# Transmission Power Control in Wireless Sensor Networks Using Fuzzy Adaptive Data Rate
## 1 Introduction  
With the advancement of technology, the concepts of smart manufacturing and smart city are popularized in the world. The Internet of Things (IoT) has been applied globally. Several technologies combined with IoT will bring some benefits, such as personnel cost reduction, real-time intelligent surveillance, etc. [1, 2]. The wireless sensor networks (WSN) could address the challenges of power and signal installation, additional deployment costs, and application field limitation. In WSN, the sensing node is usually powered by batteries; therefore, battery life and maintenance fee become a challenge for IoT applications. This study proposes Adaptive Data Rate (ADR) and Transmission Power Control (TPC) using fuzzy controllers to reduce the power consumption and extend the battery life. The common frequencies of wireless transmission are divided into Sub-1 GHz, 2.4 GHz, and 5 GHz. The high frequency has a faster data rate; however, the 5 GHz signals would cause a higher attenuation than the others when it passes through obstacles. The corresponding coverage is also less than Sub-1 GHz and 2.4 GHz [3, 4, 5, 6]. However, the Sub-1 GHzhas wider coverage and lower power consumption owing to the corresponding narrow bandwidth and low frequency. Moreover, when the power consumption of sensors is not high in WSN, the overall power consumption is mostly consumed in wireless communications. If radio function could be turned off properly, the node powered by batteries would work for several years [7]. The types of Median Access Control (MAC) include scheduling-based [8; 9; 10] and competition-based [11; 12; 13]. The competition-based ones can accommodate more nodes without maintaining time synchronization. Although the throughput of scheduling-based is not good enough compared with competition-based system, it has the features of low-power and no package conflict in air [14]. In addition, the literature [15; 16] utilizes time-slot scheduling architecture to implement a Time Division Multiple Access (TDMA) system. Every sensor node is assigned a particular time-slot and it only needs to turn on to communicate with the bridge when its time-slot is pulled. In other words, each node can keep turning off during other times to save more power. Considering the low-power and system complexity, a time-slot scheduling of TDMA is adopted in this study. In WSN fields, the power consumption of sensor nodes has become a key technology. The battery powered nodes are very convenient to place anywhere [17; 18; 19]; however, battery life and maintaining frequency is a challenge for manufacturing because it is a finite capacity. It may achieve a good communication quality and long transmission distance by transmitting with maximum power [20]. Under the condition of ensuring communication quality, adjusting the transmission power via TPC can effectively reduce power consumption [21; 22; 23; 24]. In addition to reducing the transmission power, ADR also affects the overall power consumption. When the data rate is faster, the transmission time is shortened and the overall power is reduced [25; 26]. Packet Error Rate (PER), Received Signal Strength Indicator (RSSI), and signal-to-noise ratio (SNR) are often adopted as references to reflect the current communication quality. The literature [27] indicates that RSSI is an unreliable parameter to present communication quality. A high RSSI does not imply a low PER because interference would increase RSSI. In [28], experimental results indicate the performance of Packet Delivery Rate (PDR) in different data rates. Regarding the same PDR, the higher the data rate the higher SNR; it needs higher communication quality to maintain the same PDR when delivery rate (DR) increases. An energy efficiency (EE) method is proposed to estimate which combinations of transmission power and data rate have the best value of EE [29]. In previous research [30; 31], we have proposed a transmission power and data rate control algorithm to balance power consumption and communication quality.