138 Int. J. Wireless and Mobile Computing, Vol. 19, No. 2, 2020 Copyright © 2020 Inderscience Enterprises Ltd. Enhancing uplink/downlink performance of massive MIMO system using time-shifted pilot signal transmission with pilot hopping Amrita Ruperee* and Shikha Nema Department of Communication Engineering, Usha Mittal Institute of Technology, Mumbai, Maharashtra, India Email: amritaruperee@gmail.com Email: shikhanema@gmail.com *Corresponding author Abstract: In Massive Multiple Input Multiple Output (MIMO) system, pilot signals are reused to accommodate exponential rise in user density. This contaminates the channel estimation for the intended user and affects the system performance. In the proposed Time-Shifted Pilot signal Transmission with Pilot Hopping (TSPTPH) system, pilot signal transmission is overlapped with downlink data transmission and pilot signal hopping is performed in each coherence interval. Hopping is achieved by switching user to a new pilot signal, this results in random change in interfering users. This changes the large-scale fading coefficient , which is a function of radial distance between base station and user and thus improves the system performance. Proposed system enhances the uplink and downlink signal to interference plus noise ratio and data rate by estimating the channel with minimum mean square error estimation and reduces the uplink signal to noise ratio for data transmission for normalised spectral efficiency with rising number of antennas at the base station. Keywords: channel estimation; pilot hopping; large-scale fading; pilot contamination; pilot sequence; small scale fading; transmission slot. Reference to this paper should be made as follows: Ruperee, A. and Nema, S. (2020) ‘Enhancing uplink/downlink performance of massive MIMO system using time-shifted pilot signal transmission with pilot hopping’, Int. J. Wireless and Mobile Computing, Vol. 19, No. 2, pp.138–153. Biographical notes: Amrita Ruperee received her bachelor’s degree in Electronics Engineering from Govt. College of Engineering, Ujjain, MP, India in 1991, MTech in Digital Communication from MANIT in 2000, Bhopal, MP, India and completed PhD in the area of Wireless Communication from SNDT University, Mumbai, India. With more than 25 years of teaching experience, she is currently working as an Associate Professor in Department of Electronics and Telecommunication Engineering at Vidyavardhini’s College of Engineering and Technology, Vasai, Mumbai, India. Her research areas include mobile communication, wireless networks and wireless sensor network. Shikha Nema received Bachelor of Engineering in Electronics, MTech in Digital Communication and PhD from MANIT, Bhopal, MP, India in 1994, 2004 and 2010 respectively. With more than 16 years of teaching and 4 years of industrial experience, she is currently working as Professor & Head, Electronics & Communication Engineering at Usha Mittal Institute of Technology, Mumbai, India. Her research areas include wireless communication and optical communication. She has more than 50 publications to her credit at national and international level in reputed conferences and journals. 1 Introduction Wireless communication expanse is rising exponentially for the last 20 years. To meet the requirements of increased number of users, available frequency spectrum is reused in the neighbouring cells. This causes inter-cell interference, and thus constrains the quality of service provided to the users. Interference and fading are the two main challenges that must be given consideration while designing the wireless communication system. Fading restricts the coverage area and reliability of communication link while interference limits the re-usability of spectral resources such as time, frequency and codes. Introduction of Multiple Input and Multiple Output (MIMO) technology in cellular systems not only improves the data rate but also provides link reliability. In MIMO system, multiple transmitter/receiver antennas are used to transmit multiple data streams in parallel, which is referred to as spatial multiplexing. Though