Nowadays, Internet of Things (IoT) has become popular in various applications, such as smart home networks, smart city networks, and smart grid systems. The IEEE802.11n wireless local-area network (WLAN) is one of major communication technologies relevant to IoT applications due to the flexibility and cost efficiency, where the efficient power management is a key requirement of emerging IoT applications. Previously, we have studied the elastic WLAN system with the access-point (AP) transmission power minimization method using the throughput estimation model, to minimize the power consumption of WLAN while ensuring the throughput performance. However, this method relies on the accurate model, which requires a lot of throughput measurements in the target field. In this paper, to avoid extensive measurements, we propose another AP transmission power minimization method using PI feedback control. The initial power is examined from the difference between the measured received signal strength (RSS) at the AP from the station or node and the estimated RSS necessary for the target throughput. Then, the power is minimized by using the PI control, such that the measured throughput achieves the target one. For evaluations, we implement the proposal in the elastic WLAN system testbed using Raspberry Pi devices that have been adopted in many IoT applications, and conduct experiments with five topologies. The results confirm that the proposal has significantly reduced the transmission power while achieving the target throughput.
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