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A home automation system typically comprises an intelligent electronic device network that monitors and controls the environment for the comfort and security of the residents. It may include such diverse functions as light and climate control, security and surveillance systems, multimedia home entertainment, and automated plant watering.
For instance, a homeowner unlocks her door via a wireless key. When the door opens, the system turns on nearby lights and adjusts the room temperature to her previously selected preference. As she walks through her home, the system detects her presence, and a multimedia home entertainment network seamlessly transfers video data among systems located throughout the home. Meanwhile, the security system keeps vigil, monitoring motion, smoke and fire detectors, ever ready to alert the appropriate authorities and/or the homeowner, if she is off the premises.
These varied applications have differing requirements for data rates and power consumption. Hence, multiple networking standards exist under the guise of "home automation." This article will provide a guide to the different communication protocols that form this smart network.
A home automation concept
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Depending on the installation, the network connections may be either wired or wireless. For wired networks, interdevice communications may be accomplished via dedicated control wires or, less expensively, through power lines, if applicable. For simple on/off functions such as lighting control or motion detection, a commonly used protocol is X10. It is both a power line and wireless (i.e., dual-mesh) open international standard for low-data-rate (20-bit/second), unidirectional communication.
In the United States, the wireless operating frequency is 310 MHz, but in European systems, it is 433 MHz. To overcome reliability and low-data-rate limitations, SmartLabs Technology introduced Insteon, a successor to X10. This system also is dual mesh, with both wired and wireless (900-MHz) physical layers.
Another popular wireless protocol for low-cost, low-data-rate monitoring and control applications is ZigBee. It is based on the IEEE 802.15.4 standard for wireless personal-area networks (WPANs). ZigBee operates in the industrial, scientific and medical band at 2.4 GHz. It makes significant improvements over the X10-type protocols by providing a reliable wireless, bidirectional, high-throughput (~100-kbyte/s), low-latency network that allows more than 64,000 nodes per network. Because of their very low duty cycles, ZigBee devices have ultralow power requirements and therefore have long battery lives. Individual devices may run for a year or more using the originally installed battery. ZigBee also employs a direct-sequence spread-spectrum encoding scheme. The advantage of DSSS is that the energy in the signal is spread over a broader part of the RF spectrum than in FM, improving security and reducing interference from other signals.
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