Department of Electrical and Electronic Engineering, Universiti Teknologi PETRONAS, Seri Iskandar, Perak 32610, Malaysia.
Department of Electrical and Electronic Engineering, NED University of Engineering & Technology, Karachi 75270, Pakistan.
Sensors (Basel). 2021 Apr 22;21(9):2943. doi: 10.3390/s21092943.
The bi-directional information transfer in optical body area networks (OBANs) is crucial at all the three tiers of communication, i.e., intra-, inter-, and beyond-BAN communication, which correspond to tier-I, tier-II, and tier-III, respectively. However, the provision of uninterrupted uplink (UL) and downlink (DL) connections at tier II (inter-BAN) are extremely critical, since these links serve as a bridge between tier-I (intra-BAN) and tier-III (beyond-BAN) communication. Any negligence at this level could be life-threatening; therefore, enabling quality-of-service (QoS) remains a fundamental design issue at tier-II. Consequently, to provide QoS, a key parameter is to ensure link reliability and communication quality by maintaining a nearly uniform signal-to-noise ratio (SNR) within the coverage area. Several studies have reported the effects of transceiver related parameters on OBAN link performance, nevertheless the implications of changing transmitter locations on the SNR uniformity and communication quality have not been addressed. In this work, we undertake a DL scenario and analyze how the placement of light-emitting diode (LED) lamps can improve the SNR uniformity, regardless of the receiver position. Subsequently, we show that using the principle of reciprocity (POR) and with transmitter-receiver positions switched, the analysis is also applicable to UL, provided that the optical channel remains linear. Moreover, we propose a generalized optimal placement scheme along with a heuristic design formula to achieve uniform SNR and illuminance for DL using a fixed number of transmitters and compare it with an existing technique. The study reveals that the proposed placement technique reduces the fluctuations in SNR by 54% and improves the illuminance uniformity up to 102% as compared to the traditional approach. Finally, we show that, for very low luminous intensity, the SNR values remain sufficient to maintain a minimum bit error rate (BER) of 10-9 with on-off keying non-return-to-zero (OOK-NRZ) modulation format.
光体域网（OBAN）中的双向信息传输在所有三个通信层（即内部、内部和 BAN 之外的通信）都至关重要，分别对应于第 I 层、第 II 层和第 III 层。然而，在第 II 层（BAN 之间）提供不间断的上行链路（UL）和下行链路（DL）连接是极其关键的，因为这些链路作为第 I 层（BAN 内部）和第 III 层（BAN 之外）通信之间的桥梁。这一级别的任何疏忽都可能危及生命；因此，在第 II 层提供服务质量（QoS）仍然是一个基本的设计问题。因此，为了提供 QoS，一个关键参数是通过在覆盖区域内保持几乎均匀的信号噪声比（SNR）来确保链路可靠性和通信质量。一些研究报告了收发器相关参数对 OBAN 链路性能的影响，然而，改变发射器位置对 SNR 均匀性和通信质量的影响尚未得到解决。在这项工作中，我们承担了一个 DL 场景，并分析了无论接收器位置如何，发光二极管（LED）灯的放置如何提高 SNR 均匀性。随后，我们表明，使用互易性（POR）原理并切换发射器-接收器位置，该分析也适用于 UL，前提是光通道保持线性。此外，我们提出了一种广义的最佳放置方案以及一种启发式设计公式，用于使用固定数量的发射器实现 DL 的均匀 SNR 和照度，并将其与现有技术进行比较。研究表明，与传统方法相比，所提出的放置技术可将 SNR 的波动降低 54%，并将照度均匀性提高到 102%。最后，我们表明，对于非常低的光强度，SNR 值仍然足以保持使用开关键控非归零（OOK-NRZ）调制格式的最小误码率（BER）为 10-9。
