Molecular Code-Division Multiple-Access: Signaling, Detection, and Performance
Weidong Gao, Lu Shi, Lie-Liang Yang
TL;DR
This work presents Molecular Code-Division Multiple-Access (MoCDMA) for Internet of Bio-Nano Things, enabling multiple nano-machines to share a diffusion channel to a single AP using antipodal signaling with two molecule types (Type-A/Type-B) and binary MoSK modulation. It introduces two molecular emission schemes—uniform and channel-inverse—and derives linear representations of the received signal that reveal ISI, ICI, and MAI, enabling three low-complexity detectors: MF (or MRC), ZF, and MMSE. The channel-inverse emission scheme achieves near-equal peak concentrations across NMs, improving fairness of communication quality (FoCQ) and reducing molecule usage. Through complexity and BER analyses, the paper shows that ZF and MMSE detectors offer better performance at higher computational cost, while MF provides a simple baseline; MoCDMA thus offers a scalable, energy-efficient multi-access solution for diffusion-based molecular communications in IoBNT.
Abstract
To accomplish relatively complex tasks, in Internet of Bio-Nano Things (IoBNT), information collected by different nano-machines (NMs) is usually sent via multiple-access channels to fusion centers (FCs) for further processing. Relying on two types of molecules, in this paper, a molecular code-division multiple-access (MoCDMA) scheme is designed for multiple NMs to simultaneously send information to an access-point (AP) in a diffusive molecular communications (DMC) environment. We assume that different NMs may have different distances from AP, which generates `near-far' effect. Correspondingly, the uniform and channel-inverse based molecular emission schemes are proposed for NMs to emit information molecules. To facilitate the design of different signal detection schemes, the received signals by AP are represented in different forms. Specifically, by considering the limited computational power of nano-machines, three low-complexity detectors are designed in the principles of matched-filtering (MF), zero-forcing (ZF), and minimum mean-square error (MMSE). The noise characteristics in MoCDMA systems and the complexity of various detection schemes are analyzed. The error performance of the MoCDMA systems with various molecular emission and detection schemes is demonstrated and compared. Our studies and performance results demonstrate that MoCDMA constitutes a promising scheme for supporting multiple-access transmission in DMC, while the channel-inverse based transmission can ensure the fairness of communication qualities (FoCQ) among different NMs. Furthermore, different detection schemes may be implemented to attain a good trade-off between implementation complexity and communication reliability.