Piecewise Companding Transform Assisted Optical-OFDM Systems for Indoor Visible Light Communications
Piecewise Companding Transform Assisted Optical-OFDM Systems for Indoor Visible Light Communications
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DOI：
10.1109/access.2016.2640203
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发表时间：
2017-02
期刊：
影响因子：
3.9
通讯作者：
Hongming Zhang;Lie-liang Yang;L. Hanzo
中科院分区：
文献类型：
--
作者：
Hongming Zhang;Lie-liang Yang;L. Hanzo
在依赖于强度调制和直接检测（IM/DD）的可见光通信（VLCs）中，电信号到光信号的转换和发光二极管（led）有限的动态范围构成了高完整性通信方式的根本障碍，特别是在采用正交频分复用（OFDM）时。在IM/DD VLCs中，只使用实值正信号进行信号传输。然而，OFDM系统的傅里叶变换是在复域内进行的。为了满足IM/DD VLCs的要求，以降低带宽效率为代价实现了复杂到真实的转换。此外，OFDM信号具有较高的峰均功率比；因此，通常用于将正值信号限制在LED的动态范围内的裁剪。然而，硬裁剪导致光OFDM （O-OFDM）信号的正交性丧失，产生载波间干扰。因此，基于裁剪的O-OFDM系统的性能可能会严重下降。本文将分段扩展变换（CT）的概念引入到O-OFDM系统中，形成了CTO-OFDM的结构。我们首先研究了分段式CTO-OFDM的一般原理和设计准则。在此基础上，设计了三种类型的分段比较器，即常概率子分布函数、线性PsDF （LPsDF）和非LPsDF的CT。此外，我们通过分析和仿真技术研究了硬裁剪和CT在不同场景下对O-OFDM系统的非线性影响。我们的研究表明，CTO-OFDM构成了一种很有前途的VLCs信令方案，它具有高带宽效率、高灵活性、高可靠性以及高数据速率，尽管会经历非线性失真。
In visible light communications (VLCs) relying on intensity-modulation and direct detection (IM/DD), the conversion from electrical signals to optical signals and the limited dynamic range of the light-emitting diodes (LEDs) constitute the fundamental impediments in the way of high-integrity communications, especially when orthogonal frequency-division multiplexing (OFDM) is employed. In IM/DD VLCs, only real-valued positive signals are used for signal transmission. However, the Fourier transform of OFDM systems is operated in the complex domain. In order to meet the requirements of the IM/DD VLCs, the complex-to-real conversion is achieved at the cost of reducing the bandwidth efficiency. Moreover, OFDM signals experience a high peak-to-average power ratio; hence, typically clipping is used for confining the positive-valued signals within the LED’s dynamic range. However, hard clipping leads to the loss of orthogonality for optical OFDM (O-OFDM) signals, generating inter-carrier interference. As a result, the performance of the clipping-based O-OFDM systems may be severely degraded. In this paper, the concept of piecewise companding transform (CT) is introduced into the O-OFDM system advocated, forming the CTO-OFDM arrangement. We first investigate the general principles and design criteria of the piecewise CTO-OFDM. Based on our studies, three types of piecewise companders, namely, the constant probability sub-distribution function, linear PsDF (LPsDF), and the non-LPsDF-based CT, are designed. Furthermore, we investigate the nonlinear effect of hard clipping and of our CT on O-OFDM systems in the context of different scenarios by both analytical and simulation techniques. Our investigations show that the CTO-OFDM constitutes a promising signaling scheme conceived for VLCs, which exhibits a high bandwidth efficiency, high flexibility, high reliability, as well as a high data-rate, despite experiencing nonlinear distortions.