A “Transmission Time Reservation” method in a Wireless Lighting Control System

Abstract

The lighting industry has been comprehensively developed and deployed during recent decades, especially with the rise of LED technology. As a related technique field, lighting control system has also draw more and more attention; therefore intelligent lighting control systems are needed. Nowadays, several famous lighting companies are working on a next generation of lighting control system, which apply not only a distributed network structure but also wireless communication. Rather than controlling by a single node, a distributed system will finish controlling operation in different control units. This guarantees the distributed system to be more robust and efficient. Wireless technology is also essential for a system because it is infeasible to connect distributed devices with cables. Of all the wireless communication standards, the zigbee protocol is regarded as the best solution for a lighting control system. This is because the zigbee protocol has features of low-rate and low-cost, which perfectly fit the features of a sensor network. However, this application also leads to a problem which cannot be ignored, the coexistence problem with other wireless protocols. Because both of the zigbee and other wireless protocols operate in the ISM 2.4 GHz frequency band, the coexistence problem happens. With different modulation and frequency spreading methods, different protocols will not detect each other correctly, for example if there are two different protocol packets being transmitted, a packet collision will happen. This problem is much more serious for the zigbee service, because the interference from wifi devices will be unacceptable for a zigbee transmission. How to solve this coexistence problem between zigbee and wifi devices in an indoor lighting environment is the main research question of this thesis. In this thesis, several solutions for the coexistence problem between zigbee and wifi are proposed and analyzed. With their different advantages and drawbacks, each of these methods has its own application scene. After comparing, the “Transmission Time Reservation” method has been proved to be a feasible solution as to the assumed problem, which has also been tested by simulations. Within this method, a gateway node between the zigbee and wifi network is designed cooperatively. Whenever there is a zigbee request, this node is programmed to do the reservation operation with the wifi AP node. The results of NS3 simulations and comparative tests have also shown that this method is effective to solve the coexistence problem in an indoor environment.