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.

翻译：为完成相对复杂的任务，在生物纳米物联网（IoBNT）中，不同纳米机器（NMs）收集的信息通常通过多址信道发送至融合中心（FC）进行进一步处理。本文基于两种分子类型，设计了一种分子码分多址（MoCDMA）方案，使得多个纳米机器可在扩散分子通信（DMC）环境中同时向接入点（AP）发送信息。我们假设不同纳米机器与接入点的距离可能不同，由此产生"远近效应"。相应地，提出了均匀分子发射方案和基于信道逆的分子发射方案，用于纳米机器发射信息分子。为便于设计不同的信号检测方案，将接入点接收到的信号以不同形式表示。具体而言，考虑纳米机器有限的计算能力，基于匹配滤波（MF）、迫零（ZF）和最小均方误差（MMSE）原理，设计了三种低复杂度检测器。分析了MoCDMA系统中的噪声特性及各种检测方案的复杂度，并展示和比较了采用不同分子发射与检测方案的MoCDMA系统的误码性能。我们的研究与性能结果表明，MoCDMA是一种支持DMC中多址传输的有效方案，而基于信道逆的传输可保证不同纳米机器之间的通信质量公平性（FoCQ）。此外，可实施不同检测方案以在实现复杂度与通信可靠性之间取得良好权衡。