Sensitivity evaluation of optical wireless PPM systems utilising PIN-BJT receivers

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Abstract
A new hybrid optical wireless system based on pulse position modulation (PPM) and PIN-BJT receivers is proposed and its performance is evaluated. The system is operated at a bit rate of 10 Mbit/s and λ = 0.85 µm. The receiver achieves a low noise current of ~2.7 pA/√Hz. Original results are presented demonstrating that the system can achieve a sensitivity of –50.5 dBm at an error rate of 10-9. This represents a sensitivity improvement of 9.8 dB over a comparable on-off keying (OOK) PIN-BJT system. The sensitivity enhancement has a significant impact on the optical wireless network, where the maximum allowed transmitted power is limited by safety issues. Moreover, the use of PPM offers other advantages, such as the low average power which is suited for battery operation and a high peak power that aids detection.