Turbo Coding In Wireless Optical Communications Ppm Modulation Performance Analysis

Wireless optical communication, which is also called free space optical communication, has many advantages, such as, better confidentiality, stronger anti-interference ability, higher transmitting rate, more flexible and convenient and so on.As a new communication technology, it not only can be widely applied in deep space communication,interplanetary communication as well as emergency communication,but also can meet both the bandwidth and portable need of communication services. Therefore, In recent years,wireless optical communication has draw an intensive attention by a wide range of experts in the communication field.In fact, as an important part of wireless optical communication, laser communication system, which is based on using laser as signal carrier,transmit information by modulating the laser pulses, achieving its goal of information exchange.In this process, the modulation of information plays a key role on the performance in the laser communication system.Under the circumstance, PPM (Pulse Position Modulation) is widely used in the wireless optical communication systems because of its higher power efficiency, higher transmitting efficiency and stronger anti-interference ability,etc.In1993, a new class of error-correcting code named Turbo codes was proposed by Prof. Berrou in France,whose performances are close to the Shannon limit when the data block length is long enough. So Turbo code represents the world’s most advanced code. Its birth is regarded as the milestone in channel encoding theory history,which makes us convert from increasing the minimum Hamming distance to decreaseing the numbers of light-weight codes.In this paper,it mainly conducts the theory research of performance analysis of Turbo encoding in the wireless optical PPM modulation system.The main content of the dissertation includes:1. Systematically overview the development history and classification of wireless optical communication,then analyze its technical advantages and disadvantages, introduce the research profile at home and abroad. 2. Illuminate the turbulence effect in atmospheric channel, study the impact towards optical communication system,encoding characteristics and bit error rate (BER) in the atmospheric turbulence channel. Propose using pulse position modulation (PPM) in wireless optical communication system.3. Specifically discuss the basic principles, a variety of categories and their respective characteristics and working principle of the PPM modulation. Analyze the influence of FER in PPM communication system in atmospheric weak turbulence channel.4. Describe the basic theory of channel encoding and the research status of Turbo codes,then mainly focus on the analysis of Turbo code encoding theory, equalization, Turbo Code Interleaving and puncturing techniques.5. According to the performance analysis of Turbo encoding, based on computer simulation in AWGN channel,Rayleigh Fading Channel, research the performance of Turbo code in depth.Finally,using MATLAB software to simulate program,analyze the simulation results,optimize code performance and draw a satisfactory conclusion.That is,Bit Error Rates (BER) drop from10-1(uncoded normal channel) to as low as10-5(Turbo coded channel).