Research On Indoor MIMO Visible Light Communication With White LED

The high power LED has the characteristics of higher electro-optical conversion efficiency, energy saving, more reliable, longer life, higher speed modulation, which is recognized as the next generation of green lighting products. The high power LED for indoor lighting technology combining with the optical communication technology produces a completely new technology which is referred as visible light communication (VLC). In recent years, the wireless communications technology using high power LED is one of the hot spots in optical wireless communication. This thesis focused on the existing indoor visible light communication issues to make preliminary research, and we finished some work that included two set of the point to point optical wireless communication protypes, the LED characteristics, the communications modulation and coding, the MIMO channel model, the MIMO channel characteristics, and the MIMO channel equalization.First, the thesis introduced the indoor high power LED point to point communication system components, the communication system was designed and experiment setups were also built. We analyzed the characteristics of luminous intensity of the LED, so the LEDs are divided into three categories according to their characteristics. We presented the optimum LED interior lighting design using a number of the third category LED. We also proposed an experiment to measure the modulation bandwidth, the experimental results showed that the bandwidth of the high-power LED is limited, which the high power LED only has 4.7-4.8MHz modulation bandwidth. We analyzed the LED modulation and coding, the pulse position modulation (PPM) and the multiple pulse position modulation (MPPM) were compared in their reliability and validity. We described the point to point visible light communication system that consists of the receiver PIN, pre-amplifier design. We developed two different sets of data rate communications demonstration system, one set of low-speed system using MCU and another set of devices using FPGA/CPLD. The latter improved the modulation rate and the transmission rate. The corresponding experimental results had been obtained by the experiments. We measured the relationship between drive current and distance, the communication channel fading using the least square fitting.Second, we analyzed the LED layout mode of the MIMO system, and we obtained the optimum lighting layout of the MIMO system for interior illumination. Not considering multiple reflections, the direct channel MIMO system model was established according to light transmission. Since this model which was only partially correct, so we did an amendment to take the diffuse also into account. The channel model has been further improved.Third, the high power LED MIMO indoor channel characteristics have been studied; these features included the channel impulse response, the channel frequency response and the channel dc gain. The impulse response and the frequency response of the MIMO receiver vary in accordance with their distribution. Therefore, the distribution of the receiver is divided into two categories:the decentralized layout and the centralized layout. We also proposed a simplified ray tracing method based on traditional ray tracing method, and gave out related parameters for simulation. Two types of distributions decentralized and centralized receiver were simulated using the simplified ray tracing method. We demonstrate a simplified ray tracing method is better than the traditional ray tracing methods and the statistical models. Finally, the capacity of MIMO channel, the receiver signal to noise ratio and bit error rate were also analyzed according to the communication theory.Finally, in order to reduce the ISI effect on the MIMO system, we proposed to use the adaptive equalization technology to improve the reliability of MIMO systems. We studied the most commonly of the LMS algorithm and the RLS algorithm and their performance, namely, the speed of convergence factors. The adaptive equalization system can enhance the signal to noise ratio and the bit error rate greatly.