Transmitter and Receiver Architectures for Molecular Communications: A Survey on Physical Design with Modulation, Coding and Detection Techniques <s> D. Challenges for Developing MC Channel Coding Techniques <s> Molecular communication is a novel paradigm that uses molecules as an information carrier to enable nanomachines to communicate with each other. Controlled molecule delivery between two nanomachines is one of the most important challenges which must be addressed to enable the molecular communication. Therefore, it is essential to develop an information theoretical approach to find out communication capacity of the molecular channel. In this paper, we develop an information theoretical approach for capacity of a molecular channel between two nanomachines. Using the principles of mass action kinetics, we first introduce a molecule delivery model for the molecular communication between two nanomachines called as Transmitter Nanomachine (TN) and Receiver Nanomachine (RN). Then, we derive a closed form expression for capacity of the channel between TN and RN. Furthermore, we propose an adaptive Molecular Error Compensation (MEC) scheme for the molecular communication between TN and RN. MEC allows TN to select an appropriate molecular bit transmission probability to maximize molecular communication capacity with respect to environmental factors such as temperature and distance between nanomachines. Numerical analysis show that selecting appropriate molecular communication parameters such as concentration of emitted molecules, duration of molecule emission, and molecular bit transmission probability it can be possible to achieve high molecular communication capacity for the molecular communication channel between two nanomachines. Moreover, the numerical analysis reveals that MEC provides more than % 100 capacity improvement in the molecular communication selecting the most appropriate molecular transmission probability. <s> BIB001 </s> Transmitter and Receiver Architectures for Molecular Communications: A Survey on Physical Design with Modulation, Coding and Detection Techniques <s> D. Challenges for Developing MC Channel Coding Techniques <s> Molecular communications emerges as a promising scheme for communication between nanoscale devices. In diffusion-based molecular communications, molecules as information symbols are released by transmitters and diffuse in the fluid or air environments to transmit messages. Under the diffusion channel modeled by Brownian motion, information sequences suffer from molecule crossovers, i.e., molecules released at an earlier time may arrive later, causing intersymbol interference (ISI). In this paper, we investigate practical channel codes for combating ISI. An ISI-free coding scheme is proposed to increase the communication reliability while keeping the encoding/decoding complexity reasonably low. We exemplify an ISI-free code and theoretically approximate its bit error rate (BER) performance. In addition, repetition codes are revisited out of the complexity concern and proved to be desirable. The BER approximations of the repetition code family are given as well. Compared with convolutional codes, the proposed ISI-free code and repetition codes offer comparable performance with much lower complexity for diffusion-based molecular communication systems. <s> BIB002 </s> Transmitter and Receiver Architectures for Molecular Communications: A Survey on Physical Design with Modulation, Coding and Detection Techniques <s> D. Challenges for Developing MC Channel Coding Techniques <s> Molecular communications emerges as a promising scheme for communications between nanoscale devices. In diffusion-based molecular communications, molecules as information symbols diffusing in the fluid environments suffer from molecule crossovers, i.e., the arriving order of molecules is different from their transmission order, leading to intersymbol interference (ISI). In this paper, we introduce a new family of channel codes, called ISI-free codes, which improve the communication reliability while keeping the decoding complexity fairly low in the diffusion environment modeled by the Brownian motion. We propose general encoding/decoding schemes for the ISI-free codes, working upon the modulation schemes of transmitting a fixed number of identical molecules at a time. In addition, the bit error rate (BER) approximation function of the ISI-free codes is derived mathematically as an analytical tool to decide key factors in the BER performance. Compared with the uncoded systems, the proposed ISI-free codes offer good performance with reasonably low complexity for diffusion-based molecular communication systems. <s> BIB003
Even though there is some literature on MC channel coding techniques, the field is still very new and open for research. Some of the most pressing directions are highlighted below. • Adaptive Coding: The propagation time through MC channel and detection probabilities at the receiver are affected by various environmental parameters such as temperature, diffusion speed, channel contents, reaction rates and distance between nodes, which calls for adaptive channel coding techniques for error compensation BIB001 . In this respect, none of the coding schemes investigated even considers to probe the channel for its characteristics in order to adapt itself. • Irregular Signaling: All of the coding schemes discussed have been evaluated under the regular time-slotted transmission assumption, which in any realistic MC scenario will never be the case. For instance, fluctuations in the inter-symbol duration caused by irregular transmission would have a significant effect on suffered ISI, the primary source of BER in MC, and therefore needs to be considered by channel codes. • Simplicity of Models: More channel codes for MC need to be invented. The only works that do so are BIB002 BIB003  , and they have very simple transmission and channel models, i.e., in all works the transmitter releases only a single molecule per transmission period, and the channel is one-dimensional.