**1. Introduction**

The wireless sensor network (WSN) is the one of bases in Internet of Things (IoT), and most nodes in the WSN are powered by battery. Extending battery life, saving the maintenance fee, and raising system reliability are the motivations of this paper. In addition to the battery technology improvement and power capacity increase, the low-power technology of the device is also significant. In many applications, IoT device's security and power consumption are significant issues [1]. The battery power is usually used in the application of IoT devices, and the battery life is a troublesome problem [2]. Therefore, achieving extremely low power consumption on battery IoT devices has also become a big challenge.

Moreover, wireless transmission is the highest power-consuming process in communication devices. A study pointed out that the power consumption of nodes in the wireless sensing network is mostly concentrated in the process of wireless communication [3]. Therefore, maintaining reliable communication quality and reducing the power consumption of the device through wireless communication optimization is the focus of this paper. A WSN structure-integrated time division multiple access (TDMA), transmission power control (TPC), and adaptive data rate (ADR) are proposed in this paper to reduce the power consumption of wireless communication.

This paper is based on previously published research by this paper's authors, which has discussed the relationship and performance analysis of the transmission power and data rate [4]. This paper then implements an ultra-low-power WSN IoT with transmission power and data rate hybrid control and introduces the details. The predecessor of this paper aimed to evaluate the performance difference between the transmission power and the data rate with the same packet error rate (PER) of 1% through sensitivity measurement, thereby achieving a comparison basis of hybrid control between data rate and transmission power [4]. In this paper, TDMA scheduling detail, data rate parameter settings, low current selection of transmission power, a simplified hybrid control algorithm, and practical application are discussed. Finally, this paper also places multiple sensing nodes and measures the energy-saving effect and PER state of the nodes, and the proposed hybrid control algorithm is expected to achieve reliable wireless communication and extremely low power consumption simultaneously.

In summary, this paper provides the following contributions:


#### **2. Related Research**

The architecture of the WSN in IoT application and the selection of communication frequency bands have been discussed in the following studies. The designs for power consumption reduction in the wireless network, such as media access control (MAC), transmission power, and data rate control, have also been also discussed in the following literature.

There are two data processing methods that have been proposed, centralization and distribution data fusion, which each have different benefits. Centralized data fusion processes all the data on a central node, while the nodes in distributed system process their own data [5]. In order to keep high maintainability and easy data processing, we adapted star topology network in this paper.

Compared with the 2.4 GHz or 5 GHz frequency band, the transmission distance of the Sub-1 GHz wireless communication is farther, so its coverage is wider and its power consumption is lower [6–8]. The method of multinodes communication in the WSN includes competition-based [9–12] and scheduling-based MAC [13–16]. Compared with competition-based MAC, scheduling-based MAC network throughput is not good, but the design of scheduling-based MAC is simpler. The authors of [17] proposed a TDMA structure-based MAC protocol for short and long-range networks, and the sensor node can run for about 3 years. TDMA could reduce dramatic the power consumption of the WSN, as shown in [17]. However, the proposed algorithm in this paper including ADR and TP control would lower the power requirement further. Considering the system complexity and low-power design, TDMA was adopted in this paper.

In wireless communication, transmission power is a major factor for power consumption. A method called TPC minimizes the transmission power as possible when the communication quality can be maintained [16–24]. If the environment is better, TPC can achieve more power-saving effects. In addition to the transmission power, the data rate is also a major factor affecting power consumption. In the case of packet transmission, if the transmission data rate is faster, the wireless transmission time is shorter. However, the cost of a faster data rate is transmission quality reduction. The appropriate data rate is selected based on the relative relationship between the frame delivery ratio (FDR) and the received signal strength indicator (RSSI) [25–27]. Sodhro, A.H. et al., [28] proposed an energy-efficient transmission power control (ETPC) algorithm that was based on a wireless channel estimation. The channel estimation is an important issue for communication quality and power consumption. The results of the wearable electrocardiogram, demonstrated in [28], have been validated successfully and make a great contribution in energy-saving and signal-processing. However, the complex control should be considered. The methods of combining data rate and transmission power control to achieve power saving were proposed in [29,30]. Due to the fact that ADR and TP hybrid control is complex, and there are a lack of lectures discussing it, there are research gaps to be covered in this paper. The authors of [31] also considered DSSS and MFSK for communication quality and power consumption. However, the proposed algorithm was based on the decided communication to select a suitable combination of DSSS and MFSK. In order to adapt the environmental interference, a data rate and transmission power-integrated control algorithm was proposed in this paper. The control

algorithm can adapt to the environment in which the sensor node is located and choose the best data rate and transmission power. However, the previous works have discussed the TP and ADR control individually, but there is a lack of discussion on combination control due to its complexity. Moreover, because ADR control under TDMA is more difficult because of the complicated communication handshaking, few researchers have discussed the topic. In this paper, the TP or ADR combination control TDMA are detailed.
