The Development Of The Multiple Access Technology Based On Indoor Visible Light Communication System

Visible Light Communication(VLC) is an emerging optical wireless communication technology, which has the advantages of no electromagnetic interference, no application for radio spectrum, no restrictions for transmitting power, high transmission rate, widely channel bandwidth, widely signal coverage, excellent device compatibility and etc. In the progress of practical application of indoor VLC system, a kind of multiple access technology should be adopted under the circumstance of access to group network communication of multiple users, to ensure that each user could be access to the communication network simultaneously, so that the signals of each user could be received and demodulated with no interference with each other.At present, the study on the multiple access technology of VLC system has not been reported. This paper makes full investigations of the basic principles and the key technologies of the indoor VLC system and the existed multiple access technologies in optical domain. Through analysis and comparison of the performance of the major modulation and multiple access technologies, MPPM is used as the modulation of multiple access communication system, and Optical Code Division Multiple Access(OCDMA) is selected to apply in the system as well.Based on the in-depth studies of above-mentioned, this thesis proposes a scheme of indoor VLC multiple access system based on OCDMA technology, and makes construction of the basic model of the system. Combined with practical application environment, the key parameters of the system is studied and constructed, and some theoretical derivations of the performance of symbol error rate of the system are made. On the basis of these theoretical derivations, this paper builds the experimental simulation model of multi-access communication system and makes simulation calculations on MATLAB. The results show that the symbol error rate decreases and increases with the code weight and the code length growing respectively in condition of single user access. Under the premise of controlling the other variables, the symbol error rate rises with the user capacity growing and declines with the increasing of the code weight and the code length and the level of decision threshold under the circumstance of multiple user access. Under the same conditions, Multi-User Detection could sharply increase the performance of the symbol error rate of the multiple access communication system, compared to the system of Single-User Detection.