A Time-Slotted Molecular Communication (TS-MOC): Framework and Time-Slot Errors

Abstract

Synchronization is a critical issue in molecular communications (MC). Additionally, the lack of an appropriate time-slotted framework for MC systems hinders the in-depth analysis of desynchronization. Therefore, this paper addresses both issues. First, taking inspiration from oscillators found in nature, we propose a time-slotted framework suitable for MC systems where the time instances of the oscillations demarcate the time-slot boundaries. The use of biological oscillators readily satisfies biocompatibility requirements. We name such system as a time-slotted molecular communication-based (TS-MOC) system. A TS-MOC system will be beneficial to many MC applications, such as when multiple nanomachines have to transmit data simultaneously to a control/sink node or share the channel in a time-division multiplexing manner. Second, oscillation perturbations induce desynchronization -the misalignment of time-slots. Desynchronization combined with large propagation delay results in a time difference between the arrival of a signal and the beginning of a time-slot. This phenomenon is called time-slot error, and it can degrade a system's performance. Therefore, the immediate goal is to mitigate time-slot errors. Depending on the initiation type, we propose two synchronization schemes: sender-initiated time-slot alignment and receiver-initiated time-slot alignment. An analytical model for time-slot error is also derived. Our analysis demonstrates that the proposed schemes are robust and energy-efficient -they achieve relatively low errors indicating robustness and relatively less synthesizing energy costs indicating energy efficiency. Our analysis also highlights the good agreement between the simulations and the analytical model. Finally, in conclusion, we provide brief insights into key open research challenges.

A TDMA-Based Data Gathering Protocol for Molecular Communication via Diffusion-Based Nano-Sensor Networks

“…Furthermore, the system is considered to be synchronized. Synchronization can be achieved either by executing time synchronization mechanisms [56], [57] during the network pre-initialization phase and periodically as clocks tend to drift apart with time or time-slot synchronization [41], with minor modifications. Any of these mechanisms can be applied on the basis of design requirements, such as energy efficiency and processing complexity.…”

“…Hence, there is a need to rethink the design of TDMA-based MAC protocols that are specific to MCSNs. It is worthy to note that adaptation of TDMA principles over to MC (molecular communication) have been investigated, covering a wide range of topics like scheduling optimization for neuron-based MC [38]- [40], time-slot synchronization for MCvD systems [41], and drug delivery systems for MCvD-with-drift systems [42]. Although, Rouzegar and Spagnolini [43] studied packet errors that are caused by erroneous bits considering a MIMO setting and Nakano et al [44] studied packet losses that are caused by fragmented packets colliding spatially in the medium considering a single transmitter-receiver pair setting, the issue of packet collision caused by the temporal overlapping of packets in a multiple spherical transmitter setting has not been investigated and addressed.…”

A Molecular Communication-Based Simultaneous Targeted-Drug Delivery Scheme

“…For example, the release time can be encoded in the message after the completion of the synchronization phase. However, if an attempt were made to expand the coordination scheme in [25], [26] to achieve SDD, then the schemes in [25], [26] would require a large signaling overhead, a complex estimator (maximum likelihood estimation) to estimate the perturbation issues [27] (e.g., clock skew and clock offset), and an increased energy cost [25], [26]. Furthermore, the above-mentioned MCbased TDD systems are not tailored to address the SDD problem for nanomachines at random distances.…”

A Simultaneous Drug Release Scheme for Targeted Drug Delivery Using Molecular Communications

“…For instance, after synchronization, the release time can be encoded on the messages. A similar approach can also be applied with synchronization schemes that do not use timestamps [16], but instead of sending the timing information, a special signal can be used for triggering purposes.…”

“…The existing works in MC mentioned earlier are not tailored to address the issue of drug release-time error as this error was not studied before. Additionally, even if we attempt to extend them to solve the release-time error, we note that they require high precision, have perturbation issues (e.g., clock offset and clock skew [16]), have large signaling overheads and low energy efficiency (e.g., [13], [14]), have high complexity (e.g., [15]), and pertain to single nanomachine case (e.g., [16]). Inspired by the reported benefits of not using timestamps in terms of complexity and energy [16], we develop a novel internally triggered timestamp-free simultaneous drug release scheme to reduce the releasetime errors.…”