We have 2 buildings up north, one gets internet connection through satellite, the other nothing...
My bosses now have decided that the other building needs to be connected, which means I need to figure out a way to connect them....
One guy is telling me that you can get small dishes, since the buildings are about 2 km away from each other and "in line of sight", that will "beam" the signal over....
Basically, and the easiest way to put it..... Building 1 has server, building 2 has internet. Building 1 needs access to server, then eventually building 3 (which is FAR AWAY from both these buildings) will also need access to the server in building 1. On another note, when they go to trade shows and such to sell products they will want to
be able to access the server at building 1 to set up new accounts.....
All I can think of is using netscreens...... but having very little knowledg about netscreens Im very hesitant on using them.... THERES gotta be a different way!!!
Please help me out, as this needs to happen in the very near future!!!
Currently Im looking into Yagi antennas.....Trying to get any information from suppliers is a nightmare, nobody really seems to know anything about this stuff....
Thats why you often need to hire someone specialized. Since it is a commercial application with some apparent urgency why not tell the bosses that a outside company needs to be hired just as if a new roof or conveyor line had to be installed?
Put a commercial grade access point ($500) on a 20 or 40 foot mast with omni antenna ($150) at one end and outside mounted subscriber units ($250 each) at the other ends.
I don't know how small small is (but then Clinton didn't know what is was), but a 3 ft. grill dish will run you about $400 and have same gain as a $1,000 solid dish. Or a $100 flat panel antenna good for half the range.
How far is far? Twenty miles?
You have two options here, virtual network computing or virtual desktopping.
VPN apps would include (in order of secutity) Real VNC
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Ultra VNC
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Remote Admin
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Dameware
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However, these apps talk to the remote computer's IP address and if its behind a router, its no trivial task to set them up.
Or you can use a Citrix based Remote Desktop app. The most well known is the GoToMyPC that allows one PC to connect to another. Since its a tunneling technology using the http protocol, it can see through the IT infrastructure and not worry about port forwarding, firewalls, etc.
On 6 Nov 2006 08:57:52 -0800, snipped-for-privacy@yahoo.ca wrote in :
802.11 Wi-Fi can handle 2km with line of sight, sufficient clearance/height to keep the Fresnel zone clear, and the right equipment.
The maximum range to building 3 will be on the order of a few miles *if* you satisfy the conditions above. The radios will need to be pretty high to keep the Fresnel zone clear.
802.11 can certainly be used for distances of 2 km and well beyond, although I don't whether it can be used for communications to building 1 (which is FAR AWAY in capital letters.)
For 2 KM? That's only just over a mile. Off the shelf WiFi gear will work just fine as long as you don't have obstructions. Two antennas at 20 feet should give you .3 Fresnel factor (70% encroachment of the path midway) with only about five foot variations in the ground elevations. Around 25-30 dB link budget, so with a 15 dB fade margin, you'll have room to play with. Most likely you d want to run 802.11g 54 Mbps gear for the OFDM and turn it down to only 6 Mbps.
2 KM might be really pushing it for optical gear. Proxim's TeraOpti 4221 is rated at 20 meters to 1,000 meters for a mere $17,000 for a pair of units. Other brands might be better.
At typical 802.11g system, with radios mounted near the antennas and using panel or dish antennas: TX power = +15dBm TX coax loss = 2dB (some LMR240 plus connectors) TX ant gain = +17dBi (typical panel or small dish) Distance = 2km (1.25 miles) RX ant gain = +17dBi (typical panel or small dish) RX coax loss = 2dB (some LMR240 plus connectors) RX sens = -84dBm (at 12Mbits/sec OFDM) Fade margin = unknown Plugging into: |
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crap. Looks like Proxim didn't bother to renew the domain. Nice work Proxim. Finding an alternative site for a simple path loss calculation: |
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System Performance): which yields 23dB fade margin. Good enough it should work. As for Fresnel Zone, it needs 4.8 meters clearance at midpoint, which sets the minimum mounting height of the antennas.
Plaintree is slightly cheaper. The WB500 series is rates to 2,000 meters. I can't find my price list but I'll guess about $15,000 per pair. The problem with FSO is fog, heat shimmer, solar interference, dust, condensation in the morning, and dirt on the optics. Kinda difficult to justify FSO costs when commodity wireless is 50 times cheaper.
That's a rather narrow view of the current state of wireless backhaul. There are some very good "non line of site" (NLOS) point-to-point solutions which operate in the non-licensed 5.0 GHz spectrum. I have personal experience with Orthogonal Systems' (now owned by Motorola) product and have looked at similar offerings from Solectek and Alvarion. Depending on your physical topology, this type of product may offer a cost effective solutions for connecting your two buildings together.
Here's my empirical (real life, non-calculated) measurements. I have two 60 ft. towers 2.12 KM (1.32 miles) apart. Test gear can be located at any height on the tower.
TX power = +17dBm TX coax loss = 1.2dB (measured with wattmeter) TX ant gain = +15dBi (omni) Distance = 2.1 km (1.3 miles) RX ant gain = +18dBi (patch antenna) RX coax loss = 0dB (built in antenna) RX sens = -88dBm (at 6Mbits/sec OFDM) Fade margin = -15dB
Further more, just because you have clear LOS and clear the first Fresnel zone, you will hit null spots at certain SU antenna heights. Notice the drop in signal at 28 feet and the peaks at 10-20 feet and again at 46'.
I can place two SU units almost the exact same distance from the AP tower, and both at same elevation and only a thousand feet apart, but with slightly different interfering terrain figures. One SU will work great at
40 feet and nearly dead at 32 feet, but gets better at
26 feet. The other SU was optimum at 22 feet.
Information gathered from several SUs around -
Seasonal variations and time of day can vary signal as much as 10 dB from what I have noticed. Possible factors are morning dew on the leaves, temperature inversions from sun warmed earth on a cool morning, warm sundown evening with suddenly cooling in low lying areas.
Some locations never seem to have any significant fading under the same variations.
ODFM appears more robust and works with marginal paths where DQPSK and DBPSK were unusable.
Nobody in the computer business has a "real life". Maybe a "Half-Life" or worse.
Nice. A real test range. Does it have an elevator platform for the test equipment?
How did you measure the fade margin? I previously had a BER generator. I would introduce attenuation until the BER hit 10^-5. I guess it can be done without the BER using guesswork, but it seems difficult.
Nice plot. My guess of 4.8meters (15.7ft) seems a bit low. Looks like 20ft is the minimum height.
I noticed the nulls. I usually ignore those unless I'm shooting across water, airport runway, or a parking lot. The surface scatter of most soils and surfaces is anything but perfectly reflective and will only cause problems if smooth or reflective. I've seen far more reflection problems with objects (buildings) at the antenna elevation than ground bounce. What do you have for ground surface between the antennas?
Also, having both ends of the link at identical heights is asking for reflection problems. If the ground in between is flat, the angle of incidence equals the angle of reflection and you get multipath. However, if the endpoints are at different altitudes, then the chances of finding a slightly tilted reflector is less. The point at which the incident and reflected angles are identical is moved towards the lower antenna, thus moving it further outside the beam pattern as it would be in the equal height model.
Yep. I have several over the water links that literally die when the water is smooth and the tide is exactly the right height. The standard solution is either spatial or frequency diversity, which is generally beyond the means of most users. If in a fixed location, it's easy enough to move the antennas up and down slightly to check if they're in a null and to find an optimized location.
Temperature inversion layers, condensation inside the antenna feed, hygroscopic coax cable, fog, coastal zone effects, etc. I haven't seen 10dB signal strength variations in short links except those over water or near the water. On long links, the inversion layer seems to be the predominant source of signal variations.
Yep. Especially those with 40dB fade margins and diversity systems.
Agreed. OFDM is far more tolerant of reflections than 802.11b.
Cost effective? The cheapest wireless bridge from Orthogon is the Gemini Lite 5.8GHz 21Mbits/sec for $6,000 per endpoint. The nLOS Gemini (not Lite) version is about $10,000 per end. That may be "cost effective" if you need the reliability.
Also, Orthogon and others have backed away from NLOS (non-line of sight) and are now calling it nLOS (near line of sight) primarily due to the number of disappointed customers that expect it to work with no visibility or Fresnel Zone clearance. The latest literature mumbles one line for nLOS and goes on to expound on "spectrum efficiency".
Alvarion (Breezecom) sells 900MHz as their NLOS solution because it will drill through foliage far better than 2.4 or 5.8GHz. Some early literature mumbled something about OFDM offering NLOS capeabilities, but that was dropped years ago.
Solectek offers 5.8Ghz as their NLOS solution, also using foliage attenuation and Fresnel clearances. However, they at least offer a detailed explaination of what they're selling as NLOS. |
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In my never humble opinion, NLOS is an open invitation to get sued by my customers for overselling the performance, range, and reliability.
My other half of life is bareback bronc riding - gave up bull riding as too much liability.
50 ft. climbable Rohn 25 with 10 ft. mast
Sorry, I shouldn't have implied it was a measured value - its actually a fade margin that I use in my plots that I'm comfortable with.
Scrub brush, weeds, and cow paddies.
Most hops are less than five miles due to terrain. We ran an experiment once from two points on either side of a 10 mile valley with remote monitoring thermometers at ten and twenty feet above the ground. We could see the path follow the temperature inversion. Seasonal praire grass has some effect.
The hill top to hill top ones are the most stable.
And it doesn't deplete D, P, S and K letters from my alphabet soup can.
Yuck. I really don't like the welded rod cross members. It hurts my feet when I'm hanging on for dear life trying to work. The 12.5" centers is also too small for me. (Yeah, I know... I'm spoiled).
I was hoping you had a useful way to measure fade margin in an installed system. The attenuator trick is the best I can do with bad guesswork for the BER reference level. Another trick I've used is on links where the radios have SNMP, I can usually find the OID for retransmissions or errors. 8% PER (packet error rate) is about a BER of 10^-5.
-15 dB fade margin is good enough in a fairly clean environment. I consider -20dB to be a better target value for urban links.
Hmmm... I would not expect much in the way of ground reflections. The foliage should be absorptive rather than reflective.
Yep. Valleys seem good for stable paths. I have a 5 or 6 mile shot from my house on a hillside, to a nearby peaks (Loma Prieta) that has some Wi-Fi stuff on top. I use the path to measure antenna gain (against a reference antenna). Not as accurate as a proper antenna range, but good enough.
I had a real nightmare shooting across a freeway. Range was about
2000 ft. I started with an FSO (free space optical) link. Every morning, the heat from the cars would rise to meet the cold marine air, creating an inversion layer. The light just wouldn't penetrate the layer, prefering to diffract along the boundary. There was a 15 to 30 minutes outage every morning. So, I switched to 2.4GHz wireless. Same problem, but to a much lesser degree. Maybe a 5 minute outage. I've seen similar problems shooting through the marine air boundary near the coast and the smog inversion layer during the summer.
Read the original comment. "Test gear can be located at any height on the tower". I read that to mean that a spectrum analyzer, signal generator, BER tester, and an operator can function at any level on the tower. That's quite a bit of hardware which usually requires a platform and/or elevator.
The original comments implied that it was measured, not calculated. I agree that it is easily calculated. I wish it were as easily measured.
Sheesh...Its only 50 ft. climb. But we have a steel cable that carries up a padded frame for equipment. Hang a laptop with a Cognito card and CAT5 down and remote access the laptop from another laptop.
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