A Systematic Review of NOMA Variants for 5G and Beyond

With the fast expansion of the Internet of Things (IoT), there is an exponential need for mobile intelligent terminals .However, the connectivity of large-scale intelligent terminals is constrained by increasingly restricted spectrum resources. To address this issue, non-orthogonal multiple access (NOMA) technology, which can handle more users with less resources, is predicted to enable future wireless networks beyond 5G,., 6G, to give huge terminal access. The fundamental idea behind NOMA is to superimpose signals from numerous users on the same time-frequency resource prior to transmission. At the receiver, serial interference cancellation (SIC) technology is used to reduce interference among users. In this  review paper  we discusses the principles of the strong candidate Non-Orthogonal Multiple Access (NOMA) approach, as well as how it can best match the requirements of the Fifth Generation (5G) requirements in practical applications.  

Robust MMSE Precoding Strategy for Multiuser MIMO Relay Systems with Switched Relaying and Side Information

In this work, we propose a minimum mean squared error (MMSE) robust base station (BS) precoding strategy based on switched relaying (SR) processing and limited transmission of side information for interference suppression in the downlink of multiuser multiple-input multiple-output (MIMO) relay systems. The BS and the MIMO relay station (RS) are both equipped with a codebook of interleaving matrices. For a given channel state information (CSI) the selection function at the BS chooses the optimum interleaving matrix from the codebook based on two optimization criteria to design the robust precoder. Prior to the payload transmission the BS sends the index corresponding to the selected interleaving matrix to the RS, where the best interleaving matrix is selected to build the optimum relay processing matrix. The entries of the codebook are randomly generated unitary matrices. Simulation results show that the performance of the proposed techniques is significantly better than prior art in the case of imperfect CSI.

Quantifying Potential Energy Efficiency Gain in Green Cellular Wireless Networks

Conventional cellular wireless networks were designed with the purpose of providing high throughput for the user and high capacity for the service provider, without any provisions of energy efficiency. As a result, these networks have an enormous Carbon footprint. In this paper, we describe the sources of the inefficiencies in such networks. First we present results of the studies on how much Carbon footprint such networks generate. We also discuss how much more mobile traffic is expected to increase so that this Carbon footprint will even increase tremendously more. We then discuss specific sources of inefficiency and potential sources of improvement at the physical layer as well as at higher layers of the communication protocol hierarchy. In particular, considering that most of the energy inefficiency in cellular wireless networks is at the base stations, we discuss multi-tier networks and point to the potential of exploiting mobility patterns in order to use base station energy judiciously. We then investigate potential methods to reduce this inefficiency and quantify their individual contributions. By a consideration of the combination of all potential gains, we conclude that an improvement in energy consumption in cellular wireless networks by two orders of magnitude, or even more, is possible.Comment: arXiv admin note: text overlap with arXiv:1210.843

Performance of Two-Hop DS-CDMA Systems Using Amplify-and-Forward Protocol over Different Fading Channels

This study analyses the performance of directsequence code division multiple access (DS-CDMA) based on two-hop amplify-and-forward protocol over Weibull symmetric fading channels as well as Rayleigh/Rician, Rician/Rayleigh asymmetric fading phenomenas. We investigate the bit-error rate (BER) of the considered system using multiple relays by considering the effect of Weibull fading parameter and Rician K factor on the system performance. Our simulation results demonstrate the positive impacts of the value of fading parameter, Rician K factor and increasing number of relay nodes on BER performance. It is also confirmed that the Rician K factor is more effective on the system performance over Rician/Rayleigh fading channels in comparison with Rayleigh/Rician fading environment