Random Power Level Research Articles

Bandit-Based Power Control in Full-Duplex Cooperative Relay Networks With Strict-Sense Stationary and Non-Stationary Wireless Communication Channels

Full-duplex relaying is an enabling technique of sixth generation (6G) mobile networks, promising tremendous rate and spectral efficiency gains. In order to improve the performance of full-duplex communications, power control is a viable way of avoiding excessive loop interference at the relay. Unfortunately, power control requires channel state information of source-relay, relay-destination and loop interference channels, thus resulting in increased overheads. Aiming to offer a low-complexity alternative for power control in such networks, we adopt reward-based learning in the sense of multi-armed bandits. More specifically, we present bandit-based power control, relying on acknowledgements/negative-acknowledgements observations by the relay. Our distributed algorithms avoid channel state information acquisition and exchange, and can alleviate the impact of outdated channel state information. Two cases are examined regarding the channel statistics of the wireless network, namely, strict-sense stationary and non-stationary channels. For the latter, a sliding window approach is adopted to further improve the performance. Performance evaluation highlights a performance-complexity trade-off, compared to optimal power control with full channel knowledge and significant gains over cases considering channel estimation and feedback overheads, outdated channel knowledge, no power control and random power level selection. Finally, it is shown that the sliding-window bandit-based algorithm provides improved performance in non-stationary settings by efficiently adapting to abrupt changes of the wireless channels.

Effect of Epidemic Interference on the Performance of M-ASK, M-PSK and M-QAM Modulation Schemes

This article presents a study on the performance of different digital modulation systems in the presence of epidemic interference. This type of interference is caused by the fast increase in the number of users in a system at a given time. The epidemic interference can be modeled as a non-stationary stochastic process, which presents random power levels over time. In a previous work, the authors assessed the effect of the epidemic interference on the performance of BPSK, QPSK, and M-QAM systems. The present paper extends the previous results for MASK and M-PSK systems. Furthermore, numerical results from Monte Carlo simulations are presented for all evaluated digital modulation systems.

Delay-Intolerant Covert Communications With Either Fixed or Random Transmit Power

In this paper, we study delay-intolerant covert communications in additive white Gaussian noise (AWGN) channels with a finite block length, i.e., a finite number of channel uses. Considering the maximum allowable number of channel uses to be N, it is not immediately clear whether the actual number of channel uses, denoted by n, should be as large as N or smaller for covert communications. This is because a smaller n reduces a warden's chance to detect the communications due to fewer observations, but also reduces the chance to transmit information. We show that n = N is indeed optimal to maximize the amount of information bits that can be transmitted, subject to any covert communication constraint in terms of the warden's detection error probability. To better make use of the warden's uncertainty due to the finite block length, we also propose to use uniformly distributed random transmit power to enhance covert communications. Our examination shows that the amount of information that can be covertly transmitted logarithmically increases with the number of random power levels, which indicates that most of the benefit of using random transmit power is achieved with just a few different power levels.

Modeling and SISO/MIMO Control with an Inverse Nyquist Array and Stability Analysis for Load-Follow Operation of PWR Core Without Boron

The purpose of this investigation is to design a nonlinear pressurized water reactor (PWR) core load-following control system for regulating the core power level and axial power difference and to analyze the global stability of the system. In modeling a two-point–based nonlinear PWR core without boron, the power rod and axial offset (AO) rod are considered. The two points are the bottom half and top half of the core. When the power rod and AO rod are in the same point (case 1), the power rod is an input, and the core power level is an output. When the power rod and AO rod in the core are not in the same point (case 2), the power rod and the AO rod are two inputs, and the core power level and axial power difference are two outputs. For each case, linearized models of the core at five power levels are chosen as local models of the core to substitute for the nonlinear core model over the global range of the power level. For case 1, proportional integral derivative (PID) control is utilized to design a controller of every local model as a local controller of the nonlinear core. For case 2, inverse Nyquist array control with the linear matrix inequalities method and PID control are adopted to devise a decoupling compensator and a dynamic controller for every local model, and their combination is a local controller of the nonlinear core. Based on the local models and local controllers of each case, the idea of flexibility control is used to design a decent controller of the nonlinear core at a random power level. A nonlinear core model and a flexibility controller at a random power level compose a core load-following control subsystem. The combination of core load-following control subsystems at all power levels is the core load-following control system for every case. Two global stability theorems are deduced to show that the core load-following control systems for the two cases are globally asymptotically stable within the whole range of the power level. Finally, the core load-following control system for each case is simulated, and the simulation results show that the control system is effective.

Multimodel-based power-level control with state-feedback and observer for load-follow PWR core

The purpose of this investigation is that a nonlinear Pressurized Water Reactor (PWR) core load following control system is designed and the global stability of the system is analyzed theoretically. On the basis of modeling a nonlinear PWR core and proposing the equilibrium manifold and the nonlinearity measure of the core to calculate the distribution situation of the core nonlinearity measure in the entire range of power level, linearized models of the core at five power levels are chosen as local models of the core and the set of local models is used to substitute the nonlinear core model. The full-state feedback control with a full-order observer is utilized to design a controller with robustness of every local model, which is treated as a local controller of the nonlinear core. The Kalman filter is contrived as an observer with robustness and the state feedback design with robustness is implemented via the robust pole assignment method. With the local models and local controllers, the flexibility partitioning of model and control is presented to design a decent flexibility controller of the nonlinear core at a random power level. A nonlinear core model and a flexibility controller at a random power level compose a core load following control subsystem. The combination of core load following control subsystems at all power levels is the core load following control system. Two global stability theorems are deduced to define that the core load following control system is globally asymptotically stable within the whole range of power level. Finally, the core load following control system is simulated and simulation results show that the control system is effective.

Load following control and global stability analysis for PWR core based on multi-model, LQG, IAGA and flexibility idea

The work is to design a nonlinear Pressurized Water Reactor (PWR) core load following control system and analyze the global stability of this system. On the basis of modeling a nonlinear PWR core, linearized models of the core at five power levels are chosen as local models of the core to substitute the nonlinear core model in the global range of power level. The combination control strategy of the Linear Quadratic Gaussian (LQG) control and the Proportional Integral Derivative (PID) control with an optimization process of Improved Adaptive Genetic Algorithm (IAGA) proposed is used to contrive a combined controller with the robustness of a core local model as a local controller of the nonlinear core. Based on the local models and local controllers, the flexibility idea of modeling and control is presented to design a decent controller of the nonlinear core at a random power level. A nonlinear core model and a flexibility controller at a random power level compose a core load following control subsystem. The combination of core load following control subsystems at all power levels is the core load following control system. The global stability theorem is deduced to define that the core load following control system is globally asymptotically stable within the whole range of power level. Finally, the core load following control system is simulated and the simulation results show that the control system is effective.

Flexibility control and simulation with multi-model and LQG/LTR design for PWR core load following operation

The objective of this investigation is to design a nonlinear Pressurized Water Reactor (PWR) core load following control system. On the basis of modeling a nonlinear PWR core, linearized models of the core at five power levels are chosen as local models of the core to substitute the nonlinear core model in the global range of power level. The Linear Quadratic Gaussian with Loop Transfer Recovery (LQG/LTR) robust optimal control is used to contrive a controller with the robustness of a core local model as a local controller of the nonlinear core. Meanwhile, LTR principles are analyzed and proved theoretically by adopting the matrix inversion lemma. Based on the local controllers, the principle of flexibility control is presented to design a flexibility controller of the nonlinear core at a random power level. A nonlinear core model and a flexibility controller at a random power level compose a core load following control subsystem. The combination of core load following control subsystems at all power levels is the core load following control system. Finally, the core load following control system is simulated and the simulation results show that the control system is effective.

Auto-controlled algorithm for slotted ALOHA

A multiple power level transmission system increases the maximum throughput by selecting the power levels randomly, showing the same behaviour as the standard slotted ALOHA, where the throughput decreases abruptly at higher traffic load conditions. An auto-controlled slowly decreasing throughput algorithm for slotted ALOHA is developed. Herein, a mobile terminal can transmit any packet at a higher probability at the lower power levels that increases the probability of only one packet at the highest power levels and thereby augmenting the capture probability. If the traffic load is high, the probability of interfering packets at the same slot increases. Consequently, the transmission probability at the lower power levels increases and the probability of exactly one packet at the highest power levels remains unaltered. As a result, the system is automatically controlled, since it does not need any extra information about the network. Therefore, it is very attractive from an implementation point of view for the emerging mobile networking environment. Extensive comparisons show that the proposed auto-controlled algorithm demands remarkable throughput performance compared with the traditional random power level selection algorithm particularly with a very high retransmission probability.

Improving the performance of the FPBA algorithm using random transmitter power levels

To enhance the throughput of the framed pseudo-Bayesian ALOHA (FPBA) algorithm used for reservation in wireless ATM, a scheme is described in which multiple power levels are used at the transmitters. One of the simultaneously sent packets can often be successfully received due to the power capture effect. The authors consider a capture model in which the transmitter captures the channel only if its signal-to-interference ratio is above some threshold when received at the central station. Rayleigh fading, shadowing and path loss all contribute to the capture effect in conjunction with the new physically induced random transmission power levels. Throughput equations of the algorithm are derived and the performance of the algorithm waiting time and throughput in the presence of the wireless channel is illustrated. Results show significant improvement in the throughput and low stable access delay for a wide range of traffic conditions.

Structures for radar detection in compound Gaussian clutter

The problem of coherent radar target detection in a background of non-Gaussian clutter modeled by a compound Gaussian distribution is studied here. We show how the likelihood ratio may be recast into an estimator-correlator form that shows that an essential feature of the optimal detector is to compute an optimum estimate of the reciprocal of the unknown random local power level. We then proceed to show that the optimal detector may be recast into yet another form, namely a matched filter compared with a data-dependent threshold. With these reformulations of the optimal detector, the problem of obtaining suboptimal detectors may be systematically studied by either approximating the likelihood ratio directly, utilizing a suboptimal estimate in the estimator-correlator structure or utilizing a suboptimal function to model the data-dependent threshold in the matched filter interpretation. Each of these approaches is studied to obtain suboptimal detectors. The results indicate that for processing small numbers of pulses, a suboptimal detector that utilizes information about the nature of the non-Gaussian clutter can be implemented to obtain quasi-optimal performance. As the number of pulses to be processed increases, a suboptimal detector that does not require information about the specific nature of the non-Gaussian clutter may be implemented to obtain quasi-optimal performance.

Capture Aloha with two random power levels

In this paper the interference process in an unslotted Aloha network using two power levels is used to obtain the throughput in a channel with power capture. In the model considered, each user randomly chooses a power level from a given set for each packet transmitted. It is shown that unslotted Aloha with power capture can achieve an ideal throughput of 0.26.

Erasure, capture, and random power level selection in multiple-access systems

Multiple-access algorithms that handle erasures as well as captures are introduced. The algorithms are evaluated according to the maximal throughput that they can support for a Poisson arrival process. An example is given which shows that, in practice, the positive effect of captures compensates the negative effect of erasures. An approach that effectively utilizes the capture phenomena is introduced. This approach incorporates a random power-level-selection scheme that allows each node to choose randomly to transmit in one of several allowable levels of power. Design issues such as number of levels, selection schemes, etc. are discussed. >

Bursting pressures of CO2 laser-welded rabbit ileum.

In this study, the short-term bond strength of laser-welded New Zealand white rabbit ileum was examined. Forty-eight longitudinally oriented 0.5-cm transmural, scalpel incisions were reanastomosed solely through the use of the CO2 continuous wave laser at low energy levels. Random power levels of 250, 500, 750, or 1,000 mW were delivered to weld sites by either continuous application for 30 seconds or a pulsating application (ie, 0.5 seconds on, 0.5 seconds off) for 60 seconds. This provided 53.6, 107.1, 160.7, and 214.3 J/cm2, respectively. With the aid of a plexiglass clamp and pressure monitored infusion system, each type of weld was tested six times to determine the intraluminal hydrostatic pressure required to burst the welded seam 1 minute after completing the weld. For the welds made with 107.1, 160.7, and 214.3 J/cm2 in both lasing modes, the mean bursting pressure was 40.7 mmHg (SD +/- 24.9) with no statistically significant difference in weld strengths at these energy densities. There was also no difference between continuous and pulsating delivery methods. However, the energy density of 53.6 J/cm2 in either method produced a mean bursting pressure significantly lower than those produced by the higher energy densities tested and below the estimated basal ileal intraluminal pressure of approximately 9 mmHg. Since 107.1 J/cm2 energy density caused the minimal gross tissue changes while producing an equally strong bond and since continuous is faster than pulsating, 500 mW of continuous delivery was considered the optimal setting for the CO2 laser welding of rabbit ileum.