Theoretical Performance Analysis Research Articles

Analysis and Simulation of Wheel-Track High Clearance Chassis of Rape Windrower

The middle and lower reaches of the Yangtze River are the main production area of rapeseed. Small windrowers with two tracks are adopted in this area, which have lower efficiency. With the advancement of large-scale rape planting, medium and large windrowers are urgently needed; however, most medium and large windrowers are wheeled machines which have poor adaptability to sticky soil in rice–rape rotation areas. Therefore, a wheel-track high clearance chassis for rape windrower was developed. Theoretical analysis and simulation of the main performance of this chassis were investigated. Mathematical models of the relationship between the chassis eccentricity and running resistance, uphill and downhill angle and the height of obstacle were established. Then, three-dimensional modeling and dynamic simulations of a wheel-track high clearance chassis of a rape windrower in wet clay soil were carried out based on Pro/E and RecurDyn software. The simulation results indicated that when the chassis ran on flat hard road at the same speed, eccentricity had little effect on average walking speed; the coefficient variation of speed decreased with the increase of eccentricity, while the driving torque and its coefficient variation decreased first and then increased. The minimum driving torque and the coefficient variations were obtained when the eccentricities were 1484 mm and 1584 mm. Field experiments were carried out on two kinds of ground. The results showed that on flat hard road, the speed of the wheel-track high clearance rape windrower was 0~20.22 km/h, the minimum turning radius was 5.965 m; on rice stubble field with 38.7% water content, the working speed was 0~9.12 km/h, the minimum turning radius was 6.498 m, and the climbing angle was over 20°. All parameters of the wheel-track high clearance chassis met the design specifications, and the working efficiency increased over 100% compared with the existing two-tracked rape windrower. A new kind of rape windrower for the middle and lower reaches of the Yangtze River was provided.

On the Statistical Delay Performance of Large-Scale IoT Networks

Large-scale Internet of things (IoT) networks have shown great advantages and attracted much attention in 5G networks due to its high-speed Internet connectivity, high data rate, ultra reliability and low latency. However, the diversity of ubiquitous IoT devices and complex transmission environment lead to the difficulty of theoretical analysis of delay performance. In order to capture the characteristics of large IoT networks, a novel integrated analysis framework is developed to build the performance model and analyze the statistical delay performance in this paper. Specifically, we model the spatial distribution of IoT devices with heterogeneous Poisson point processes. With the Laplace transform of signal-to-interference-plus-noise ratio, the service capability of the wireless channel with multiple interferes is determined with a mathematical stochastic-network-calculus aided approach in the exponential domain for Poisson bipolar and cellular networks. Then, the upper bound of delay is achieved by the Mellin transform of the service incremental process. We extend our work to a <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> -tier heterogeneous network and apply the analysis results to a practical two-tier cognitive radio IoT network. Simulation results validate the theoretical analysis of delay performance with various network parameters.

Rectangular Differential OFDM With Index Modulation Using Coordinate Interleaving

Differential subcarrier index modulation (DSIM) is an emerging OFDM with index modulation (OFDM-IM) technique, which does not require channel state information (CSI) at the receiver. However, the DSIM scheme has two drawbacks of lower spectral efficiency and lacking transmit diversity. In this letter, by combining rectangular differential coding and coordinate interleaving orthogonal design, a novel rectangular differential OFDM-IM using coordinate interleaving (CI-OFDM-RDIM) scheme is proposed. In this scheme, the dispersion matrix is projected to a dispersion vector that is transmitted in a single symbol interval, so that CI-OFDM-RDIM improves spectral efficiency compared with DSIM. Since the symbols in two adjacent differential groups are interleaved, the proposed scheme obtains diversity gain. Furthermore, owing to the orthogonality of its processing matrix, a low-complexity decoupled maximum likelihood (D-ML) detector is proposed. Theoretical performance analysis and simulation results show that CI-OFDM-RDIM outperforms DSIM in terms of the bit error rate (BER) performance.

Distributed cohesive configuration controller for a swarm with low‐cost platforms

AbstractThis study presents a cohesive configuration controller for distributed space coverage by a swarm of robots. The goal is to build a dense, convex network that is robust against disconnection while robots are flocking with only incomplete knowledge about the network. The controller is an integrated framework of two different algorithms. First, we present a boundary force algorithm: physics‐based swarm intelligence that borrows the concept of surface tension force between liquid molecules. The combination of such a force with conventional flocking produces a convex and dense configuration without knowledge of the complete geometry of a robot network. Second, robots distributively determine when a configuration is on the verge of disconnection by identifying a local articulation point—a region where the removal of a single robot will change the local topology. When such a point is detected, robots switch their behavior to clustering, which aggregates them around the vulnerable region to remove every articulation point and retain a connected configuration. Finally, we introduced an index that objectively represents the level of risk of a robot configuration against the massive fragmentation, called vulnerability index. We provide theoretical performance analyses of each algorithm and validate the results with simulations and experiments using a set of low‐cost robots.

Error Probability Analysis for Time-Varying Chaos Unitary Matrix-Based Differential MIMO System

The time-varying (TV) chaos unitary matrix based differential multiple-input multiple-output (D-MIMO) system is capable of achieving beneficial performance gains without channel state information (CSI). To elaborate a little further, the chaos sequence is embedded into the data-carrying matrices by a unique time-varying matrix. By employing differential coding during two adjacent signal blocks, a non-coherent detector can be developed without CSI knowledge. However, its theoretical performance analysis becomes challenging due to its complex construction. To address this issue, the theoretical average bit error probability (ABEP) lower and upper bounds of the TV-D-MIMO system are analyzed using the moment generating function (MGF) over generalized fading channel. The experimental results are shown that the derived ABEP upper and lower bounds are tight with the simulation results, which is helpful for future performance evaluation.

Theoretical modelling and simulation analysis of the thermal performance of a steel-basalt fiber polymer concrete machine tool joint surface

Theoretical modelling and simulation analysis of the thermal performance of a steel-basalt fiber polymer concrete machine tool joint surface

PkCOs: Synchronization of Packet-Coupled Oscillators in Blast Wave Monitoring Networks

Blast waves with a large amount of energy, from the use of explosive weapons, is a major cause of traumatic brain injury in armed and security forces. The monitoring of blast waves is required for defence and civil applications. The utilization of wireless sensing technology to monitor blast waves has shown great advantages, such as easy deployment and flexibility. However, due to drifting embedded clock frequency, the establishment of a common timescale among distributed blast monitoring sensors has been a challenge, which may lead to a network failing to estimate the precise acoustic source location. This work adopts a packet-coupled oscillators (PkCOs) protocol to synchronize drifting clocks in a wireless blast wave monitoring network. In order to address packet collisions caused by the concurrent transmission, an anti-phase synchronization solution is utilized to maintain clock synchronization, and the corresponding superframe structure is developed to allow the hybrid transmission of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Sync</i> packet and the blast wave monitoring data. As a network scales up and the hop distance grows, the packet exchange lag increases during a superframe. This, along with the drifting clock frequency, leads to the degradation of synchronization performance while the clock frequency is usually assumed to be zero and nondrifting. Thus, a compensation strategy is proposed to eliminate the joint impacts and to improve synchronization precision. The theoretical performance analysis of the PkCOs algorithm in the network is presented along with verification by simulation means. Finally, the performance of the PkCOs synchronization protocol is evaluated on an IEEE 802.15.4 hardware testbed. The experimental results show that the PkCOs algorithm provides an alternative clock synchronization solution for blast wave monitoring networks.

Theoretical Performance Analysis of Distributed Queue for Massive Machine Type Communications: Throughput, Latency, Energy Consumption

Massive machine type communications (mMTC) is one of main application cases in 5G, which is supposed to support communications of massive number of machine-type devices (MTDs). Distributed queue (DQ) is a variant of tree splitting protocol which combines an m-ary tree splitting algorithm with a set of simple smart rules, organizing every terminal in one out of two virtual queues. Theoretically, DQ allows access to infinite terminals and is stable under any traffic condition, which alleviates the unstable problem of slotted ALOHA, and is especially suitable for mMTC. However, its theoretical comprehensive performance analysis as well as related statistical characteristics is still missing, which severely restricts the full manifestation of its performance advantages. In view of this, the paper proposes a general performance analysis framework for DQ, with which full probability space of DQ evolution process is presented for the first time. To be more specific, probability distribution function (PDF), mean and variance of throughput, latency and energy consumption of DQ is analytically derived to comprehensively evaluate performance. Taking the IEEE 802.15.4 standard for mMTC as example, numerical results validate the accuracy of the proposed analysis framework and the stability of DQ, present effects of number of MTDs, number of contention slots ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${m}$ </tex-math></inline-formula> ), and maximum number of transmissions ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}$ </tex-math></inline-formula> ) on DQ in terms of aforementioned performance metrics. These results together provide good reference to find appropriate value of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${m}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}$ </tex-math></inline-formula> to balance the performance metrics and enable more practical network optimization.

Partial Self-Concatenation Structure and Performance Analysis of Spinal Codes Over Rayleigh Fading Channel

Spinal codes are a new family of rateless codes which have been proved to be capacity-achieving over both the additive white Gaussian noise (AWGN) channel and the binary symmetric channel (BSC). However, over the Rayleigh fading channel between the vehicle nodes, the error performance of Spinal codes is not satisfactory since the tail message blocks of Spinal codes are prone to error. To solve this issue, this paper proposes a new practical partial self-concatenation coding structure of Spinal codes, named <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> tail-protected Spinal codes, to pointedly protect tail message blocks of Spinal codes over the flat Rayleigh fading channel. Theoretical performance analysis and simulation results are also provided to validate and verify the effectiveness of the proposed <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> tail-protected Spinal codes.

An Improved Random Access Scheme Using Directional Beams for 5G Massive Machine-Type Communications

In the 5th generation (5G) massive machine-type communication (mMTC), random access is the limiting factor of performance because there may be massive user equipments (UEs) up to 1 million unit competing for the access opportunities. Existing random access schemes in the 4th generation (4G) or 5G systems are not able to handle such large amount of concurrent random access requests. This paper proposes a random access scheme based on directional beams, which offers a new spatial degree of freedom to improve the random access performance in 5G mMTC. In this scheme, a cell is divided into beam zones in space domain. UEs in different beam zones choose a certain physical random access channel (PRACH) resource with different probability. When preamble collision occurs, uplink radio resource is allocated to the beam zone which has low collision probability. We provide theoretical performance analysis of the proposed scheme using different performance metrics. Comparisons are carried out between the proposed and several existing random access schemes. The proposed scheme can be easily deployed without any modification to 5G framework. Existing random access optimizing algorithms can also be applied to the proposed scheme.

A Deep Learning-Based User Selection Scheme for Cooperative NOMA System with Imperfect CSI

This paper studies the user selection problem for a cooperative nonorthogonal multiple access (NOMA) system consisting of a base station, a far user, and N near users. The selected near user receives its own message and assists the far user by relaying the far user’s message. Firstly, we propose a user selection strategy to maximize the selected near user’s data rate while satisfying the quality-of-service (QoS) requirement of the far user. Considering that the channel state information (CSI) of users in actual communication is usually imperfect, we then analyze the outage probability of the NOMA system based on the user selection strategy under imperfect CSI and obtain a closed-form expression. The theoretical analysis shows that the diversity order of the NOMA system under imperfect CSI is 0, which means the multiuser diversity order disappears. In order to improve the impact of imperfect CSI on system performance, we use the deep learning method to identify and classify channels of imperfect CSI and improve the accuracy of CSI. The simulation results show that the theoretical analysis of outage performance is consistent with the numerical results. Compared with the strategy without the deep learning method, the proposed deep learning-based user selection scheme significantly improves the system performance. Furthermore, we verify that our scheme recovers the diversity gain.

Constrained Cramér–Rao bounds for reconstruction problems formulated as coupled canonical polyadic decompositions

We propose a theoretical performance analysis for a class of reconstruction problems, formulated as coupled canonical polyadic decompositions of two low-resolution tensor observations. We study a particular case when all the modes of the tensors are coupled. Unlike the case of a single coupling constraint, a fully-coupled model requires nonlinear constraints in some estimation scenarios. Thus we introduce two probabilistic scenarios. For each scenario, we derive the constrained Cramér–Rao bounds for the parameters and for the mean-squared error of the reconstructed tensor. We show that with a carefully chosen initialization, the maximum likelihood estimators reach the bounds, even in challenging cases (low signal-to-noise ratio or large tensor rank).

Comparison and theoretical analysis of the photocatalytic performance of Ni2+-Fe3+-CO32−-LDHs and Ni2+-Al3+-CO32−-LDHs

The photocatalytic materials of nickel-iron hydrotalcite materials (Ni2+-Fe3+-CO32−-LDHs) and nickel-aluminum hydrotalcite materials (Ni2+-Al3+-CO32−-LDHs) were prepared by homogeneous precipitation method assisted by complexing agents. XRD and SEM research results show that Ni2+-Fe3+-CO32−-LDHs and Ni2+-Al3+-CO32−-LDHs are layered structures with hexagonal morphology. The experiment of degrading dye wastewater methyl orange shows that the photocatalytic activity of Ni2+-Fe3+-CO32−-LDHs is better than that of Ni2+-Al3+-CO32−-LDHs. Ultraviolet diffuse reflectance spectroscopy confirms that the band gap of Ni2+-Fe3+-LDHs is narrower than that of Ni2+-Al3+-CO32−-LDHs. In order to further study the reasons for the low band gap of Ni2+-Fe3+-LDHs, we used the first-principles DFT theory to calculate the density of states of the two hydrotalcites. Theoretical calculations show that Fe in Ni2+-Fe3+-LDHs provides d-orbital single electrons, while metal Al does not provide d-orbital single electrons, resulting in a lower band gap of Ni2+-Fe3+-LDHs. Ni2+-Fe3+-LDHs is an ideal photocatalyst for degradation of methyl orange in dye wastewater. It is magnetic and can be promoted as an excellent wastewater treatment agent.

Theoretical Calculation and Performance Analysis of Four-Element Metal Nitride Coatings Based on First Principles

Theoretical Calculation and Performance Analysis of Four-Element Metal Nitride Coatings Based on First Principles

Theoretical Analysis of Solar Cell Performance with Different Backsurface‐Filed Layers Utilizing Experimental Results of CdS Films Deposited by Pulsed Laser

Herein, three different backsurface‐filed (BSF) layers “SnS, PbS, and V2O5” are investigated on Mo/BSF/CZTS/CdS/AZO heterojunction solar cells using experimental data of CdS thin films. CdS thin films are produced by means of the pulsed laser deposition (PLD) technique with three different deposition periods. With increasing deposition time, the crystalline sizes of CdS thin films are larger and their crystal structures are developed. In addition, the optical bandgap of CdS thin films is calculated to be 2.4 eV using the absorbance data. Using the solar cell–capacitance–simulator‐1D (SCAPS‐1D) program, the experimental properties of CdS thin films to estimate the performance of p‐CZTS/n‐CdS/AZO heterojunction solar cells are introduced. The best efficiency is 9.32% when the thickness of CdS reaches 150 nm. To further improve the efficiency, different BSF layers (SnS, PbS, and V2O5) are tested in Mo/BSF/CZTS/CdS/AZO solar cells. According to the thickness of the BSF layer, the efficiency of the solar cell increases up to 13.47%, 14.7%, and 17.41% using SnS, PbS, and V2O5 as BSF layers with 0.1 μm thickness.

Experimental analysis of droplet impacting on inclined wall of the corrugated plate dryer in steam generator of nuclear power plants

Corrugated plate dryer (CPD) plays a vital role in the steam generator. In the CPD, the droplet impinging on the corrugated plate (CP) of the CPD, and the behavior after the impacting affects the separation efficiency of the CPD. The mechanical study of droplets movement on corrugated plate provides a theoretical basis for optimizing the design of the CPD. This paper analyzes the experimental phenomenon of droplet impacting on the dry inclined wall (DIW). The maximum spreading diameter (MSD) of droplet on the DIW is analyzed by combining theory with experiment, and a semi-empirical equation is obtained, which is fits well with the experimental data with error within 5%. The secondary droplet is analyzed by pixel analysis. The following conclusions were obtained that with the inclination angle (IA) increasing, the front spreading factor (FSF) will increases, the back spreading factor (BSF) decreases. When We increases, the SF of the droplet impacting the DIW increases, and when the Oh increases, the SF of the droplet impacting the DIW decreases. In the theoretical analysis of the separation performance of the dryer of a nuclear power plant, the influence of the Oh needs to be considered in the early stage of operation. The influence of We is mainly considered in the middle and late stages of the operation process. In the operation of nuclear power plants, artificial intelligence algorithms and control methods can be used to adjust the operating conditions of the CPD inlet droplets to ensure that the steam-water separation efficiency of CPD reaches the highest value. The above conclusion can provide guidance for the design of the CP of the steam generators in nuclear power plants.

An improved communication resource allocation strategy for wireless networks based on deep reinforcement learning

With the advent of 5G networks, user demand for high-speed, low-latency, and high-reliability services continues to grow. When traditional communication technologies cannot meet the needs, wireless network LoRa technology has emerged. Although LoRa has low power consumption, Long-distance, and other advantages, terminal nodes still face frequent data collection and energy consumption issues how to more efficiently combine the deep reinforcement learning method for LoRa wireless network communication and allocate resources reasonably and effectively. This paper proposes a communication channel resource allocation strategy based on deep reinforcement learning, the CL-LoRa strategy. It uses extended preamble and low-power interception technologies to achieve on-demand synchronization and low-power communication. The basic idea of this strategy is to detect channel quality based on CAD, coordinate node scheduling, and wireless channel allocation. The node will choose different ways to acquire the channel according to the current network load, namely CSMA-CA competition and dynamic duty cycle communication. In this way, the channel utilization rate is improved, and the energy consumption problem of the long-distance communication data volume is perfectly solved. The duty cycle access method is based on the imbalance of energy consumption in the Internet of Things. It uses the remaining energy of the remote central node to dynamically adjust the duty cycle of the node, wake up the working time of the node, and send more beacons to the sleeping node. Reduce the sleep delay of the node. Through theoretical analysis of CL-LoRa protocol performance, compared with DDC-LoRa protocol and ADC-LoRa protocol, CL-LoRa protocol can increase channel utilization by 9%, reduce terminal energy consumption by 1.6%, and increase throughput by 1.5%.

Highly Reliable Transmission and Channel Assignment for CR-IoT Networks

In this article, we propose a highly reliable transmission strategy based on exploiting channel diversity for Internet of Things (IoT) networks equipped with cognitive radio (CR) capabilities (referred to as CR-IoT networks). Specifically, we investigate the channel-assignment problem with the objective of minimizing the number of assigned channels for each CR transmission subject to link reliability, data rate, and success probability constraints. We use the theory of continuous-time Markov chains to derive mathematical expressions for channel availability and reliability. These expressions are employed in a binary linear program model to formulate the channel assignment optimization problem, which is suboptimally solved using a polynomial-time sequential fixing procedure. Theoretical performance analysis of the proposed channel assignment scheme is derived in terms of a lower bound on the achievable probability of successful packet transmission. Through simulation experiments, we demonstrate significant performance enhancement compared to existing reliability-unaware CR channel assignment algorithms.

Performance Analysis of Opportunistic Beam Splitting NOMA in Millimeter Wave Networks

Applying non-orthogonal multiple access (NOMA) in millimeter-wave (mmWave) networks has the potential to significantly enhance the spectral efficiency. In this paper, we propose an opportunistic beam-splitting NOMA scheme to fully exploit the antenna array gain in downlink mmWave networks, where single- and double-beam NOMA transmissions are dynamically enabled according to the spatial angle difference between the paired NOMA users, thereby enhancing the flexibility of applying NOMA in mmWave networks. The base station with a single radio frequency chain implements the double-beam NOMA transmission by adopting the beam-splitting technique. We develop a unified theoretical performance analysis framework for the proposed scheme, while taking into account the spatially random users, link blockage model, and general distance-based user pairing strategy. By using tools from stochastic geometry, we derive the exact expressions of the coverage probability and the sum rate of the proposed scheme under both the LoS exponential and ball models. We further derive the corresponding upper bound to simplify the analytical expressions. Simulations validate the theoretical analysis and demonstrate the performance gains of the proposed scheme in terms of the coverage probability and sum rate over the conventional single-beam NOMA and orthogonal multiple access (OMA) schemes.

Performance Analysis of the Hybrid Satellite-Terrestrial Relay Network With Opportunistic Scheduling Over Generalized Fading Channels

A hybrid satellite-terrestrial relay network (HSTRN) has been envisioned as a promising communication architecture for future wireless communications, which can prominently reduce the impact of shadow fading and expand service coverage. In this paper, we conduct theoretical performance analysis for a dual-hop communication system, consisting of multiple relays and multiple users in the HSTRN with the amplify-and-forward protocol. For the shadowing effect and the multipath effect, we introduce the shadowed-Rician distribution and Nakagami-<inline-formula><tex-math notation="LaTeX">$m$</tex-math></inline-formula> fading to characterize the channel models for the satellite-relay and the relay-user links, respectively. Additionally, the opportunistic scheduling scheme is employed, where the optimal relay and the optimal user are selected from the alternative nodes with the maximum instantaneous signal-to-noise ratio. Thereafter, the analytical expressions including ergodic capacity and average symbol error rate (SER) are derived. More specifically, we also present the asymptotic behavior of the average SER at the high signal-to-noise ratio (SRN) regime. The theoretical analysis is validated by the numerical results. Moreover, the results also reveal that the performance of the system can be improved by increasing the number of relays and users under different channel parameters and various modulation schemes.