Abstract
This paper proposes a novel linear precoder design based on the singular value decomposition (SVD) for multi-input multi-output visible light communications (MIMO VLC). We provide an analytical expression on power allocation subject to the function of maximizing the lower bound of capacity according to the optical wireless communication channel model. The expression is rather different from the radio frequency (RF) communications due to the non-negativity of the transmitted signals in VLC. Furthermore, we design an adaptive bit loading scheme for sub-streams with consideration of the tremendous gain difference among subchannels. Performances of the proposed adaptive power and bits allocation strategy are evaluated in two traditional MIMO VLC scenarios, i.e., a practical $2\times 2$ indoor scenario and a classical $4\times 4$ system that is generated according to the MIMO model. In simulations, the techniques of unipolar M -level pulse amplitude modulation ( M -PAM) and spatial-multiplexing (SMP) are employed, and the performance comparison with other SVD-based linear precoders is also given. Simulation results show that the proposed approach can effectively improve the spectral efficiency and guarantee the bit error rate (BER) performance under the same constraints of aggregate optical power budget and non-negativity included by the intensity modulation. It indicates that the strategy of uneven bits and power allocation with full consideration of the ill-conditioned characteristics of subchannels performs better than that based on equal bits transmission in VLC systems.
Highlights
Due to its low cost, high power efficiency, low electromagnetic interference [1] and use of license-free spectrum [2], visible light communication (VLC) has become a potential candidate for wideband communications
Simulation results demonstrate that the proposed scheme can effectively improve the performance in terms of bit error rate (BER) compared with some recently proposed SVDbased precoder designs
It has been found that several lightemitting diode (LED) arrays would result in channel matrices with unacceptably high condition numbers even in massive 16 × 16 multi-input multi-output (MIMO) VLC systems
Summary
Due to its low cost, high power efficiency, low electromagnetic interference [1] and use of license-free spectrum [2], visible light communication (VLC) has become a potential candidate for wideband communications. A direct current (DC) bias is added to the modulated signal to ensure non-negativity signaling [10] Other constraints such as illumination control [11] and power variation [12] may be considered. Gong et al designed a bit and power allocation method for SVD-based precoding in color-division VLC systems [2], in which different transmitted colors are incorporated. An alternative SVD-based precoder that optimizes the capacity of the electrical channel without considering the non-negativity constraint [17]. We design an SVD-based low-complexity scheme for point-to-point MIMO VLC and provide an analytical expression for power and bits allocation subject to the function of maximizing the lower bound of capacity. Simulation results demonstrate that the proposed scheme can effectively improve the performance in terms of BER compared with some recently proposed SVDbased precoder designs
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