Archive for the ‘Wireless sensor networks (WSNs)’ Category

ZigBee Smart Energy Certified Products

Wednesday, April 7th, 2010

As the industry leader, only ZigBee offers an established, competitive marketplace providing the core technology for monitoring, controlling, and automating the delivery and use of energy and water. ZigBee Smart Energy is the affordable and easy way to improve energy efficiency and reduce environmental impact.

The following ZigBee Smart Energy Certified Products were tested to ensure they meet all of the Alliance’s strict specifications and perform as promised. These products represent solutions across the entire efficiency ecosystem – energy services portals, meters, displays, thermostats and load controllers. Each product may wear the ZigBee Certified logo and the green ZigBee Smart Energy icon so that they may be easily identified in the marketplace.

Alektrona offers embedded communications engineering design services. Our specialization is in systems that leverage IP network and wireless ZigBee\ISM band connectivity. As a core member of the ZigBee Gateway group, Alektrona is an active participant in the design and specifications within the Alliance. Our team focuses on engineering high reliability solutions emphasizing system level design with a business level approach. Alektrona Engineering Expertise Includes: ” ZigBee networking and Gateway product design ” ISM band wireless ” Embedded Systems and Microcontroller Hardware ” Firmware and software design ” Sensor and control networks. ” NMS, SCADA and BMS integration ” Internet appliance design ” End to end embedded product design and manufacturing Please contact us at: solutions@alektrona.com 401-228-2962
Z-Aperture ZA07-200-ESP
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Alektrona’s Z-Aperture™ ZA07-200-ESP is the first broadband Energy Service Portal and Internet Gateway to receive ZigBee Smart Energy Golden Unit certification.
Aztech Associates, Inc.
In-Home Display
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Aztech’s In-Home Display communicates directly with smart meters.
Computime International Limited
CTW200
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CTW200 is a thermostat which monitors, controls and displays energy consumption and rate information for ZigBee-enabled residences.
CTW300
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CTW300 is an In Home Display with a large dot matrix screen for users to monitor energy rate and consumption information in residences supporting the ZigBee Smart Energy profile.
Comverge is a leading provider of clean energy solutions that improve grid reliability and supply electric capacity on a more cost effective basis than conventional alternatives by reducing base load and peak load energy consumption
DCU
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Comverge DCU offers a wide range of functionality – from individual addressing to adaptive algorithms
PowerPortal
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Comverge PowerPortal® IHD is an easy to use, AMI ready display that allows consumers to closely track their electricity consumption and receive messages or alerts from their utility provider.
SuperStat Pro
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Comverge’s SuperStat™ Pro is a state-of-the-art “smart” thermostat.
Control4
EC-100
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The EC-100 is an easy to use energy controller that empowers consumers and utilities to better manage energy use and costs.
Cooper Power Systems, Inc., with revenues of approximately $1 billion, is a division of Cooper Industries, Ltd. (NYSE: CBE). Cooper Power Systems is a global manufacturer of world-class power delivery and reliability solutions for the electrical and industrial markets. Cooper Power Systems manufactures distribution transformers, distribution switchgear, reclosers, capacitors, protective relays, voltage regulators, automated switches, cable accessories, surge arrestors, transformer components and dielectric fluids, fuses and tools and it provides engineering services for the electrical and industrial markets. Through its Energy Automations Solutions group, it is also a leading provider of software, communications and integration solutions that enable customers to increase productivity, improve system reliability, and reduce costs. For more information visit www.cooperpower.com or www.cooperpowereas.com.
UtilityPro ZigBee
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Cooper Power Systems – The ZigBee®-enabled UtilityPRO™ is a Honeywell touchscreen programmable thermostat designed for utility-sponsored demand response programs and is equipped with a Cooper demand response module.
Digi International is the leader in device networking for business. Drop-in Networking solutions include ZigBee/802.15.4 embedded modules, stand-alone adapters, extenders and environmental sensors, plus wireless mesh gateways that collect and transport data from the ZigBee network to an IP network via cellular, Wi-Fi or Ethernet. Reliably network-enable devices and sensors where no wired networking infrastructure exists, where network access is prohibited, or when laying cable is impractical or cost-prohibitive.
ConnectPort X2 ESP
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Digi’s ConnectPort X2 ESP enables energy service providers to deploy HAN devices that are completely managed by the Digi gateway over a broadband or cellular connection, allowing Smart Grid services to be deployed in areas not covered by Smart Metering networks.
Smart Energy Range Extender
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Digi’s XBee Range Extender is a certified ZigBee Smart Energy device.
ecobee�s mission is to help homeowners conserve energy, save money and reduce their environmental impact. Our green automation platform sits at the convergence of energy conservation, green technology, the networked home and consumer electronics. Our products automate energy conservation, making it easier to save on energy costs without sacrificing comfort. ecobee targets the large markets of heating, cooling and ventilation, utility demand response and green automation.
Ecobee Smart Thermostat
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ecobee’s green automation platform sits at the convergence of energy conservation, green technology, the networked home and consumer electronics.
Energate Connecting Conservation with Comfort Energate lets you take your smart grid strategy beyond smart meters, to where demand is rooted — in the home. Energate’s home energy management solutions let consumers and utilities manage energy use and reduce peak demand without sacrificing comfort and convenience. Building upon over 25 years of HVAC industry experience, Energate smart thermostats offer industry-leading equipment interface technology and comfort control algorithms.
Pioneer Z100
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Energate Pioneer Z100 – Energate has expanded its Pioneer series of smart thermostats to support the Smart Energy Profile.
Pioneer Z107
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Energate Pioneer Z107 – Energate has expanded its Pioneer series of smart thermostats to support the Smart Energy Profile. Incorporating next generation technology beyond the features found on today’s most sophisticated thermostats, Energate’s Pioneer Series of smart thermostats provide unparalleled performance with an exceptional user interface to meet your current and future needs.
Founded in 2005, Energy Aware Technology is a Canadian company focused on demand side management products that increase awareness of resource consumption and help people save money. Energy Aware’s first product, the PowerTab, is an in-home energy display designed for deployment with smart metering infrastructure.
PowerTab / PowerPortal
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Energy Aware’s PowerTab is an in-home display that uses the Zigbee Smart Energy profile to allow consumers to closely track electricity consumption and costs. The PowerTab’s attractive design and user-friendly interface encourage energy conservation and facilitate increased data flow to end users. The PowerTab’s features include a 100 mW radio, a magnetic backing, and three colour LEDs to indicate tariff rates.
Itron Inc. is a leading technology provider to the global energy and water industries. Itron Inc. consists of Itron in North America and Actaris outside of North America. Our company is the world’s leading provider of metering, data collection and utility software solutions, with nearly 8,000 utilities worldwide relying on our technology to optimize the delivery and use of energy and water. Our products include electricity, gas and water meters, data collection and communication systems, including automated meter reading (AMR) and advanced metering infrastructure (AMI); meter data management and related software applications; as well as project management, installation, and consulting services. To know more, start here: www.itron.com.
Open Way Gas Module
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Itron – OpenWay Gas Module accurately measures natural gas consumption and supports two-way communication with the Itron
OpenWay
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Itron® OpenWay™ is an advanced metering infrastructure (AMI) solution built around OpenWay
In Chinese, Jetlun means literally “save energy”. Jetlun is building the last mile to the Smart Grid and providing an integrated energy network management solution for residential and commercial markets using standard-based network technologies that maximizes the use of a building’s existing wires and wireless networks for total coverage and connectivity. The Jetlun Intelligent Management solution (“JIM”) is a family of energy network management products that provides granular energy usage information– by whole-home, by phase, by circuit, and by appliance– enabling a homeowner or property manager to pinpoint areas that are consuming the most power.
JIM Gateway Pro RD75606
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The JetLun Gateway SE (model RD75606) is the world’s first integrated ZigBee and HomePlug® enabled gateway that collects.
JIM Gateway Pro RD75607
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The JetLun Gateway (model RD75607) is the world’s first integrated ZigBee and HomePlug® enabled gateway that collects, stores and displays real-time energy consumption information and helps you manage and control- both onsite and remotely- your energy usage through a simple user interface on any web browser or any web-enabled phone, such as the Blackberry® or iPhone®.
JIM Gateway Pro RD75609
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The JetLun Gateway Lite SE (model RD75609) is an ZigBee® to IP enabled gateway that collects, stores and displays real-time energy consumption
KDN is providing high-tech total electric power IT service in entire processes of electric power system, such as from power generation to transmission, distribution and sale. As such, KDN is largely contributing to achieving efficiency and advancement in electric power business by establishing IT system. Furthermore, KDN, by securing international competitiveness in international power IT market, will grow into a global specialist in power IT.
KDN Smart Meter
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KDN Smart Meter Single-Phase and Poly-Phase Smart Meters produced by Korea Electric Power Data Network Co.[KDN] are highly accurate, intelligent, and fully featured electricity meters with integrated communication modules. The Smart Meters have special features such as two-way communication via standard-based ZigBee and PLC(Power Line Communication) technologies, two-way measurement, Power Quality measurement(Sag and Swell), Tamper detection and Remote connect/disconnect. IEC standards (IEC 62052, IEC 62053, and IEC 62056) are applied to Smart Meter.
Landis+Gyr is the leading provider of advanced metering, energy efficiency, and infrastructure communication systems to electric, gas, and water utilities worldwide. Landis+Gyr’s proven record of customer satisfaction and value creation is supported by over 20 million customer advanced metering end points in production or under contract worldwide. Landis+Gyr supports its 500+ customers with a staff of over 700 professionals located in offices across the United States.
Landis + Gyr E35C-A
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Landis + Gyr E35C-A is a high performance 2.4GHz ZigBee transceiver that is supplied loaded with ZigBee Smart Energy firmware. The unit is fully certified and works with Landis + Gyr E350 U-Series meters.
The EcoMeter Energy Monitor
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The ecoMeter energy monitor is a critical component in the final delivery of the benefits of the smart grid to its energy end-users; and an integral component in Landis Gyr’s Smart Grid solution – Gridstream. The ecoMeter P250 is the means for energy consumers to become fully informed and directly engaged to their energy consumption; and is the tool of choice to empower consumers to manage energy better.
The Landis Gyr Focus AX
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The Landis Gyr Focus AX endpoint is a ZigBee-enabled advanced metering endpoint that provides two-way communication with the utility, meter and home-area networks.
LS Industrial Systems has been leading the industrial electric controls and automation field in Korea with the advanced technology for decades. Providing top quality products, LS Industrial Systems set the long term goal as “Superiority over quality and product development”. To set the standard of digitalization which will drive the future of the industry, LS Industrial Systems provides Total Solution found on abundant industrial knowledge and technology in electric control, automation, tube & pipe and the new business area.
LK Meter
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The LK Series Single-Phase and Poly-Phase Electric Meters are intelligent, fully featured revenue-grade energy meters with integrated communication function. These solid-state meters feature two-way communication via plug-in type communication modules using standard-based ZigBee® and PLC (Power Line Communication) technology. Each meter complies with IEC 62052, 62053, and 62056 standards.
LS Research is a leading design firm specializing in providing turnkey RF and wireless design services. A perfect match for OEM customers looking to develop high performances low cost short range wireless solutions based on 802.15.4 radio and the Zigbee stack. A sister company, LS Compliance, is an FCC-certified and A2LA-approved EMC testing laboratory offering comprehensive EMC testing and consulting services. L.S. Research and L.S. Compliance W66 N220 Commerce Court Cedarburg, Wisconsin 53012 USA Phone: (262) 375-4400 Fax: (262) 375-4248 E-mail: sales@lsr.com www.lsr.com
RS-SE-24-01
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RS-SE-24-01 – The RATE$AVER is an In-Home-Display device capable of communicating with ZigBee Smart Energy Profile Compliant Energy Service Portals (ESP) withn Utility Meters displaying energy usage data.
OpenPeak Inc. creates, designs, and develops innovative systems and devices that enable simple control of home energy usage, VoIP telephony, digital media, Internet content, and consumer electronics on a single touch screen device. OpenPeak allows utilities to deliver service updates to users on demand today, and provides a platform for the deployment of future energy applications as they are developed. Through the OpenPeak App Shop, the same device can deliver a complete communications package including news, sports, weather, social networking, and instant messaging and is compatible with a variety of communication standards, including ZigBee and Wi-Fi. For more visit www.openpeak.com.
OpenFrame 7EZ
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OpenPeak’s OpenFrame 7E – touch screen device provides an engaging way for consumers to take an active role in managing their energy consumption. By integrating home energy management with on-board multi-media functions, the same device can deliver a complete information and communication experience including news, sports, weather, social networking, music, and family photos.
PRI Limited
Customer Information Panel
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Home Energy Controller (HEC) monitors and displays electricity and gas consumption and cost information on a customer friendly display. Using the ZigBee Smart Energy Profile, it can read any meter that meets the standard and display the data in tabular and/or graphical format to encourage consumers to reduce their energy consumption through better information.
Horstmann S23 Meter Interface
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Single and Poly Phase Multi Rate Meters – ZigBee Smart Energy Certified meter interface can be fitted to PRI and Horstmann electricity meters to provide consumption data to other Smart Energy devices on a network. The meters conform to IEC 62052-11 and are available with optional load control switches, as well as a variety of power ratings to suit any market.
Rainforest Automation makes products that enable residential energy management, and allow utilities to rapidly deploy Smart Grids that are less expensive and more reliable. Our products include EMU™, a utility targeted in-home display (IHD) designed with simplicity and high-volume deployments in mind, and Orchid™, an energy services platform that serves as a low-cost gateway between the utility and the consumer.
Energy Monitoring Unit
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Rainforest Automation’s EMU™ – Energy Monitoring Unit is an In-Home Display designed specifically to meet the technical and budget requirements of utility deployments. The EMU™ has a simple user interface, runs on standard AA batteries, and displays real-time usage, accumulated statistics and provides a peak pricing “traffic-light”. With its 2-way link to the smart meter, EMU can support custom features such as pre-payment, opt-out, and messaging response.
Silver Spring Networks, the leader in IP networking, connects utilities with their customers over a two-way, IP based network, enabling innovation and change. Utilities can enhance the way they interact with customers. Customers are empowered to manage their energy more efficiently. Using this IP-based network, utilities can deploy a scalable, reliable infrastructure from the substation to the customer premise and implement advanced metering, demand response and other applications at a fraction of comparable costs. An open, IP -based network lowers not just capital costs, but total cost of ownership. When planning the network of tomorrow, it helps to partner with a company that makes it available today
Interactive Energy Management
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The Silver Spring CustomerIQ web portal by Greenbox delivers near real-time data on their energy efficiency programs, including consumption and pricing
Telegesis develops and manufactures advanced wireless products to provide low cost, high performance solutions. Telegesis ZigBee ready Module and Development Kit is based upon Ember Corporation’s meshing technology and is the first in a family of products, others of which are already at prototype testing stage. Our low cost Development Kit enables an out-of-the-box mesh network in less than half an hour. Telegesis range of ZigBee products will aid rapid development and integration into OEM products through the provision of complete ‘plug-in’ modules. Telegesis AT-style command line interface software further speeds and facilitates the building of total solutions.
ETRX2USB & ETRX2USB-PA ZSE IHD
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ETRX2USB ZSE-IHD In Home Display – The Telegesis ETRX2USB ZSE-IHD is a high performance 2.4GHz ZigBee transceiver in USB stick form which is supplied loaded with ZigBee Smart Energy (ZSE) IHD firmware. The unit is a fully certified In Home Display and can be supplied with Certicom test or full certificates. An AT command layer on top of the ZSE IHD firmware allows a host application to easily control the stick.
Range Extender & Range Extender-PA
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Telegesis Smart Energy Range extender – The Telegesis Range Extender and Range Extender-PA are fully certified ZigBee Smart Energy (ZSE) units which enable increased distance between nodes in a ZigBee Smart Energy network. If the distance between nodes is too great for communication to be established. By adding one or more Routers in-between an extended ZSE mesh network can be formed.
Tendril focuses on network operations and deployment – the next big stage of the Wireless Sensor and Control Network industry. Our software allows companies to access, deploy, monitor, manage, and integrate networks into the real world. This approach allows Tendril to address the macro trends of energy efficiency, security and life expectancy.
Tendril Insight
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Tendril Insight is an in-home display that communicates with networked smart devices, such as thermostats, electricity meters and outlets, and displays information about consumption levels and energy rates. Empowered with real-time information, energy customers can potentially save money, while utilities can reduce customer service incidents and improve overall load balancing and demand response capabilities.
Tendril Relay
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Tendril Relay is a ZigBee device router that plugs into a standard household outlet. The Tendril Relay extends the range of a smart energy network, making it easier to access and connect devices in large homes and hard-to-reach places, like garages and sheds.
Tendril Transport
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Tendril Transport is an IP gateway that opens a new channel of interaction and collaboration between consumers and their utilities. The Tendril Transport delivers two-way information to consumers and utilities, providing insight into household energy footprints. With the Tendril Transport, customers gain more access to energy-related information and more control over energy consumption decisions. Utilities can better manage supply, demand response and load control scenarios, and costs.
Volt
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Tendril Outlet is a 3-prong, ZigBee Smart Energy electrical outlet that can be plugged into a standard home outlet to monitor and control the energy consumption of any electrical appliance or device. Multiple Tendril Outlets in the same home can be tracked individually or as a group over the Internet or from a local Tendril Display device. The Tendril Outlet gives the consumer unprecedented insight into and control over their household energy footprint, improving their overall energy efficiency.
Volt
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Tendril Volt is a three-prong, standards-based smart electrical outlet that can be plugged into a 110Volt/15A AC standard wall power outlet to turn off or on any connected electrical appliance or device. When used in conjunction with the Tendril Insight or the Tendril Vantage web portal, multiple outlets in the same home can be managed individually or as a group over the Internet, giving consumers unprecedented insight into and control over wasted energy and their household energy footprint.
Trilliant Networks, Inc. is the industry leader in open solutions for advanced metering infrastructure (AMI), demand response, and grid management. The company is focused on delivering ANSI and IEEE standards-based AMI, without vendor lock-in, enabling choice of meter, network and IT infrastructures. Trilliant brings over 20 years’ experience solving AMI needs for utility customers through the legacy of its Nertec brand founded in 1985. Additionally Trilliant is the originator of the first ANSI tools for development, simulation and compliance now used by most meter manufacturers and AMI companies to develop and test ANSI meters as well as meter communication products. Trilliant has more than 100 utility customers including Baltimore Gas & Electric, Duke Energy, Hydro One, Hydro Quebec, Milton Hydro, Northeast Utilities, OneOK, Public Service Electric & Gas and San Diego Gas & Electric.
SecureMesh Micro Access Portal
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Trilliant SecureMesh™ Micro Access Portal is independent from the meter and can be embedded in any end-point device including thermostats, in-home displays, appliance controllers or meters. Trilliant’s SecureMesh AMI Network is based on the same IEEE 802.15.4 standard as ZigBee providing an end-to-end fully standards-based solution for energy applications.

Building wireless sensor networks

Tuesday, June 9th, 2009

Competitive pressures, globalization, rising energy prices, and increasingly stringent regulations are driving companies to cut costs while increasing efficiency and productivity. Industry leaders feel pressure to adopt new technologies that will help them gain competitive advantages wherever they can find them. One of these promising new technologies is wireless sensor networking. Wireless sensor networks (WSNs) dramatically reduce the cost of installing and commissioning instrumentation in industrial facilities. More instrumentation means better visibility into operational and environmental variables that affect overall uptime, safety, and compliance.

WSNs connect critical processes and assets with the systems or experts that can interpret the data or take immediate action. At the end of the day, operational teams with more visibility into their processes can prevent unplanned shutdowns, increase efficiency, and keep workers safe.

WSN is a term used to describe an emerging class of embedded communication products that provide redundant, fault-tolerant wireless connections between sensors, actuators and controllers or systems. WSNs provide access to assets or instruments that were previously deemed unreachable due to physical or economic barriers.

The WSN label typically describes products that provide performance above and beyond traditional point-to-point solutions, particularly in areas of fault tolerance, power consumption and installation cost.

Wireless Challenges While wireless provides clear cost and flexibility advantages, it also presents some challenges. Point-to-point radio communication links are notoriously variable and unpredictable.

A link that is strong today may be weak tomorrow due to environmental conditions, new obstacles, unanticipated interferers and myriad other factors. These factors can be boiled down into three major failure modes: interference, changes in the physical environment that block communication links, and loss of individual nodes.

RF interference: The small portion of the electromagnetic spectrum devoted to general-purpose wireless communication devices is crowded with traffic from Wi-Fi networks, cordless telephones, bar-code scanners, and innumerable other devices that can interfere with communications. Because there is no way to predict what interferers will be present in a facility at a given location, frequency, and time, a reliable network must be able to continually sidestep these interferers on an ongoing basis.

Blocked Paths: When a network is first deployed, wireless paths are established between devices based on the immediate RF environment and available neighbors. Unlike wired networks, these variables often change; paths may later be blocked by new equipment, repositioned partitions, delivery trucks, or very small changes in device position.

Assuring reliability for the life of the network, not just the first few weeks after installation, requires continually working around these blockages in a transparent, automatic fashion.

Node Loss: Node loss is an important issue to consider with wireless sensor networks. While node failure because of semiconductor or hardware malfunction is rare, nodes may be damaged, destroyed or removed during the life of the network.

Additionally, power surges, blackouts, or brownouts can cause nodes to fail unless they have an independent power source. End-to-end reliability requires the networking intelligence that routes around the loss of any single node.

Any of these problems will bring down a point-to-point wireless link. However, with a network architecture designed to protect against these issues, the network can isolate individual points of failure and eliminate or mitigate their impact, allowing the network as a whole to maintain very high end-to end reliability in spite of local failures.

Similarly, a well-designed wireless network architecture will transparently adapt to changing environments, allowing long-term operation with zero-touch maintenance.

WSNs aim to overcome these challenges by applying self-organizing and self-healing intelligence to continuously adapt to unpredictable conditions. The goal of WSN technology is to provide extremely high reliability and predictability for years at a time without constant tuning by wireless experts.

Time Synchronized Mesh Protocol (TSMP) provides a mechanism for WSN intelligence. By defining how a wireless node utilizes radio spectra, joins a network, establishes redundancy and communicates with neighbors, TSMP forms a solid foundation for WSN applications.

TSMP Overview TSMP is a media access and networking protocol that is designed specifically for low power, low-bandwidth reliable networking. Current TSMP implementations operate in the 2.4 GHz ISM band on IEEE 802.15.4 radios and in the 900 MHz ISM band on proprietary radios.

TSMP is a packet-based protocol where each transmission contains a single packet, and acknowledgements (ACKs) are generated when a packet has been received unaltered and complete. Mechanisms are in place to transport packets across a multi-hop network as efficiently and reliably as possible. All measures of reliability and efficiency are done on a per-packet basis.

Packet Structure TSMP packets consist of a header, a payload and a trailer. Packets contain fields that identify the sending node, define the destination, ensure secure message transfer and provide reliability and quality of service information. For the purposes of this article we will discuss the implementation of TSMP on IEEE 802.15.4 radios.

The IEEE 802.15.4 standard specifies a maximum packet size of 127 B, TSMP reserves 47 B for operation, which leaves 80 B for payload.

Time Synchronized Communication All node-to-node communication in a TSMP network is transacted in a specific time window. Commonly referred to as Time Division Multiple Access (TDMA), synchronized communication is a proven technique that provides reliable and efficient transport of wireless data.

Unlike wired systems where nodes can be directly connected by a dedicated wire (media), to the exclusion of neighbors, in a wireless system all devices within range of each other must share the same media. Several other Media Access Control (MAC) mechanisms are available including CSMA, CDMA and TDMA. TSMP is based on TDMA.

Timeslots and Frames In TSMP, each communication window is called a timeslot. A series of timeslots makes up a frame, which repeats for the life of network. Frame length is counted in slots and is a configurable parameter. In this way a particular refresh rate is established for the network.

A shorter frame length increases refresh rate, increasing effective bandwidth and increasing power consumption. Conversely, a longer frame length decreases refresh rate, thereby decreasing bandwidth and decreasing power consumption.

A TSMP node can participate in multiple frames at once allowing it to effectively have multiple refresh rates for different tasks. The concept of slots and frames is illustrated in Figure 1.


Figure 1. TSMP Timeslots and Frames.
Synchronization A critical component of any TDMA system is time synchronization. All nodes must share a common sense of time so that they know precisely when to talk, listen, or sleep. This is especially critical in power-constrained applications like WSNs where battery power is often the only option, and changing batteries can be costly and cumbersome.In contrast to beaconing strategies employed by other WSN implementations, TSMP does not begin each frame with a synchronization beacon. Beaconing strategies can require long listen windows which consume power.Instead, TSMP nodes maintain a precise sense of time, and exchange offset information with neighbors to ensure alignment. These offset values ride along in standard ACK messages and cost no extra power or overhead.A common sense of time enables many network virtues: bandwidth can be pre-allocated to ensure extremely reliable transmission and zero self-interference; transmitting nodes can effectively change frequencies on each transmission and the receiving node can keep in lock-step; bandwidth can be added and removed at will in a very predictable and methodical way to accommodate traffic spikes; and many others.

Duty Cycling It is important to note that TSMP nodes are only active in three states: 1) sending a message to a neighbor, 2) listening for a neighbor to talk, and 3) interfacing with an embedded sensor or processor.

For all other times the node is asleep and consuming very low power. In a wireless device the majority (generally >95%) of the total power budget is consumed by the radio, not the processor.

To achieve low power, it is clear that one must minimize radio on time. TDMA is very good at this. Timeslots are measured in milliseconds and in typical WSN applications this leads to a duty cycle of less than 1% for all nodes in the network (including those relaying messages for neighbors).

Because all nodes (including those often called .routers.) can be aggressively duty cycled, TDMA is the only practical solution for a fully battery-powered network.

In addition to slicing the wireless media across time, TSMP also slices it across frequency. This provides robust fault tolerance in the face of common RF interferers as well as providing a tremendous increase in effective bandwidth.

Commonly referred to as Frequency Hopping Spread Spectrum (FHSS), hopping across multiple frequencies is a proven way to sidestep interference and overcome RF challenges with agility rather than brute force.

Another technique to overcome RF challenges is Direct Sequence Spread Spectrum (DSSS). DSSS provides a few dB of coding gain and some improvement in multi-path fading. While beneficial, DSSS is not sufficient in the face of common interferers in the band, including Wi-Fi equipment, two-way radios or even Bluetooth (see figure 2 below).


Figure 2. Frequency Hopping vs. DSSS in 802.15.4 Networks.
It should be noted that a combination of FHSS and DSSS provides both interference rejection (FHSS) and the coding gain (DSSS).The other technique for overcoming interference is increasing the radio power, effectively turning up the volume. Although often effective, turning up the volume on IEEE 802.15.4 radios kills battery life and is not an ideal solution for low-power WSNs.Hopping Sequence Upon joining a network, a TSMP node (call it node C) will discover available neighbors and establish communication with at least two nodes already in the network, call them parent A and parent B (more on this in later sections).During this process node C will receive synchronization information and a frequency hopping sequence from both parent A and parent B. The IEEE 802.15.4 standard specifies 16 distinct frequency channels within the 2.4000-2.4835 MHz ISM band . so let’s use 16 as our number. The hopping sequence is a pseudo-random sequence of all available channels. For example the sequence may be: 4,15,9,7,13,2,16,8,1,etc.

Node C receives a distinct start point in the sequence from each parent, and when a new node joins it, it will in turn give a distinct start point to this new child node. In this way each pair-wise connection is ensured to be on a different channel during each timeslot enabling broad use of the available band in any one location.

In operation, each node-to-node transmission (say C to A) is on a different frequency than the previous transmission. And should a transmission be blocked, the next transmission will be to an alternate parent (C to B) on a different frequency. The result is simple but extremely resilient in the face of typical RF interferers.