Abstract
Layered asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) with high spectral efficiency is proposed in this paper for optical wireless transmission employing intensity modulation with direct detection. In contrast to the conventional ACO-OFDM, which only utilizes odd subcarriers for modulation, leading to an obvious spectral efficiency loss, in layered ACO-OFDM, the subcarriers are divided into different layers and modulated by different kinds of ACO-OFDM, which are combined for simultaneous transmission. In this way, more subcarriers are used for data transmission and the spectral efficiency is improved. An iterative receiver is also proposed for layered ACO-OFDM, where the negative clipping distortion of each layer is subtracted once it is detected so that the signals from different layers can be recovered. Theoretical analysis shows that the proposed scheme can improve the spectral efficiency by up to 2 times compared with conventional ACO-OFDM approaches with the same modulation order. Meanwhile, simulation results confirm a considerable signal-to-noise ratio gain over ACO-OFDM at the same spectral efficiency.
Highlights
Motivated by the dramatic development of light emitting diode (LED) technologies as well as the scarce spectrum of the radio frequency, optical wireless communication (OWC) has gained increasing attention from both of academia and industry
A spectrally efficient layered ACO-orthogonal frequency division multiplexing (OFDM) scheme is proposed for intensity modulation with direct detection (IM/DD) optical wireless transmission, where different layers of ACO-OFDM are combined for simultaneous transmission
The subcarriers are divided into different layers, modulated by different sizes of ACO-OFDM, and combined for simultaneous transmission
Summary
Motivated by the dramatic development of light emitting diode (LED) technologies as well as the scarce spectrum of the radio frequency, optical wireless communication (OWC) has gained increasing attention from both of academia and industry. Performance analysis shows that the proposed scheme can improve the spectral efficiency by up to 2 times compared with conventional ACO-OFDM with the same modulation order. Afterwards, the signal is parallel to serial (P/S) converted into a single signal stream, which is clipped at zero and used for modulating the LEDs. LED nonlinearity is a challenge for optical wireless transmission systems, which degrades its performance. The optical signal is detected by avalanche photodiode (APD) and converted to the electronic signal It has been proven in [12] that the negative clipping distortion only falls on the even subcarriers when transformed to the frequency domain, which is orthogonal to the transmitted data on the odd subcarriers. After serial-to-parallel (S/P) conversion and CP removal, the transmitted signal on the odd subcarriers can be recovered by using a simple FFT operation at the receiver
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