Decode and forward relaying in diffusion-based molecular communication between two populations of biological agents

Molecular communication allows bio nodes to communicate and cooperate in an aqueous environment. We recently proposed an m-ary modulation scheme in which the information is encoded into the concentration of molecules emitted by the bio nodes. The performance of such scheme, among other factors, is limited by the maximum concentration of molecules that can be induced by the transmitter at the receiver. This paper investigates relaying to improve the reliability of such molecular communication. We consider the case that nodes consist of a population of biological agents and study the scenario in which the relay node decodes the incoming information symbol and forwards it to the destination using the same or a different type of molecules as the transmitter. We show how the use of relaying in molecular communication can increase the effective range of molecular concentration induced at the receiver and also can help with achieving diversity at the receiver. We use a generalized form of Maximum Ratio Combining (MRC) and show as to how the probability of error is improved using the optimal relaying. We also compare this scenario with the case that the relay node uses the same type of the molecule.