## 1 Introduction  
Molecular communication (MC) [1, 2, 3] has emerged as a groundbreaking method of communication inspired by biological mechanisms observed in nature. By leveraging chemical signals for the transmission of information, MC presents itself as a viable alternative to conventional electromagnetic (EM) wave-based methods, offering new perspectives and solutions in the field of communication technology [4, 5]. As an interdisciplinary domain, MC encompasses the integration of nanotechnology, biotechnology, and communication technology, comprising components such as transmitters, channels, and receivers. Its reliance on the chemical movement of molecules facilitates effective communication in environments with substantial spatial limitations, exemplifying its utility in nanoscale communication, such as intra- and inter-cellular communication [6]. This enables the establishment of molecular nanonetworks within the human body [7, 8], which could revolutionize applications such as targeted drug delivery [9]. Other applications of MC exist in the fields of medicine [10] and the Internet of Bio-Nano Things [11, 12]. Unlike EM communication, which depends on external energy sources like batteries and can consume considerable power, MC operates through chemical interactions between molecules, optimizing energy efficiency. This characteristic is particularly beneficial in applications requiring operation at a microscopic scale or where prolonged battery life is paramount. Furthermore, MC's biocompatibility makes it a promising option in scenarios where EM methods face challenges, including applications within human bodies [13]. Regarding communication, MC exploits modulation techniques that leverage the unique physical characteristics of molecules for data transmission, namely concentration, type, timing, and space [1; 14]. Concentration-based modulation represents a method whereby data encoding is achieved through the quantitative manipulation of the amount of molecule emitted by the transmitter. This method facilitates the conveyance of information via the control of the molecular concentration at the receiver [15; 16]. In contrast, type-based modulation utilizes various molecular species as discrete informational entities, wherein each molecule type embodies a distinct bit or signal, permitting the transmission of complex data through the amalgamation of different molecular species. Timing-based modulation [17], another critical technique, governs the temporal emission of molecules, encoding data within specific time intervals by modulating the emission timing of molecules across communication slots, where the sequence and presence or absence of molecular emissions are instrumental in the information transfer process. Spatial-based modulation, particularly relevant in molecular multiple-input multiple-output configurations [18; 19], employs multiple spatially distinct molecular emitters within a single transmitter apparatus. This method encodes information via the spatial distribution of molecular emissions, facilitating data recovery at the receiver through the interpretation of signals received from different paths [14]. From the perspective of communications engineering, MC is still in its infancy, with the identification of an optimal modulation technique for encoding data onto transmitting particles as its foundational challenge. Concentration shift keying (CSK), analogous to on-off keying in EM communications, prevails as the predominant modulation method in MC [15; 20; 21; 22; 23]. In CSK, no molecules are emitted for bit '0', and some concentration of molecules is emitted to represent bit '1'. However, CSK faces a problem called inter-symbol interference (ISI), where some molecules from one transmission linger in the channel and interfere with the next transmission. This is a major issue that can lower the performance of CSK-CEMC systems. To deal with ISI, pulse-position modulation (PPM) is often used in EM communication, where the timing of pulses carries the information.