Análise do impacto da comunicação em redes wirelesshart no desempenho de sistemas de controle

Este trabalho analisa o uso do protocolo WirelessHART para a implementação de sistemas de controle em laço fechado. São discutidas possíveis arquiteturas de implementação de laços de controle, as quais se diferem basicamente pelo local na arquitetura do sistema de controle em rede em que o controlador será executado. Optou-se pela análise do comportamento do protocolo WirelessHART numa arquitetura que considera o módulo de controle localizado num dispositivo host, o qual se comunica via HART-UDP com o gateway da rede. Para a análise da proposta desta dissertação foram descritos os mecanismos necessários para a realização do laço de controle sobre uma rede WirelessHART real, em um ambiente que apresenta todas as características de uma instalação industrial. Os resultados obtidos mostram que, com a arquitetura proposta, o laço de controle apresenta latências não determinísticas. Para a realização deste trabalho, foram apresentados dois estudos de caso: (i) o controle de uma válvula comumente utilizada na indústria de petróleo; (ii) e um processo simulado, que considera um controlador baseado em eventos, onde o sinal de controle é calculado de acordo com os tempos de comunicação permitidos pela rede entre o controlador e o processo. Os resultados obtidos mostram que é possível efetuar controle apesar dos atrasos ocasionados pela rede, desde que sejam levados em conta estes atrasos no cálculo do sinal de controle, podendo assim mostrar há degradação no desempenho do sistema sob controle.This work analyzes the use of WirelessHART protocol for the implementation of closed-loop control systems. It discusses possible architectures for implementing control loops, which differ by the location where the controller is executing. For the performance evaluation of the WirelessHART protocol behavior, an architecture that considers the control module located in a device, which communicates via Hart-UDP with the network gateway. The Experimental evaluations presented in this dissertation were performed in a setting that has all the characteristics of an industrial installation. The results showed that in the proposed architecture, the control loop has not deterministic latencies. Two case studies were carried on: (i) the control of a valve commonly used in oil and gas industrial applications; (ii) and a simulated process that considers an event-based controller where the control signal is calculated according to the communication time allowed by the network between the controller and the process. The results show that it is possible to perform control despite network delays, when taking into account the delays in the calculation of the control signal

Visoko-pouzdan prenos podataka kod bežičnih senzorskih mreža sa malom potrošnjom energije primenom 2D-SEC-DED tehnike kodiranja

This dissertation deals with the challenges of energy efficiency in systems with limited resources of homogeneous and heterogeneous wireless sensory networks for data collection applications in real environmentals. This research covers several fields from physical layer optimization up to network layer solutions. The problem which has to be solved is viewed from three different perspectives: the energy profile of the nodes with a special emphasis on the activity of the sensing block, the network protocol with a special focus on finding an adequate coding technique that need to reduce or eliminate the request for retransmission and evaluating the range of transmission for the proposed encoding technique. If energy efficiency in wireless sensor networks is formulated as a load balancing problem then the power management unit can significantly contribute to reduction in power consumption. Power management is implemented by switching on/off individual subblocks of the sensor node independently of the hardware platform. By reducing energy consumption both an extension of the lifetime of the sensor node and sensor network, is achieved. The obtained energy profiles reveal significant differences in energy consumption of wireless sensor nodes depending in terms of external sensors number, resolution of the analog-to-digital converter, network traffic dynamics, topology of the network, applied coding techniques, operating modes and activities during the lifetime of the sensor node and other factors. In this sense, the application of combination of power aware techniques, such as the duty-cycling at system-level, and power gating at the level of sensor elements, i.e. sensors, is proposed. An evaluation of the approach shows that energy consumption reduction three orders of magnitude on average can be achieved, when these two techniques are incorporated into the sensor node. On the other hand, in the wireless sensor networks, the choice of coding scheme, i.e. channel coding depends on the application and characteristics-, model-, type-errors appearing in the wireless channel. For example, one encoding technique is preferred for use when burst errors patterns are dominant, while another coding technique is more acceptable in situations where noise causes random errors that are either single or double in nature. Bearing this in mind, along with the analysis of channel characteristics, in this dissertation, we propose a new massage coding technique by which on extend traditional protocols with aim to improve energy efficiency, while maintaining high reliability in data transmission and low latency of message transfer. Namely, channel evaluation in wireless sensor networks used in industry shows that most of the errors are of single or double nature, and burst type errors are present, but rarely. In this context, in this dissertation, an effective technique for correcting errors at a destination (FEC) based on Hamming's coding scheme of relatively low complexity, called Two Dimensional-Single Error Correction- Double Error Detection (2D-SEC-DED) was developed. The proposed encoding technique is intendet to minimize packet retransmissions, thus saving energy. Evaluation of the proposed encoding scheme shows that the code is able to correct all single errors and 99.99% of double/multiple errors. The analysis was carried out through the implementation, in MATLAB, of two versions of Rendezvous Protocol for Long Life (RPLL), called Modified RPLL (M-RPLL) and Ordinary RPLL (O-RPLL), respectively. The energy gain achieved in this way is used to improve the performance of wireless transmission, such as increasing of the transmission range. As illustration, for indoor environment characterized by the path loss exponent 4 at the target BER of 5 10 4 , the proposed encoding scheme is able to improve the transmission distance by about 18 m , or the received signal strength (RSSI) by about 8.5 dBm compared to wireless sensor networks with encoding schemes without possibility to correct errors