Abstract
In the VLC context, pulse position modulation (PPM) and similar modulations are typically used when the overall complexity of the transmitter is required to be low or the system needs to support dimming, i.e., dynamically control the illumination level of the transmitter. However, despite the power efficiency of PPM, it is known to be bandwidth inefficient. Having known the trade-off between reliability and spectral efficiency, in this paper we propose a PPM-based space-time block coding (STBC) technique named as quasi-trace-orthogonal (QTO), derived from trace-orthogonal, to increase the spectral efficiency of PPM VLC’s by limiting the reliability loss. We provide Monte-Carlo simulations for a $4\times 4$ MIMO-VLC system and validate the results experimentally, and show that for a given signal-to-noise-ratio, the QTO-STBC based 4-PPM VLC system offers higher spectral efficiency at a cost of higher symbol error rate compared to trace-orthogonal STBC.
Highlights
Visible light communications (VLC) is a promising complementary access technology to radio frequency (RF) systems, offering high data rates over a transmission span of a few meters, with low energy consumption and deployment cost as detailed in [1], [2]
We show that QTO-space-time block coding (STBC) are able to outperform SMP in terms of bit error rates (BER) and OSTBC in terms of the spectral efficiency perspective
THEORETICAL RESULTS By comparing the results offered by the above mentioned schemes that are, OSTBC, SMP, TO-STBC and the proposed QTO-STBC we can consider the behaviour of the Maximum likelihood (ML) detection for an assigned channel, meaning that the error probability is conditioned to the channel realization
Summary
Visible light communications (VLC) is a promising complementary access technology to radio frequency (RF) systems, offering high data rates over a transmission span of a few meters, with low energy consumption and deployment cost as detailed in [1], [2]. 1) proposing a QTO-STBC technique based on the distance among codewords for optical wireless communications, which offers a trade-off between the spectral efficiency and the symbol error rates; 2) considering dimming in the proposed scheme and discussing other opportunities with concurrent systems; 3) providing analytical and simulation results for the proposed method and its competitors; 4) comparing the performance of the proposed method with the TO-STBC counterpart, in terms of symbol error rate and spectral efficiency. We can anticipate here that the proposed scheme lose a bit in terms of reliability with respect to TO-STBC and OSTBC, even though the gain offered in terms of spectral efficiency, that is, transmission speed, largely counterbalance the limited error rate loss.
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