Concentration-encoded Molecular Communication Research Articles

A machine learning-based concentration-encoded molecular communication system

Molecular communication (MC) is a recent novel communication paradigm, which could enable revolutionary applications in the fields of medicine, military, and environment. Inspired by nature, MC uses molecules as information carriers to transmit and receive data. Concentration-encoded molecular communication (CEMC) is an information encoding approach, where the information is encoded in the concentration of the transmitted molecules. In this paper, we propose a machine learning (ML)-based CEMC system. In particular, we propose a modulation scheme named concentration position-shift keying (CPSK), which encodes information as the position of the transmitted molecular concentration. After passing through a diffusion-based channel, the molecules are captured via a ligand–receptor binding process (LRBP) at the nanoreceiver. Then, a ML-based approach is employed to decode the data bits. From numerical simulations, it has been shown that increasing the transmission time and using 4-ary CPSK would enhance the communication performance of the proposed ML-based CEMC system. In addition, we found that the ML receiver mitigates the bias effect and reduces inter-symbol interference (ISI) of the diffusion-based molecular channel. As a result, the proposed ML-based receiver shows better performance than the conventional maximum-likelihood (MLE) receiver.

Achievable Strength-Based Signal Detection in Quantity-Constrained PAM OOK Concentration-Encoded Molecular Communication.

In this paper, the expressions of achievable strength-based detection probabilities of concentration-encoded molecular communication (CEMC) system have been derived based on finite pulsewidth (FP) pulse-amplitude modulated (PAM) on-off keying (OOK) modulation scheme and strength threshold. An FP-PAM system is characterized by its duty cycle α that indicates the fraction of the entire symbol duration the transmitter remains on and transmits the signal. Results show that the detection performance of an FP-PAM OOK CEMC system significantly depends on the statistical distribution parameters of diffusion-based propagation noise and intersymbol interference (ISI). Analytical detection performance of an FP-PAM OOK CEMC system under ISI scenario has been explained and compared based on receiver operating characteristics (ROC) for impulse (i.e., spike)-modulated (IM) and FP-PAM CEMC schemes. It is shown that the effects of diffusion noise and ISI on ROC can be explained separately based on their communication range-dependent statistics. With full duty cycle, an FP-PAM scheme provides significantly worse performance than an IM scheme. The paper also analyzes the performance of the system when duty cycle, transmission data rate, and quantity of molecules vary.

Concentration-Encoded Subdiffusive Molecular Communication: Theory, Channel Characteristics, and Optimum Signal Detection.

Unlike normal diffusion, in anomalous diffusion, the movement of a molecule is described by the correlated random walk model where the mean square displacement of a molecule depends on the power law of time. In molecular communication (MC), there are many scenarios when the propagation of molecules cannot be described by normal diffusion process, where anomalous diffusion is a better fit. In this paper, the effects of anomalous subdiffusion on concentration-encoded molecular communication (CEMC) are investigated. Although classical (i.e., normal) diffusion is a widely-used model of diffusion in molecular communication (MC) research, anomalous subdiffusion is quite common in biological media involving bio-nanomachines, yet inadequately addressed as a research issue so far. Using the fractional diffusion approach, the molecular propagation effects in the case of pure subdiffusion occurring in an unbounded three-dimensional propagation medium have been shown in detail in terms of temporal dispersion parameters of the impulse response of the subdiffusive channel. Correspondingly, the bit error rate (BER) performance of a CEMC system is investigated with sampling-based (SD) and strength (i.e., energy)-based (ED) signal detection methods. It is found that anomalous subdiffusion has distinctive time-dispersive properties that play a vital role in accurately designing a subdiffusive CEMC system. Unlike normal diffusion, to detect information symbols in subdiffusive CEMC, a receiver requires larger memory size to operate correctly and hence a more complex structure. An in-depth analysis has been made on the performances of SD and ED optimum receiver models under diffusion noise and intersymbol interference (ISI) scenarios when communication range, transmission data rate, and memory size vary. In subdiffusive CEMC, the SD method.

A comprehensive analysis of strength-based optimum signal detection in concentration-encoded molecular communication with spike transmission.

In this paper, a comprehensive analysis of strength-based optimum signal detection model has been presented for concentration-encoded molecular communication (CEMC) with spike (i.e., impulsive) transmission based on amplitude-shift keying (ASK) and on-off keying (OOK) modulations. Strength-based optimum signal detection problem in diffusion-based CEMC system has been investigated in detail in the presence of both diffusion noise and intersymbol interference (ISI). The receiver for optimum signal detection has been developed theoretically and explained with both analytical and simulation results of binary signal detection. Results show that the receiver thus developed can detect CEMC symbols effectively; however, the performance is influenced by three main factors, namely, communication range, transmission data rate, and receiver memory. For both ASK and OOK receivers, exact and approximate detection performances have been derived analytically depending on the probabilistic nature of molecular availability and the relationship between mean and variance of signal strengths. Correspondingly, bit error rate (BER) performance of the optimum receiver in a single CEMC link is further evaluated under various scenarios through extensive simulation experiments.

A comprehensive study of sampling-based optimum signal detection in concentration-encoded molecular communication.

In this paper, a comprehensive analysis of the sampling-based optimum signal detection in ideal (i.e., free) diffusion-based concentration-encoded molecular communication (CEMC) system has been presented. A generalized amplitude-shift keying (ASK)-based CEMC system has been considered in diffusion-based noise and intersymbol interference (ISI) conditions. Information is encoded by modulating the amplitude of the transmission rate of information molecules at the TN. The critical issues involved in the sampling-based receiver thus developed are addressed in detail, and its performance in terms of the number of samples per symbol, communication range, and transmission data rate is evaluated. ISI produced by the residual molecules deteriorates the performance of the CEMC system significantly, which further deteriorates when the communication range and/or the transmission data rate increase(s). In addition, the performance of the optimum receiver depends on the receiver's ability to compute the ISI accurately, thus providing a trade-off between receiver complexity and achievable bit error rate (BER). Exact and approximate detection performances have been derived. Finally, it is found that the sampling-based signal detection scheme thus developed can be applied to both binary and multilevel (M-ary) ASK-based CEMC systems, although M-ary systems suffer more from higher BER.

Strength-based optimum signal detection in concentration-encoded pulse-transmitted OOK molecular communication with stochastic ligand-receptor binding

In this paper, a strength-based optimum signal detection scheme for binary concentration-encoded molecular communication (CEMC) system has been presented. In CEMC, a single type of information molecule is assumed to carry the information from the transmitting nanomachine (TN), through the propagation medium, to the receiving nanomachine (RN) in the form of received concentration of information molecules at the location of the RN. We consider a pair of nanomachines communicating by means of on–off keying (OOK) transmission protocol in a three-dimensional ideal (i.e. free) diffusion-based unbounded propagation environment. First, based on stochastic chemical kinetics of the reaction events between ligand molecules and receptors, we develop a mathematical receiver model of strength-based detection scheme for OOK CEMC system. Using an analytical approach, we explain the receiver operating characteristic (ROC) curves of the receiver thus developed. Finally, we propose a variable threshold-based detection scheme and explain its communication range and rate dependent characteristics. We show that it provides an improvement in the communication ranges compared to fixed threshold-based detection scheme. (Part of this paper has been peer-reviewed and published in BWCCA-2012 conference in Victoria, BC, 12–14 November, 2012 [20].)

Performance Analysis of Convolutional Coding Techniques in Diffusion-Based Concentration-Encoded PAM Molecular Communication Systems

In this paper, we investigate the performance of convolutional coding techniques in an ideal diffusion-based concentration-encoded molecular communication (CEMC) channel with pulse amplitude modulation (PAM) transmission scheme. Convolutional codes have shown to provide a significant amount of gain in the signal-to-interference strength (energy) ratio between a pair of communicating nanomachines and thus help increase the communication range and improve the end-to-end system performance. We have also determined the impact of convolutional codes for several key performance factors, e.g. transmission data rate, communication range, and the constraint length of the convolutional code in the context of diffusion-based CEMC. In addition, we have compared the PAM system with the impulse modulation system in CEMC. We have found that the use of a multilevel (M-ary) signalling scheme in the CEMC system provides a degraded bit error rate performance even in short communication ranges. Therefore, a convolutional coded scheme with larger alphabet size should not be recommended for a CEMC system because of the stronger intersymbol interference produced within symbols. As an alternative, a convolutional coded scheme with binary alphabet and higher symbol rate was evaluated and found to provide a gain in the signal-to-interference energy ratio of the system and is therefore recommended for short- to medium-range CEMC. For long communication ranges, an uncoded system can rather be preferred to convolutional coded schemes.

On the characterization of binary concentration-encoded molecular communication in nanonetworks

In this study, nanoscale communication networks have been investigated in the context of binary concentration-encoded unicast molecular communication suitable for numerous emerging applications, for example in healthcare and nanobiomedicine. The main focus of the paper has been given to the spatiotemporal distribution of signal strength and modulation schemes suitable for short-range, medium-range, and long-range molecular communication between two communicating nanomachines in a nanonetwork. This paper has principally focused on bio-inspired transmission techniques for concentration-encoded molecular communication systems. Spatiotemporal distributions of a carrier signal in the form of the concentration of diffused molecules over the molecular propagation channel and diffusion-dependent communication ranges have been explained for various scenarios. Finally, the performance analysis of modulation schemes has been evaluated in the form of the steady-state loss of amplitude of the received concentration signals and its dependence on the transmitter–receiver distance.