ZigBee protocol is a global open standard to provide low-power wireless connections for many applications that implement measurement and control functions. ZigBee enhances the IEEE802.15.4 function with flexible and expandable network topology, easy-to-install comprehensive settings and intelligent routing technology, and high fault-proof capability. ZigBee also has strict security measures and can coexist peacefully in the same working environment with other wireless technologies, such as Bluetooth and WiFi. Communication security and reliability ZigBee's wireless transmission distance is closely related to the working environment. When the standard wireless control module is at 0dBm output power, the outdoor working distance can reach 450 meters, but indoors, the distance is greatly shortened due to the effects of absorption, reflection, diffraction, standing wave, etc. of the wall and other objects; the output power is greater than 15dBm power module The working distance can be increased by about 10 times. In addition, the network and cluster tree topology can further increase the working distance. Because communications are disrupted by wireless interference and poor transmission / reception conditions, ZigBee uses multiple technologies to ensure the reliability of communications. First, the ZigBee network uses an encoding mechanism for wireless transmission. In the 2.4GHz band, quadrature phase-shift keying (QPSK) modulation technology is used, and 4-bit data symbols are converted into 32-bit chip sequences. In this way, even if there are other wireless signals in the same channel at the same time, the ZigBee message can reach the destination completely. Secondly, its transmission adopts carrier sensing with collision avoidance and multi-point access scheme. Simply put, a node must first listen to the channel before sending to see if it is unblocked. If the channel is working, the node listens again after a delay, so it does not start sending messages until the channel is clear. Second, after the message arrives at the destination, the receiving device sends an acknowledgment signal to indicate that the message has been received. If the sending device does not receive the confirmation signal, it will send the original message again within a certain time interval. ZigBee has a “security toolbox†to provide high security. The main measures are: · Access control list: only predefined "friendly" nodes can join the network; 128-bit AES-based encryption technology: a highly secure key-based encryption system, some wireless microcontrollers are also equipped with hardware security functions. · Message update timer: Reject time-out messages to prevent external messages from attacking the network. Breathing Simulator And Heart Beating Device Breathing Simulator and Heart beating device Heart Beating Mechanism,Pulsing Device,Breathing Simulator,Heartbeat Simulating Mechanism AST Industry Co.,LTD , https://www.astsoundchip.com