Research On Modulation And Demodulation Method Of Delta-sigma For White LED Communication

As the diverse requirement for wireless communications and the rapid development of optical technology, the wireless communication technology, with visible light as information carrier, air as transmission medium, attracts the attention of many enterprises and research institutions. Visible light communication(VLC) is mainly based on white LEDs as light source, with illumination and communications, which is different from other wireless optical communication technology. VLC has good performance in low energy consumption, high confidentiality and no electromagnetic radiation, etc. At present, due to the limits of communication distance and communication rate, the VLC research is still at the experimental stage. The article puts forward a kind of Sigma-Delta modulation/demodulation method used in white LED communi- cation to improve the signal-to-noise ratio of communication system and increase the communication distance.Based on Delta-Sigma modulation theory, the article studies and analyzes the oversampling and noise shaping characteristics. Then, the article makes a research about the higher order system to study the effect on the noise shaping characteristics and the stability of the system. Continuous-time 2nd structure is chosen as the structure of the modulation system through the research on the performance of different order delta-sigma modulators. In the circuit design, the system, with using modular design method, is divided into signal modulation module, the LED driver module and signal demodulation module. In addition, the simulation and debugging of the modulation circuit is carried out. At last, the article makes experiments on the delta-sigma modulation circuit applied to white LED communication, including multiple modulation methods comparison, system stability analysis, relation between LED modulation bandwidth and system bandwidth, system phase shift analysis. The experimental results show that the Delta-Sigma modulation system can make the noise distribute in high frequency area with the selection of integration constant. When the noise frequency is located outside the white LED modulation bandwidth, white LED is equivalent to a low-pass filter to filter the high frequency noise so that it can obtain high signal-to-noise ratio in communication bandwidth.