EET

Wireless sensor networks get super-low-power nodes

The claim to fame of the new SmartMesh family of wireless sensor network chips is that they run on a mere 4.5 mA when receiving and 5.4 mA when transmitting at 0 dBm. This lets the devices consume less than one-fifth the power of competing devices and have about five-time the battery life, claims the developer of the chips Linear Technology Corp.

The LTC5800 system-on-chip (SoC) includes sensor networking software in a 72-pin 10 x 10-mm QFN package. The LTC5800 integrates all radio circuitry components, including an on-board power amplifier and an ARM Cortex M3 32-bit microprocessor. To get up and running, it needs only power, ground and an antenna.

The LTP5901/LTP5902 mote modules consist of a surface-mount printed circuit board (PCB) that has undergone FCC, CE and IC modular radio certifications. The LTP5901 module includes an onboard chip antenna, while the LTP5902 module includes an MMCX antenna connector.

The WSN modules implement the 2.4 GHz WirelessHART wireless sensor networking technology based on the Highway Addressable Remote Transducer Protocol (HART). SmartMesh IP also adheres to the 6LoWPAN (IPv6 over Low power Wireless Personal Area Networks) standard.

The SmartMesh WirelessHART manager (LTP5903) can support up to 500 nodes per network, SmartMesh IP managers can support up to 100 nodes per network, and multiple instances of SmartMesh subnetworks can be deployed side-by-side to create very large networks. SmartMesh networks use channel hopping, spread-spectrum techniques to ensure reliable communications. Linear Technology says they also use advanced algorithms and power saving technologies that enable deterministic power management and optimization, auto-forming and self-healing mesh technology, zero-collision low-power packet exchange, and scalability to large, dense, deep networks.

Also of interest for networks in the area of machine monitoring is the availability of time stamping at every network node that is accurate to less than a millisecond, potentially useful for recording real-time actions and events. "In an application where you get, say, ten pieces of data from ten different sensors, the application can know exactly when those sensors read those particular measurements and can reconstruct that accurately," explains Joy Weiss, president of Linear Technology's Dust Networks product group. "It can deduce a sequence of events and do diagnostics that might otherwise be difficult to do. Conversely, in networks containing actuators, You might have situation where six nodes in the network all do something at the proscribed time within milliseconds of each other."

The chips implement the “e” revision to the IEEE 802.15.4 standard. Though the 15.4 standard has been published for years, most commercial WSN applications have used non-standard medium access (MAC) rules to optimize the performance of their own networks. WirelessHART, ISA100.11a, ZigBee and IPv6 sensor networks all depended on a customized MAC layer. This limited the value of the IEEE standard, because applications needed their own specialized MACs. IEEE 802.15.4e makes changes to the defined MAC layer. It creates a standard and fully defined MAC that can support diverse types of networks. This includes 6LoWPAN-compressed IPv6 networks. It also supports synchronized TDMA network properties used in industrial low-power applications (e.g., WirelessHART and ISA100.11a). Finally, 15.4e accommodates extensions, so that these diverse networks (as well as future ones) can extend the standard MAC without violating the standard itself.

Linear Technologies Corp., http://www.linear.com/product/LTP5903-WHR

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