Combination Of Selection Research Articles

Multiple Nodes Co-Carrier Cooperative Transmission in LEO Communication Networks: Developing the Diversity Gain of Satellites.

Low Earth orbit (LEO) satellite communication (SATCOM) networks have gradually been recognized as an efficient solution to enhance ground-based wireless networks. As one of the main characteristics of LEO SATCOM, the beam-edge area could be covered by multiple satellite nodes. In this case, user terminals (UTs) located at the beam-edge have the chance to connect one or more LEO satellites. To develop the diversity gain of multiple nodes in the overlapping area, we propose two high spectral efficiency cooperative transmission strategies, i.e., directly combining (DC) and selection combining (SC). In the DC scheme, signals arrived at the UT simultaneously could be combined into one enhanced signal. For downlink time division multiplexing, the SC scheme enables the UT to select the strongest signal path. Further, as there exists a significant channel gain difference of the beam-center and beam-edge areas, UTs in these two areas can be allocated in one resource block. In this case, we derive co-carriers based on DC and SC, respectively. To deeply analyze the novel methods, we study the ergodic sum-rate and outage probability while the outage diversity gain is further provided. Simulation results show that the co-carrier-based DC method has the ability to provide a higher ergodic sum-rate while the SC method performs better in terms of the outage probability.

Performance implications of channel aware cooperative probing-GBN ARQ in the context of wireless body area networks

The advent of Wireless Body Area Networks (WBAN) in patient care has revolutionized the healthcare sector as patients can now be monitored continuously in real-time and as well remotely. Despite its significant advantages, WBAN encounters a notable challenge in the fading aspect, which undermines its effectiveness. Improving WBAN efficiency involves tackling signal fading, which is crucial. Cooperative communication offers a promising solution by introducing spatial diversity to counteract fading effects. We propose a scheme that uses cooperative communication and the Probing-Go Back N Automatic Repeat Request (P-GBN ARQ) technique to reduce the fading effect. The proposed method uses feedback to predict the channel's current state, and the probing interval is determined by the received signal's Average Fading Duration (AFD). The proposed scheme's performance is also assessed extensively through simulations employing various metrics. The results demonstrate a considerable improvement in throughput performance with the inclusion of knowledge about channel fading. The Bit Error Rate (BER) execution is compared with Selection Combiner (SC) and conventional Maximal Ratio Combining (MRC). At 10−3, the cooperative method achieves it at 13 dB SNR, whereas the direct approach reaches it at 24 dB SNR, requiring an additional 11 dB. The proposed approach minimizes BER, enhancing throughput and reliability in WBAN.

Enhancing uplink NOMA cooperative networks with RIS-UAV assistance in Nakagami-[formula omitted] fading channels

Reconfigurable intelligent surfaces (RIS) emerges as a novel communication technology for the 6G networks, boasting advantages such as low cost, high energy efficiency, and wide coverage. To enhance spectrum utilization and ensure signal transmission stability in complex communication scenarios, this paper presents an uplink cooperative non-orthogonal multiple access (NOMA) transmission network assisted by unmanned aerial vehicles (UAV) equipped with RIS. Firstly, a direct link is established between near users and the base station, while a decode-and-forward (DF) relay R and RIS-UAV are deployed between far users and the base station to achieve reliable transmission in a dynamic environment through joint NOMA. Furthermore, an incremental cooperative NOMA scheme is proposed for the uplink transmission, where the relay R remains silent if the RIS-UAV successfully transmits the signal of distant users; if the RIS-UAV fails to transmit the signal to the base station, the relay R is activated to complete the communication between distant users and the base station. Then, the base station employs a selection combining (SC) scheme to process the received signals. Finally, exact expressions of the outage probability under various power allocation strategies are derived. The research results indicate that the outage performance improves with an increase in the number of RIS reflection elements. Moreover, the presence of RIS-UAV can reduce the impact of power allocation strategies on the performance of the uplink NOMA network compared to networks without RIS-UAV.

Hybrid selection combining scheme for correlated cooperative communication over [formula omitted]-[formula omitted] fading channels

Due to poor (limited) scattering, a correlation among channels is inevitable, resulting in performance degradation of wireless communication systems. In this paper, we propose a hybrid selection combining (SC), also known as switched scaled – SC for correlated cooperative communication over κ-μ fading channel. By using paired error analysis, we derive the end-to-end symbol error probability of this system over bivariate κ-μ channel fading with M-ary phase shift keying (MPSK) modulation. In addition, we obtain significant parameters of hybrid SS-SC, such as the optimum scaling factor and optimum threshold by using the second derivative test. For every signal to noise ratio (SNR), we obtain different optimum thresholds and scaling factors. Our analytical results were found to overlap significantly with those of the simulation results. They were also compared with the variants of SC and switched diversity techniques. Our study demonstrates that the proposed hybrid technique performs better than the other SC and switched diversity schemes over correlated and uncorrelated fading channels. Furthermore, we derive an asymptotic symbol error probability for the proposed system, and the asymptotic results are in agreement with the analytical results at higher SNRs. Our study also shows that the diversity order of the system depends on the mutually exclusive events of the proposed technique.

MDE and LLM Synergy for Network Experimentation: Case Analysis of Wireless System Performance in Beaulieu-Xie Fading and κ-µ Co-Channel Interference Environment with Diversity Combining.

Channel modeling is a first step towards the successful projecting of any wireless communication system. Hence, in this paper, we analyze the performance at the output of a multi-branch selection combining (SC) diversity receiver in a wireless environment that has been distracted by fading and co-channel interference (CCI), whereby the fading is modelled by newer Beaulieu-Xie (BX) distribution, and the CCI is modelled by the κ-µ distribution. The BX distribution provides the ability to include in consideration any number of line-of-sight (LOS) useful signal components and non-LOS (NLOS) useful signal components. This distribution contains characteristics of some other fading models thanks to its flexible fading parameters, which also applies to the κ-µ distribution. We derived here the expressions for the probability density function (PDF) and cumulative distribution function (CDF) for the output signal-to-co-channel interference ratio (SIR). After that, other performances are obtained, namely: outage probability (Pout), channel capacity (CC), moment-generating function (MGF), average bit error probability (ABEP), level crossing rate (LCR), and average fade duration (AFD). Numerical results are presented in several graphs versus the SIR for different values of fading and CCI parameters, as well as the number of input branches in the SC receiver. Then, the impact of parameters on all performance is checked. From our numerical results, it is possible to directly obtain the performance for all derived and displayed quantities for cases of previously known distributions of fading and CCI by inserting the appropriate parameter values. In the second part of the paper, a workflow for automated network experimentation relying on the synergy of Large Language Models (LLMs) and model-driven engineering (MDE) is presented, while the previously derived expressions are used for evaluation. Due to the aforementioned, the biggest value of the obtained results is the applicability to the cases of a large number of other distributions for fading and CCI by replacing the corresponding parameters in the formulas for the respective performances.

Scaled Selection Combining Receiver for Cooperative NOMA-based 5G Cellular Systems

Non-Orthogonal Multiple Access (NOMA) technology can accommodate more subscribers concurrently and achieve higher spectrum efficiency than Orthogonal Multiple Access (OMA) technologies. This work investigates the performance of the two subscriber downlink cooperative NOMA system with Scaled Selection Combining (SSC) comprising a Base Station (BS), a cell edge subscriber and a near subscriber. Due to the channel conditions, the error performance of the cell edge subscriber is poorer compared to the near subscriber. To mitigate this and enhance the performance, the proposed SSC combines signals from BS and near subscriber and chooses the best signal between them. The Symbol Error Probability (SEP) of this cellular system with M−ary Phase Shift Keying (MPSK) modulation is derived under the Rayleigh fading environment. The optimum scaling factor to reduce the SEP is also obtained. The theoretical SEP expressions of SSC are validated with the Monte-Carlo simulations. The proposed system provides better SEP and outperforms the non-cooperation and traditional Selection Combining (SC) schemes. Additionally, the efficacy of the proposed system under various modulation schemes is studied.

Outage of cooperative NOMA with an energy harvesting relay in an underlay cognitive radio network

SummaryThis paper analyzes the performance of a cooperative nonorthogonal multiple access (NOMA) in an underlay cognitive radio network aided by an energy harvesting relay. A secondary source transmits signal for two users, where a near user acts as a relay for the far user. The far user applies the selection combining (SC) approach on the signals which were relayed by the near user and received via direct path from the secondary source. We analytically derive the outage probability (OP) of each user separately, the overall system OP, and the throughput of the system. The impact of the power allocation coefficient of NOMA and energy harvesting parameters on outage is indicated. Further, the performance of the network is investigated with imperfection in successive interference cancellation (SIC), maximal ratio combining (MRC) at relay, and Nakagami‐m fading. The results derived analytically are supported by simulation in MATLAB.

Coding techniques for diversity enhancement of dense wavelength division multiplexing MIMO‐FSO fault protection protocols systems over atmospheric turbulence channels

AbstractAn enhanced transmission is presented in a multiple‐input‐multiple‐output (MIMO) dense‐wavelength division multiplexed (DWDM) free‐space‐optical (FSO) communication link using diversity coding techniques under the effect of turbulent weather phenomenon. The findings show good performance with an (8 channels × 2.5 Gbps data rate/channel) 20 Gbps 1500 m transmission distance. The bit‐error‐rate (BER), outage probability (OP), and signal‐to‐noise ratio (SNR) of the diversity combining techniques using maximum‐ratio combining (MRC), selection combining (SC), and equal‐gain combining (EGC) technique are evaluated in this work. The obtained results illustrate that Alamouti, space‐time coding (STC), space‐time block coding (STBC), space‐time trellis code (STTC), orthogonal STBC (O‐STBC), and quasi‐orthogonal STBC (QO‐STBC) on the minimum mean‐square‐error, and MRC are worth implementing on the DWDM‐FSO wireless communication systems. The mitigation of atmospheric turbulence is achieved using MIMO diversity combining techniques coding. The simulation results for diversity coding techniques using QO‐STBC/STTC and SC/MRC in the MIMO‐DWDM FSO communication system can improve BER performance, OP, and SNR. The MRC exhibits the lowest OP and BER when compared with the SC and EGC. The numerical results demonstrate that the FSO communication link using DWDM QO‐STBC/STTC improves the power penalty at both BER values under varying atmospheric turbulence conditions for ST, MT, and WT, in comparison to FSO systems without DWDM QO‐STBC/STTC diversity coding techniques.

Age of Information for Partial Earliest Relay Aided Short Packet Status Update With Energy Harvesting

This paper focuses on the timely delivery of status updates for a multi-relay assisted energy harvesting (EH) Internet of Things system with short packet communications (SPC), where an EH-powered source transmits status updates to a destination with the aid of multiple EH-powered relays. To improve the energy efficiency and information freshness, an earliest-ℓ partial relay selection scheme is proposed, in which the earliest ℓ relays that successfully receive the status update from the source will be selected to forward the status update to the destination, and the selection combining (SC) and maximal-ratio combining (MRC) schemes are used at the destination. Firstly, we investigate the update packet delivery schemes of source-relay (S-R) and relay-destination (R-D) links, and present the packet error probabilities under the SC and MRC schemes based on SPC theory. Secondly, after characterizing the full charge time durations of both the source and relay, we investigate the statistical description of the number of the packet transmission attempts from the source to relay as well as the one from the relay to destination by using order statistics. With the analysis of the evolution of the instantaneous age of information (AoI), the expression for average AoI is derived. Finally, we investigate the average AoI minimization, which is formulated as a coupled triplet problem of the packet lengths at the source and relays and the value of ℓ. To overcome the coupling, we present the convexity approximation of the average AoI as well as the concise proof. Then, an efficient gradient-based two-step optimal search algorithm is proposed to solve the optimization problem, which searches the local optimal packet lengths for S-R and R-D links by iteratively updating the value of ℓ until the global optimal objective parameters are found. Numerical analyses give the effect of the key parameters on the average AoI, and the comparison demonstrates that the proposed gradient-based method converges quickly than the conventional greedy search method.

ANALYSIS OF THE USER PAIRING NOMA SYSTEM OVER THE NAKAGAMI-M FADING CHANNEL CONDITIONS

The potential of non-orthogonal multiple access (NOMA) as a multiple access strategy for 5G and LTE upgrades has attracted much attention. In this study, we examine user pairing in NOMA strategy for multiple-input multiple-output (MIMO) users. The simulation results for near-near (N-N) and near-far (N-F) user pairing shames have been provided. The channel becomes time-selective after considering the node mobility situation. Furthermore, simulation curves demonstrate that adopting the user pairing approach reduces computing cost. The network's sum rate performance was further tested utilizing selection combining (SC) NOMA and time division for multiple access (TDMA). It is shown that when a user nearest to the base station is linked with the farthest user from the base station, the total sum rate dramatically increases. When the channel conditions between the two users are varied, the NOMA performs significantly better. The NOMA still surpasses TDMA in terms of sum rate when N-N and far-far (F-F) pairings are used, but the difference isn't significant. The SC-NOMA has a low performance when compared to TDMA. It was discovered that when the shape parameter is adjusted to two, the outage probability (OP) performance of three NOMA mobile users and a standard orthogonal multiple access (OMA) mobile user improved (multipath propagation scenario).

On the block error rate performance of cooperative non‐orthogonal multiple access short‐packet communications with full‐duplex relay and partial relay selection

AbstractIn this paper, we mathematically investigate a downlink non‐orthogonal multiple access (NOMA) system for short‐packet communications (SPC) in which the near users are used as full‐duplex (FD) relays to forward intended signals from the source to a far user. In addition, partial relay selection is employed to enhance the performance of the FD relays under the impact of imperfect interference cancellation. At the far user, selection combining (SC) or maximal ratio combining (MRC) is employed to combine the signals received from the source and the selected FD relay. The analytical expressions for the average block error rate (BLER) of two users over flat Rayleigh fading channels are derived. Furthermore, closed‐form asymptotic expressions of the average BLERs at the near and far users in high signal‐to‐noise ratio (SNR) regimes are obtained. The numerical results show that the analytical BLERs of the near user and far user closely match the simulation results.

Intelligent-reflecting-surfaces-assisted hybrid FSO/RF communication with diversity combining: a performance analysis

Free space optics (FSO) and radio frequency (RF) communication systems exhibit complementary characteristics, with FSO being susceptible to fog, turbulence, and pointing errors, whereas RF is susceptible to rain and small scale fading. These inherent complementary characteristics between FSO and RF communication systems enable the hybrid configuration to effectively alleviate the impact of environmental impediments. This paper presents the performance analysis of an intelligent reflecting surfaces (IRSs)-assisted hybrid FSO/RF system under atmospheric turbulence (AT), pointing errors (PE), small scale fading effects, and attenuation due to climatic conditions such as fog, rain, etc. To characterize the AT, gamma–gamma distribution is used, and the multipath fading in the RF link is modeled using Nakagami-m distribution. At the receiver, signals from both the FSO and RF links are combined using either the selection combining (SC) or maximal-ratio combining (MRC) technique. We derive the exact closed-form expressions for outage probability and average symbol error rate (ASER) for both diversity combining schemes. The proposed system is compared with the direct link (DL) FSO system, IRSs-assisted FSO system, and hybrid FSO/RF system with diversity combining schemes. Further, the performance comparison between the SC and MRC schemes is also reported. Finally, the accuracy of the analytical expressions is verified by utilizing Monte Carlo simulations.

Gain of Spatial Diversity with Conjoint Signals in Arbitrarily Correlated Rayleigh Fading Channels

Coding gains for arbitrarily correlated signals in a spatial diversity system with conjoint signals are presented in this study. The basic form of the proposed signal synthesizer evenly produces phase changes in the output signals. The mixer is an orthogonal transformation matrix, which is energy preserving and blind to the channel correlation matrix. The idea is to synthesize additional conjoint signal copies from the received signals that would be received if there were more antennas. However, these conjoint signals contain a level of correlation with the received signals. With the assumption of flat Rayleigh fading channels, simulation results for symbol error probability (SEP) are presented for different numbers of receive branches and varying correlation conditions. It is shown that under binary phase shift keying (BPSK), the synthesizer achieves decorrelation coding gains of about 1 dB when selection combining (SC) or equal gain combining (EGC) is used. The synthesizer’s performance across M-ary quadrature amplitude modulation (MQAM) signals is also tested. In addition, analytical frameworks are derived for BPSK and MQAM, which are tightly bound by the Monte Carlo simulation results obtained using Matlab. The correlation analysis is performed for different numbers of antennas and varied antenna spacings.

Performance Analysis and Deep Learning Design of Short-Packet Communication in Multi-RIS-Aided Multiantenna Wireless Systems

This paper studies short-packet communication (SPC) in multi-reconfigurable intelligent surface (RIS)-assisted multi-antenna wireless systems. In this system, a sensor node communicates with another sensor node through the help of an access point (AP) and two sets of distributed RISs. Aiming to enhance system performance, we combine the best RIS selection strategies with maximum-ratio transmission (MRT) beamforming designs to improve the transmitted signal and selection combining (SC) or maximum-ratio combining (MRC) to increase the received signals. Closed-form expressions for the block error rate (BLER) BLER, throughput, latency, and reliability of the receivers over Rayleigh fading channels are derived to evaluate the system performance. Numerical results show that, in the first transmission phase, employing MRC with optimal phase shift (OPS) occurring at RIS can help AP achieve the best BLER performance, while SC with OPS provides better BLER performance than MRC and uncertain phase shift (UPS). In the second transmission phase, the reflective-path beamforming design shows better performance than the direct-path beamforming design, where OPS also attains outstanding performance when compared to UPS. Aiming for real-time system configurations with high reliability along with minimizing costs and resources, we propose a deep learning (DL) approach to optimize the number of reflective elements at each RIS or the number of RIS in a set of distributed RISs. Our work shows that the prediction results of the DL framework match the analytical derivations and the deep neural network (DNN) can help the systems save overhead and resources while satisfying the requirement of real-time communication.

Swarm Algorithm-based Power Optimization in Cooperative Communication Network

Background: Due to the environmental effects, the signal fades abruptly and is sometimes lost in the transmission path, which results in weak signal reception at the destination node. The Cooperative Communication Network (CCN) overcomes this problem and provides better spectral efficiency. The source node and the helper node both send the information to the receiver. In spite of many advantages, there are some limitations to such networks. Improving the system efficiency by power, energy, or relay selection optimization is quite desirable as multiple helper nodes are used in the network. Considering this crucial requirement of optimization, the proposed work presents optimal power allocation of the system. Methods: Here, tunicate-swarm optimization is implemented to improve the system parameters, symbol error rate (SER), outage probability, and bit error rate (BER). Two relaying protocols are used for analysis, i.e., Amplify-and-Forward (AF) and Differential AF (Diff-AF), with two combining schemes: Selection-Combining (SC) and Maximal-Ratio-Combining (MRC). Results: The results obtained are further compared with other metaheuristics algorithms, such as Particle- Swarm-Algorithm (PSO), Black-Widow-Optimization (BWO), and the traditional method of Equal-Power-Allocation (EPA).Equal-Power-Allocation (EPA). Conclusion: The simulation result shows that the proposed algorithm improves the system parameters compared to algorithms with less time.

Exact analysis of two‐branch SC receiver over α$$ \alpha $$‐κ$$ \kappa $$‐μ$$ \mu $$ fading

AbstractWe analyze the exact and generalized performance of two‐receiving antennas‐aided selection combining (SC) receivers over ‐‐ faded propagation medium. Especially, we have derived exact new expressions for the average bit/symbol error rate (ABER/ASER), and average channel capacity (ACC) for the considered system. The cumulative distribution function‐based method and probability density function‐based method are employed to derive ABER/ASER, and ACC expressions, respectively. Further, asymptotic ABER/ASER expressions are presented to examine diversity order which depends only on and . The change of fading parameters , , and are highlighted in the system's performance. Further, the correctness of all derived expressions is confirmed through simulations.

Hybrid FSO/RF system over proposed random dust attenuation model based on real-time data combined with G–G atmospheric turbulence

Free-space optical (FSO) communication links are thought to be most negatively impacted by fog and sandstorms. Several probabilistic models for signal attenuation in various types of fog have been proposed in the literature. To the best of our knowledge, there is no prior probabilistic signal attenuation model for dusty channels. As a result, in this study, we analyse the probabilistic behaviour of the FSO channel during sandstorms using real-time data from the Egyptian Meteorological Authority and propose the negative-exponential (NE) distribution as a novel statistical model for signal attenuation in dust. A probability distribution function (PDF) is then derived for the random dust channel state. Also, a closed-form channel state distributional formulation is derived for a stochastic FSO channel model that considers both dust effects and Gamma–Gamma (G–G) atmospheric turbulence-induced fading. Next, closed formulas are derived for both the average bit-error rate (BER) and outage probability for the FSO system operating in this channel environment. Using the forms derived, it can be shown that the dust storm has a significant impact on the system’s performance. Finally, to overcome this degradation, we suggest utilizing a hybrid FSO and radio frequency (RF) wireless communication system. The received signals are combined using the well-known diversity selection combining (SC) technique. Further, the hybrid system’s performance was compared to that of an FSO-only system.

Selection Combining Over Log-Logistic Fading Channels With Applications to Underwater Optical Wireless Communications

We study the performance of a selection combining (SC) receiver operating over independent but non-identically distributed log-logistic ($\mathcal{LL})$ fading channels. We first characterize the statistics of the output instantaneous signal-to-noise ratio (SNR) of the SC receiver. Based on the SNR statistics, we derive exact analytical expressions, in terms of multivariate Fox H-functions, for the outage probability, the average bit error rate, and the ergodic capacity. We also derive exact expressions for such performance measures when all channels are independent and identically distributed, as a special case. Furthermore, we deduce simplified asymptotic expressions for these performance metrics assuming high values of average transmit SNR. To demonstrate the applicability of our theoretical analysis, we study the performance of an SC receiver in underwater optical wireless communication systems. Finally, we confirm the correctness of the derived analytical results using Monte Carlo Simulations.

Hybrid Transmission Scheme for Improving Link Reliability in mmWave URLLC Communications

Ultra-Reliable and Low-Latency Communication (URLLC) represents a key ingredient of current 5G and future 6G mobile communication networks. The demanding reliability requirement set for URLLC claims for novel techniques that can deliver the necessary level of reliability without sacrificing the overall system capacity. In this context, this work presents and analyses a hybrid transmission scheme for improved reliability in millimetre wave bands with adaptive diversity combining. The proposed scheme is based on a hybrid approach that combines two links, one in the FR1 band (characterised by lower capacity but higher reliability due to more favourable propagation) and one in the FR2 band (offering higher capacity but experiencing a less reliable connectivity). The proposed scheme dynamically adapts the usage of both links in order to exploit the complementary characteristics of both bands (reliability of FR1 bands and capacity of FR2 bands) by switching between FR2-only and joint FR1-FR2 transmission according to the instantaneous channel quality in the main FR2 link. The performance is evaluated under two popular and well-known diversity combining techniques, namely Selection Combining (SC) and Maximal Ratio Combining (MRC). The obtained results demonstrate that the proposed scheme can achieve the same level of reliability as a continuous dual-link transmission scheme but with a much lower level of links usage and without sacrificing (and indeed enhancing) the capacity, thus making it a suitable candidate to deliver URLLC services in a resource-efficient manner.

Impacts of Diversity Technique Application in Order to Reduce the Fading in IEEE 802.15.4 Networks

The paper discusses the operation of wireless sensor networks consisting of nodes based on the IEEE 802.15.4 ZigBee transceiver operating in the presence of Rayleigh or Nakagami-m fading, additive white Gaussian noise (AWGN) and interference. Analytical expressions for bit error rate (BER) for the IEEE 802.15.4 network were obtained when Rayleigh and Nakagami-m fading were processed with a selection-combining (SC) and maximum-ratio-combining (MRC) combiner and when AWGN and interference were present. Analytical results are presented graphically in the form of BER change, depending on the signal-to-noise ratio (SNR) for different values of network parameters: fading parameter (m), number of branches of MRC combiner (L), modulation parameter (M), and spreading sequence lengths (Lc). Graphical results are presented for the system when there are no combiners and when the SC and MRC combiners are included. Numerical results were confirmed by Monte Carlo simulation. Analysis of the SC and MRC combiner application impact on the performance improvement of the IEEE 802.15.4 network and the received signal was performed.