Comparing the GPS capabilities of the iPhone 4 and iPhone 3G for vehicle tracking using FreeSim_Mobile

摘要

In this paper, we present a comparison between the Apple iPhone 3G™ [2] and the iPhone 4™ [2] using the real-time vehicle tracking application FreeSim_Mobile [24]. The built-in GPS receiver and web capabilities of the iPhone™, coupled with a V2I architecture, are used to send a continuous flow of data to a central server for processing by FreeSim [13–15], which is a real-time traffic simulator. The proportional model algorithm [18] is then used to determine the time to traverse a roadway in order to report in real-time the current flow of traffic. At the University of Alaska Anchorage, we currently have vehicle tracking devices installed in 80 probe vehicles that traverse the Anchorage area. Due to the high cost associated with vehicle tracking devices, it is difficult to penetrate a large vehicular network on a finite amount of money, so we must look towards other available technologies, such as the constantly-expanding cellular network. In this paper we look at the iPhone 4™ capability of reporting accurate and reliable locations and compare it to the recent study of the iPhone 3G™ [24]. Drivers equipped with an iPhone 4™ cellular phone and a vehicle tracking device manually timed how long it took to travel along a 0.99 mile/1.59 kilometer section of roadway. The vehicle tracking device and the iPhone 4™ report speed and location every 10 seconds whereas the iPhone 3G™ reported every 8 seconds [24]. From this data, we calculated the amount of time to traverse the test section of roadway using the proportional model algorithm [18] and compared it to the actual amount of time it took to traverse the test section of roadway as manually timed. We found that the vehicle tracking device had an average error factor of 4.94% from the actual time to traverse the section of roadway (as determined by the stopwatch), whereas the iPhone 4™ was found to have an error factor of 1.10%. The outcome of --the case study is used to determine that the iPhone 4™ has higher accuracy than a vehicle tracking device, though it is important to note that the iPhone™ is more limited than a device attached to a vehicle since it can only report its location. If paired with another third party OBD device, however, it can also send the same information as a vehicle tracking device.