One thing I have noticed after adding 50+ customers on a omni is that you get better performance by turning the TX power DOWN on the clients within 1 mile. I would assume this is so because of some kind of self interference.
Kurt Fankhauser WAVELINC P.O. Box 126 Bucyrus, OH 44820 419-562-6405 www.wavelinc.com -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Friday, February 15, 2008 1:07 AM To: [EMAIL PROTECTED]; 'WISPA General List' Subject: Re: [WISPA] [WISPA Members] WLAN stress test uncovers802.11performance problems Jack I will give in to your challenge, and focus on outdoors setups :) But first, I agree with you 100% about your comments; some venders saying "add more APs will help" as well as " their smart systems will solve all their performance issues. We have been watching, talking and helping some of the people involved in the so called "city wide wifi" and many if not all of them are simply not adhering to the strengths of wifi and trying to make the protocol do things it will not. When we get calls like this the most common misconceptions is they expect laptops to work miles away from the AP, Non-LOS, and Omni installs to keep it simple. Then we put on our training hats to bring them down to earth on what to really expect and how to design a system correctly. Ok now to a design ideas, first I want to point out that each design is going to be different but if the basic concepts are followed it will work each and every time. 1. Before any design can be started you really want to get a base line as to what one is starting with. We always recommend rents hand held SA and do field tests to see what other frequencies are out there being used and do your best to triangulate and find out where they are coming from. This data should be recorded on a map for future reference. 2. 90% of our customers try to find the highest place in the middle of the area they are trying to serve, while this could be the best choice for a design it's not the only or best one. See if you can service the same area from the outside in, for example if you are able to find three locations on the outer rim of an area and use 120 degree antennas this will increase your true coverage area exponentially as the installers now have three locations to try vs. one. The latest customer we helped with a design went from 25% install rate to 90%, thus it's well worth the costs for the extra two locations up front where the costs of a truck role is about $50 minimum if the customer is installed or not! The first month this design saved the customer well over $5000 in install fees plus he now over 100 customers generating income that he would not have at this point! 3. Once the locations are found on the tower or building you REALY want to avoid installing antennas anywhere near each other. On a tower try to install the antennas with 10' vertical separation at a minimum, more is better and vertical is more important than horizontal. Also try to have 2-3' horizontal separation. Ideally you want to create a spiral stair case effect with the antennas. 4. This is where the setup is very important, you NEED to limit the distance of each antennas to be practical. For example if you are in a rural area this could be 10+ miles where you do not see any other radio signals via the antenna, yes you want to test with an SA directly on the antennas to confirm! In other locations this could be less than 1 mile. As an example let's assume a WISP wants to reach a max of 5 miles, having a person on the tower to adjust the down tilt, you want to have an install at the 5 mile mark (and center of antenna be is 180, 120 etc) and tune the strongest signal at this point. With this setup you can rest assure that the antennas will only pick up interference from 5 miles in and not from 5 miles out. The name of the game with wireless is single to noise levels, lots of signal will do nothing if there is also lots of noise. 5. The other major issue we see is self interference. If you have more than one antenna at a locations, you want to test with the SA each antenna how much it's sees from the other antennas. So for example if you have three radios at a sight plug the SA in to one antennas and turn on one radio then the other and see how much signal the antennas pick up from the other radios and do the same for the other two. The issue here is even though each antennas/radio is on a different channel too much power from the side radios can cause major problems with the receivers, basically overloading them. This is the major reason you need to have good separation. There are a few other tricks but I think I have hit on the major ones, I am sure Jack will fill in if I missed something major. Anyway hope this helps and if anyone wants to talk more you can hit me off list or call me or my techs at the office. Sincerely, Tony Morella Demarc Technology Group, A Wireless Solution Provider Office: 207-667-7583 Fax: 207-433-1008 http://www.demarctech.com This communication constitutes an electronic communication within the meaning of the Electronic Communications Privacy Act, 18 USC 2510, and its disclosure is strictly limited to the recipient intended by the sender of this message. This communication may contain confidential and privileged material for the sole use of the intended recipient and receipt by anyone other than the intended recipient does not constitute a loss of the confidential or privileged nature of the communication. Any review or distribution by others is strictly prohibited. If you are not the intended recipient please contact the sender by return electronic mail and delete all copies of this communication -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Jack Unger Sent: Thursday, February 14, 2008 2:17 AM To: WISPA General List Cc: [EMAIL PROTECTED] Subject: Re: [WISPA Members] [WISPA] WLAN stress test uncovers 802.11performance problems Yep. Very few people (less than 5%) who deploy dense wireless LANs understand that the interference radius around each access point Omni antenna is 4 times to 8 times (or more) GREATER than the usable communications radius. People end up putting too many access points too close together resulting in a huge DECREASE in aggregate throughput and REDUCED network reliability. These symptoms will only emerge once traffic levels build up and wireless frames are colliding with each other all over the place. Then the network manager starts adding access points and makes the problem worse. On top of that, most wireless LAN vendors push the idea that throughput and reliability problems will be SOLVED by adding more access points. The wireless LAN vendors also tell the customer that their "smart" controller will help reduce the self-interference between the access points by "intelligently" managing access point power and channel. Those of you who don't live in a major city will have to use your imagination to follow this example but this vendor argument is like saying that placing a traffic cop with a whistle in the middle of a freeway that is moving at 2 miles per hour will help to "manage" the flow of traffic and speed the traffic up; it won't. The cop will only manage to distract the drivers and slow the traffic down even more. So if you are deploying a wireless LAN that needs a lot of access points to handle a many simultaneous users and high levels of user traffic and different types of user traffic (like voice and data), what should you do to get your WLAN to work and to meet management and end-user expectations? Let's hear a few opinions from people about how to get good WLAN performance. BTW, these very same principles apply outdoors in WISP deployments. After we hear from five or six people, I'll offer my solutions (if you all don't beat me to it). ;-) Oh yeah, one more thing... PLEASE post your solutions over on the WISPA Members list. This is the kind of info that I feel paying WISPA members deserve to have access to. In my view (I know this is "old-school" thinking these days but remember, I'm old), there really is no such thing as a "free lunch". Those folks who support WISPA deserve to receive information that is a cut above the "free information" (and dis-information and advertising hype) that has distorted people's sense of reality these days. Your normally quiet and humble servant, jack ------------------------------------------------------------------------ -------- WISPA Wants You! Join today! http://signup.wispa.org/ ------------------------------------------------------------------------ -------- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/ -------------------------------------------------------------------------------- WISPA Wants You! 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