Spectral Efficiency Optimization of Massive MIMO System Under Channel Varying Conditions
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Spectral Efficiency Optimization of Massive MIMO System Under Channel Varying Conditions Satyasen Panda1 Accepted: 29 October 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this paper, the performance of the cell free Massive multiple-input multiple-output (MIMO) system with realistic channel impairment conditions is discussed. The channel impairment conditions arise due to various issues like the pilot contamination, high speed user mobility, accumulated phase noise and Doppler shifts etc. At first, we provided a system model with channel aging due to Doppler shift, during uplink and downlink for channel estimation and data transmission. An optimization objective problem is formulated to improve the joint spectral efficiency during both uplink and downlink. The primary objective problem is partitioned into two different sub-problems, which are solved by a user defined joint frame allocation and user matching (JFAUM) algorithm based on efficient allocation of pilot resources and matching techniques for user clustering. Finally, the numerical results prove the improvement in spectral efficiency of massive MIMO system by using the proposed JFAUM algorithm under various practical conditions. Keywords Massive MIMO · Channel aging · Spectral efficiency · Frame allocation · User clustering
1 Introduction To match the ever increasing demand of wireless connectivity in the fifth generation (5G) era telecommunication network, Massive multiple-input multiple-output (MIMO) system is considered as a key enabling technology due to its various features. The advanced features of massive MIMO system include high energy efficiency, large spectral efficiency and simultaneous service to large number of user equipments (UEs) [1, 2]. The primary architecture of Massive MIMO system involves base station (BS) with large number of antennas, synchronously serving relatively less number of single antenna UEs in the exact frequency band. The huge difference in the BS antennas K and UE terminals M for every cell, achieves large degrees of freedom and small inter-stream interference which permits the simple designs of transmitter and receiver [3]. The large numbers of BS antennas contribute to higher array gain and spectral efficiency. The estimation of near accurate channel * Satyasen Panda [email protected] 1
Department of ECE, GITA, Bhubaneswar, Odisha, India
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state information (CSI) plays an important role in the performance of Massive MIMO system. At the BS, the imperfect CSI is mainly due to Doppler shift, pilot contamination and channel aging. The channel aging condition is caused due to the time variation of the channel as a consequence of high speed UE movement with respect to the BS [4]. The channel aging factor brings in inequality between the actual CSI and estimated CSI during training at a certain instant of time. The CSI inequality degrades the performance of Massive MIMO system with increase in the system dimension. The maximum number of UEs can
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