As far as I am aware, off-the-shelf batteries are not designed for long lifetime use, in the order of years. Yet they are being used for long term deployment in WSN. I’ve seen theoretical projections of how long low power wireless motes can last. But there still seems to be an unknown quantity on the profiles of batteries, when used for a long time by wireless motes, drawing µA current…

Having not been keeping in touch with news about WSN for 3 weeks while I was on holiday, I’m notified by my colleague today that SunSPOTs are now finally available in the EU area. But checking on their website myself, it seems that it costs much more to get a Sun SPOT development kit in Europe than in the US after currency conversion (€627 compared to $550 excluding tax), which is probably not news anymore given the fact that it’s almost always more expensive to buy goods in Europe than in the US. However Europeans can probably take heart from the news that they are soon going to change the pricing in the US from $550 to $750 (apparently as of 27th Feb 2008) Well, perhaps not, €627 is still a lot of money. Just shows that wireless sensor motes are still very much in the prototype stage.

ZigBee modules are readily available nowadays. Assuming that they can all live up to their expectations, providing the network stack that allows wirelss sensor motes to be easily organised into a network fit for deployment, we will be seeing a host of software applications to be developed for wireless sensor networks this year. My concerns with ZigBee are, forget about large-scale or maybe even medium-scale sensors deployment, the ease of deployment of a ZigBee wireless sensor network and the lifetime of the network. Remember, there were a lot of hypes around multiple hops wireless ad hoc networks not that long ago when the concept was first put into trial. Don’t get me wrong, the potential of such networks is still there. But, under the constraints of current underlying technologies, the deployment of these networks for the applications initially expected of them is not as simple as the name of these networks would have you believed. Work is currently still on-going in this area, so I won’t be surprised if the ZigBee stack is still someway away from being ready for some serious applications. What I’m more interested in is better tools to diagnose a wireless sensor network as at the moment troubleshooting a network of these little motes when something goes wrong is still painfully difficult.

There was a short article in the October IET magazine about using a small ZigBee sensor the size of a hearing aid to collect and transmit data from the human body. I suspect that hearing-aid-size sensor, which is “inspired by the semicircular canals of the inner ear responsible for controlling motion and balance”, is probably only made up of a simple accelerometer sensor, which can be easily found in most prototype wireless sensor motes on offer in the market nowadays. Nothing earth-shattering really, in my opinion, merely decoupling a simple sensor from wires. If the “whole package” is just about monitoring raw data collected from the sensor then that is even more disappointing. The power of modern sensor network lies in its ability to gather information from multiple cheap wireless sensors, with the resultant information giving more accurate insight into the sensed object or enviroment than a single sensor can achieve. I’d expect more from the “pioneer” in body sensor networks!

About a year ago we wanted to get our hands on some Sun SPOTs motes for our project because we have more people around that know how to write Java applications and use the familiar development tools (not many people heard of TinyOS’s nesC, and using the primitive word editor to write applications seems to be the norm!). But unfortunately Sun, or more precisely that particular team, was unable to deliver their products on time, not to mention shipping products outside the US, due to ROHS issues.

Now another major mote manufacturer seems to share the vision of using Java as the platform for developing applications for the wireless sensor motes. “We at Sentilla (formerly Moteiv) are extremely excited about the use of Java technology in our products”, quoted from Joe Polastre of Sentilla (see here for more details). As I said, this makes a lot of sense and it will be interesting to see if Crossbow will soon follow suit. Java may soon be the future.