ISI-Avoiding Modulation for Diffusion-Based Molecular Communication

Abstract

A diffusion molecular channel is a channel with memory, as molecules released into the medium hit the receptors after a random delay. Coding over the diffusion channel is performed by choosing the type, intensity, or the released time of molecules diffused in the environment over time. To avoid intersymbol interference (ISI), molecules of the same type should be released at time instances that are sufficiently far apart. This ensures that molecules of a previous transmission are faded in the environment, before molecules of the same type are reused for signaling. In this paper, we consider ISI-free timeslotted modulation schemes. The maximum reliable transmission rate for these modulations is given by the constrained coding capacity of the graph that represents the permissible transmission sequences.However, achieving the constrained coding capacity requires long blocklengths and delays at the decoder, making it impractical for simple nanomachines. The main contribution of this paper is to consider modulations with small delay (short blocklength) and show that they get very close to constrained coding capacity. June 13, 2018 DRAFT arXiv:1508.02495v1 [cs.IT] 11 Aug 2015 2 I. INTRODUCTION Molecular communications (MC) via diffusion is one of the most promising approaches for communications among nanonetworks [1], [2]. In this approach, information is conveyed to a nano-receiver by nano-transmitter's choice of the concentration, type, or the release time of the molecules diffused into the medium. The motion of the released molecules are described by a Brownian motion process, that can be with or without drift. A molecule released from a transmitter can follow different trajectories before reaching a receiver. Thus, diffusion-based communication suffers from intersymbol interference (ISI) due to molecules from previous transmission that follow longer trajectories before hitting the receiver. The effect of ISI in diffusion based MC has been studied extensively in the literature [3]-[6], with the general conclusion that ISI reduces the performance in a communication setup consisting of one transmitter and one receiver. The authors in [7], [8] have proposed two modulation schemes, Concentration Shift Keying (CSK) and Molecular Shift Keying (MOSK), where both suffer from the ISI caused by molecules from previous transmissions. Authors in [9] have proposed the Molecular Concentration Shift Keying (MCSK) modulation scheme, where the main idea is to use the distinct molecule types for consecutive time slots at the transmitter, thus effectively suppressing the ISI. In [10] the authors take advantage of a limited memory in the transmitter to propose an adaptive transmission rate scheme that reduces ISI. An on-off MOSK modulation scheme has been proposed in [11] which increases the transmission rate compared to MOSK but still suffers from the ISI. In [12], a modulation, called run-length hybrid aware, has been presented, which considers the runs (the same value occurs in several consecutive bits) for encoding: the run-value is...

Interference Mitigation in Large-Scale Multiuser Molecular Communication

“…In this proposed technique, molecular diffusion rate is adjusted for each bit interval by taking advantage of the memory. Another ISIfree modulation scheme for a given maximum transmission delay is proposed in [17], where symbols of the same type are released sufficiently far apart to reduce the ISI in the system. Inspired from modern advancements in digital communication applications, the authors in [10] proposed Reed Solomon (RS) codes as an error correction technique for a diffusion-based MC system, with a point transmitter and a full absorbing receiver, as they are highly effective against burst and random errors.…”

Diffusive Molecular Communications With Reactive Molecules: Channel Modeling and Signal Design

“…In a similar manner, we apply L'Hopital's rule to C fr i (r, t + ∆t) given in (22a) and (22b) for c 1 (r, t) 0 in order to find the corresponding expressions when c 1 (r, t) = 0. For the case, when κ f = 0, it is easier to solve the original PDEs in (13) which simplifies to ∂C br i (r,t) ∂t = κ b and has the immediate solution given in (23). This completes the proof.…”

Molecular Communication in H-Diffusion

“…, y N } at the RN. Since H-noise can be the heavytailed random variable, it may have a large waiting time for molecules arriving at the RN, i.e., there exists a positive probability that the molecule will not have arrived at TN within finite 15 The number of molecule types used for this model can be minimized by introducing the lifetime of molecules [21], [62] and the chemical reactions in the medium [3], [63], [64]. ... time.…”