Abstract
The promising solution for short-reach optical communication, discrete multitone (DMT) system suffer from high peak-to-average power ratio (PAPR). It is easy for the DMT signal to enter the nonlinear region of the components in the systems, which distorts the signal and limits the modulation efficiency. It is well-known that the precoding technique can suppress the PAPR of DMT without loss of spectral efficiency. We found that, in the I/Q plane, the nonlinear distortion clusters in the constellation points with higher power due to the joint precoding and inverse fast Fourier transform. The principle of this phenomenon has been studied. To cope with the specially distributed nonlinear distortions induced by precoding, we adopted the probabilistic constellation shaping (PCS) technique to reduce the probability of constellation points with high power, resulting in the overall performance improvement. Joint precoding and PCS significantly improve the resistance to nonlinear distortions for DMT systems. Simulations and experiments of 16-QAM and 64-QAM DMT transmission systems were conducted to evaluate the performance. The experimental results show that at the NGMI threshold of 0.92, up to 4 dB enhancement of the receiver sensitivity has been achieved by the proposed scheme when 4-GBd 64-QAM signals are transmitted.
Highlights
The orthogonal frequency division multiplexing (OFDM) system has been considered as a promising solution to deal with the rapidly growing demand for high transmission rate [1]
discrete multitone (DMT) systems suffer from a high peak-to-average power ratio (PAPR), which severely limits the modulation efficiency
In the precoded DMT system, we studied the effect of modulation nonlinearity and found that the constellation points with higher power suffer more from the nonlinear distortion
Summary
The orthogonal frequency division multiplexing (OFDM) system has been considered as a promising solution to deal with the rapidly growing demand for high transmission rate [1]. DMT systems suffer from a high peak-to-average power ratio (PAPR), which severely limits the modulation efficiency. With the help of joint IFFT and precoding operation, the amplitude distribution of the DMT signal in time domain is completely changed, making the DMT signal more like a single-carrier signal. Though this phenomenon has been observed by some researchers [15], we first explained it from the perspective of matrix analysis to our best knowledge.
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