A multilevel modulation scheme for high-speed wireless infrared communications

To investigate short-distance, point-to-point, infrared channels, a test-bench and circuits were constructed to determine the limitations of existing optoelectronics. The results of these measurements are used to formulate a channel model which is employed for the subsequent analysis of candidate bandwidth efficient modulation schemes. A new multilevel modulation scheme, Adaptively Biased QAM (AB-QAM), is proposed which has an asymptotic 3 dB SNR improvement over PAM and a 4.5 dB improvement over QAM for large constellations while maintaining the same bandwidth efficiency. Expressions are derived for the performance of each modulation scheme and are verified in simulation.