ZigBee
This paper presents the feature analysis of zigbee technology based on IEEE 802.15.4 standard. . Due to characteristics such as low data rate, low price, and low power consumption, ZigBee is expected to be used in wireless sensor networks for remote monitoring, home control, and industrial automation.
Introduction to Zigbee
ZigBee is the most popular industry wireless mesh networking standard for connecting sensors,instrumentation and control systems.ZigBee provides several benefits just because it is an industry standard supported by multiple solution providers.ZigBee solutions are relatively inexpensive because several suppliers have already implemented ZigBee-based integrated circuits and modules in anticipation of high volumes for a standard solution.ZigBee-based solutions also offer users independence from any one supplier because one company’s ZigBee networking solution can be substituted for another’s.ZigBee also offers the potential for interoperability among different suppliers’ products. Finally, in theory, a ZigBee application deployed in a location can use other existing ZigBee nodes in that location to extend its range and improve its communication reliability.ZigBee delivers solid wireless connectivity for sensors and actuators in applications that can need the general benefits of mesh networking (i.e., coverage and reliability) at a reasonable price and tolerate ZigBee’s limitations in mesh size, power consumption, node-to-node range, and master-oriented operation. ZigBee is actually a network layer protocol standard, but it is designed to operate over a radio defined by the IEEE 802.15.4 standard for the physical and data link protocol layers.
ZigBee operates in two main modes: non-beacon mode and beacon mode. Beacon mode is a fully coordinated mode in that all the device know when to coordinate with one another. In this mode, the network coordinator will periodically "wake-up" and send out a beacon to the devices within its network. This beacon subsequently wakes up each device, who must determine if it has any message to receive. If not, the device returns to sleep, as will the network coordinator, once its job is complete. Non-beacon mode, on the other hand, is less coordinated, as any device can communicate with the coordinator at will. However, this operation can cause different devices within the network to interfere with one another, and the coordinator must always be awake to listen for signals, thus requiring more power. In any case, ZigBee obtains its overall low power consumption because the majority of network devices are able to remain inactive over long periods of time.
How zigbee works?
ZigBee basically uses digital radios to allow devices to communicate with one another. A typical ZigBee network consists of several types of devices. A network coordinator is a device that sets up the network, is aware of all the nodes within its network, and manages both the information about each node as well as the information that is being transmitted/received within the network. Every ZigBee network must contain a network coordinator. Other Full Function Devices (FFD's) may be found in the network, and these devices support all of the 802.15.4 functions. They can serve as network coordinators, network routers, or as devices that interact with the physical world. The final device found in these networks is the Reduced Function Device (RFD), which usually only serve as devices that interact with the physical world.
The figure below introduces the concept of the ZigBee network topology. Several topologies are supported by ZigBee, including star, mesh, and cluster tree. Star and mesh networking are both shown in the figure above. As can be seen, star topology is most useful when several end devices are located close together so that they can communicate with a single router node. That node can then be a part of a larger mesh network that ultimately communicates with the network coordinator. Mesh networking allows for redundancy in node links, so that if one node goes down, devices can find an alternative path to communicate with one another.
A comparison between zigbee and bluetooth
The ZigBee standard can operate in the 2.4GHz band or the 868MHz and 915MHz ISM (industrial, scientific and medical) bands used in Europe and the US respectively It sits below Bluetooth in terms of data rate: 250kbps at 2.4GHz (compared to Bluetooth's 1Mbps) and 20-40kbps in the lower frequency bands.
The operational range is 10-75m, compared to 1Om for Bluetooth (without a power amplifier). One other important difference between ZigBee and Bluetooth is in how their protocols work. ZigBee's uses a basic master-slave configuration suited to static star networks of many infrequently used devices that talk via small data packets. This aspect suits ZigBee to building automation and the control of multiple lights, security sensors and so on. Bluetooth's protocol is more complex because it's geared towards handling voice, images and file transfers in ad hoc networks. Bluetooth devices can work peer-to-peer and support scatternets of multiple smaller non-synchronised networks (piconets). The protocol, however, only allows up to eight slave nodes in a basic master-slave piconet set-up.
ZigBee allows up to 254 nodes. Masters can talk to each other and the number of memory size of the protocol stack that will lower the mice of ZirBee to around $2 ~ per chip; the ZigBee protocol stack will occupy around 30kwords of programme space compared to Bluetooths 25fikwords.
The main features of zigbee are:-
- Dual PHY (2.4GHz and 868/915 MHz)
- Data rates of 250 kbps (@2.4 GHz), 40 kbps (@ 915 MHz), and 20 kbps (@868 MHz)
- Optimized for low duty-cycle applications (<0.1%)
- CSMA-CA channel access
- Yields high throughput and low latency for low duty cycle devices like sensors and controls
- Low power (battery life multi-month to years)
- Multiple topologies: star, peer-to-peer, mesh
- Addressing space of up to:
- 18,450,000,000,000,000,000 devices (64 bit IEEE address)
- 65,535 networks
- Optional guaranteed time slot for applications requiring low latency
- Fully hand-shaked protocol for transfer reliability
- Range: 50m typical (5-500m based on environment)
Zigbee has low data rate
The radio channel data rate is a gross indicator of the throughput of the wireless connection, all else being equal. A higher data rate is not always better, depending on the requirements of the application. For a given transmitter power, higher data rate can be achieved by sacrificing range – or range can be increased by using a lower radio channel data rate
Low latency of zigbee
Low latency is another important feature of ZigBee.When a ZigBee device is powered down (all circuitry switched off apart from a clock running at 32kHz), it can wake up and get a packet across a network connection in around 15 milliseconds. A Bluetooth device in a similar state would take around three seconds to wake up and respond. According to CCL home,the latency gives you some power consumption advantages and it‘s important for timing-critical messages. A sensor in an industrial plant needs to get its messages through in milliseconds.
Low power consumption of zigbee
ZigBee’s reliance on a central mains-powered controller minimises the power consumption of the nodes. “They will only need to turn on when they want to transfer data,” explains Horne. “There is a beacon scheme that the master uses to define slots. The nodes can then wake up, listen, synchronise to a slot and send data back. It reduces the time that the outlying nodes need to be on for.”
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