DBMC-aNOMAly: Asynchronous NOMA with Pilot-Symbol Optimization Protocol for Diffusion-Based Molecular Communication Networks

Multiple access (MA) schemes can enable cooperation between multiple nodes in future diffusion-based molecular communication (DBMC) networks. Non-orthogonal MA for DBMC networks (DBMC-NOMA) is a promising option for efficient simultaneous MA using a single molecule type. Expanding significantly upon previous work on the topic, this paper addresses the question of parameter optimization and bit error probability (BEP) reduction in an asynchronous network using DBMC-NOMA. First, we analytically derive the associated BEP and use the result for a thorough comparison with other MA schemes like time-division and molecule-division MA. We show that the asynchronous nature of the system can be exploited for performance gain, and the upper-bound performance can be achieved in all circumstances by avoiding a few worst-case offset configurations. Subsequently, we propose DBMC-aNOMAly, a pilot-symbol-based optimization protocol for asynchronous DBMC-NOMA, and extensively evaluate it using Monte-Carlo simulations. DBMC-aNOMAly is shown to provide robust BEP reduction for different network sizes, noise levels, subjected to sampling jitter, as well as for changing conditions during runtime, particularly, compared to protocols in previous work. DBMC-aNOMAly consists of a set of simple operations such as comparisons and additions, deliberately designed to be implementable with chemical reaction networks, setting up future work on the realistic modeling of the protocol.