Communication over fading dispersive channels with feedback

In this paper, we study the problem of stabilizability of LTI systems over both the forward (from the controller to the plant) and feedback (from the sensor to the controller) channel. We adopt the additive white noise (AWN) channel with a prescribed power constraint as our channel model. For first order systems, we derive explicitly the necessary and sufficient conditions for stabilizability and show the tradeoff between the minimum signal-to-noise ratio (SNR) required for the forward and feedback channel. We also show explicitly that the use of two-parameter controller in this problem assumes better performance.

This paper investigates the event-triggered predictive control problem of networked control systems (NCSs) with the event-triggered mechanism adopted both in the forward and feedback channels to save the network resources. The transmition time instants of states are determined by an event-triggered mechanism, which contains a dynamic reference state, in the feedback channel. Combination of the event-triggered mechanism and the networked predictive control approach is employed to estimate states as well as future control input sequences of the system in the forward channel. The derived estimate state error system of the networked event-triggered predictive control system is proven to be uniformly globally asymptotic stable. Simulation results are provided to demonstrate the effectiveness and applicability of the proposed event-triggered predictive control scheme.

The paper is concerned with an improved predictive control method of NCSs (Networked Control Systems) with random time delay and data dropout. The design of networked control system we proposed is based on Scenario-Based Networked Control (SBNC). Through this method the NCSs' performance is relative with an equivalent data-dropout probability. In this paper, the improved method is applied on the linear systems, and the network is in both forward and feedback channels that is more realistic. The buffer in feedback channel makes the system equivalent to a system with an extra forward delay, and the feedback channel has no delay. The simulation on the ball and beam system verifies the effectiveness and rationality of the proposed control algorithm. Besides, the comparison between a different predictive method and this improved one is achieved, and the latter one shows better tracking properties even when the network is very bad. The effects of the parameters are also considered in the simulation.

Nonlinear feedback communication schemes proposed up to now have been restricted to coherent channels. This paper describes a scheme which not only lacks this restriction but yields performance better than the coherent ones that have been analyzed. Block coded orthogonal signals together with incoherent receiver forms are used on both forward and feedback links. It is assumed that the transmitter has a high peak power capability. However, it is shown that by increasing the code length the duty cycle of this mode can be made sufficiently small so that the contribution to average power is negligible. It is found that the probability of error for every message is upper-bounded by exp[-E(R)T], where T represents the code length and E(R) is a function of the transmission rate, R , the capacities of the forward and feedback channels, and a parameter that determines the rate with which the duty cycle decreases with increasing code length. When the forward and feedback capacities are equal, say C , the E(R) versus R curve can be made to approach a curve that starts at 2C and decreases monotonically to the value C at R = C . This contrasts with the corresponding curve without feedback which starts at C/2 and decreases to zero at R = C . The main advantage of information feedback over no feedback, namely E(R = C) > 0 , where C is the forward channel capacity, can also be obtained even when the capacity of the feedback channel is less than that of the forward. To obtain such behavior, existing schemes require that the feedback channel capacity be at least as great as the forward.

Many industrial systems exhibit the nonlinear characteristics. Generally, the structure of the system is taken by feedback closed-loop for the purpose of realising the automatic control of industrial processes. Therefore, the industrial systems are the closed-loop feedback nonlinear systems which have complicated structures. The mathematical models of systems provide the support and basis for the design of the control system and the better control performance. However, it is hard to determine the models of closed-loop feedback nonlinear systems due to the complex structures. The goal of this study is to develop an identification way for a feedback nonlinear system including a forward channel and a feedback channel, where the forward channel is described by a controlled autoregressive model and the feedback channel takes the form of a static nonlinear function. By taking advantage of the least squares optimisation, a recursive least squares algorithm is established and shows its good performance to solve the identification problem for the feedback nonlinear system.

This paper aims at comparing the performance of numerous space-time trellis coded modulations (STTCM) over slow and fast Rayleigh fading channels in order to identify the most efficient ones. After a brief presentation of the STTCM concept, we propose to recall the criteria used to construct the codes studied herein, depending on the channel properties and the number of transmit and receive antennas. Then, we introduce our new representation of the STTCM as an extension of the one currently used to describe regular trellis codes, namely the polynomial representation. Simulation results and especially new performance relative to BER scale are then given in order to compare the behavior of Tarokh's, Baro's, Blum's, Chen's and Firmanto's codes over slow and fast Rayleigh fading channels. From these comparisons, it follows that the codes constructed with the trace criterion, namely Chen's codes, outperform all the other tested codes over both channels.

In this paper, the receiver performance of Alamouti coded orthogonal frequency division multiplexing (OFDM) systems is analyzed. When the channel is not constant during the period of Alamouti codeword transmission, the conventional linear maximum likelihood (ML) receiver suffers from performance degradation. We use three different receiver combining methods and study the error performance. The sensitivity of different receivers is investigated by varying the correlation coefficient. Our results can be easily extended to be applicable to other block coded OFDM schemes with different antenna configurations. The performance loss in linear ML receiver can be partially improved by employing a decision-feedback strategy. In the decision feedback steps preliminary decisions are used to subtract the intercodeword coupling. However this increases the computational complexity of the receiver.

In this paper, we use the minimum mean square error (MMSE) criterion to design the scaled and offset belief propagation (BP)-based decoding algorithms for short low-density parity-check (LDPC) codes on the fast Rayleigh fading channel. Based on the MMSE criterion, the theoretical formulas and numerical calculations on the optimum factors for these two improved BP-based algorithms are provided. The simulation results for several short (Chen et al., 2005 and Gallager, 1962) regular LDPC codes on the fast Rayleigh fading channel demonstrate that the scaled and offset BP-based algorithms with our proposed factors can achieve the performance better than that of the BP algorithm.

This paper investigate the properties of space-time bit-interleaved coded modulation (ST-BICM) systems in fast Rayleigh fading channels. We first show that ST-BICM with QPSK signaling in fast fading channels possesses the uniform distance property, which makes performance analysis tractable. We also derive the probability distribution of the squared Euclidean distance between space-time symbols assuming uniform bit-interleaving. Based on the distribution, we show that the diversity order for each codeword pair becomes maximized as the frame length becomes sufficiently long. We analyze the performance of ST-BICM in fast fading channels by deriving an FER upper bound. The derived bound turns out very accurate, requiring only the distance spectrum of the binary channel codes of ST-BICM. Numerical results demonstrate that the bound is tight enough to render an accurate estimate of performance of ST-BICM systems.

We investigate the detection of space time coded (STC) signals modulated using continuous phase modulation (CPM) in fast Rayleigh fading channels. A symbol-by-symbol iterative detector with an optimum front-end is derived, and its practical implementation using the concept of principal component analysis (PCA) is considered. To assess the performance, numerical examples for different STC-CPM schemes are presented. According to the simulation results, the proposed detector obtains very good power efficiencies. Moreover, the bit error rate (BER) performance of the proposed detector is in the range of 0.5-1 dB from the case without fading, highlighting its effectiveness to mitigate fading.

To the question of networked control system with random time-delay in both forward and feedback channels, a new class of Smith predictor combined to Fuzzy PID control is presented. It sets up a new Smith forecast model and designs the parameter self-tuning fuzzy PID controller. The results of system simulation using MATLAB show that the network control system of the proposed scheme has better dynamic and stability, and in the case of model miss-matching has high robustness.

This paper focuses on a new H∞ controller design issue for networked control systems with external disturbance as well as random time delays and packet dropouts in forward and feedback channels, which are modeled by multiple Markov chains in a unified style. The output feedback controller is designed to stabilize the networked control system and also achieves the prescribed H∞ disturbance attenuation level. The addressed controller design problem is transformed into a nonlinear minimization problem with LMI constraints. An illustrative example is provided to show the effectiveness of the proposed methods. Copyright © 2014 John Wiley & Sons, Ltd.

Observer-based HOFA predictive cooperative control for networked multi-agent systems under time-variant communication constraints

Existing SCMA systems presented for multiuser detection has high computational complexity. The complexity is a prime concern considering its implementation in a machine-to-machine (M2M) communication involving limited capacity devices. Since these devices have low processing power, so practical implementation of SCMA needs to be optimised for better performance. This paper proposes an SCMA decoder with a soft demapping technique to reduce the computational complexity, providing better performance. To improve the stability of SCMA system for M2M communication, this paper proposes the use of noise variance threshold ψ, to handle the system’s stability. Results confirmed that the proposed soft demapper-based SCMA reduced the execution time to 33% and the iteration number to 63% compared to the conventional SCMA scheme deploying message passing algorithm (MPA)-based decoding. The proposed SCMA provides an improvement of 2.5 dB at a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> under the block Rayleigh fading channels and an improvement of approximately 1.1 dB at a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> dB under the fast Rayleigh fading channels. The improvements come from the fast convergence of iterative decoding using a soft demapper supported by a variance threshold ψ that avoids the duality decision at the border of the decision area.

A secret key agreement framework involving three users is considered in which each of the users 1 and 2 intends to share a secret key with user 3 and users 1 and 2 are eavesdroppers with respect to each other. There is a generalized discrete memoryless multiple access channel (GDMMAC) from users 1 and 2 to user 3 where the three users receive outputs from the channel. Furthermore, there is a feedback channel from user 3 to users 1 and 2 through which user 3 sends information extracted from the received output from the GDMMAC to increase the key rates. We consider both noiseless and noisy feedback. In the case of noiseless feedback, a public channel of unlimited capacity from user 3 to users 1 and 2 is used only once. In the case of noisy feedback, a noisy broadcast channel (BC) from user 3 to users 1 and 2 can be repeatedly used, like GDMMAC. In both setups, inner bounds of the secret key capacity region are derived. The secret key capacity region is derived in some special cases where the channel inputs and outputs form Markov chains in certain orders. For illustration, the corresponding results are also derived and discussed for Gaussian channels. The cases with noiseless feedback, noisy feedback, and no feedback at all are compared with each other.