Cooperative Selection Diversity in Wireless Multiuser Relay Networks

The use of aerial platforms has recently attracted significant interest in Internet of Things (IoT)-based heterogeneous communication networks to support flexible and efficient network connection. This work investigates the performance of a ground-aerial autonomous aerial vehicle (AAV)-assisted hybrid power line communication (PLC)/free-space optical (FSO) communication system employing both decode-and-forward (DF) and fixed-gain amplify-and-forward (AF) relaying protocols. It is assumed that the PLC channel gain is Log-normally distributed while the Bernoulli-Gaussian random process models the PLC channel noise. The FSO link established between the FSO transmitter and the AAV considers the combined influence of the generalized Málaga distributed atmospheric turbulence (AT), random fog, nonzero boresight pointing errors, and Angle-of-Arrival (AoA) fluctuations of the AAV. Based on this, we evaluate the cumulative distribution function (CDF) and probability density function (PDF) of the end-to-end signal-to-noise ratio (SNR). Further, capitalizing on the statistical characterization of CDF and PDF, we derive series-based expressions for average symbol error rate (ASER), outage probability (OP), and average channel capacity (ACC) utilizing both heterodyne detection (HD) and direct detection (DD) techniques. Additionally, we conduct an asymptotic analysis of ASER in terms of the coding gain and diversity order in a high SNR regime. Likewise, a detailed analysis is carried out to find the optimal value of the field-of-view (FOV) angle and average SNR to achieve minimum ASER under the combined influence of the aforementioned channel conditions using the DF relaying scheme. Furthermore, the impact of all the considered channel parameters and impairments is demonstrated through the numerical results.

In this paper, we investigate the theoretical performance analysis of opportunistic scheduling for dual-hop cognitive relay network with multiuser in the secondary system. Different from the existing work, we take the consideration of primary user's interference with opportunistic scheduling technique and theoretically derive the influence of the interference from primary transmitter for the scenario. The cumulative distribution function (CDF) of signal-to-noise ratio (SNR) is formulated and the exact close-form expression of the cognitive relay network outage probability is derived. After calculating the asymptotic outage probability in high SNR regime and asymptotic error probability, we provide an adaptive power allocation scheme in the secondary system to optimize the capacity of system. It is confirmed that the opportunistic scheduling technique for multiuser has a positive influence on the performance of cognitive networks. Moreover, the adaptive power allocation can also promote system performance. Finally, numerical simulations are provided to support and directly reflect the correctness of our analytic results.

This paper analyzes the performance of a power line carrier communication (PLCC) system under the effect of complex channel gain and additive background noise utilizing quadrature phase shift keying (QPSK) transmission scheme. The background noise considered here is complex in nature whose envelope is Nakagami-m distributed while phase follows uniform distribution. The magnitude and phase of complex channel gain coefficients are assumed to have Rayleigh and uniform distribution, respectively. Utilizing the sub-optimal decision rule for the real and imaginary parts of the complex data, and after deriving the expressions for the conditional probability density function (PDF) of the decision variables, we obtain a closed from expression for the conditional symbol error rate (SER) of the QPSK data for the considered system. Further, we analyze the outage performance of the considered PLCC system and derive the expression for conditional outage probability. The derived expressions of SER and outage probability are conditioned on the phase of the complex channel gain and the noise, which has been numerically averaged to get the analytical values for average SER and average outage probability. The analytical results presented in this paper have been verified by the simulations.

In the context of two-wave with diffuse power (TWDP) fading scenarios, this paper analyzes the outage probability and symbol error rate (SER) of single relay cooperative networks using amplify-and-forward (AF) relaying. Each channel in the network is assumed to be independently and non-identically distributed. The statistical result of the upper bound on the received signal-to-noise ratio (SNR) is derived. We derive the closed-form asymptotic expressions to approximate the outage probability and SER in the high SNR regime, respectively. Based on the asymptotic results, the diversity order and coding gain of the cooperative network is analyzed. Simulation results show that these asymptotic results are tight particularly in the high SNR regime for cooperative networks in different fading scenarios.

In this study, the authors consider distributed orthogonal space–time block coding for relay‐based channel state information‐assisted amplify‐and‐forward networks. Specifically, they show that opportunistic relaying (OR) is an optimal solution in terms of instantaneous signal‐to‐noise ratio (SNR), that is, it provides the maximum instantaneous SNR under the constraint of fixed transmit power for the relays. In particular, instead of allocating the given transmit power to all relays, letting the best relay transmit with this power is an optimal solution for maximising the received SNR. To exhibit this benefit, Monte Carlo simulations are presented showing superior performance of the OR scheme compared to equal power allocation policy for the considered relay networks. For the considered optimal scenario, the authors further derive analytical expressions for the outage probability and symbol error rate (SER) over quasi‐static independent, not necessarily identically distributed Nakagami‐ m fading channels. They further present asymptotically tight approximations for the outage probability and SER in the high SNR regime, rendering insights into the cooperative diversity behaviour. Finally, numerical results are provided to examine the effect of network parameters on the system performance of the considered network.

In this study, the authors investigate the performance of opportunistic scheduling for the dual‐hop amplify‐and‐forward multi‐user cognitive relaying network. Expressions are derived for the cumulative distribution function (CDF) and probability density function of the equivalent signal‐to‐noise ratio (SNR). From the derived CDF, the outage performance of the cognitive network is investigated. Then, an expression for average error probability is derived. Furthermore, simple and generic asymptotic expressions for the outage and error probabilities are obtained and discussed. In addition, a closed‐form expression for the system's ergodic capacity is derived. Their asymptotic results show that opportunistic scheduling has no impact on diversity gain. It is confirmed that the array gain determines the SNR advantage of opportunistic scheduling over the single‐user scenario. Moreover, they study adaptive power allocation under the total transmit power constraint in order to minimise the average error probability. As expected, the results show that optimum power allocation improves system performance compared with uniform power allocation. Finally, numerical results and Monte Carlo simulations are also provided to support the correctness of the analytical calculations.

On the maximal-ratio combining of FSO and RF links over generalized distributions and its applications in hybrid FSO/RF systems

In this paper, we study the performance of multiuser two-way relaying (TWR) system in cellular environment, wherein an N a -antenna base station (BS) wants to exchange information bidirectionally with one of the several single-antenna users (USs) with the aid of a fixed gain single-antenna relay terminal under different target rate requirements. In particular, we employ maximal ratio transmission (MRT)/maximal ratio combining (MRC) beamforming (BF) at the BS with user scheduling that maximizes the end-to-end signal-to-noise ratio (SNR). We deduce a new expression for the exact overall outage probability (OOP) of the considered system under independent and identically distributed (i.i.d.) Rayleigh fading channels. Moreover, we also derive a closed-form expression for the sum symbol error rate (SSER) to analyze the system error performance under various modulation schemes. Finally, the analytical findings are validated by the numerical and simulation results, and reveals that the diversity order of the considered system is independent of traffic asymmetry and decided by the minimum of the number of BS antennas and the number of USs.

In this work, we explore the outage probability (OP) analysis of selective decode and forward (S-DF) cooperation protocol employing multiple-input multiple-output (MIMO) orthogonal space-time block-code (OSTBC) over time varying Rayleigh fading channel conditions with imperfect channel state information (CSI) and mobile nodes. The closed-form expressions of the per-block average OP, probability distribution function (PDF) of sum of independent and identically distributed (i.i.d.) Gamma random variables (RVs), and cumulative distribution function (CDF) are derived and used to investigate the performance of the relaying network. A mathematical framework is developed to derive the optimal source-relay power allocation factors. It is shown that source node mobility affects the per-block average OP performance more significantly than the destination node mobility. Nevertheless, in other node mobility situations, cooperative systems are constrained by an error floor with a higher signal to noise ratio (SNR) regimes. Simulation results show that the equal power allocation is the only possible optimal solution when source to relay link is stronger than the relay to destination link. Also, we allocate almost all the power to the source node when source to relay link is weaker than the relay to destination link. Simulation results also show that OP simulated plots are in close agreement with the OP analytic plots at high SNR regimes.

In this paper we consider a multi relay Decode and Forward (DF) relay network assisted by Hybrid automatic repeat request (HARQ) in a Rayleigh block fading environment. The system uses an incremental relaying strategy in which the best relay is selected to cooperate with source. A Space-Time Block coding (STB) is used for cooperation between source and selected relay to transmit the data to the destination. Relays and destination use maximum ratio combining (MRC) technique to decode the sent message using previously received versions. We derive a closed-form expression of asymptotic outage probability at high Signal-to-Noise Ratio (SNR) regime. We also derive the average delay and throughput in a delay constrained application. The derivation method is based on the Laplace transform, which proves to be a very effective analytical tool when combined with the properties of the special functions. In addition, we investigate the optimum power allocation strategy to minimize the outage probability and consequently maximize the average throughput perceived by the end user. The simulation results show that the obtained analytical bound for the outage probability is very tight at high SNR regime. In addition the proposed power allocation scheme clearly outperforms the equal power allocation.

A performance analysis is presented for amplify-and-forward (AF) cooperative relay networks employing transmit antenna diversity with orthogonal space-time block codes (OSTBCs), where multiple antennas are equipped at the transmitter. We develop a symbol-error-rate (SER) and outage performance analysis for OSTBC transmissions with and without cooperative diversity over flat Rayleigh fading channels. We first derive exact probability density functions (pdf's) and cumulative distribution functions (cdf's) for the system SNR without direct transmission with an arbitrary number of transmit antennas and then present the exact closed-form SER and outage probability expressions. Next, we derive the moment-generating function (MGF) for the overall system SNR with direct transmission and present the exact SER and outage probability with joint transmit antenna diversity and cooperative diversity. The theoretical analysis is validated by simulations, which indicate an exact match between them. The results also show how the transmit antenna diversity and the cooperative diversity affect the overall system performance.

In this article, a signal-to-noise ratio (SNR)-based hybrid decode-amplify-forward scheme in a distributed Alamouti-coded cooperative network is proposed. Considering a flat Rayleigh fading channel environment, the MATLAB simulation and analysis are carried out. In the cooperative scheme, two relays are employed, where each relay is transmitting each row Alamouti code. The selection of SNR threshold depends on the target rate information. The closed form expressions of symbol error rate (SER), the outage probability and average channel capacity with tight upper bounds are derived and compared with the simulation done in MATLAB environment. Furthermore, the impact of relay location on the SER performance is analysed. It is observed that the proposed hybrid relaying technique outperforms the individual amplify and forward and decode and forward ones in the distributed Alamouti-coded cooperative network.

In this paper, the effect of feedback delays on the performance of multiple-input multiple-output antenna amplify-and-forward relay networks with the best transmit/receive antenna pair selection over Rayleigh fading is studied. The cumulative distribution function and the moment generating function of the end-to-end signal-to-noise ratio (SNR) are derived. Closed-form expressions for the outage probability, average symbol error rate (SER), and the SNR moments are also derived. To gain further insights, the asymptotic outage probability, average SER, diversity order, and coding gain are presented. Numerical results and Monte-Carlo simulations are provided to illustrate the detrimental effects of feedback delays on the system performance and to verify the accuracy of our analysis.

The performance of multihop detect‐and‐forward relaying system is analyzed over fluctuating two‐ray fading channels for 28 GHz millimeter wave communications. Exact closed‐form expressions for outage probability and average symbol error rate of various modulation schemes over nonidentically distributed fluctuating two‐ray fading channels have been obtained. The derived expressions are given in terms of the Lauricella hypergeometric functions and . Moreover, the derived expressions also accommodate several others reported results in the literature for two‐wave diffuse power, Rician, Rician shadowed, Nakagami‐m, and Hoyt fading channels. Asymptotic outage probability and average symbol error rate expressions are also derived, which provide useful insights on the factors governing the performance of the considered system. The numerical results have been verified with Monte‐Carlo simulation results.

In this paper, we study the performance of mixed free space optical (FSO)-radio frequency (RF) multi-user relay network with aperture selection and opportunistic user scheduling in the presence of Poisson field interference. The considered system includes multiple optical sources (apertures), one amplify-andforward (AF) relay, and multiple users. The source is connected with the relay node through FSO links and the relay is connected with the users through RF links with a Poisson field interference at the users. The FSO-RF channels are assumed to follow Málaga-M/shadowed κ-μ fading models with pointing errors on the FSO links. Exact closed-form expressions are derived for the outage probability and average symbol error probability (SEP). Moreover, the system performance is studied at the high signal-to-noise ratio (SNR) regime, where an approximate expression for the system outage probability is derived, in addition to deriving the system diversity order and coding gain. Then, the optimum source and relay transmission powers and relay position are determined to minimize the system asymptotic outage probability. The Monte-Carlo simulations are provided to validate the achieved exact and asymptotic results.