Feedback Capacity Research Articles

Allostasis and organizational excellence

Organizational excellence is critical towards the development of organizations and, considering organizations’ role in the modern world, for societies’ economic and social development. The ability of organizations to adapt and adjust to the contingencies of the change and recover the stability of organizational systems through organizations’ own dynamic process is known as allostasis. This research focuses on the relationship between allostasis and organizational excellence. Based on a sample of 205 firms from Portugal and Spain, and resorting to fuzzy-set QCA (fsQCA), this research reveals that there are different combinations (equifinality) of conditions inherent to allostasis (adaptive capacity, feedback capacity, stigmergy capacity and integration intensity) leading to sustainable high outcomes (employee satisfaction, stakeholder satisfaction and organizational performance, jointly selected as proxies for organizational excellence). The analysis also shows that organizations that match those combinations simultaneously achieve high employee satisfaction, stakeholder satisfaction and organizational performance (multifinality), which is aligned with the premises of organizational excellence. Finally, the results reveal that in the different contexts (countries) analyzed, the combinations leading to high outcomes differ, thus supporting the idea that the ability to adapt and adjust that characterizes allostasis is critical towards organizational excellence.

New Result on the Feedback Capacity of the Action-Dependent Dirty Paper Wiretap Channel.

The Gaussian wiretap channel with noncausal state interference available at the transmitter, which is also called the dirty paper wiretap channel (DP-WTC), has been extensively studied in the literature. Recently, it has been shown that taking actions on the corrupted state interference of the DP-WTC (also called the action-dependent DP-WTC) helps to increase the secrecy capacity of the DP-WTC. Subsequently, it has been shown that channel feedback further increases the secrecy capacity of the action-dependent DP-WTC (AD-DP-WTC), and a sub-optimal feedback scheme is proposed for this feedback model. In this paper, a two-step hybrid scheme and a corresponding new lower bound on the secrecy capacity of the AD-DP-WTC with noiseless feedback are proposed. The proposed new lower bound is shown to be optimal (achieving the secrecy capacity) and tighter than the existing one in the literature for some cases, and the results of this paper are further explained via numerical examples.

Partial-state feedback multivariable MRAC and reduced-order designs

This paper develops a new model reference adaptive control (MRAC) framework using partial-state feedback for solving a multivariable adaptive output tracking problem. The developed MRAC scheme has full capability to deal with plant uncertainties for output tracking and has desired flexibility to combine the advantages of full-state feedback MRAC and output feedback MRAC. With such a new control scheme, the plant-model matching condition is achievable as with an output or state feedback MRAC design. A stable adaptive control scheme is developed based on LDS decomposition of the plant high-frequency gain matrix, which guarantees closed-loop stability and asymptotic output tracking. The proposed partial-state feedback MRAC scheme not only expands the existing family of MRAC, but also provides new features to the adaptive control system, including additional design flexibility and feedback capacity. Based on its additional design flexibility, a minimal-order MRAC scheme is also presented, which reduces the control adaptation complexity and relaxes the feedback information requirement, compared to the existing MRAC schemes. New results are presented for plant-model matching, error model, adaptive law and stability analysis. A simulation study of a linearized aircraft model is conducted to demonstrate the effectiveness and new features of the proposed MRAC control scheme.

Implementing programmatic assessment transforms supervisor attitudes: An explanatory sequential mixed methods study

Introduction Programmatic assessment (PA) is an increasingly popular approach to competency-based assessment (CBA), yet evaluation evidence is limited. This study aimed to identify and explore supervisor attitudes before and after implementing a novel PA using a sequential explanatory mixed methods design. In phase one, a survey was used to identify supervisor perspectives on work-based placements, PA and CBA. Survey results were then applied to develop focus group questions to further explore supervisor attitudes. Results PA was found to improve supervisor-student relationships by removing high-stakes assessment decisions and creating greater capacity for feedback and teaching, leading to a productive learning environment. Assessment was perceived as an important role and supervisors wanted to feel valued and heard within PA. Trust was conceptualised as a triad between supervisor, student and university, and enabled supervisors to engage with PA which was important for success. Supervisor learning of PA was experiential and often supported by students, highlighting the need for hands-on training. Conclusion Participants reported a high level of agreement with PA and CBA principles which may have made them amenable to educational change. Further research is needed to explore the experience of all stakeholders and to understand how worldviews and culture influence assessment initiatives.

Analysis of Information Feedback on Residential Energy Conservation and the Implications: The Case of China

Household electricity consumption has increased significantly over the last two decades, leading to a series of policy interventions targeting to reduce electricity consumption in the residential sector. Information feedback regarding household electricity consumption is considered a cost-effective approach to promoting energy conservation. Various studies have so far covered the effects of information feedback on electricity consumption, yet the variations in both the types of feedback provided and the research methodologies have made it difficult to draw plausible conclusions. In China’s case, less due regard has been given to the effectiveness of various types of information feedback. This study has compared the effectiveness of information feedback between emailing electricity bills to households and installing smart meters in terms of promoting electricity conservation by employing empirical survey data from the Chinese General Social Survey with the help of the propensity score matching method. The results show that information provision via information bills curtails electricity consumption by around 20%, whereas information feedback via smart meters installation has no positive effects on household electricity conservation due to lack of access and knowledge to understand the displays of advanced meters. In light of the above results, the study suggests that policy-makers stress the importance of information feedback-based initiatives and improve the information feedback capacity of smart meters through training and education.

Optimizing HARQ and Relay Strategies in Limited Feedback Communication Systems

One of the key challenges for future communication systems is to deal with fast changing channels due to the mobility of users. Having a robust protocol capable of handling transmission failures in unfavorable channel conditions is crucial, but the feedback capacity may be greatly limited due to strict latency requirements. This paper studies the hybrid automatic repeat request (HARQ) techniques involved in re-transmissions when decoding failures occur at the receiver and proposes a scheme that relies on codeword bundling and adaptive incremental redundancy (IR) to maximize the overall throughput in a limited feedback system. In addition to the traditional codeword extension IR bits, this paper introduces a new type of IR, bundle parity bits, obtained from an erasure code across all the codewords in a bundle. The type and number of IR bits to be sent as a response to a decoding failure is optimized through a Markov Decision Process. In addition to the single link analysis, the paper studies how the same techniques generalize to relay and multi-user broadcast systems. Simulation results show that the proposed schemes can provide a significant increase in throughput over traditional HARQ techniques.

Researching the efficiency of buck converter synchronous rectifier

The object of study is synchronous buck-voltage converter with digital control system. One of the most problematic things is energy changing and transmission in converters to reach certain numerical range with minimal losses in the components of the electrical circuit. An enormous calculated parameters of electrical scheme. There was advised and described both structure and electrical scheme of synchronous converter, which, thanks to digital system, provides dates with more accuracy connected with an impact on working scheme. There was shown detailed analysis example with a numerical value for the certain elements of electrical scheme. It’s a fundament in order to choose certain parts of electrical scheme according to the certain categories.During research there was used selection of hardware and software tools: elements for buck-converter – key, diode and capacitor; certain voltage and frequency range for microcontroller; control of the power keys of the circuit with the corresponding operating parameters for driver. There was analyzed and calculated all over the possible losses during the process bucking of the voltage to the certain level, an enormous losses in the components of the converter electrical scheme – induction coil, keys and capacitors. It’s an important part of synchronous buck-converter. There was calculated power losses and efficiency through the received graphics of keys commutation in electrical scheme. There were received graphic dependence of converter efficiency on output power; time characteristics of the control signal pulse-width modulation (PWM) and output voltage; dependence on the commutation losses. This is because advised synchronous converter has a set of features. Particularly analog to digital converter in the capacity of feedback, digital regulation system with a discrete step and rectification by replacing diodes with actively controlled switches. There are keys of low-side and high-side levels according to the passing voltage and current values. Therewith provides possibility for receiving more accuracy value. In comparison with analogic buck-converters, this converter has voltage parameter with fractional error.

Abstract 1474: IDO1 signaling supports inflammatory neovascularization

Abstract We have identified a distinct role for the immunoregulatory, tryptophan-catabolizing enzyme IDO1 (indoleamine 2,3-dioxygenase) in supporting neovascularization through its positioning as a key regulatory node between the inflammatory cytokines IFNγ (interferon γ) and IL6 (interleukin 6). IFNγ is a primary inducer of IDO1, but is also a key mediator of immune-based tumor suppression, which some studies have associated with its anti-angiogenic activity. Conversely, genetic studies in mice have clearly established a tumor-promoting role for IDO1, suggesting that it may interact with IFNγ in a negative feedback capacity. Targeted disruption of the Ido1 gene in mice resulted in enhanced resistance to lung tumor and metastasis development. This corresponded with attenuated induction of the pro-angiogenic cytokine IL6, which, when provided through ectopic expression, was able to restore pulmonary metastasis susceptibility to Ido1-/- mice. These initial findings suggested that IDO1 might contribute to cancer promotion by countering the anti-neovascular effect of IFNγ, possibly through IDO1-potentiated elevation of IL6. Consistent with this hypothesis, mice lacking either IDO1 or IL6 exhibited pulmonary metastasis resistance that was dependent on IFNγ and coupled with reduced tumor neovascularization. Neovascularization in a mouse oxygen-induced retinopathy model was likewise affected by IDO1 or IL6 loss, separating this process from the contextual complexity of the tumor microenvironment. Investigation into the cellular and molecular basis for the observed biology revealed that, within the heterogeneous expanse of Gr1+ MDSCs (myeloid-derived suppressor cells), the ability to independently elicit neovascularization in vivo was restricted to a highly autofluorescent population of CD11blo cells. This included a discrete, IDO1-expressing subpopulation, designated IDVCs (IDO1-dependent vascularizing cells), that, in an IDO1-dependent fashion, dominantly determined whether neovascularization was sustained. Mechanistically, the induction of IDO1 in IDVCs was found to provide a negative feedback constraint on the anti-angiogenic effect of host IFNγ through GCN2 (general control nonderepressible 2)-mediated activation of the integrated stress response and potentiation of IL6 production within these cells. These findings reveal fundamental molecular and cellular insights into how IDO1 interfaces with the inflammatory milieu to support neovascularization. Citation Format: Souvik Dey, Arpita Mondal, James B. DuHadaway, Erika Sutanto-Ward, Lisa Laury-Kleintop, Sunil Thomas, George C. Prendergast, Laura Mandik-Nayak, Alexander J. Muller. IDO1 signaling supports inflammatory neovascularization [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1474.

An Expandable, Contextualized and Data-Driven Indoor Thermal Comfort Model

Abstract Continuous discrepancies in building performance predictions creates an ongoing inclination to link contextualized, real-time inputs and users’ feedback for not only building control systems but also for simulation tools. It is now seeming necessary to develop a model that can record, find meaningful relationship and predict more holistic human interactions in buildings. Such model could create capacity for feedback and control with a level of intelligence. Fuzzy Logic Systems (FLSs) are known as robust tools in decision making and developing models in an efficient manner. Considering this capability, in this paper, FLSs is implemented to make a thermal comfort model in an educational building in the UK. Such implementation has an ability to respond to some identified desires of developers and performance assessors in addressing uncertainty in thermal comfort models. The results demonstrate the proposed method is practical to simulate the value of comfort level based on the input data.

Circuit design of buck-voltage converter with digital control system

The objects of research are processes in electrical scheme and enormous digital control systems in converter. One of the most problematic things is transfer and energy change in converter for current and voltage in order to reach certain value of digital range with a minimal percentage of error.This work explores buck-voltage converter with digital control system. An enormous considered procedure of projecting electrical scheme. There was described electrical scheme with a control system, which, thanks to the digital system, provides dates with more accuracy in the output of converter, among them: assignment of certain digital range of output voltage and system’s impact on working scheme.During the research there was used selection of hardware features and software tools, accepting peripheral devices, which let quickly and simply set up microcontroller for certain operating mode and to realize controlling system for buck converter in a programmatic manner.There was analyzed procedure of solving and choosing of the certain parts of electrical scheme, where was used to construct:– microcontroller for receiving, processing and issuance of information in electrical scheme;– driver operating and analog-to-digital conversion;– driver for control of the switches – basically transistors;– components of the buck-converter circuit.There is description and schematic choice of the certain parts of the scheme. There was included switch, capacitor and diode for buck converter; certain range of the frequency and voltage for microcontroller; control of the power keys of the circuit with the corresponding operating parameters for driver.There was received a system, which in prospect will become a basis to step down voltage value to the certain level. This is because defined method has a set of features, particularly digital regulation system with a discrete step and analog-to-digital converter in the capacity of feedback. Therewith provides possibility for receiving more accuracy value. In comparison with analogic buck converters, this converter has voltage parameter with fractional error.

Conditions that enable effective feedback

ABSTRACTDespite an increasing focus on assessment feedback, educators continue to find that simply replicating an effective feedback practice from one context does not guarantee success in the next. There is a growing recognition that the contextual factors surrounding successful practices need to be considered. This article reports on a large-scale mixed methods project and proposes 12 conditions that enable successful feedback in higher education. The conditions were distilled from seven rich case studies through multiple stages of thematic analysis, case comparison and reliability checking. The conditions were also evaluated by surveying senior leaders of Australian universities. These conditions highlight the importance of carefully designing feedback processes, along with the need for addressing capacity and culture for feedback. This helps to explain why there are such variances in effective feedback across contexts, and offers insight into how it may be achieved.

Secrecy Capacity of Colored Gaussian Noise Channels With Feedback

In this paper, the finite-order autoregressive moving average (ARMA) Gaussian wiretap channel with noiseless causal feedback is considered, in which an eavesdropper receives noisy observations of signals in both forward and feedback channels. It is shown that the generalized Schalkwijk–Kailath scheme, a capacity-achieving coding scheme for the Gaussian feedback channel, achieves the same maximum rate for the same channel even with the presence of an eavesdropper. Therefore, the secrecy capacity is equal to the feedback capacity without the presence of an eavesdropper for the Gaussian feedback channel. Furthermore, the results are extended to the additive white Gaussian noise (AWGN) channel with quantized feedback. It is shown that the proposed coding scheme achieves a positive secrecy rate. Our result implies that as the amplitude of the quantization noise decreases to zero, the secrecy rate converges to the capacity of the AWGN channel.

Feedback Capacity and Coding for the $(0,k)$ -RLL Input-Constrained BEC

The input-constrained binary erasure channel (BEC) with strictly causal feedback is studied. The channel input sequence must satisfy the $(0,k)$ -runlength limited (RLL) constraint, i.e., no more than $k$ consecutive ‘0’s are allowed. The feedback capacity of this channel is derived for all $k\geq 1$ , and is given by $C^{\mathrm {fb}}_{(0,k)}(\varepsilon ) = \max \frac {\overline {\varepsilon }H_{2}(\delta _{0})+\sum _{i=1}^{k-1}\left ({\overline {\varepsilon }^{i+1}H_{2}(\delta _{i})\prod _{m=0}^{i-1}\delta _{m}}\right )}{1+\sum _{i=0}^{k-1}\left ({\overline {\varepsilon }^{i+1} \prod _{m=0}^{i}\delta _{m}}\right )}$ , where $\varepsilon $ is the erasure probability, $\overline {\varepsilon }=1-\varepsilon $ and $H_{2}(\cdot )$ is the binary entropy function. The maximization is only over $\delta _{k-1}$ , while the parameters $\delta _{i}$ for $i\leq k-2$ are straightforward functions of $\delta _{k-1}$ . The lower bound is obtained by constructing a simple coding for all $k\geq 1$ . It is shown that the feedback capacity can be achieved using zero-error, variable length coding. For the converse, an upper bound on the non-causal setting, where the erasure is available to the encoder just prior to the transmission, is derived. This upper bound coincides with the lower bound and concludes the search for both the feedback capacity and the non-causal capacity. As a result, non-causal knowledge of the erasures at the encoder does not increase the feedback capacity for the $(0,k)$ -RLL input-constrained BEC. This property does not hold in general: the $(2,\infty )$ -RLL input-constrained BEC, where every ‘1’ is followed by at least two ‘0’s, is used to show that the feedback capacity can be strictly smaller than the non-causal capacity.

On the feedback capacity of the first-order moving average Gaussian channel

In this paper, we study the discrete-time additive Gaussian noise channel given by \(Y_i=X_i+Z_i\), \(i=1,2,\ldots ,\) where the input signal \(\{X_i\}\) satisfies an average power constraint and the noise \(\{Z_i\}\) is a stationary Gaussian process. We are interested in the capacity of the channel with feedback. Despite numerous lower and upper bounds having been reported, except for some special cases, it is an open problem to find the closed form for the feedback capacity. In the paper, we consider the case where the Gaussian noise \(\{Z_i\}\) is a first-order moving average process defined by \(Z_i=W_i+\alpha W_{i-1}\), \(|\alpha |\le 1\), with white Gaussian innovations \(W_i\), \(i=0,1,2,\ldots\). For this channel, Kim (IEEE Trans Inf Theory 52(7):3063–3079, 2006; IEEE Trans Inf Theory 56(1):57–85, 2010) showed that a modified Schalkwijk–Kailath scheme achieves the feedback capacity and obtained the closed form of the feedback capacity. The main aim of the paper is to give a new proof of the optimality of the coding scheme given by Kim. In our proof, decompositions of the input signal \(X_i\) and the Gaussian innovation \(W_i\) into independent components play important roles. For this channel, the minimum decoding error probability decreases with an exponential order which linearly increases with block length.

Multiplexing Zero-Error and Rare-Error Communications Over a Noisy Channel

Two independent data streams are to be transmitted over a noisy discrete memoryless channel with noiseless (ideal) feedback. Errors are tolerated only in the second stream, provided that they occur with vanishing probability. The rate of the error-free stream cannot, of course, exceed the channel's zero-error feedback capacity, and nor can the sum of the streams' rates exceed the channel's Shannon capacity. Using a suitable coding scheme, these necessary conditions are shown to characterize all the achievable rate pairs. Planning for the worst channel behavior-as is needed to achieve zero-error communication-and planning for the typical channel behavior-as is needed to communicate near the Shannon limit-are thus not incompatible. It is further shown that feedback may be beneficial for the multiplexing problem even on channels on which it does not increase the zero-error capacity.

Feedback Capacity of Stationary Gaussian Channels Further Examined

It is well known that the problem of computing the feedback capacity of a stationary Gaussian channel can be recast as an infinite-dimensional optimization problem; moreover, necessary and sufficient conditions for the optimality of a solution to this optimization problem have been characterized, and based on this characterization, an explicit formula for the feedback capacity has been given for the case that the noise is a first-order autoregressive moving-average Gaussian process. In this paper, we further examine the above-mentioned infinite-dimensional optimization problem. We prove that unless the Gaussian noise is white, its optimal solution is unique, and we propose an algorithm to recursively compute the unique optimal solution, which is guaranteed to converge in theory and features an efficient implementation for a suboptimal solution in practice. Furthermore, for the case that the noise is a k-th order autoregressive moving-average Gaussian process, we give a relatively more explicit formula for the feedback capacity; more specifically, the feedback capacity is expressed as a simple function evaluated at a solution to a system of polynomial equations, which is amenable to numerical computation for the cases k=1, 2 and possibly beyond.

Feedback Capacity of Gaussian Channels Revisited

In this paper, we revisit the problem of finding the average capacity of the Gaussian feedback channel. First, we consider the problem of finding the average capacity of the analog Gaussian noise channel, where the noise has an arbitrary spectral density. We introduce a new approach to the problem, where we solve the problem over a finite number of transmissions and then consider the limit of an infinite number of transmissions. Furthermore, we consider the important special case of stationary Gaussian noise with finite memory. We show that the channel capacity at stationarity can be found by solving a semi-definite program, and hence computationally tractable. We also give new proofs and results of the non-stationary solution which bridges the gap between results in the literature for the stationary and non-stationary feedback channel capacities. It is shown that a linear communication feedback strategy is optimal. Similar to the solution of the stationary problem, it is shown that the optimal linear strategy is to transmit a linear combination of the information symbols to be communicated and the innovations for the estimation error of the state of the noise process.

Capacity Achieving Distributions and Separation Principle for Feedback Gaussian Channels With Memory: the LQG Theory of Directed Information

A method is developed to realize optimal channel input conditional distributions, which maximize the finite transmission feedback information (FTFI) capacity, often called $n$ -block length feedback capacity, by information lossless randomized strategies. The method is applied to compute closed form expressions for the FTFI capacity and feedback capacity, of nonstationary, nonergodic, unstable, multiple input multiple output Gaussian channels with memory on past channel outputs, subject to average transmission cost constraints of quadratic form in the channel inputs and outputs. It is shown that randomized strategies decompose into two orthogonal parts-an deterministic part, which controls the channel output process, and an innovation part, which transmits new information over the channel. Then a separation principle is shown between the computation of the optimal deterministic part and the random part of the optimal randomized strategies. Finally, the ergodic theory of linear-quadratic-Gaussian stochastic optimal control theory, is applied to identify sufficient conditions, expressed in terms of solutions to matrix difference and algebraic Riccati equations, so that the optimal control part of randomized strategies induces asymptotic stationarity and ergodicity, and feedback capacity is characterized by the per unit time limit of the FTFI capacity. The method reveals an interaction of the control and the information transmission parts of the optimal randomized strategies, and that whether feedback increases capacity, is directly related to the channel parameters and the transmission cost function, through the solutions of the matrix Riccati equations. For unstable channels, it is shown that feedback capacity exists and it is strictly positive, provided the power exceeds a critical threshold.

Sensory Feedback and Animal Locomotion: Perspectives from Biology and Biorobotics: An Introduction to the Symposium.

The successful completion of many behaviors relies on sensory feedback. This symposium brought together researchers using novel techniques to study how different stimuli are encoded, how and where multimodal feedback is integrated, and how feedback modulates motor output in diverse modes of locomotion (aerial, aquatic, and terrestrial) in a diverse range of taxa (insects, fish, tetrapods), and in robots. Similar to biological organisms, robots can be equipped with integrated sensors and can rely on sensory feedback to adjust the output signal of a controller. Engineers often look to biology for inspiration on how animals have evolved solutions to problems similar to those experienced in robotic movement. Similarly, biologists too must proactively engage with engineers to apply computer and robotic models to test hypotheses and answer questions on the capacity and roles of sensory feedback in generating effective movement. Through a diverse group of researchers, including both biologists and engineers, the symposium attempted to catalyze new interdisciplinary collaborations and identify future research directions for the development of bioinspired sensory control systems, as well as the use of robots to test hypotheses in neuromechanics.

Feedback Capacity and Coding for the BIBO Channel With a No-Repeated-Ones Input Constraint

In this paper, a general binary-input binary-output channel is investigated in the presence of feedback and input constraints. The feedback capacity and the optimal input distribution of this setting are calculated for the case of an $(1,\infty )$ -RLL input constraint, that is, the input sequence contains no consecutive ones. These results are obtained via explicit solution of an equivalent dynamic programming optimization problem. A simple coding scheme is designed based on the principle of posterior matching, which was introduced by Shayevitz and Feder for memoryless channels. The posterior matching scheme for our input-constrained setting is shown to achieve capacity using two new ideas: history bits , which captures the memory embedded in our setting, and message-interval splitting , which eases the analysis of the scheme. Additionally, in the special case of an S-channel, we give a very simple zero-error coding scheme that is shown to achieve capacity. For the input-constrained binary symmetric channel, we show using our capacity formula that feedback increases capacity when the cross-over probability is small.