Independent Rayleigh Fading Research Articles

Analyzing device-to-device communication performance with amplify-and-forward relaying amid co-channel interference

<p>Currently, the pressing issue of spectrum limitation, driven by the increasing demand for wireless communication services, has led to the challenge of co-channel interference (CCI) due to the reuse of frequencies in wireless networks. To address this, non-orthogonal multiple access (NOMA) has emerged as a solution. This report conducts a thorough evaluation of NOMA’s system performance over independent and non-identical Rayleigh fading channels in device-to-device (D2D) communications networks, where CCI is significant. The analysis includes examining the probability density function (PDF) and cumulative distribution function (CDF) of the upper SINR threshold. Communication channels are defined as independent and non-identical Rayleigh fading channels, and probability expressions are formulated to assess system failure likelihood for two users. Additionally, Monte-Carlo simulations are conducted to validate the proposed theoretical mathematical expressions.</p>

Efficient User Scheduling for Uplink Hybrid Satellite-Terrestrial Communication

Due to increasing demands of seamless connection and massive information exchange across the world, the integrated satellite-terrestrial communication systems develop rapidly. To shed lights on the design of this system, we consider an uplink communication model consisting of a single satellite, a single terrestrial station and multiple ground users. The terrestrial station uses decode-and-forward (DF) to facilitate the communication between ground users and the satellite. The channel between the satellite and the terrestrial station is assumed to be a quasi-static shadowed Rician fading channel, while the channels between the terrestrial station and ground users are assumed to experience independent quasi-static Rayleigh fading. We consider two cases of channel state information (CSI) availability. When perfect CSI is available, we derive the instantaneous achievable sum rate of all ground users and formulate an optimization problem to maximize the sum rate. When only channel distribution information (CDI) is available, we derive a closed-form expression for the outage probability and formulate another optimization problem to minimize the outage probability. Both optimization problems correspond to scheduling algorithms for ground users. For both cases, we propose low-complexity user scheduling algorithms and demonstrate the efficiency of our scheduling algorithms via numerical simulations.

Performance evaluation of cognitive relay networks for end user mobile over mixed realistic channels

Cognitive relay network is a spectrum dynamic paradigm that exploits the unused portions of the licensed spectrum. This is based on merging both cooperative relaying techniques and cognitive radio network to achieve spectrum efficiency and enhance the overall system performance. In this paper, the presence of mobile users at the destination node is considered. Here, the end users can navigate at relatively fast vehicular velocities causing dynamic multipath fading and high Doppler shift. which can be fairly modelled using Nakagami- m $m\;$ fading channel (i.e. m < 1 $\;m < 1$ ). In a spectrum scarcity environment, a secondary user must deploy an optimal power allocation policy to get higher transmission rates while the overall interference affecting the primary user (PU) is kept below a certain threshold value. In particular, the outage probability (OP) performance is studied over the mixed Rayleigh and Nakagami-m fading channels for different scenarios and a tight closed-form expressions are derived for the system OP of underlay dual-hop cognitive relay networks with a single amplifiy-and-forward (AF) relay with and without the use of the direct link transmission and selection diversity at the destination with interference power constraints for the primary network over independent and non-identical (i.n.i.d) Rayleigh and Nakagami-m fading channels when m < 1 $m < 1$ based on the statistical characteristics of signal-to-noise ratio. Numerical results are presented to evaluate the impact of the fading parameter, m, the maximum aggregated intrusion constraint, and the locations of the primary users (PUs) on different channel scenarios at high vehicular speeds. Monte Carlo simulations are presented to verify and validate analytical results.

Multi-User Holographic MIMO Surfaces: Channel Modeling and Spectral Efficiency Analysis

The multi-user Holographic Multiple-Input and Multiple-Output Surface (MU-HMIMOS) paradigm, which is capable of realizing large continuous apertures with minimal power consumption, has been recently considered as an energy-efficient solution for future wireless networks, offering increased flexibility in impacting electromagnetic (EM) wave propagation according to the desired communication, localization, and sensing objectives. The tractable channel modeling in MU-HMIMOS wireless systems is one of the most critical research challenges, mainly due to the coupling effect induced by the excessively large number of closely spaced patch antennas. In this paper, we focus on this challenge for the downlink of multi-user MIMO communications and extend an EM-compliant channel model to multi-user case, which is expressed in the wavenumber domain using the Fourier plane wave approximation. Based on the presented channel model, we investigate the spectral efficiency of maximum-ratio transmission and Zero-Forcing (ZF) precoding schemes. We also introduce a novel hardware efficient ZF precoder, leveraging Neumann series (NS) expansion to replace the required matrix inversion operation, which is very hard to be computed in the conventional way due to the extremely large number of patch antennas in the envisioned MU-HMIMOS communication systems. In comparison with the conventional independent and identical Rayleigh fading channels that ignore antenna coupling effects, the proposed EM-compliant channel model captures the mutual couplings induced by the very small antenna spacing. Our extensive performance evaluation results demonstrate that our theoretical performance expressions approximate sufficiently well the simulated achievable spectral efficiency with the considered linear precoding schemes, even for the highly correlated cases, thus verifying the effectiveness and robustness of the presented analytical framework. In addition, it is verified that the proposed NS-based ZF precoder achieves similar performance to conventional ZF, while requiring lower hardware complexity, thus, providing a hardware efficient solution for practical design of MU-HMIMOS communications systems.

Performance analysis of SWIPT‐assisted adaptive NOMA/OMA system with hardware impairments and imperfect CSI

AbstractThis paper investigates the effect of hardware impairments (HIs) and imperfect channel state information (ICSI) on a SWIPT‐assisted adaptive nonorthogonal multiple access (NOMA)/orthogonal multiple access (OMA) system over independent and nonidentical Rayleigh fading channels. In the NOMA mode, the energy‐constrained near users act as a relay to improve the performance for the far users. The OMA transmission mode is adopted to avoid a complete outage when NOMA is infeasible. The best user selection scheme is considered to maximize the energy harvested and avoid error propagation. To characterize the performance of the proposed systems, closed‐form and asymptotic expressions of the outage probability for both near and far users are studied. Moreover, exact and approximate expressions of the ergodic rate for near and far users are investigated. Simulation results are provided to verify our theoretical analysis and confirm the superiority of the proposed NOMA/OMA scheme in comparison with the conventional NOMA and OMA protocol with/without HIs and ICSI.

Error Rates for 4-Branch Equal-Gain Combining in Independent Rayleigh Fading: A Simple Explicit Solution

Error Rates for 4-Branch Equal-Gain Combining in Independent Rayleigh Fading: A Simple Explicit Solution

Semi-Blind Multiuser Detection Under the Presence of Reconfigurable Intelligent Surfaces

A multiuser multiple-input multiple-output wireless communication system is analytically studied, which operates with the aid of a reconfigurable intelligent surface (RIS). The intermediate RIS is equipped with multiple elements and operates via random phase rotations to simultaneously serve multiple users. Independent Rayleigh fading conditions are assumed among the included channels. The system performance is analytically studied when the linear yet efficient zero-forcing detection is implemented at the receiver. In particular, the outage performance is derived in closed-form expression for different system configuration setups with regards to the available channel state information at the receiver. Further, a joint coherent/noncoherent linear detection is analytically presented. Finally, some new engineering insights are provided, such as how the channel state information and/or the volume of antenna/RIS arrays impact on the overall system performance as well as the arising efficiency on the performance/complexity tradeoff by utilizing the joint coherent/noncoherent scheme.

Local Partial Zero-Forcing Combining for Cell-Free Massive MIMO Systems

Cell-free massive multiple-input multiple-output (MIMO) provides more uniform spectral efficiency (SE) for users (UEs) than cellular technology. The main challenge to achieve the benefits of cell-free massive MIMO is to realize signal processing in a scalable way. In this paper, we consider scalable fullpilot zero-forcing (FZF), partial FZF (PFZF), protective weak PFZF (PWPFZF), and local regularized ZF (LRZF) combining by exploiting channel statistics. We derive closed-form expressions of the uplink SE for FZF, PFZF, and PWPFZF combining with large-scale fading decoding over independent Rayleigh fading channels, taking channel estimation errors and pilot contamination into account. Moreover, we investigate the impact of the number of pilot sequences, antennas per AP, and APs on the performance. Numerical results show that LRZF provides the highest SE. However, PWPFZF is preferable when the number of pilot sequences is large and the number of antennas per AP is small. The reason is that PWPFZF has lower computational complexity and the SE expression can be computed in closed-form. Furthermore, we investigate the performance of PWPFZF combining with fractional power control and the numerical results show that it improves the performance of weak UEs and realizes uniformly good service for all UEs in a scalable fashion.

Multidimensional Constellation Design for Spatial Modulated SCMA Systems

In this paper, multidimensional constellation designs of spatial modulated sparse code multiple access (SM-SCMA) systems with arbitrary number of transmit antennas are investigated to improve the system performance. Firstly, the symbol error rate (SER) performance of single-user and multi-user systems under flat independent Rayleigh fading channels is analyzed. It is shown that except for the product distance of the sub-constellation of each antenna, the product of the norm of symbols on each-dimension can affect single-user performance. Then, based on the performance analysis, a symmetric multidimensional constellation (SMC) and a golden-angle-modulation-based constellation (GAMC) are proposed for the general case where the number of transmit antennas is an arbitrary integer, and a low-complexity SMC (LSMC) is proposed for the special case where the number of transmit antennas is a power of two. Finally, the three proposed design schemes are extended to transmit correlated scenarios. Simulation results show that for uplink systems, compared with existing schemes, SMC provides the best SER performance and has no limitation on the number of transmit antennas. When the transmitter has no spatial correlation and the number of transmit antennas is a power of two, LSMC can achieve comparable performance to SMC with reduced computational complexity. For downlink systems, GAMC can obtain a considerable performance gain (up to 3 dB) over other solutions under transmit correlated channels.

Research on cluster overlap and non-overlap region for 5G-IoV networks with NOMA

As a multi hop self-organizing network, wireless sensor network has the ability to cooperatively sense, collect and process the information of the sensed objects. The applications of WCN in 5G-based Internet of Vehicles (5G-IoV), using information fusion and intelligent information processing technologies, can obtain more reliable and accurate detection parameters, which has been widely concerned. However, the massive connectivity and information exchange in 5G-IoV pose great challenges to the bandwidth efficiency. In order to overcome these issues in 5G-IoV networks, a performance enhanced scheme based on non-orthogonal multiple access (NOMA) is proposed. In the proposed scheme, different vehicle locations are respectively discussed, i.e., whether in the overlap region of cluster head vehicles (CHVs). In particular, different to conventional works, each receiving node only decodes the desired signal to avoid performance loss provided from the poor channel quality limitation. On the other hand, all CHVs decode-and-forward new superposition coded signals with new power allocation factors, while that the maximum ratio combining is utilized at receivers to further improve the ergodic sum-rate (SR) and probability of conflict. The closed-form expressions of ergodic SR for our proposed scheme are analyzed under the independent Rayleigh fading channels. Numerical results corroborating our theoretical analysis show that the superposition coded signal transmission scheme applied to the proposed NOMA-IoV improves the ergodic SR performance significantly compared with the existing works, especially for the high signal-to-noise region.

Enhanced Normalized Conjugate Beamforming for Cell-Free Massive MIMO

In cell-free massive multiple-input multiple-output (MIMO) the fluctuations of the channel gain from the access points to a user are large due to the distributed topology of the system. Because of these fluctuations, data decoding schemes that treat the channel as deterministic perform inefficiently. A way to reduce the channel fluctuations is to design a precoding scheme that equalizes the effective channel gain seen by the users. Conjugate beamforming (CB) poorly contributes to harden the effective channel at the users. In this work, we propose a variant of CB dubbed enhanced normalized CB (ECB), in that the precoding vector consists of the conjugate of the channel estimate normalized by its squared norm. For this scheme, we derive an exact closed-form expression for an achievable downlink spectral efficiency (SE), accounting for channel estimation errors, pilot reuse and user's lack of channel state information (CSI), assuming independent Rayleigh fading channels. We also devise an optimal max-min fairness power allocation based only on large-scale fading quantities. ECB greatly boosts the channel hardening enabling the users to reliably decode data relying only on statistical CSI. As the provided effective channel is nearly deterministic, acquiring CSI at the users does not yield a significant gain.

Layered D2D NOMA

This paper investigates a layered power allocation (PA) non-orthogonal multiple access (NOMA) scheme for device-to-device (D2D) relaying networks, where the strategy of partial data transmission at relay nodes are adopted to improve the efficiency of resources. In addition, to satisfy different quality-of-service (QoS) requirements from multiple users, layered and grouped manners are involved. Moreover, the closed-form expressions in terms of the sum-rate (SR) and outage probability of the proposed scheme are derived for independent Rayleigh fading channels, which demonstrates our theoretical analysis. Both analytical and simulation results are provided to show the superiority of our proposed scheme compared with existing works.

Outage Probability Analysis of Decode-and-Forward Two-Way Relaying System with Energy Harvesting Relay

In this paper, we evaluate a two-way relay system consisting of two terminals and an intermediate relay. In this model, two terminals do not have a direct link but exchange data with each other via the relay in three phases. The relay utilizes energy harvesting technology to collect energy from the received signals of two terminals in the first two phases and then uses the obtained energy for signal transmission in the third phase. Each node is equipped with a single antenna and operates under a half-duplex mode. All wireless channels are influenced by reversible independent flat Rayleigh fading. Using analytical methods, we provide the exact and approximate closed-form expressions of user outage probability and system outage probability. The approximate expressions of these outage probabilities are more explicit and straightforward, providing a better understanding of the influences of network parameters on the system quality. Monte-Carlo simulations are used to confirm the correctness of mathematical analyses.

Local Partial Zero-Forcing Precoding for Cell-Free Massive MIMO

Cell-free Massive MIMO (multiple-input multiple-output) is a promising distributed network architecture for 5G-and-beyond systems. It guarantees ubiquitous coverage at high spectral efficiency (SE) by leveraging signal co-processing at multiple access points (APs), aggressive spatial user multiplexing and extraordinary macro-diversity gain. In this study, we propose two distributed precoding schemes, referred to as \textit{local partial zero-forcing} (PZF) and \textit{local protective partial zero-forcing} (PPZF), that further improve the spectral efficiency by providing an adaptable trade-off between interference cancelation and boosting of the desired signal, with no additional front-hauling overhead, and implementable by APs with very few antennas. We derive closed-form expressions for the achievable SE under the assumption of independent Rayleigh fading channel, channel estimation error and pilot contamination. PZF and PPZF can substantially outperform maximum ratio transmission and zero-forcing, and their performance is comparable to that achieved by regularized zero-forcing (RZF), which is a benchmark in the downlink. Importantly, these closed-form expressions can be employed to devise optimal (long-term) power control strategies that are also suitable for RZF, whose closed-form expression for the SE is not available.

Performance Analysis of Spatial Modulation Aided NOMA With Full-Duplex Relay

A spatial modulation aided non-orthogonal multiple access with full-duplex relay (SM-NOMA-FDR) scheme is proposed for the coordinated direct and relay transmission in this paper. Specifically, the signal of the near user is mapped to an $M$ -ary modulated symbol and the signal of the far user is mapped to an SM symbol. The base station first transmits signals to the near user and relay via SM-NOMA, and then the relay decodes and retransmits the signal of the far user. An SM-assisted FDR is used in this scheme to improve the spectral efficiency while reducing energy consumption and making full use of the antenna resources at the relay, since SM only activates one antenna in each transmission. We derive the ergodic capacity and bit error rate of the proposed scheme over independent Rayleigh fading channels. Numerical results validate the accuracy of the theoretical analysis and show the superior performance of the proposed SM-NOMA-FDR scheme.

Evaluating secrecy performance of cooperative NOMA networks under existence of relay link and direct link

SummaryThe secrecy performance of a nonorthogonal multiple access (NOMA) system is examined in this study by employment of a dual‐hop decode‐and‐forward (DF) relay under existence of eavesdropper. Due to the fact that the relay is trusted or untrusted device and thus eavesdropper may wiretap information from the base station or the relay. In this regard, three scenarios related to trusted and untrusted relays are proposed, with different assumptions on the information overhearing ability of the eavesdropper; ie, the first scenario is that an eavesdropper overhears signal from the relay while the BS is overheard by eavesdropper in the second scenarios. More specifically, we derive closed‐form expressions for the secure probability metrics when the direct and relay links experience independent Rayleigh fading. There metrics include strictly positive secrecy capacity (SPSC) and the secure outage probability (SOP). Furthermore, secure performance of traditional orthogonal multiple access (OMA) is also provided as further comparison with NOMA counterpart. We analyze the influence of main coefficients such as the target rates and the transmit SNR factors on the secrecy performance. Our results specify that for reasonable selection of such parameters, secrecy performance can be enhanced remarkably. Numerical results are delivered to corroborate the derived results.

Downlink Training in Cell-Free Massive MIMO: A Blessing in Disguise

Cell-free Massive MIMO (multiple-input multiple-output) refers to a distributed Massive MIMO system where all the access points (APs) cooperate to coherently serve all the user equipments (UEs), suppress inter-cell interference and mitigate the multiuser interference. Recent works demonstrated that, unlike co-located Massive MIMO, the \textit{channel hardening} is, in general, less pronounced in cell-free Massive MIMO, thus there is much to benefit from estimating the downlink channel. In this study, we investigate the gain introduced by the downlink beamforming training, extending the previously proposed analysis to non-orthogonal uplink and downlink pilots. Assuming single-antenna APs, conjugate beamforming and independent Rayleigh fading channel, we derive a closed-form expression for the per-user achievable downlink rate that addresses channel estimation errors and pilot contamination both at the AP and UE side. The performance evaluation includes max-min fairness power control, greedy pilot assignment methods, and a comparison between achievable rates obtained from different capacity-bounding techniques. Numerical results show that downlink beamforming training, although increases pilot overhead and introduces additional pilot contamination, improves significantly the achievable downlink rate. Even for large number of APs, it is not fully efficient for the UE relying on the statistical channel state information for data decoding.

Wireless Channel Dynamics and Robustness for Ultra-Reliable Low-Latency Communications

Interactive, immersive, and other timing-critical applications demand ultra-reliable low-latency communication (URLLC). To build wireless communication systems that can support these applications, understanding the relevant characteristics of the wireless medium is paramount. Although wireless channel characteristics and dynamics have been extensively studied, it is important to revisit these concepts in the context of the strict demands of low-latency and ultra-high reliability. In this paper, we bring a modeling approach from robust control to wireless communication—the wireless channel characteristics are given a nominal model around which we allow for some quantified uncertainty. We propose certain key URLLC-relevant parameters along which the model uncertainty is to be bounded. To validate the nominal model of the spatially independent quasi-static Rayleigh fading, we take an in-depth look at the spatial and temporal correlations based on Jakes’ model. We find that although the Rayleigh fading process is band-limited, the quasi-static assumption is not safe for relay selection even well within a single coherence time. We also find that under reasonable conditions, the spatial correlation of channels provide a fading distribution that is not too far off from an independent spatial fading model. In addition, we look at the impact of these channel models on cooperative communication-based systems. We find that while spatial-diversity-based techniques are necessary to combat the adverse effects of fading, time-diversity-based techniques are necessary to be robust against unmodeled errors. Robust URLLC systems need to operate with both an adequate SNR margin and a time margin through repetitions.

Optimum SWIPT relaying in bidirectional non‐regenerative relay networks

The authors study the optimal design of simultaneous wireless information and power transfer relaying in bidirectional non-regenerative relay networks. They consider both power splitting relaying and time switching relaying. Since there are two opposite traffic flows between two sources, they characterise the transmission rate performance by the minimum rate of two opposite traffic flows. Specifically, they first obtain closed-form expressions for the optimum power splitting and time switching coefficients to maximise the minimum transmission rate of bidirectional non-regenerative relaying. They also derive the resulting maximum transmission rate expressions. Furthermore, they consider a minimum input radio frequency (RF) power level to turn on diodes, and derive the turn-on probability of the RF energy harvesting circuit when two channels experience independent Rayleigh fading. Numerical results confirm that the authors' analyses exactly match with simulation results and that the two relaying strategies with optimum coefficients give almost the same transmission rate performance.

Outage Performance Comparison of Dual-Hop Full Duplex Underlay Cognitive Relay Networks

This paper investigates the outage probability performance of the secondary user (SU) in an underlay dual-hop, decode and forward (DF), full duplex cognitive relay network (FDCRN). First, we develop analytical closed form expression for outage probability and throughput for a dual-hop DF FDCRN by making use of the direct link signal as a useful signal to improve the signal-to-noise ratio at the secondary destination. Next, we compare the outage and throughput performance of various FDCRN and half duplex cognitive relay network (HDCRN) protocols, namely, (1) dual-hop DF FDCRN with direct link treated as interference, (2) dual-hop DF FDCRN with direct link signal cancelled by employing recursive backward interference cancellation technique, and (3) dual-hop DF HDCRN that employs maximal ratio combining at SD. Closed form expressions for the outage probabilities experienced in the secondary network are derived by taking into account the residual self-interference at the full duplex relay node, in independent non-identical Rayleigh fading channels. The analysis considers the maximum transmit power constraint of the individual secondary nodes and the tolerable interference threshold power constraint of the primary destination as well. The results demonstrate that the outage performance of the SU gets improved significantly when the direct link is exploited at the secondary destination. Further, we evaluate the impact of relay location and the power allocation ratio among secondary source and relay on the outage probability. The analytical results are validated by extensive Monte-Carlo simulations.