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Volume 73 (Dec 14, 2007)

ZigBee, An Embedded Wireless Network Protocol, Connects Every Microcontroller Embedded Everywhere

How many microcontrollers do you think you have at home? Probably a hundred or more—because microcontrollers are built into every consumer electronics product. For instance, you may have a disk player, camera/camcorder, audio system, video game console, telephone, fax machine, printer, refrigerator, coffee maker, microwave oven, electric/gas range, washing machine, vacuum cleaner, ventilation system, utility meter, room air conditioner, and more.

Imagine what it would bring to your life if every embedded microcontroller everywhere in your home started talking to each other over a radio wave. Hopefully it would make life more convenient, environmentally friendly and safe. To explore these possibilities, we interviewed Hidekazu Umeda, CEO of Skyley Networks, Inc., a network technology supplier that specializes in ad-hoc mesh networking, and Hirokazu Yuasa of NEC Electronics' Multipurpose Microcomputer Systems Division.

Peer-to-Peer Network

Q: Mr. Umeda, whenever we talk about "wireless communication," we usually think of mobile phones or wireless LANs for personal computers. What is different in the wireless network technology you are dealing with?

Mr. Umeda: "For instance, if you try to talk to someone in the room next to this room via mobile phone, RF signals are first sent to the ground station antenna of the mobile phone company, after which they pass through the mobile phone company's server and then once again return to the ground station antenna before finally reaching the mobile phone in the next room. Makes for quite the detour, doesn't it? That is why we are trying to develop a technology with RF signals that need not pass through the mobile phone company's ground station antenna, but rather can directly connect to the mobile phone in the next room via wireless communication. This is commonly referred to as P2P (Peer-to-Peer) communications (*1). With this technology, communication can also be carried out via relay of transmissions from the next room to the room next to that, much like the way a bucket brigade works.

Because the communications standard for P2P protocol has recently been released as the ZigBee standard, we are now in the process of developing the communications protocol software that works on NEC Electronics' microcontrollers. The name ZigBee (*2) came from the way bees fly as they communicate with each other, exchanging information about how to reach good nectar. Earlier I gave an example of communication between the room next door and the room two doors down. With the ZigBee protocol, P2P communications have expanded even further, and it has now become possible to build mesh networks (*3), which allows communication with multiple terminals simultaneously (Figure 1).

Compared to Bluetooth® technology, the ZigBee protocol allows one to 65,000 nodes of communication, while the Bluetooth one allows one to only seven nodes, though the data rate in ZigBee-based products is slower. Additionally, the ZigBee standard requires much less power—to the extent that ZigBee end devices can operate for a hundred days, or even several years, with a battery (Figure 2). Moreover, ZigBee technology is easy to apply, compact in size, and cheap enough to become more versatile in various applications.

Prospect for various applications

Q: Thank you, Umeda. That is very interesting indeed. Much like a bucket brigade, a communications network can be expanded to include one terminal after another. But is there actually a practical use for this?

Mr. Yuasa: "We are so accustomed to star-shaped networks such as those in mobile phones. For most people, it is not easy to think of the possible benefits of P2P mesh networking in a practical application. One real application seriously being investigated is automated meter reading, AMR, of utility meters for electricity, water, gas and heat. AMR using a P2P mesh network is expected to contribute to energy conservation by real-time monitoring of consumption. Another application could be a disaster-monitoring system used during a major earthquake or other natural disaster. The self-recovery function of mesh networking will enable the monitors to better grasp the extent of damage via sensor networks. Environment monitoring, via the placement of sensors throughout forests to gather environmental parameters for use in nature conservation efforts, may be another possibility. However, these application areas are just the beginning. If the development of other uses for mesh networks advances, there would be good potential for us to see this technology used in a broad range of fields. Though, at the beginning of this discussion, we briefly touched on possibilities for household use, the implementation of the P2P mesh networking first will be used for industrial applications, such as for the management of buildings and factories."

At the Office & Security EXPO (OSEC) held this past July in Japan, there was an exhibit by Skyley Networks, Inc. in which a compact board equipped with NEC Electronics' 78K 8-bit microcontroller and an IEEE 802.15.4 controller from Uniband Electronic Corporation (UBEC) were used to connect a building's temperature-monitoring system with a ZigBee mesh network. In the demonstration, sensors were placed in each room and then used to transmit data from room to room in a bucket brigade-type fashion. If communications in one room went down, a detour route was automatically detected, thus preventing data transmission from being disrupted.

NEC Electronics' ZigBee solutions

NEC Electronics offers a wide selection of all flash microcontrollers for use with ZigBee wireless networks, thus allowing customers to choose from 8-, 16- and 32-bit microcontrollers to meet their own individual needs. Boasting low power consumption and a wide operating voltage range between 1.8V and 5.5V, NEC Electronics' all flash microcontrollers are the optimum choice for battery-powered wireless stations. In addition, 8-, 16- and 32-bit microcontrollers are also common for network development environments.

Q: What have been the advantages of working in collaboration with NEC Electronics?

Mr. Umeda: "All flash microcontrollers are well suited for use with ZigBee wireless networks. For example, thanks to the self-writing function of NEC Electronics' all flash microcontrollers, as long as you save the network settings to memory, you can quickly rebuild the network during recovery if it happens to go down. Also, although we had been carrying out research and development on our own for a multi-hop wireless network technology (*4) capable of bringing together wireless communications and P2P technology, working in collaboration with NEC Electronics has allowed us to offer wireless network solutions that capitalize on our wealth of experience and know-how in network software development, which is one of our company's greatest strengths."

In addition to Skyley Networks, Inc., NEC Electronics has also teamed with UBEC and Application Corporation. The team has developed a development platform that uses the ZigBee SDK software development kit for building mesh networks via P2P communications, and already has a framework in place that will make it possible to start application development at any time. Next on our list is collaboration with customers. As we work toward our goal of making mesh networks a reality, we will continue to provide ZigBee network solutions.

Notes(*)

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