【作者】 赵明；

【导师】 元秀华；

【作者基本信息】 华中科技大学 ， 光电信息工程， 2011， 硕士

【摘要】 在大气光通信系统中由于大气信道的特殊性和随机性，大气吸收和散射使携带数据信息的光信号严重衰减，大气湍流使信号光强闪烁发生波前畸变，导致通信系统的误码率上升，系统的可靠性降低。本论文研究的大气光通信中的调制编码技术是选择合适的调制格式的编码方式保证高传输速率和低误码率，能够较好的降低大气对光信息传输的干扰，提高通信系统的可靠性和降低误码率以及克服信道的随机性误差。本论文从大气光通信系统的特点与实际系统中实现的可行性出发，采用强度调制/直接探测的方式，从理论上分析了几种调制方式的性能，建立起具有加性高斯白噪声干扰和乘性大气湍流干扰的信道模型，理论推导了各种调制格式的平均发射功率、频带利用率、误码率表达式，并通过仿真研究了不同调制格式下的光信号性能，表明脉冲位置调制(PPM)信号在大气中的传输性能相比其他调制格式最优，具有较高的功率利用率，但是需求带宽大。尤其是PPM的调制阶数越大，其抗干扰性能就越好，相应的带宽也越大，在实际的应用中结合通信速率采用适宜的调制阶数可保证PPM调制信号的性能。基于理论分析，本论文中设计并实现了以语音为信源的二进制开关键控(OOK)与4-PPM调制解调的大气通信系统，采用现场可编程逻辑阵列(FPGA)作为调制编码系统的核心，完成语音信号的调制编码与解调通信系统实验硬件平台，详细设计了语音信号4-PPM与OOK的调制与解调、发送与接收的FPGA硬件逻辑电路实现方法，完成各个功能模块的时序仿真。采用论文设计的硬件实验平台，并设计合理的实验方案完成了语音光信号的4-PPM调制解调的通信实验的调试与测量，通过比较OOK与PPM调制信号在大气信道中传输的实测波形图，PPM信号抗干扰优于OOK，从实验上验证了论文理论分析的结果，达到论文通信系统设计的要求。更多还原

【Abstract】 Because of atmosphere channel’s specificity and randomness in the atmosphericoptical communication system, laser signals which carry digital information are severelyattenuated by the atmospheric molecular absorption and scattering, light fluctuating thatcaused by the atmospheric turbulence occurs wavefront distortion, those factors lead tocommunication system instability, which causes high bit error rate and low reliability of thesystem. In this paper, the modulation and coding technology in the atmospheric opticalcommunication must be the appropriate modulation format encoding which can ensure hightransmission rate and low bit error rate, be better able to reduce atmospheric interferenceand improve the reliability of communication systems and overcome the randomness of thechannel.In this paper, on the basis of the characteristics of atmospheric opticalcommunication system and the feasibility of practical application, the system uses the wayof intensity modulation/direct detection. The performance of several modulation schemesare analyzed, while the communication channel model is set up with additive whiteGaussian noise and multiplicative interference of the atmospheric turbulence. the averagetransmit power, bandwidth utilization, error rate expressions of the various modulationformats are derivation and simulated. It’s indicating that the pulse position modulation(PPM) signal has optimal anti-interference performance with high power efficiency in theatmosphere compared to other modulation formats, but the PPM’s bandwidth is relativelylager. Especially the modulation order is larger, the better the performance of PPM’santi-interference, the corresponding bandwidth is also greater. In the actual communicationapplication system, using the appropriate modulation order combination of transmissionrate can guarantee the performance of PPM modulation signal.Based on theoretical analysis, this paper designed and implemented voice-sourceatmosphere communication system that used binary off keying (OOK) and4-PPM modulation and demodulation. It used field programmable logic array(FPGA) as the coremodulation encoding system and completed the voice signal modulation and demodulationcommunication system experimental hardware platform. At the same time the logic of theFPGA implementation of voice signal4-PPM’s modulation and demodulation, sending andreceiving were detailed designed, and each module’s timing simulation was completed.Experiment used the designed hardware platform and formulated a reasonable program,completed the voice of the optical signal modulation and demodulation of the4-PPMcommunication debugging and measurements to the paper’s communication system designrequirements. Compared the measured waveform of OOK and PPM signal whichtransferred in the atmosphere channel, PPM signal’s anti-interference performance arebetter than OOK. Thus the results of experiments verify the theoretical analysis of the paper,which achieved paper communication system design requirements.更多还原