LED, which is well know as new generation of lighting device, is also found to be
useful in realizing visible light communication. In our project, we used LED ...
iLight - Visible Light Communication Transceiver Design Using Integrated LED Micro-arrays Project code: LKM1-11
Students: LUO Weile
Supervisors: Lau, Kei May
TSO Ka Ho
Yue, Patrick
NGAN Yuk Hung
1. Introduction LED, which is well know as new generation of lighting device, is also found to be useful in realizing visible light communication. In our project, we used LED arrays to achieve visible light communication for multiple channels. It allows more than one user to transmit data and signal at the same time.
3. Methodology There are 2 major sources of undesirable signal: 1. the background noise from indoor lighting devices 2. the interference from other channels To solve the problem, 2 stages of modulation are implemented in the transmitter.
For the receiver, we used a band-pass filter with adjustable center frequency to select channel. For example, if the user want to select channel 1, the center frequency should be adjusted to 30k. Finally, AM demodulation is implemented by an envelope detector.
2. System diagram 3 LEDs represent 3 independent channels
Channel
AM carrier
1
30KHz
2
70KHz
3
110KHz
2nd modulation: Pulse Width Modulation
The user can adjust the filter to select one of the channels to listen to
Compare AM output with a sawtooth of 500KHz. The pulses are used to control LED ON/OFF.
Our system can achieve single-channel transmission fully switching between 2 channels but interference from the undesired channel cannot be completely eliminated 3-channel transmission partially, interference is quite big compared to the case of 2-channel transmission Therefore, with increasing number of channels, the interchannel interference is more critical than background noise.
Suggestion for better performance: 1. Use coherent demodulator in the receiver 2. Use FM rather than AM for the first stage of modulation
