Performance Comparison of MIMO Techniques for Optical Wireless Communications in Indoor Environments
Performance Comparison of MIMO Techniques for Optical Wireless Communications in Indoor Environments
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DOI：
10.1109/tcomm.2012.120512.110578
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发表时间：
2013-02-01
影响因子：
8.3
通讯作者：
Haas, Harald
中科院分区：
文献类型：
--
作者：
Fath, Thilo;Haas, Harald
在本文中，我们比较多输入多输出（MIMO）技术应用于室内光无线通信（OWC）假设视线（LOS）信道条件下的性能。具体地，考虑具有不同发射器间距和接收器阵列的不同位置的几个4x4设置。考虑以下MIMO算法：重复编码（RC）、空间复用（SMP）和空间调制（SM）。特别是，我们开发了一个框架来解析近似这些方案的误码率（BER），并通过仿真验证了理论界。结果表明，由于分集增益，RC对各种收发机对准具有鲁棒性。然而，由于RC不提供空间复用增益，因此它需要大的信号星座尺寸以实现高频谱效率。相比之下，SMP通过利用复用增益来实现高数据速率。为了提供这些增益，SMP需要足够低的信道相关性。SM是一种组合的MIMO和数字调制技术。我们表明，SM是更强大的高信道相关性相比，SMP，同时使更大的频谱效率相比，RC。此外，我们研究了多个发射机之间的感应功率不平衡的影响。结果发现，功率不平衡可以大大提高SMP和SM的性能，因为它降低了信道相关性。在这种情况下，我们还表明，阻止一些链接是一种可以接受的方法，以减少信道相关性。即使阻塞减少了接收到的能量，但是通过为SMP和SM提供改善的信道条件，它超过了这种降级。例如，阻塞4x4设置的16个链路中的4个链路将SMP的BER性能提高超过20 dB，而有效信噪比（SNR）由于阻塞而降低约2 dB。因此，MIMO技术即使在仅提供很小信道差异的LOS条件下也可以提供增益。
In this paper, we compare the performance of multiple-input-multiple-output (MIMO) techniques applied to indoor optical wireless communications (OWC) assuming line-of-sight (LOS) channel conditions. Specifically, several 4 x 4 setups with different transmitter spacings and different positions of the receiver array are considered. The following MIMO algorithms are considered: Repetition Coding (RC), Spatial Multiplexing (SMP) and Spatial Modulation (SM). Particularly, we develop a framework to analytically approximate the bit error ratios (BERs) of these schemes and verify the theoretical bounds by simulations. The results show that due to diversity gains, RC is robust to various transmitter-receiver alignments. However, as RC does not provide spatial multiplexing gains, it requires large signal constellation sizes to enable high spectral efficiencies. In contrast, SMP enables high data rates by exploiting multiplexing gains. In order to provide these gains, SMP needs sufficiently low channel correlation. SM is a combined MIMO and digital modulation technique. We show that SM is more robust to high channel correlation compared to SMP, while enabling larger spectral efficiency compared to RC. Moreover, we investigate the effect of induced power imbalance between the multiple transmitters. It is found that power imbalance can substantially improve the performance of both SMP and SM as it reduces channel correlation. In this context, we also show that blocking some of the links is an acceptable method to reduce channel correlation. Even though the blocking diminishes the received energy, it outweighs this degradation by providing improved channel conditions for SMP and SM. For example, blocking 4 of the 16 links of the 4 x 4 setup improves the BER performance of SMP by more than 20 dB, while the effective signal to noise ratio (SNR) is reduced by about 2 dB due to the blocking. Therefore, MIMO techniques can provide gains even under LOS conditions which provide only little channel differences.