Issue #170 | Nov. 14, 2008 | by Cees Links
In general, asset tracking or logistical management with RFID is very similar to applications in wireless sensor control networks. However, RFID and sensors use wireless connectivity differently.
Wireless sensor networks use small, inexpensive, wireless transceivers integrated into compact sensors that can be used to monitor a wide range of changes like temperature, humidity, vibrations and fluid levels. This data is passed via a gateway to the enterprise net.
Over time, it is expected that wireless sensor networks and RFID will integrate and that RFID systems will be extended and evolve into “Smarter RFID Tags” which can sense, act and display.
More precisely, RFID tags will not create the “Internet of Things;” they will tag the things so the things can become members of the internet.
However, because of this extended functionality and connectivity, these connected RFID tags require greater amounts of energy, and will need to be powered by batteries. At that point, it is clear that the RFID industry will be able to benefit from the ultra low power concept (and its alternative “no-batteries” capabilities) as developed by companies like GreenPeak wireless sensor networks.
Ultra low power wireless sensor applications
An ultra-low-power application is able to live maintenance free off just a coin cell battery or off energy harvested from the environment through a solar cell, a vibration energy harvester or any other environment energy converter.
CAPTION: Next generation RFID networks will benefit from a combination of low power requirements, energy harvesting and the reliability provided by mesh networks and antenna diversity.
Most of today’s “standard” wireless sensor network applications solve the wiring problem in industrial applications to make the networks easier to install and to re-architect as needed. However, they do not deal with power or the associated maintenance issues.
Ultra low power wireless network solutions can also address the maintenance problem. For example, a network consisting of 4000 nodes that have an average battery life of ten years requires, on average, one battery per day to be changed. This can become quite an annoyance, especially if the sensors are located in dangerous and/or and hard to reach locations.
Because the majority of the sensors used are battery powered, it requires a lot of labor to change and maintain the individual sensor batteries as well as to reintegrate the downed nodes after the battery change. This can get very expensive. To avoid these costs, the industrial sector requires self-powered nodes that can run off of energy harvesting devices or by using sensors networks that can be powered by a single battery that outlasts the life of the sensor and never needs replacement.
The biggest technical challenge is managing energy consumption without compromising on range, functionality, communication speed and standards compliance. The elimination of battery replacement then simplifies maintenance, is safer and easier to use.
In an industrial environment, low power networks need to be very reliable. The most critical challenge to reliability is wireless interference coming from other users of the same wireless frequency band. As you might expect, the most common interferers for IEEE 802.15.4 based devices that operate in the 2.4 GHz frequency band are Wi-Fi and Bluetooth transceivers, most of which also operate in the same frequency band.
Most interfering devices will not fully block out an IEEE 802.15.4 device, but will cause some wireless packets to get lost some times. The industrial standards provide a mechanism that allows the system to automatically recover from these packet losses without the user noticing. On top of that, IEEE 802.15.4 includes automatic mechanisms that will discover alternative channels for re-establishing connection, in case a disturbance is dominating a certain channel.
Antenna diversity
To further increase reliability, companies like ours have added antenna diversity to ensure a larger reliable range and to prevent the signal fading that can occur in environments with non-line-of-sight connections where obstructions can (temporarily) block transmission of radio signals.
If there is not a clear line-of-sight (LOS) between transmitter and receiver and the signal is reflected along multiple paths before finally being received, each of these bounces can introduce phase shifts, time delays, attenuations and even distortions that can destructively interfere with one another at the aperture of the receiving antenna.
Antenna diversity is based on the use of two antennas to afford a receiver several observations of the same signal and improve reliability by mitigating these multipath situations. Both antennas will experience interference differently; and if one antenna experiences a deep fade, it is likely the other has a sufficient signal. Collectively such a system provides a robust link.
Wireless Sensor Network Standards
For wireless sensor transceivers the dominant and probably only real worldwide standard is the IEEE 802.15.4 specification.
There have been efforts to use Bluetooth and Wi-Fi for sensor applications. In all the cases reported, Bluetooth and Wi-Fi were used in a non-standard way, weaving the principles of IEEE 802.15.4 into their native implementation.
In addition to the IEEE 802.15.4 standard, a number of technology suppliers have chosen to build a proprietary transceiver. The main motivation seems to be a reduction of the complexity and thus a potential lower cost point. But proprietary technologies are vulnerable for two reasons: (1) the owner of the technology controls the specification and thus also the price, and (2) the customer depends on the technology owner for upgrades and uninterrupted sourcing.
Even within the boundaries of standards, technology providers discover differentiation opportunities. As an example, GreenPeak provides transceiver and network stack technology compliant to the IEEE 802.15.4 standard and with the additional functionalities required for ultra low power applications.
New innovations and extended capabilities of low power wireless communication technology are the key factors enabling real-time asset tracking and management.
RFID is suitable for pure identification applications where readers are located close to goods at reader points. Wireless sensor networks are able to track active tags over large areas and combine RFID and sensor readings. Clearly, the combination can provide a better monitoring system in asset tracking and achieve a whole new level of value.
Cees Links is CEO of GreenPeak Technologies, a Dutch company innovating green, ultra-low power wireless communication technology. GreenPeak Technologies - Ultra Low Power Wireless Control Networks
