COMPARISON OF TIME- AND EVENT-TRIGGERED STRATEGIES FOR WIRELESS COMMUNICATION IN EMBEDDED SYSTEMS : Design of a lab assignment for university level course on data communication in embedded systems

Sammanfattning: Embedded systems (ESs) and wireless technologies are in constant rapid development and therefore it is important to educate people in these subjects. This thesis work has the goal of developing a lab assignment for a university level course on data communication in embedded systems. Embedded systems have reliability and timeliness requirements that have to be fulfilled. These criteria pose problems to be addressed while ESs are used in conjunction with communication over wireless medium, which has some underlying limitations. These limitations come in the form of interference, degradation of signal strength with the distance and possible unwanted delays. This thesis work starts with a literature study on medium access control (MAC) methods and their possibilities for adoption of time-triggered and event-driven strategies for ESs with time constraints and continues with the lab assignment design, implementation and testing. Taking into account timing requirements brought by ESs and the specifics of the lab, i.e., limited time given to the students to solve the problem and compulsory usage of available lab equipment, a design with two communicating raspberry Pis was proposed. The system consists of a sensor node sending its readings to a controller, which is responsible for analyzing the data and actuating a set of LED lights as a response to the input data. The communication is done over a WiFi network and three different programs, organizing the communication in time-triggered, eventdriven or a combination of the two fashions are developed. Each program is tested under three environmental conditions and the results from these tests clearly show the limitation of the underlying CSMA/CA MAC adopted in WiFi and give a greater understanding of the advantages and disadvantages of different strategies for communication design.