Forward Channel Research Articles

Input-to-State Stability for Networked Predictive Control With Random Delays in Both Feedback and Forward Channels

The input-to-state stability (ISS) for a class of networked control systems with random delays and packet dropouts appearing simultaneously in both feedback and forward channels is thoroughly investigated in this paper. A new network predictive controller scheme is introduced in order to compensate the effect of transmission delays and packet dropouts. By making use of the small gain theorem, the stability criteria of the considered new system are derived. The proposed stability conditions are fairly easy to check and considerably less conservative than the existing ones. These criteria reveal that, if the original linear systems are controllable and observable, then, by adopting the proposed networked-predictive-control scheme, the ISS properties can be guaranteed for the overall system despite the effects of networking such as transmission bounded delays, packet dropouts, and possible disturbance inputs. When no disturbance inputs occur, the system stability can be guaranteed for random delays with a certain bound or else for any large constant delays. Results for two illustrative examples are given to validate the proposed control scheme, the second one being a laboratory-scale dc-motor rig.

On using noisy feedback in a Gaussian channel

For information transmission, a discrete-time channel with independent additive Gaussian noise is used. There is also another channel with independent additive Gaussian noise (the feedback channel), and the transmitter observes all outputs of the forward channel without delay via that channel. Transmission of nonexponentially many messages is considered (i.e., the transmission rate is zero), and the achievable decoding error exponent for such a combination of channels is investigated. The transmission method strengthens the method previously used by the authors for the BSC and Gaussian channels. In particular, for small feedback noise, this yields a gain of 33.3% (instead of 23.6% earlier in the similar case of a Gaussian channel).

Networked Predictive Fuzzy Control of Systems with Forward Channel Delays based on a Linear Model Predictor

This paper presents a novel networked control framework, using fuzzy logic control, for systems with network delays which are known to greatly weaken the control performance of the controlled system. To deal with the network delays, the predicted differences between the desired future set-points and the predicted outputs from a model predictor are utilized as the inputs of a fuzzy controller, thus a series of future control actions are generated. By selecting the appropriated control sequence in the plant side, the network delays are compensated. The simulative results demonstrate that the proposed method can obviously reduce the effect of network delays, and improve the system dynamic performance.

Exploitation of spatial diversity in a novel cooperative spectrum sharing method based on PAM and modified PAM modulation

This article presents a novel cooperative spectrum sharing (CSS) scheme. The primary transmitter transmits a complex Quadrature amplitude modulation (QAM) signal in the first phase, and CSS occurs in the second phase. The secondary transmitter with the largest forwarding channel gain among the nodes that successfully decode the primary signal in the first phase is selected for CSS. This selected node employs a pulse-amplitude modulation (PAM) signal for primary information message (IM) instead of the QAM signal, and it employs a modified PAM signal for the secondary IM. The proposed modified PAM signal depends on the amplitude of the primary PAM signal. This method results in no mutual interference and negligible primary interference constraint and allows a higher degree of exploitation of spatial diversity, thus enabling increase in secondary power to improve primary transmission. The outage performance is enhanced in both the primary and secondary systems. The critical region, in which the primary outage performance is enhanced with the proposed CSS scheme, can be adjusted and widened by varying either the modulation cooperation sharing factor or the number of secondary transmitters.

On the Performance of MIMO-ARQ Systems with Channel State Information at the Receiver

This paper investigates the performance of multiple-input-multiple-output (MIMO) systems in the presence of automatic repeat request (ARQ) feedback. We show that, for a large range of performance metrics, the data transmission efficiency of the ARQ schemes is determined by a set of parameters which are scheme-dependent and not metric-dependent. Then, the results are used to study different aspects of MIMO-ARQ such as the effect of nonlinear power amplifiers, large-scale MIMO-ARQ, adaptive power allocation and different data communication models. The results, which are valid for various forward and feedback channel models, show the efficiency of the MIMO-ARQ techniques in different conditions.

Stabilization of Optimal Dynamic Quantized System with Packet Loss

This paper is concerned with the stabilization problem of an optimal dynamic quantized system with packet loss. The optimal dynamic quantizer, which minimizes the quantized output error, is designed for a discretetime system with packet loss occurring in the forward channel. A sufficient condition for the system’s mean square stability is developed based on matrix inequality method. A state feedback controller design method is also proposed, and numerical simulation demonstrates the effectiveness of the proposed method.

On Forward Channel Estimation for MIMO Precoding in Cooperative Relay Wireless Transmission Systems

Linear precoding for wireless multi-input multi-output (MIMO) transceivers has demonstrated substantial strength in cooperative relay networks for achieving high system throughput and performance. However, traditional precoder optimization critically assumes knowledge of channel state information (CSI) at source nodes. For linear MIMO source precoding design, we propose a novel method to estimate the quadratic product of forward-link channel information between source and relay nodes. To conserve bandwidth, our source estimates the forward-link MIMO CSI by utilizing inherent signals transmitted by amplify-and-forward (AF) relays without requiring the cumbersome default method of coordinated relay channel estimation and relay feedback of its estimated CSI. From the overheard AF relay signal, the source node simply extracts the quadratic channel information of its forward-link for designing its precoder. In addition to presenting a low overhead method for forward channel estimation, we also analyze the channel estimation performance by investigating its bias and its Cramer-Rao lower bound. Finally, we present analytical results in comparison with simulations.

BER analysis of space‐time coded RFID system in Nakagami‐ m fading channels

The exact bit error rate (BER) analysis of a space-time coded radio frequency identification (RFID) system is presented, where the tag has multiple antennas and the reader has a single antenna. In the analysis, the forward and backward channels exhibiting independent but not necessarily identically distributed Nakagami-m fading are considered, and the diversity order that the system can achieve is found to be Nmin(m h, m g), where N is the number of antennas at the tag and m h and m g are the fading parameters corresponding to the forward and backward channels, respectively. The analytical results are verified through comparison with the simulation results.

Networked Control Systems Based on New Smith Predictor and Fuzzy-PID Controller

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.

Control Schemes for Passive Teleoperation Systems over Wide Area Communication Networks with Time Varying Delay

In this paper, the problem of time varying telecommunication delays in passive teleoperation systems is addressed. The design comprises delayed position, velocity and position-velocity signals with the local position and velocity signals of the master and slave manipulators. Nonlinear adaptive control terms are employed locally to cope with uncertain parameters associated with the gravity loading vector of the master and slave manipulators. Lyapunov-Krasovskii function is employed for three methods to establish asymptotic tracking property of the closed loop teleoperation systems. The stability analysis is derived for both symmetrical and unsymmetrical time varying delays in the forward and backward communication channel that connects the local and remote sites. Finally, evaluation results are presented to illustrate the effectiveness of the proposed design for real-time applications.

Neural network observer-based networked control for a class of nonlinear systems

A new neural network observer-based networked control structure for a class of nonlinear systems is developed and analyzed. The structure is divided into three parts: local linearized subsystem, communication channels and remote predictive controller. A neural-network-based adaptive observer is presented to approximate the state of the time-delay-free nonlinear system. The neural-network (NN) weights are tuned on-line and no exact knowledge of nonlinearities is required. The time delays considered in the forward and backward communication channels are constant and equal. A modified Smith predictor is proposed to compensate the time delays. The controller is designed based on the developed NN observer and the proposed Smith predictor. By using the Lyapunov theory, rigorous stability proofs for the closed-loop system are presented. Finally, simulations are performed and the results show the effectiveness of the proposed control strategy.

A Closed-Loop Supply Chain Problem with Retailing and Recycling Competition

We investigate a durable product retailing and recycling problem in a closed-loop supply chain consisting of a single manufacturer and two competitive retailers, in which the manufacturer collects used products via retailers from the consumers and has sufficient channel power over the retailers to act as a Stackelberg leader; the retailers compete in retail products and recycling used products. In order to analyze the impact of retailing and recycling competitions on the profits of the manufacturer and the competitive retailers, two collection models (coordinated collection (ModelC) and decentralized collection (ModelD)) are established, respectively. Then, based on game theory, we derive the optimal retail price, the optimal repurchase price, and the optimal profits of the manufacturer and the retailers. The managerial insights demonstrate that more intense retailing competition induces the increase of the manufacturer's profits in both forward and reverse channels and retailers' profits in the forward channel and the decrease of retailers' profits in the reverse channel, while more intense recycling competition induces the decrease of the profits of the manufacturer and retailers in both forward and reverse channels. Finally, numerical examples are given to illustrate the effectiveness of the proposed models.

A QoS-based routing approach using genetic algorithms for bandwidth maximisation in networks

This paper addresses the path selection problem from a known source to the destination in dense networks. The proposed solution for route discovery uses the genetic algorithm approach for a QoS based network. The multi point crossover and mutation helps in determining the optimal path and alternate path when required. The input to the genetic algorithm is a learnt module which is a part of the cognitive router that takes care of four QoS parameters. Here the set of nodes selected for routing is determined by delay, jitter and loss. On this graded surface of nodes selected, the bandwidth parameter is considered for path selection. The aim of the approach is to occupy the maximized bandwidth along the forward channels and minimize the route length. The population size is considered as fixed nodes participating in the network scenario, which will be limited to a known size of topology. The simulated results show that by using genetic algorithm (GA) approach the probability of convergence to shortest path is higher.

LabVIEW Based Design Implementation of M-PSK Transceiver Using Multiple Forward Error Correction Coding Technique for Software Defined Radio Applications

Software-Defined Radio (SDR) is an enabling technology which is useful in a wide range of areas within wireless systems. SDR offers a perfect solution to the problem of spectrum scarcity in wireless communication. With the significant increase in the demand for reliable, high data rate transmission these days, a different number of modulation techniques need to be adopted. The main objective of this paper is to design and analyze an SDR based M-Phase Shift Keying (PSK) transceiver using LabVIEW (Laboratory Virtual Instrumentation Engineering Workbench) and to measure the Bit Error Rate (BER) in the presence of Additive White Gaussian Noise (AWGN) introduced in the channel. Forward Error Correction (FEC) is used as a channel coding scheme in this paper. FEC codes are used where the re-transmission of the data is not feasible, thus redundant bits are added along with the message bits and transmitted through the channel. This paper describes the fundamental concept for the design & development of an SDR -based transceiver simulation model under PSK Scheme & analyses the performance of two Forward Error Correction channel coding algorithms namely the Convolution and the Turbo Codes. In this paper we have shown that how fast and effectively we can build a PSK transceiver for interactive Software Defined Radio. With the help of this design we are able to see and prove that data errors can be minimized using coding techniques, which in turn improves the Signal to noise ratio (SNR).

Using time delay compensation scheme in dynamic output feedback controller for networked control systems

This paper proposes a new method to design the dynamic output feedback controller for networked control systems (NCS) with communication delay in both forward and feedback channels. In order to remove the effects of the communication delay according to one's will, two different network delay compensation schemes are provided in two cases: the controlled plant whose state vectors can be measured and the one whose state vectors cannot be measured. Furthermore, another key part of this paper is to analyse the stability of the closed-loop networked control system. Finally, numerical simulation results show the effectiveness of the proposed method.

Closed-loop supply chain network configuration by a multi-objective mathematical model

Integration of forward and reverse channels results in closed-loop supply chain networks. In this research, a mixed-integer linear programming model is proposed to configure a closed-loop supply chain network. The network includes multiple products, plants, recovery technologies, demand markets, and collection centres. The objective function is minimisation of the total cost. The model can determine number and locations of open facilities, and flows of products in the network. In addition, we develop the model to multi-objectives by considering minimisation of defect rates and time of operations in collection centres. To solve the model, weighted-sums and distance methods are applied in copier remanufacturing example and the results are analysed. Moreover, value path approach is applied to compare the results of different methods.

Broadcast Approaches to the Diamond Channel

The problem of dual-hop transmission from a source to a destination via two parallel full-duplex relays in block Rayleigh fading environment is investigated. All nodes in the network are assumed to be oblivious to their forward channel gains; however, they have perfect information about their backward channel gains. We also assume a stringent decoding delay constraint of one fading block that makes the definition of ergodic (Shannon) capacity meaningless. The focus of this paper is on simple, efficient, and practical relaying schemes to increase the expected-rate at the destination. For this purpose, various combinations of relaying protocols and the broadcast approach (multi-layer coding) are proposed. For the decode-forward (DF) relaying, the maximum finite-layer expected-rate as well as two upper-bounds on the continuous-layer expected-rate are obtained. The main feature of the proposed DF scheme is that the layers being decoded at both relays are added coherently at the destination although each relay has no information about the number of layers being successfully decoded by the other relay. It is proved that the optimal coding scheme is transmitting uncorrelated signals via the relays. Next, the maximum expected-rate of ON/OFF based amplify-forward (AF) relaying is analytically derived. For further performance improvement, a hybrid decode-amplify-forward (DAF) relaying strategy, adopting the broadcast approach at the source and relays, is proposed and its maximum throughput and maximum finite-layer expected-rate are presented. Moreover, the maximum throughput and maximum expected-rate in the compress-forward (CF) relaying adopting the broadcast approach, using optimal quantizers and Wyner-Ziv compression at the relays, are fully derived. All theoretical results are illustrated by numerical simulations. As it turns out from the results, when the ratio of the relay power to the source power is high, the CF relaying outperforms DAF (and hence outperforms both DF and AF relaying); otherwise, DAF scheme is superior.

Performance of channel adaptive random access with imperfect channel reciprocity

The performance of channel adaptive random access is investigated with imperfect channel reciprocity between the forward channel gain at the measurement time and the reverse channel gain at the random access packet transmission time.

An MMSE Strategy at Relays With Partial CSI for a Multi-Layer Relay Network

We consider a relay network with a single source-destination pair and multiple layers of relays between them. We assume that these layers sequentially relay the signal transmitted by the source to the destination. Unlike existing work, we also assume that the destination and all the forward layers present between the transmitting layer and the destination receive signals during every transmission phase. We optimally combine these signals, say μ of them, using a precoder at each relay layer for onward transmission. We obtain this precoding matrix by minimizing the mean-squared error (MSE) at the relays, and do not require channel-state-information (CSI) of the forward channels at the relays unlike existing systems that minimize MSE at the destination and require CSI of the forward channels at the relays. Our closed-form solution for this matrix is valid for any K number of layers, whereas minimizing MSE at the destination does not have closed-form solution for K > 1. For K > 1, we enhance an existing scheme to obtain a sub-optimal closed-form precoder solution and use it for comparison. We show using simulations that our scheme approaches the bit-error-rate (BER) performance of this scheme, when μ is increased, even with partial CSI.

Design and Stability Analysis of Uncertain Networked Predictive Control Systems with Multiple Forward Channels

This paper is concerned with the design and stability of networked predictive control for uncertain systems with multiple forward channels. The delays and packet dropouts are distributed such that the classic networked predictive control (NPC) needs modifications to be implemented. An improved control signal selection scheme with distributed prediction length is proposed to increase the prediction accuracy and hence achieve better control performance. Moreover, stability analysis results are obtained for both constant and random cases. Interestingly, it is shown that the stability of the closed-loop NPC system is not related to the distributed delays when they are constant and the system model is accurate. Finally, a two-axis milling machine example is given to illustrate the effectiveness of the proposed method.