Diffusive Molecular Communication Research Articles

Diffusive molecular communication for bacterium propagation over human gut track

Diffusive molecular communication for bacterium propagation over human gut track

On Secrecy Performance in D-MoSK-Based 3-D Diffusive Molecular Communication System.

This paper studies the secrecy performance in a 3-D diffusive molecular communication system with the general depleted molecule shift keying (D-MoSK) modulation, where a point transmitter Alice transmits through diffusion multiple types of molecules modulation to a legitimate absorbing receiver Bob, suffering the eavesdropping from an absorbing eavesdropper Eve. We first develop a solid theoretical framework to determine the probabilistic distributions for the number of molecules absorbed by Bob and Eve, respectively. Based on the results, we then derive the average symbol error rate (SER) as well as the mutual information of Alice-Bob and Alice-Eve, and further apply the Shannon theory to determine the secrecy capacity of Alice-Bob transmission. We also develop the closed-form results for the optimal detection threshold at Bob to achieve the secrecy capacity, and thus devise a complete algorithm for secrecy capacity maximization. Finally, we provide numerical results to illustrate the secrecy performance in the concerned system.

Heuristic Barycenter Modeling of Fully Absorbing Receivers in Diffusive Molecular Communication Channels

Heuristic Barycenter Modeling of Fully Absorbing Receivers in Diffusive Molecular Communication Channels

Adaptive multi-layer reward based Q-learning for source tracing in diffusive molecular communications environment with obstacles

Benefiting by the fast development of nanotechnology, molecular communication (MC) has received great attention in recent years. In many potential applications of MC, such as drug delivery and pollution prevention, it is essential to locate or trace the target. In this paper, we consider a 3D diffusive MC environment consisting of several obstacles, a molecule-releasing source (RS) and a mobile molecule sensor (MS) which aims to find the RS within a time constraint. The problem is reformulated using Markov Decision Process (MDP) and an adaptive multi-layer reward based Q-Learning (AMR-Q Learning) approach is proposed. By exploiting information from the number of received molecules and adaptively setting multi-layer rewards, MS with AMR-Q Learning can find the RS efficiently, unlike the gradient based method which is usually trapped in locally optimal points. Numerical results demonstrate that the proposed AMR-Q Learning approach outperforms existing path-planning schemes with significantly reduced training overhead.

Channel modeling and achievable data rate for 1-D molecular communication in bounded environments

In this paper, we propose the analytical propagation model for diffusive molecular communication in an one-dimensional bounded environment, and determine the available data rate for a given limit of interference. Molecular communication is a promising solution for applications when the typical electromagnetic communication is not available. However, due to the randomness of the molecule movement, it is challenging to analyze the channel in molecular communication. Taking into account the impact of an absorbing boundary to the one-dimensional vessel-like channel, we model the time-varying distribution of the releasing molecules. Accordingly, we derive the hitting probabilities for an information molecule to separately reach the receiver or the boundary, and present the impulse response of the channel at a given time t. Moreover, under the same environment, we consider the time duration between transmissions of a binary modulation system for a given level of inter-symbol interference. Our analysis shows that, for a certain degree of interference, the available data rate of the system can be expressed as 2Dαth2S2, where S is the distance between the receiver and the boundary, and D is the diffusion coefficient of the channel, and αth2 is the corresponding index to the interference degree. The authenticity of our analysis are verified via simulations.

Channel Characteristics for Diffusive Molecular Communications in a Spherical Shell

Diffusive molecular communication (DMC) is a bio-mimicking communications paradigm that exploits the Brownian motion of dedicated information carrying molecules for signal transmission. The characteristics of the communication channel in a DMC system heavily depends on the transmitter and receiver mechanisms, on the medium of propagation and its boundaries, and on the way they interact with the molecules. In this work, we investigate the DMC channel in a spherical shell, with inner and outer surfaces which may be partially or perfectly absorptive, or reflective, where either of the boundary surfaces can be considered as the DMC receiver. These geometry and boundary conditions can be used to model a variety of practically relevant scenarios, which are investigated in detail. We derive the general parametric solution of the partial differential equation for this case and provide, for the first time in the literature, expressions for the resulting channel response. We verify the results of our analysis numerically via particle based simulations.

Localizing the Unknown Receiver in a Diffusive SIMO Molecular Communication System

This letter introduces a method to estimate the position of an unknown fully absorbing (FA) spherical receiver in a diffusive molecular communication (MC) system. This latter consists of a point transmitter and multiple FA spherical receivers in a three-dimensional space. The method relies on a temporal asymptotic single-input multiple-output (SIMO) channel model for diffusive MC systems that takes into account the interaction among receivers. By relying on the asymptotic model, a grid-based likelihood function is a priori created from each known receiver’s perspective. The likelihood function’s computation requires information about the number of molecules released by the transmitter, its position, and the position of known receivers. From the cumulative number of molecules absorbed by the known FA receivers, different likelihood maps are obtained, where each map corresponds to the likelihood of the position of unknown receiver from a specific known receiver’s perspective. By combining the receivers’ likelihood maps, which is equivalent to cooperation by sharing their knowledge, the position of the unknown receiver is estimated. The quality of the estimation is evaluated in terms of root mean squared error (RMSE) between the estimated position of the unknown receiver and its true position for different number of released molecules.

Joint localization and channel estimation in flow-assisted molecular communication systems

In this paper, we present a joint localization and channel parameter estimation method in the presence of signal-dependent noise and inter-symbol interference for diffusive molecular communication systems. The joint parameter estimation of the nanomachine can provide reliable communication in a generic diffusive molecular communication system. In particular, an iterative maximum likelihood estimation (MLE) approach for jointly estimating locations, flow velocity, and diffusion coefficient is carried out. The Cramer–Rao lower bound on the variance of channel parameters and location is derived. The normalized estimation error is marginally higher for unknown parameters case than that of some known parameters. The individual result (location estimation or channel parameters estimation) outperforms the existing methods.

Ambient Environmental Parameter Estimation for Reliable Diffusive Molecular Communications

Molecular communication is a promising communication technology that uses biomolecules such as proteins and ions to establish a communication link between nanoscale devices. In diffusive molecular communication, which uses diffusion characteristics of transfer molecules, the diffusion mechanism is mathematically derived as a Channel Impulse Response (CIR) to design an optimal detector structure. However, an ideal environment is assumed for deriving a CIR. Hence there is a concern that developed systems based on the derived CIR may not operate well in a realistic environment. In this study, based on the finite element method (FEM), we constructed a model of the environment with heterogeneous temperature distribution and actual volume of transmitting molecules to not only demodulate the bit information via maximum likelihood sequence estimation (MLSE) but also to estimate the temperature and volume of the transmitting molecules. Furthermore, in this study, we evaluated the performance of the MLSE method and investigated the effects of ambient environmental temperature distribution and volume of the transmitted molecules on diffusive molecular communication. The evaluation results demonstrated that the proposed method can improve the communication performance by approximately 9 dB by estimating the temperature and transmit molecule volume.

Asymptotic MIMO Channel Model for Diffusive MC With Fully-Absorbing Receivers

This letter introduces an analytical model that gives the expected asymptotic cumulative number of molecules absorbed by each spherical receiver in a diffusive multiple-input multiple-output (MIMO) molecular communication (MC) system with pointwise transmitters. The reciprocal effect among the fully absorbing (FA) receivers is taken into account by using the recently introduced concept of fictitious pointwise negative source of molecules. An agreement is shown between the proposed asymptotic model and the numerical solution of the exact analytical one from the literature describing the interaction among the receivers, which is computed for a sufficient long time.

Joint Optimizations of Relays Locations and Decision Threshold for Multi-Hop Diffusive Mobile Molecular Communication With Drift.

In this paper, we study diffusive multi-hop mobile molecular communication (MMC) with drift in one-dimensional channel by adopting amplify-and-forward (AF) relay strategy. Multiple and single molecules type are used in each hop to transmit information, respectively. Under these two cases, the mathematical expressions of average bit error probability (BEP) of this system based on AF scheme are derived. We implement joint optimization problem whose objective is to minimize the average BEP with (Q + 2) optimization variables including (Q + 1) -hop distance ratios and decision threshold. Q is the number of relay nodes. Furthermore, considering that more optimization variables result in higher computation complexity, we use efficient algorithm which is adaptive genetic algorithm (AGA) to solve the optimization problems to search the location of each relay node and the decision threshold at destination node simultaneously. Finally, the numerical results reveal that AGA has a faster convergence speed and it is more efficient with fewer iterations compared with Bisection algorithm. The performances of average BEP with optimal distance ratio of each hop and decision threshold are evaluated. These results can be used to design multi-hop MMC system with optimal optimization variables and lower average BEP.

An Analytical Propagation Model for Diffusion-Based Molecular Communication Systems

A novel analytical propagation model for diffusive molecular communication systems in a three-dimensional fluid environment is derived. The model takes into account the geometry of a spherical receiver, the inclination angle, and the reaction rate of the receiver to accurately model the time-varying distribution and the number of absorbed information molecules at the receiver over a period of time. Accordingly, we derive an expression for the net number of accumulatively-absorbed information molecules at the surface of the receiver. We also study the bit error rate (BER) performance of diffusion-based molecular communications in the presence of the inter-symbol interference. Simulations based on the developed model show the impact of the transmitter-receiver distance, the reaction rate at the surface of the receiver and the diffusion constant of the environment on the fraction of absorbed molecules and the BER performance. A particle-based simulator is implemented to verify the accuracy of the proposed model. Moreover, our results are compared with that of a conventional model, where the geometry of the receiver and the inclination angle are ignored. It is shown that, especially at small transmitter-receiver separation distances, the proposed model predicts a significantly smaller number of absorbed molecules compared to the conventional models.

Molecule Harvesting Transmitter Model for Molecular Communication Systems

This paper develops mathematical models for molecule harvesting transmitters in diffusive molecular communication (MC) systems. In particular, we consider a communication link consisting of a spherical transmitter nano-machine and a spherical receiver nano-machine suspended in a fluid environment. The transmitter and the receiver exchange information via signaling molecules. The transmitter is equipped with molecule harvesting units on its surface. Signaling molecules which come into contact with the harvesting units may be re-captured by the transmitter. For this system, we derive closed-form expressions for the channel impulse response and harvesting impulse response. Furthermore, we extend the harvesting transmitter model to the case of continuous signaling molecule release. In particular, we derive closed-form expressions for the average received signal at the receiver and the average harvested signal at the transmitter for different temporal release rates namely, constant, linearly increasing, and linearly decreasing release rates. Finally, we validate the accuracy of the derived mathematical expressions via particle-based simulations.

Secrecy Capacity of Diffusive Molecular Communication Under Different Deployments

Currently, the physical layer security is considered as one of the most suitable security techniques in Diffusive Molecular Communication (DMC) because of ease to implement. A recent piece of literature has presented the Secrecy Capacity (SC) of DMC system under the rectangular deployment. To evaluate the information capacity (IC) and thereby SC using the Concentration Greens Function (CGF) in the molecular communication depends on the biological structures of tissues. In this paper, we have investigated the analytical expressions of IC under both the Biological Cylindrical Deployment (BCD) and Biological Spherical Deployment (BSD). Therefore, the analytical expressions of IC have been employed to derive the mathematical expressions of SC under the BCD and BSD environment. Further, the SC is analyzed as a function of distance/radius considering the power and/or bandwidth as the parameter. In addition, the effect of distance of authentic receiver on SC is also explored. It is observed that irrespective of the deployments, the distance of the authentic receiver illustrates predominant effect on the value of SC. The proposed analysis is useful in the implementation of DMC under different tissues structures. The numerically simulated results show close agreement with the theoretical background.

Equal-gain combining with interference mitigation for molecular type hopping assisted molecular shift keying systems

In multiple access molecular diffusive communications, many nano-machines exchange information and fuse data through a common Diffusive Molecular Communication (DMC) channel. Hence, there is Multiple-Access Interference (MAI), which should be sufficiently mitigated so as to achieve reliable communications. In this paper, we propose a novel low-complexity detection scheme, namely Equal-Gain Combining with Interference Mitigation (EGC-IM), for signal detection in the Molecular Type Hopping assisted Molecular Shift Keying (MTH-MoSK) DMC systems. By removing a number of entries from each row of the detection matrix formed during detection, the EGC-IM scheme shows its potential to significantly mitigate MAI and hence, outperform the conventional EGC scheme. Furthermore, the EGC-IM scheme has lower complexity than the conventional EGC scheme and therefore, it is beneficial for practical implementation.

Layered Molecular Shift Keying for Molecular Communication via Diffusion

Molecular communication (MC) is a promising communication paradigm for realizing nano-networks, where molecules are employed as an information carrier. In this letter, based on diffusive MC we propose a novel modulation scheme, called layered molecular shift keying (LMoSK), where several types of molecule form different layers to encode information bits, which can not only improve the data rate but also reduce the effect of inter-symbol interference (ISI). For detection of LMoSK, we formulate an ideal maximum likelihood (ML) receiver assuming knowledge of the ISI. Considering the limited capability of the receiver, we further propose a practical ML detection, enjoying both reduced computational complexity and memory of the receiver. The error performance of the LMoSK with practical ML receiver is analyzed and compared with that of molecular shift keying modulation and molecular type permutation shift keying modulation. Simulation results demonstrate that the proposed LMoSK outperforms benchmark schemes.

A Novel Method to Improve Performance of Diffusive Molecular Communication Systems with On-Off Keying Modulation

The Bit Error Rate (BER) of the diffusive molecular communication (DMC) systems employing on-off keying (OOK) modulation. We also analyze the BER of the OOK-modulated DMC systems with inter- symbol interference cancellation (ISIC). Our main motivation is to introduce alternative tools for analyzing and efficiently computing the BER of the DMC systems without or with ISIC. Specifically, for the OOK-modulated DMC systems without ISIC, we first derive an exact BER expression based on the Poisson modeling of DMC systems. Then, the Gaussian- and Gamma-approximation approaches are introduced to approximate the discrete Poisson distribution, and based on the approximation approaches, the corresponding BER expressions are derived.

3-D Diffusive Molecular Communication With Two Fully-Absorbing Receivers: Hitting Probability and Performance Analysis

Exact analytical channel models for molecular communication via diffusion (MCvD) systems involving multiple fully absorbing receivers (FARs) in a three-dimensional (3-D) medium are hard to obtain due to the mathematical intractability of corresponding diffusion equations. Therefore, this work considers an MCvD system with two spherical FARs in a 3-D diffusion-limited medium and develop several insights using an approximate analytical expression for the hitting probability of information molecule (IM). Further, based on the hitting probability, a novel approximate closed-form analytical expression for the area under the receiver operating characteristic curve (AUC) is derived to analyze the detection performance at each FAR in the presence of other FAR. Finally, simulation results are presented to validate the analytical results using the particle-based and Monte-Carlo simulations and to yield important insights into the MCvD system performance with two FARs.

Fractionally Spaced Equalization and Decision Feedback Sequence Detection for Diffusive MC

In this letter, 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.

Generalized Molecular-Shift Keying (GMoSK): Principles and Performance Analysis

A generalized molecular-shift keying (GMoSK) modulation scheme is proposed for supporting diffusive molecular communication (DMC). Instead of activating one type of molecules in the traditional molecule shift keying (MoSK) modulation, GMoSK simultaneously activates several types of molecules, with the objective to increase data rate and the potential to further mitigate inter-symbol interference (ISI) beyond MoSK. For signal detection in the GMoSK-modulated DMC (GMoSK-DMC) systems, we first derive a symbol-based idealized maximum likelihood (IML) detector, from which we then deduce two practical detection schemes, namely, the zero-level decision feedback maximum likelihood (ZDF/ML) detector and the one-level decision feedback maximum likelihood (1DF/ML) detector. The error performance of the GMoSK-DMC systems with the IML- and ZDF/ML-detectors is mathematically analyzed. Furthermore, the error performance of the GMoSK-DMC systems with our proposed detection schemes is investigated and compared, which is also compared with that of the DMC systems employing the legacy MoSK modulation, the binary concentration shift keying (BCSK) modulation, the depleted MoSK (D-MoSK) modulation, and the Molecule-as-a-Frame (MaaF) modulation. Our studies and performance results demonstrate that GMoSK has the potential to achieve the performance beyond the above four modulation schemes, and employs the merit of high-flexibility for attaining relatively high data rate and also for ISI mitigation.