Author(s): Shini M S
Published in: International Journal of Engineering Research & Technology
License: This work is licensed under a Creative Commons Attribution 4.0 International License.
Volume/Issue: Volume. 4 - Issue. 09 , September - 2015
Indoor diffuse wireless optical intensity channels are bandwidth constrained channels in which all transmitted signals must be non-negative. In this work, a new signaling method for ISI-free transmission for bandlimited intensity modulated direct detection channels using higher level modulation schemes is presented. Taking this into account, the channel can be modeled as a band limited channel with non-negative input and additive white Gaussian noise (AWGN). Due to the non-negativity constraint, standard methods for coherent band limited channels cannot be applied here. Previously established techniques for the IM/DD channel require bandwidth twice as that required for the conventional coherent channel. This paper proposes a method to transmit the information without inter-symbol interference in a bandwidth smaller than the bit rate. By this method, it is possible to transmit the information with a bandwidth equal to that of conventional coherent channels without ISI. This can be achieved by combining Nyquist or root-Nyquist pulses with a constant bias and using higher-order modulation formats. A trade-off between optical power gain and the required bandwidth is investigated. For a particular bandwidth, the most power-efficient transmission is obtained either by the parametric linear pulse or by better than Nyquist pulse.
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