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 (IID) 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.

中文翻译：

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改进的光无线 OFDM 接收器：信息论视角

我们考虑了非对称削波光正交频分复用 (ACO-OFDM) 和相关光 OFDM 方案的性能增强，它们是强度调制光无线通信中 OFDM 的变体。与大多数关于改进接收器的特定设计的现有研究不同，本文研究了所有可能接收器的信息论极限。对于独立同分布 (IID) 复高斯输入，我们获得了 ACO-OFDM 信息速率的精确表征，并针对所有 SNR 改进了接收器。经证明，改进型接收机的高信噪比增益渐进达到每信道使用1/4比特，相当于电信噪比3dB或光信噪比1.5dB；随着 SNR 的降低，改进的接收器的最大可实现 SNR 增益单调下降到非零低 SNR 限制，对应于 36.3% 的信息速率增益。对于实际使用的星座，我们推导出改进接收器增益的上限。数值结果表明，通过结合现有的改进接收器和编码调制，光 SNR 的上限可以接近 1 dB 以内。我们还表明，我们的信息论分析可以扩展到 Flip-OFDM 和 PAM-DMT。我们的结果表明，对于所考虑的方案，改进的接收器可以在低到中等 SNR 下显着减少与信道容量的差距。数值结果表明，通过结合现有的改进接收器和编码调制，光 SNR 的上限可以接近 1 dB 以内。我们还表明，我们的信息论分析可以扩展到 Flip-OFDM 和 PAM-DMT。我们的结果表明，对于所考虑的方案，改进的接收器可以在低到中等 SNR 下显着减少与信道容量的差距。数值结果表明，通过结合现有的改进接收器和编码调制，光 SNR 的上限可以接近 1 dB 以内。我们还表明，我们的信息论分析可以扩展到 Flip-OFDM 和 PAM-DMT。我们的结果表明，对于所考虑的方案，改进的接收器可以在低到中等 SNR 下显着减少与信道容量的差距。