Enhanced unipolar orthogonal frequency division multiplexing (eU-OFDM) and layered asymmetrically clipped optical OFDM (LACO-OFDM) are spectrally efficient modulation techniques for intensity modulated systems which layer multiple non-negative signals. In this paper, we propose absolute value layered asymmetrically clipped optical OFDM (ALACO-OFDM), which further improves the spectral efficiency while using a smaller number of layers and no explicit direct current (DC) bias. In ALACO-OFDM, asymmetrically clipped optical OFDM (ACO-OFDM) signals are sent at the first $L$ layers and absolute value optical OFDM (AVO-OFDM) is used for the remaining subcarriers and transmitted simultaneously. Analysis indicates that ALACO- achieves higher spectral efficiency than eU- or LACO-OFDM while using a smaller number of layers. Bounds on achievable information rates of ALACO-OFDM and related layered ACO-OFDM techniques are also developed. Two optical power allocation schemes over the layers of ALACO-OFDM are developed with the objective of optimizing uncoded transmission performance and the achievable information rate respectively. Additionally, a theoretical bound on the uncoded BER of ALACO-OFDM is derived. Monte Carlo simulation results indicate ALACO-OFDM with the optimum power allocation achieves significant uncoded BER performance gains compared to its counterparts at the same spectral efficiency while having a smaller peak-to-average power ratio.

中文翻译：

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用于强度调制光无线信道的绝对值分层 ACO-OFDM

增强型单极正交频分复用 (eU-OFDM) 和分层非对称限幅光 OFDM (LACO-OFDM) 是用于强度调制系统的频谱高效调制技术，可将多个非负信号分层。在本文中，我们提出了绝对值分层非对称限幅光 OFDM (ALACO-OFDM)，它进一步提高了频谱效率，同时使用更少的层数和没有明确的直流 (DC) 偏置。在 ALACO-OFDM 中，非对称限幅光 OFDM (ACO-OFDM) 信号在前 $L$ 层发送，绝对值光 OFDM (AVO-OFDM) 用于其余子载波并同时传输。分析表明，ALACO- 比 eU- 或 LACO-OFDM 实现了更高的频谱效率，同时使用的层数更少。还开发了 ALACO-OFDM 和相关分层 ACO-OFDM 技术可达到的信息速率的界限。为了分别优化未编码传输性能和可实现的信息速率，在 ALACO-OFDM 层上开发了两种光功率分配方案。此外，还推导出了 ALACO-OFDM 未编码 BER 的理论界限。Monte Carlo 仿真结果表明，在相同频谱效率下，具有最佳功率分配的 ALACO-OFDM 与其对应物相比实现了显着的未编码 BER 性能增益，同时具有较小的峰均功率比。为了分别优化未编码传输性能和可实现的信息速率，在 ALACO-OFDM 层上开发了两种光功率分配方案。此外，还推导出了 ALACO-OFDM 未编码 BER 的理论界限。Monte Carlo 仿真结果表明，在相同频谱效率下，具有最佳功率分配的 ALACO-OFDM 与其对应物相比实现了显着的未编码 BER 性能增益，同时具有较小的峰均功率比。为了分别优化未编码传输性能和可实现的信息速率，在 ALACO-OFDM 层上开发了两种光功率分配方案。此外，还推导出了 ALACO-OFDM 未编码 BER 的理论界限。Monte Carlo 仿真结果表明，在相同频谱效率下，具有最佳功率分配的 ALACO-OFDM 与其对应物相比实现了显着的未编码 BER 性能增益，同时具有较小的峰均功率比。