Diffusive molecular communication (DMC) is one of the most promising approaches for realizing nano-scale communications in biological environments for healthcare applications. In this paper, a DMC system in biological cylindrical environment is considered, inspired by blood vessel structures in the body. The internal surface of the cylinder boundary is assumed to be covered by the biological receptors which may irreversibly react with hitting molecules. Also, information molecules diffusing in the fluid medium are subject to a degradation reaction and flow. The concentration Green's function of diffusion in this environment is analytically derived which takes into account asymmetry in all radial, axial and azimuthal coordinates. Employing obtained Green's function, information channel between transmitter and transparent receiver of DMC is characterized. To evaluate the DMC system in the biological cylinder, a simple on-off keying modulation scheme is adopted and corresponding error probability is derived.Particle based simulation results confirm the proposed analysis. Also, the effect of different system parameters on the concentration Green's function are examined. Our results reveal that the degradation reaction and the boundary covered by biological receptors may be utilized to mitigate intersymbol interference and outperform corresponding error probability. Index TermsDiffusive molecular communication (DMC), biological environment, partial differential equation, Green's function.

Diffusive molecular communication (DMC) is envisioned as a promising approach to help realize healthcare applications within bounded biological environments. In this paper, a DMC system within a biological spherical environment (BSE) is considered, inspired by bounded biological sphere-like structures throughout the body. As a biological environment, it is assumed that the inner surface of the sphere's boundary is fully covered by biological receptors that may irreversibly react with hitting molecules. Moreover, information molecules diffusing in the sphere may undergo a degradation reaction and be transformed to another molecule type. Concentration Green's function (CGF) of diffusion inside this environment is analytically obtained in terms of a convergent infinite series. By employing the obtained CGF, the information channel between transmitter and transparent receiver of DMC in this environment is characterized. Interestingly, it is revealed that the information channel is reciprocal, i.e., interchanging the position of receiver and transmitter does not change the information channel. Results indicate that the conventional simplifying assumption that the environment is unbounded may lead to an inaccurate characterization in such biological environments. Index TermsDiffusive molecular communication (DMC), bounded biological environment, Green's function, Error probability.

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Diffusion-based molecular communication (DMC) is envisioned to realize nanonetworks for health applications. Inspired by sphere-like entities in the body, modeling diffusion channel in the biological sphere is motivated. The boundary condition in such biological environments is considered as homogeneous boundary conditions (HBC) that can simply model the molecular processes over biological barriers, e.g., carriermediated transport and transcytosis over the blood vessel walls. In this paper, we model the diffusive communication channel between a point source transmitter and a transparent receiver arbitrarily located inside a spherical environment with HBC. To this end, the concentration Green's function (CGF) is analytically derived in the Fourier domain. Statistics of the signal received at the receiver is computed based on the derived CGF to obtain the analytical results. The analytical results are accurately confirmed with particle-based simulation (PBS). The performance of a simple on-off keying modulation scheme is also examined in terms of error probability.

The extracellular vesicles (EVs) role in intercellular communication of transferring the cargoes of biomolecules such as proteins and nucleic acid between cells has been revealed recently. EV-mediated molecular communications (MC) is involved in targeted cells that receive EVs following the mechanisms of endocytosis. Such mechanisms comprise various processes of EV binding, internalization, and recycling that are characterized by specific factors of reaction. Accurate estimation of these factors is essential for the MC receiver assessment upon EV signaling. Here, we propose a fitting model to approximate the reaction rate parameters based on a suggested scenario corresponding to an experimental setup. The results of relative error for the estimated rates based on the simulated data are presented. The estimation method given in this paper can help future works on data analysis and minimizing the experimental resources. CCS CONCEPTS• Applied computing → Computational biology; Health care information systems; Physical sciences and engineering.

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Channel modeling is a challenging vital step towards the development of diffusion-based molecular communication networks (DMCNs). Analytical approaches for diffusion channel modeling are limited to simple and specific geometries and boundary conditions. Also, simulation-and experiment-driven methods are very time-consuming and computationally complex. In this paper, the channel model for DMCN employing the fundamental concentration Green's function (CGF) is characterized . A general homogeneous boundary condition framework is considered that includes any linear reaction systems at the boundaries in the environment. To obtain the CGF for a general DMCN including multiple transmitters, receivers, and other objects with arbitrary geometries and boundary conditions, a semi-analytical method (SAM) is proposed. The CGF linear integral equation (CLIE) is analytically derived. By employing the numerical method of moments, the problem of CGF derivation from CLIE is transformed into an inverse matrix problem. Moreover, a sequential SAM is proposed that converts the inversion problem of a large matrix into multiple smaller matrices reducing the computational complexity. Particle-based simulator confirms the results obtained from the proposed SAM. The convergence and run time for the proposed method are examined. Further, the error probability of a simple diffusionbased molecular communication system is analyzed and examined using the proposed method.

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