【作者】 谭家杰；

【导师】 杨克成；

【作者基本信息】 华中科技大学 ， 光电信息工程， 2011， 博士

【摘要】 可见光LED具有电光转换效率高、节能、可靠、使用寿命长、高速调制特性好等特点,是公认的下一代绿色照明产品。室内可见光LED照明通信就是将LED照明技术和光通信技术相结合产生一种新技术。该技术是目前光无线通信的热点之一。本论文围绕室内可见光通信存在的相关问题开展了初步的研究工作。其中,在点对点通信、LED特性、通信的调制编码、MIMO信道模型、信道特性以及MIMO信道均衡方面做了深入细致的工作。首先,论文介绍了室内可见光LED点对点通信系统的组成。分析了LED光源特性,将LED划分为三类,给出了多个第三类LED室内最佳照明设计方案。根据LED特性提出了测量其调制带宽实验,用实验证明了大功率LED的带宽有限。分析了LED调制编码,并将单脉冲位置调制与多脉冲位置调制的可靠性和有效性进行了对比。介绍了室内点对点可见光通信系统组成,研究了接收器PIN的选择,前置放大电路设计。进行了对点对点通信系统的进行了设计和实验,研制出了两套不同传输速率的通信演示系统。一套采用单片机构成的低速系统；另一套装置采用FPGA/CPLD的高速系统。该系统改进前面系统的调制速率,提高了传输速率。两套通信系统都给出了相应的实验结果。最后,测量了LED通信距离与驱动电流关系、点对点信道衰落,并得出了相应的最小二乘拟合关系式。其次,分析了MIMO通信系统LED发射装置的布设方式,得出MIMO系统最佳的照明布局；建立了MIMO系统直射信道的模型；并在直射信道模型的基础上,将其修正,且将经系统的多次反射部分考虑进来,信道模型进一步完善。再次,首先对室内可见光LED MIMO信道特性进行了研究,特性包括信道脉冲响应、信道频率响应和信道的直流增益。并按照MIMO的接收器分布方式将它划分为：分散式布设和集中布设两种类型。提出了简化的光线追迹法,该方法沿用传统的光线追迹法,按照接收器接收的信号经过的反射次数来计算系统脉冲响应,根据脉冲响应分别求出频率响应和直流增益。给出了系统的仿真参数。并用简化的光线追迹法对分散式和集中式接收进行了仿真。论证了简化的光线追迹法优于传统的光线追迹法和统计模型法。最后对MIMO信道的容量,接收机的信噪比及误码率进行了研究。最后,为了减少码间串扰对MIMO系统的影响,提出了用自适应均衡技术来提高MIMO通信系统的可靠性。研究最常用的LMS和RLS两种算法性能,即影响算法收敛速度的相关因素,研究了经自适应均衡后系统的信噪比和误码率的分布规律。更多还原

【Abstract】 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.更多还原