Since Wireless Sensor Tags were released 1 year ago, they have been tried out by thousands of customers, many of whom have provided us with valuable feedback, bug reports and requests for new features and improvements. During the first few months of the release, we were updating the software almost daily to fix bugs and adding those improvements.
However, one common issue that persisted is sporadic "loss of link" which is caused by the limited range and reliability of the wireless connection. People also noted that the sensor tag range reduced significantly when placed inside metal fridge or behind metal door. We then realized that the final hurdle to our initial goal, a product with lasting value, was to improve the wireless performance.
We spent the last eight months not on ads or marketing, but on listening to our existing customers and building the best performing wireless platform possible for our application. Wireless Sensor Tags only need to send a few bytes once a while, while WLAN or Bluetooth are used to send megabytes of videos or voice, so they are clearly not efficient for our applications. Meanwhile new "narrow band radio" chips are emerging for applications such as wireless meter reading. They are able to reach kilometers range by using very low data rate and receiver bandwidth, using expensive frequency reference (crystals) and big antennas (and with radio operator license). Utilizing these new wireless technologies, we developed a solution using less expensive crystals and same antennas to keep the same form factor to achieve 4x improvement in the range.
We did this by a combination of increasing output power to FCC limit, using optimal frequency modulation index, better crystal and new frequency control techniques to allow 7x narrower receiver bandwidth to filter noise. Completely new radio IC with better noise figure and rewritten firmware are used in each tag and tag manager. We completed FCC part 15.231a certification for both the tags and tag managers.
Taking advantage of the much improved range, we implemented features to trade-off range with battery life, because not every application requires such a long range.
- The new radio IC we used contains a neat feature to turn off receiver immediately after it determines radio power within the narrow channel bandwidth to be no stronger than the background noise it estimated over the last few cycles. We fine tuned parameters to make this work perfectly on each Wireless Tags. The result is 1/4 of the receiver on duty cycle in stand-by (vs. the old sensor tags and with the mode disabled) and hence ~4x longer battery life (not considering power consumption of sensors like angle based motion).
- We implemented transmit power control in each tag, i.e. the tag manager automatically send out command to each tag based on received signal strength, so that each tag uses just enough transmit power to reliably reach tag manager. This means if the tag is installed in a location close to the tag manager, its battery will last proportionally longer.
All these performance improvement and new features come at only $1 increase in cost to you. This covers the increased components for a new front-end filter, higher price of the new radio IC and a better crystal.