Читать книгу Industry 4.0 Vision for the Supply of Energy and Materials - Группа авторов - Страница 38

Wi-Fi is a family of wireless network protocols regulated by the IEEE 802.11 standard [84], originally designed to offer high data rate connectivity and Internet access to a limited number of devices for WLAN. The early versions of the standard (IEEE 802.11b/g/n/ac) are limited by high power consumption and frame overhead. In addition, they do not fully support small and deterministic payloads required for mission-critical IoT applications. Thus, a set of modifications is proposed by IEEE 802.11 working group to amend WLAN to IoT scenarios. The first of such efforts was IEEE 802.11ah, known as Wi-Fi HaLow, which fulfills IoT requirements and could achieve denser deployment, lower overhead, and less energy consumption compared with legacy Wi-Fi networks [85]. The main features of the IEEE 802.11ah PHY layer are inherited from IEEE 802.11ac, which accommodates relatively narrow channel bandwidths. Its MAC layer has adopted some enhancements to improve power-saving features, to assist large number of devices, and to increase data rate. IEEE802.11ah supports machine-to-machine (M2M) communications for IoT services such as smart metering and industrial automation [86].

The IEEE 802.11ax standard, also called Wi-Fi6, is another effort that supports mission-critical data transmissions [87]. It underpins complex applications such as VR and robotic motion control [88]. To ensure distinct transmission scheduling for time-critical and delay-sensitive use cases, the MAC layer of Wi-Fi6 adopts orthogonal frequency division multiple access (OFDMA). Moreover, adaptive modulation and coding schemes are used in MAC protocol to tackle high levels of variations in wireless links [89].