6 Object autonomy management

Communicating objects can calculate for themselves their energy autonomy and send the results to a common station (PC, TV, PDA). This station can then show graphically the energy levels of objects and localise them in the environment. The service offered consists in editing the list of batteries to be bought, the automatic writing of the list in the PDA, a budget estimation, the observed replacement period and advice (for example, to use rechargeable battery in place of primary cells ).

Of course, the object should have a visual indicator (blinking LED for example) warning of the end of discharge .

For complex objects, the problem is very difficult. The autonomy is a function of several parameters: the remaining capacity of the energy source, the discharge rate (ratio capacity/discharge current), temperature, ageing, storage self discharge, history of operation of sources affected by "memory effect".

Self-discharge is an irreversible loss of capacity ranging from some % per year to some % per day depending on the technology of the source, temperature and ageing.

Ageing creates not only self discharge increase and loss of capacity, but also impedance degradation. This last effect leads to abnormal loss of voltage during current pulses , common features of fast processors or mobile radio emitters .

Due to rapid change of consumed current, the determination of consumed capacity can only be approached by precise real time measurements and calculations. The problem of measurement is then the high dynamic between the active state and standby state. The problem of calculation is the need for perfect knowledge of the consumption of the different operating states.

Generally the capacity gauge is completely wrong and prediction of autonomy still more, not to mention the rechargeable battery heath state indicator. The TRUST study [1 GREWAL, 2001], has proposed for mobiles 3 and 4 G the use of neural networks and fuzzy logic to improve this.

It may be said also that some objects may create an affective link to the user because they become indispensable . Simulating expressive reactions reinforce this, so that the user wants to take care of them (tamagochi, robots, PDA, MP3 players) and powering them is almost like feeding them.

Energy management is essential especially when communicating objects become numerous . An energy information frame in the radio link protocol should be defined with at least the energy gauge and source description, and even the source state of heath. An " intelligent " help will reduce random interruption and will lighten the replacement task of primary and rechargeable batteries, but for complex objects, autonomy prediction is very difficult. Real use analysis will help to optimise the source (primary and rechargeable battery) and the "energy" budget.