In this paper, we introduce a novel method for free-space optic communication. Normally, the free-space optic communication is sensitive to atmospheric turbulence. In order to overcome the weakness, we utilize two differential modulation optical beams, which improve markedly the quality of free-space optic communication.
The experiments, based on two wave mixing scheme were<sup>1</sup> done using photorefractive crystal LiNbO3. Photorefractive grating will be changed with the electrical signals, which will results in the energy transfer process between two beams, and then form two differential modulation optical beams. Firstly, we will present a brief introduction to the theoretical arguments for energy transfer process in two wave mixing experiments. After briefly explaining the method to achieve two differential modulation optical beams we discuss
the experiments for free-space optic communication. Finally, we conclude that the novel method improve markedly the quality of free-space optic communication.
This paper uniforms the communication between devices by the already existing objects and services in BACnet protocol and two new proprietary objects to realize the interoperability of home control subsystem. As the major challenge in developing home network is supporting automated maintenance to control device, a new architecture is designed to integrate the middleware into the subsystem based on these objects and services.
Proc. SPIE. 6022, Network Architectures, Management, and Applications III
KEYWORDS: Detection and tracking algorithms, Data modeling, Reliability, Control systems, Optoelectronics, Local area networks, Control systems design, Network architectures, Standards development, Network security
BACnet is an open building automation and control network protocol used extensively in building automation and control systems. To guarantee security and reliability of BACnet network, congestion control is important in BACnet network. Considering BACnet router's out-port rate and packet's priority, this paper proposes a rate based priority random early detection (RPRED) algorithm to realize congestion control in BACnet network. RPRED algorithm detects congestion according to the average queue length, and estimates congestion trend according to relationship between packets arriving rate and out-port rate. In congestion control, RPRED randomly drop packets and manage queue according to packets' priority. These features of RPRED algorithm ensure the security and reliability of BACnet network. Some experimental investigation was undertaken to compare RPRED algorithm with conventional Drop Tail algorithm. Test result shows that when traffic load increased in BACnet network, RPRED algorithm could decrease time delay and drop ratio of high priority BACnet packets.