Comparison of Efficiency of <italic>N</italic>-Dimensional CAP Modulations

Abstract

There is a growing interest in applying carrierless amplitude-phase (CAP) modulation in intensity modulated optical links. CAP as a multilevel modulation scheme can reach high spectral efficiency and be generated at low cost. An interesting feature of CAP is that its signal basis can be extended to three or more dimensions (D). This paper aims to complete the knowledge on 3-D CAP. Discussed are design of transceiver filters, spectral efficiency, and digital equalization in 3-D. Several problems accompanying 3-D CAP transmission are identified. The most significant are the peak to average power ratio, which is higher than in one or two dimensions and noise correlation at the output of a 3-D equalizer. It is found that the latter problem severely degrades bit error rates achieved but can be efficiently mitigated using noise whitening equalization. Finally, 1-D, 2-D, and 3-D CAP are compared experimentally in a step-index polymer optical fiber link.

Experimental Comparison of PAM, CAP, and DMT Modulations in Phosphorescent White LED Transmission Link

“…After transmission the signal was resampled, filtered with transceiver filters and downsampled to the symbol rate. The DFE, its convergence algorithm and training sequence length was the same as in PAM case, with the only difference that now it is a complex equalizer (with 2 Â 4 filters) [17].…”

A Carrierless Amplitude Phase (CAP) Modulation Format: Perspective and Prospect in Optical Transmission System

“…The unavoidable increase of signal bandwidth accompanying the increase of dimension number compensates the higher number of symbols in the alphabet and leads to the same SE of CAP modulations irrespective of the dimensionality [7]. However, the advantage of additional dimensions lies in the possibility to flexibly allocate different services to different users [6].…”

Multiband carrierless amplitude and phase index modulation

“…Typically, the main approach adopted is to exploit extra degrees of freedom such as spatial multiplexing (SM), polarization‐division multiplexing (PDM), and multilevel modulation. Some examples of different schemes that have been proposed are nonorthogonal multiple access (NOMA), 3–5 spatial division multiplexing (SDM), 6–9 and multidimensional schemes such as 3‐D/4‐D carrierless amplitude phase (CAP) modulation 10,11 . Recently, there has been a growing interest in index modulation (IM) techniques.…”