Diffusion-Based Molecular Communication With Limited Molecule Production Rate

The biocompatibility and nanoscale features of Molecular Communication (MC) make this paradigm, based on molecules and chemical reactions, an enabler for communication theory applications in the healthcare at its biological level ( e.g. , bimolecular disease detection/monitoring and intelligent drug delivery). However, the adoption of MC-based innovative solutions into privacy and security-sensitive areas is opening new challenges for this research field. Despite fundamentals of information theory applied to MC have been established in the last decade, research work on security in MC systems is still limited. In contrast to previous literature focused on challenges, and potential roadmaps to secure MC, this paper presents the preliminary elements of a systematic approach to quantifying information security as it propagates through an MC link. In particular, a closed-form mathematical expression for the secrecy capacity of an MC system based on free molecule diffusion is provided. Numerical results highlight the dependence of the secrecy capacity on the average thermodynamic transmit power, the eavesdropper’s distance, the transmitted signal bandwidth, and the receiver radius. In addition, the concept of secure distance in an MC system is introduced and investigated for two different techniques of signal detection, i.e. , based on energy and amplitude. The secrecy capacity can be used to determine how much secure information (bit/sec/Hz) can be exchanged and within which operative range, while the secure distance can be used to set the transmit power to obtain a secure channel at a given distance. We envision these metrics will be of utmost importance for a future design framework tailored to MC systems and their practical applications.

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%.

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.

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, the effects of the variations in human body temperature on molecular communication systems that are diffusion-based are presented. In particular, we address this concern with respect to two functions, the molecular concentration at some displacement from the transmitter, and the information theoretic capacity of the system. Numerical results are provided to accentuate the temperature effect analysis. Results show that while concentration (which is more obvious at the peaks) decreased with increase in temperature, theoretic capacity increases with temperature at 50-450 μm for receiver radius of 5 μm.

In this paper, we consider diffusive molecular communication (MC) systems affected by signal-dependent diffusive noise, inter-symbol interference, and external noise. We design linear and nonlinear fractionally-spaced equalization schemes and a detection scheme which combines decision feedback and sequence detection (DFSD). In contrast to the symbol-rate equalization schemes in the MC literature, the proposed equalization and detection schemes exploit multiple samples of the received signal per symbol interval to achieve lower bit error rates (BERs) than existing schemes. The proposed DFSD scheme achieves a BER which is very close to that achieved by maximum likelihood sequence detection, but with lower computational complexity.

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.

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.

Inter-symbol interference (ISI) may result in substantial performance degradation in molecular communication systems. In this paper, we propose a more accurate and realistic ISI model compared to the literature, by quantifying the ISI in a three-dimensional fluid environment with a spherical receiver. Moreover, due to the propagation delay in a fluid environment, a large number of the molecules absorbed earlier in a transmission interval are due to the previous transmissions. Therefore, we find the optimal delay time, that the receiver should wait at the beginning of each time interval before counting the absorbed molecules, to reduce the effect of the ISI. Further, and to enhance the performance of the system, we adopt a detection approach based on multiple molecular observations at the receiver, and introduce a weighted sum detector, in which the transmission interval is divided into a number of sub-intervals. We analytically derive the weights, assigned to different sub-intervals, that minimize the bit error rate (BER). Simulations, based on the presented approaches, show the impact of the transmitter-receiver distance, the reaction rate, and the diffusion constant of the environment on the BER performance. We also show that using a weighted sum detector significantly improves the BER performance.

This paper studies the capacity of molecular communications in fluid media,\nwhere the information is encoded in the number of transmitted molecules in a\ntime-slot (amplitude shift keying). The propagation of molecules is governed by\nrandom Brownian motion and the communication is in general subject to\ninter-symbol interference (ISI). We first consider the case where ISI is\nnegligible and analyze the capacity and the capacity per unit cost of the\nresulting discrete memoryless molecular channel and the effect of possible\npractical constraints, such as limitations on peak and/or average number of\ntransmitted molecules per transmission. In the case with a constrained peak\nmolecular emission, we show that as the time-slot duration increases, the input\ndistribution achieving the capacity per channel use transitions from binary\ninputs to a discrete uniform distribution. In this paper, we also analyze the\nimpact of ISI. Crucially, we account for the correlation that ISI induces\nbetween channel output symbols. We derive an upper bound and two lower bounds\non the capacity in this setting. Using the input distribution obtained by an\nextended Blahut-Arimoto algorithm, we maximize the lower bounds. Our results\nshow that, over a wide range of parameter values, the bounds are close.\n

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 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.

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.