Picking the right technologies for your home network design - Embedded.com

Picking the right technologies for your home network design


Over the last few years, a great expansion in the variety of remote control devices has occurred in our day-to-day life. A few years back, IR remotes for the TV were the only such devices in the homes. But today, almost all the electronic devices are controlled using a remote, which results in large numbers of remotes in our homes.

Now the question arises as to why we need a lot of remotes. Devices such as TVs, garage door openers, light and fan controls etc. predominantly necessitate one-way, point-to-point control.

They're not interchangeable, and they usually don't support more than one device. Because most remotely controlled devices are proprietary and are not standardized among manufacturers—even those remotes used for the same function (like turning on and off lights) are not interchangeable with similar remotes from different manufacturers.

In other words, the consumer has as many separate remote control units as devices to be controlled. To solve this problem, the universal remote controllers with learning capability are already in the market for the last few years.

But because of their line of sight and short range of communication and limitation in the number of supported devices, they find only limited use in the home entertainment segment.

In addition to comfort, home security is a consumer's significant concern. Home security systems like burglar alarms, motion detectors and surveillance cameras are already emerging as popular products in the market. But these products offer somewhat limited security.

All these needs have triggered the requirement of a home network that can control and monitor a number of devices without any line of sight or range limitations. A home network is a method of allowing different devices to communicate with one another.

In a home network, one or more devices have the power to monitor or control the other devices in the network. Generally the home networks are used for communication between digital devices used within the household, usually a small number of PCs and accessories, such as printers and mobile computing devices. The major purpose is the sharing of Internet access (often a broadband service through a cable TV or DSL provider) or sharing of files and utilities.

Today, however, home networks are finding extended applications involving data collection from several devices or specific sensors for centralized control from a single control unit that monitors the premises even when one is far away.

This article explores various home network techniques and the application possibilities with an implementation example. It also further explores Zigbee as the choice for a localized home network and explores the possibility of GSM for remote operation.

Implementation techniques
A home network was implemented in 1978 for the Sears Home Control System and the Radio Shack Plug'n Power System. It used power-line wiring to send and receive commands. After this, a lot of technologies have been explored for home networking, ranging from wired networks to wireless.

With the advancement of technology, Ethernet became the traditional choice in homes, but wireless technologies are gaining ground fast. While both wired and wireless technologies claim advantages over the other, both represent viable options for home networking.

In wired networks, one or more devices are connected through cable to a central hub through routers or repeaters. The central hub is connected to a user interface from which it gets the commands and in turn sends them to the connected devices (Figure 1 below ).

Figure 1: In wired networks, one or more devices are connected through cable to a central hub through routers or repeaters.

Of the various wired technologies, Ethernet 10/100Mbps is the most popular network method because of the low price of the network cards, reliability and speed; but this comes with the initial trouble of laying out the network cabling within the household; future expansion to cater for newer devices may not be possible or very limited.

HPNA, also called PhoneLine or HomePNA, is another home networking technique. Its advantage is that it works over the existing copper telephone wires in the home without interfering with voice or DSL communications.

But this offers a speed of only 10Mbps. FireWire networking is supported by most of operating systems these days. This is most suitable for the short-range high-speed communication. Apart from these approaches, there are other wired technologies like PLM, Ethernet Gigabit and USB.

A common problem in wired topologies is that they are difficult to be done in existing homes and don't give much freedom to move nodes from one place to another. Installation is difficult and costly, thus restricting user flexibility.

The wired network's installation difficulty has encouraged wireless networks. In wireless networks, the devices are connected to a central hub or station using a wireless communication standard, which in turn interacts with the user interface (Figure 2 below ).

Figure 2: In wireless networks, the devices are connected to a central hub or station using a wireless communication standard, which in turn interacts with the user interface.

The popular wireless technologies for home networking include Wi-Fi, Zigbee, wireless HomeRF and Bluetooth.

To maintain uniformity among different vendors, all the wireless communication protocols follow some IEEE standards. Although wireless technologies may suffer from signal interference, higher cost and lower data rate compared with wired ones, they offer more desirable features like easy installation, easy accessibility and enhanced user friendliness.

Lower data rate does not block the road of wireless technology in home networking, as the offered data rate is sufficient for control and monitoring applications, and signal interference is taken care of by software techniques. Moreover, adding a new device to the existing network is as simple as just switching it on. Table 1 below compares the various networking technologies in terms of speed, range and cost.

Table 1: Here's a comparison of the various networking technologies in terms of speed, range and cost.

Wireless home networks are getting even more popular day by day. Depending on user requirements, home networks can be developed using wired or wireless, or mixed technologies (Figure 3 below ).

Figure 3: Depending on user requirements, home networks can be developed using wired or wireless, or mixed technologies, which is shown above.

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.

Home Network Applications
Convenience and control. Home networks have empowered the user to monitor and control devices from anywhere in the home or even far away. Now the user has the comfort to control devices with one gadget.

A user can switch on/off the lights or appliances in a room while being in another room. Now, if a user wants to take a shower as soon as he reaches home, then he can turn on the faucet while on the way.

The user can operate the doors and windows at home while sitting in one corner of the home. Many a times, one leaves home and later realizes that he/she has forgotten to switch off the television. Home networks provide the facility to switch off the TV remotely. There is no doubt that home networks are reducing the stress level of a user by making things easier and more manageable.

Safety and security. The ability to link different types of devices such as lighting, security and sensors into a single system provides greater safety and security. Various dedicated devices containing sensors for temperature, humidity, fire, smoke, gas, glass break and motion (MEMS) can be installed in the home network.

When these devices detect any abnormal condition, they send a message to the hub/main station, which can raise any alarm signal and alert the user. For example, devices with gas, fire and smoke sensors can be placed in the kitchen; glass-break sensors can be installed in various windows/doors, temperature and fire; and humidity sensors can be installed in other areas of the house. A device containing a camera and microphone can be installed at the door. Thus, when the bell rings, the homeowner can see the person outside and can interact without opening the door.

The network can be made more intelligent by preprogramming actions to be taken for specific cases. For example, the network can be developed so that on detection of a fire, the sprinklers turn on. And when theft is detected, the police are automatically called. Home networks provide the ability to do remote monitoring in other ways, too. One can use the home network to monitor babies, the elderly and pets.

Energy management, conservation. Electrical energy is something we can't live without, and to ensure its availability for a long time everyone has to use it ef- ficiently. In many cases, even if one wants to conserve energy by switching off unwanted devices, one may not do it. With a home network, one can control the devices from remote locations through a single remote control.

Specific gadgets or devices can be developed and can be installed on the switch board/power board of every room of the home, and all the switches get controlled by a single gadget. Automated controls can make the network more energy-efficient. For example, if there is no one in the room, the lights and fan could be switched off automatically. These small savings of electrical energy could contribute a lot multiplied across many users worldwide.

Implementation example
The system approach of home networks can be understood by exploring a small home network, which is specifically designed for illustration purposes only. This home network works on the Zigbee standard, where the central station or the base station acts as the coordinator of the network, and the nodes act as the end devices.

In the Zigbee network, the coordinator is a device having the power to create a network, while the nodes are the devices that can receive and send commands and data to the coordinator and control the actions of the end devices.

Both coordinator and nodes are MCU-based devices with a Zigbee transceiver. The MCU operates the Zigbee transceiver, TFT display, touchscreen/LCD, USB.

The base station can control and monitor up to eight different nodes, and each node can be connected to one or more home devices including a microwave, lights, fans and air conditioners. The nodes also have sensors for temperature, humidity, motion and ambient light, and this data can be communicated to the base station on the Zigbee network.

The base station and the nodes are individually powered by 3.7V Li-ion battery, which can be recharged by power supplied through a USB ( Figure 5 below ).

Figure 5: Shown is an example of base station of a home networking system.

During the installation of the network, when the base station is switched on for the very first time, it scans the environment and creates a unique Zigbee network.

Now, when any node is powered up in the network periphery, the base station gets its complete information and creates a unique identification or name for this newly joined node. Depending on the device connected to the node, the user can assign names like “heater,” “air conditioner” or “bedroom light” to the node.

The user can also see the status of every node. Using the touch display of base station, the status of devices can be changed remotely. This gives the user freedom to remotely monitor and control appliances.

Apart from the control, the base station periodically collects data from the sensors at different nodes and stores this in its internal memory. This data can be downloaded to a PC via USB for further usage or analysis.

An interesting application of this network is in wireless-controlled plugs, which are Zigbee-enabled nodes that can be connected to any switch or power board in a room to control one or more power switches (Figure 6 below ).

Figure 6: Block diagram of a Zigbee-enabled node.

In this system, a Zigbee-enabled node is connected between the electrical on/off switch present on the switch board and electrical appliances. Upon reception of control commands from the base station, the node controls the attached appliances.

With this installation, one can control a number of devices with one Zigbee-enabled node. Although developed for the illustration with minimal features, the above system can be customised or expanded to any level to cover the requirements of the consumer.

With the continuous advancement of the technology, consumers' expectations and requirements are increasing. They want to control and monitor their world and are looking for the systems that provide the power of control with high levels of security and safety. Home networks are already trying to fulfill the needs of the consumer. Undoubtedly, home networks will become an integral part of every consumer's life.

Munish Mangal and Nishant Omar are design engineers at STMicroelectronics Pvt. Ltd India.

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