PASS‐NOMA: Waveguide Channel‐Aware User Pairing With Adaptive SIC

Massive-Multi Input and Multi Output (MIMO) antenna system is considered as the key technology to improve both spectral efficiency (SE) and energy efficiency (EE) for 5G systems. Where pilot contamination and inter-cell interference have been considered as basic limiting factors to achieve high data rate. These parameters will saturate the SE and truncate to a constant value. In this work, we explore the effective evaluation of SE and EE of the M-MIMO antenna system with optimal users. In this work, we basically considered linear processing algorithms such as zero-forcing (ZF), maximum ratio combing (MRC) and minimum mean square error (MMSE) for the analysis SE for the both single and multi-cell scenario in M-MIMO systems. In this paper, we provide a platform to improve the SE and EE with a variation of base station (BS) antennas M and pilot reuse factor λ. We also derived the explicit and exact expressions for the analysis of SE and EE with perfect and imperfect channel state information (CSI). Which are very tight and tractable approximations in the prospective of realistic system scenario. We mainly focused on the asymptotic limit of SE and also obtain optimal user terminals K. It has been noticed that the SE performance greatly depends on the receiving combined scheme. We compared the simulation results for SE based the parameters such as varying antennas at the BS M, optimal UTs K and finally pilot reuse factors λ=4 and λ=7. Here, the simulation results of the BS antennas per-user (M/K) and optimal users K, highly depend on the receive technique and the BS antennas M. We also demonstrated the simulation results with the variation of per-user SE versus the BS antennas. The simulation results were performed by using Matlab 2015b.

Intelligent Reflecting Surfaces (IRSs), comprised of numerous reflecting elements, offer a promising solution for enhancing wireless communication. By manipulating the wireless propagation environment, IRSs can mitigate the effects of non-line-of-sight propagation and extend signal coverage. This paper focuses on the performance of an IRS-aided wireless communication system when the direct link between the Base Station (BS) and receiver is obstructed, relying solely on the IRS for signal transmission, by using the pilot transmission and channel least square method in calculation of the received signal. We investigate the impact of IRS element components (effective capacitance , bottom layer inductance , top layer inductance , and effective resistance R) and the frequency of the incident signal on system performance. These components significantly have an influence on reflection coefficients, where higher values of them leads to an increase in the amplitude response of reflection coefficient and hence, stronger reflected signals. The variation of those components can adjust the phase response of the reflected signal. In this paper, assessment of performance of IRS-aided 6G wireless communication system for single user is studied. The received power, SNR, and the spectral efficiency were estimated and used as metrics for the system performance. It has been cleared that the received power, SNR and the spectral efficiency are increased with increasing the size of IRS and transmitted power for both of the strongest and weakest configuration. Also, it has been shown that the received power, SNR and the spectral efficiency are decreased with increasing the AP-IRS horizontal distance. Higher degree of bandwidth improves the received power and the spectral efficiency whereas it reduces the SNR. The performance comparison between the spectral efficiency of system with IRS and without IRS at different values of transmitted power and bandwidth is introduced. It is shown that, at bandwidth = 5 MHz, the system with IRS achieves nearly 3 times the spectral efficiency of the system without IRS and at bandwidth = 25 MHz, the system with IRS achieves nearly 14 times the spectral efficiency of the system without IRS. Also, at transmitted power = 0.5 Watt, the system with IRS achieves nearly 5 times the spectral efficiency of the system without IRS and at transmitted power = 2.5 Watt, the system with IRS achieves nearly 5.7 times the spectral efficiency of the system without IRS. So, The IRS can be used and aided in improvement of the spectral efficiency in 6G wireless communication. The evaluation of performance of IRS-aided wireless communication system in a multi-user scenario is discussed. The data rate, spectral and energy efficiency were evaluated by using four different methods (power method, uniform metal surface method, IRS with best pilot method and with the case of no IRS). It has been shown that the received power method and the best pilot method give the best data rate, spectral and energy efficiency at any value for each of the transmitted power, the bandwidth, the size of IRS and AP-IRS horizontal distance and consequently, enhance the performance of IRS- aided 6G wireless communication system.

Cell-free (CF) massive multiple-input multiple-output (MIMO) has recently emerged as a highly promising technology for supporting future six-generation (6G) networks, owing to its unique ability to provide high data rates and reliable connectivity. However, a primary challenge in CF massive MIMO is severe inter-user interference, which is caused by densely located user equipments (UEs) and the presence of imperfect channel state information (CSI). Fortunately, the rate-splitting (RS) strategy offers significant benefits by enabling partially interference decoding, thereby greatly enhancing overall system performance. In this paper, we investigate the performance of uplink RS in CF massive MIMO systems. Considering the inevitable channel estimation errors caused by pilot contamination, we first derive a novel closed-form expression for characterizing spectral efficiency (SE). Moreover, we propose two innovative decoding strategies tailored to the 6G scenario, highlighting their role in enhancing the interference management capabilities of RS, while balancing decoding performance with computational complexity. To ensure successful decoding of each sub-message to the greatest extent possible, we devise an optimization-based power control scheme to maximize the minimum SE of the sub-messages, and propose a low-complexity scheme for comparative analysis. Additionally, we investigate the total energy efficiency (EE) of the system and propose a power control scheme for maximizing EE by exploiting fractional programming (FP) theory. Simulation results corroborate our theoretical expressions and demonstrate that both RS and the proposed power control schemes can significantly improve both SE and EE.

In this paper, we propose a novel hybrid user pairing (HUP) scheme in multiuser multiple-input single-output non-orthogonal multiple access networks with simultaneous wireless information and power transfer. In this system, two information users with distinct channel conditions are optimally paired while energy users perform energy harvesting (EH) under non-linearity of the EH circuits. We consider the problem of jointly optimizing user pairing and power allocation to maximize the overall spectral efficiency (SE) and energy efficiency (EE) subject to user-specific quality-of-service and harvested power requirements. A new paradigm for the EE-EH trade-off is then proposed to achieve a good balance of network power consumption. Such design problems are formulated as the maximization of non-concave functions subject to the class of mixed-integer non-convex constraints, which are very challenging to solve optimally. To address these challenges, we first relax binary pairing variables to be continuous and transform the design problems into equivalent non-convex ones, but with more tractable forms. We then develop low-complexity iterative algorithms to improve the objectives and converge to a local optimum by means of the inner approximation framework. Simulation results show the convergence of proposed algorithms and the SE and EE improvements of the proposed HUP scheme over state-of-the-art designs. In addition, the effects of key parameters such as the number of antennas and dynamic power at the BS, target data rates, and energy threshold, on the system performance are evaluated to show the effectiveness of the proposed schemes in balancing resource utilization.

Multiple input multiple output (MIMO) based orthogonal frequency division multiplexing (OFDM) has widely been used in a wireless communications system for its robustness to frequency-selective channels and better spectral efficiency. The introduction of full-duplex (FD) and device-to-device (D2D) communications, which are potential candidates of fifth-generation (5G) and beyond, further improve the spectral efficiency of MIMO-OFDM based systems. This paper proposes a novel MIMO-OFDM based FD Cooperative-D2D (C-D2D) communications system wherein a cellular user (CU) acts as an FD relay to facilitate seamless communications between D2D transmitter and receiver. The complete analytical framework is presented to analyze the end-to-end performance of the proposed system. Specifically, the closed-form expression for symbol error rate (SER) of the proposed system is derived in the presence of multipath Rayleigh fading channel and residual self-interference (RSI) due to the FD mode. Further, the performance of the system is analyzed in the presence of a nonlinear high power amplifier (HPA) which introduces the nonlinear distortion. Finally, simulation results are presented to verify the derived expressions. The results show that there is higher SER in the presence of nonlinear HPA due to nonlinear distortion, which can be reduced by increasing input back off (IBO). The presence of RSI also increases the SER at CU, which is further reduced by employing self-interference cancellation (SIC) techniques. A complete end-to-end analytical framework is designed to compare the performance of the proposed system with the conventional system with linear HPA and no RSI.

User pairing and power allocation strategies for downlink NOMA-based VLC systems: An overview

In order to tackle the increasing heterogeneous global Internet traffic, mixed-line-rate (MLR) optical wavelength division multiplexed (WDM) networks have emerged as the cost- and power-efficient solution. In MLR WDM networks, channels are structured as sub-bands, each of which consists of wavelengths operating at a similar data rate. By reducing the (1) spacing within a sub-band, or (2) spacing between sub-bands operating at different data rates, spectral efficiency can be improved. However, owing to high physical layer impairment levels, decrease in sub-band spacing adversely affects transmission reach of the channels, which results in higher power consumption due to requirement of increased signal regeneration. In this work, we compare power efficiency of various MLR and single-line-rate (SLR) solutions, and also investigate the trade-off that exists between spectral and power efficiency in a WDM network. Simulation results indicate that (1) for high transmission capacities, a combination of 100 Gbps transponders and 40 Gbps regenerators will obtain the highest power efficiency; (2) for long connection distances, a point ofmerging occurs for various SLR and MLR designs, where power consumption is independent of the frequency band distribution; and (3) for MLR systems, both spectral and power efficiency can be improved by using either shorter links with higher bandwidth assignment to 100 Gbps wavelengths, or longer links with higher bandwidth assignment to 40 Gbps wavelengths. Finally, the results indicate that focusing on spectral efficiency alone results in extra power consumption, since high quality of transmission and spectral efficiency leads to increased regeneration.

For 5G and beyond 5G systems, many technologies such as Carrier Aggregation (CA) have been suggested to improve the Spectral Efficiency (SE). Along with SE, Energy Efficiency (EE) is another key parameter to be considered while designing such systems. Judiciously using available power will not only help in reducing operational costs but also make the system more environment friendly by reducing greenhouse gas emissions. From an operator’s point of view, providing better data rates to users as well as reducing operational costs is important. This paper focuses on the tradeoff between SE and EE for a system operating in the FR1 frequency band (5G) and also using CA. Detailed analysis on the effect of various parameters such as 5G NR numerology, user velocity (Doppler shift), static and signal processing power consumption of base station and power amplifier efficiency at the base station in the tradeoff between SE and EE is performed. From the simulation results, it can be observed that while varying Doppler shift has very little impact, other parameters such as numerology, static and signal processing power consumption and power amplifier efficiency greatly affect the tradeoff between SE and EE. Tradeoff improves for lower subcarrier spacing, lower static and signals processing power consumption and higher power amplifier efficiency. For simulations, a TDL-A channel model is used. A base station power consumption model which takes into account both static and signal processing power consumption and power amplifier efficiency are considered in order to provide a more practical analysis of EE.

Multi User Massive MIMO (MU-Massive MIMO) is a form of multi-user large-scale antennas technology, in which hundreds number of antennas serve a significantly smaller number of users. This system is assumed operates over a frequency-selective and uses Orthogonal Frequency Division Multiplexing (OFDM). The system performance is observed in two conditions, the first condition is that the BS is assumed to know the channel information perfectly (perfect CSI condition), the second condition is that the BS performs the channel estimation process at a certain coherence interval (imperfect CSI condition). The BS estimates channel information from the pilot sent by user using Minimum Mean Square Error (MMSE) estimator. Several precoding techniques are used to overcome Multiuser Interference (MUI) at the receiver, namely Maximum Ratio (MRT), Zero Forcing (ZF) and MMSE. The observed parameter are Bit Error Rate (BER) and Spectral Efficiency (SE). From the simulation results, it can be seen that the use of a large number of array antennas can significantly increase the spectral efficiency. ZF and MMSE precoding work better than MRT precoding in minimizing MUI. Spectral efficiency is also affected by the channel model, where the spectral efficiency on the UR-LOS channel is higher than Rayleigh channel. In the imperfect CSI condition, the channel estimation error is getting bigger, so that the spectral efficiency will decrease and become lower than the perfect CSI condition.

Based on today’s foreseen service requirements, such as live TV, video streaming, and file uploading and downloading; its needed to increase the data rates up to extreme level. This enhancement of data rates is highly depending on the usage of spectrum that how we are utilizing the available band to transmit data efficiently. In the present generation cellular networks, the channel estimation consumes some band of frequencies to determine the characteristics of wireless channel. Due to its (wireless channel) dynamic characteristics with respect to time and frequency, the conventional methods uses the more number of frequency bands hence the spectral efficiency decreases. This paper provides a technique to achieve higher spectral efficiency in next generation mobile networks with better system performance. In this method, a training sequence (reference pilot sequence) is superimposed along with the data sequence. At the receiver side, the same training sequence is used for estimating channel impulse response and then the data detection through the equalization. This estimated data are used recursively for channel re-estimation to increase the accuracy by minimizing the mean square error. From the simulation results and the numerical analysis, we show that the proposed method offers the better system performance with good spectral efficiency requirements.

For some time the magnetotail has been considered as a possible region where hydromagnetic waves can propagate as waveguide modes. Recently, attention has turned to the magnetospheric flanks as waveguides, and much useful insight has been gained into propagation of fast waveguide modes there, and the structure of the field line resonances they can drive. We return to the magnetotail and investigate hydromagnetic wave propagation and coupling in a magnetotail waveguide. This problem is significantly different from the flank waveguide as the ambient magnetic field is directed along the waveguide rather than across. Field line resonances of the flank type are not possible in the lobe waveguide. We describe a numerical simulation of a model waveguide in which the Alfvén speed decreases across the waveguide to the central plasma sheet. The waveguide is stimulated by a short compressional perturbation located in the far tail. The cross‐tail spatial structure is chosen to give relatively weak coupling between fast and Alfvén modes so that phase and group velocities of uncoupled fast modes can be used to interpret the results. We find that the perturbation propagates dispersively down the waveguide in the form of fast waveguide modes. Fourier components with small parallel wavenumber contain most of the energy, and propagate relatively slowly toward the “Earth.” These act as moving sources which launch Alfvén waves continuously earthward. The wave dispersion relations are such that the waveguide modes couple with Alfvén waves only in a limited region of the transverse Alfvén speed gradient. The Alfvén waves travel at the local Alfvén speed along each field line, so that as they travel the wave on a given field line becomes increasingly out of phase with waves on adjacent field lines. The phase mixing in our model is novel in that it includes the effects of transverse gradients in both Alfvén frequency and parallel wavenumber which tend to cancel each other out. Nevertheless, the phase‐mixing process leads to increasingly fine transverse structure as the waves progress down the waveguide. The results are likely to be applicable in regions such as the plasma sheet boundary layer and the plasma mantle.

Certain 5G METIS scenarios [1] such as Amazingly Fast, Best Experience Follows You , and Service in a Crowd create extreme requirements on data rate, traffic handling capability, and availability of high capacity transport respectively. These scenarios map to corresponding requirements that will entail support of over 10 Gbps, 10–100 times the number of connected devices, 1000 times the traffic, and 5 times lower end-to-end latency than possible through IMT-Advanced. The peak data rate requirements of these scenarios will entail acquisition of several hundreds of MHz of spectrum. These requirements do not encompass 5G, but instead offer one avenue of stressing system capabilities along a limited set of dimensions. Several traffic forecasts [2][3] also predict a tenfold increase in traffic volume from 2015 to 2020. The 5G requirements of interest to this chapter relate mainly to data rates and traffic volumes and can be met using techniques that are tried and tested in past generations of mobile networks. These are to (1) gain access to new spectrum, (2) improve spectral efficiency, and (3) densify the networks using small cells. In the case of 5G, these techniques are given new life using two means: the use of millimeter Wave (mmW) spectrum for the availability of large blocks of contiguous spectrum, and the subsequent adoption of beamforming as an enabler for high spectrum efficiency. The propagation of millimeter waves is naturally affected by physics to reduce coverage to shorter ranges. Ultra-Dense Network (UDN) deployments are therefore a consequence of the choice of frequency band, and will lead to a tremendous increase in capacity over the covered area. The increase in spectral efficiency arises out of the drastic reduction of interference in relation to signal power due to the high gain beamforming. Spectrum and regulations The primary motivation for using millimeter waves is the promise of abundant spectrum above 30 GHz. While mmW spectrum spans the range from 30 GHz–300 GHz, it is widely believed that the reach of mass market semiconductor technology extends up to around 100 GHz and will inevitably surpass that limit with time. Microwave bands from 3 GHz–30 GHz are just as relevant to meeting extreme requirements for 5G, and much of the discussion in this chapter is relevant to those parts of the centimeter Wave (cmW) band outside of the reach of existing systems as well, namely the region 10 GHz–30 GHz (see Figure 6.1).

Massive multiple-input multiple-output (MIMO) is a key technology for improving the spectral and energy efficiency in 5G-and-beyond wireless networks. For a tractable analysis, most of the previous works on Massive MIMO have been focused on the system performance with complex Gaussian channel impulse responses under rich-scattering environments. In contrast, this paper investigates the uplink ergodic spectral efficiency (SE) of each user under the double scattering channel model. We derive a closed-form expression of the uplink ergodic SE by exploiting the maximum ratio (MR) combining technique based on imperfect channel state information. We further study the asymptotic SE behaviors as a function of the number of antennas at each base station (BS) and the number of scatterers available at each radio channel. We then formulate and solve a total energy optimization problem for the uplink data transmission that aims at simultaneously satisfying the required SEs from all the users with limited data power resource. Notably, our proposed algorithms can cope with the congestion issue appearing when at least one user is served by lower SE than requested. Numerical results illustrate the effectiveness of the closed-form ergodic SE over Monte-Carlo simulations. Besides, the system can still provide the required SEs to many users even under congestion.

The performance analysis of discrete-rate adaptive modulation (AM) for MIMO-OFDM systems with space-frequency block code (SFBC) in Rayleigh fading channels is presented. The fading gain value in each subchannel is partitioned into a number of regions by which the modulation is adapted in terms of the region the fading gain falls in. The fading gain region boundaries are attained for attaining maximum spectral efficiency (SE) under a target bit error rate (BER) constraint. Based on accurate BER expression, the improved switching thresholds for the AM are proposed. By the switching thresholds, we obtain accurate closed-form expressions of the SE and average BER. With these expressions, the system performance can be effectively evaluated. Simulation results show that the SE based on the improved switching thresholds is higher than that based on the conventional ones, and the derived theoretical SE and BER are in good agreement with the corresponding simulation results.

This paper designs an angle-selective surface (ASS) composed of two identical layers of frequency-selective surfaces (FSS) with regular hexagonal structures. By leveraging the equivalent circuit model (ECM) theory and the modal interaction poles (MIPs) principle, the interlayer height is optimized to modulate electromagnetic coupling between layers, thereby achieving angular selectivity. The structure exhibits excellent ultra-narrow angular domain transmission characteristics, with the width of the transmission angle domain where |S21| > -1dB is less than 0.1° under TE polarization and only 0.7° under TM polarization. Yet also has the characteristic of a narrow transition angular domain, where the widths of the transition angle domains on both sides, where 1dB ≤ |S21| ≤ ~ - 20dB, are both 2.6° under TE polarization, and 16° and 9.3° under TM polarization. Meanwhile, the proposed structure also exhibits angular selectivity with broadband characteristics that it maintains angular selectivity over a 4.1 GHz bandwidth from 17.6GHz to 21.7GHz under TE polarization, and the angular selectivity spans a 5.4 GHz bandwidth from 17.6GHz to 23GHz under TM polarization. Finally, a prototype of this structure was fabricated, and the actual measurement results are in good agreement with the simulation results. This paper is the first to propose the concept of broadband characteristics for ASS, and the structure integrates the three advantages of narrow-angle domain transition, ultra-narrow-angle domain transmission, and dual polarization. With superior angle-selective performance compared to existing solutions, this structure offers important application potential, especially for applications in the front end of telescope imaging systems, optical coupling in AR waveguides, enhancing the signal-to-noise ratio (SNR) of signal detection in optical communications, and offering privacy protection for transmitters.