Modeling and Analysis of Transmitter Performance in Visible Light Communications

Deng, Xiong; Arulandu, Kumar; Wu, Yan; Mardanikorani, Shokoufeh; Zhou, Guofu; Linnartz, Jean-Paul M. G.

doi:10.1109/tvt.2019.2891639

Cited by 41 publications

(20 citation statements)

References 45 publications

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“…where V 0 can be interpreted as the turn-on limit and R LED is the dynamic plus parasitic resistance of the LED [32], [33]. So the total electrical power consumed by the LED is,…”

Section: Owc Power Constraintsmentioning

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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“…where V 0 can be interpreted as the turn-on limit and R LED is the dynamic plus parasitic resistance of the LED [32], [33]. So the total electrical power consumed by the LED is,…”

Section: Owc Power Constraintsmentioning

confidence: 99%

“…(32) For a given γ, the optimum modulation bandwidth and the throughput are implicitly given by the inverse of (31) and by (32), respectively. Practical algorithms such as Hughes-Hartogs (HH) [21], [22] provide an iterative, discretized algorithm to calculate the optimum bit and power loading distribution.…”

Section: B Ofdm With Waterfillingmentioning

confidence: 99%

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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“…We linearize the LED model as a fixed junction voltage V J in series with a dynamic and Equivalent Series Resistance (ESR) resistance R LED [16]. Thus,…”

Section: A Linearized Led Modelmentioning

confidence: 99%

“…Assuming the same power after IFFT, the ACO/Flip/PAM-OFDM PAPR is 6.9 dB higher than the DCO-OFDM PAPR, due to the halved power after the clipping or flipping. For the impact of the PAPR on the extra power lost in the LED modulator, we refer to [16]. Secondly, LED nonlinearities tend to be smaller at the center of the dynamic range and are higher at the edges.…”

Section: Introductionmentioning

confidence: 99%

DC-Bias for Optical OFDM in Visible Light Communications

et al. 2019

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The requirement of a DC-bias is known to make DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) less energy efficient. This can be improved by asymmetrically clipped optical OFDM (ACO-OFDM), pulse amplitude modulated OFDM (PAM-OFDM) or Flip-OFDM, but these variants use the bandwidth inefficiently. Our trade-off between energy and spectrum efficiency considers a given limited channel bandwidth of the light emitting diode (LED) and then attempts to get the highest throughput per unit of energy. We investigate previous findings that clipped OFDM can be more attractive in a low-SNR regime. More specifically, we consider visible light communication (VLC) in which the average light level, i.e., the bias, is prescribed by illumination requirements, thus comes for free. ACO/PAM/Flip-OFDM can convert the DC-bias into power for communication, but all variants of OFDM, including DCO-OFDM consume extra electrical power. We conclude that in this scenario, advantages attributed to ACO/PAM/Flip-OFDM vanish, as DCO-OFDM outperforms its variants in all SNR conditions, in terms of achieved throughput over a bandlimited channel as a function of extra electrical power required. For hybrid solutions, such as Asymmetrically clipped DC biased Optical OFDM (ADO-OFDM) and Hybrid ACO-OFDM (HACO-OFDM), we optimize a new adaptive power and rate splitting between odd (clipped) and even (biased/clipped) subcarriers to balance power and bandwidth efficiency.

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“…This VLC-LED driver is simple and high-power efficient (higher than 90%). Only Pulse-Based Modulation (PBM) schemes can be reproduced using this solution [6][7][8][9]; however, PBM schemes are not the best option for providing a high bit-rate and for avoiding the multipath issue (an issue arising from the different paths that the light rays can follow from the light focus to the receiver). Although some PBM proposed solutions achieve a very high bit-rate (10 Mbps) at higher power levels associated with the light emitted for communications (up to 10 W) [8,9], they are far from the theoretically achievable bit-rate using advanced modulation schemes.…”

mentioning

confidence: 99%

Adapting Techniques to Improve Efficiency in Radio Frequency Power Amplifiers for Visible Light Communications

et al. 2020

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It is well known that modern wireless communications systems need linear, wide bandwidth, efficient Radio Frequency Power Amplifiers (RFPAs). However, conventional configurations of RFPAs based on Class A, Class B, and Class AB exhibit extremely low efficiencies when they manage signals with a high Peak-to-Average Power Ratio (PAPR). Traditionally, a number of techniques have been proposed either to achieve linearity in the case of efficient Switching-Mode RFPAs or to improve the efficiency of linear RFPAs. There are two categories in the application of aforementioned techniques. First, techniques based on the use of Switching-Mode DC–DC converters with a very-fast-output response (faster than 1 µs). Second, techniques based on the interaction of several RFPAs. The current expansion of these techniques is mainly due to their application in cellphone networks, but they can also be applied in other promising wireless communications systems such as Visible Light Communication (VLC). The main contribution of this paper is to show how Envelope Tracking (ET), Envelope and Elimination (EER), Outphasing, and Doherty techniques can be helpful in developing more efficient VLC transmitters capable of reaching high bit-rates (higher than 1 Mbps) by using advance modulation schemes. Finally, two examples based on the application of the Outphasing technique and the use of a Linear-Assisted Envelope Amplifier (EA) to VLC are presented and experimentally verified.

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Modeling and Analysis of Transmitter Performance in Visible Light Communications

Cited by 41 publications

References 45 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

DC-Bias for Optical OFDM in Visible Light Communications

Adapting Techniques to Improve Efficiency in Radio Frequency Power Amplifiers for Visible Light Communications

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