Molecular Communication Via Diffusion Research Articles

Influence of Red Blood Cells on Channel Characterization in Cylindrical Vasculature.

Molecular communication via diffusion (MCvD) expects Brownian motions of the information molecules to transmit information. However, the signal propagation largely depends on the geometric characteristics of the assumed flow model, i.e., the characteristics of the environment, design, and position of the transmitter and receiver, respectively. These characteristics are assumed to be lucid in many ways by either consideration of one-dimensional diffusion, unbounded environment, or constant drift. In reality, diffusion often occurs in blood-vessel-like channels. To this aim, we try to study the effect of the biological environment on channel performance. The Red-Blood Cells (RBCs) found in blood vessels enforces a higher concentration of molecules towards the vessel walls, leading to better reception. Therefore, in this paper we derive an analytical expression of Channel Impulse Response (CIR) for a dispersion-advection-based regime, contemplating the influence of RBCs in the model and considering a point source transmitter and a realistic design of the receiver.

Efficient Nanosystem for Nanomedicine Applications Based on Molecular Communications

The authors propose an efficient nanosystem based on molecular communication technology. Molecular communication via diffusion (MCvD) is a promising trend for exchanging biochemical signals between a nanotransmitter (NT) and a nanoreceiver (NR) in aqueous media over short distances. Nanosystem-based MCvD has recently received a lot of attention in advanced targeted nanomedicine applications such as targeted drug delivery and healthcare monitoring (disease/diagnosis/analysis). However, the random nature of molecular diffusion causes counting noise, which significantly degrades the performance of the nanosystem-based molecular communication. In this paper, a reliable and simple denoising technique, namely Savitzky–Golay (SG) filter, is developed in the nanosystem-based MCvD to provide high accuracy of molecular information reception. The performance of the proposed nanosystem is evaluated in terms of bit error rate (BER) and correlation efficiency. The results reveal that the nanosystem-based MCvD using the proposed SG filter outperforms the MCvD using current denoising techniques such as moving average filter, wavelet denoising and I-filter. Actually, it was found that the SG filter increases the gain efficiency in terms of the correlation coefficient by more than 60% in comparison to the I-filter at low and high signal-to-noise ratios (SNRs), whereas in comparison to wavelet denoising, the SG filter achieves more than 10% enhancement in gain efficiency at low SNRs.

Performance analysis of nanosystem based on cooperative relay for nanonetworks

<abstract> <p>Recent nanomedical applications, particularly targeted drug delivery system (TDDS) scenarios, have made use of molecular communications via diffusion (MCvD) based on nanosystems. In order to improve the performance of such nanosystems, nanonetworks-based molecular communication is investigated. Employing a nanorelay approach and cooperative molecular communications, we provide a method for optimizing the performance of the nanosystem while taking blood flow effects into consideration in terms of drift velocity. Unlike the earlier studies, the position of the nanorelay and the allocated amount of molecular drugs will be optimized. We provide closed-form expressions for molecular channel capacity and the error probability of a molecular frame. According to the simulation results, it is possible to significantly reduce error probability of a molecular frame and thus increase channel capacity by optimizing the drift velocity, detection threshold and the location of the nanorelay within the proposed nanosystem.</p> </abstract>

Optimization of Decision Thresholds in Two-Way Molecular Communication via Diffusion With Network Coding

In this paper, we investigate a two-way molecular communication via diffusion (MCvD) system, which consists of two source nanomachines and one relay nanomachine in three-dimensional channel. The combinations of decode-and-forward (DF) relaying protocol and network coding (NC) scheme are implemented by using same number of molecules (SNM) and different number of molecules (DNM) which are released by source nanomachines. First, both the effects of actual and estimated inter-symbol interference (ISI) sequences are taken into account under SNM and DNM. Then the mathematical expression of the average probability of error for this two-way MCvD system are derived by using the Genie-aided detector and the detector which estimates the ISI sequence. Furthermore, we use particle swarm optimization (PSO) algorithm to solve the optimization problem whose objective is to minimize the average probability of error to search decision threshold at each nanomachine simultaneously. Finally, the numerical results show the DF and NC scheme outperforms the DF-No-NC scheme which is without NC. Moreover, PSO algorithm has good convergence behaviors and it is the most efficient to find optimal thresholds with fewest iterations compared with gradient descent algorithm and the iterative algorithm based on block coordinate descent algorithm. The obtained results are expected to provide guidance significance in designing two-way MCvD system with optimal decision thresholds and lower average probability of error.

Levenberg–Marquardt Method-Based Cooperative Source Localization in SIMO Molecular Communication via Diffusion Systems

Molecular communication underpins nano-scale communications in nanotechnology. The combination of multi-nanomachines to form nano-networks is one of the main enabling methods. Due to the importance of source localization in establishing nano-networks, this paper proposes a cooperative source localization method for Molecular Communication via Diffusion (MCvD) systems using multiple spherical absorption receivers. Since there is no exact mathematical expression of the channel impulse response for multiple absorbing receivers, we adopt an empirical expression and use Levenberg-Marquardt method to estimate the distance of the transmitter to each receiver, based on which the location of the transmitter is obtained using an iterative scheme where the initial point is obtained using a multi-point localization method. Particle based simulation is carried out to evaluate the performance of the proposed method. Simulation results show that the proposed method can accurately estimate the location of transmitter in short to medium communication ranges.

Detection Interval of Aerosol Propagation From the Perspective of Molecular Communication: How Long is Enough?

In this paper, we propose a two-layer heterogeneous network to realize the remote monitoring and advanced warning for infectious diseases spread by airborne pathogens, whose detection can be considered as a binary detection problem. To intuitively study the detection process, we abstract it as a molecular communication via diffusion (MCvD) model and uncover that one of the key factors to impact the detection performance is inter-symbol interference (ISI), i.e., the viral aerosol from other biological entities. Therefore, overcoming ISI is imperative to ensure reliable detection. In the abstracted MCvD model, the detection performance can be described by the bit error rate (BER) performance. Following this assumption, we propose to optimize the detection interval to minimize the impact of ISI while ensuring the accurate detection of the transmitted information symbol, which is suitable for both the absorbing and passive receivers. For tractability, based on the signal-to-interference difference (SID) and signal-to-interference-and-noise amplitude ratio (SINAR), we design a modified-SINAR (mSINAR) to measure BER performance for the MCvD system with a variable detection interval. Besides, we derive the optimal detection interval in closed-form. Using simulation results, we show that in terms of BER, our proposed mSINAR scheme is superior to the competitive schemes, and performs similarly to the scheme with optimal intervals determined by the exhaustive search.

Low Complexity First: Duration-Centric ISI Mitigation in Molecular Communication via Diffusion

In this letter, we propose a novel inter-symbol interference (ISI) mitigation scheme for molecular communication via diffusion (MCvD) systems with the optimal detection interval. Its rationale is to exploit the discarded duration (i.e., the symbol duration outside this optimal interval) to relieve ISI in the target system. Following this idea, we formulate an objective function to quantify the impact of the discarded time on bit error rate (BER) performance. Besides, an optimally reusable interval within the discarded duration is derived in closed form, which applies to both the absorbing and passive receivers. Finally, numerical results validate our analysis and show that for the considered MCvD system, significant BER improvements can be achieved by using the derived reusable duration.

Molecular index modulation using convolutional neural networks

As the potential of molecular communication via diffusion (MCvD) systems at nano-scale communication increases, designing molecular schemes robust to the inevitable effects of molecular interference has become of vital importance. There are numerous molecular approaches in literature aiming to mitigate the effects of interference, namely inter-symbol interference. Moreover, for molecular multiple-input–multiple-output systems, interference among antennas, namely inter-link interference, becomes of significance. Inspired by the state-of-the-art performances of machine learning algorithms on making decisions, we propose a novel approach of a convolutional neural network (CNN)-based architecture. The proposed approach is for a uniquely-designed molecular multiple-input–single-output topology in order to alleviate the damaging effects of molecular interference. In this study, we compare the performance of the proposed network with that of an index modulation approach and a symbol-by-symbol maximum likelihood estimation and show that the proposed method yields better performance.

Asymmetrical Relaying in Molecular Communications

Molecular communication via diffusion (MCvD) is a novel communication technique that uses the diffusive characteristics of molecules for enabling the communication between nanomachines. Since the molecules propagate following a random motion, MCvD schemes are usually limited to a short communication range. Most of the molecular relaying schemes in the literature consider symmetric setups where transmitters and receivers are placed at the same distance from the relay, which is difficult to provide in practical scenarios and a possible cause of failure. In this study, asymmetric molecular links of a relay system are investigated. In order to achieve a satisfactory overall performance in spite of the asymmetries, two parameter optimization methods are proposed for the uplink of a relaying system, based on emitting different types of molecules with different diffusion coefficient values from the transmitters. Due to the channel symmetry, the solutions presented in this study are expected to hold for the downlink as well. The resulting bit error rate (BER) performances are presented and discussed.

Optimal relaying in molecular communications

Molecular communication via diffusion (MCvD) schemes are limited to short distances between the nanomachines due to the transmitted signal becoming rapidly weaker as the distance increases. Additionally, these schemes are very often affected by high inter-symbol interference, which makes them prone to errors, thus leading to unreliability. In this paper, a novel system is proposed, which aims to enhance the received signal shape and the overall performance of MCvD schemes over longer distances. A relay nanomachine is introduced between the transmitter–receiver pair, which collects the first portion of the molecules emitted from the transmitter and keeps them for some delay time τ, then releases them towards the receiver, such that the delayed and non-delayed portions of the molecules arrive almost at the same time. In this way, the signal’s strength is enhanced by pointing more molecules towards the intended direction, that is, the receiver node. An analytical model for the optimal relaying scheme is proposed, alongside with an optimization problem to find the most advantageous τ value. Comparison between the proposed scheme and the conventional single-input single-output scenario is provided by means of analytical and computer simulation results, showing a promising improvement in error rates when the relay is introduced.

Iterative signal detection to mitigate ISI and MUI for diffusion-based molecular communications

Molecular communication via diffusion (MCvD) where bio-molecules carry information is a most promising and viable solution for communication between nanoscale devices. However, slow moving molecules cause inter-symbol-interference (ISI) which is one of the major impediments in MCvD systems. In this work, a novel iterative block-wise non-coherent signal detection method is proposed to mitigate the ISI at the receiver. Since the proposed method does not require the channel state information at the receiver, this reduces the molecular communication system’s complexity. The bit error rate (BER) performance of the proposed iterative detection method is evaluated in the presence of both ISI and counting noise. Substantial improvement in MC system’s BER performance is observed by using the proposed detection method as compared to conventional approach. Furthermore, effectiveness of the proposed scheme is also analyzed in the presence of multiuser interference.

Effect of the Viscocity on Molecule Reception Ratio for Mobile Nano Systems

Studies regarding Molecular Communication via Diffusion (MCvD) are considered to highly contribute to the developments in the field of nano-technology. Therefore, in this study, software-based a new MC model that could potentially be used in nano-scale systems was developed and analyzed in terms of communication performance. The information about the carrier particles used in such communication systems consists of biological components such as DNA and protein components. MC model that can possibly be used in nano-scale systems is analyzed in terms of channel performance of communication such as viscosity of the medium. The physical properties of the channel models such as viscosity and hitting probability of received molecules are analyzed in this study using the mobile point transmitter and spherical receiver. As a result, the probability of a molecule reception of the receiver and number of received molecules increase with increasing viscosity.

On the Exact Performance Analysis of Molecular Communication via Diffusion for Internet of Bio-Nano Things.

Internet of Bio-Nano Things, (IoBNT), is an ecosystem, where integration of micro and nano scale devices designed via synthetic biology communicates information. One of the communication concepts adopted in IoBNT is molecular communications via diffusion (MCvD). Inter-symbol interference (ISI) is a major cause of the performance degradation in MCvD systems. The accurate determination of the bit error probability (BEP) when ISI is present is therefore important. Most of the past literature has used the normal approximation to a binomial distribution to evaluate the approximate BEP in MCvD systems. In this paper, we derive a new expression to evaluate the exact BEP without using a normal or any other approximation when the ISI caused by a bit extends over an arbitrary number of future bit intervals. Our BEP expression applies to any receiver, full or partial absorbing, as long as its hitting probability distribution is known. In order to prove the applicability of the new expression, we present the numerical results for the BEP computed using our expression for a full absorption spherical receiver and compare them with the results obtained by particle-based simulations. Our results agree closely with the simulation results.

Molecular-Type Permutation Shift Keying in Molecular MIMO Communications for IoBNT

Molecular communication (MC) is a bio-inspired communication paradigm, which lays the foundation for the Internet of Bio-NanoThings (IoBNT) in the medical field. As a high energy-efficient information transfer method, MC via diffusion (MCvD) is envisioned as a promising candidate for IoBNT but suffers from low date rates due to the long tail of the channel impulse response (CIR). To this end, the multiple-input–multiple-output (MIMO) technique has been introduced to MCvD. However, the intersymbol interference (ISI) and interlink interference (ILI) deteriorate the bit error rate (BER) performance of MIMO MCvD systems. In this article, molecular type permutation shift keying in the space domain (MTPSK-SD) and time-interleaved MTPSK-SD are proposed for MIMO MCvD systems to improve the BER performance by reducing ILI. The principle of MTPSK-SD is further generalized to the spatiotemporal domain, yielding three spatiotemporal modulation schemes, which can provide desirable BER performance without requiring any CIR information in the communication scenarios affected by different levels of ISI and ILI. Two low-complexity detectors are proposed to obtain different tradeoffs between anti-ILI and anti-ISI performance. Furthermore, a complementary coding scheme, which can effectively reduce the ILI under the considered symmetrical system topology, is designed and applied to all the proposed modulation schemes. Additionally, the BER upper bound is analyzed. Numerical simulations on BER corroborate the analysis and show that the proposed schemes are promising multimolecule modulation alternatives, which outperform the existing MIMO MCvD modulation schemes.

A Noise Suppression Filter for Molecular Communication via Diffusion

Molecular communication via diffusion (MCvD) is one of the most feasible communication paradigms for nanonetworks, especially for bio-nanonetworks in water-rich biological environments. Noise is an unwanted signal that severely limits the receiver’s ability to detect the wanted signal. The dominant noise in MCvD is counting noise, which is much different from traditional communication paradigms. However, noise suppression in MCvD has not been explicitly investigated. Therefore, it is necessary to propose a practical noise-suppression approach to diminish the impact of noise in MCvD. In this letter, we propose a simple but effective noise-suppression filter for MCvD, the I-filter. Moreover, the proposed noise-suppression filter has low computational complexity. Our work shows that the proposed filter performs much better than current noise-suppression approaches, the moving average algorithm, in the state-of-the-art detection schemes in terms of bit error rate (BER) performance in the severe noise scenarios.

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.

Unsupervised Clustering-Based Non-Coherent Detection for Molecular Communications

As an emerging communication paradigm, molecular communication is suitable for exchanging information between nano-machines in a fluid medium (e.g., in vivo), utilizing molecules as a major carrier. Subject to the inherent long tail characteristic of channel response and the difficulties in obtaining Channel State Information (CSI), conventional coherent detection schemes prevalent in wireless scenarios are no longer attractive. To achieve reliable communication, this letter proposes a novel non-coherent detection method based on unsupervised Fuzzy C-means (FCM) clustering exploiting the transient features of molecular signal for Molecular Communications via Diffusion (MCvD). Numerical results demonstrate that the performance of bit error rate (BER) is significantly improved by the proposed method compared with other non-coherent schemes and is comparative to the optimal coherent method. Especially, in the scenario of multi-level modulation, almost all threshold-based non-coherent detection schemes perform badly except for our method.

Molecular Index Modulation With Space-Time Equalization

Molecular multiple-input-multiple-output (MIMO) techniques are proposed in the literature to improve the overall throughput of molecular communication via diffusion (MCvD) systems. Among these methods, molecular index modulation (molecular-IM) schemes are recently introduced as novel molecular MIMO approaches to provide significant improvements in terms of communication efficiency. However, despite molecular-IM’s strong combating capability against inter-symbol interference (ISI) and inter-link interference (ILI), they are still prone to them due to the characteristics of a molecular MIMO MCvD channel. With the goal of further mitigating ISI and ILI, this letter introduces memory-assisted, linear time and space-time equalization methods for molecular-IM schemes. It is shown that the proposed equalization methods yield significant improvements in error performance while retaining low decoding complexity due to the linear combining.

Simulation Study and Analysis of Diffusive Molecular Communications With an Apertured Plane.

Molecular communication via diffusion (MCvD) is a method of achieving nano- and micro-scale connectivity by utilizing the free diffusion mechanism of information molecules. The randomness in diffusive propagation is the main cause of inter-symbol interfe-rence (ISI) and the limiting factor of high data rate MCvD applications. In this paper, an apertured plane is considered between the transmitter and the receiver of an MCvD link. Either after being artificially placed or occurring naturally, surfaces or volumes that resemble an apertured plane only allow a fraction of the molecules to pass. Contrary to intuition, it is observed that such topology may improve communication performance, given the molecules that can pass through the aperture are the ones that take more directed paths towards the receiver. Furthermore, through both computer simulations and a theoretical signal evaluation metric named signal-to-interference and noise amplitude ratio (SINAR), it is found that the size of the aperture imposes a trade-off between the received signal power and the ISI combating capability of an MCvD system, hinting to an optimal aperture size that minimizes the bit error rate (BER). It is observed that the trend of BER is accurately mirrored by SINAR, suggesting the proposed metric's applicability to optimization tasks in MCvD systems, including finding the optimal aperture size of an apertured plane. In addition, computer simulations and SINAR show that said optimal aperture size is affected by the location of the aperture and the bit rate. Lastly, the paper analyzes the effects of radial and angular offsets in the placement of the apertured plane, and finds that a reduction in BER is still in effect up to certain offset values. Overall, our results imply that apertured plane-like surfaces may actually help communication efficiency, even though they reduce the received signal power.

Electric Field Assisted Molecular Communication for High Data Rate Transmission

The molecular communication via diffusion (MCvD) is one of the most promising molecular communication (MC) techniques to construct the nano-networks due to its advantages of good bio-compatibility and high energy efficiency. However, due to the diffusion nature of information molecules, the data rate of MCvD is slow and the inter-symbol interference (ISI) effect is quite severe which limits the development and application of MCvD. In this letter, an electric-field assisted MCvD (EF-MCvD) is proposed to mitigate the ISI effect and improve the date rate. The impacts of the electric field on the data rate and the bit error rate performance of the proposed scheme are investigated. The results demonstrate that, the proposed EF-MCvD scheme effectively suppresses the ISI effect and improves the data rate of the MCvD system.