Abstracts:A one-dimensional (1-D) anomalous-diffusive molecular communication channel is considered, wherein the devices (transmitter (TX) and receiver (RX)) can move in either direction along the axis. For modeling the anomalous diffusion of information carrying molecules (ICM) as well as that of the TX and RX, the concept of time-scaled Brownian motion is explored. In this context, a novel closed-form expression for the first hitting time density (FHTD) is derived. Further, the derived FHTD is validated through particle-based simulation. For the transmission of binary information, the timing modulation is exploited. Furthermore, the channel is assumed as a binary erasure channel (BEC) and analyzed in terms of achievable information rate (AIR).

Abstracts:Secure transmission of information to a desired receiver is an important attribute of any molecular communication system. This paper analyzes the secrecy performance for a multi-particle diffusive molecular timing channel. We first obtain the fractional equivocation and then employ three standard secrecy performance metrics, namely, generalized secrecy outage probability, average fractional equivocation, and average information leakage rate to evaluate the secrecy performance of the channel in the presence of an eavesdropping user. We then propose a new secrecy performance metric, the amount of confusion level, which quantifies the severity of the confusion level at the eavesdropping user. Compared to the aforementioned metrics which are mainly based on the first-order statistics, the amount of confusion level is a second order measure that characterizes the eavesdropping effect in a better way, especially in environments with very small value of the Lévy noise parameter. The dependence of various secrecy metrics on various physical parameters, especially the Lévy noise parameter and the degradation rate of information molecules, is studied. Our analysis suggests that an increase in the value of each of these parameters results in an improvement in the secrecy performance. Numerical results corroborate the derived analytical findings.

Abstracts:While molecular communication via diffusion experiences significant inter-symbol interference (ISI), recent work suggests that ISI can be mitigated via time differentiation pre-processing which achieves pulse narrowing. Herein, the approach is generalized to higher order differentiation. The fundamental trade-off between ISI mitigation and noise amplification is characterized, showing the existence of an optimal derivative order that minimizes the bit error rate (BER). Theoretical analyses of the BER and a signal-to-interference-plus-noise ratio are provided, the derivative order optimization problem is posed and solved for threshold-based detectors. For more complex detectors which exploit a window memory, it is shown that derivative pre-processing can strongly reduce the size of the needed window. Extensive numerical results confirm the accuracy of theoretical derivations, the gains in performance via derivative pre-processing over other methods and the impact of the optimal derivative order. Derivative pre-processing offers a low complexity/high-performance method for reducing ISI at the expense of increased transmission power to reduce noise amplification.

Abstracts:Astrocytes, the most abundant glial cells in brain, being in physical proximity of pre- and postsynaptic terminals of the chemical synapse, form tripartite synapses. The feedback from astrocytes introduces synaptic plasticity, which modulates information transmission through neurons. Various other synaptic events also cause plasticity, hence combining them in a single model is quite challenging. In this paper, we study the combined effect of short-term depression (STD) and long-term potentiation (LTP) on vesicle release process in a tripartite synapse. STD decreases the release probability due to slower replenishment rates of releasable vesicles, whereas LTP is due to the positive feedback from astrocytes that increases release probability. Thus, we evaluate vesicle release probability and mutual information between input spikes and vesicle release to quantify the effects of STD and LTP on information transmission. Moreover, the effect of different synaptic parameters such as number of releasable vesicles, input spike rate and replenishment rate of the vesicles, is analyzed on information transmission. It is observed that release probability is predominantly affected by LTP, however, presence of STD decreases the achievable average mutual information over time. Furthermore, the synapses with higher number of releasable vesicles are observed to become stronger with time.

Abstracts:In this paper, an underlay cognitive molecular communication (MC) system with anomalous diffusion inside a blood-vessel like cylindrical channel is considered. We consider the presence of a primary and a secondary link in coexistence, with primary link having a higher priority for communication. To meet a certain quality of standard (QoS) at primary link, the interference due to the secondary is minimized by controlling the transmission at the secondary. The expressions for the concentration Green’s function (CGF) for anomalous diffusion and the number of molecules transmitted by the secondary transmitter are derived. The CGF is validated using the particle-based simulations. We analyze the channel performance in terms of probability of error, maximum achievable rate, receiver operating characteristics (ROC) and area under the curve (AUC). The decision threshold is optimized based on the log-likelihood ratio-test (LLRT) in order to minimize the probability of error. Furthermore, the effects of various parameters such as drift, diffusion, concentration degradation, channel radius and interference limit are analyzed. The derived expressions are validated through the Monte-Carlo simulations.

Abstracts:Diffusion-based molecular communication (DBMC) systems allow messenger molecules to reach the intended receiver using laws of diffusion. The Brownian motion of messenger molecules introduces delay in the system causing the problem of inter-symbol interference (ISI). Along with ISI, the problem of inter-link interference (ILI) comes into picture in the diffusion-based molecular multiple-input multiple-output (DB-MoMIMO) systems. To combat against ISI and ILI issues, index modulation (IM) approaches are recently proposed in the literature for improving the performance of DB-MoMIMO systems. Despite the existence of IM approaches, problems of ISI and ILI still persist due to the slow random motion of molecules in DB-MoMIMO channels. Motivated by this, a novel coded modulation approach called molecular spatio-temporal coded modulation (MSTCM) is proposed in this paper which shows promising improvement in the performance of DB-MoMIMO systems by encoding the information both in space and time axes. Further, if system has access to two types of molecules, the dual-type modulation schemes are discussed for the same. Moreover, the encoder and decoder designs for the proposed mapping strategy are provided. In addition, a theoretical bit error rate expression for the MSTCM scheme is derived and simulation results are shown to corroborate the theoretical ones.

Abstracts:Presents a listing of the editorial board, board of governors, current staff, committee members, and/or society editors for this issue of the publication.

Abstracts:Besides mimicking bio-chemical and multi-scale communication mechanisms, molecular communication forms a theoretical framework for virus infection processes. Towards this goal, aerosol and droplet transmission has recently been modeled as a multiuser scenario. In this letter, the “infection performance” is evaluated by means of a mutual information analysis, and by an even simpler probabilistic performance measure which is closely related to absorbed viruses. The so-called infection rate depends on the distribution of the channel input events as well as on the transition probabilities between channel input and output events. The infection rate is investigated analytically for five basic discrete memoryless channel models. Numerical results for the transition probabilities are obtained by Monte Carlo simulations for pathogen-laden particle transmission in four typical indoor environments: two-person office, corridor, classroom, and bus. Particle transfer contributed significantly to infectious diseases like SARS-CoV-2 and influenza.