Abstract
Probabilistic shaping (PS) is a powerful tool that can realize a flexible data rate and high spectrum efficiency. However, the performance of PS is closely related to the quadrature amplitude modulation (QAM) order, source entropy (SE), normalized generalized mutual information (NGMI), and achievable information rate (AIR). In this paper, we investigated the relationship between PS QAM order, SE, NGMI, and AIR performance for the first time in the visible light communication (VLC) system. Under a specific signal-to-noise ratio (SNR), the PS QAM order and SE in this paper can realize a high AIR at a preset NGMI threshold with the lowest computation complexity, which is just 0.1 bit smaller than the highest AIR. Simulation and experimental results show that the NGMI fluctuates between only ±0.005 of the preset NGMI threshold, which proves that the scheme proposed in this paper is feasible.
Highlights
Visible light communication (VLC) is a promising candidate for future wireless communication [1,2]
The optimization problem in this paper is related to four variables: source entropy (SE), signal-to-noise ratio (SNR), normalized generalized mutual information (GMI) (NGMI), and quadrature amplitude modulation (QAM)
According to Equation (8), the system achievable information rate (AIR) without redundancy is closely related to the QAM order and SE at a specific NGMI threshold
Summary
Visible light communication (VLC) is a promising candidate for future wireless communication [1,2]. Traditional QAM is not the optimal constellation for the channel, which has an apparent gap to the Shannon capacity [8]. It is proven that in the additive white noise Gaussian (AWGN) channel, the Maxwell–Boltzmann distribution is the optimal probability distribution for the standard QAM constellation, which could provide shaping gain of at most 1.53 dB [11]. In [22], PS constellations with static entropies could provide more than 1 dB signal-to-noise ratio (SNR) sensitivity gain for 256QAM in the AWGN fiber system. SE, according to different channel state information, which is a fundamental issue to realizing higher system performance. In the VLC system, there is little research on the selection of the PS QAM order and SE, which can meet the specific NGMI threshold with high AIR.
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