自由空间光标识双幅度脉冲位置调制方法

Flag dual amplitude pulse position modulation for free space optical communications

自由空间光通信中,为了兼备自带符号同步和调制符号长度固定等优点,提出了一种新的光标识双幅度脉冲位置调制方法(FDAPPM),分析了它的符号结构,传输速率和湍流信道中的差错性能。采用最大似然检测时,推导出高信噪比时FDAPPM误码率的简单近似值表达式,并给出系统的分集级数和调制增益。最后与OOK、PPM、FDPIM和FDAPIM等方法进行比较。结果表明:在相同的湍流条件下,FDAPPM的传输速率和差错性能均优于FDPIM和FDAPIM;相对于PPM系统,其传输速率高,不需要符号同步,接收器复杂度大为简化;且符号长度固定,不会引起调制器等待或缓冲器溢出。

In free space optical communications, in order to get the self-symbol synchronization and fixed symbol length, a novel flag dual amplitude pulse position modulation（FDAPPM） was proposed. The symbol structure, transmission rate and error probability of the FDAPPM system over atmospheric turbulence-induced fading channel were presented. By using the maximum-likelihood sequence detection, the high SNRs asymptotic on the error probability of the FDAPPM was analyzed and the diversity order and SNR modulation gains were calculated. The performance of the FDAPPM was compared with the conventional OOK, PPM, FDPIM, FDAPIM and FDAPPM. Numerical results indicate that under the same turbulence condition, the FDAPPM possesses the advantages over the FDPIM and FDAPIM in terms of transmission rate and error performance. It also provides high transmission rate than the PPM and simplifies the receiver design owing to the built-in symbol synchronization. Moreover, it does not have insertion/deletion error in modem due to the fixed symbol length.