Evaluation of Multi-band Carrier-less Amplitude and Phase Modulation Performance for VLC under Various Pulse Shaping Filter Parameters

Abstract

In multi-band carrier-less amplitude and phase modulation (m-CAP), the transmitter and receiver pulse shaping filters have a significant impact on the signal performance. Since m-CAP is an emerging and promising modulation format for visible light communications (VLC), it is necessary to balance the system performance and the filter length, due to limited integration density in field programmable gate arrays (FPGAs). In this paper we investigate the m-CAP VLC system performance for different number of sub-bands m = {2, 5, 10} under varying finite impulse response (FIR) filter parameters, such as the filter length Lf and the roll-off factor β. We show that increasing both β and Lf improves the bit error rate (BER) performance of the system substantially. We demonstrate that a BER target of 10-4 is achieved using Lf ≤ 12 symbols for m = 5 and 10 for low order subcarriers. Moreover, the BER limit is attained for β = 0.2 by all subcarriers, except the last two for m = 5 and 10, which is a significant improvement, even considering the slightly increased excess bandwidth in comparison to the literature.

Analysis of Nyquist Pulse Shapes for Carrierless Amplitude and Phase Modulation in Visible Light Communications

“…Both p(t) and p (t) have a finite filter length L s . As has been shown in the literature [13,16], the effect of L s can have a significant impact on the bit-error rate (BER) performance. As a result, we select several different values of L s as described later in the section.…”

“…The Xia pulse is asymmetrical, where more energy exists before the peak than after it, whilst still satisfying the Nyquist first criterion for zero ISI [10]. This introduces an interesting characteristic because the FIR filters adopted in a digital implementation of CAP are computationally demanding as the number of operations increases linearly with the filter length and this has an impact on the link BER performance [12,13]. Thus, if asymmetrical clipping of the filter could be achieved without a significant impact on the BER performance, this would be advantageous.…”

Variable m-CAP for bandlimited Visible Light Communications

“…1. The principle of the system will be described briefly, for a detailed description of the m-CAP functionality, see previous reports in the literature [9,13]. Independent data streams D are generated for each subcarrier and consequently mapped into M-quadrature amplitude modulation (QAM) symbols, where M is the order of QAM.…”

“…Besides OFDM, the m-CAP modulation technique has recently been the focus of extensive investigation [9][10][11][12][13][14]. The multiband form of CAP, which splits the total signal bandwidth into m equally spaced subcarriers, was developed for optical fibre communication systems, showing enhanced performance over a traditional 1-CAP in terms of bandwidth efficiency, dispersion, reduced sampling rate and slightly increased data rate [10].…”

“…For instance, numerical simulations of m-CAP in a highly bandlimited VLC link were reported in [12] showing 40% improvement in data rate over traditional 1-CAP technique when 10-CAP is employed. The work presented in [13] focused on the analysis of pulse shaping filters, which are important for both overall system performance and complexity that is crucial for the development of VLC systems in real environments. Note that 2m filters must be used in both the transmitter and the receiver side, giving an overall 4m filter requirement per deployment.…”