Outage Performance Of System Research Articles

Hybrid full-duplex/half-duplex relay selection scheme with optimal power under individual power constraints and energy harvesting

In practice, full-duplex (FD) transmission achieves better system outage performance than that of half-duplex (HD) transmission but suffers from strong self-interference (SI). In this paper, we provide performance analysis of relay selection (RS) schemes in multi-relay wireless networks, where we obtain the exact and approximate closed-form expressions for outage probability (OP) in the high signal-to-noise ratio (SNR) regime over independent and identically distributed (i.i.d.) Rayleigh fading channels in three proposed optimal RS schemes, i.e., HD deploying maximal ratio combine (HDMRC) and FD deploying joint decoding (FDJD) and hybrid FD/HD relaying transmission scheme (HTS). Most importantly, these schemes operate in two proposed optimal power supply policies so-called optimal power under the individual power constraints (OPIPC) and optimal power with energy harvesting ability (OPEHA). Additionally, asymptotic expressions in high SNR regime are given to help gain better insights on the system performance. It is also shown that the proposed HTS scheme outperforms HDMRC and FDJD schemes in terms of outage performance, where OPEHA is better than OPIPC under the impact of SI. Besides that, HTS RS scheme significantly decreases the power consumption which helps enhance energy efficiency. The validity of the proposed analyses is proven by simulations.

Cooperative spectrum sharing‐based relaying protocols with wireless energy harvesting cognitive user

In this study, the authors consider an energy-constrained secondary user which harvests energy from the primary signal and forwards this latter with the guarantee of spectrum access. Two key protocols are proposed, namely time-splitting cooperative spectrum sharing (TS-CSS) and power-sharing cooperative spectrum sharing (PS-CSS), based on time splitting and power sharing at the relay, respectively. Assuming a Nakagami-m fading model, exact closed-form expressions for the outage probabilities of the primary and secondary users are derived in decode-and-forward and amplify-and-forward relaying modes. From the obtained results, it is shown that the secondary user can carry its own transmission without any adverse impact on the performance of the primary user and that the PS-CSS protocol outperforms the TS-PSS protocol in terms of outage probability over a wide range of signal-to-noise ratio. Furthermore, the effect of various system parameters, such as splitting ratio, distance between nodes and harvesting efficiency, on the system outage performance on employing the proposed protocols is investigated and several insights are drawn.

Outage Analysis for Downlink NOMA With Statistical Channel State Information

Conventional non-orthogonal multiple access (NOMA) schemes assume perfect channel state information (CSI) at the transmitter side, which is nearly impractical for many communication scenarios. Instead, this letter considers a practical downlink NOMA system in the Nakagami-m fading channels, of which the transmitter only knows the statistical CSI associated with each user. We analyze the outage performance of the proposed system and derive a closed-form formulation of each user's outage probability. Moreover, based on statistical CSI, the transmitter can optimize the system's sum throughput over power allocation for different users. The accuracy of our outage analysis and the efficacy of the proposed optimization algorithm are both confirmed by simulation results.

Performance analysis of energy-harvesting-aware multi-relay networks in Nakagami-m fading

This paper investigates the outage performance of an energy-harvesting(EH) relay-aided cooperative network, where the source node transmits information to its destination node with the help of multiple energy-harvesting cooperative nodes. For such a system, we derive an explicit closed-form expression of outage probability over Nakagami-m fading channels, where the on-off EH model is considered. We simulate the explicit closed-form expression of outage probability with different parameters compared with the related Monte Carlo method. It is shown that the simulation results match well with the numerical ones, which demonstrates the correctness of our theoretical analysis. It indicates that to evaluate the system outage performance, our theoretical results can be applied without running the complex Monte Carlo simulation. Via simulations, it is observed that the system outage performance will be improved when natural source EH relays are employed. Besides, more relays, better system performance.

Evaluation on the capacity and outage performance of the free space optical system impaired by timing jitters over an aggregate channel

This paper proposed an analytical approach to evaluate the timing jitter’s impairment to the ergodic capacity and outage performance of an on-off keying wireless optical link, where the compound channel consists of Gamma–Gamma turbulence and pointing errors. Due to the complexity in deducing ergodic capacity, the closed-form bounds are developed, as well as the asymptotic limit. Meanwhile, the Gaussian–Hermite polynomial approximation is exploited to obtain the closed-form expression of outage probability in series. It has been verified by both theoretical results and the Monte-Carlo simulations that the timing jitter leads to a restriction of the ergodic capacity, even with tremendous transmitting power. In the meantime, small timing jitters could be endurable in the analysis of outage probability, whereas the large timing jitters diverge from the lower ones.

Outage Performance Analysis of Multi-User Selection for Two-Way Full-Duplex Relay Systems

In this letter, we consider a multi-user two-way full-duplex (FD) relay system, where the user pairs are predefined and the multiple pairs are competing one relay node to exchange messages within the pair. The system is suffering from independent but not identically distributed fading channels. We analyze the system outage performance with Max–Min scheduling scheme. The exact closed-form outage probability expressions are derived. In addition, the impacts of the residual self-interference incurred by the FD mode are considered. Moreover, we obtain some insights on the self-interference cancellation requirements for the FD mode. The superiority of FD mode and the multi-user diversity gain of the system are verified by the analytical results, which are corroborated by the numerical simulations.

Cognitive Multi-Relay Transmission over Asymmetric Fading Channels with Imperfect CSI

Outage performance of a cognitive multi-relay system using imperfect channel state information (CSI) of interfering links is formulated in this paper. In the considered cognitive system, it is assumed that wireless channels in the secondary network (source-to-relay and relay-to-destination links) experience Rician fading whereas interfering channels between primary and secondary networks undergo Rayleigh fading. Under the assumption of asymmetric fading, an outage probability (OP) expression of the secondary network is approximately formulated. Analytical OP values are in good agreement with related empirical ones in low signal-to-noise ratio (SNR) regimes. As a result, the approximate OP expression can be used to quantify the effect of asymmetric fading channels and CSI imperfection on the performance of cognitive multi-relay systems in practical SNR ranges.

Multi-User Scheduling of the Full-Duplex Enabled Two-Way Relay Systems

In this paper, we address the multi-user scheduling problem of the multi-user two-way full-duplex (FD) decode-and-forward relay system. According to the availability of the channel state information (CSI) and system state information (SSI), three scheduling schemes are investigated in terms of the system outage performance. Specifically, for the non-CSI case, we analyze the random scheduling scheme, which serves as a baseline for comparison. For the full CSI case, we propose the Max–Min scheduling scheme, which is theoretically proved to be sub-optimal in the low signal-to-interference-plus-noise ratio (SINR) regime but optimal in the high SINR regime. To minimize the outage probability, we propose the optimal scheduling scheme, which involves the full SSI. In addition, the exact closed-form outage probability expressions corresponding to different schemes are derived under the general independent but not identically distributed channels. The residual self-interference incurred by the FD mode is taken into account. Moreover, independent and identically distributed channels are also considered as special cases. Finally, numerical simulations are performed to corroborate the theoretical results. The results reveal that the Max–Min scheduling and optimal scheduling schemes significantly improve the outage performance compared with the random scheduling scheme.

Cooperative In-Vivo Nano-Network Communication at Terahertz Frequencies

Nano-devices have great potential to play a vital role in future medical diagnostics and treatment technologies because of its non-invasive nature and ability to reach delicate body sites easily as compared with conventional devices. In this paper, a novel concept of cooperative communication for in vivo nano-network is presented to enhance the communication among these devices. The effect on the system outage probability performance is conducted for various parameters, including relay placement, number of relays, transmit power, bandwidth, and carrier frequency. Results show approximately a tenfold increase in the system outage performance whenever an additional relay is included in the cooperative network, and hence show a great potential of using cooperative communication to enhance the performance of nano-network at terahertz frequencies.

Outage Performance of the Full-Duplex Two-Way DF Relay System Under Imperfect CSI

Contrary to the most existing works about the full-duplex (FD) relaying with perfect channel state information (CSI), this paper studies the outage performance of the two-way FD decode-and-forward relay network under the joint effects of the residual self-interference and imperfect CSI. We first derive the exact closed-form expressions of the system outage probability, based on which we obtain the outage probability under the perfect self-interference cancellation to investigate the impacts of the imperfect CSI on the system performance. In addition, to gain more insights about the imperfect CSI, we analyze the optimal power allocation scheme and an optimal relay node placement strategy, which minimize the system outage probability. The results reveal that the imperfect CSI will only affect the optimal power allocation, and the optimal relay node placement is related to the power ratio between the user nodes. Finally, analytical evaluations are performed to verify the theoretical results, and Monte Carlo simulations guarantee the correctness of the analytical evaluations.

Secrecy Outage Analysis on Underlay Cognitive Radio System With Full-Duplex Secondary User

In this paper, an underlay cognitive radio system, which consists of a primary-user (PU) transmitter (TX), a PU receiver (RX), a secondary-user (SU) TX, and a SU_RX, is considered. Benefitting from the underlay mode, SU_TX can deliver its information to SU_RX by sharing the spectrum resource authorized to PU. It is assumed that SUs are equipped with a single transmitting antenna and a single receiving antenna, which are isolated, and work in full-duplex (FD) mode. By considering that the information signal transmitted from PU_TX to PU_RX may be eavesdropped by SU_TX if SU_TX is malicious, we investigate the secrecy outage performance of the PU system. The approximated closed-form expression for secrecy outage probability (SOP) and the lower boundary of the asymptotic SOP have been derived and verified by simulation results. Our results reveal the impact of the eavesdropping of the SU and the FD mode adopted at the SU transmitter on the secrecy performance of the PU system in underlay spectrum sharing mode.

Joint User and Relay Selection for Cooperative NOMA Networks

This paper investigates the joint user and relay selection algorithm for cooperative non-orthogonal multiple access networks, where multiple users transmit messages to two destinations by utilizing multiple amplify-and-forward relays. To improve the outage performance of system, an optimal selection criterion is proposed at the user-relay pairs. We derive the closed-form analytical expressions on the outage probability, as well as the asymptotic expressions for large transmission power. Based on the derived analytical expressions, the effect of the number of relays and the target data rate on the outage performance is revealed. Results indicate that when the target data rate becomes small enough, the diversity order of the outage probability equals to the number of relays, while the target data rate grows without bound, the outage probability achieves one.

Joint relay selection and power allocation in energy harvesting AF relay systems with ICSI

In various wireless networks, power allocation scheme promises significant benefits in energy harvesting (EH) wireless networks. However, these benefits depend on the knowledge of the channel state information (CSI), which is hardly perfect. Therefore, in this study, the authors investigate an EH two-way relaying network with channel estimation error taking into consideration. First, the system outage performance is studied and closed-form expressions for the outage probability are derived. On the basis of minimising the outage probability, an optimal power allocation (OPA) scheme is proposed and the effective ways to solve this OPA scheme are presented. In addition, a joint relay selection and the OPA scheme is provided to further improve the system performance. Finally, by comparing the OPA scheme with conventional power allocation schemes via simulations, the superiority of the OPA scheme is demonstrated. Moreover, the impact of imperfect CSI on the system performance is analysed and the simulation results show the robustness of the OPA scheme.

Power Waveforming: Wireless Power Transfer Beyond Time Reversal

This paper explores the idea of time-reversal (TR) technology in wireless power transfer to propose a new wireless power transfer paradigm termed power waveforming (PW), where a transmitter engages in delivering wireless power to an intended receiver by fully utilizing all the available multipaths that serve as virtual antennas. Two power transfer-oriented waveforms, energy waveform and single-tone waveform, are proposed for PW power transfer systems, both of which are no longer TR in essence. The former is designed to maximize the received power, while the latter is a low-complexity alternative with small or even no performance degradation. We theoretically analyze the power transfer gain of the proposed power transfer system over the direct transmission scheme, which can achieve about 6 dB gain, under various channel power delay profiles and show that the PW is an ideal paradigm for wireless power transfer because of its inherent ability to recollect all the power that is possible to harvest from the surrounding environment. In addition, the outage performances in harvesting power of the PW system and the conventional multiple-input multiple-output (MIMO) system are derived. It reveals that the PW system can achieve the same outage performance of the MIMO system as long as the number of resolvable multipaths is sufficiently large. Simulation results validate the analytical findings and experimental results demonstrate the effectiveness of the proposed PW technique.

Secrecy outage analysis with Kth best relay selection in dual-hop inter-vehicle communication systems

In this paper, we investigate the secrecy outage performance of a dual-hop inter-vehicle communication system, in which all nodes are in motion and all fading channels are assumed to undergo cascaded Rayleigh distributions. In particular, a mobile node (source) with a single antenna transmits confidential information to another mobile node (destination) equipped with M(M⩾1) antennas through N(N>1) single-antenna road-side relays in the presence of an eavesdropper with L(L⩾1) antennas. Assuming decode-and-forward relaying, the Kth best relay is selected to assist source–destination transmission based on two classical relay selection schemes: (i) the optimal source-relay link scheme; and (ii) the optimal source-relay-destination link scheme. Closed-form analytical expressions for secrecy outage probability of those two schemes are derived, and verified with Monte Carlo simulation results.

Performance Analysis and Power Allocation for Underlay Cognitive MIMO Relaying Networks with Transmit Antenna Selection Under Antenna Correlation

In this paper, we examine transmit antenna selection with receiver maximal ratio combining (TAS/MRC), and selection combining (TAS/SC) in underlay multiple-input multiple-output cognitive relay networks with decode-and-forward relaying protocol, considering optimal and suboptimal cases. The considered secondary user (SU) network consists of a source, a relay and a destination each equipped with multiple correlated antennas. On the other hand, the primary network is composed of L primary users (PU) destinations, each of which is equipped with multiple correlated antennas. The SU transmission power is limited to the minimum between the maximum allowable power for transmission and the maximum interference power allowed by the PU network. In the analysis, all the channel coefficients between the PU and SU networks and between the SU nodes are assumed to follow independent and identically distributed (i.i.d.) Rayleigh fading distribution. Hence, new exact closed-form expressions are derived to study the outage performance of the considered CRN system. Moreover, for the high SNR values, simple asymptotic expressions for the outage probability are obtained to get more insights on the characterization of the achievable diversity orders and coding gains. The impact of antenna correlation on the system outage probability is investigated for special correlation cases. To enhance SU network performance, a power allocation optimization problem is formulated to minimize the SU asymptotic outage probability by optimally distributing the SU power budget between the SU source and SU relay under the constraints of total allowable SU transmission power and maximum allowable PU interference limit. The derived analytical formulas herein are supported by numerical and simulation results to clarify the main contributions. The results show that although the antenna correlation harms the system coding gain, the considered system can still achieve a full diversity order. Also, The results show that although the outage performance of optimal case outperforms the suboptimal case, the optimal case is more complicated compared to the suboptimal one. Moreover, the optimal power allocation solutions enhance the system outage performance compared to equal distribution model.

Effect of channel correlation on multi‐hop data transmission over power lines with decode‐and‐forward relays

The authors presents a study of the effect of correlation among the multi-hop path gains on the average channel capacity and the outage performance of a power line communication system equipped with decode-and-forward relays. The path gain of each hop follows a log-normal distribution and the joint density is modelled by a multivariate log-normal distribution with exponential correlation. A distance dependent signal attenuation factor is added to the channel model to incorporate the effect of physical distance between the nodes. Furthermore, a Gaussian mixture (Bernoulli-Gaussian) noise is included in the system model to analyse the effect of impulsive noise together with thermal noise. Approximate closed-form expressions for the end-to-end average channel capacity and the outage probability are derived. Numerical results showing the impact of the amount of correlation, the number of hops, the impulsive noise power, and the spread of the average power of the path gains on the performance are presented. The results show that for a fixed transmit power and end-to-end distance between source and destination, the performance improves with increasing number of hops; however, the amount of improvement reduces with increasing channel correlation.

Outage performance of multihop free-space optical communication system over exponentiated Weibull fading channels with nonzero boresight pointing errors

The outage performance of the multihop free-space optical (FSO) communication system with decode-and-forward (DF) protocol is studied by considering the joint effects of nonzero boresight pointing errors and atmospheric turbulence modeled by exponentiated Weibull (EW) distribution. The closed-form analytical expression of outage probability is derived, and the results are validated through Monte Carlo simulation. Furthermore, the detailed analysis is provided to evaluate the impacts of turbulence strength, receiver aperture size, boresight displacement, beamwidth and number of relays on the outage performance for the studied system.

An analysis of secrecy outage performance of DF and RF \\relaying SIMO system with imperfect CSI

This paper presents an investigation of the physical layer secrecy outage performance of the cooperative system in the typical four-node (source, relay, destination, and eavesdropper) scenario with imperfect channel state information (CSI). Specifically, we consider the single-input multiple-output wiretap channels, where the source (S) and the relay (R) are equipped with a single antenna, and the destination (D) and the eavesdropper (E) are equipped with multiple antennas. D and E adopt maximal ratio combining to process multiple copies of signals, and the relay adopts decode-and-forward (DF) and randomize-and-forward (RF) schemes to forward the received signal to the destination. E overhears the information transmitted over both the S-R and R-D links. We derive the closed-form and asymptotic expressions for the secrecy outage probability under both the DF and RF schemes with imperfect CSI, respectively, the accuracy of which is verified by simulation results.

Performance of Virtual Full-Duplex Relaying on Cooperative Multi-path Relay Channels

We consider a cooperative multi-path relay channel (MPRC) where multiple half-duplex relays assist in the packet transmissions from a source to its destination. A virtual full-duplex (FD) relaying scheme is proposed that allows the source to transmit a new packet simultaneously with the selected best relay, with the rest of the relays attempting to decode this new packet. Thus, a new source packet can be served in each time slot, as in FD relay systems. Taking into account the effect of inter-relay interference (IRI) that is caused by simultaneous relay and source transmissions, a Markov chain analytical model is used to characterize the decoding performance at the relays, based on which the overall outage probability of MPRC is obtained in closed-form expressions. The asymptotic performance analysis reveals that in low rate scenarios, a close-to-full diversity order is achieved by the proposed scheme while substantially improving the spectrum efficiency. In high rate scenarios, the decoding performance of relays is limited by IRI and the system outage performance experiences an error floor. Simulation results demonstrate the performance gains of the proposed scheme by comparisons with existing half-duplex and FD relay systems in the literature.