Non-Orthogonal Multi-band CAP for Highly Spectrally Efficient VLC Systems

Abstract

In this work we propose and experimentally demonstrate a novel non-orthogonal multi-band carrier-less amplitude and phase (NM-CAP) scheme for bandlimited visible light communication systems in order to increase the spectral efficiency. We show that a bandwidth saving up to 30% can be achieved thus resulting in 44% improvement in the measured spectral efficiency with no further bit error rate performance degradation compared to the traditional m-CAP scheme. We also show that higher order systems can provide higher bandwidth compression than low order systems. Furthermore, with no additional functional blocks at the transmitter or the receiver the proposed scheme introduces no extra computational complexity. Keywords-multi-band carrier-less amplitude and phase modulation; non-orthogonal; visible light communications

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

“…In this paper, we extend the studies on super-Nyquist CAP for 4-and 16-QAM VLC links by investigating the bit-error rate (BER) performance for m = 2 to 10 and a varying the sub-band compression factor α up to 50%. There are several key differences from our previous work reported in [23], in particular, the results shown are based on the total achievable BER performance of the system, while [23] focuses on the individual sub-band performance. We show that by reducing the spacing between individual sub-bands spectral efficiency gains of up to 40% can be achieved.…”

“…Hence, we note that there is a trade-off between the level of IBI and the baud rate relating to the excess bandwidth factor as R s = B C AP /(1 + β). As outlined, the main motivation behind compressing the sub-bands is to increase η se , which is given by [23]:…”

“…In these systems, knowledge of the interference characteristics allows amelioration of interference effects at the receiver and in SEFDM this has resulted in the demonstration of systems that can increase throughput by up to 60% with a tolerable loss of performance [19][20][21][22]. Such an approach has already been applied to m-CAP as reported in the literature [10,23] and was termed non-orthogonal m-CAP (NM-CAP) in [23] and super-Nyquist CAP in [10]. In [23] it was reported that the performance gains can be achieved by overlapping subcarriers for 4-level quadrature amplitude modulation (4-QAM) and 10 sub-bands, thus resulting in a 44% increase in spectral efficiency.…”

“…Such an approach has already been applied to m-CAP as reported in the literature [10,23] and was termed non-orthogonal m-CAP (NM-CAP) in [23] and super-Nyquist CAP in [10]. In [23] it was reported that the performance gains can be achieved by overlapping subcarriers for 4-level quadrature amplitude modulation (4-QAM) and 10 sub-bands, thus resulting in a 44% increase in spectral efficiency. For all intents and purposes, super-Nyquist is intended to mean the baud rate is far in excess of the bandwidth occupied in this paper, as in [24].…”

Non-Orthogonal Variable Multi-Band Carrier-Less Amplitude and Phase Modulation with Reduced Subcarriers

“…Secondly, we allocate higher transmission bandwidth by about 1.2 to the 1 st subcarrier, which is in the pass-band region, compared to the others. Thirdly, we have introduced an overlap between subcarriers in line with the work reported in [16] in order to increase the transmission data rate at the cost of increased ISI. Note that, by overlapping of subcarrier, the orthogonality is no longer valid in m-CAP.…”