Low-Power Networked Solution

Colin Faulkner, Product Manager Low Power RF Solutions, NXP Semiconductors


At home with the wireless internet

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Figure 1: JenNet-IP Stack build-up

All households and businesses are under pressure to fulfil the twin ideals of reduced energy consumption and reduced costs. There have been many advances in building technology such as double glazing, and roof and wall insulation, which improve the loss of energy, but to date, very little has been done to minimise consumption at the source. Conventional heating and lighting systems are not much more sophisticated than piling more wood on the fire if it's cold! Conventional thermostats and lighting systems often operate at a whole house level and provide uneven distribution of comfort around the building. This is true for both residential and commercial buildings. One reason for this condition is "installation costs". It is possible to wire up control signals to individual lamps or to place thermostats in every room, but in practice, the cost of installation is prohibitive. Even for a new build, cabling is expensive to install, making it uneconomic to specify improved control. However, the "Internet of Things", particularly when connected with wireless technologies, is set to change the situation by offering a means to install many sensors and actuators at very low cost. IPv4 (Internet Protocol version 4) as the transport mechanism of choice for data on the internet has served the world well for many years, but has been restricted from dramatic expansion by the limited number of IP addresses. This has recently been addressed by the introduction of IPv6 which now offers around 5*1028 addresses for every person on the planet. This is plenty for any currently conceivable control systems and in principle, any device around the world could be given a unique IP address. If this can be applied to lighting and climate control within buildings, we have a mechanism to realise complex control systems. The issue, of course, is how to communicate with the devices in a cost-effective fashion and this is where a wireless network comes into play. What is required is a low-power networked solution specially designed for building automation solutions. The IEEE802.15.4 standard provides a radio and Media Access Control (MAC) platform designed for low-power wireless networks, including systems where devices are connected together in a tree or mesh arrangement. These techniques allow messages to bounce from node to node, making their way across the network. If a building has these nodes installed, in every light fixture, for example, then it ensures that all devices are within range of one of the radios. One of the most common standards using IEEE802.15.4 is ZigBee, which defines both the networking to connect devices together and "profiles" for interoperability, allowing devices from different manufacturers to work together. As an alternative to ZigBee and to provide IP connectivity to all nodes, the Internet Engineering Task Force (IETF) has developed a standard named 6LoWPAN. This is designed to allow IPv6 communications over wireless networks with low bandwidth, such as IEEE802.15.4. 6LoWPAN describes two main techniques; i) fragmentation of large IP packets so that they can be transmitted within the 128 byte payload of IEEE802.15.4 and ii) compression of the IP headers within the wireless network, again in order to provide as much payload space as possible. 6LoWPAN therefore is the key enabler in achieving our dream of IP connectivity to all devices in the home. However, there are other parts of this picture - we still require methods to network devices together and to provide a common way of operating so that some kind of interoperability is possible. NXP has solved this problem with the creation of JenNet-IP, which provides the optimum combination of standards-based and proprietary solutions to provide ready-to-use networked wireless solutions. The structure of JenNet-IP is shown in Figure 1.



JenNet-IP uses NXP's proven JenNet networking layer to provide the connectivity between devices. This is a tree-based networking layer, with the capability to create networks of up to 500 nodes. It has one of the key features of a so-called Mesh network, in that it allows self-healing. If one of the established routes fails ? for example, due to a faulty router ? the network will detect this and will automatically try o re-establish alternative routing through a nearby node, providing a high degree of robustness and reliability which is essential to successful deployments. It also includes techniques for applying a high level of data security using the 128-bit AES encryption built into IEEE802.15.4. This ensures that networks cannot be hacked maliciously and that they remain unique to their owner and do not overlap with adjacent ones. In addition to providing true IP connectivity from the internet to devices in the home, JenNet-IP also implements a gatewayless mode of operation. This allows the system to carry on working even if the internet gateway fails. It also allows the sale of starter kits comprising just a few devices and a remote control in order to allow consumers to try out and become familiar with the technology before investing in a full internet connected system. One of the other important features is the provision for interoperability and device control. This is implemented in a simple application layer named SNAP (Simple Network Application Protocol). This uses the concepts of the common SNMP protocol but has been architected to provide a solution appropriate for low-cost embedded devices. Put simply, it provides a small database of device characteristics, such as name, group membership, and capabilities (On, Off, Dim, Up/Down, etc/). This can then be interrogated and manipulated by external devices. So a SNAP application will run on a bulb and this can then be controlled by another SNAP application running on either a remote control device, or on a device such as a tablet PC connected to the internet. In this way, individual bulbs can be controlled and put into groups, enabling the provision of lighting "scenes" ? for example with just one lamp illuminated for reading or dimming the lamps close to the TV for watching a film. With wireless connectivity enabling implementation of complex control systems with minimal installation costs, seamless integration with the internet, and a powerful and flexible means of providing interoperability, JenNet-IP goes a long way to facilitating the systems needed to maximise energy efficiency within all sorts of buildings. Installation costs are minimised as the only wiring required is power which is already required for most devices. Switches and remote controls can be easily battery-powered or even use energy harvesting. The use of IP to all nodes ensures that the wireless system can interface directly with existing or new building management systems which can interact with the data generated to accurately control light levels, temperature and humidity to ensure user comfort with a minimum of energy usage. For example, in an office system, if each lamp can be individually controlled, it becomes straightforward to dim lamps where the exterior ambient light level means that little or no additional light is required. Likewise, at home, with groups and scenes, there is no need to have unused lamps on, again minimising energy usage. In summary, JenNet-IP is a low power wireless networking system that provides IPv6 connectivity to any device within buildings, providing flexible individual control and monitoring of lights and heating, without the huge expense of cabling installation, hence making an important contribution to the efficient use of energy The Wireless capability is fully integrated into the bulbs themselves, using NXP's GreenChip solution which combines the JN5148 wireless microcontroller with the TEA1721 power supply devices and SSL2108 (for LED lamps) or UBA2028 (for compact fluorescents) into the body of the bulb itself. The lamps can be set up and controlled individually or in groups, and scenes comprising different light levels on each lamp can be set, for example for reading or for watching TV. The remote control is a full member of the network and can control devices within it, but the beauty of the IP provision is that external devices can easily control the system. This is demonstrated by the use of an Android application running SNAP and communicating into the network via the Wi-Fi router and also by the provision of a web interface, again manipulating the SNAP databases. The smart plug devices allow both on-off control of equipment such as a TV or monitor, but also monitoring of energy usage. This allows users to see exactly where their energy usage is going and to take steps to minimise consumption. www.nxp.com