Spectrum-efficient hybrid PAM-DMT for intensity-modulated optical wireless communication

Abstract

In optical wireless communication (OWC), the superimposed optical orthogonal frequency division multiplexing (O-OFDM), such as layered asymmetrically clipped O-OFDM (LACO-OFDM), can improve spectrum efficiency by appropriately combining multiple O-OFDM signals for simultaneous transmission. However, it suffers from increased receiver complexity and latency. Therefore, a novel architecture of hybrid pulse-amplitude-modulated discrete multitone modulation (HPAM-DMT) is proposed in this paper to support a spectrum-efficiency OWC link. In HPAM-DMT, a PAM-DMT signal is carefully designed by using the real parts of subcarriers and is then superimposed on the classic PAM-DMT signal for simultaneous transmission, which fully exploits the spectrum in terms of subcarriers. Moreover, thanks to the well-designed aritecture of the two superimposed PAM-DMT signals, the proposed HPAM-DMT achieves the same spectrum efficiency as the LACO-OFDM, with much lower complexity and latency. Notable improvement of the bit-error rate (BER) performance is observed for the proposed HPAM-DMT compared to LACO-OFDM under the corruption of the transmitter nonlinearity. Moreover, HPAM-DMT achieves a relatively higher power efficiency than conventional O-OFDM schemes, which makes it a competitive O-OFDM scheme for IM/DD-based OWC.

Joint Dimming Control and Optimal Power Allocation for THO-OFDM Visible Light Communications

“…DCO-OFDM offer low energy efficiency (EE) due to the bias power, whereas ACO-OFDM and PAM-DMT suffer from reduced SE due to not utilizing half the spectrum. In addition, to improve the SE other schemes such as (i) hybrid schemes have been proposed including asymmetrically clipped DC biased O-OFDM (ADO-OFDM) [20], hybrid asymmetrically clipped OFDM (HACO-OFDM) [21], asymmetrically clipped absolute value optical OFDM (AAO-OFDM) [22], hybrid PAM-DMT (HPAM-DMT) [23], and polarization OFDM [24] have been proposed to improve the SE; And (ii) layered (or enhanced) schemes including enhanced U-OFDM (eU-OFDM) [25], layered ACO-OFDM (LACO-OFDM) [26], absolute value layered ACO-OFDM (ALACO-OFDM) [27] and augmented SE-DMT (ASE-DMT) [28], where infinite layer unipolar U-OFDM, ACO-OFDM or PAM-DMT can be superimposed. Superior to the layered/enhanced schemes with infinite layers superimposition, a triple-layer hybrid optical OFDM (THO-OFDM) scheme reaching the SE limit of LACO-OFDM was proposed with enhanced performance and reduced computation complexity [14], [29].…”

Optical OFDM for SiPM-Based Underwater Optical Wireless Communication Links

“…It also benefits from more flexibility, in the sense that the overall transmission data rate and performance can be adjusted by setting independently the signal constellation size and the allocated power within each layer. Another proposed scheme, called hybrid PAM-DMT (HPAM-DMT) [35], uses a similar concept as LACO, where the transmitted signal is composed of different "groups" of signals: The first group consists of a real PAM-DMT (RPAM-DMT) signal, and the successive groups are obtained from RPAM-DMT modulated signals sent on specific sub-carriers. The advantage of HPAM-DMT over LACO is its lower computational complexity at the Rx, but this comes at the drawback of a lower power efficiency.…”

Selectively Biased Optical Orthogonal Frequency Division Multiplexing for Visible Light Communication Systems

“…In order to make the signal suitable for visible light communication transmission, many OFDM schemes have been proposed for VLC systems. Among them, there are several well-known methods: DC biased O-OFDM (DCO-OFDM) [3], asymmetric limiting O-OFDM (ACO-OFDM) [4,5,6] and also Pulse Amplitude Modulated Discrete Multi Tone (PAM-DMT) [7]. In DCO-OFDM, a constant DC bias needs to be added to convert the signal to a unipolar real signal that can be transmitted by the LEDs.…”