Picking the right technologies for your home network design

Munish Mangal and Nishant Omar

November 10, 2009

Munish Mangal and Nishant Omar

Going wireless
So which wireless technology should you use? The answer depends on the specifications of the home network. Some networks are deployed such that they are suitable for use only within a house, while some offer extended control ranges beyond the perimeter. Zigbee wireless network for home automation control

For local operation, Zigbee is one of the best candidates for wireless home networking. It is a communication standard developed by the Zigbee Alliance for low-cost, low data rate, low-power, two-way wireless communication (Figure 4 below).

Figure 4: The block diagram of the Zigbee-based home network system.

Zigbee has evolved into the IEEE 802.15.4- 2003 standard and operates in the 2.4GHz frequency band. Zigbee gets its name from the zig-zag pattern of a bumble bee that it emulates when transmitting data over its mesh network. Zigbee offers some advantages, making it a potential candidate for home networking solutions:

1. Long life. While devices based on other technologies can last for a few hours on a charge, Zigbee devices are designed to last for years. The Zigbee devices can be even be made to go into low power mode, which further enhances the life of the network.

2. Long communication range. One of Zigbee's key features is its ability to cover large areas with routers. This feature helps differentiate Zigbee from other technologies. Mesh networking extends the range of the network through routing while even without routers, Zigbee devices can transmit as far as several tens of meters. Furthermore, one Zigbee network can support up to 65,536 devices and with mesh networking the network range can be extended even more.

Secure network. Zigbee features include energy detection, clear-channel assessment and channel agility, thus helping devices pick the best possible channel and avoid other wireless networks. Message acknowledgement, on the other hand, ensures that the data was delivered to its destination.

Multiple levels of security ensure that the network and data remain intact and secure. Zigbee devices create the network with the specific network identification numbers, thereby avoiding interference between the different networks of Zigbee itself.

Flexibility. Zigbee-based networks are flexible and can be extended to a large network with very minimal efforts. The commands or data in a Zigbee network is sent as messages. With a message field of more than 100bytes, one Zigbee node can be made to control a large number of device parameters and/or multiple devices.

Support . The Zigbee standard is managed by the Zigbee Alliance, an association of companies providing everything from silicon to finished products with service, support, tools and testing platforms.

Low data rate. Although Zigbee offers the low data rates up to 250Kbit/s but this data rate is suitable for home network applications where the primary function is to monitor and control appliances. Foreseeing the usage of Zigbee in home networking, a Home Automation profile has been introduced in the Zigbee standards. This profile ensures that Zigbee-based home networking devices become more and more mass market products than just being prototypes.

Zigbee technology and the Home-Automation profile provide interoperability between similar products from different vendors, allowing a greater range of control and integration of different devices at home. This gives consumers the freedom to buy and install devices at their discretion.

Because of the low RF power involved, Zigbee cannot be used for long-distance communication. Imagine that you are on your way home and you want to switch on the air conditioner of your home or switch on the water heater to enjoy a shower immediately after you reach home. This type of networking cannot be implemented by Zigbee because one cannot install the routers all along the road! But this feature can be achieved by clubbing the Zigbee network with GSM networks.

GSM for distant contro. Technology has advanced in leaps and bounds over the last two to three decades, and the single invention that has impacted the life of the consumer the most is the cellphone. Internet connections are now freely available even in entry-level Edge phones. This can be further networked to deliver access to other appliances at home.

This cellphone feature can be used for control of the home network from remote locations. With this, a consumer could setup a camera to periodically transmit images onto their cellphone via the Internet. The same application can be used by working parents to check on children at home.

These applications rely on an Internet connection with the cellphone, but other applications with limited supervision and control can also be built using SMS. With this messaging service, one can send the predefined SMS from the cellphone to the central hub of the network and control the devices connected in the network and similarly receive SMS from the network. With this, one can switch on/off the air conditioner, water heater, lights, microwave oven and any other connected appliance while on the move.

In GSM-controlled home networks, the central hub of the local network is empowered with a GSM interface. This hub/station receives commands from a remote cellphone through the GSM network provided by the service provider, and then this GSM interface further gives commands to the local home network to control the devices.

The communication can be done in the form of SMS or GPRS depending on how the network is implemented. While this implementation offers control from distant places, it may cost the consumer a bit much. The consumer has to take a GSM connection from a service provider and pay the periodic service charge.