| Communications WLAN links | - Comms WLAN |
A Wireless Local Area Network ("WLAN") can be used to link several Unmanned Aircraft to a Command and Control ("C2") Unmanned Aircraft, where only the C2 Unmanned Aircraft needs to maintain contact with the Ground Control Station. |
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Using metallic tape was experimentally found to improve the antenna efficiency by providing a better antenna ground plane. Seen on an Unmanned Aircarft at the AUVSI North America 2010 Conference.
The IEEE 802.11 channel frequency assignment is shown above. All frequencies are in MHz. Non-overlapping channels are channels 1, 6 and 11. These are the most popular WLAN channels in use.
- from http://www.cisco.com/en/US/docs/.../Channel.html#wp134190
Above and below from http://www.broadcom.com/docs/WLAN/802_11n-WP100-R.pdf
Next section from http://en.wikipedia.org/wiki/IEEE_802.11 802.11a
The 802.11a standard uses the same core protocol as the original standard, operates in 5 GHz band with a maximum raw data rate of 54 Mbit/s, which yields realistic net achievable throughput in the mid-20 Mbit/s. Since the 2.4 GHz band is heavily used to the point of being crowded, using the relatively un-used 5 GHz band gives 802.11a a significant advantage. However, this high carrier frequency also brings a slight disadvantage: The effective overall range of 802.11a is slightly less than that of 802.11b/g; 802.11a signals cannot penetrate as far as those for 802.11b because they are absorbed more readily by walls and other solid objects in their path. 802.11b
802.11b has a maximum raw data rate of 11 Mbit/s and uses the same media access method defined in the original standard. 802.11b products appeared on the market in early 2000, since 802.11b is a direct extension of the modulation technique defined in the original standard. The dramatic increase in throughput of 802.11b (compared to the original standard) along with simultaneous substantial price reductions led to the rapid acceptance of 802.11b as the definitive wireless LAN technology. 802.11b devices suffer interference from other products operating in the 2.4 GHz band. Devices operating in the 2.4 GHz range include: microwave ovens, Bluetooth devices, baby monitors and cordless telephones. Interference issues, and user density problems within the 2.4 GHz band have become a major concern and frustration for users. 802.11g
In June 2003, a third modulation standard was ratified: 802.11g. This works in the 2.4 GHz band (like 802.11b) but operates at a maximum raw data rate of 54 Mbit/s, or about 19 Mbit/s net throughput. 802.11g hardware is fully backwards compatible with 802.11b hardware. The then-proposed 802.11g standard was rapidly adopted by consumers starting in January 2003, well before ratification, due to the desire for higher speeds, and reductions in manufacturing costs. By summer 2003, most dual-band 802.11a/b products became dual-band/tri-mode, supporting a and b/g in a single mobile adapter card or access point. Details of making b and g work well together occupied much of the lingering technical process; in an 802.11g network, however, activity by a legacy 802.11b participant will reduce the speed of the overall 802.11g network. Like 802.11b, 802.11g devices suffer interference from other products operating in the 2.4 GHz band. Devices operating in the 2.4 GHz range include: microwave ovens, Bluetooth devices, baby monitors and cordless telephones. Interference issues, and user density problems within the 2.4 GHz band have become a major concern and frustration for users. 802.11n
802.11n is a proposed amendment which improves upon the previous 802.11 standards by adding multiple-input multiple-output (MIMO) and many other newer features. Though there are already many products on the market based on Draft 2.0 of this proposal, the TGn workgroup is not expected to finalize the amendment until November 2008. [4]
- from https://store.metageek.net/ Detailed Description The 2.4 GHz band is getting crowded, so you need better wireless networking tools to quickly resolve interference issues. That's why we here at MetaGeek have been working feverishly on Wi-Spy 2.4x, our second generation Wi-Spy with three times the frequency resolution, three times the amplitude resolution, and twice the amplitude range of our original Wi-Spy. With the higher resolution and improved amplitude range of Wi-Spy 2.4x it is now even easier to identify wireless signals that could be causing interference with your Wi-Fi networks. With Wi-Spy 2.4x... "now you'll know, and knowing is half the battle." Specifications
Above, a snapshot of the spectrum for an 802.11b WLAN system. The original of the above image is to be found at http://www.metageek.net/docs-sample-recordings/80211b .
802.11g at max throughput. Measurement of Linksys WRT54G and WPC54G 11g WLAN driven by IxChariot throughput script. From http://www.metageek.net/docs/sample-recordings/80211g-max-through-put .
802.11N at maximum throughput. Measurement of D-Link DIR-655 and DWA-652 draft 11n WLAN driven by IxChariot throughput script with AP in 40MHz bandwidth mode set to Channel 1. This image was derived from http://www.metageek.net/docs/sample-recordings/80211n-max-through-put .
We use WiFi Hopper from http://wifihopper.com/ to monitor WLAN activity. To quote from their web site: "WiFi Hopper is a WLAN utility that combines the features of a Network Discovery and Site Survey tool with a Connection Manager. Sporting a comprehensive arsenal of network details, filters, RSSI graphing and built-in GPS support, WiFi Hopper is invaluable for identification and advanced characterization of neighboring wireless devices. Additionally, WiFi Hopper can connect to unsecured, WEP, WPA-PSK and WPA2-PSK networks directly from within the application. With editable network profiles and dedicated Connection Manager execution mode, WiFi Hopper can be used as a significantly more transparent replacement for Windows and manufacturer-provided wireless clients."
The signal strength indication could be used as a basis for a site survey, or one could monitor the data transmission rate when sending large files over the wireless network. A free network discovery software is called "Net Stumbler", although we were not as impressed with this software. The web site is http://www.netstumbler.com/ form where you can download a free copy of their software.
- from http://airsnort.shmoo.com/ Introduction AirSnort is a wireless LAN (WLAN) tool which recovers encryption keys. AirSnort operates by passively monitoring transmissions, computing the encryption key when enough packets have been gathered.802.11b, using the Wired Equivalent Protocol (WEP), is crippled with numerous security flaws. Most damning of these is the weakness described in " Weaknesses in the Key Scheduling Algorithm of RC4 " by Scott Fluhrer, Itsik Mantin and Adi Shamir. Adam Stubblefield was the first to implement this attack, but he has not made his software public. AirSnort, along with WEPCrack , which was released about the same time as AirSnort, are the first publicly available implementaions of this attack. AirSnort requires approximately 5-10 million encrypted packets to be gathered. Once enough packets have been gathered, AirSnort can guess the encryption password in under a second. |
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