ZigBee

ZigBee, developed by ZigBee alliance, is an adaptation of IEEE 802.15.4, classified as a Wireless Sensor Network (WSN) for the IoT applications. Indeed, it transmits data at low rate and low power, saving as much battery as possible. A lot of applications can use this protocol such as the home automation, medical device collection, industry monitoring, … To achieve this goal, it also spends the majority of the time in sleep mode, making it more difficult to have a fast responsive communication with ZigBee nodes: communications are scheduled around beacons that are periodically sent, allowing to define sleep periods and active periods in the network. Due to its low emission power, it is not robust against noise and the ZigBee systems working in the 2.4 GHz band will be interference-sensitive (Wi-Fi, Microwave). ZigBee implements a mechanism to avoid this kind of interference: if a node detects interferences, the entire network will switch to another frequency. Two modulation schemes are used : BPSK (binary phase-shift keying) for sub-GHz applications and O-QPSK (offset quadrature phase shift keing) for the 2.4 GHz band. The last one thus offers higher data rate. The ZigBee can be used in multiple network topologies (star, mesh or tree), and can adapt as well to infrastructure mode as to ad-hoc mode. ZigBee implements a built-in encryption scheme. As oppose to the Thread, the Zigbee can support much more devices in one network (more than 653356). The range can reach 150 meters thanks to the direct sequence spread spectrum.