可见光通信中的Hadamard编码调制
Hadamard Coded Modulation for Visible Light Communications
摘要：
使用室内照明系统也提供下行链路通信的可见光通信（VLC）系统需要高平均光功率以便满足照明需要。这可能导致高阶调制方案中常见的高幅度信号被发光二极管（LED）的峰值功率约束限幅，并导致高信号失真。在本文中，我们介绍了阿达玛编码调制（HCM），以实现低错误概率在基于LED的VLC系统需要高的平均光功率。该技术使用快速Walsh-Hadamard变换（FWHT）来调制数据，作为正交频分复用（OFDM）的替代调制技术。HCM由于其较小的峰均功率比（PAPR），在高照度水平下实现了更好的性能。HCM的功率效率可以通过在不丢失任何信息的情况下减少发射信号的DC部分来提高。由此产生的所谓的DC降低的HCM（DCR-HCM）非常适合于需要调光照明的环境，因为与HCM相比，它传输具有较低峰值幅度的信号，从而受到较少的非线性失真。交织可以应用于HCM，以使所得到的信号更能抵抗色散VLC链路中的符号间干扰（ISI）。
英文摘要：
Visible light communication (VLC) systems using the indoor lighting system to also provide downlink communications require high average optical powers in order to satisfy the illumination needs. This can cause high amplitude signals common in higher-order modulation schemes to be clipped by the peak power constraint of the light emitting diode (LED) and lead to high signal distortion. In this paper we introduce Hadamard coded modulation (HCM) to achieve low error probabilities in LED-based VLC systems needing high average optical powers. This technique uses a fast Walsh-Hadamard transform (FWHT) to modulate the data as an alternative modulation technique to orthogonal frequency division multiplexing (OFDM). HCM achieves a better performance for high illumination levels because of its small peak to average power ratio (PAPR). The power efficiency of HCM can be improved by reducing the DC part of the transmitted signals without losing any information. The resulting so-called DC-reduced HCM (DCR-HCM) is well suited to environments requiring dimmer lighting as it transmits signals with lower peak amplitudes compared to HCM, which are thus subject to less nonlinear distortion. Interleaving can be applied to HCM to make the resulting signals more resistant against inter-symbol interference (ISI) in dispersive VLC links.
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