Shootout in the desert

LAS VEGAS — Under any circumstances, the first DEFCON Wi-Fi Shootout held Aug. 1-2 in conjunction with the DEFCON “hacker” convention promised to be a challenge. Contestants were expected to try to achieve the greatest Wi-Fi/802.11b connection distance, using anything from off-the-shelf hardware and commercial omni directional antennas to highly improvised devices built with $98 of Home Depot parts at the last minute. Other Wi-Fi protocols, such as 802.11a and 802.11g, were not permitted. Signal relaying also was ruled out.

However, an additional challenge was thrown in at the last minute. The event staff had planned to operate the contest from the roof of the Alexis Park Hotel in Las Vegas, but on July 26, the local fire marshal banned use of the space for any purpose. In previous years, the rooftop had served as a command post and open-air presentation area. It was a convenient space for a wireless contest, but the opportunity for RF interference from both convention activities and other WiFi equipment around the city could have played a significant role in interfering with the planned proceedings.

Organizer Dave Moore and the Shootout staff saw the dislocation as an opportunity to find a location that would put configurations to the test. Several sites outside of the city were surveyed and a final one selected roughly 40 miles northeast of Las Vegas. Participants took exit 64 from I-15 onto Nevada State Highway 93 and followed the two-lane road north for about 20 miles, just past a ridge and marked by a couple of trash cans. Beyond the ridge, the terrain stretched flat along the desert valley for more than 40 miles, a long straight ribbon of highway paralleled by power lines and little else. With the closest gas station at least 25 miles away, teams had to pack their own water and refreshments, and provide their own equipment power. One team brought along a tent, fan and generator, but other teams roughed it.

Further hurdles faced the contestants on the first day of the contest. Road construction along I-15 backed up traffic, adding an additional hour or more to a 45-minute drive from the Alexis Park Hotel to the remote desert site. When they finally arrived, teams were greeted with a downburst of rain, rapidly dropping the temperature from a hot 90F to a cool 60-70F and turning the desert sands into mud. Teams were able to set up their equipment, get a feel for the site, and get in a first day of results logged. Most teams chose to lug their equipment to the top of the craggy hill to get height for better transmission range, a distance of several hundred steep feet from the road below.

Rules of the contest were fairly simple: Each team would have a fixed position and a traveling “roamer.” The roamer would move farther and farther down the road to find the edge of transmission coverage, then coded text messages would be passed between the roamer and fixed site, with judges on both ends verifying the transmission and logging positions via GPS.

Entries were broken down into the following categories:

Adversarial Science Laboratory (ASLRulz, as they prefer), won Category 6 and was the overall distance winner, logging a transmission distance of 35.2 miles – more than two times longer than any commercial entry.

They also won a spontaneously generated “Most Innovative Antenna” award. Their design was based on work done in the amateur radio world to communicate with the AMSAT Oscar-40 satellite in the 2.4 GHz/S-band with a pyramidal horn antenna. A number of initial “core” horns using simple cardboard, duct tape, and aluminum foil were prototyped and tested, with one packed up and taken out to Vegas. The core horn was about 26 inches long, 15.25 inches high and 20 inches wide at the mouth. Estimated cost to build the foil horn is around $3 and loose change.

Friday’s initial tests using the foil core antenna were promising, logging distances of 4.6 miles with a full 11 Mbps data rate. Building on the initial cone, ASLRulz added another $98 in Home Depot parts purchased at closing time on Thursday evening. Metal screen mesh is used to extend outward from the core to a length of ten feet (including the length of the core) with a height of 76 inches and width of 56 inches. Inner core was jointed to the outer mesh with non-conductive fishing line, and everything was held together with old-fashioned duct tape. Construction of the larger cone took place in the sudden downpour and cold that followed and wasn’t finished until late in the evening. Initial testing without the officials around logged distances of 33.5 miles before darkness set in.

The team also had to work around communications between the antenna team and the “roving” team, since cell phones coverage was spotty at best and the distances pushed the edge of their available amateur radio equipment.

Saturday’s finals proved to be just as challenging. The desert sun rose into a clear sky and over 100 degrees F, baking both people and equipment. Some of the supporting duct tape had melted and stretched, requiring replacement.

However, other contestants also added some tension by broadcasting the same SSID as ASLRulz, resulting in a denial of service until the others shut down. According to the group, other contestants were using the ASLRulz broadcasts as a beacon to point their own equipment. Once the others shut down their transmissions, ASLRulz was able to establish a working connection and have the judges verify the winning distance.

The ASLRulz winning design represents an interesting solution for certain problems. According to the group’s estimates, the antenna adds between 27 to 30 dBi of performance. Given the relatively low-cost of antenna construction (around $100), it could be used in a fixed location for remote areas or to extend the range of an existing WiFi setup in an emergency. Replacing the cardboard and duct tape with some more durable materials would seem to be a relatively simple matter. Due to the antenna’s size, it is not likely to be the most aesthetic choice in an urban location.

Winners in the other categories were also a colorful lot, between commercial and amateur participants. The best homemade directional antenna (Category 4) was constructed out of a pair of Hormel Chili cans and logged a distance of 5.1 miles. Two categories (1 and 2) were captured by the “4DI” group, with both omni and directional antennas logging distances of around 10.2 miles. Category 5 — the only category captured by a commercial vendor — was won by 5G Wireless Communication with a confirmed distance of 14.9 miles. There were no entries in category 3.

In addition to bragging rights, winners of each category received $500 gift certificates from Best Buy provided by lead sponsor Tech TV, a free pass to DEFCON 2004, and plenty of other vendor gifts or “swag” ranging from books and T-shirts to antennas and other hardware.

Next year’s contest promises to be more interesting. ASLRulz already is planning to return and defend its title. Dave Moore is looking for a site with more length and better terrain; according to Shootout Coordinator Michele Moore, the ASLRulz “roamer” car literally ran out of highway at the far north end of the valley and their signal likely traveled farther than the logged distance.

One Canadian group that didn’t make it to Vegas insists they can go more than 100 miles.

The WiFi shootout was inspired by a Guinness World Book Record logged earlier in 2003 for 310 kilometers (about 192 miles) between a ground station and a wandering Swedish weather balloon using a BreezeNET DS.11 bridge unit connected to a high-powered amplifier and using a 2.4-meter dish antenna. The antenna position was directed by an automatic tracking system using GPS technology.

Use of balloons or other airborne platforms for the DEFCON shootout was deemed inappropriate due to the commercial and military traffic in the area.