We consider performance enhancement of asymmetrically-clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and related optical OFDM schemes, which are variations of OFDM in intensity-modulated optical wireless communications. Unlike most existing studies on specific designs of improved receivers, this paper investigates information theoretic limits of all possible receivers. For independent and identically distributed complex Gaussian inputs, we obtain an exact characterization of information rate of ACO-OFDM with improved receivers for all SNRs. It is proved that the high-SNR gain of improved receivers asymptotically achieve 1/4 bits per channel use, which is equivalent to 3 dB in electrical SNR or 1.5 dB in optical SNR; as the SNR decreases, the maximum achievable SNR gain of improved receivers decreases monotonically to a non-zero low-SNR limit, corresponding to an information rate gain of 36.3%. For practically used constellations, we derive an upper bound on the gain of improved receivers. Numerical results demonstrate that the upper bound can be approached to within 1 dB in optical SNR by combining existing improved receivers and coded modulation. We also show that our information theoretic analyses can be extended to Flip-OFDM and PAM-DMT. Our results imply that, for the considered schemes, improved receivers may reduce the gap to channel capacity significantly at low-to-moderate SNR.
翻译:我们考虑的是,非对称的光学或地心频率分光分多氧化(ACO-OFDM)及相关的光学ODM机制的性能增强,这些机制在强度调制光学无线通信中是ODM的变异。与大多数关于改进接收器具体设计的现有研究不同,本文件调查所有可能的接收器的信息理论限度。对于独立和同样分布的复杂高斯输入,我们获得了对ACO-ODM信息率的精确定性,并改进了所有空间核子网络接收器接收器接收器接收器的接收器。事实证明,改进的接收器接收器接收器的高度增益在每频道使用中达到四分之一比特,相当于电频调频调频频通信中的3 dB位或光频光学光频光频通信中的1.5 dB位。随着SNR的减少,改进接收器接收器的最大可实现SNRR的增量增量,我们目前改进的SMRM的升级后,我们也可以在1 dRMRM的升级后,我们现在的SMMMM的升级的接收器分析中,我们的升级的SMMMMM的升级的升级的升级的升级的升级的升级的升级和升级后,可以显示。