Research On High - Speed Communication Superposition Coding Technology Of Visible Light

Visible light communication(VLC) is a wireless communication technology which uses Light Emitting Diode(LED) as transimitter and photodiode(PD) is the receiver. As a potential future high-speed wireless communication technology, pursuing higher speed has become a struggling target in telecommunication industry these years. Due to the intensity modulation/direct detection methods used in optical communication, the low commercial LED modulation bandwidth, the nonlinearity of electro-optical conversion and so on, the transmission rate of a single wick is often limited. To solve the above problems, this paper analyzes a superimposed communication system that use multi-LED wick in a single lamps as the transimitter and a single PD as the receiver. The main work is as follows:1. As the transmission rate of a single wick is limited, a multi-LED wick superimposed and parallel transmission scheme is put forward to increase visible light transmission rate multiply. In this paper, the correlative analysis and study are based on indoor line of sight link. As the electrical modulation bandwidth of commercial LED is limited, the range of linear electro-optic conversion is narrow and other shortcomings, and the intensity modulation / direct detection methods decided by the physical characteristics of LED and PD, the transmittion rate is limited. While the normal lighting is carry out by a number of LEDs in collaboration, and the signal to noise(SNR) conditions is better in VLC. Thus a multi-LED superimposed transmission scheme is proposed. The system transmission rate could be promoted to K times equivalently by using K LED wick this way.2. In order to detect multi-LED superimposed convergence signal, the visible superposition coded modulation(VLC-SCM) model is established and the joint detection algorithm that the driving voltages are different by superposition coded modulation(SCM) technology is given. Firstly, the parallel transmission structure at the transmitter of VLC-SCM systemis analyzed. Since the transient driving voltage of LED is non-negative, a data processing method based on on-off keying(OOK) modulation that adds DC-bias before LED is presented. The multi-LED system channel based on Lambertian model is studied. The result shows that superposition transmission system does not depend on channel difference to distinguish the data. In order to detect the multi-LED converging signal, the driving voltage difference is introduced at the transmitter. Finally, the joint detection algorithm based on OOK is proposed concerning multi-LED constraints, coding constraints. The simulation results confirm VLC-SCM multi-LED superimposed high-speed transmission systems have better transmission performance.3. In order to enhance the anti-nonlinearity performance of superimposed transmission system, the visible interleave division multiple access(VLC-IDMA) model is established, a successive and parallel detection algorithm and a fast performance estimation algorithm are given which the interleaver is different by interleave division multiple access(IDMA) technology. The system transmission structure in the transmitter is analyzed. The converging signals could be detected by the single interleaver difference. The whole ―+1‖ repetition code structure is put forward when using low bit rate coding. The successive and parallel detection algorithm in the receiver is studied and the analysis indicates some trade offs should be balanced between the system performance and implementation complexity. Then a multi-LED superimposed transmission system performance estimation algorithm is given to predict the system performance quickly. The simulation results prove the excellent high-speed transmission and anti-nonlinearity properties of the VLC-IDMA multi-LED system.4. According to the driving voltage difference, the interleaver difference and the nonlinearity characteristics of LED, a joint power allocation scheme is proposed to enhance the system efficiency and the performance of detection system. As the single driving voltage difference of LED tends to access into nonlinear range, the single interleaver difference makes the coding efficiency low. The multi-dimensions difference is put forward to improve system performance. Due to the moderate number of LEDs in a lamp, the joint power allocation method meets the actual need by the use of SNR evolution and endless search algorithm. The simulation shows that the proposed scheme enables LED works in the linear range. The proposed scheme is more efficient compared to the low-rate scheme under the constant driving voltage of multiple LED wick.