CMOS-integrated GaN LED array for discrete power level stepping in visible light communications

Abstract

We report a CMOS integrated micro-LED array capable of generating discrete optical output power levels. A 16 × 16 array of individually addressable pixels are on-off controlled through parallel logic signals. With carefully selected groups of LEDs driven together, signals suitable for discrete transmission schemes are produced. The linearity of the device is assessed, and data transmission using pulse amplitude modulation (PAM) and orthogonal frequency division multiplexing (OFDM) is performed. Error-free transmission at a symbol rate of 100 MSamples/s is demonstrated with 4-PAM, yielding a data rate of 200 Mb/s. For 8-PAM, encoding is required to overcome the baseline wander from the receiver, reducing the data rate to 150 Mb/s. We also present an experimental proof-of-concept demonstration of discrete-level OFDM, achieving a spectral efficiency of 3.96 bits/s/Hz.

Low complexity OFDM VLC system enabled by spatial summing modulation

“…Although the 3-dB modulation bandwidth of a single COTS illuminating LED can be up to several MHz [3,5], it reduces to around 350 KHz for grouped LEDs as illustrated in Fig. 3(a) due to the connections of LEDs and driving transistors, which is in line with the observation in [13,18]. It is intuitive to be observed that the larger group with more LED chips has slightly lower running frequency due to the more LED chips in one group have relatively complex wiring connection with each other which delays the control signal.…”

“…To be more specific, the quantization error has limited impact on the BER performance, and the results clearly show that a proper quantization resolution may improve the BER. Agreed with the early work of [18] which revealed the performance saturates for highest bit resolution due to the increased nonlinearity, so in our test the properly low 6 bit resolution has the best performance thanks to the larger quantization step space. We also directly present the comparison under different quantization resolutions to intuitively illustrate the experiment results as shown in Fig.…”

“…To be more specific, we put the first group of one LED chip at the center of transmitter and the last group with 128 LED chips at the periphery. Therefore, it can largely reduce the control complexity because only 8 digital control signals are needed to modulate the 255 LED chips and meanwhile guarantee the output linearity by fully leveraging the benefit of spatial distribution of LED chips, comparing with the existing works of [16,18] which used current-limiting cumbersome resistors to fine tune the output light intensity. To drive the LED chip groups, one or multiple low cost transistors of MMSS8050 according to the driving current are used thanks to its simple driving circuitry.…”

“…In [17], Mohammed et al detailedly studied to use spatial summing modulation for suppressing the high peak-to-average power ratio (PAPR) in OFDM based VLC, and proposed to partition high PAPR OFDM signals into many low-PAPR narrowband signals which were transmitted by grouped LED chips individually. To evaluate the availability of spatial summing modulation in a real OFDM VLC system, most recently the authors of [18] implemented a prototype consisting of a 16 × 16 CMOS-integrated GaN LED array to realize discrete-level OFDM with spatial summing modulation, and achieved a spectral efficiency of 3.96 bits/s/Hz. However, those existing works do not investigate the feasibility of employing commercial white LEDs with spatial summing modulation for OFDM enabled VLC, while VLC systems are envisioned to piggyback on lighting infrastructure built upon commercial off-the-shelf (COTS) white LEDs.…”

Discrete Power-Stepping Pulse Amplitude Modulation for Optical Camera Communications Employing a CMOS-Integrated GaN µLED Array

“…1(a). In the absence of a DAC, an LED array can be employed to generate an analog signal by aggregating the intensity of individual LEDs, also referred to as digital-to-light conversion (DLC) [5]. In this paper, we demonstrate a DLC technique for PAM similar to [5] for non-line-of-sight RS-based (NLOS) OCC.…”