Run-length aware hybrid modulation scheme for diffusion-based molecular communication

In order to speed up inherently slow diffusion-based molecular communication method, in this paper, we propose a hybrid modulation scheme employing two baseline modulation schemes, namely concentration shift keying and molecular shift keying. Furthermore, we also present two design alternatives to implement the proposed scheme. The main objective of the proposed hybrid modulation scheme is to improve offered symbol rate of diffusion-based communication method by opportunistically transmitting multiple information symbols in a single transmission slot. Opportunities to transmit multiple information symbols in a slot are determined based on run length (i. e., number of consecutive repetitions) of symbols in transmission buffer. Our preliminary analysis shows that the lower the modulation order of the proposed hybrid modulation scheme is, the higher will be the achieved channel capacity gain in comparison to the baseline modulation schemes. For example, in case of binary modulation, channel capacity gain is up to nearly 100% while for the quaternary modulation it is up to around 33%.