and SE, it is not practically feasible due to limited resources. To reduce pilot overhead in transmission frames, pilot reuse is employed, where multiple MSs share the same pilot. However, both extremely low and high pilot reuse factors (PRFs) fail to optimize SE, making it essential to determine the optimal PRF under given system constraints. The receive combining method also significantly impacts SE and is closely tied to the channel estimation approach. The combining vector is used to extract relevant information from the received signal, and the optimal PRF may vary depending on the chosen combining method. Rician fading is adopted in this study as a realistic channel fading model for evaluating SE performance and results are also compared with the Rayleigh fading model for benchmarking. Minimum mean square error (MMSE) is selected for channel estimation. The PRFs considered in the analysis are 1, 2, 4, 8, and 16, while the receive combining techniques analyzed include multi-cell MMSE (M-MMSE), single-cell MMSE (S-MMSE), regularized zero-forcing (RZF), zero-forcing (ZF), and maximum ratio (MR). The resulting SEs are 103, 71.7, 58.2, 58.2, and 18.4 bits/sec/Hz/cell, respectively, using M-MMSE (with PRF = 4), S-MMSE (PRF = 2), RZF (PRF = 2), ZF (PRF = 2), and MR (PRF = 1). These results demonstrate that selecting the optimal PRF for a given receive combining method yields significantly better SE compared to arbitrary PRF values.
Keywords
Spectral efficiency, Massive MIMO, Pilot reuse factor (PRF), Rician fading, Channel state information (CSI), Minimum mean square error (MMSE).
Cite this article
Patel ND, Patel VK. A novel approach to enhancing spectral efficiency in massive MIMO using optimal pilot reuse factor and receive combining techniques. International Journal of Advanced Technology and Engineering Exploration. 2025;12(127):990-1008. DOI : 10.19101/IJATEE.2024.111100841
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