Feedback Communication Systems Research Articles

Design and Analysis of Analog Feedback Communication System with Rayleigh Fading Channel Model

In this work, we mathematically model a wireless Analog feedback communication system (AFCS) using a Rayleigh fading channel. AFCS system is a new research area and has promising applications, especially in low-power devices such as sensors. Compared to AWGN, Rayleigh fading channel more closely models the real wireless environment. In this work, AFCS Rayleigh fading channel is considered in forward transmission while AWGN is considered in the feedback channel. We evaluated the performance of the system which is mostly based on the minimization of mean square error (MSE) at the receiver. Even in presence of a wireless fading environment, the AFCS attains a 0 MSE value in 2-3 iterations if a noise power of 10dB is considered while in 10-15 iterations if a noise power of 20dB is considered.

Analog Feedback Communication System with Receive Diversity and MRC

This study investigates the analog feedback communication system (AFCS) architecture considering Rayleigh fading channel model and receive diversity maximum ratio combining (MRC). This architecture employs a power-efficient transmitting unit, an estimator at the receiver side and iterative algorithm that minimizes the mean square error (MSE). Using the feedback channel, the estimated received sample is fed back to the transmitter. The performance of AFCS with the Rayleigh fading channel model is evaluated using MSE optimization. The investigation revealed that when compared to a single input single output AFCS system, the diversity-enabled AFCS system achieves negligible MSE in fewer iterations. MSE of order 10 −3 is achieved by 6 receive antennas with MRC in only 4 iterations at 0dB channel signal-to-noise ratio (SNR), compared to a single input single output AFCS system that requires more than 10 iterations to achieve the same order of MSE.

Molecular communication network and its applications in crop sciences

Plant molecular biology and bacterial behaviour research in the future could focus on using genetically engineered bacteria as a sensor, hormonal/disease detector, and target gene expression, as well as establishing a bioluminescence feedback communication system. Over the last two decades, understanding plant signal transduction pathways of plant hormones has become an active research field to understand plant behavior better. To accomplish signal transduction, plants use a variety of hormones for inter- and intra-communication, and biotic or abiotic stressors activate those. Signal transduction pathways refer to the use of various communication methods by effectors to elicit a response at the molecular level. Research methodologies such as inter-kingdom signaling have been introduced to study signal transduction and communication pathways, or what we can term plant molecular communication. However, stochastic qualities are inherent in most technologies used to monitor these biological processes. Molecular communication (MC) is a new research topic that uses the natural features of biological organisms to communicate and aims to manipulate their stochastic nature to achieve the desired results. MC is a multidisciplinary research field inspired by the use of molecules to store, spread, and receive information between biological organisms known as "Biological Nanomachines." It has been used to demonstrate how biological entities may be characterised, modelled, and engineered as communication devices in the same manner as traditional communication technologies are. We attempted to link MC and PLANT'S MC in this studyand we believe that reasonable combined efforts may be made to use the functional applications of MC for detecting and understanding molecular-level activities such as signaling transduction pathways in crops.

Perfect SDR transmitters with feedback for small satellites and their metrological characteristics

The paper discusses general preconditions for the development of a new class of high-efficient low energy adaptive feedback communication systems (AFCS) used as communication channels between the small satellites and ground base stations (BS). The particularity of AFCS is that they transmit data without coding using adaptive PAM modulation, with a bit rate and energy-spectral efficiency attaining the limits established by the information theory (“perfect” transmission). The absence of coders simplifies the construction of satellites forward transmitters (FT) and permits to reduce their energy consumption, sizes, weight, and cost. This also enables a formulation of Bayesian optimization task and derivation of optimal transmission-reception algorithms permitting to design “perfect” AFCS, as well as to implement their FT transmitters as flexible software-defined radio (SDR) units. Moreover, feedback enables the elaboration of adaptive algorithms maintaining perfect mode of transmission in various, also non-stationary scenarios. The paper also discusses the not used before metrological characteristics of AFCS performance and explains the approach to their measurement. The results of experiments with the hardware prototype of AFCS confirmed its work as the perfect transmission system. The paper also discusses the potential advantages of SDR AFCS application for small satellite – earth communications.

Optimizing Transmission Lengths for Limited Feedback With Nonbinary LDPC Examples

This paper presents a general approach for optimizing the number of symbols in increments (packets of incremental redundancy) in a feedback communication system with a limited number of increments. This approach is based on a tight normal approximation on the rate for successful decoding. Applying this approach to a variety of feedback systems using nonbinary (NB) low-density parity-check (LDPC) codes shows that greater than 90% of capacity can be achieved with average blocklengths fewer than 500 transmitted bits. One result is that the performance with ten increments closely approaches the performance with an infinite number of increments. The paper focuses on binary-input additive-white Gaussian noise (BI-AWGN) channels but also demonstrates that the normal approximation works well on examples of fading channels as well as high-SNR AWGN channels that require larger QAM constellations. This paper explores both variable-length feedback codes with termination (VLFT) and the more practical variable length feedback (VLF) codes without termination that require no assumption of noiseless transmitter confirmation. For VLF, we consider both a two-phase scheme and CRC-based scheme.

Convergence of fundamental limitations in feedback communication, estimation, and feedback control over Gaussian channels

In this paper, we establish the connections of the fundamental limitations in feedback communication, estimation, and feedback control over Gaussian channels, from a unifying perspective for information, estimation, and control. The optimal feedback communication system over a Gaussian necessarily employs the Kalman filter (KF) algorithm, and hence can be transformed into an estimation system and a feedback control system over the same channel. This follows that the information rate of the communication system is alternatively given by the decay rate of the Cramer-Rao bound (CRB) of the estimation system and by the Bode integral (BI) of the control system. Furthermore, the optimal tradeoff between the channel input power and information rate in feedback communication is alternatively characterized by the optimal tradeoff between the (causal) one-step prediction mean-square error (MSE) and (anti-causal) smoothing MSE (of an appropriate form) in estimation, and by the optimal tradeoff between the regulated output variance with causal feedback and the disturbance rejection measure (BI or degree of anti-causality) in feedback control. All these optimal tradeoffs have an interpretation as the tradeoff between causality and anti-causality. Utilizing and motivated by these relations, we provide several new results regarding the feedback codes and information theoretic characterization of KF. Finally, the extension of the finite-horizon results to infinite horizon is briefly discussed under specific dimension assumptions (the asymptotic feedback capacity problem is left open in this paper).

Decision Threshold Controlled in Both Receivers of a Communication System with Information Feedback

In this work the efficiency of a coded Communication System with Information Feedback (CSIF) is analyzed when its direct and feedback channels are affected by white Gaussian noise. The configuration of the system under consideration is constructed on the basis of two recent patents. These patents are related with the control of detection thresholds in the receivers of both direct and feedback channels. Expressions for calculating the a priori probabilities of the received redundancy symbols in a linear systematic code are obtained. An easy technique to improve the performance of the CSIF direct channel based in the use of optimized detection thresholds for the redundancy symbols in a linear systematic is suggested. The method of using optimized detection thresholds in the feedback channel receiver is also considered. The use of this method on both channels of the CSIF makes this communication system more efficient, because of the energy saving when the signal to noise ratio on both direct and feedback channels is significantly small. A main application area of this improved CSIF scheme is in satellite communications. Keywords: Coded communication system with information feedback, error probability, feedback communication systems, Gaussian white noise, linear systematic codes

Capacity and Power-Bandwidth Efficiency of Wireless Adaptive Feedback Communication Systems

In this study, the bit-rate and power-bandwidth (P-B) efficiency of wireless adaptive feedback communication systems (AFCS) are considered. The analysis is based on the results of AFCS optimization [1], [2]. It is shown that the capacity of optimal AFCS is equal to that of the forward channel in the initial n* cycles of the samples transmission, and decreases for n>;n*. Transmission in the threshold number of cycles n* provides ideal P-B trade-off and full utilization of the resources of the system.

A negative feedback system between oocyte bone morphogenetic protein 15 and granulosa cell kit ligand: its role in regulating granulosa cell mitosis.

Although the existence of a regulatory paracrine feedback system between oocytes and follicular somatic cells has been postulated for some time, there has not yet been any definitive evidence that such a communication system exists. Herein we present a previously undescribed oocyte-granulosa cell (GC) feedback communication system involving an oocyte-derived factor, bone morphogenetic protein-15 (BMP-15) and a GC-derived factor, kit ligand (KL), both of which have been shown to be crucial regulators of female reproduction. We used a coculture system of rat oocytes and GCs and found that BMP-15 stimulates KL expression in GCs, whereas KL inhibits BMP-15 expression in oocytes, thus forming a negative feedback loop. Moreover, KL, like BMP-15, exhibited mitotic activity on GCs in the presence of oocytes. Because c-kit (KL receptor) is expressed in oocytes but not GCs, the oocytes must be involved in mediating the KL-induced GC mitosis. Furthermore, the blockage of c-kit signaling in oocytes by using a c-kit neutralizing antibody markedly suppressed BMP-15-induced GC mitosis, suggesting that the oocyte must play a role in the GC responses to BMP-15. In contrast, the c-kit antibody had no effect on the mitotic activities of two other known GC mitogens, activin-A and BMP-7. Altogether, this study presents direct evidence of a negative feedback system governed by oocyte-derived BMP-15 and GC-derived KL, and demonstrates that the mitotic activities of BMP-15 and KL for GCs depend on this oocyte-GC communication system. We hypothesize that the negative feedback system most likely plays a pivotal role in early folliculogenesis.

Linear feedback communication systems with Markov sources: optimal system design and performance evaluation

The optimal analog discrete-time feedback communication system is designed for the transmission of a Markov process, such as that generated by a combined source/channel encoder. The forward channel is affected by an additive white Gaussian noise, while the feedback channel is causal and noiseless; no repetition of the transmitted sample is assumed. On the basis of the minimum mean square error (MMSE) criterion, the optimal transmitter and receiver are derived under the constraint of a maximum power level for the transmission over the forward channel. The resulting optimized system is adaptive and fully exploits the available power, thus maximizing the information rate transferred by the system itself. For comparison purposes, the optimal MMSE communication system without feedback link is also designed. The MSE performance of both systems, with and without feedback link, is evaluated by means of closed-form expressions and their convergence rate to the steady state is also computed. Using the feedback link gives significant performance improvements when the input-encoded process is moderately or highly correlated; in this case, the advantages offered by the combined source-channel coding techniques are fully exploited by the proposed optimized feedback communication systems.

Performance of M-ary feedback communication systems

An M-ary decision feedback communication system with the MAP strategy is investigated. The performance of this system is analytically evaluated as follows. First, an approximate lower performance bound is found by means of the Cauchy inequality. Then an approximate lower performance bound is found by means of the Jensen inequality. Finally, the bounds are compared and found to coincide, yielding an approximate estimate of the system performance. The same estimate may also be obtained by means of mean path approximation. Thus, the mean path approximation tends to underestimate the system average transmission time. For verification purposes, the results are compared with those obtained from computer simulation and are found to be in good agreement. Furthermore, the feedback transmission is compared with one-way transmission. It is shown that feedback systems are better than one-way systems in terms of the signal/noise ratio required to achieve a prescribed error probability. The estimated power advantage of feedback systems is between 5.4 dB and 3 dB, depending on the number of possible signals M; the power advantage decreases as M increases. The results obtained for M→ ∞ imply that the feedback increases the capacity of an infinite-bandwidth Gaussian channel. However, the last result was not proved with the degree of rigour required in mathematics; rather, we have used approximate performance bounds and computer simulation data in our analysis.

On Noise Immunity of Feedback Communication Systems

This paper compares the noise immunities of feedback communication systems for two particular types of systems noise: Gaussian white noise, which is typical of radio and telephone communication, and Poisson-distributed noise, which is typical of laser communication. The comparison shows that as the error probability requirement is made more stringent, the use of feedback will save commensurately more energy in both cases.

Analysis of feedback communication systems

Analysis of feedback communication systems

A note on feedback communication with noisy side information at the receiver (Corresp.)

A feedback communication system which has noisy side information at the receiver is considered. The estimation scheme is a simple extension of the conventional one without side information. The resulting mean-squared error is compared with the rate-distortion bound obtained recently by Wyner and Ziv.

On the Performance of a Feedback Communication System Utilizing a Cumulative Decision Scheme

A cumulative decision scheme that can be employed in a feedback communication system is treated. Any decision to decode depends upon all messages that have been received prior to the decision. The average error over all transmissions as well as the forward error may be controlled. Performance is compared to an error-detection repeat-request noncumulative scheme utilizing group codes. Optimal performance of the cumulative scheme with respect to the noncumulative scheme is given for short-length best group codes. It is also demonstrated that the use of feedback does not necessarily increase appreciably the amount of hardware necessary to effect error control.

Communication over fading dispersive channels with feedback

An intermittent on-off noiseless feedback scheme for binary communication over the slow- and fast-fading Rayleigh channels is proposed and analyzed. At high energy-to-noise ratios, doubling the number of feedback iterations yields a 3-dB power saving for the slowly fading channel. Power savings ranging from 1 dB for one feedback iteration to 9 dB for 16 iterations are typical for the fast-fading model. Also for the fast-fading model, by picking the optimum number of forward transmissions for each value of energy-to-noise ratio, the best achievable performance requires approximately 7.5 dB more energy than the minimum predicted by the rate-distortion bound. Also presented is a feedback communication system for wide-sense stationary, uncorrelated-scatterer, fading, and dispersive forward and feedback channels. The model used for both forward and feedback channels is Kennedy's. Upper and lower bounds on the error probability for block orthogonal <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> -ary communication are presented for this system.

Repetitive signaling using a noisy feedback channel

Several feedback coding schemes considered recently are repetitive signaling schemes. The sender retransmits the message, if necessary, on the basis of information received over the feedback channel. This paper considers a repetitive signaling scheme in which the user's estimate of the transmitted message is sent over the feedback channel to the sender with high energy if the user is uncertain of the estimate and with lower energy if otherwise. The sender retransmits the message with high energy if it decides the user's estimate is incorrect. This scheme is applied to a wide-band, additive-white-Gaussian-noise, average-power-constrained feedback communication system. Orthogonal signals are used for transmission over both forward and feedback channels. A lower bound is obtained for the probability of error when arbitrary decision rules are used. This lower bound is achieved asymptotically for long block duration by using decision rules implemented with correlation receivers. The resulting asymptotic error performance is superior to that of any feedback coding scheme previously considered for use in a wide-band additive-white-Gaussian-noise system for any values of the forward and feedback channel capacities.

Gaussian feedback communication systems with weak noise in the feedback link

The feedback coding problem for a feedback communication system with additive white Gaussian noise is investigated. Using mean-square estimation error as a performance measure, a recursive algorithm is given for evaluating the asymptotically optimal code of a specified form to be used when the signal-to-noise ratio in the feedback link is high. The relationship between this code and the coding procedure of Butman is given. When the signal-to-noise ratio in the forward channel is low, the transmitted signal sequence is given explicitly, and is compared with center-of-gravity methods.

Feedback communication using orthogonal signals

We consider a feedback communication system in which the forward and feedback channels are disturbed by additive noise and constrained in average power. Two block coding schemes are proposed in which the signals are orthogonal waveforms. A finite number of forward and feedback transmissions per message is made. Information received over the feedback channel is used to reduce the expected value of forward signal energy on all iterations after the first. Similarly, the expected value of feedback signal energy is reduced on all iterations after the first. These schemes, which are modifications of a feedback coding scheme due to Kramer, obtain improved error performance over one-way coding at all rates up to the forward channel capacity, provided only that the feedback channel capacity is greater than the forward channel capacity. They require less feedback power than existing feedback coding schemes to achieve a given error performance.

A general formulation of linear feedback communication systems with solutions

The feedback coding problem for additive noise systems, in which the noise may be colored, nonstationary, and correlated between channels, is formulated in terms of arbitrary linear operations at the transmitting and receiving points. This rather general linear formulation provides a unified approach for deriving new results, as well as previous results obtained under more restrictive assumptions, in a straightforward manner. Thus the sequential form of the optimum linear feedback code with an average power constraint on the transmitter is derived for noiseless feedback but forward noise of arbitrary covariance. It is shown explicitly that noiseless feedback increases the capacity of a channel with colored noise. The noisy feedback problem is considered and upper and lower bounds on the performance presented.