In recent years, with the development of new technologies like smart driving, internet of things, and virtual reality, wireless communication systems with excessive data transfer capacity are increasing needed. For conventional radio frequency (RF) communication systems, spectrum congestion has become the biggest bottleneck for increasing the transmission speed. Therefore, visible light generated by light emitted diodes (LEDs) or laser diodes (LDs) is employed for high-speed data transfer. This is called visible light communication (VLC). Simultaneous illumination and data transmission, unlicensed visible light spectrum, low cost for the frontend, and radio sensitive environment applications are the advantages of VLC compared to traditional RF communication. The wide use of LEDs has fu...[ Read more ]

In recent years, with the development of new technologies like smart driving, internet of things, and virtual reality, wireless communication systems with excessive data transfer capacity are increasing needed. For conventional radio frequency (RF) communication systems, spectrum congestion has become the biggest bottleneck for increasing the transmission speed. Therefore, visible light generated by light emitted diodes (LEDs) or laser diodes (LDs) is employed for high-speed data transfer. This is called visible light communication (VLC). Simultaneous illumination and data transmission, unlicensed visible light spectrum, low cost for the frontend, and radio sensitive environment applications are the advantages of VLC compared to traditional RF communication. The wide use of LEDs has further promoted the application of VLC technology.

The bandwidth limitation of LEDs limits the improvement of VLC systems. Various techniques applied to hardware and algorithms have been developed to increase the data transfer capability. For example, The VLC system bandwidth can be significantly extended by employing pre-equalization and post-equalization in both the time and frequency domain. In addition, advanced modulation schemes, such as pulse amplitude modulation (PAM), carrier-less amplitude phase (CAP) modulation and orthogonal frequency division multiplexing (OFDM), can be utilized to improve the spectrum efficiency. In this thesis, we design and implement circuits of the digital baseband, utilizing advanced modulation schemes and supporting equalization technologies.

The first work presents a real-time visible laser light communication (VLLC) system with a baseband design in a field programmable gate array (FPGA) platform using an 8B/10B encoding and non-return-to-zero on off keying (NRZ-OOK) modulation scheme. Based on the proposed system, a video can be transmitted through the system at a data rate of 500 Mbps over a 2-meter distance in real-time.

The second work presents a novel RGB PAM-4 transceiver employing a digitally-controlled asymmetric feed forward equalizer (FFE) and cascaded continuous time linear equalizer (CTLE). The PAM-4 signal with a one-tap FFE is composed of six OOK signals with different delays in the optical domain. Delay control is implemented in the digital baseband and no digital-to-analog converter (DAC) is needed in the system. The transceiver achieves a 250% increase in the bandwidth extension ratio in the VLC links using ordinary RGB LEDs by allowing independent PAM-4 eye-height tuning.

The third work designs and implements a VLC transmitter baseband circuit supporting OFDM with bit and energy allocation (BEA) on an FPGA. The training sequence and the pilot subcarrier are also added for frame synchronization, symbol synchronization, channel estimation, and sampling offset compensation. The test result shows that the transmitter can generate the OFDM signal supporting BEA and the signal can be synchronized and demodulated. Compared with modulation with a fixed bit number and energy on each subcarrier, the proposed transmitter increases the data rate from 15 to 20.5 Mbps when the bit error rate (BER) equals 3 x 10^-3 and transmission distance is 0.3 m.