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Realization of New Radio 5G-IoT Connectivity Using mmWave-Massive MIMO Technology
Published in Parag Chatterjee, Robin Singh Bhadoria, Yadunath Pathak, 5G and Beyond, 2022
Priyanka Pateriya, Rakesh Singhai, Piyush Shukla, Jyoti Singhai
Precoding is a signal processing technique that uses the CSI at the transmitting end to maximize the link performance of the communications system. Downlink transmission performance is dependent on CSI at the transmitter and the corresponding precoding technique used. Where the CSI is well known at the transmitting end, precoding can reduce interference and enhance the achievable sum rates. The multiple-antenna system with the appropriate precoding method increases the spectral efficiency and energy efficiency [13, 21–28] of the communications system. There are three significant precoding techniques, which are discussed in the next sections.
Advances in Millimeter Wave Propagation for 5G Mobile Communication Systems
Published in Athanasios G. Kanatas, Konstantina S. Nikita, Panagiotis Mathiopoulos, New Directions in Wireless Communications Systems, 2017
Massive MIMO is also acknowledged as an emerging technology for 5G networks. The Massive MIMO and mm-Wave technologies provide vital means to resolve many technical challenges of the future wireless networks, and they can be seamlessly integrated with the current networks and access technologies. The concept of Massive MIMO is based on the use of a very large number of antenna elements to multiplex messages for several users. The main principle of operation is that the Massive MIMO antennas can focus the radiated energy toward desired directions while minimizing intra- and inter-cell interference, and enhancing significantly the spectral and energy efficiency. In a rich scattering environment, these performance gains can be achieved with simple beamforming strategies, such as maximum ratio transmission (MRT) or zero forcing (ZF) (Bogale and Le 2016). Another critical issue in mm-Wave MIMO is to cope with the existing hardware constraints due to the high bandwidth and operational frequencies. Therefore, there is the need for hybrid precoding, which is a combination of analog and digital processing. Analog beamforming solutions are mainly based on controlling the phase of the signal transmitted by each antenna, but their performance is relatively low. In order to achieve larger gains, hybrid analog/digital processing strategies are proposed. The use of precoding techniques on an antenna array can be used to form a beam toward the receiver or even multiple beams in a multiuser scenario. The aim of precoding is to suppress the cochannel interference between the users, which communicates at the same frequency. More specifically, in precoding techniques, the symbols that are to be transmitted are processed in order to minimize the interference, for example, maximizing the signal-to-noise-interference ratio (SNIR) (Kourogiorgas et al. 2016). A common problem that arises is the channel state information (CSI) at the base stations, especially in case of Massive MIMO where the number of elements of the channel matrix is very large. The tasks of channel estimation and precoder extraction for the large channel matrix become cumbersome. Efficient ways to exploit correlations and sparsity in order to decompose the complicated task must be developed and evaluated. Moreover, it is unrealistic to assume perfect CSI to the transmitter, therefore the effects of partial CSI in the Massive MIMO transmitter must be considered. Assuming that all the cells were served by a single base station, as the CSI would be known at this base station, the intra-cell interference could be resolved. However, as there are many base stations there would be inter-cell interference with the fundamental problem that the one base station does not have the appropriate knowledge of CSI of the adjacent cells. The problem may be solved through the coordination of the different base stations. It must be noted that the interference between the different cells strongly depends on the frequency reuse factor.
Scanning the Issue
Published in IETE Journal of Research, 2023
Shiban K Koul, Arun Kumar, Ranjan K Mallik
The paper entitled “A Transmit Antenna Selection based Energy Harvesting MIMO Cooperative Communication System” considers a cooperative wireless system with multiple antennas at the source. A multi antenna relay equipped with a power splitter is introduced between the source and destination. It utilizes the energy from the received signal for amplification and transmit it to the destination. The linear precoding techniques such as zero forcing (ZF) and minimum mean square error (MMSE) are used to reduce the interference. Two antenna selection techniques viz. norm-based antenna selection (NBAS) and received signal-to-noise ratio (SNR) based antenna selection (RSBAS) are compared. It has been shown that the BER is improved with the reduction in the distance between source and relay for the given value of energy harvesting efficiency.
Performance analysis of joint transmit antenna selection and user scheduling for massive MIMO systems
Published in Cogent Engineering, 2021
Fikreselam Gared Mengistu, Gizachew Worku
In multi-user system, linear precoding techniques are implemented to reduce the effect of inter-user interference. When the number of antennas is large as compared to the number of users, linear precoding system in the downlink and linear detection in the uplink result in optimal performance (Ngo, 2015). In this paper, we implement three conventional precoding techniques which are MMSE, MRT and zero forcing (ZF) precoding. The linear precoder apply linear processing on the users’ data before transmission so that inter-user interference becomes negligible or totally canceled in the desired spatial direction. Each user symbol is multiplied by its respective weight vector ; then the weighted symbols are added together to form a transmitted vector (Ngo et al., 2013).
Spectral Efficient Precoding Design for Multi-cell Large MU-MIMO System
Published in IETE Journal of Research, 2022
The precoding is a signal processing scheme, which is performed at the BS prior to the transmission of the signal. The process of precoding is necessary to lower the interference between the UEs. The transmitted signal is obtained by the multiplication of the precoding matrix with the information data vector. The precoding matrix is designed with the acquired channel estimates at the BS through the TDD mode of operation. To diminish the effect of intracell interference, the precoding schemes like ZF, MRT, MMSE are investigated for downlink [11,15,31] and receive combining schemes such as MRC, ZF, MMSE for the uplink [11,17]. The linear detection schemes are investigated in [32,33] and the non-linear precoding methods such as dirty paper coding (DPC) and vector perturbation (VP) [34] provide improved performance with greater complexity of implementation. However, linear detection and precoding methods become nearly optimal when the antennas at the base station increases [11]. In [13], authors derive rate bounds for ZF, MRT, and MMSE detectors and analyze the energy and spectral efficiency assuming an uplink single-cell scenario. The utilization of precoding methods in large MIMO systems can improve the spectral efficiency of the system [35]. Authors in [35] propose a hybrid precoding scheme to lower the complexity at the BS of a mmWave Massive MIMO system. The proposed precoding scheme provides better spectral efficiency as compared to conventional orthogonal matching pursuit (OMP) based hybrid precoding technique [35]. Authors in [36] adopted a ZFBF precoding scheme to enhance the spectral efficiency in the single-cell downlink multiuser non-orthogonal multiple access (NOMA) system. The authors observed that the NOMA-ZFBF technique provides better sum rates in comparison to TDMA-ZFBF technique [36].