New Wi-Fi Distance Record Set In Utah

cold_sake writes "Wireless guru Rob Flickenger details the known records for Wi-Fi link distances on his latest blog. Included is a new distance record for an un-amplified Wi-Fi link, set by the students of Utah's Weber State University. 82 miles was accomplished with 802.11b."

Comments

Re:Hmm..

[Stray7Xi]

But it's unamplified.. it just means they had a really big antennas.

Fine tradition of microwave hacking

[isdnip]

Weber State is famous for having launched its own satellite, Webersat, one of the OSCAR series. These kids are really at home with UHF and microwave radios!

In practical terms, the range of a microwave link, such as 2.4 GHz, is based on having line of sight without attenuation. The radio line of sight path is based on the horizon, with a simple guideline of roughly horizon (miles) = 1.4 * sqrt(height-in-feet). So if you have totally flat ground and 100-foot towers, your range to the horizon is 14 miles. The range of a hop is the sum of both sides' horizons. Now if you have a 2500-foot-high mountain to stand on, then your horizon is stretched to 70 miles.

The path loss is a function of distance, which antenna gain can make up for. The legality of doing this with unlicensed WiFi is a different question. Ham radio operators do this stuff routinely, but ham power limits are much higher, and there's no ERP limit. The 10 GHz band in particular is said to be popular in England. The crowded 144 and 430 MHz bands respond to similar rules. Attenuation by moisture in the air (serious form: rain fade) can get in the way, though. So if you're really looking for good distance, a nice place might be, oh, the Utah desert. Flat and no humidity.

So while it's possible to hack a good range with enough effort, conventional WiFi equipment is still not reliable getting from one side of my house to the other. It's really not a threat to the phone companies, especially in non-rural areas.

Re:Fine tradition of microwave hacking

[PureFiction]

So while it's possible to hack a good range with enough effort, conventional WiFi equipment is still not reliable getting from one side of my house to the other.

I hear this complaint often. The problem is that AP's use weak radio's, especially the cheap ones. Sometimes as low as 30mw.

Client cards use low power, almost always 30mw.

You want good signal? Use two 200mw senao/engenius/teletronics cards (boy, these companies change hands quickly...)

They sell them for $100 at teletronics.com and you can still find the old senao/engenius models on ebay and elsewhere for less.

200mw on both ends of a link lets you cut through the walls in your house, through the neighbors house, and out into the street :-)

Lessons Learned

[numbski]

Lessons Learned

1. Unsure of FCC regulations. Experiment could not be put into commercial application

The part15 rules would allow this so far as amplification goes. The part that would get you into trouble in a commercial application is the fact that your antenna, radio, and amp are not FCC certified as a system. You can't take a certfied amp, a certified radio, and a certified antenna, throw them together and call it a 'system'. You have to certify each combination individually, which costs roughly $10k. That being said, if you were were going to sell more than 10 of them, it would be worth the money.

2. Better inventory of equipment.

Spectrum analysis would probably be good too. Search for the least impeded part of the spectrum using peak hold, and use that area. Probably could have gotten better throughput that way. Just plug your antenna into the SA and viola!

3. Better P.R. and release of information to the public.

Local newspapers have been latching onto wireless broadband around here...especially ConvergeNow, which claimed a launch a year ago...one of the biggest wireless broadband scams EVER. And I had the misfortune of being a tech in a legally binding contract with them to help deploy. Screwed individuals out of thousands on their credit cards.

4. Smaller teams with designated responsibility and tasks. Groups were to large for interactions

Makes sense. ;)

5. Defined budget - working within a budget

That being said...someone want to lend me about $50k to finish up deployment in St. Louis? We're not on 2.4Ghz, and it's good tech! :)

Looks like it was amplified

[rednaxela]

Equipment List:

2- Primestar Satellite Dishes with modified feedhorns
2- Laptop computers with 350 Cisco wireless cards
2- Bidirectional Amplifiers (1.5 watt)
Compass & GPS
Tripods
Cables and wires - MMCX RT ANG male to N Male on RG174, 72".
http://classes.weber.edu/wireless/Project%20 Inform ation.htm

They also stated they weren't sure of FCC regulations in the Lessons Learned page.
http://classes.weber.edu/wireless/Lesson%20 Learned .htm

FCC Regs state that the maximum power level for unlicensed devices in the 2.4 GHz range are:
Field Strength of Fundamental (millivolts/meter) - 50
Field strength of fundamental frequency harmonics (microvolts/meter) - 500

See http://www.hallikainen.com/FccRules/2002/15/249/

In other words, it's cool, but it's illegal.

Re:Hmm..

[tzanger]

The Project Information page lists two 1.5W bidirectional amplifiers. But you are right, two primestar dishes with modified feedhorns, that's good for about 30dB of gain per dish/feedhorn assembly.

Re:With Distances this great...

[tonyr60]

I would not get too optimistic about the opportunties that this accomplishment appears to offer rural communities. I am not familiar with the area, but it looks like most of the link is over water and I am sure that it is line of sight. I suspect any sort of obstruction, rain, maybe fog, dust etc. would stuff it up. In addition any sort of interference from portable phones, microwaves etc. etc. would also affect it.

Reliable rural connection would need more than 802.11b power for anything close to that range.

Re:huh?

[dwillden]

Well being a CS student at Weber, I had no knowledge of this except for the local newspaper.

However the discrepancy in the distances is due to the time frame. The newspaper The Standard Examiner www.standard.net reported that they reached the 72 mile distance last week. And that they would attempt a longer distance over the weekend. They were going to try for 90 miles but I guess they settled for 82.

Re:I wonder what they tweaked

[PureFiction]

Arg, I hate doing the EIRP limit math! *grin*

Here is the FCC law (which no one cares about, but I brought it up)

1. The limint for directional links is 4W EIRP at 6dBi. That means 1W dBm output (from radio), plus antenna gain. The 6dBi bit is important. The higher gain your antenna, the more you have to reduce output power.

2. For every 3dBi over 6dBi in antenna gain, you need to reduce output power by 1dBm. This means that your effective signal output is higher, while the transmit power from the radio is lower than 1W.

So, here is a handy table of legal radio + antenna pairs starting with the most powerful radio combination first:

1.0 W radio + 6dBi antenna == 4W EIRP
500 mW radio + 9dBi antenna == 4W EIRP
250 mW radio + 12dBi antenna == 4W EIRP
125 mW radio + 15dBi antenna == 4W EIRP
62 mW radio + 18dBi antenna == 4W EIRP
31 mW radio + 21dBi antenna == 4W EIRP

Re:I wonder what they tweaked

[PureFiction]

I need to quit posting sans-caffeine. The above are for multipoint. For directional the table is as follows:

1.0 W radio + 6dBi antenna == 4W EIRP
500 mW radio + 15dBi antenna == 16W EIRP
250 mW radio + 24dBi antenna == 63W EIRP

Re:Actually

[aXis100]

We had this problem on the WaFreenet, so we set about creating some software to fix it.

The result was frottle. It's a bit of a kludge, but essentially provides a virtual token bus over ethernet. It runs at the wrong layer (UDP), but is suprisingly effective. Before, with 14 clients to the HillsHub AP (many clients in the 10's of kilometers), we'd get crippled throughput rates below 10kB/sec. Now multiple users can sustain data rates above 80kB/sec (or better depending upon load).