Mobile Molecular Communication System Research Articles

Detection and ISI mitigation in mobile molecular communication system for targeted drug delivery

This paper proposes a targeted drug delivery system based on mobile molecular communication (MMC). The system consists of a mobile transmitter and a mobile reactive receiver. The transmitter can sense the required drug concentration and send commands to the receiver for drug delivery in the extracellular fluid (ECF). The commands are sent in the form of bits and the received signal is prone to noise and inter-symbol interference (ISI). Hence, at the receiver, two detection techniques, differential amplitude detector (DAD) and differential energy detector (DED) with ISI mitigation are proposed for MMC. Manchester-coded bits are transmitted using modified concentration shift keying (MCSK). In the proposed detection mechanism, an adaptive threshold technique is used for estimating the number of signaling molecules using the maximum a posteriori probability (MAP) rule. Further in each bit interval, dynamic distance estimation, signal reconstruction, and ISI mitigation are performed. Particle-based simulation for reactive receiver is also carried out to validate the results. A low bit error rate (BER) in the MMC system signifies the promising performance of the drug delivery system.

Evaluation of Non-Coherent Signal Detection Techniques for Mobile Molecular Communication.

In recent years, there have been more and more research on molecular communication (MC). Because the deployment of mobile nanomachines may be required in some applications of MC, research on mobile MC has become a trend. The signal detection schemes for static MC are no longer applicable due to the time varying channel impulse response (IR), which is caused by the mobile characteristics of nanomachines. In this paper, a low complexity and non-coherent detection scheme is proposed for mobile scenario, which is based on the energy difference between two adjacent symbols. Most of the existing signal detection methods do not consider inter-symbol interference (ISI). Compared with those methods, the proposed scheme can achieve signal detection utilizing ISI without knowing channel state information (CSI). The bit error rate (BER) performance of the proposed method is investigated under different conditions through simulations. Besides, the influence of mobility features of nanomachines on the signal detection accuracy is also investigated in detail. The simulation results demonstrate that the BER performance of the proposed scheme outperforms the latest signal detection scheme for short-distance mobile MC system with high velocity. Consequently, the detection scheme proposed in this paper can reduce the influence of nanomachines' mobility and has the potential to be used in mobile MC systems.

Rescaled Brownian Motion of Molecules and Devices in Three-Dimensional Multiuser Mobile Molecular Communication Systems

This paper considers a three-dimensional anomalous-diffusive mobile molecular communication (MC) channel. Herein, the communicating devices, i.e., point transmitter (Tx) and passive receiver (Rx) can also move anomalously with the information-carrying molecule (ICM). In order to incorporate the anomalous diffusion phenomenon, the concept of rescaled-Brownian motion is explored. Two different scenarios, named point-to-point and multi-user MC systems, are considered for the analysis. First, considering the point-to-point scenario, the expressions for the channel impulse response (CIR) incorporating static and mobile Tx and Rx are derived. Further, the expressions for the peak time of CIR and the corresponding peak value are also derived. Furthermore, the point-to-point MC system is exploited in terms of bit-error-rate (BER), minimum BER, maximum mutual information, and throughput. A multi-user MC system is considered in the second scenario, and a molecular division multiple access (MDMA) method is used. The system is analyzed in terms of BER and throughput. Further, the system performance is optimized using two schemes known as min-max fairness for error probability and max-min fairness for throughput. Furthermore, we use best-to-best and best-to-worst assignment strategies to allocate different types of ICMs for each Rx. Subsequently, the optimal allocation for the number of ICMs is obtained when specific ICMs are assigned to all users/receivers for a two-user scenario. All the channel metrics are verified through particle-based and Monte-Carlo simulations.

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.

Analysis and classification of the mobile molecular communication systems with deep learning

Analysis and classification of the mobile molecular communication systems with deep learning

Membrane Fusion-Based Transmitter Design for Static and Diffusive Mobile Molecular Communication Systems

This paper proposes a novel imperfect transmitter (TX) model, namely the membrane fusion (MF)-based TX, that adopts MF between a vesicle and the TX membrane to release molecules encapsulated within the vesicle. For the MF-based TX, the molecule release probability and the fraction of molecules released from the TX membrane are derived. Incorporating molecular degradation and a fully-absorbing receiver (RX), the channel impulse response (CIR) is derived for two scenarios: 1) Both TX and RX are static, and 2) both TX and RX are diffusion-based mobile. Moreover, a sequence of bits transmitted from the TX to the RX is considered. The average bit error rate (BER) is obtained for both scenarios, wherein the probability mass function (PMF) of the number of molecules absorbed in the mobile scenario is derived. Furthermore, a simulation framework is proposed for the MF-based TX, based on which the derived analytical expressions are validated. Simulation results show that a low MF probability or low vesicle mobility slows the release of molecules and reduces the molecule hitting probability at the RX. Simulation results also indicate the difference between the MF-based TX and an ideal point TX in terms of the inter-symbol interference (ISI).

Modulation and Signal Detection for Diffusive-Drift Molecular Communication with a Mobile Receiver

Molecular communication (MC), which allows nanomachines to communicate with each other by using chemical molecules, is considered to be a promising method for communications in liquid environment. Available works on MC mainly focus on modulation and signal detection schemes for MC systems with fixed nanomachines, i.e., fixed molecular communication (FMC) systems. However, the more complex systems with mobile nanomachines (i.e., mobile molecular communication (MMC) systems) have been largely unexplored. This paper considers a MMC system with a fixed transmitter and a mobile receiver communicating over diffusive-drift channels of a limited boundary. We first propose a new modulation scheme to address the issue of misalignment in the signal detection of MMC systems by adopting three types of molecules in the signal modulation and modulating the transmitted signals into blocks with equal length to avoid the transferring of a signal error in the current block on the signal detection in other blocks. We then propose a new signal detection scheme of the MMC systems by calculating the distance between the transmitter and the receiver based on a distance prediction method and detecting signals at the receiver based on the decided adaptive concentration threshold in each time interval. To verify the efficiency of our proposed scheme, we then conducted extensive simulations by the Monte Carlo simulation, and comparisons are also made among our proposed schemes, a well-known fixed threshold signal detection scheme, the CATD scheme, the PAD scheme, and a low complexity signal detection scheme for MMC systems in terms of the BER (bit error rate). Results show that our proposed schemes can outperform these schemes regarding the BER.

Clock Synchronization for Mobile Molecular Communication Systems.

Molecular communication (MC) is a promising paradigm, which conveys messages at the nano- or micro- scale for information exchange by using molecules or particles as signal carriers. Clock synchronization between transmitters and receivers in MC systems plays an important role in information exchange and nanodevices' collaboration. The current research about the synchronization mainly focuses on fixed MC systems. However, the movements of transmitters and receivers commonly exist in MC systems. In this paper, two clock synchronization schemes, the least square method and the peak time method, are proposed to estimate the clock offset between a mobile transmitter and a mobile receiver in mobile MC systems. The synthesis time of information molecules is also taken into consideration in the proposed schemes, and by using different types of molecules, the influence of the synthesis time of molecules can be solved. The effects of the movement of receiver on the received signal are discussed. The performance of the proposed schemes is evaluated by simulations and discussed.

Initial Distance Estimation and Signal Detection for Diffusive Mobile Molecular Communication.

Mobile molecular communication (MC) attracts much attention in recent years where mobile nanomachines exchange information using molecules. In this paper, we consider a diffusion-based mobile MC system consisting of a pair of diffusive nanomachines. Due to the Brownian motion of nanomachines, the communication distance between the transmitter and the receiver is dynamic. Thus, the channel impulse response (CIR) is a stochastic process. The stochastic CIR brings the difficulty in the detection process. Contrast to the common static MC characterized by the deterministic CIR, in a mobile MC system, the receiver needs to estimate the dynamic distance for CIR reconstruction and detection threshold setting at each bit interval, which achieve high computational complexity. To tackle these difficulties, a new detection technique for mobile MC is proposed in this paper. It is unnecessary to estimate the dynamic communication distance at each bit interval. Instead, the receiver estimates the initial distance between it and the transmitter. The estimated initial distance can be used to reconstruct the statistical characteristics of CIR, setting detection threshold for all the bit intervals in advance. To achieve this goal, a novel two-step scheme based on maximum likelihood (ML) is proposed to estimate the initial distance. In the first step, the transmitter releases some molecules as a pilot signal before the information bits transmission. Then the receiver estimates releasing distance by observations of received signal. In the second step, the estimated value obtained in the previous step is used to estimate the initial distance by ML estimation. The performances of proposed two-step scheme and the detection technique are evaluated via particle-based simulation of the Brownian motion.

Low-Complexity Adaptive Signal Detection for Mobile Molecular Communication.

Currently, most of the researches in molecular communication (MC) domain focus on the static MC scenarios. However, some envisioned important MC applications require mobile MC system. The investigation on mobile MC, especially the signal detection of mobile MC is limited. This work considers the problem of signal detection for mobile MC scenarios where the receiver nano-machine performs random movement. Due to the random movement of the receiver, the channel impulse response (CIR) changes over time which makes the received signal stochastic and complicated. This further complicates the signal detection in mobile MC and leads to that the state-of-the-art signal detection schemes for static MC scenarios fail for the mobile MC scenarios. To solve this issue, an adaptive detection scheme has been proposed by our group previously, based on dynamic estimation of the stochastically varying distance between the transmitter and receiver and the reconstruction of CIR in each interval. However, its computational complexity is high. Limited capability of current nano-machines desire low-complexity detection algorithm. In this work, we further propose an adaptive detection scheme for mobile MC with a low computational complexity by utilizing the local convex property of the CIR. With on-off keying (OOK) modulation, the signal of symbol "1" presents local convex property while that of symbol "0" presents local concave property. The convexity extent varies with the stochastic distance. A simple indicator, local maximum convexity is proposed which adapts to the stochastic distance. By comparing the adaptive indicator with an adaptive threshold within each symbol interval, the signal is detected without the need to estimate the stochastically changing distance or to reconstruct the CIR. Therefore, the computational load is effectively reduced. Numerical simulations are performed to evaluate the proposed scheme. The results show that the proposed scheme achieves good detection accuracy with low computational complexity and it could be a promising detection scheme for mobile MC scenarios.

Channel Characterization for Devices in a Turbulent Diffusive Environment: A Mobile Molecular Communication Approach

Mobile molecular communication among nano-devices has potential applications in diverse fields such as targeted drug delivery systems, designing and deploying nano-sensors and nano-actuators for detection, treatment of a large set of diseases, and monitoring of environmental conditions. In this paper, we consider a mobile molecular communication system where the fluid medium has a fully developed homogeneous turbulence, and both the transmit and the receive nano-devices are mobile. The considered molecular communication system uses information molecules to transmit information from a transmit nano-device to a receive nano-device. To fully characterize and describe this mobile molecular communication channel, we derive its statistical properties like mean, correlation function, and distribution functions. We then analyze the performance of the system in terms of its symbol error probability and channel capacity. Numerical results corroborate the derived analytical findings.

Diffusive Mobile MC With Absorbing Receivers: Stochastic Analysis and Applications

This paper presents a stochastic analysis of the time-variant channel impulse response (CIR) of a three dimensional diffusive mobile molecular communication (MC) system where the transmitter, the absorbing receiver, and the molecules can freely diffuse. In our analysis, we derive the mean, variance, probability density function (PDF), and cumulative distribution function (CDF) of the CIR. We also derive the PDF and CDF of the probability ${p}$ that a released molecule is absorbed at the receiver during a given time period. The obtained analytical results are employed for the design of drug delivery and MC systems with imperfect channel state information. For the first application, we exploit the mean and variance of the CIR to optimize a controlled-release drug delivery system employing a mobile drug carrier. We evaluate the performance of the proposed release design based on the PDF and CDF of the CIR. We demonstrate significant savings in the amount of released drugs compared to a constant-release scheme and reveal the necessity of accounting for the drug-carrier’s mobility to ensure reliable drug delivery. For the second application, we exploit the PDF of the distance between the mobile transceivers and the CDF of ${p}$ to optimize three design parameters of an MC system employing on-off keying modulation and threshold detection. Specifically, we optimize the detection threshold at the receiver, the release profile at the transmitter, and the time duration of a bit frame. We show that the proposed optimal designs can significantly improve the system performance in terms of the bit error rate and the efficiency of molecule usage.

Cluster Formation by Mobile Molecular Communication Systems

This paper considers mobile molecular communication systems where mobile bio-nanomachines release signaling molecules to form a cluster of bio-nanomachines. This paper examines how the sensitivity of bio-nanomachines to detect signaling molecules impacts on cluster formation. When the sensitivity is high, each bio-nanomachine reacts to signaling molecules that it releases. When the sensitivity is low, a bio-nanomachine reacts to signaling molecules only when a group of bio-nanomachines collectively releases signaling molecules. We extend a rotational diffusion model to describe the mobility of bio-nanomachines by considering the sensitivity of bio-nanomachines to detect signaling molecules. We also develop measures to characterize formed clusters. Simulation experiment results are shown to demonstrate how the sensitivity of bio-nanomachine to detect signaling molecules impacts the number of clusters formed, the mean cluster size, the mean cluster diameter, and the mean nearest neighbor distance between clusters.

Optimal Transmitted Molecules and Decision Threshold for Drift-Induced Diffusive Molecular Channel With Mobile Nanomachines.

We study a drift-induced diffusive mobile molecular communication system where source, destination and cooperative nanomachines follow the one-dimensional Brownian motion. For information exchange from source nanomachine to receiver nanomachine, both direct and decode-forward (DF) relay-assisted cooperative paths are considered. The closed-form expressions for the probabilities of detection and false alarm are derived at the cooperative and destination nanomachines considering the multiple-source interference (MSI) and the inter-symbol-interference (ISI). The closed-form expressions for end-to-end average probability of error, and maximum achievable rate are also obtained. Moreover, to achieve minimum expected probability of error the optimum number of molecules to be transmitted from transmitter and optimal detection threshold in receiver nanomachine are found. The analytical expressions are validated through particle-based and Monte-Carlo simulation methods.

Statistical Analysis of Received Signal and Error Performance for Mobile Molecular Communication.

Molecular communication (MC) is a promising paradigm for conveying information in nanonetworks, where small particles like molecules are the carriers of information. In this paper, we investigate a special communication scenario, where the MC system consists of a pair of mobile transmitter and receiver nanomachines. Both of them move randomly in a free diffusion manner. Due to the randomness generated by the motion of nanomachines and particle counting noise, the received signal at the receiver nanomachine, i.e., the number of molecules within the volume of the receiver, is a stochastic process on observing time. The statistical analysis of the received signal is provided. The closed-form expressions of the mean and variance of the received signal are derived by considering two kinds of randomness mentioned above. Besides, the distribution of the received signal is investigated. The probability mass function (PMF) of the received signal is given by generalized Gauss-Laguerre quadrature, a numerical analysis method. Furthermore, to obtain the closed-form expression of the PMF of the received signal, we prove that under certain conditions, the received signal follows a Poisson-lognormal distribution and can be approximated by a Poisson distribution. Another interest in this paper is the error performance of the mobile MC systems. Considering the effect of inter-symbol interference (ISI) and noise on detection process, an analytical expression for the probability of error of a simple detector is derived by Gaussian approximation. The accuracy of the proposed analytical expressions and distributions is validated via particle-based simulations.

Mutual Information and Maximum Achievable Rate for Mobile Molecular Communication Systems.

Molecular communication (MC) enables conveying information at nano- to micro-scales via molecules or nanoscale particles. MC systems for fixed transmitter and receiver nanomachines have been extensively investigated. However, the scenarios for mobile MC are seldomly studied. In the paper, the mutual information and achievable rate in the presence of inter-symbol interference and noise for the mobile MC is investigated. The scenario that both the transmitter and the receiver are in independent random motions is considered. Due to the mobility, the channel impulse response varies and results in a varying received signal with varying signal-dependent noise. This further leads to the random variation of the probability density functions of received concentration for symbols which further generates varying error probability and therefore varying mutual information and maximum achievable rate. In this paper, the mutual information and maximum achievable rate for mobile MC scenario are derived and analyzed. The impacts of different parameters, such as the initial transmitter-receiver distance, the number of released molecules, symbol interval, the mobility of nanomachine, and priori probabilities of the transmitted symbol on the mutual information and maximum achievable rate in mobile MC scenario are studied by simulation investigations.

Graph-Based Modeling of Mobile Molecular Communication Systems

This letter develops a graph-based model of mobile molecular communication systems to study the spatio-temporal dynamics of bio-nanomachine concentration in a complex environment, such as the human circulatory system. We first consider the steady-state problem under the assumption that background flows are absent, and show that, at steady-state, bio-nanomachines on a graph distribute according to the target distribution. We then examine through numerical experiments the evolution of bio-nanomachine concentration on a graph in the presence of background flows. The graph-based model developed in this letter is useful to examine optimal conditions, under which drug-carrying bio-nanomachines distribute at target locations in a circulatory system.