Secrecy Capacity and Secure Distance for Diffusion-Based Molecular Communication Systems

This paper studies the impact of a transmitter's molecule generation process on the capacity of a concentration-based molecular communication (MC) system. Constraints caused by the molecule generation process affect the availability of the molecules at the transmitter. The transmitter has a storage of molecules, and should decide whether to release or save the currently produced molecules. As a result, the MC system has conceptual connections with energy harvesting systems. In this paper, we consider two scenarios on the propagation channel. The first scenario assumes a channel with no inter-symbol interference (ISI), i.e., a memoryless channel. We derive bounds on the capacity of the MC system in this scenario. The second scenario assumes an MC channel with ISI, in which the output of the channel depends on the history of released molecules in the previous time-slots. Based on the assumptions that either the transmitter or the receiver knows the channel statistics, we compute a lower bound on the channel capacity.

Molecular communication is a bioinspired communication that enables macro-scale, micro-scale and nano-scale devices to communicate with each other. The molecular communication system is prone to severe signal attenuation, dispersion and delay, which leads to performance degradation as the distance between two communicating devices increases. To mitigate these challenges, relays are used to establish reliable communication in microfluidic channels. Relay assisted molecular communication systems can also enable interconnection among various entities of the lab-on-chip for sharing information. Various relaying schemes have been proposed for reliable molecular communication systems, most of which lack practical feasibility. Thus, it is essential to design and develop relays that can be practically incorporated into the microfluidic channel. This paper presents a novel design of passive in-line relay for molecular communication system that can be easily embedded in the microfluidic channel and operate without external energy. Results show that geometric modification in the microfluidic channel can act as a relay and restore the degraded signal up-to 28%.

Molecular communication provides a mechanism for the coordination and control of micro-scale and nano-scale devices. In this paper, we describe simulation models to evaluate a molecular communication system that uses molecular motors to transport information molecules over a filament network. The molecular communication system includes an abstracted sender device that releases the information molecules into the environment and a receiver device that detects those molecules as information. In biological systems, molecules move through the environment using methods such as molecular motors that walk on filaments (for certain intracellular transport) or passive diffusion through Brownian motion (for both inter and intracellular transport). We perform simulations to compare the molecular motor system and a Brownian diffusion system and measure the success rate and delay of communicating to receivers. Recent research in engineering biological systems focuses on communication on a two-dimensional surface, and thus we focus on characterizing communications between a sender and receiver that are randomly located on a surface.

In this paper, we derive the analytical successful transmission probability for a fluorescence resonance energy transfer (FRET) based molecular communication system. In molecular communications, FRET process is a promising means of propagation but lacks investigation in the current literature. To tackle the challenge, we propose a stochastic analysis scheme on a FRET-based molecular communication system in order to capture its successful transmission probability. Our analysis shows the impact of the laser pulse duration on transmission performance. When the laser pulse duration is increased, the transmission performance becomes better. Particularly, when the laser pulse duration is larger than 10 ns, the probability for bit ’1’ to successfully transmit approaches 1. Via simulations our analysis is verified.

In recent years, conveying information using molecules via diffusion has attracted significant interest in micro and nanoscale applications. Yet, very little research have been conducted on the performance analysis of large-scale molecular communication (MC) systems with swarm of interfering receivers. In this type of MC system, the collective signal strength at a desired receiver can be impaired by the interference caused by other MC transmitters. The paper presents the first tractable analytical framework for the collective signal strength at a partially absorbing receiver due to a desired transmitter under the impact of a swarm of interfering transmitters in a three-dimensional (3D) large-scale MC system using stochastic geometry. We propose Reed Solomon (RS) coding as an error correction technique to combat the effects of interference caused by the multiple transmitters and the delayed molecules from the previous bits. We derive analytical expressions for the bit error probability (BEP) to evaluate the level of reliability that can be achieved by the proposed scheme. The results obtained using Monte Carlo simulations, matched extactly with the anlytical results, justifying the accuracy of the derivations. Results reveal that the RS codes are capable of providing an acceptable level of improvement in terms of BEP. Furthermore, by carefully selecting the code length, n, and the message length, k, of the RS(n, k) code, we can fine tune the BEP improvement to match the system requirements.

Increase in research focus on developing lab-on-chip based devices like Body-on-chip and Organ-on-chip, have led to a higher number of functional entities in lab-on-chip. This, in turn, has led to increasingly complex microfluidic channel networks. Thus, there arises a need to characterize the microfluidic networks and establish communication among various entities of lab-on-chip. Electric circuit analogy is one of the options for the characterization of such a microfluidic network. Further, the dielectrophoresis relay-assisted molecular communication system can help in establishing interconnection among various entities using molecular communication. We propose to use an electrical transmission line technique to model and characterize the dielectrophoresis relay-assisted molecular communication system. We use transmission line parameters- resistance, inductance, and capacitance for characterizing the said molecular communication system. The numerical results obtained show that the peak concentration reduces as a function of distance, and the attenuation of the transmitted signal decreases with the increase in the number of relays in the system. This implies that the dielectrophoresis relay-assisted molecular communication system can help in transmitting low-frequency concentration signal with low attenuation. The results obtained are consistent with those obtained with already existing techniques. Thus, the transmission line technique can be utilized for characterizing a microfluidic system for molecular communication.

Molecular communications, where information is passed between the Transmitter (TX) and the Receiver (RX) via molecules is a promising area with vast potential applications. However, the infancy of the topic within the overall taxonomy of communications has meant that to date, several channel models are in press, each of which is applied under various constraints and/or assumptions. Amongst them is that the arrival of molecules in different time slots can be, or is, considered as independent events. In practice, this assumption is not accurate, as the molecules arriving in the previous slot reduce the possible number of molecules in the next slot and hence make them correlated. In this letter, we analyze a more realistic performance of a molecular communication assuming correlated events. The key result shown, is that the widely used model assuming independent events significantly overestimates the error rates in the channel. This result is thus critical to researchers who focus on energy use at the nano-scale, as the new analysis provides a more realistic prediction and therefore, less energy will be needed to attain a desired error rate, increasing system feasibility.

Molecular communication (MC) is an interdisciplinary research area with vast potential in biomedical applications, including delivery of drugs or other therapeutic molecules in cardiovascular and other pathological conditions. The bio-molecules release modeling in MC systems is an open problem in designing the physical and chemical signal interaction level in the MC hierarchy. This also includes the release of extracellular vesicles (EVs), which are shed by all cell types and serve as nano-vehicles carrying various molecular cargo. In this paper, we propose to use engineered human induced pluripotent stem cells differentiated into atrial cardiomyocytes (ACMs) in a cardiac bio-nanonetwork and mathematically model the release of therapeutic EVs under voltage clamp. We study the stochastic nature of the proposed targeted drug delivery system by modeling the release process from engineered ACMs as a Poisson process. We model the engineered ACMs as an EV emission model, where the input signal is the voltage clamp to modulate the EV release, and the output signal is the rate of released EVs. We also study the non-linearity of the proposed EV emission system by a non-linear autoregressive exogenous model. Future drug delivery applications for cardiovascular diseases can utilize the proposed EV release modeling for engineered ACMs.

Molecular Communication (MC), a new paradigm of communication, is evolving to serve almost each and every aspect of human life. Noise is one of the serious issue in MC among the fading and interference. Never the less, literatures present various noise models in MC system under different scenarios. Modified Nakagami-m distribution is among the different distribution which is validated experimentally. In this paper, however, we present a new noise distribution namely, Gamma distribution. It is noteworthy to mention that for given set of parameters Gamma distribution represent modified Nakagami-m as it's special case. Moreover, this paper deduces a relation between the PDF of Gamma and Nakagami-m distribution. In addition, derives expression for CDF of Gamma distribution. Finally, PDF of proposed noise distribution is compared with that of Nakagami-m noise distribution.

Data transmission rate in molecular communication systems can be improved by using multiple transmitters and receivers. In molecular multiple-input multiple-output (MIMO) systems which use only single type of molecules, the performance at the destination is limited by inter-symbol interference (ISI), inter-link interference (ILI) and multi-user interference (MUI). This work proposes a new hybrid modulation for a system with multiple transmitters and receivers which uses different types of molecules to eliminate ILI. Further, to enhance the data rate of the proposed system under ISI and MUI, Mary CSK modulation scheme is used between each transmitter-receiver pair. In this paper, the random locations of transmitters present in the three dimensional (3-D) space are modeled as homogeneous Poisson point process (HPPP). Using stochastic geometry tools, analytical expression is derived for the probability of symbol error for the aforementioned scenario. Finally, the performance of the proposed system is compared using the different existing modulation schemes such as on-off keying (OOK), binary concentration shift keying (BCSK) and quadruple concentration shift keying (QCSK) to develop several important insights.

In molecular communication systems operating in a crowded biochemical environment, there is the potential for unintended chemical or physical interactions with external biochemical systems. In order to avoid these interactions, or ensure coexistence , it is necessary to tailor the signaling scheme. In this paper, we propose a signaling strategy exploiting chemical reactions between different transmitted chemical species. While intuitively appealing, the non-linear nature of the governing partial differential equations (PDE) means that selecting the signaling strategy to minimize the probability of error is computationally challenging. To reduce this computational burden, we introduce a new proxy metric called the modified signal-to-interference difference ( mSID ). We show that optimizing the mSID yields low complexity and near-optimal solutions, requiring only deterministic nonlinear programming rather than standard brute force Monte Carlo methods.

Precise synchronisation of transmitters and receivers is particularly challenging in diffusive molecular communication environments. To this end, a point-to-point molecular communication system is examined wherein the design of the transceiver offers resilience to synchronisation errors. In particular, the development of a sequential probability ratio test-based detector, which allows for additional observations in the presence of uncertainty due to mis-synchronisation at the receiver, and a modulation design which is optimised for this receiver strategy, is considered. The structure of the probability of molecules hitting a receiver within a particular time slot is exploited. An approximate maximum log-likelihood estimator for the synchronisation error is derived and the Cramér-Rao bound (CRB) computed, to show that the performance of the proposed estimator is close to the CRB at low transmission rates. The proposed receiver and modulation designs achieve strongly improved asynchronous detection performance for the same data rate as a decision feedback based receiver by a factor of 3 to 5 on average.

In a diffusion-based molecular communication system, molecules are employed to convey information. When we focus on absorbing receivers, we need to consider propagation and reception processes in a framework of first passage processes. For this kind of molecular communication system, the characteristics of the channel is also affected by the shape of the transmitter. In the literature, most studies focus on systems with a point transmitter due to circular symmetry. In this letter, we address the propagation and reception patterns of chemical signals emitted from a spherical transmitter. We also investigate the directivity gain achieved by the reflecting spherical transmitter. We quantify the power gain by measuring the received power at different angles on a circular region.

The complexity of molecular communications system, involving a massive number of interacting entities, makes scalability a fundamental property of simulators and modeling tools. A typical scenario is that of targeted drug delivery systems, which makes use of biological nanomachines close to a biological target, able to release molecules in the diseased area. In this paper, we propose a simple but reliable receiver model for diffusion-based molecular communication systems tackling the time needed for analyzing such a system. The proposed model consists of using an equivalent markovian queuing model, which reproduces the aggregate behavior of thousands of receptors spread over the receiver surface. It takes into account not only the fact that the absorption of molecules can occur only through receptors, but also that absorption is not an instantaneous process and may require a significant time during which the receptor is not available to bind to other molecules. Our results, expressed in terms of number of absorbed molecules and average number of busy receptors, demonstrate that the proposed approach is in good agreement with results obtained through particle-based simulations of a large number of receptors, although the time taken for obtaining the results with the proposed model is an order of magnitudes lower than the simulation time. We believe that this model can be the precursor of novel class of models based on similar principles that allow realizing reliable simulations of much larger systems.

In a molecular communication system, molecules convey the information by traversing from the transmitter to the receiver through the medium, which is often liquid. The time for a molecule to travel a fixed distance according to Brownian motion with a constant drift has the inverse Gaussian distribution. Hence the molecular communication channel is modeled by an additive inverse Gaussian noise channel, the input of which is the release times of the molecules. This paper studies the capacity-achieving input distribution for such a channel, where the release time is subject to both peak and average constraints. Several properties of the capacity-achieving input are established. A numerical method for computing the optimal input distribution is developed. The result complements some existing bounds on the capacity of molecular channel.