Energy Efficiency in IoT Networks: Integration of Reconfigurable Antennas in Ultra Low-Power Radio Platforms Based on System-on-Chip

The current state-of-the-art of Internet of Things witnesses the development of low-cost and smart-connected wireless sensor networks (WSNs) placed at the edge of clouds, enabling new services over the Internet. In these interconnected smart sensors, energy consumption is an important issue. This paper deals with decreasing energy consumption in WSN nodes by means of antennas with reconfigurability at radiofrequency. Our research has yielded two important novelties. First, the reconfiguration is accomplished with a platform comprised of a commercial ultra low-power (ULP) micro-controller and system-on-chip radio. Second, we consider explicitly the energy overhead involved in the antenna configuration process and its impact on the global energy efficiency of the system. We discuss two complementary ways of reducing the energy consumption; one by lowering the amount of transmitted power, the other by increasing the transmission rate. We employ an antenna array with a steerable beam, controlled by an algorithm embedded in the firmware of the ULP platform. This is designed for line-of-sight conditions, and the beam steering maximizes the received power. Our results show that with a common IEEE 802.11 b/g system-on-chip module and an antenna gain of 12 dB, a net power saving factor of 28% can be obtained by reducing the transmitted power, at unchanged data rate; additionally, by keeping the transmit power constant, but increasing the data rate, an energy saving from 18% to 96% can be achieved, depending on the link distance and achievable data rate. Our experiments have confirmed both routes of energy saving.