Acoustic distance measurement test results
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Joyride builds currently include my Acoustic Tape Measure activity, designed to turn any pair of laptops into a tool for measuring distance. Today, I decided to test the maximum range. I used two B4's running clean installs of joyride 289. I went to the MIT football field, because it is a large, flat, open space with clearly labeled distance markings. Unfortunately, there were no markings visible on the field, so I made measurements on the adjacent long-jump track, which is labeled in feet. Measurement worked perfectly up to 30 m (100 ft), with at most 1 cm of variability, and usually none. Measurement worked unreliably up to 40 m, giving spurious answers except during lulls in the wind. (Almost all microphones record high-amplitude noise in the presence of wind.) I have several ideas for increasing range (or equivalently, improving noise tolerance). However, I did not make any attempt to implement them, because it was too cold out for programming. I also encountered some difficulty when sharing the activity over the mesh at distances greater than 25 meters. This might be because the default mesh frequency (Channel 1) is the same as MIT's pervasive wireless network. After switching to mesh channel 11, I had no difficulty sharing over distances up to 40 m. - --Ben Schwartz -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.7 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFHQMRCUJT6e6HFtqQRAiaLAKCMbxGd4W0kk9WutMSuGrwxSohkQQCdECDB hTrx9Mz95WyPW4zFVmT3Ub0= =hRjf -END PGP SIGNATURE- ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Acoustic distance measurement test results
On Sun, Nov 18, 2007 at 06:01:22PM -0500, Benjamin M. Schwartz wrote: I also encountered some difficulty when sharing the activity over the mesh at distances greater than 25 meters. This might be because the default mesh frequency (Channel 1) is the same as MIT's pervasive wireless network. After switching to mesh channel 11, I had no difficulty sharing over distances up to 40 m. Your observations are consistent with mine, subject to variables you didn't mention. How high off the ground were the laptops? At ground height, with ears up, the node to node transmission distance is very small. That's why school server antennas will be mounted high. A football field normally has very little slope, so the terrain obstruction is easily understood. It might also be an area with a large radio noise background. By placing the laptops on the ground you may also have reduced the noise from nearby transmitters. With two laptops in a paddock or dirt road away from any city, I can easily get to 300m on with the laptops at 1.5m above ground. Nearby, I can reproduce 1.6km on a tar road with about 5% packet loss. -- James Cameronmailto:[EMAIL PROTECTED] http://quozl.netrek.org/ ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Acoustic distance measurement test results
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 [EMAIL PROTECTED] wrote: How high off the ground were the laptops? At ground height, with ears up, the node to node transmission distance is very small. That's why school server antennas will be mounted high. The laptops were sitting directly on the ground. A football field normally has very little slope, so the terrain obstruction is easily understood. Specifically, the laptops were sitting on the rubberized track surrounding the field. The surface appeared perfectly level to me, and free of obstructions apart from myself. It's entirely possible that what I saw was actually some unknown unrelated software bug. I wasn't intending to test wireless range, so I can't really say anything more conclusive than it worked easily to at least 25m. - --Ben -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.7 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFHQNlHUJT6e6HFtqQRArurAJ0en7WqDgiPnXT5YUgI8SdKWtjK6ACfUVLG d29XGyyeDz+LXB2U5BWHwxA= =8Vqm -END PGP SIGNATURE- ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Acoustic distance measurement test results
On 19/11/2007, at 11:31 AM, Benjamin M. Schwartz wrote: The laptops were sitting directly on the ground. Good, consistent results confirmed. Specifically, the laptops were sitting on the rubberized track surrounding the field. The surface appeared perfectly level to me, and free of obstructions apart from myself. Hmm, interesting. Black rubberised track may contain a lot of carbon, may end up behing a good reflector for the signal. Excluding grass improves the signal. -- James Cameron ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Acoustic distance measurement test results
Heh. He said MIT; the field is surrounded by dormitories: very noisy environment -- Jim Gettys One Laptop Per Child ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
