Visible light communications: multi-band super-Nyquist CAP modulation

Abstract

In this paper, we experimentally demonstrate the performance of a non-orthogonal multi-band super-Nyquist carrier-less amplitude and phase (m-SCAP) modulation for visible light communications (VLC). We break the orthogonality between sub-bands in the frequency domain by compressing the spectrum, purposely overlapping them, and introducing inter-band interference (IBI). We demonstrate that our proposed system can tolerate IBI, and hence spectral efficiency can be increased without introducing additional complexity to the receiver. We show that m-SCAP can tolerate up to 30% and 20% compression for 4-and 16-level quadrature amplitude modulation, respectively, thus leading to an improvement in spectral efficiencies up to 40% and 25%, respectively, at the cost of bit error rate performance, which however remains below the 7% forward error correction limit. Moreover, the experimental results are supported by numerical simulations. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Experimental multi-user VLC system using non-orthogonal multi-band CAP modulation

“…Here, we consider three optimization schemes: (i) uniform optimization of β, i.e., 0 ≤ β ≤ 1, where higher values of β result in δ-times wider bandwidth; (ii) optimization of α, i.e., 0 ≤ α ≤ 0.3, using m-ESCAP, where the spacing between carriers is uniform and the total system bandwidth is limited to 100 MHz. Note, reducing the carrier spacing leads to inter-carriers interference (ICI), thus resulting in higher BER [12]; (iii) full-optimization, which is a combination of (i) and (ii). The BER target is set to the 7% forward error correction (FEC) limit of 3.8×10 −3 .…”

“…Note, m-ESCAP and conventional m-CAP have the same B tot (i.e., 100 MHz), and with no changes in the subcarrier spacing (i.e., f c remain the same). Note the followings: (i) to improve the data rate while maintaining the same B tot , the individual sub-bands can be expanded by increasing R s of the individual subcarriers; and (ii) compressing the sub-bands beyond their orthogonality limit will result in electrical power penalty due to sub-band overlapping and improved spectral efficiency with no additional computational complexity at the receiver but at the cost of higher BER [12]. Finally, Figs.…”

“…An experimental m-CAP VLC link over a 1 m distance with a high spectral efficiency of 4.85 b/s/Hz for a single user scheme was demonstrated in [11]. Further modification of subcarrier spacing below orthogonality can improve the spectral efficiency about 25% for a direct LOS link without considering a multi-user scenario, which was demonstrated in [12]. In [13], an additional 20% improvement in the data rate was achieved by increasing the baud rates of individual non-orthogonal sub-bands while utilising the same signal bandwidth.…”

Hybrid Super-Nyquist CAP Modulation based VLC with Low Bandwidth Polymer LEDs

“…3. Note the ∼6 dB power penalty, which is dependent on both n and β as reported in [12]. The entire physical setup is controlled and automated using LabVIEW to ensure equivalent test conditions for all signals under test.…”

“…Note, the introduction of interference enables transmission of more symbols-per-second in the same time period compared to conventional orthogonal systems. In [12], a non-orthogonal variation on m-CAP was proposed called super-Nyquist m-CAP (m-SCAP), where SBs are purposely overlapped reducing the total signal bandwidth and causing inter-band interference (IBI). Hence, higher symbol rates can be supported at the cost of BER.…”