Molecular communication with Brownian motion and a positive drift: performance analysis of amplitude modulation schemes

In this study, the authors consider molecular communication between two nanomachines placed in a fluid medium for three different amplitude modulation schemes. The number of molecules transmitted represents the amplitude levels for these schemes. Each molecule released by the transmitter travels with Brownian motion and a positive drift to reach the receiver nanomachine. They consider a time slotted channel, where the information in every slot is corrupted by stray molecules from the previous slots. The capacity of such a molecular communication channel is investigated for all the three modulation schemes. Analytical expressions for the end-to-end symbol error probability are derived, considering maximum likelihood detection at the receiver. Numerical results indicate that arbitrarily low probabilities of error can be achieved for high drift velocities. An increase in the slot length further improves the performance, albeit at the cost of data rate. The results also demonstrate the improvements offered by the amplitude modulation schemes over the previously proposed time modulation schemes.