Successive Approximation Research Articles

A comparative study to solve fractional initial value problems in discrete domain

Abstract In this article, we used some methods to solve Riemann-type fractional difference equations. Firstly, we use a method that is a composite method based on the successive approximation method with the Sumudu transform. Secondly, we use a method that is a composite method that consists of the homotopic perturbation method with the Sumudu transform. It was found that the results obtained from these combined methods are identical when compared. We also provided theories and illustrative examples to support the research findings.

A scientist’s take on scientific evidence in the courtroom

Scientific evidence is frequently offered to answer questions of fact in a court of law. DNA genotyping may link a suspect to a homicide. Receptor binding assays and behavioral toxicology may testify to the teratogenic effects of bug repellant. As for any use of science to inform fateful decisions, the immediate question raised is one of credibility: Is the evidence a product of valid methods? Are results accurate and reproducible? While the rigorous criteria of modern science seem a natural model for this evaluation, there are features unique to the courtroom that make the decision process scarcely recognizable by normal standards of scientific investigation. First, much science lies beyond the ken of those who must decide; outside “experts” must be called upon to advise. Second, questions of fact demand immediate resolution; decisions must be based on the science of the day. Third, in contrast to the generative adversarial process of scientific investigation, which yields successive approximations to the truth, the truth-seeking strategy of American courts is terminally adversarial, which risks fracturing knowledge along lines of discord. Wary of threats to credibility, courts have adopted formal rules for determining whether scientific testimony is trustworthy. Here, I consider the effectiveness of these rules and explore tension between the scientists’ ideal that momentous decisions should be based upon the highest standards of evidence and the practical reality that those standards are difficult to meet. Justice lies in carefully crafted compromise that benefits from robust bonds between science and law.

A Hybrid CMOS Digital-to-Analogue Converters Design for High Resolution SAR ADC

The paper describes the design and implementation of a 14-bit differential Digital-to-Analogue Converter (DAC) based on the Silterra 0.18µm Complementary Metal-Oxide-Semiconductor (CMOS) process to be established in a Successive Approximation Register (SAR) Analogue-to-Digital Converter (ADC) for the purpose of high-resolution, high accuracy and low power applications. The proposed differential DAC aims to eliminate the issue of stringent matching requirements imposed on high-resolution DACs while leveraging both linearity performance and power consumption parameters at a balanced point. The overall differential circuit consists of two parallel single-ended DACs that utilize a 4-bit Capacitor DAC (CDAC) and 10-bit Resistor DAC (RDAC) on each end, thereby establishing a hybrid-based architecture. Furthermore, the authors illustrate the proposed switching procedures applied to the sub-DAC circuits to ensure a low-power design is established. The new method effectiveness evaluation is confirmed by detailed transient simulations implemented on the DAC where the circuit performs the required conversions at a maximum conversion frequency of 2.5 MS/s with a peak power consumption of 0.1496mW for the standard voltage supply of 2.1V. Meanwhile, the schematic and post-layout simulations performed on the DAC registers peak DNL errors of -0.1612 and -0.8272, respectively. New research results depict performance improvements in terms of resolution and power consumption which facilitates the DAC implementation in contemporary electronic devices such as microcontroller peripherals and audio amplification devices. The overall deigned circuit is capable of achieving the desired 14-bit digital-to-analogue conversions under the CMOS 0.18µm technology, proving the DAC’s high-resolution efficacy.

RIS-Aided Cell-Free MIMO System: Perfect and Imperfect CSI Design for Energy Efficiency

Thanks to the development of the 6th generation mobile network that makes it possible for us to move towards an intelligent ubiquitous information society, among which some novel technologies represented by cell-free network has also attracted widespread academic attention. Cell-free network has brought distinguished gains to the network capacity with its strong ability against inter-cell interference. Unfortunately, further improvement demands more base stations (BSs) to be settled, which incurs steep cost increase. To address this issue, reconfigurable intelligent surface (RIS) with low cost and power consumption is introduced in this paper to replace some of the trivial BSs in the system, then, a RIS-aided cell-free network paradigm is formulated. Our objective is to solve the weighted sumrate (WSR) maximization problem by jointly optimizing the beamforming design at BSs and the phase shift of RISs. Due to the non-convexity of the formulated problem, this paper investigates a joint optimizing scheme based on block coordinate descent (BCD) method. Subsequently, on account of the majority of the precious work reposed perfect channel state information (CSI) setup for the ultimate performance, this paper also extends the proposed algorithm to the case wherein CSI is imperfect by utilizing successive convex approximation (SCA). Finally, simulation results demonstrate that the proposed scheme shows great performance and robustness in perfect CSI scenario as well as the imperfect ones.

Secrecy-Energy-Efficiency Maximization for UAV-Enabled Two-Way Relay Systems

In wireless communication, unmanned-aerial-vehicle (UAV) relay seems to be an available paradigm to combat path-loss and expand signal coverage. Due to the openness of wireless channel and the inconvenient recharging, transmission security and energy efficiency are the most concerned issues for UAV-enabled communication. In this paper, for an UAV-enabled two-way relay system, where two wireless terminals exchange their information assisted by a flying UAV and a malicious user tries to eavesdrop the transmitted information, the achievable secrecy energy-efficiency is formulated when the UAV speed, trajectory, allowable power and the time scheduling in the uplink and downlink transmission are considered in a comprehensive manner. To solve this non-convex problem, we decompose it into three subproblems based on the block coordinate descent (BCD) method. Then, the successive convex approximation (SCA) technique and the Dinkelbach algorithm are combined to obtain the global solution in an iterative manner. Simulation results show that the proposed schemes have higher secrecy energy-efficiency compared to the existing baseline schemes.

A Deep Reinforcement Learning Scheme for Sum Rate and Fairness Maximization Among D2D Pairs Underlaying Cellular Network With NOMA

Device-to-device (D2D) communication is an emerging technology in 5G and upcoming 6G networks due to its properties to enhanced spectral efficiency (SE), energy-efficiency (EE), and sum rate. Despite these advantages, co-channel and cross-channel interference, and ultra-massive connectivity are major issues which can deteriorate performance of any implemented solution in this environment. To address these issues, in this paper, we integrated the power domain non-orthogonal multiple access techniques (PD-NOMA) on the base station (BS). NOMA serves more than one user using the same resource block (RB) and reduces the effect of interference at CUs due to the presence of successive interference cancellation (SIC). The problem is formulated as a mixed-integer non-linear programming (MINLP) with associated resources and power constraints of the BS and DDPs with an aim to maximize the sum rate and fairness among the NOMA-enabled CUs and D2D pairs (DDPs). We firstly used the centralized deep deterministic policy gradient (DDPG) and arithmetic-geometric mean approximation (AGMA) technique to reduce cross-channel interference (CR-CI) and control the power. Then, to provide fairness to all the users, we transformed the proposed solution into distributed deep deterministic policy gradient (D3PG). Also, the successive convex approximation technique is then integrated into the D3PG to mitigate the effect of co-channel (CO-CI) interference among DDPs. The experimental results show that the proposed scheme has superior performance with respect to sum rate and fairness. Also, the results reveal that the proposed scheme has 21.05%, 34.21%, and 49.8% higher sum rate in comparison to DDPG, Deep dueling, and DQN scheduling.

Exploiting NOMA and RIS in Integrated Sensing and Communication

A novel integrated sensing and communication (ISAC) system is proposed, where a dual-functional base station is utilized to transmit the superimposed non-orthogonal multiple access (NOMA) communication signal for serving communication users and sensing targets simultaneously. Furthermore, a new reconfigurable intelligent surface (RIS)-aided-sensing structure, where a dedicated RIS is deployed to provide virtual line-of-sight (LoS) links for radar targets, is also proposed to address the significant path loss or blockage of LoS links for the sensing task. Based on this setup, the beampattern gain at the RIS for the radar target is derived and adopted as a sensing metric. The objective of this paper is to maximize the minimum beampattern gain by jointly optimizing active beamforming at the base station (BS), power allocation coefficients among NOMA users and passive beamforming at the RIS. To tackle the non-convexity of the formulated optimization problem, the beampattern gain and constraints are first transformed into more tractable forms. Then, an iterative block coordinate descent (IBCD) algorithm is proposed by employing successive convex approximation (SCA), Schur complement, semidefinite relaxation (SDR) and sequential rank-one constraint relaxation (SRCR) methods. To reduce the complexity of the proposed IBCD algorithm, a low-complexity iterative alternating optimization (IAO) algorithm is proposed. Particularly, the active beamforming is optimized by solving a semidefinite programming (SDP) problem and the closed-form solutions of the power allocation coefficients are derived. Numerical results show that: i) the proposed RIS-NOMA-ISAC system always outperforms the RIS-ISAC system without NOMA in beampattern gain and illumination power; ii) the low-complexity IAO algorithm achieves a comparable performance to that achieved by the IBCD algorithm. iii) high beampattern gain can be achieved by the proposed joint optimization algorithms in underloaded and overloaded communication scenarios.

Joint Optimization of Secure Over-the-Air Computation and Reliable Multicasting Assisted by a MIMO Untrusted Two-Way Relay

In this paper, we investigate joint optimization of secure AirComp and reliable multicasting assisted by a multiple-input multiple-output untrusted two-way relay, where artificial noise is employed at the access point (AP) to interfere the relay for ensuring secure AirComp. We aim to minimize the computation distortion at the AP by jointly designing the transmit variables of all the nodes and the aggregation variables at the AP and relay, under the secure AirComp constraint, the reliable multicasting constraint, and the transmit power constraints of all the nodes. We consider two scenarios that perfect and imperfect channel state information (CSI) are available. For the former, the formulated optimization problem is highly nonconvex, and we propose an effective block coordinate descent (BCD)-penalty successive convex approximation (penaltySCA) method to solve the nonconvex problem. For the latter, we model the imperfect CSI by using worst-case criterion and the formulated robust optimization problem is much more challenging than its counterpart with perfect CSI. To solve the robust problem effectively, we first transform it to a deterministic optimization problem by employing some powerful mathematical lemmas, and then apply the proposed BCD-penaltySCA method to solve the reformulated deterministic problem. The proposed methods are shown by simulations to significantly reduce the computation distortion compared with other benchmarks under considering secure AirComp and reliable multicasting.

Sensing-Efficient NOMA-Aided Integrated Sensing and Communication: A Joint Sensing Scheduling and Beamforming Optimization

Integrated sensing and communication (ISAC) system has been expected to play a vital role in future wireless networks and services. In this paper, we investigate a non-orthogonal multiple access (NOMA)-aided ISAC system in which the ISAC base station utilizes NOMA to serve multiple NOMA-users while performing radar sensing towards a group of sensing targets by leveraging the superimposed NOMA signals for NOMA-users. To investigate this problem, we formulate a joint optimization of the beamforming, the NOMA transmission duration and the sensing scheduling of sensing targets, with the objective of maximizing the sensing efficiency (i.e., the number of sensed targets within a time-interval) of ISAC system, while satisfying both the communication quality requirement of each NOMA-user and the sensing quality requirement of each selected targets. Despite that the formulated joint optimization problem is strictly non-convex, we propose a decomposition-based algorithm for solving the problem. Specifically, we exploit the successive convex approximation and penalty function method to equivalently transform the problem of optimizing the beamforming into a convex problem which can be addressed efficiently. Furthermore, with the optimal beamforming, we leverage the monotonic feature and adopt a bisection-search method to determine the NOMA transmission duration. Finally, we utilize an algorithm based on the cross-entropy learning to compute the optimal sensing scheduling. Numerical results verify the effectiveness of our proposed algorithms and show the performance advantage of our NOMA-aided ISAC system. Compared with some benchmark schemes, our NOMA-aided ISAC sensing scheduling scheme can achieve better performance in communication and sensing.

Sensing Fairness-Based Energy Efficiency Optimization for UAV Enabled Integrated Sensing and Communication

Integrated sensing and communication (ISAC) is developing rapidly due to the advantages of bandwidth saving, hardware cost reduction and energy saving. This paper proposes a unmanned aerial vehicle (UAV) enabled ISAC (UAV-ISAC) system, where the UAV will sense ground users and forward sensed information to base station (BS). Radar mutual information (MI) is introduced to measure the UAV sensing performance. On the basis of sensing fairness for each user, a multi-objective resource optimization problem of maximizing both energy efficiency (EE) and minimum radar MI is studied by jointly optimizing user scheduling, transmit power and UAV trajectory. To solve the non-convex optimization problem, we decompose it into three sub-problems: user scheduling optimization, transmit power optimization, and UAV trajectory optimization. Each subproblem can be solved by successive convex approximation (SCA), fractional programming and relaxation technique. By iteratively optimizing the three sub-problems, we can obtain the suboptimal solution to original optimization problem. Simulation results show that the proposed optimization scheme can maximize the EE of UAV while ensuring sensing fairness for all users.

Joint Trajectory Design and Power Allocation for UAV Assisted Network With User Mobility

This paper investigates the unmanned aerial vehicle (UAV) assisted wireless communications where the UAV acts as the aerial base station to provide downlink data service to the ground users. We consider a typical hot-spot scenario in which the ground users move towards the target points of interests (PoIs) in groups. The UAV can also fly in air to cope with the movement of users. To maximize the system throughput, an optimization problem is formulated to jointly determine the subchannel assignment, the trajectory of UAV and its power allocation per time slot, where the navigation power of UAV, the co-channel interference as well as the quality of service (QoS) requirements of users are taken into account. As the problem is non-convex and hard to solve, we propose a cascade approach. First, we design a user clustering and pairing algorithm to accomplish the subchannel assignment. Then, we apply the block coordinate descent (BCD) based framework to decompose the remaining problem into the power allocation sub-problem and the trajectory design one. The sub-optimal solution can be gradually achieved through alternatively solving these two sub-problems. As for the power allocation sub-problem, we opt to the difference of convex (DC) functions form and the successive convex approximation (SCA) method to solve it. While for the trajectory design sub-problem, the auxiliary variables and SCA method are utilized. Vivid simulation results reveal that the proposed iterative algorithm can well satisfy the QoS of users and achieve significant performance gain compared with other benchmark schemes.

Dynamic NOMA-Based Computation Offloading in Vehicular Platoons

Both the Mobile edge computing (MEC)-based and fog computing (FC)-aided Internet of Vehicles (IoV) constitute promising paradigms of meeting the demands of low-latency pervasive computing. To this end, we construct a dynamic NOMA-based computation offloading scheme for vehicular platoons on highways, where the vehicles can offload their computing tasks to other platoon members. To cope with the rapidly fluctuating channel quality, we divide the timeline into successive time slots according to the channel's coherence time. Robust computing and offloading decisions are made for each time slot after taking the channel estimation errors into account. Considering a certain time slot, we first analytically characterize both the locally computed source data and the offloaded source data as well as the energy consumption of every vehicle in the platoons. We then formulate the problem of minimizing the long-term maximum task queue by optimizing the allocation of both the communication and computing resources. To solve the problem formulated, we design an online algorithm based on the classic Lyapunov optimization method and successive convex approximation (SCA) method. Finally, the numerical simulation results characterize the performance of our algorithm and demonstrate its advantages both over the local computing scheme and the orthogonal multiple access (OMA)-based offloading scheme.

An Analog Side-Channel Attack on a High-Speed Asynchronous SAR ADC Using Dual Neural Network Technique

This brief presents a side-channel attack (SCA) technique on a high-speed asynchronous successive approximation register (SAR) analog-to-digital converter (ADC). The proposed dual neural network based on multiple noise waveforms separately discloses sign and absolute value information of input signals which are hidden by the differential structure and high-speed asynchronous operation. The target SAR ADC and on-chip noise monitors are designed on a single prototype chip for SCA demonstration. Fabricated in 40 nm, the experimental results show the proposed attack on the asynchronous SAR ADC successfully restores the input data with a competitive accuracy within 300mV rms error.

A 540-mA, 0.0487-ps-FOM Digital LDO based on Bi-directional Binary Search with Dual-loop Control

A dual-loop digital low-dropout regulator based on the bi-directional binary search method is implemented in a 0.18-μm CMOS process in this paper. To improve the transient response, a bi-directional successive approximation register without initialization is proposed in coarse loop. To speed up fine adjustment during heavy loads, a two-dimensional MOSFET array is adopted to improve fine regulation step. Simulation results demonstrate that, during load current steps between 540 mA and 40 mA, the undershoot/overshoot is 364 mV/161 mV, and the digital LDO settles within 210 ns. For a supply voltage of 1.4 V with 200 mV dropout, the current efficiency is as high as 99.99% and the figure of merit is as low as 0.0487 ps.

Solving three-dimensional contact problems for foundation design in green building

Design of foundations on an elastic base is carried out using the solution of three-dimensional problems of contact interaction. Improving the accuracy of engineering calculations is necessary to ensure economic efficiency and increase energy savings in green building. The problems of indentation of punches with a flat base bounded by doubly connected close to polygonal contact areas are researched in the present work. Small parameter method is used to obtain explicit analytical expressions for the contact pressure distribution and the punch displacement dependence in a simplified form, which is convenient for engineering practice. The found load-displacement dependence satisfies the known inequalities that are valid for an arbitrary contact domain. Also a numerical-analytical method is in consideration. It uses the simple layer potential expansion and successive approximations for the problems accounting roughness of the elastic half-space. Roughness coefficient is considered as a parameter of regularization of the integral equation for the smooth contact problem. The results of both methods coincide with sufficient accuracy.

A calibration-free 10.7 fJ/conv.-step 12-bit 120-MS/s pipelined SAR ADC in 40nm CMOS

A calibration-free 12-bit 120-MS/s 2-stage pipelined successive approximation register (pipelined SAR) analog-to-digital converter (ADC) is presented in this paper. In asynchronous SAR ADCs, capacitive digital-to-analog converters (CDACs) are designed with bottom-plate sampling to improve sampling accuracy and split-capacitor array to save switching energy. Furthermore, both reference scaling technique and a PVT-stabilized closed-loop residue amplifier are implemented in this design to obtain an accurate inter-stage gain, enabling no additional calibration required in the pipelined SAR ADC. The prototype ADC in 40nm CMOS technology achieves a peak signal-to-noise-distortion ratio (SNDR) of 73.4 dB and 88.91dB spurious-free-dynamic-range (SFDR) at 120 MS/s sampling rate, consuming 4.88 mW power from 0.9 V supply voltage, and corresponding to an excellent figure-of-merit (FoM) of 10.7 fJ/conv.-step.

A high precision and low power consumption switching capacitor readout circuit

In this paper, a high precision and low power switching capacitor readout circuit for MEMS sensors is proposed. The capacitance readout circuit is realized by using the total difference separation loop structure composed of a switching capacitor charge amplifier. In order to reduce the aggravation of common-mode parasitic capacitance to the input offset error and amplifier gain error in the readout circuit, the input common-mode feedback compensation structure and oversampled successive approximation (OSA) readout technology are introduced. In addition, the circuit adopts a non-overlapping nested clock to reduce charge injection and improve output accuracy. Based on SMIC 0.18 μm CMOS technology, the circuit can recognize 0-0.2 pF capacitance signals and convert them into voltage signals, achieving good linear fitting. When the common-mode parasitic capacitance is 1-16 p, it has good resistance to common-mode parasitic capacitance, and the precision of the capacitor readout circuit is increased by 3.9%. Compared with traditional readout circuits, it has a simple structure and low power consumption.

Towards Reliable Design and Operation of Electric Road Systems for Heavy-Duty Vehicles Under Realistic Traffic Scenarios

Decarbonizing heavy-duty vehicles through electrification is a demanding task due to their large energy and power requirements. One promising solution to address this problem are electric road systems (ERS), which provide dynamic charging and traction power for electric vehicles. While their technological feasibility has been proven in numerous pilot projects, its reliability under realistic traffic scenarios is yet to be thoroughly investigated. In this paper, we define the reliability criteria for ERS and investigate how they are influenced by various realistic traffic scenarios. Then, the relationship between the ERS reliability criteria and the key system parameters such as the DC link voltage, distance between substations and feeding arrangement is analyzed. We find that the continuous current limit is the most critical criterion under heavy traffic conditions. Furthermore, we look into a number of run-time techniques to cope with electrical stress on the system and propose a technique based on successive approximation of the total current demand. We compare and evaluate the effectiveness of the run-time techniques and show that our proposed technique is able to improve ERS utilization while ensuring reliable operation.

A 3.07 mW 30 MHz-BW 73.2 dB-SNDR Time- Interleaved Noise-Shaping SAR ADC With Self-Coupling Second-Order Error-Feedforward

A noise-shaping successive approximation register (NS-SAR) ADC combines the merits of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta $</tex-math> </inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Sigma $</tex-math> </inline-formula> and SAR ADC, transforming it into an emerging ADC architecture to reach high resolution with good power efficiency. The single-channel NS-SAR with high resolution, however, suffers from bandwidth (BW) limitations. The time-interleaved (TI) NS-SAR mitigates the speed bottleneck but faces challenges in obtaining high resolution and BW simultaneously due to the lack of a sharp noise transfer function (NTF). This article presents a calibration-free two-channel TI-NS-SAR with an aggressive second-order NTF for high resolution. Based on a one-time error feedback (FB) at midway, we propose a second-order error-feedforward (FF) to enhance the noise-shaping (NS) effect further meanwhile avoiding the excessive NTF peaking and dynamic range (DR) loss. A dynamic residue amplifier shared between two channels lowers the offset, which reduces the redundant bit to only one bit, thus improving the efficiency of SAR conversion. Fabricated in a 28 nm CMOS with 1 V supply, the prototype achieves 73.2 dB-signal-to-noise-and-distortion-ratio (SNDR) over 30 MHz-BW when operating at 330 MHz. It consumes 3.07 mW and exhibits a Schreier FoM (FoMs) of 173.1 dB.

Математическое моделирование прогноза урожайности сельскохозяйственных культур на основе данных полевого мониторинга и дистанционного зондирования

A mathematical model for forecasting crop yields based on field monitoring data and remote sensing of the Earth has been constructed. The model includes the following main values: vegetation indices NDVI, total solar radiation flux at the lower boundary of the atmosphere, efficiency of using photosynthetically active solar radiation, biomass respiration costs. After the parameterization of the mathematical model using observational data, the number of uncertain (calibration) coefficients of the model decreases from 8 to 2. These coefficients are determined by the method of successive approximations when comparing the results of calculations with observational data on the yield of a particular agricultural crop (ACC) in a given field. It is shown that the values of these coefficients strongly depend on the choice of optimal conditions for the growth of ACC. To reduce the yield forecast error, an approach based on the numerical integration of the total energy flux density by methods of the second and fourth orders of accuracy is proposed. When using numerical integration methods of a high order of accuracy, the yield forecast error decreases on average by 20% compared to the widely used model for calculating biomass growth, which has the first order of accuracy.