Robust Molecular Communications: DFE-SPRTs and Synchronisation

Molecular communication has been proposed as a signaling mechanism to enable communication between nano-machines via molecular diffusion. Precise synchronization of transmitters and receivers is particularly challenging in diffusive molecular communication environments due to the propagation characteristics. To mitigate sensitivity to synchronization errors, a decision feedback equalizer, sequential probability ratio test (DFE-SPRT) based receiver and an approximate maximum-likelihood delay estimator are derived. The performance of the delay estimator is shown to be close to a Cramer-Rao bound at low transmission rates. Numerical results show that the DFE-SPRT makes a decision well before the full symbol interval is exhausted; the desirability of this effect is theoretically justified through the adaptation of the analysis of the log-loss function for mismatched Poisson random variables. Performance bounds on the DFE-SPRT are employed to design optimized modulation for the mis-synchronized communication channel. The proposed receiver and modulation designs achieve strongly improved asynchronous detection performance for the same data rate relative to recently proposed receiver designs that also exploit decision feedback.

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.

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.

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 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.

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.

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 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 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.

A data frame can piggyback a control frame to increase the channel efficiency in a wireless communication such as IEEE 802.11 WLAN. However, the piggyback scheme may cause the decrease of the channel efficiency and the increase of the frame transmission delay for other stations if the station has the low transmission rate and the control frame presents the global control information such as the channel reservation time. It is similar to the anomaly phenomenon in the network which supports the multi-rate transmission. In this paper, we define this phenomenon as "the piggyback problem at low physical transmission rate" and evaluate the effect of this problem with respect to the physical transmission rate and the normalized traffic load. Then, we propose the delay-based piggyback algorithm which decides to use the piggyback scheme for a control frame based on the delay efficiency in IEEE 802.11 WLAN. In the simulation results, the proposed algorithm reduces the average frame transmission delay and the channel utilization about 24% and 25%, respectively even if there is one station which has low physical transmission rate.

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.

Motivated by the study of security issues in molecular communication, this paper addresses the problem of secure communication in a bio‐inspired field where confidentiality of the information is of significant importance. The new metrics are used for the secrecy analysis where eavesdropper's decodability of confidential message and amount of information leakage is taken into account, which is not considered using conventional secrecy outage probability. A diffusion‐based molecular communication system is considered where the information to be transmitted is the time of release of the molecules. Typically in the existing literature in molecular timing channels, the position of the eavesdropper is known, which is usually an unpractical assumption. If no information about eavesdropper is known, it could be located at any distance with probability distribution be assumed to be uniform and Gaussian. In this paper, the closed‐form expressions for the eavesdropper capacity, generalised secrecy outage probability, average fractional equivocation and average information leakage rate have been obtained when the eavesdropper is located at a random distance from the transmitter.