On the Use of Class D Switching-Mode Power Amplifiers in Visible Light Communication Transmitters

Round 1

Reviewer 1 Report

1) In the introduction, the sentence “It is important to note that these modulation schemes, such as such as Quadrature Amplitude Modulation (QAM) and Orthogonal Frequency Division Multiplexing (OFDM), are the preferred ones for VLC applications due to their high spectral efficiency and high robustness against the multipath issue of wireless-transmission scenarios [9], [10]” is not strictly correct. QAM cannot be implemente using IM/DD as typically occurs in VLC. Indeed, QAM can only be applied for DCO-OFDM, ACO-OFDM… schemes that are a modification of OFDM in order to obtain a real and non-negative signal.

 

2) The idea of using SMPA for Visible Light Communications is considerably novel. However, there are many issues that should be solved. 

 

2a) The electrical equivalent of most of the illumination LEDs is unknown, is it necessary to adapt the impedances of the SMPA and the LED? That is, if the input/output impedances are unmatched, the energy transfer could be ineficiente.

 

2b) What is the maximum power for the considered LED? For instance, could it be applied to a CoB LED with more that 0.5 A of drive current? 

 

2c) What is the maximum bandwidth? The bottleneck is in the SMPA or in the LED? 

 

3) In Figure 17, the 8-QAM is very very unfrequent, typically a 8-PSK is employed for RF transmission. Indeed, APSK schemes are employed in satellite communications because of the non-linearities of the satellite amplifiers. Please, justify the use of APSK modulation. 

Author Response

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Reviewer 2 Report

The manuscript investigates the possibility to introduce Class D Switch-Mode Power Amplifiers (SMPA) in VLC short-range transmitters, based on High-Brightness LED and QAM + OFDM modulation scheme, in order to increase power efficiency with respect to Linear Power Amplifiers. The paper first investigates between the possible implementations and choose half-bridge topology, in order to reduce the number of components, and RF-PWM to drive the Class D SMPA. A prototype of the Class D SMPA is accurately designed and tested in order to verify its performance. The paper is clear and well-written and in my opinion is ready for publication.    

Author Response

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Reviewer 3 Report

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Comments for author File: Comments.pdf

Author Response

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