A secured communication link design using narrow line of sight technique

In recent wireless networking optical communication is an emerging field. Another novel approach of optical communication using Narrow Line of Sight technique is discussed. Array of trans­receivers are placed on the ceiling to communicate with the mobile nodes (users / trans­receivers) instead of a single transmitter. An intelligent position tracking technique based on the informations available from prepositioned sensors and using them in simple geometric equations is described. Intelligent cell concept is used to facilitate the tracking system. The whole wide area is divided into several sub areas and some of the sub areas are designated as boundary sub areas which hold the data regarding the movement of the mobile nodes. The Diffie­Hellman simple authenticated key agreement is used for secure communication. 1. INTRODUCTION In the emerging field of computing, wireless networking is one of the most attractive trends. Users want to establish a high speed communication link among themselves as well as with the external environment without being tethered to wires as well as wall jacks. So mobility has become an important issue in common office networking environments. At present there are two parallel important technologies, i.e. the radio communication link and the wireless optical link. [1] The wireless optical link has its own advantage like high bandwidth, security and low component price. So with the advent of new technologies the wireless optical network becomes an attractive alternative to its nearest competitor. Development of several optical network architecture has been accomplished according to two main categories : the diffused system and Line of Sight (LOS) system. [2,3] The diffused system suffers from multi path effect. The achievable bit rate is about 52 Mbps in a 5 meter room [4]. Again the LOS system is only limited by the capability of the component used. With the rapid advancement of transmitter and receiver designing techniques, it gradually becomes a suitable choice. The Line of Sight can be categorized in Wide Line of Sight (WLOS) and Narrow Line of Sight (NLOS) categories. In WLOS one ceiling mounted transmitter is used to cover a wide area with its spread beam of light. As a result the launch power of the laser transmitter should be relatively high resulting a threat to eye safety. The paper concentrates on the NLOS system in which the spread beam from the laser diode is directed towards the optical receiver. The covered area being small the launch power from …