A typical IEEE 803. 15. 4-based, ZigBee-complaint device is shown in figure 1. [pic] Figure 1.
Typical 802. 15. 4/ZigBee Device that has included antenna, RF data modem, applications processor, all necessary passive and 16MHz crystal about 15x40mm – Courtesy Freescale Semiconductor. The ZigBee Alliance released their specification to the public in June 2005, and since then the playing field has become much simpler for product designer who want to their sensor or control application.An open and growing industry group of more than 180 companies from product/system OEMs to application developers to semiconductor companies, the Alliance has worked hard to provide a technology that takes best advantages of the robust IEEE STD 802. 15. 4 short-range wireless protocol, adding flexible networking, strong security tools, well-defined application profiles, and a complete interoperability, compliance and certification program to ensure that end products designed for residential, commercial and industrial spaces work well and network information smoothly.
Need of ZigBee:There are a multitude of standards that address mid to high data rates for voice, PC LANs, video, etc. However, up till now there hasn’t been a wireless network standard that meets the unique needs of sensors and control devices. Sensors and controls don’t need high bandwidth but they do need low latency and very low energy consumption for long battery lives and for large device arrays. There are a multitude of proprietary wireless systems manufactured today to solve a multitude of problems that also don’t require high data rates but do require low cost and very low current drain.
These proprietary systems were designed because there were no standards that met their requirements. These legacy systems are creating significant interoperability problems with each other and with newer technologies. The ZigBee Alliance is not pushing a technology; rather it is providing a standardized base set of solutions for sensor and control systems. The physical layer was designed to accommodate the need for a low cost yet allowing for high levels of integration. The use of direct sequence allows the analog circuitry to be very simple and very tolerant towards inexpensive implementations.
The media access control (MAC) layer was designed to allow multiple topologies without complexity. The power management operation doesn’t require multiple modes of operation. The MAC allows a reduced functionality device (RFD) that needn’t have flash nor large amounts of ROM or RAM. The MAC was designed to handle large numbers of devices without requiring them to be “parked”. The network layer has been designed to allow the network to spatially grow without requiring high power transmitters.
The network layer also can handle large amounts of nodes with relatively low latencies. Network Feature: While ZigBee supports a variety of network topologies, including star, mesh and cluster networks, mesh networking is a fundamental and differentiating attribute to ZigBee’s design. In fact, mesh network support is so integral to ZigBee’s value proposition that the name is based on the ZigBee Principle; the zigzag path of bees that serves to signal a new food source to other members of the colony. The bees’ survival depends on the continuous communication of information between every member of the colony.
A mesh network is comprised of a network coordinator or master device and can connect up to 65,000 network nodes, serving as full-function devices (FFD) or reduced-function devices (RFD). A full-function device (FFD) carries full 802. 15. 4 functionality and all features specified by the standard.
Its computing power makes it well suited for a network router function. A reduced-function device (RFD) is generally used at the network edge. All of these devices can be no more complicated than a transceiver, a simple 8-bit MCU and a pair of AAA batteries.Through a series of redundant pathways, a signal initiated from a sensor or node on the network seeks out the closest connection for routing data and allows for either a single hop to the master device or multiple hops to successfully conclude its data transmission.
The continuous flow of communication exacted by a mesh network topology provides the reliability required for wireless-based connectivity of remote monitoring and sensing controls. By providing multiple pathways for data to travel, a mesh network eliminates the single point of failure scenario and affords a transparent recovery of a network node.Designed to be highly adaptive and scalable, the ZigBee specification allows a new device or network node to be added and adjusts to the addition through a simple request to the master device. Low power consumption, simply implemented. Users expect batteries to last many months to years! Consider that a typical single family house has about 6 smoke/CO detectors. If the batteries for each one only lasted six months, the homeowner would be replacing batteries every month! Bluetooth has many different modes and states depending upon your latency and power requirements such as sniff, park, hold, active, etc. ZigBee/IEEE 802.
15. 4 has active (transmit/receive) or sleep. Application software needs to focus on the application, not on which power mode is optimum for each aspect of operation. Even mains powered equipment needs to be conscious of energy. Consider a future home with 100 wireless control/sensor devices, ZigBee devices will be more ecological than its predecessors saving megawatts at it full deployment.
Low cost (device, installation, maintenance). Low cost to the users means low device cost, low installation cost and low maintenance.ZigBee devices allow batteries to last up to years using primary cells (low cost) without any chargers (low cost and easy installation). ZigBee’s simplicity allows for inherent configuration and redundancy of network devices provides low maintenance. High density of nodes per network. ZigBee’s use of the IEEE 802. 15. 4 PHY and MAC allows networks to handle any number of devices.
This attribute is critical for massive sensor arrays and control networks. Simple protocol, global implementation.ZigBee’s protocol code stack is estimated to be about 1/4th of Bluetooth’s or 802. 11’s. Simplicity is essential to cost, interoperability, and maintenance. The IEEE 802. 15.
4 PHY adopted by ZigBee has been designed for the 868 MHz band in Europe, the 915 MHz band in N America, Australia, etc; and the 2. 4 GHz band is now recognized to be a global band accepted in almost all countries. ? Technical data: |1. |Carrier frequency |2. 4 GHz | |2.
Micro-controller |8 bit | |3 |Power Consumption |30 (W (sleep) | | | |6 mW (micro controller active) | | | |60 mW (radio active) | |4. Range (node to node, outside) |125 m | |5. |Data Rate |250 kbps | |6. |Operating Temperature Range |-20 to +70(C | |7. |Size (of PCB) |33x55mm2 | Operating Frequency: |Frequency |Band |Coverage |Data Rate |# Channels | |2.
4Ghz |ISM |Worldwide |250Kbps |16 | |818Mhz | |Europe |20Kbps |1 | |915Mhz |ISM |Americas |40Kbps |10 | ZigBee Network Model: [pic] ZigBee Stack: [pic] ? Application:ZigBee networks consist of multiple traffic types with their own unique characteristic, including periodic data, intermitted data and repetitive low latency data. The characteristics of each are as follows: * Periodic data- usually defined by the application such as a wireless sensor or meter. Data typically is handled using a beaconing system whereby the sensor wakes up at a set time and checks for the beacon, exchanges data and goes to sleep. * Intermitted data- either application or external stimulus defined such as a wireless light switch.Data can be handled in a beaconless system or disconnected operation, the device will only attach to the network when communication is required, saving significant energy. *Repetitive low communication data- uses time slot allocation such as a security system.
These applications may use the guaranteed time slot (GTS) capability. GTS is a method of QoS that allows each device a specific duration of time as defined by the PAN coordinator in the Superframe to do whatever it requires without contention or latency. Market Opportunities: ZigBee is the only standards-based technology designed to address the unique needs of low-cost, low-power, wireless sensor networks for remote monitoring, home control, and building automation network applications. Within the residential control market, intelligent sensors will provide greater control of lighting, heating, cooling, watering, appliance-use and security systems from anywhere in the home.With greater automation of home control systems, homeowners can adjust their environment to run more efficiently, reducing utility costs.
Homeowners will be able to buy off-the-shelf products and be assured that they’ll work together in their networked environment. Because ZigBee is well suited for applications that require low power, such as light switches and sensors, it can operate using standard off-the-shelf batteries for months, years or even decades.Homes equipped with ZigBee-based networks will make it easy for builders, contractors, and home-supply manufacturers to reconfigure heating, lighting, and security systems to accommodate additions and the remodeling of kitchens, bathrooms and other property-value–enhancing projects. Developers for building automation can take advantage of the ZigBee specification to build and deploy wireless monitoring networks that help to centralize the management of lighting, heating, cooling and security systems and provide the flexibility to reconfigure systems quickly and ost-effectively to adjust for individual or tenant changes within a building structure.
While initially focused on the home automation and building automation market segments, ZigBee has the potential to be a key driver in enabling the broad-based deployment of wireless networks for a variety of market segments including industrial automation and controls, automatic meter reading, personal health-care–monitoring devices, PCs and peripherals, supply-chain and logistics management, and other future market segments. ?ZigBee v/s Bluetooth: Bluetooth seems best suited for: Synchronization of cell phone to PDA Hands-free audio PDA to printer @ While ZigBee is better suited for: • Controls • Sensors • Lots of devices • Low duty cycle • Small data packets • Long battery life is critical @ Air Interface comparison: ZigBee Bluetooth Peak Information Rate Peak Information Rate ~128 Kbit/second ~108-723 Kbit/second @ Power consideraion: ZigBee Bluetooth # 2+ years from ‘normal’ batterie# Power model as a mobile phone (Regular daily charging) Designed to optimize slave# Designed to maximize ad-hoc Power requirements functionality ? Conclusion: ZigBee devices can quickly attach, exchange information, detach, and then go to deep sleep to achieve a very long battery life. ZigBee devices have a real potential to solve the challenge of bringing simple, effective wireless connectivity to low-rate sensors and control devices at an effective cost. ? Bibliography: 1. www. zigbee. org 2. www.
frescales. com/zigbee 3. www.
silabs. com/zigbee 4. www. google. com.
5. IEEE network magazine – [pic]