Abstract
A major shortcoming of light-emitting diodes (LEDs) is their highly
non-linear optical-power-versus-current characteristic. This non-linearity
largely restricts the dynamic range and the transmission power of common optical
wireless transmitters. This restriction degrades the performance of optical
wireless communication (OWC) systems. In this paper, a novel transmitter concept
for OWC is proposed which employs discrete power level stepping. The transmitter
consists of several on-off-switchable emitter groups. These groups are individually
controlled and emit fixed specific optical intensities in parallel. As optical
intensities constructively add up, the total emitted intensity is generated
by the sum of the emitted intensities of all activated emitter groups. Therefore,
the proposed transmitter solution can generate several discrete optical intensity
levels which can be used for optical wireless signal transmission. The transmitter
design allows the utilisation of the full dynamic range of LEDs or laser diodes
by avoiding non-linearity issues. Moreover, costs and complexity of the optical
front-end are significantly reduced as neither a (DAC) nor high-speed current
controllers are required. This simple design also provides improved power
efficiency. Transmission experiments prove the functionality of the implemented
optical transmitter. It is shown that the practical performance of the transmitter
closely matches the expected performance determined by computer simulations.
Moreover, the implemented optical transmitter is compared to an electrical
transmission which provides ideal linearity characteristics, and therefore
corresponds to an ideal conventional optical transceiver.
© 2013 IEEE
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