How To Spread Pheromone In An Rfid Tag

Transcription

1 Physical Deployment of Digital Pheromones Through RFID Technology Marco Mamei, Franco Zambonelli {mamei.marco, Università

2 Outline Università Motivation RFID Pheromone Deployment Pheromone-based Object Tracking Experiments Conclusion

3 Motivation Università Stigmergy and in particular pheromone-based interaction are inspiring several pervasive and ubiquitous computing applications Users and robots navigation and coordination Implementations are often troublesome. The reason for this problem is rather clear: where to store pheromones in pervasive computing environment?

4 Where to Store Pheromones? (Related Works) Remotely-accessible database bottleneck, single point of failure, scalability concerns. Ad-hoc network consistency problems, requires nodes at high-density, costly. Sensor network very promising, but still very costly. Real physical markers who really wants pheromone-graffiti covering home?!

5 RFID Tags RFID Tags and Readers Radio-Frequency Identification Tags are passive Dynamic Read-Write Capabilities Each tag has a small amount of storage Each tag costs less than 0.20 It is likely they will be on every object, like barcode today!

6 Deploy Pheromones in RFID Università Tags Write pheromones!

7 Deploy Pheromones in RFID Università Tags - details Call L(t) the set of location-tags being read at time t. TAG ID INDEX An application agent sees that the user is moving if L(t) L(t-1) and, to spread pheromone O, it will write O in all the L(t)-L(t-1) tags as it moves. Moreover, an increasing counter C(O) and a timestamp T(O) are needed to give direction and evaporation Since tags are passive, evaporation have to be carried on by users. Users delete old pheromones when crossing upon them. PHEROMONE ID #1 COUNTER #1 TIMESTAMP #1 PHEROMONE ID #n COUNTER #n TIMESTAMP ID #n

8 Deploy Pheromones in RFID Università Tags Want to spread pheromone O= Marco L(t) = (door-tag, laserjet-tag) In all the L(t) tags write: [Marco, 1, 3:05:40]

9 Deploy Pheromones in RFID Università Tags L(t-1) = (door-tag, laserjet-tag) L(t) = (inject-tag) L(t)!= L(t-1) the user has moved! Write [Marco, 2, 3:05:41] in all the L(t) tags

10 RFID Pheromones Paths 1 3:05:40 2 3:05:41

11 Pheromone-based Object Università Tracking Let s present an application to find everyday objects (glasses, keys, etc.) forgot somewhere in our homes. The application allows everyday objects to leave virtual pheromone trails. Objects can be easily tracked afterwards, by following the relative pheromone trail.

12 Spreading Object Pheromones Let us call O(t) the set of object-tags being sensed at time t. If the agent senses an object-tag O such that O O(t), O O(t-1), and L(t) L(t-1), then the user picked-up the object O and the object is moving around. In this situation, the agent has to spread O pheromone in the new location. Similarly, if O O(t-1), but O O(t), then the agent infers that the user left object O and stops spreading O pheromone.

13 Tracking Objects To track an object O the agent will start looking for an O-pheromone within the sensed location-tags L(t). If such a pheromone is found, this implies that the user crossed a suitable pheromone trail. Two alternatives: L(t) contains two location-tags having O-pheromones with different C(O) Gradient Search L(t) contains only one location-tag. Local Search

14 Implementation

15 # locations searched before finding an obj ect Experiments time BLIND SEARCH LOCAL SEARCH GRAD SEARCH # locations searched before finding an object time If the number of locations is small, then local search is almost equal to random search. Lot of time is wasted dowsing in the neighborhood. If the number of location is high the local search is almost equal to gradient search. Time spent dowsing is negligible

16 # locations searched b efo re fin d in g an obj ect BLIND SEARCH LOCAL SEARCH GRAD SEARCH Experiments t ag st orage capacit y # locations searched b e f o r e f in d in g a n o b je c t GRAD SEARCH (T = 500) GRAD SEARCH (T = 50) GRAD SEARCH (T = 5) tag storage capacity When tags become full, objects are moved without leaving traces. This breaks the pheromone trails. The problem cannot be solved by simply using different pheromone evaporation rates. Still, with current RFID technology (~KB storage, the approach scales to hundreds of objects being tracked)

17 Other Applications and Future Università Development Besides the presented application, RFID pheromone deployment can be applied to a number of scenarios: Context-awareness: complex pheromones representing structured contextual information Motion coordination Robotic coordination Our future research aims at solving the tag saturation problem Idea: store pheromones also in the object tag. The system becomes automatically scalable. The more object, the more space. But need to manage object reconfigurations.

18 Further Info