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The Project |
The Road Talk application allows sharing roadside location dependent messages between drivers that meet in traffic. A message in Road Talk is constituted by audio recordings, or voice memos, together with a location reference. When a memo is recorded, it is simultaneously associated with a GPS position. The Road Talk application also tracks the current GPS position and whenever coinciding with the location for a memo, that particular memo is played. Furthermore, in the background Road Talk shares the memos and as such, a user will be able to hear what other users have recorded. We envision Road Talk to be used like in the following scenario. Sue-Ellen heads out on the road and sees the neighbour's boy playing in a water puddle dangerously close to the street. She decides to record a memo to warn others and she pushes the record button while speaking out loud: 'oops kids.' She drives on and in an intersection she meets many other cars and drivers. Some of them are using Road Talk and in the background memos are exchanged. Bobby, an occasional driver in the area, receives Sue-Ellen's warning as he is heading in the opposite direction. Furthermore, he is speeding, as he is late to a meeting. Fortunately he hears Sue-Ellen's voice: 'oops…kids' through his PDA running RoadTalk and slows down in advance of the boy. |
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The Road Talk prototype is an application for PDAs with GPS positioning and wireless ad hoc networking implementing the concept outlined above. It uses standard GPS positioning to track current location and associate memos to physical locations. Further, it uses wireless ad hoc network to synchronize memos with other Road Talk units. As such it is an application for PDAs running the PocketPC 2003 operating system and it is implemented in C++. Positioning is achieved with Bluetooth GPS receivers and sharing of memos is accomplished with popular standards such as XML, and HTTP over IEEE 802.11b wireless networks in ad hoc mode. These wireless networks are automatically established between the PDAs mounted in cars that move at the speed of traffic.
Figure 1. The PDA and the Bluetooth GPS |
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It is not obvious that Road Talk is technically feasible. After all, the hardware we used here is intended for indoor office settings where people at most walk about. Therefore, we decided to examine the prototype performance in terms of sharing memos in mobile situations. First we recorded 22 memos together with the memo database constituting about 92 kilobytes of data. We kept one PDA with Road Talk stationary and drove by in various speeds with another installed in a car. The PDAs were used "as is" and no extra equipment, such as range extending antennas, was used. In the first ten drive-bys we kept speed to about 50-60 km/h and cleared the stationary PDA of downloaded memos for every second run. Altogether we had five complete downloads and one failure. This also means for four drive-by runs there was no download operation simply because the synchronization was complete. We then increased the speed to about 80 km/h and cleared the stationary Road Talk of memos for each complete download. At this speed the download immediately failed once. At the time we believed this was due to some signal path problems caused by an elevation in the road. When we moved the stationary PDA about 100 meters to the crest of it, downloading worked for three straight runs at this velocity. We then increased speed to about 100 km/h and performed a successful download.
Figure 2. Screenshot where the memos are visible
Figure 3. Results from the performance evaluation
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Oskar Juhlin [Personal page] Mattias Östergren [Personal page] |