Expressions For Ergodic Capacity Research Articles

A Three-Phase CDRT Strategy Based on Successive Relay for Smart Grid

In the vision of the future smart grid, the communication is often featured by wide range, massive connect, and low latency, which poses new requirements on the reachable distance and spectral efficiency of wireless communication. In this regard, this paper studies ergodic capacity enhancement by applying successive relay (SR) technology to a non-orthogonal multiple access (NOMA) based Coordinated Direct and Relay transmission (CDRT) system, where a base station (BS) communicates with a near user (NU) directly while communicating with a far user (FU) with the help of a group of relays. We design a novel three-phase CDRT strategy based on SR technology to overcome the half-duplex (HD) constrain without introducing additional noise. The proposed strategy can improve the spectral efficiency while expanding the communication coverage, which to some extent improves the communication quality of the edge users of the smart grid and reduces the communication delay. To analyze the performance of the proposed three-phase CDRT strategy, an exact and closed-form expression for ergodic capacity of the NU, the FU, and the whole system is derived. Finally, the numerical and simulation results validate the analysis results and show that the proposed strategy can improve the ergodic capacity of FU without reducing the capacity scaling of NU.

NOMA Enhanced Hybrid RIS-UAV-Assisted Full-Duplex Communication System With Imperfect SIC and CSI

In this work, we consider a hybrid aerial full-duplex (FD) relaying protocol consisting of a reconfigurable intelligent surface (RIS) mounted over an FD unmanned aerial vehicle (UAV) relay operating in the decode and forward mode to assist the information transfer between the base station and multiple users. For better spectral efficiency, we investigate the use of non-orthogonal multiple access (NOMA) in such networks and focus on both the performance analysis and design optimization of the considered RIS-NOMA network under imperfect channel state information (CSI) and successive interference cancellation (SIC) at each user, and residual-self interference (RSI) at UAV. We first formulate the sum rate maximization problem and adopt the block coordinate descent method to deal with the non-convex nature of the problem. Thereafter, we propose an algorithm based on the Riemannian conjugate gradient method to get the optimal phase shifts at the RIS, an iterative algorithm to obtain the optimal UAV/RIS position and the exhaustive method to obtain the optimum power allocation coefficients. Next, with obtained optimal position, phase shift and power coefficients, we further analyze the performance of the network and derive the closed-form expressions of outage probability, achievable throughput and ergodic capacity. We present Monte Carlo simulation-based results to validate the accuracy of the proposed algorithms and derived expressions and demonstrate the superiority of NOMA over OMA.

Comprehensive performance analysis of hybrid FSO/RF space–air–ground integrated network

Free space optics (FSO) communication due to its large optical carrier bandwidth offers better data rates close to gigabits per second (GBPS) compared to radio frequency (RF) communication and can support seamless ubiquitous high-speed broadband connectivity, which is a significant requirement for sixth-generation (6G) communication. It is also envisioned that the data transmission in 6G communication will be over space–air–ground integrated network (SAGIN) to provide broadband global mobile connectivity. Thus, our main aim in this paper is to investigate the performance of a dual-hop (DH) system model utilizing high-altitude platform station (HAPS) as a relay station with FSO communication for SAGIN scenario, which is expected to be featured in 6G communication. Despite various advantages, HAPS-based FSO satellite communication (SATCOM) is undermined by several factors such as atmospheric turbulence, pointing errors, and atmospheric attenuation. To improve the system performance in terms of capacity and reliability, hybrid FSO/RF communication with RF link as a backup is utilized between ground station (GS) and HAPS. Further, comprehensive end-to-end system performance is investigated by deriving unified closed-form expressions for outage probability and average symbol error rate (SER). We also obtain approximate upper bound expressions for ergodic capacity and outage capacity. The asymptotic expressions are also derived to obtain the diversity order. Here, FSO and RF links are modelled using generalized Malaga distribution with non-zero boresight pointing errors and shadowed κ−μ distribution, respectively. Further, the closed-form expressions for optimum switching threshold signal-to-noise ratio (SNR) are derived and the obtained optimal SNR values are verified using a numerical optimization technique. Finally, the results show that the proposed DH SAGIN-based hybrid FSO/RF SATCOM system is more reliable as well as achieves higher capacity compared to the FSO-based SATCOM systems.

Analysis of RIS-Assisted FSO Systems Over F Turbulence Channel With Pointing Errors and Imperfect CSI

Reconfigurable intelligent surface (RIS) is an enabling solution to enhance the wireless communication system performance by smartly tunning the signal reflection via a large number of reconfigurable passive elements. In this letter, we present the performance analysis of RIS-assisted FSO communication systems over Fisher-Snedecor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathcal {F}$ </tex-math></inline-formula> distribution channel considering imperfect channel state information (CSI) and pointing errors under two types of detection schemes. The probability density function (PDF) and cumulative distribution function (CDF) of signal-to-noise ratio (SNR) are deduced in terms of multivariable Fox’s H function. Utilizing these results, the novel expressions for outage probability, average BER and ergodic capacity are derived. All presented results are verified by Monte Carlo simulations.

Performance Analysis of IRS-Assisted Full-Duplex Wireless Communication Systems With Interference

This letter considers a full-duplex wireless communication system, where two users communicate to each other through an intelligent reflecting surface (IRS). Each user is assumed to be equipped with two antennas, one each for reception and transmission. The system suffers from loop-interference (LI) between the transmit and receive antennas, self-interference (SI) through the IRS, and external interferers (EI) available at the IRS and users. The fading channels are modelled by Weibull distribution as it is a generalized and accurate model for both indoor and outdoor communications. By taking into account the IRS random reflection coefficient (RRC), and by applying the Laguerre expansion approximation, we derive closed-form expressions for outage probability and ergodic capacity. Numerical and simulation results show that LI, SI, EI and RRC have sever impacts on the system performance. The results also show the robustness of the Laguerre expansion approximation compared to non-central Chi-squared distribution, in particular, for a small number of IRS elements.

Performance Analysis of Cooperative Nonorthogonal Multiple Access Scheme in Two-Layer GEO/LEO Satellite Network

Multilayer satellite networks (MLSNs) are viewed as a promising framework of the future satellite communication networks by realizing cooperative communication among satellites in different orbits. In this article, we introduce the cooperative nonorthogonal multiple access (C-NOMA) scheme into a two-layer geostationary Earth orbit/low Earth orbit satellite network in a frequency coexistence scenario and investigate the performance of the considered network. Taking into account the dynamic properties and channel characteristic of the satellite nodes, we first establish the generic architecture and then obtain the equivalent end-to-end signal-to-interference-plus-noise ratios along with the feasible region of power allocation coefficients based on the C-NOMA principle. Furthermore, the analytical expressions of the system ergodic capacity and outage probability are derived and approximated using Meijer-G functions to evaluate the system performance efficiently. Finally, simulation results are provided to attest the validity of the theoretical results as well as show the superiority of the C-NOMA scheme and the impact of various parameters on the system performance.

Performance of a hybrid dual-hop and multi-hop network based on NOMA

ABSTRACT In this work, a novel network is proposed, which supports simultaneous dual-hop and multi-hop transmissions using the key concept of non-orthogonal multiple access (NOMA). The proposed network is designed in such a way that the existing infrastructure of a multi-hop network can be utilised efficiently for concurrent dual-hop transmissions. While one source transmits its signal to a remote destination via relay nodes in time slots, a maximum of another sources may transmit their information to the corresponding destinations using dual-hop transmissions via the same relay nodes over time slots. The performance of this hybrid dual-hop/multi-hop network is analysed and the impact of number of hops, transmit signal-to-noise ratio (SNR) and imperfection of successive interference cancellation (SIC) on the outage performance of each source is evaluated. Novel closed-form expressions for outage probability and ergodic capacity have been developed to assess the performance of the proposed network. In addition, an asymptotic performance analysis has also been also carried out for both outage probability and ergodic capacity of the proposed network.

Unified Performance Analysis of Reconfigurable Intelligent Surface Empowered Free-Space Optical Communications

Reconfigurable intelligent surface (RIS) is an excellent use case for line-of-sight (LOS) based technologies such as free-space optical (FSO) communications. In this paper, we analyze the performance of RIS-empowered FSO (RISE-FSO) systems by unifying Fisher-Snedecor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathcal{F}}$ </tex-math></inline-formula> ), Gamma-Gamma ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cal {GG}$ </tex-math></inline-formula> ), and Malága ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cal {M}$ </tex-math></inline-formula> ) distributions for atmospheric turbulence with zero-boresight pointing errors over deterministic as well as random path-loss in foggy conditions with heterodyne detection (HD) and intensity modulation/direct detection (IM/DD) methods. By deriving the probability density function (PDF) and cumulative distribution function (CDF) of the direct-link (DL) with the statistical effect of atmospheric turbulence, pointing errors and random fog, we develop exact expressions of PDF and CDF of the resultant channel for the RISE-FSO system. Using the derived statistical results, we present exact expressions of outage probability, average bit-error-rate (BER), ergodic capacity, and moments of signal-to-noise ratio (SNR) for both DL-FSO and RISE-FSO systems. We also develop an asymptotic analysis of the outage probability and average BER and derive the diversity order of the considered systems. We validate the analytical expressions using Monte-Carlo simulations and demonstrate the performance scaling of the FSO system with the number of RIS elements for various turbulence channels, detection techniques, and weather conditions.

Uplink Interference and Performance Analysis for Megasatellite Constellation

Satellite communications play an important role in future Internet of Things (IoT) networks, and megasatellite constellations can further provide global coverage and high-quality services for IoT communications. In the megaconstellation, large-scale satellites are launched to enhance the capacity. However, the dense distribution of satellites brings intraconstellation interference, limiting the performance. In order to evaluate the restriction of interference caused by system parameters, such as the scale of constellation or the frequency reuse factor, we investigate uplink intraconstellation interference and performance of the megasatellite constellation. First, a multibeam polar constellation with uplink spatial frequency reuse is assumed. Then, the interference model is constructed considering the antenna gain of interfering user terminals and multibeam satellites, where the details of the satellite-fixed frequency reuse scheme and coordinates of co-frequency cells are provided. To evaluate the performance, expressions of outage probability, ergodic capacity, and sum ergodic capacity are driven. The analytical results disclose the impact of system design on the performance, and the accuracy of analysis results is obtained through extensive simulation evaluation. The results show that sum ergodic capacity achieves highest in the case of full frequency reuse for the frequency-limited constellation system, and it gets a linear growth at first but then keeps flat with a trend of fluctuating downward as the scale increases; therefore, the impact of the scale should be considered when constructing megaconstellations.

NOMA-Based Overlay Cognitive Satellite-UAV-Terrestrial Networks with Multiple Primary Users

Satellite communication is becoming more and more significant in present and future communication systems for its unique advantages of strong survivability and seamless coverage, which can offset the defects of terrestrial communication such as being restricted by terrain and little coverage. Moreover, unmanned aerial vehicle (UAV)-assisted communication is considered as a promising development direction due to its flexibility and expansibility in the integrated satellite-terrestrial networks (ISTN). In addition, to overcome the spectrum shortage and low spectrum utilization problems, cognitive radio and nonorthogonal multiple access (NOMA) has been widely utilized to enhance spectrum efficiency, which is considered as the key technologies of the next generation communication. In this regard, our paper investigates the performance of cognitive satellite-UAV-terrestrial networks with NOMA scheme and multiple primary users. Specifically, the exact expressions of outage probability (OP) and ergodic capacity for both primary network and secondary network are derived. To gain further views, the asymptotic expression of OP and diversity orders for the two networks are provided. Finally, through numerical simulations, the correctness of the theoretical derivations is verified and the influences of critical variables on system indexes are also analyzed.

Effects of Hardware Impairments on IRS-Enabled MISO Wireless Communication Systems

This letter considers an intelligent reflecting surface (IRS)-enabled multiple-input single-output (MISO) wireless communication system, where the direct link between the transmitter and receiver is assumed to be blocked. It assesses the effects of transceiver hardware impairments (HWI), IRS channels correlation and phase errors on the system performance. New accurate expressions for ergodic capacity, outage probability, average symbol error rate, and diversity order are derived. Numerical and simulation results show that the IRS channels correlation, phase errors and transceiver HWI adversely affect the system performance. It is also shown that transceiver HWI impose a finite limit on the ergodic capacity, which is irrespective of the number of IRS elements and transmit antennas, transmitted power, phase errors, spatial correlation, and fading conditions.

On the Capacity Performance of Hybrid FSO/RF System With Adaptive Combining Over Generalized Distributions

This paper investigates the ergodic capacity performance of hybrid free space optics (FSO)/ radio frequency (RF) system by employing an adaptive-combining-based switching scheme. In the adaptive combining scheme, the FSO and RF links are combined using the maximal-ratio combining (MRC) at the output, when the instantaneous signal-to-noise ratio (SNR) of the FSO link drops below a predefined threshold SNR value. The FSO link experiences the atmospheric turbulence, which is modeled using the generalized Malaga distribution, non-zero boresight misalignment or pointing errors, and atmospheric attenuation, under two types of detection techniques, i.e. heterodyne detection (HD) and intensity modulation/direct detection (IM/DD). Similarly, the fading of the RF link is characterized using the generalized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\kappa$</tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> distribution. In particular, we derive the probability density function (PDF) of the instantaneous SNR of the adaptive combining scheme. Capitalizing on the SNR statistics, we obtain the unified closed-form ergodic capacity expressions for the adaptive-combining-based hybrid FSO/RF system. In addition, the asymptotic expressions for the ergodic capacity of the system at the high-SNR region are presented. All the derived analytical expressions are validated by using Monte-Carlo simulations. Numerical results and discussions are provided to compare the ergodic capacity performance of the adaptive-combining-based hybrid FSO/RF system with the existing system models such as single-link FSO, MRC-based hybrid FSO/RF, and hard-switching-based hybrid FSO/RF systems.

On Performance of STAR-RIS-Enabled Multiple Two-Way Full-Duplex D2D Communication Systems

This paper investigates performance of simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-enabled multiple two-way full-duplex device-to-device (D2D) communication systems over Rayleigh fading channels under optimal and uncertain phase shift alignments. We derive closed-form expressions for outage probability (OP), sum throughput, ergodic capacity (EC) and energy efficiency. To gain insights, we quantify and reveal some useful guidelines for the performance behavior of the OP and the EC, such as diversity order and ergodic slope from high transmit power configuration. In addition, some critical points also deduced for the sum throughput and the system energy efficiency. Moreover, the impacts of the transmit power configurations, RIS deployments, allocating target data rate transmission, and the number of user deployments on the system performance are examined. Finally, we present some extensive simulations using Monte-Carlo method to corroborate the accuracy of the theoretical analysis.

Performance Analysis of NOMA-Enabled Vehicular Communication Systems With Transmit Antenna Selection Over Double Nakagami-m Fading

In this paper, we investigate the performance of downlink multiple-input-single-output (MISO) non-orthogonal multiple access (NOMA) aided vehicular communication systems. To prepare the background for MISO NOMA-based vehicular systems, we first derive the exact outage probability (OP), average bit error rate (ABER), and ergodic capacity (EC) expressions for the single-input-single-output (SISO) NOMA-based vehicular systems over independent but not necessarily identically distributed (i.ni.d.) double Nakagami- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> fading channels. Furthermore, we propose two transmit antenna selection schemes at multiple-antenna source vehicle for both far user and near user. Based on these antenna selection strategies, we derive the exact expressions for the OP, ABER, and EC, of the MISO NOMA-based vehicular systems over i.ni.d. double Nakagami- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> fading channels. The derived ABER expressions for both SISO and MISO NOMA-enabled vehicular systems can be applicable for various modulation schemes. Moreover, to reveal better insights into the diversity orders of SISO and MISO NOMA-enabled vehicular systems, we present the asymptotic OP analysis in the high signal-to-noise ratio (SNR) regime. The numerical and simulation results corroborate our theoretical and analytical findings, and demonstrate the effects of transmit power, power allocation factor, fading severity parameters, and number of antennas, on the system's performance. We further compare the performance of both systems, and show that the multiple antennas can improve the performance of vehicular systems, which can be further improved significantly with the simultaneous improvement in fading severity parameters.

ASER Analysis of Hybrid Receiver Based SWIPT Two-Way Relay Network

In this paper, we investigate the performance of a hybrid receiver-based simultaneous wireless information and power transfer (SWIPT) two-way relay network over Nakagami- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> faded channels. A hybrid receiver is adopted at the relay node that utilizes both the time switching (TS) and power splitting (PS) protocols for energy harvesting and information transmission. Amplify-and-forward relaying protocol is utilized at the relay node to process the information in half-duplex mode. In the considered network, impact of a practical non-linear power amplifier (NLPA) at the relay node is considered. Selection combining is performed at the destination node to utilize the direct-link and relay assisted signals. For the considered system, the analytical expressions of outage probability (OP) and asymptotic OP are derived over Nakagami- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> faded channels for both the integer and non-integer value of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> . The analytical expression of the system throughput and energy efficiency of the considered network are also derived. Further, the analytical expression of ergodic capacity is derived in terms of the Meijer-G function. By utilizing a cumulative distribution function based approach, analytical expressions of average symbol error rate (ASER) for general order hexagonal quadrature amplitude modulation (QAM), general order rectangular QAM, and 32-cross QAM schemes are derived. For different QAM constellations, a comparative ASER analysis is also illustrated. Furthermore, the impact of TS factor, PS ratio, energy conversion efficiency, NLPA, and threshold data-rates on the considered network is also highlighted. Finally, Monte-Carlo simulations are performed for validation of the derived analytical expressions.

Performance analyses of TAS/Alamouti‐MRC NOMA system with channel estimation error, feedback delay, and imperfect SIC

AbstractIn this article, the performance of a power domain downlink multiple‐input multiple‐output non‐orthogonal multiple access system, where the base station (BS) equipped with three antennas communicates simultaneously with three mobile users equipped with multiple antennas, is analyzed over Nakagami‐m fading channels in the presence of channel estimation error (CEE), feedback delay (FBD), and imperfect successive interference cancellation. In the considered system, the BS applies transmit antenna selection (TAS)/Alamouti‐space‐time block coding (STBC) scheme while mobile users are assumed to adopt maximum‐ratio combining technique in order to take advantage of the combination of transmit and receive diversities. In particular, in order to apply Alamouti‐STBC scheme at the BS, one of the transmit antennas is determined randomly while the other one is selected according to decision of the majority of mobile users. For performance metrics, closed‐form outage probability (OP) and ergodic capacity (EC) expressions derived with the help of moment generating function approach. Moreover, asymptotic analyses are maintained to demonstrate the effects of CEE and FBD in terms of diversity order and array gain. We show that the proposed system provides better OP and EC performance than the system without antenna selection for different users and conditions.

NOMA-Based Integrated Satellite-Terrestrial Relay Networks Under Spectrum Sharing Environment

With the increasing requirements for efficient utilization of satellite resources, both non-orthogonal multiple access (NOMA) scheme and cognitive radio (CR) have been recognized as one of the promising solutions, particularly, for the enhancement of spectrum efficiency. This letter investigates the performance of NOMA-based integrated satellite-terrestrial relay network (ISTRN) in the presence of multiple primary users (PUs) under spectrum sharing environment. Specifically, we derive the closed-form expressions of outage probability (OP) and ergodic capacity (EC) of the considered system under the interference constraint imposed by multiple adjacent PUs. To get further insights, the asymptotic analysis for OP at high signal-to-noise ratios (SNRs) is also obtained. Numerical results are provided to verify our analysis and reveal the impacts of key parameters on system performance.

Performance analysis for the forward link of multiuser satellite communication systems

SummaryBroad‐band satellite communication is an indispensable method to provide seamless connectivity for people especially in remote areas. This paper analyzes the performance of the forward link of a multiuser satellite system operating in Ka band, where a gateway delivers signal to a satellite that forwards the amplified signal to multiple users on the ground. By assuming that satellite links experience double lognormal fading due to rain attenuation and taking the effects of antenna pattern and path loss into account, we first exploit the opportunistic user scheduling (OUS) scheme to obtain the maximal output signal‐to‐noise ratio (SNR) expression of the satellite system. Then, the analytical expressions for both outage probability (OP) and ergodic capacity (EC) of the considered satellite system are derived. Finally, simulation results demonstrate the validity of the theoretical analysis and the superiority of the OUS scheme in comparison with round‐robin scheme.

Benefiting wireless power transfer scheme in power domain based multiple access: ergodic rate performance evaluation

Power domain based multiple access scheme is introduced in this paper, namely Non-orthogonal multiple-access (NOMA). We deploy a wireless network using NOMA together with a wireless power transfer (WPT) scheme for dedicated user over Nakagami-$m$ fading channel. When combined, these promising techniques (NOMA and WPT) improve the system performance in term of ergodic performance at reasonable coefficient of harvested power. However, fixed power allocation factors for each NOMA user can be adjusted at the base station and it further provide performance improvement. We design a new signal frame to deploy a NOMA scheme in WPT which adopts a linear energy harvesting model. The ergodic capacity in such a NOMA network and power allocation factors can be updated frequently in order to achieve a fair distribution among NOMA users. The exact expressions of ergodic capacity for each user is derived. The simulation results show that an agreement between analytic performance and Monte-Carlo simulation can be achieved.

Performance assessment of orthogonal space‐time block codes in Nakagami‐m/inverse Gaussian fading MIMO channels

This paper evaluates the performance of multiple-input multiple-output systems with orthogonal space-time block code transmit diversity technique experiencing over G composite fading channels. Particularly, closed form expressions for ergodic capacity, average symbol error rate and outage probability are presented in high SNR regime. The ergodic capacity of multiple-input multiple-output systems with orthogonal space-time block code is also measured in low signal-to noise ratio regime. Other essential statistical properties such as variance and probability density function of capacity are also explored for comprehensive analysis. Compared to the exact expressions, the derived analytical formulations are found to be involved with considerably less mathematical exercise and provide additional insights into the implications of model parameters on system performance. The accuracy of G distribution in approximating Nakagami- m / lognormal over several realistic scenario are examined and simultaneously the efficiency of distribution is compared with that of Nakagami- m / Gamma distribution. The obtained analytical expressions are corroborated using Monte-Carlo simulations where it is observed that the approximated results remain notably tight in asymptotically high signal-to noise ratio regime.