In this letter, we consider the problem of channel estimation for diffusive molecular communication (MC) systems. The presence of memory in diffusive MC channels, along with channel noise caused by various sources, necessitate the development of accurate channel estimators to acquire the channel impulse response (CIR). Previous works proposed pilot-based estimators based on the maximum likelihood (ML) and least squares (LS) criteria. In contrast, we propose three novel semi-blind estimators, one based on the expectation maximization (EM) framework and two based on the decision-directed (DD) estimation strategy. We also obtain the corresponding semi-blind Cramer-Rao bound (CRB). Our simulation results show that all the proposed semi-blind estimators offer substantially lower mean-squared error than the existing pilot-based estimators. The EM estimator provides the highest accuracy and converges to the semi-blind CRB, while the DD estimators offer convenient low-complexity alternatives. Importantly, the proposed estimators allow for a significant reduction in the number of transmitted pilots, without compromising the estimation accuracy.

中文翻译：

---

扩散分子通信的半盲通道估计


在这封信中，我们考虑了扩散分子通信（MC）系统的信道估计问题。扩散 MC 通道中内存的存在，以及各种来源引起的通道噪声，需要开发精确的通道估计器来获取通道脉冲响应 (CIR)。之前的工作提出了基于最大似然（ML）和最小二乘（LS）标准的基于试点的估计器。相比之下，我们提出了三种新颖的半盲估计器，一种基于期望最大化（EM）框架，另一种基于决策导向（DD）估计策略。我们还获得了相应的半盲 Cramer-Rao 界（CRB）。我们的模拟结果表明，所有提出的半盲估计器均提供比现有的基于导频的估计器低得多的均方误差。 EM 估计器提供最高的精度并收敛到半盲 CRB，而 DD 估计器提供方便的低复杂性替代方案。重要的是，所提出的估计器允许显着减少发射导频的数量，而不影响估计精度。