Low Power Sensor Networks

Low power sensor networks have many attractive attributes and with appropriate care in selection can out perform traditional wired systems. But not all wireless systems are equal. Systems operating on a static frequency channel are often plagued by interference and co-existence problems and point-to-point topologies do not always align well with actual field requirements. The SensiNet system has grown from years of field experience and been optimized to deliver world class performance at an attractive price, by utilizing the following techniques:

1. Amplification
2. Frequency Diversity (Frequency hopping)
3. Path Diversity (Mesh Network)
4. Self Healing Protocol

Amplification: SensiNet is based on standard IEEE 802.15.4 radios specifically designed to coexist with WiFi (IEEE 802.11.X) systems thus reducing a significant source of RF interference. SensiNet is amplified to provide 30 times (15 dB) the native transmit power of the IEEE 802.15.4 radio, allowing longer range between hops and more robust point to point communication than systems utilizing unamplified radios such as Zigbee. This additional power also reduces the effects of physical interference such as partitions and equipment in the field environment. "Shouting louder", although useful, is only part of the solution and the other attributes of SensiNet are equally important.

Frequency Diversity: The IEEE 802.15.4 radio employs a Direct Sequence Spread Spectrum (DSSS) technique designed to minimize the effects of interference by "spreading" the radio signal over a 3 MHz band and many wireless systems based on the Zigbee protocol rely solely on this technique. SensiNet utilizes this technique but also dynamically utilizes all 16 channels available in the IEEE 802.15.4 radio in a random hopping pattern. This "frequency diversity" virtually eliminates the effects of RF interference and destructive reflections, which can render other systems unreliable. In essence, if the SensiNet system experiences a corrupted transmission it simply switches channels, an operation which is done continuously and automatically. SensiNet further enhances this technique with a blacklisting algorithm (not enabled in the EU) which removes error-prone channels from the hopping pattern until they are determined to be reliable through periodic "probing". This is a dramatic difference compared to systems employing the Zigbee protocol, which only operate on a single, manually selected channel and are incapable of dynamic channel hopping.

Path Diversity (Mesh Network): SensiNet components automatically and autonomously form into a multipath mesh network upon power up, and each element determines a primary and secondary path with "parents" based on a variety of Quality of Service factors. This allows multiple communication paths to be immediately available in the event of disruption of any path due to physical interference or hardware failure. This attribute also allows the network to be extended beyond the distance available from a single "hop" greatly increasing reliability and range of the system. Network communications are bi-directional and each transmission is error checked (CRC) and acknowledged at each "hop" further enhancing transmission integrity.

Self-Healing Protocol: SensiNet is not only "expert" at network formation but constantly monitors the health of the network and is able to "repair" itself in the event of a major system fault by initiating a reformation process, if links remain unavailable for an extended period of time. This process is monitored by the SensiNet Services Gateway which will notify upstream elements of this status and flag individual elements as "off line". Link status, battery health and other network attributes are constantly reported, eliminating the possibility of sensors unknowingly "dropping out". Smart RTD sensors even monitor connected sensors by providing notification of open or short circuit sensor status.

Flexible: systems are deployed or reconfigured in hours, sensors can be added or removed without any reconfiguration. Embedded gateway architecture supports stand-alone operation or integration with existing systems through multi-protocol support.

Reliable: Multipath mesh networks provide redundant paths for sensor data and frequency hopping radio technology eliminates effects of interference to support the most stringent disaster prevention program. The system is self-healing and all communications acknowledged and checked for errors.