Position encoded asymmetrically clipped optical orthogonal frequency division multiplexing in visible light communications

Abstract

A PE-ACO-OFDM (Position-Encoded Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing) signaling scheme for intensity modulation and direct detection is introduced in this paper, where the anti-asymmetry characteristics of ACO-OFDM are exploited to improve the rate of data transmission. This is achieved by reducing the symbol duration of the ACO-OFDM signal, where only the first half of ACO-OFDM is used to transmit the ACO-OFDM data symbol after inverting its negative samples to positive ones. In addition, encoded ACO-OFDM samples are combined with every ACO-OFDM symbol to allow the receiver to identify the position of the inverted samples. Simulation results are introduced, and it is shown that the data rates of PE-ACO-OFDM improve by 33% compared with ACO-OFDM, when a 256-quadrature amplitude modulation scheme is considered as the encoded constellation order. It is also shown that the signal to noise ratio of the proposed PE-ACO-OFDM is higher by almost 1 dB compared with the traditional ACO-OFDM.

DFT Spread-Optical Pulse Amplitude Modulation for Visible Light Communication Systems

“…As a result, a bipolar and complex signal such as the traditional OFDM signal must be first converted into real and unipolar signal before modulating an LED. To make signal real and unipolar in DC-biased optical OFDM (DCO-OFDM), Hermitian Symmetry (HS) is imposed before inverse fast Fourier transform (IFFT) at a cost of halving the available electrical bandwidth [17] followed by addition of a DC-bias [18]. However, adding a DC-bias to a large peak to average power ratio (PAPR) signal, and passing it through the limited LED linear dynamic range makes this scheme unsuitable in some VLC applications where the power efficiency is a crucial requirement such as in diming control [19].…”

Unipolar-pulse amplitude modulation frequency division multiplexing for visible light communication systems

“…As compared with RF systems, in IM/DDbased OFDM VLC transmission, the electrical spectral efficiency is halved for DCO-OFDM while it is reduced to one fourth in ACO-OFDM and PAM-DMT. However, ACO-OFDM and PAM-DMT are more optical power efficiency and have lower noise clipping compared with DCO-OFDM [16][17][18][19][20]. Due to inclusion of a number of SC components during IFFT operation, OFDM waveforms suffer from high peak to average power ratio (PAPR).…”

Optical single carrier-interleaved frequency division multiplexing for visible light communication systems

“…VLC systems are cost-effective, energy efficient and highly secure. Furthermore, VLC occupies the unlicensed portion of the electromagnetic spectrum and offers a very large transmission bandwidth (BW) in comparison to the RF spectrum [1][2][3]. However, the standard high power white phosphor light emitting diodes (WPLED) used for illumination have a limited modulation BW (typically a few MHz [1,2]), which limits the maximum data rates that can be achieved.…”