Cancellation Operation Research Articles

Distributed Memory Algorithms for Weight Cancellation in Monte Carlo Particle Transport Simulations

Recent literature has demonstrated use cases for Monte Carlo transport simulations where particles can have statistical weights that are positive or negative. There are even examples which require particles to have complex statistical weights, and the real and imaginary components can be positive or negative. In such cases, weight cancellation algorithms can be very efficient at reducing the variance, or might even be required for a simulation to converge. Previous works that have employed weight cancellation in distributed memory simulations required that all fission particles be sent to a single node for the cancellation operation. This work examines possible implementations of distributed memory weight cancellation algorithms that do not require the transfer of the fission source to a single node.

Performance Improvement and Analysis of NOMA in densely populated networks

ABSTRACT Non Orthogonal Multiple Access technique (NOMA) is a potential and promising candidate for 5 G and beyond 5 G due to its better spectral efficiency and low latency. However, it faces implementation challenges in densely populated networks due to its computational complexity. In NOMA, for decoding user information at the receiver end, it needs to perform times perfect Successive Interference Cancellation (SIC) operation. Hence, in a dense network, where the number of users is high, the implementation of NOMA becomes tedious. In order to improve the performance of NOMA implementation, in this work, the concept of Cooperative Modulated-NOMA (CM-NOMA) is applied in the considered densely populated networks model. Performance analysis of the system in terms of outage probability, Symbol-to-Error Rate (SER) and achievable data rate in both one-to-one and cooperative communications scenarios are done. The analytical expressions are also validated using Monte Carlo simulation. The results show that the deployment of CM-NOMA in a densely populated network increases the performance of the system, and also reduces the computational complexity.

RIS Partition-Assisted Non-Orthogonal Multiple Access (NOMA) and Quadrature-NOMA With Imperfect SIC

Reconfigurable intelligent surface (RIS)-assisted power-domain non-orthogonal multiple access (PD-NOMA) system has emerged as a revolutionary technology to enhance the spectrum efficiency for future wireless networks. This work introduces two novel RIS systems, namely, RIS partition-assisted (RISP) PD-NOMA (RISP-PD-NOMA) and RISP-Quadrature-NOMA (RISP-Q-NOMA), to maximize the diversity order and to improve the signal quality of all users by dedicating fixed RIS units to each user. The closed-form expressions of average sum-rate, outage probability, and diversity order are evaluated for both systems under the Rician fading channel for perfect and imperfect successive interference cancellation (SIC) operations. Further, the performance of both RISP-PD-NOMA and RISP-Q-NOMA systems is compared with RIS partitioned PD-NOMA, RIS-assisted PD-NOMA, and PD-NOMA systems. It is noticed from the analysis that under perfect SIC, RISP-PD-NOMA outperforms all other systems. However, under imperfect SIC, RISP-Q-NOMA demonstrates superior performance to other systems due to the lesser number of SIC operations that reduce detection delay and decoding complexity. Furthermore, the analytical expression for bit error rate (BER) of RISP-PD-NOMA and RISP-Q-NOMA is derived, and then the closed-form expression of average-BER is evaluated. Numerical results demonstrate that RISP-Q-NOMA is superior to RISP-PD-NOMA.

Performance Modeling and Analysis of BASUR-CARQ Protocol Based on Interrelay Interference Cancellation

To recover the performance loss of nodes in half-duplex mode, this paper proposes a buffer-aided successive relay protocol based on cooperative automatic repeat request mechanism (BASUR-CARQ). Based on the fact that interrelay interference (IRI) will occur when relay nodes transmit or receive simultaneously, an interference cancellation operator is proposed to determine whether the interference is eliminated to reduce the outage probability. Moreover, a delay model for data frame transmission is proposed based on CARQ mechanism, and a closed-form expression for the average delay is derived. A 6-state discrete-time Markov chain (DTMC) model is developed to obtain the system throughput, and a closed-form expression for the system energy efficiency under M-ary modulation is derived. Finally, the simulation results show that with the setting of parameters that can balance the main performance, the delay performance of BASUR-CARQ protocol is significantly enhanced compared to the traditional protocols, and the throughput of BASUR-CARQ protocol is also optimized at high signal-to-noise ratio (SNR). Meanwhile, the energy efficiency of BASUR-CARQ protocol is significantly improved for the successive relay communication system without interference cancellation technique.

A Phase-Locked Loop With Inherent DC Offset Rejection for Single-Phase Applications

In this article, we aim to design a simple dc immune phase-locked loop (PLL) for single-phase applications. The dc offset is inherently rejected using only two delay operators. The dc offset in the synchronization unit is a challenging problem that causes oscillation in the estimated grid information. Using conventional filters to solve this problem is ineffective since this degrades the synchronization unit's dynamic performance. Different PLLs have been introduced in this article to mitigate the dc offset. Each has its merits and demerits, such as complex structure, high computational burden, and slow transient response. The proposed PLL incorporates two cascaded delayed signal cancellation operators with an arbitrary-length time delay, rejects the dc offset, and perfectly synchronizes with the grid. This article also presents a small-signal model to facilitate the loop filter design and stability analysis. Besides the simulations, the PLL's performance is validated experimentally under various disturbance conditions, with comparisons with other PLLs.

Uplink Multiple Access for Reconfigurable Intelligent Surface-Aided Wireless Systems

The integration of reconfigurable intelligent surface- (RIS-) aided wireless communication and multiple access is an attractive and promising scheme for next-generation wireless networks. In this research work, separate uplink RIS-aided nonorthogonal multiple access (NOMA) and uplink relay-assisted NOMA schemes are studied, where the RIS and relay devices are deployed to enhance the coverage of an obstructed single-antenna far user by assisting it to communicate with a single-antenna base station. In each scenario, both perfect successive interference cancellation (pSIC) and imperfect successive interference cancellation (ipSIC) operations are considered in the proposed multiple access network. To characterize the system performance, the associated residual interference caused by ipSIC and relay loop self-interference is characterized using the Rayleigh fading model; subsequently, new channel statistics are derived based on the Gauss-Laguerre polynomial. Consequently, the closed-form approximate outage probability expressions are derived for each scenario in the high signal-to-noise ratio (SNR) regime. To gain further insight, the system throughput in the delay-limited transmission is also obtained for each scenario. The formulated expressions are validated via Monte-Carlo simulations. Finally, the obtained simulation results demonstrate and validate the superiority of the RIS system over the relay device under several system parameters of interest despite the limitation of ipSIC.

A Novel User Grouping in Phase Rotation Based Downlink NOMA

Non-orthogonal multiple access (NOMA) is a promising candidate beyond 5G and 6G to improve spectral efficiency by sharing the same resource block with other users. However, as the number of users increases in a single NOMA cluster, not only the spectral efficiency but also the interference increases. Therefore, to ensure a trade-off between capacity and error performance in NOMA systems, this study introduces a novel downlink NOMA scheme using the phase rotation. In the system, four users can create a single NOMA cluster and are grouped into two subgroups by exploiting conventional NOMA. Within each subgroup, the symbols of two users, near user and far user, are rotated and multiplexed by the power domain. Subsequently, the final transmitted signal is obtained by multiplexing the in-phase and quadrature components of the first and second subgroups, respectively. By superposing signals from two independent subgroups, the number of successive interference cancellation (SIC) operations are reduced compared to the existing NOMA. Moreover, the analytical bit error rate (BER) for a four-user scenario is derived, and the optimal rotation angle and power allocation are proposed to minimize the BER performance. Numerical results demonstrate the improved performance of the proposed NOMA scheme over several existing schemes, such as conventional NOMA and orthogonal multiple access (OMA).

Multistage Least Squares Algorithms for Clutter Suppression in Airborne Passive Radar Based on Subband Operation

This article firstly analyzes the influence of utilizing the space-time adaptive processing (STAP) approaches in airborne passive radar (APR) systems on the dimension of the clutter subspace, and the signal-plus-noise ratio loss of the target, and illustrates that it is necessary to propose clutter cancellation algorithms suitable for APR systems. Combined with the property of APR systems, the multistage least squares algorithm based on subband operation (MLS-S) and the multistage least squares algorithm based on subband operation in temporal domain (MLS-ST) are proposed for the Doppler-shift clutter cancellation. The first method, in the case of the clutter with integer Doppler-shift bins, proves to be a simple solution. The second approach, at the expense of an additional stage, is suitable for more situations. Due to the use of Doppler-angle-dependence and subband operation to coarsen the range resolution, the proposed methods not only suppress effectively clutter along the clutter ridge, but also cancel the fractional-order-range clutter. In addition, the computational complexity of the proposed algorithms is low, and the clutter cancellation operations can be performed in parallel, which provide the possibility of real-time clutter suppression for APR systems. The feasibility of the proposed approaches is verified by diverse simulated scenarios.

Backscatter Assisted NOMA-PLNC Based Wireless Networks

In this paper, sum capacity maximization of the non-orthogonal multiple access (NOMA)-based wireless network is studied in the presence of ambient backscattering (ABS). Assuming that ABS is located next to far nodes, it improves the signal strength of far node cluster. By applying suitable successive interference cancellation (SIC) operation, far node cluster act as an internet of things (IoT) reader. Moreover, to improve the uplink performance of the nodes, a physical layer network coding (PLNC) scheme is applied in the proposed network. Power optimization is employed at the access point (AP) to enhance the downlink performance with total transmit power constraint and minimum data rate requirement per user constraint using Lagrangian’s function. In addition, end-to-end outage performance of the proposed wireless network is analyzed to enhance each wireless link capacity. Numerical results evident that the outage performance of the proposed network is significantly improved while using the ABS. Furthermore, the average bit error rate (BER) performance of the proposed wireless network is studied to improve the reliability. Simulation results are presented to validate the analytical expressions.

A Robust Three-Phase Prefiltered Phase Locked-Loop for the Subcycle Estimation of Fundamental Parameters

This article shows a proposal for a nonadaptive prefilter based three-phase type-I synchronous reference frame-based phase locked-loop (PLL) algorithm. This solution is simpler than the widely accepted type-II PLL algorithms, which require a great deal of effort as regards tuning the proportional-integral gains. In the proposed approach, a type-I controller that is merely a proportional gain with a fixed magnitude is employed. Moreover, improvements are made to the implementation of the nonadaptive demodulation based prefiltering approach, which consist of moving average filters and delayed signal cancellation operators. In the event of a fault, the improved prefilter structure is still incapable of rejecting the fundamental negative sequence (FNS) component. We propose to overcome this issue by using a nonadaptive computationally simplified structure to improve the immunity to the adverse effects of FNS. It is consequently possible to avoid the dependence on the frequency feedback loop while involving a simple and fast feed-forward error compensation approach. Finally, the performance of the proposed PLL is experimentally verified using a real-time controller to demonstrate its feasibility for grid synchronization applications.

Implementation of enhanced non-adaptive cascaded DSC-PLLs for renewable energy systems

In recent years, to fast and accurately extract the grid voltage information, using cascaded delayed signal cancellation (CDSC) operators in the prefiltering stage of phase locked loops (PLLs) has become highly popular. Non-adaptive CDSC (NCDSC) operators do not cause the stability problems unlike adaptive CDSC operators. So, researchers use the NCDSC operators intensely. Nonetheless, the NCDSC operators have two main drawbacks: (1) the dynamic responses of NCDSC-PLLs are not fast enough, similar to adaptive CDSC operators-based PLLs; and (2) the imbalance rejection capability of the NCDSC-PLLs dramatically deteriorates in case of large frequency variations. In this paper, to overcome these problems, two enhanced NCDSC-PLLs, which are called the ENCDSC-PLL1, and ENCDSC-PLL2, are suggested. The parameter design procedures of suggested PLLs are given by means of their small- signal models. Since the proposed ENCDSC-PLLs are the nonminimum-phase systems, their stability analyses are evaluated by Nyquist diagram. The feasibility and effectiveness of the proposed ENCDSC-PLLs are validated by experimental results.

Coordinated Direct and Relay Transmission for Multiuser Networks: NOMA or Hybrid Multiple Access?

This letter proposes non-orthogonal multiple access (NOMA) based coordinated direct and relay transmission (CDRT) and hybrid multiple access (HMA) protocols for a general CDRT system, where a base station directly serves cell-center users (CCUs), while it communicates with cell-edge users (CEUs) via a relay. The ergodic sum capacity (ESC), capacity scaling and the number of successive interference cancellation (SIC) operations are derived correspondingly. If the number of CCUs is less than that of CEUs and the interference level of imperfect SIC is small, the proposed NOMA-based CDRT can achieve much better ESC than HMA. Otherwise, the proposed HMA achieves a better performance-complexity tradeoff. Numerical results verify the effectiveness and superiority of the proposed protocols.

NOISE CANCELLATION WITH LMS VARIANTS

The noise is one of the important factors that affect negatively the operation of circuits and systems. There are different methods and techniques for cancelling/reducing/de-noising these unwanted signals that mix with the original signal. In this study, an application/simulator that performs noise cancellation operations with least mean-squares algorithms was designed. The application, which has powerful visual support and a user-friendly interactive interface, can make single or comparative noise cancellation operations and performance analyzes with different algorithms on noisy signals. The effects of the algorithm parameters can be observed, information about the related algorithms can be obtained via the developed application that can also be used for educational purpose.

An improved Quasi-Type-1 PLL based on paralleled filtering stage

In three-phase grid synchronization applications, the performance of traditional phase-locked loops will decrease under non-ideal grid voltage conditions. In order to solve the above problem, moving average filters (MAF) has been widely studied and utilized in PLLs in recently published papers with the expense of slower transient speed. This paper proposes a paralleled filtering stage to improve the dynamic performance of PLL. The suggested filter with smaller time delay is based on MAF and delay signal cancellation (DSC) operator, which is integrated in quasi-type-1 structure based PLL (QT1-PLL). Compared with differential MAF-PLL (DMAF-PLL) and QT1-PLL, the proposed filter can obtain a faster transient response without degrading phase estimation accuracy. The experimental results demonstrate that the proposed method can provide satisfactory performance.

A Demodulation-Based Method for Instantaneous Phase-Angle Estimation of Unbalanced Three-Phase Voltage Systems

This article proposes an open-loop-based demodulation technique for the instantaneous phase-angle estimation of three phase voltage systems. The proposed demodulation-based method relies on the Clarke transform, finite-impulse-response filters, and algorithms for phase-angle and frequency deviation estimation. When compared to a frequency-locked loop (FLL) based on dual second-order generalized integrators and a phase-locked loop (PLL) relying on adaptive delayed signal cancellation operator, the proposed one does not use any integrators, recursive signals, and feedback of frequency or phase angle, thus unconditionally stable and relatively simple tuning is achieved. In addition, the proposed method is computationally efficient due to avoiding interpolation, square-root, trigonometric functions or their inverse operations. Moreover, under equal dynamic condition, the proposed one generates improved steady-state accuracy in a range of the frequency deviation specified by standard and grid code. Simulated and experimental results are presented to verify the efficacy of the proposed method.

Modified natural frame control of single‐phase cascaded H‐bridge multilevel converter under distorted grid voltage

Cascaded H-bridge multilevel converter is widely applied in flexible AC transmission and grid connection of renewable energy, but its current quality decreases as the grid voltage distortion continues to deteriorate. A modified natural frame control method to enhance the harmonic elimination ability of converters is proposed in this paper. A single-phase cascaded delayed signal cancellation operator is applied to deal with the distorted grid voltage signals. Benefit from a system structure without any feedback loops or integral items, the transient response of single-phase cascaded delayed signal cancellation operator is faster than commonly-used second-order generalised integrator. The settling time of single-phase cascaded delayed signal cancellation operator facing grid voltage phase jump is less than one grid period. After immunising the synchronisation reference against harmonic distortion by using the single-phase cascaded delayed signal cancellation operator, the modified natural frame control method can then generate high-quality sinusoidal current. Phase-locked loop and coordinate transformation are unnecessary for the proposed method, which decreases the system complexity. Various simulations and experimental tests based on a down-scaled platform demonstrate the performance of the proposed modified natural frame control method under distorted grid voltage.

On the Continuous Cancellative Semigroups on a Real Interval and on a Circle and Some Symmetry Issues

Let S denote the unit circle on the complex plane and ★:S2→S be a continuous binary, associative and cancellative operation. From some already known results, it can be deduced that the semigroup (S,★) is isomorphic to the group (S,·); thus, it is a group, where · is the usual multiplication of complex numbers. However, an elementary construction of such isomorphism has not been published so far. We present an elementary construction of all such continuous isomorphisms F from (S,·) into (S,★) and obtain, in this way, the following description of operation ★: x★y=F(F−1(x)·F−1(y)) for x,y∈S. We also provide some applications of that result and underline some symmetry issues, which arise between the consequences of it and of the analogous outcome for the real interval and which concern functional equations. In particular, we show how to use the result in the descriptions of the continuous flows and minimal homeomorphisms on S.

Current Feedback Instrumentation Amplifier With Built-In Differential Electrode Offset Cancellation Loop for ECG/EEG Sensing Frontend

This work describes a compact and low-power current feedback instrumentation amplifier (CFIA) that can effectively eliminate differential electrode offset (DEO), amplifier input offset, and light motion artifacts. The proposed approach is using a local feedback loop in the first stage of the CFIA which can eliminate dc and low frequency offset whereas by-passes useful components such as EEG and ECG signals. As a result, the DEO and amplifier input offset can be eliminated in the first stage of the CFIA while still amplifying the desired signal components. This enables offset cancellation operation with low bias current that leads to higher energy efficiency compared to existing CFIA offset cancellation schemes. The proposed CFIA is implemented using CMOS 0.18-μm technology, that can eliminate up to 250-mV DEO with a supply voltage of 1.8 V. Measurement results show common mode rejection ratio (CMRR) 120 dB (without DEO) and 95 dB (with DEO of 250 mV) at 10 Hz, input noise 3.8 μVrms, power consumption 12.7 μW, and NEF 39 with core area of 73.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Furthermore, the actual EEG and ECG waveforms are obtained using the proposed CFIA under an actual clinical setting.

A Novel Phase-Locked Loop for Mitigating the Subsequent Commutation Failures of LCC-HVDC Systems

The AC fault ride-through and support capability of line commutated converter based high voltage direct current (LCC-HVDC) have significant influence on the safe operation of power system. The ability of phase locked loop (PLL) to synchronize with the voltage phase under AC faults would affect the recovery performance of LCC-HVDC systems. This paper analyzes the influence of the conventional PLL on the subsequent commutation failure (SCF) of LCC-HVDC systems and points out that the conventional PLL has some problems such as slow dynamic response, significant frequency fluctuation, and coupling of phase and frequency detection under fault conditions. A novel PLL is proposed to address the problems. Cascade delayed signal cancellation operators are combined with a mathematical filter, forming a hybrid pre-filter to extract fundamental positive sequence voltage for the PLL. To reduce the fluctuation of PLL's frequency during AC faults, the estimated frequency is fixed when the fault is detected by a fault detector. As a consequence, the decoupling between phase detection and frequency detection is realized, and the proposed PLL's dynamic response performance is enhanced. Simulation results show that the proposed PLL can provide accurate phase reference for the DC control system and reduce the probability of SCFs of LCC-HVDC system.

Non-orthogonal multiple access in cell-free massive MIMO networks

In this paper, we investigate the downlink performance of cell-free massive multi-input multi-output non-orthogonal multiple access (CF-mMIMO-NOMA) system with conjugate beamforming precoder and compare against the orthogonal multiple access (OMA) counterpart. A novel achievable closed-form spectral efficiency (SE) expression is derived, which characterizes the effects of the channel estimation error, pilot contamination, imperfect successive interference cancellation (SIC) operation, and power optimization technique. Then, motivated by the closed-form result, a sum-SE maximization algorithm with the sequential convex approximation (SCA) is proposed, subject to each AP power constraint and SIC power constraint. Numerical experiments indicate that the proposed sum-SE maximization algorithms have a fast converge rate, within about five iterations. In addition, compared with the full power control (FPC) scheme, our algorithms can significantly improve the achievable sum-SE. Moreover, NOMA outperforms OMA in many respects in the presence of the proposed algorithms.