Closed-form Outage Probability Research Articles

Performance of STAR-RIS-aided cooperative NOMA networks under Nakagami-[formula omitted] fading

In this work, we investigate the performance of the cooperative non-orthogonal multiple access (CNOMA) downlink wireless communication system assisted by the newly emerged technology of simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) over Nakagami-m fading channels. Specifically, outage probability (OP), spectral efficiency (SE), and energy efficiency (EE) are used as the performance metrics. The near user’s mathematically intractable probability density and cumulative distribution functions were approximated through the Gamma moment-matching technique. This was followed by the derivation of the users’ closed-form OP and ergodic rates expressions, where the latter was used to determine the SE and EE of the system. Further, extensive Monte-Carlo simulations confirmed the correctness of the obtained analytical findings. In addition, to inspect the usefulness of CNOMA in the proposed communication system, the comparison with its NOMA counterpart was incorporated into the numerical results. Finally, it was found that the cooperative link can further enhance the SE and EE of the STAR-RIS-based NOMA network.

Performance analysis of cooperative multi-relay spatial modulation based OTFS system in V2V communication

Owing to the characteristics of spatial modulation (SM) and orthogonal time frequency space (OTFS) modulation, SM based OTFS (SM-OTFS) system has an excellent capability to improve the effectiveness and reliability of vehicle-to-vehicle (V2V) communication. To further combat the severe shadow effect, improve the system performance, and extend the transmission range of V2V communication in the urban scenario with dense buildings, we propose a cooperative multi-relay SM-OTFS system with the optimal relay selection in this paper, where both amplify-and-forward (AF) and decode-and-forward (DF) protocols have been employed and only the optimal relay participates in the signal forwarding. Moreover, the fast time-selective fading is mainly considered, the closed-form outage probability and the system capacity of the cooperative SM-OTFS (CSM-OTFS) system are derived from the viewpoint of signal transmissions in the time domain. Numerical results verify the superiority of the proposed CSM-OTFS system over the non-cooperative SM-OTFS system and illustrate the influence of the main system parameters on the system outage probability and capacity, such as the relaying protocol, the number of relays, the estimation rate of channel state information (CSI), and the time-varying channel characteristic.

Relay Selection for Dual-Hop Cooperative Ambient Backscatter Communication Systems.

Previous works only focus on the optimization design for the dual-hop cooperative ambient backscatter communication (AmBC) system with single-relay selection. The impact of relay selection on the outage performance of dual-hop cooperative AmBC systems is still missing. Motivated by this, in this paper, we investigate the outage performance of a dual-hop cooperative AmBC system with single-relay selection, where the backscatter link shares the receiver with the cellular link and the harmful direct-link interference (DLI) is mitigated by using successive interference cancellation (SIC). In the system considered, the selected relay has dual functions. One is to forward message for the cellular link, and the other is to act as the radio-frequency (RF) source for the backscatter device (BD). Specifically, after proposing two novel single-relay selection schemes (RSSs), namely reactive RSS and proactive RSS, we derive the closed-form outage probability (OP) expressions for both RSSs, which can be performed in a distributed manner. To gain more insights, the asymptotic OPs at high signal-to-noise ratio (SNR) are explored and the outage performance comparison between the reactive RSS and proactive RSS are also provided. Results show that the proposed reactive RSS is outage-optimal among all possible single-relay selection schemes. The theoretical analysis is validated by Monte Carlo simulations. The results also show that the relay selection scheme, the number of relays, the location of BD, and the reflection coefficient of BD have great impact on the outage performance of cooperative AmBC systems.

Performance Analysis of Active RIS-Aided Systems in the Face of Imperfect CSI and Phase Shift Noise

The linear minimal mean square error (LMMSE) estimator for active reconfigurable intelligent surface (RIS)-aided wireless systems is formulated. Furthermore, based on the moment-matching method, we employ the Gamma distribution to approximate the distribution of the instantaneous received signal-to-interference-plus-noise ratio (SINR), and then derive the closed-form outage probability and ergodic channel capacity in the presence of realistic channel estimation errors, the thermal noise of RIS amplifiers and the RIS phase shift noise. Our theoretical analysis and simulation results show that the introduction of RIS amplifiers is equivalent to increasing of the transmit power, and also present the performance degradation resulting from the channel estimation error and the RIS phase noise.

Outage and Throughput Analysis of UAV-Assisted NOMA Relay Systems With Indoor and Outdoor Users

Non-orthogonal multiple access (NOMA) and unmanned aerial vehicle (UAV) are two promising technologies for the fifth generation (5G) and beyond networks. On the other hand, the transition environment from outdoor to indoor is an important problem in practical wireless communication. In this paper, we mathematically study a multi-antenna UAV-assisted communication system where a multi-antenna base station (BS) communicates with indoor and outdoor users through a multiantenna UAV using the power-domain NOMA technique. The metric used to evaluate the system performance are outage probability (OP) and throughput of indoor and outdoor users under different communication urban environments. Moreover, the impacts of the UAV's altitude and location and the light-of-sight (LoS) probability on system performance are also considered. We give the exact and asymptotic closed-form OP expressions and then optimize the transmission rate to maximize the throughput of each user and the overall system throughput. Numerical results show that better system performance can be achieved by controlling the altitudes and location of the UAV, selecting an appropriate transmission rate, or equipping BS and UAV with more antennas. Monte-Carlo simulation results are provided to demonstrate the performance of the investigated system and the accuracy of the developed analytical results.

Performance of STAR-RIS assisted NOMA networks in Nakagami-[formula omitted] fading channels

The concept of simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) has been proposed to overcome the limitation of conventional reflecting-only RISs, which only allow users to be located on the same side of the RIS. This novel STAR-RIS technology can serve all users on both sides of the space surrounding the RIS by reflecting and transmitting the incident wireless signal. Future wireless networks can improve their energy and spectrum efficiencies by combining STAR-RISs with the promising multiple access candidate non-orthogonal multiple access (NOMA). This paper analyzes the performance of STAR-RISs-assisted NOMA networks in terms of outage probability (OP) and bit error rate (BER). First, the closed-form OP expression is derived for each NOMA user in Nakagami-m fading channels. Next, the asymptotic OP expression in a high signal-to-noise ratio (SNR) region is obtained to express the behavior of the network with diversity and array gains. Then, the BER expression is also derived in closed form. The accuracy of the theoretical analysis is finally verified through Monte Carlo simulation.

Ensemble Learning-Based Edge Caching Strategies for Internet of Vehicles: Outage and Finite SNR Analysis

In this paper, an ensemble learning-driven edge caching (ELDEC) strategy and a meta-based ensemble learning-driven edge caching (MELDEC) strategy are proposed for content popularity prediction and cache content placement in Internet-of-Vehicles (IoV) networks. Specifically, the proposed MELDEC and ELDEC strategies incorporate meta learning and ensemble learning for enhanced content popularity prediction in IoV networks. Closed-form outage probability and finite signal-to-noise ratio (SNR) diversity gain expressions are also derived to establish the relationship between the proposed edge caching strategies and the wireless performance of IoV networks. When compared against benchmark schemes, the proposed MELDEC and ELDEC strategies achieve near-optimal cache hit rates, outage probability, and finite SNR diversity gain under imperfect channel state information (CSI) estimation. We also show that the outage probability decay rate in the IoV network depends on the number of base stations and roadside units, and it is independent of the content popularity prediction of the MELDEC strategy, ELDEC strategy, and benchmark schemes. The performance analysis demonstrates that the proposed MELDEC and ELDEC strategies are promising solutions towards achieving reliable content access in IoV networks.

Performance Analysis of NOMA-Based Hybrid Satellite-Terrestrial Relay System Using mmWave Technology

This paper investigates the performance of NOMA-based hybrid Satellite-Terrestrial relays system (HSTR) using the millimeter wave (mmWave) technology. Furthermore, the relays are equipped with multiple antennas and utilize the amplify and forward (AF) protocol to forward the satellite’s superimposed information to multiple destinations. Then, the rain coefficient is considered as the fading factor of the mmWave band to choose the best relay. We considered the shadowed-Rician fading and Nakagami-m fading for satellite links and terrestrial links respectively, and in addition, we evaluated the shadowing effect for satellite links with two modes of: frequent heavy shadowing (FHS) and average shadowing (AS). With these suggestions, the closed-form outage probability (OP) and approximate ergodic capacity (EC) are derived to evaluate the efficiency of the proposed system. Next contribution of the research is an asymptotic analysis for the OP, which is derived in order to gain additional insight into important system parameters. Finally, the theoretical derivation is validated through simulation results and analyzed the impact of significant parameters. These results demonstrate NOMA’s superiority to the traditional orthogonal multiple access (OMA) method in the proposed system.

Spectrally Efficient Uplink Cooperative NOMA With Joint Decoding for Relay-Assisted IoT Networks

We propose a spectrally efficient uplink cooperative relaying protocol with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> multiple half-duplex relay stations (RNs) for wireless Internet of Things (IoT) networks, where two IoT devices (IDs) and an access point (AP) cannot directly communicate with each other. The two IDs simultaneously transmit signals over the same spectrum resource using the nonorthogonal multiple access (NOMA) technique. In the proposed technique, at a certain time slot, a single RN is selected to send the received packets from two IDs in the previous time slot, while the remaining <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K-1$ </tex-math></inline-formula> RNs receive new packets from two IDs. Thus, the proposed relaying protocol can send <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> packets from an ID to the AP during <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N+1$ </tex-math></inline-formula> time slots without a duty-cycle loss in conventional half-duplex relaying schemes. We call the proposed protocol a spectrally efficient cooperative NOMA. The main highlight of our results is that we mathematically derive a closed-form outage probability of the proposed protocol by considering inter-relay interference, assuming an optimal joint decoding technique instead of successive interference cancelation (SIC) decoding at each RN. To the best of our knowledge, this is the first theoretical result in the literature. Extensive computer simulations are used to validate the mathematical results. Furthermore, it is shown that the proposed protocol significantly outperforms the existing two-hop half-duplex cooperative NOMA technique and the SIC decoding scheme in terms of outage probability.

Optical Intelligent Reflecting Surface for Mixed Dual-Hop FSO and Beamforming-Based RF System in C-RAN

Optical intelligent reflecting surface (IRS) is an emerging and low-cost technology that can establish a stable communication route in free space optical (FSO) transmission environment with obstacles. In this work, optical IRS-aided dual-hop mixed FSO and RF system is first proposed for cloud radio access network (C-RAN). Specifically, polar codes are introduced to combat turbulence and building sway induced fading in FSO link, and transmit beamforming (TBF) technique is designed to achieve optimal data-rate for RF link. Supposing that the IRS-aided FSO link is subject to exponentiated Weibull distribution with geometric and misalignment loss, whereas the RF link experiences the 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> composite fading, the analytical closed-form outage probability expression is derived in terms of Meijer G and Lauricella multivariate hypergeometric functions with decode-and-forward strategy. Exact closed-form average bit error rate expressions are obtained when the relay of C-RAN adopts single antenna and multiantenna beamforming techniques. On the basis of moment generating function of end-to-end signal-to-noise ratio, the ergodic capacity is obtained in terms of univariate and multivariate Fox H-functions over independent but not identically distributed 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> fading channels. The correctness of the analytical results is verified through Monte-Carlo simulations. We further provide an asymptotic analysis and discuss the achievable diversity orders.

Outage Analysis of NOMA-Enabled Backscatter Communications With Intelligent Reflecting Surfaces

Intelligent reflecting surface (IRS) has emerged as a potential technology to achieve smart wireless communications and high energy efficiency. On the other hand, nonorthogonal multiple access (NOMA)-enabled backscatter communications have shown a great potential in large-scale Internet of Things (IoT) networks. In this article, we consider a downlink IRS-assisted backscatter communication with NOMA. We further consider a two-user scenario with channel disparity from the base station. We first derive the probability density function of the sum of the modulus of reflected channels, where each channel follows the Rayleigh distribution with dissimilar variances. The respective and generalized closed-form outage probability expressions are derived for the considered scenario. Simulation results validate the accuracy of the analytical outage probability expressions. We demonstrate that the far user can achieve a superior performance with the increase of reflecting elements or the reflection coefficients.

Outage Analysis and Beamwidth Optimization for Positioning-Assisted Beamforming

Beamforming based on channel estimation can be computationally intensive and inaccurate when the antenna array is large, while positioning information can reduce the complexity. In this work, we study the outage probability of positioning-assisted beamforming systems. Closed-form outage probability bounds are derived by considering positioning error, link distance and beamwidth. Based on the analytical result, we show that the beamwidth should be optimized with respect to the link distance and the transmit power, and such optimization significantly suppresses the outage probability.

Exploiting user grouping and energy harvesting in downlink cellular system

A mobile communication system combining energy harvesting with a cooperative nonorthogonal multiple access (NOMA) system is presented in this research. In the proposed scheme, the relay is assumed to have a limited power source, and it will harvest radio energy from the base station (BS) to serve the near and far users. In this scenario, we consider two possible situations during information transmission in the NOMA application system: perfect successive interference cancellation (SIC) and imperfect successive interference cancellation. The system performance is assessed primarily based on closed-form outage probability expressions. Numerical simulations are conducted to examine the outage probability of the proposed scheme and to verify the derived formulas. The study results have proved that the system performance is still good under the imperfect SIC condition, and several optimal parameters to improve the system performance have been found. Moreover, our research results have shown the superior performance of the proposed model compared with current orthogonal multiple access (OMA) networks.

Fog-RAN Enabled Multi-Connectivity and Multi-Cell Scheduling Framework for Ultra-Reliable Low Latency Communication

Ultra-Reliable Low Latency Communication (URLLC) is a newly introduced service class targeting emerging Internet-of-Things (IoT) application scenarios. This paper assumes an interference-limited Fog Radio Access Network (F-RAN) setup composed of multiple Remote Radio Heads (RRHs) equipped with multiple antennas serving single-antenna users. F-RAN facilitates collaborative solutions while reducing delay by pushing the network capabilities beyond the edge. By leveraging diversity, RRHs may cooperate through silencing, reducing interference, or joint transmission strategies such as maximal ratio transmission. We derive closed-form outage probability expressions and attain their diversity gain. We validate the derived analytical results through extensive numerical simulations. Furthermore, we propose a mini-slots-based scheduling framework to serve URLLC users within their fixed latency budget. In an interference-limited regime with the proposed scheduling framework, we show that a performance gain is superior when RRHs cooperate compared to when they do not. We briefly discuss the cost of reliability, i.e., the impact on the system&#x2019;s average sum throughput under cooperation. Moreover, numerical results verify that cooperating transmission schemes boost transmission reliability with a significantly improved latency performance at the cost of reduced system&#x2019;s average sum throughput.

Outage Performance Analysis of NOMA in Wireless Powered Cognitive Radio Networks with AF and DF Relaying Techniques.

Improving spectral efficiency under a certain energy limitation is an important design metric for future wireless communications as a response to the growing transmission demand of wireless devices. In order to improve spectral efficiency for communication systems without increasing energy consumption, this paper considers a non-orthogonal multiple access (NOMA)–based cognitive radio network, with the assistance of a wireless-powered relay station (RS), and then analyzes the system outage performance under amplified-and-forward (AF) and decoded-and-forward (DF) cooperative transmission modes. Specifically, the base station (BS) has the opportunity to cooperate by transmitting information through the RS, depending on whether the RS can harvest sufficient RF energy for cooperative transmission. That is to say, when the energy stored by the RS is sufficient for cooperative transmission, the RS will assist the BS to forward information; otherwise, the BS will send information through direct links, while the RS converts the radio frequency (RF) signals sent by the BS into energy for future transmission. Moreover, the transmission power required by the RS for cooperative transmission is usually relatively large, while the amount of harvested energy by the RS in a transmission slot is usually low, so it takes several consecutive time slots to accumulate enough transmission energy. To this end, we utilize a discrete-time Markov chain to describe the processes of charging and discharging of the RS. Subsequently, we derive the closed-form outage probabilities of both the primary and secondary systems for the considered system in AF and DF modes through mathematical analysis, and verify the accuracy of the analyses through Monte Carlo simulation. The simulation results show that the two proposed cooperative transmission schemes with AF and DF relaying techniques outperform both direct transmission and other similar schemes in both the primary and secondary system, while the DF scheme can provide better performance than the AF scheme within the range of setting values.

Performance analysis of downlink-NOMA over generalized-k fading channels

Due to the increasing demand for higher capacity in mobile communication devices, non-orthogonal multiple access (NOMA) has become a promising technique. Compared to existing orthogonal multiple access methods, NOMA can serve multiple users with better spectral efficiency by allowing co-channel interference, thus its reliability performance over various channel models needs further research. In this paper, closed-form outage probability, average channel capacity and symbol error rate are derived for a downlink-NOMA system with an arbitrary number of users over generalized-K fading channels. Finally, theoretical findings are validated via Monte Carlo simulations for several channel parameters.

Effect of Node Mobility on MU-MIMO Transmissions in Mobile Ad Hoc Networks

In this paper, we investigate the expected outage probability and expected throughput of a multi-user multiple-input multiple-output (MU-MIMO) transmission in mobile ad hoc networks (MANET) in the presence of co-channel interference and unpredictable inter-beam interference. In order to achieve multi-user diversity gain, the receiving nodes are required to report measured channel information to the transmitting node. During the time gap between channel measurement and data transmission, the channel may change with the location of moving nodes. The unpredictable behavior may cause a mismatch between the weight of beams and the instantaneous channel and the inter-beam interference in the data transmission phase. In order to obtain the closed form expected outage probability, we categorize the behavior of nodes according to whether the inter-beam interference exists or not and the number of received interference beams. The probability of each category and the closed form outage probability of an instantaneous MU-MIMO transmission of each category are derived. Additionally, the expected throughput of an MU-MIMO transmission which changes with the number of receiving nodes is obtained, and the optimal value of receiving nodes to maximize the expected throughput is discussed. Numeric results show the unpredictable inter-beam interference degrades the outage probability performance. Reducing the duration of the time gap could improve the expected outage probability and expected throughput.

Security-Reliability Tradeoff for Friendly Jammer Aided Multiuser Scheduling in Energy Harvesting Communications

In this paper, we investigate the physical-layer security in an energy-harvesting (EH) multiuser network with the help of a friendly jammer (J), where multiple eavesdroppers are considered to tap the information transmission from users (Us) to base station (BS). In this system, a power beacon (PB) transmits radio frequency (RF) signals to Us for charging. In order to enhance the security of wireless transmission, we propose non-energy-aware multiuser scheduling (NEAMUS) scheme and energy-aware multiuser scheduling (EAMUS) scheme. For the purpose of comparison, we introduce conventional round robin multiuser scheduling (CRRMUS) scheme. The closed-form outage probability (OP) and intercept probability (IP) expressions of NEAMUS, EAMUS, and CRRMUS schemes are derived over Rayleigh fading channels. Additionally, we analyze the security-reliability tradeoff (SRT) of NEAMUS, EAMUS, and CRRMUS schemes in terms of OP and IP. Numerical results show that the proposed EAMUS scheme is superior to the CRRMUS scheme and NEAMUS scheme in terms of SRT, demonstrating the advantage of the proposed EAMUS scheme in improving the physical-layer security and reliability. Moreover, SRT performance of NEAMUS and EAMUS schemes can also be improved by increasing the number of users.

Outage performance of UAV-assisted AF relaying with hardware impairments

The use of unmanned aerial vehicle (UAV) as aerial relay, i.e. UAV-assisted relaying, has the advantages of easy deployment, agility, and mobility compared to the traditional ground relaying. In this paper, our goal is to acquire the universal outage probability (OP) analytical expression for multi-rotor UAV-assisted AF relaying with transceiver hardware impairments (HIs) while considering a practical large-scale fading. Contrary to the existing works on the UAV-assisted relaying, where the OP was derived by assuming a specific small-scale fading, we make a more general assumption of arbitrary small-scale fading and thereafter apply an integral region shape-based approximate method (IRS-AM) to deduce a closed-form OP expression with adjustable error in a more common way. The derivation process is free of the concrete model of the small-scale fading while the final OP expression has a concise and intuitive form, which is determined by the cumulative distribution function (CDF) of the small-scale fading in both two links. Based on the derived results, we demonstrate the ceiling effect caused by HIs on the multi-rotor UAV-assisted AF relaying and obtain the end-to-end signal-to-noise-and-distortion ratio (SNDR) bound, which depends on the aggregate HIs levels and determines whether the considered relay network is always in outage or not. Computer simulations validate our studies and reveal the influence of HIs on the OP and the optimal UAV altitude.

On the performance of cooperative NOMA Using MRC at road intersections in the presence of interference

As the traffic safety has become of utmost importance, much attention is given to intelligent transportation systems (ITSs), and more particularly to vehicular communications (VCs). Moreover, 50 % of all crashes happen at road intersections, which makes theme critical areas. In this paper, we investigate the improvement when implementing maximum ratio combining (MRC) in cooperative VCs transmission schemes using non-orthogonal multiple access scheme (NOMA) at road intersections. We consider that a source transmits a message to two destinations with an aid of a relay. The transmission undergoes interference generated from a set of vehicles on the roads. We obtained closed form outage probability expressions, and we extended the derivations for a scenario involving K destination nodes and several road lanes. The performance of MRC cooperative NOMA are compared with the standard cooperative NOMA, and we show that implementing MRC with NOMA offers a significant improvement over the standard cooperative NOMA. Also, we compare the performance of MRC using NOMA with MRC cooperative orthogonal multiple access (OMA), and demonstrate that NOMA significantly outperforms OMA. We conclude that, it is always beneficial for vehicles to use MRC and NOMA even at the cost of implementation complexity. Finally, we demonstrate that the outage probability increases drastically when vehicles are closer to the road intersection, and that using MRC with NOMA improves significantly the performance in this context. To verify the correctness of our analysis, extensive Monte-Carlo simulations are carried out.