Line of sight issues and WLANs

[mperetz]

Is line of sight an issue for 802.11 deployments? If it is, at what point in the development of the network infrastructure? Aren't multiple Access Points sufficient as repeaters?

[MoleStrangler]

Line of sight is a problem, but mostly you will find that the signal will go through walls (thinking of a normal home now). The more objects between the client and Access Point the more interferance and weaker the signal.

Repeating is only necessary when no physical network infrastructure exists in a location so you should be able to wirelessly bridge to that Access Point and create RF coverage.

When I teach RF site surveys I go through the process of showing the difference in range when placing an Access Point in different places. After a few years (I've been doing this for 7 years now) you gain experaince with different materials and what is not a problem and what is and good places to locate Access Points and bad places. This is not something one can teach in a classroom, you have to get out there and do it.

[KevinReichard]

Originally posted by MoleStrangler
When I teach RF site surveys I go through the process of showing the difference in range when placing an Access Point in different places. After a few years (I've been doing this for 7 years now) you gain experaince with different materials and what is not a problem and what is and good places to locate Access Points and bad places. This is not something one can teach in a classroom, you have to get out there and do it.

Out of curiosity, what materials do you find to be problematic and what are the best places for access points? I have a problem in my home with distance: my access point is in the basement near my office, but when I'm working in my living room one flight up I have problems with connectivity. Between the first and second floors are a wood floor and a suspended ceiling, with several walls between.

[MoleStrangler]

Very dense materials are the worst like concret, air brick. Also liquids and powers are very bad. You want to visualise what will be between you and you Access Point.

I deal with industrial applications so freezer walls and kevlar stops a signal because of the very nature of their construction.

What is the roof of the basement made off? I can imagine one small exit/entrance (the door). You could be enclosing your Access Point under a concrete floor and is surrounded by dirt behind the four walls. The best place for an Access Point is a very open space.

I always go for height, it may sound silly but your basement is in the ground and most of your signal is wasted. I would try and move the Access Point higher. Try mounting it on the cieling off your basement.

I always say to people I am training that they should imaginge the Access Point as being a very powerfull smoke machines and you need to get the smoke to travel as far as possible. The more objects between the Access Point and the client the less smoke that will reach.

There is also the computer you are using. Some laptops are very bad with RF cards becuase the electrical noise they create.

[KevinReichard]

Originally posted by MoleStrangler
What is the roof of the basement made off? I can imagine one small exit/entrance (the door). You could be enclosing your Access Point under a concrete floor and is surrounded by dirt behind the four walls. The best place for an Access Point is a very open space.

I always go for height, it may sound silly but your basement is in the ground and most of your signal is wasted. I would try and move the Access Point higher. Try mounting it on the cieling off your basement.

I am in a standard American walk-out: my basement is actually the lower level, and it opens to the back yard, so only half of the basement is actually below ground. The roof of the basement is just a normal plywood floor with standard joyces, but there is an additional layer with a dropped ceiling, and in between the dropped ceiling and the floor are the normal mechanicals (HVC, etc.). The access point is in my office, which is a very open space.

I will try putting the access point higher, though. Also, one of the perks of my job is that I get other review units, so this weekend I''ll be installing another access point and see what that does.

Thanks for the help!! :D

--Kevin

[MoleStrangler]

If here is a lot of wood that makes up the fabric of your house; wood is a very dense material.

Another question, have you fixed the speed of the RF interface @ 11mbps or do you allow he speed to drop to 5.5, 2 & 1mbps. If you are forcing the Access Point to stay @ 11mbps then you will get problems, always.

The range of 11mbps can be as little as 5 meters, depending on the environment. I never fix the speed @ 11mbps unless testing for specific applications or large client populations.

2mbps should be fast enough for most home applications, how fat is your Internet pipe?

[KevinReichard]

Originally posted by MoleStrangler
If here is a lot of wood that makes up the fabric of your house; wood is a very dense material.
Yes, there is a lot of wood.

Another question, have you fixed the speed of the RF interface @ 11mbps or do you allow he speed to drop to 5.5, 2 & 1mbps. If you are forcing the Access Point to stay @ 11mbps then you will get problems, always.
I don't know offhand. I'll check that tonight when I have more time to play with it.

2mbps should be fast enough for most home applications, how fat is your Internet pipe?
Cable modem. Pretty fast. ;)

Thanks!

--Kevin

[esutherland]

At the Wireless Communications Association in California this week, several companies were displaying ways of getting around the LOS problem. IoSpan was showing how its product could blast through a metal cookiepan, supposedly a real killer for 802.11 signals. Another company set up a demonstration broadcasting a broadband Internet connection from a rooftop five miles away and through the brick wall of the San Jose hotel where WCA was meeting.

How does distance factor into the loss of coverage?

Ed

[MoleStrangler]

There are many different antenna designs that can do many different things. I have instalations that use yagi antenna that project the signal many miles. In the states the rules on using high power antenna is quite relaxed. In Europe and some parts of Africa we are not allowed to use antenna beyond 3dBi. In the states you can use 19dBi yagi antenna.

You have to remember that the 2.5GHz ferquency is in the microwave band and can be quite unheathly when using high power antenna.

In europe they are not allowed to use 500mw radios. In the USA it is allowed.

[kgrr]

Ed,
There is a neat link budget calculator at
http://www.techsplanet.com/calc.htm that factors in link-to-link distance and length of feeder coax.


Molestrangler,
Here in the US, the FCC regs, sec 15.247, basically allows 1 watt (30dBm) transmitter into a 6 dB antenna. You can even use a 10 milliwatt (10dBm) transmitter with a 26dB gain antenna. (The FCC in fact likes directional antennas) But legally you cannot use a 500 mw transmitter (27dm) into a 19 dB antenna as you may be implying. In all cases, the EIRP will cannot exceed 4 watts (36 dBm).

Please see
http://frwebgate.access.gpo.gov/cgi-bin/get-cfr.cgi?YEAR=current&TITLE=47&PART=15&SECTION=247&TYPE=TEXT

Konrad Roeder
http://www.springswireless.com