Monday, 20 October 2008

Final Year Project- Wireless Sensor Networks


just getting my teeth into my final year project.
The original title was: Very Small Short Range Radio Transceiver.
Although the project has now been given an application so the focus is more on wireless sensor networks (WSN).
I have been reading two books on the subject:
Networking wireless sensors / Bhaskar Krishnamachari

Wireless sensor networks : architectures and protocols / Edgar H. Callaway

So far they have both been useful in gaining an insight into the main limiting factors of wireless sensor network technology. Chief among which is network lifetime. This can be viewed in one of two ways.
1) The ability of the batteries to store enough energy to keep the network online.
2) The ability of the device to save power or minimise consumption to the point where energy is only being expended when strictly necessary to maintain network operation.

The first problem is not one which I will be able to tackle within the scope of this project although the choice of battery technology and the way in which the power is drawn from the batteries does require some careful consideration. For example, although many batteries might have a certain mAH rating, when they are loaded this rating, effectively, tends to fall as the load increases (due to heating effects and, presumably, some other effect of which I am not yet aware). Thus, if the instantaneous current being demanded at any given time can be reduced, I believe that more power can be drawn from the battery because the system is operating in a higher-efficiency region. I.e. thinking to when the radio transceiver becomes active and the power consumption rockets by upwards of ~36mA above the base current required to power the circuitry. If I can charge, perhaps, a capacitor or use some kind of low current drawing circuitry, then maybe it will be possible to reduce or minimise the effect on the battery life due to these inefficient regions of energy consumption. Before I get too ahead of myself I may just go and ask my project supervisor if this effect is likely to be significant. Heaven forbid, I might actually take the initiative and do the sums/look into it myself!
Thoughts of the day:
What do mobile phones do to combat this peak in current demand when on an active call?
What other power-saving strategies do they employ?