Mitigating LED Nonlinearity to Enhance Visible Light Communications

Deng, Xiong; Mardanikorani, Shokoufeh; Wu, Yan; Arulandu, Kumar; Chen, Bin; Khalid, Arslan; Linnartz, Jean-Paul M. G.

doi:10.1109/tcomm.2018.2858239

Cited by 67 publications

(43 citation statements)

References 38 publications

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“…A filter inverts the LED low-pass response in the frequency range [0, f p ]. The throughput R p is derived from (29) and (8) with the back-off κ given in (9):…”

Section: ) Arbitrary Modulation Constellationsmentioning

confidence: 99%

“…In the previous subsection, we implicitly assumed a continuous-valued M , but in this section, we assume an M 2 -QAM modulation that can only take integer values of an even power of 2 (M = 2, 4, 8, ..) and identical on all sub-carriers. We use the relation (23) to express N /N 0 in terms of SNR(f ), as in (6) but with a preemphasized spectral density (8),…”

Section: ) Arbitrary Modulation Constellationsmentioning

confidence: 99%

“…Dashed lines in Fig. 3 In future systems, the distortion may be overcome by a pre or post-distortion compensation method, such as in [8]. Therefore, we do not elaborate on invertible distortion as limiting the throughput, so we focus on non-invertible clipping.…”

Section: A Conservatively Choosing Low Modulation Depthmentioning

confidence: 99%

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Optimization and Comparison of M-PAM and Optical OFDM Modulation for Optical Wireless Communication

Mardanikorani

Deng

Linnartz

2020

IEEE Open J. Commun. Soc.

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Illumination LEDs, but also infrared LEDs have limited bandwidth. To achieve high throughput, one needs to modulate the LED significantly above its 3 dB bandwidth. Orthogonal Frequency Division Multiplexing (OFDM) is a popular modulation technique to cope with the frequency selectivity of the LED channel. In this paper, we challenge whether its large Peak-to-Average-Power Ratio (PAPR) and resulting large DC bias are justified. We compare systems using the same power and derive how PAM and OFDM variants reach their optimum throughput at different bandwidths and differently shaped spectral densities, thus at very different Signal to Noise Ratio (SNR) profiles but nonetheless the same transmit power. When corrected for the path loss and normalized to the noise power in the 3 dB bandwidth of the LED, we call this the Normalized Power Budget (NPB). OFDM can exploit the low-pass LED response using a waterfilling approach. This is attractive if the NPB exceeds 60 dB. OFDM will then have to spread its signal over more than ten times the LED bandwidth and requires a DC bias of more than 4 times the rms modulation depth. Second-order distortion and LED droop may then become a limitation, if not compensated. At lower power (NPB between 30 and 60 dB), DCO-OFDM outperforms PAM, provided that it significantly reduces its bias and only if it uses an appropriate adaptive bit and power loading. Without adaptive bit loading, thus using a frequency-constant modulation order, for instance made feasible by a pre-emphasis, OFDM always shows lower performance than PAM; about 2.5 dB at a NPB around 60 dB. Below 30 dB of NPB, even waterfilling cannot outweigh the need for a larger bias in OFDM, and PAM should be preferred. We argue that a mobile system that has to operate seamlessly in wide coverage and short-range high-throughput regimes, needs to adapt not only its bandwidth and its bit-loading profile, but also its DCO-OFDM modulation depth, and preferably falls back from OFDM to PAM.

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“…A filter inverts the LED low-pass response in the frequency range [0, f p ]. The throughput R p is derived from (29) and (8) with the back-off κ given in (9):…”

Section: ) Arbitrary Modulation Constellationsmentioning

confidence: 99%

Section: ) Arbitrary Modulation Constellationsmentioning

confidence: 99%

See 1 more Smart Citation

Optimization and Comparison of M-PAM and Optical OFDM Modulation for Optical Wireless Communication

Mardanikorani

Deng

Linnartz

2020

IEEE Open J. Commun. Soc.

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“…Nevertheless, white LEDs have several limitations which might greatly hinder the development and implementation of VLC systems in practical applications. One limitation is the small modulation bandwidth (typically a few MHz) due to the physical mechanism in the LED quantum well [5] and the long photoluminescence lifetimes of the phosphor, resulting in inter-symbol interference [6]. Several techniques have already been reported for capacity improvement of VLC systems, such as spectral efficiency enhancement employing orthogonal frequency division…”

Section: Introductionmentioning

confidence: 99%

LED Nonlinearity Estimation and Compensation in VLC Systems Using Probabilistic Bayesian Learning

et al. 2019

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In this paper, we propose and evaluate a novel light-emitting diode (LED) nonlinearity estimation and compensation scheme using probabilistic Bayesian learning (PBL) for spectral-efficient visible light communication (VLC) systems. The nonlinear power-current curve of the LED transmitter can be accurately estimated by exploiting PBL regression and hence the adverse effect of LED nonlinearity can be efficiently compensated. Simulation results show that, in a 80-Mbit/s orthogonal frequency division multiplexing (OFDM)-based nonlinear VLC system, comparable bit-error rate (BER) performance can be achieved by the conventional time domain averaging (TDA)-based LED nonlinearity mitigation scheme with totally 20 training symbols (TSs) and the proposed PBL-based scheme with only a single TS. Therefore, compared with the conventional TDA scheme, the proposed PBL-based scheme can substantially reduce the required training overhead and hence greatly improve the overall spectral efficiency of bandlimited VLC systems. It is also shown that the PBL-based LED nonlinearity estimation and compensation scheme is computational efficient for the implementation in practical VLC systems.

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“…Regardless of the type of LEDs, they all suffer from nonlinear effects associated with the output power -input drive current characteristic [4]. There are a number of schemes for addressing the non-linearity problem in VLC systems.…”

Section: Introductionmentioning

confidence: 99%

Investigation into Using Compensation for the Nonlinear Effects of the Output of LEDs in Visible Light Communication Systems

Burton

Ghassemlooy

Zvánovec

et al. 2019

2019 2nd West Asian Colloquium on Optical Wireless Communications (WACOWC)

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This paper investigate the effects of the nonlinear output power to the input current transfer function of a light emitting diode (LED) used as the transmitter in visible light communication systems, and proposes a compensation technique to mitigate the non-linearity. Using an off the shelf red, amber, blue, green (RAGB) LED the nonlinear transfer function is measured and then compensated for. The results show that, for the green LED, which has the highest degree of nonlinearity, an improvement in the received error vector magnitude (EVM) of almost 7 dB can be achieved. We also show that, the improvement in EVM over the uncompensated scheme decreases with increased LED linearity.

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Mitigating LED Nonlinearity to Enhance Visible Light Communications

Cited by 67 publications

References 38 publications

Optimization and Comparison of M-PAM and Optical OFDM Modulation for Optical Wireless Communication

Optimization and Comparison of M-PAM and Optical OFDM Modulation for Optical Wireless Communication

LED Nonlinearity Estimation and Compensation in VLC Systems Using Probabilistic Bayesian Learning

Investigation into Using Compensation for the Nonlinear Effects of the Output of LEDs in Visible Light Communication Systems

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