mungmaster2000 writes: "Picture this. Approximately 100 vehicles (busses) arrive at a security gate of an oil refinery, within the space of about twenty minutes. Some of the busses will be bumper-to-bumper with each other; others will be somewhat staggered. The busses are all outfitted with some kind of purpose-built on-board computer, listing which persons "swiped" onto the bus at boarding time. This computer uses some manner of wireless communications, to upload the swipe data, to a server located somewhere in (or near) the security gate, once the gate gets to (or near) the security gate.
Each bus contains a maximum of say, 60 persons. The on-board bus computers each wish to report to the security gate, their event log for that bus run. This means that for each, "swipe" on the bus, there will be about 80 bytes of information per line (for every bus passenger). Ie) Date/time, unique identifier number, status, etc. So for a full bus, that means an event log of approximately 5000 bytes to upload to the security gate server, each time that it gets to the gate.
The busses will proceed through the security gate without stopping. The maximum speed for this will be 30 km/h, but may be as low as 5 km/h in some cases. A long-range RFID tag affixed to the bus (and independent of the on-board bus swiping computer) will signal the security server at the gate, that a bus is crossing the gate threshold, and to expect a data dump within a specified interval. Therefore it is mission-critical that the data dumps proceed as expected.
Can such a system be implemented using commercial-off-the-shelf unlicensed WiFi? What is the best way to design such a communication system, with the following factors in mind?:
- That communication between the bus computers and the security server is protected by something like TwoFish Rijndael (AES) encryption. - That the wireless system be only used for this specific purpose, and nothing else. - That there is lots of concrete, asphalt, underground cabling, sheet metal, structural steel, and other vehicular traffic in the immediate vicinity. - That the security gate has two lanes; one inbound, and one outbound. The system must function in the opposite direction as well, indicating which passengers are leaving the facility. Keep in mind that an outbound and an inbound bus could potentially simultaneously try to upload their event logs.
Can COTS Wifi be used in this situation, or are there better alternatives available using GPRS, packet radio, EVDO, etc?"