WiFI going bust? Wimax coming on strong

On Thu, 30 Aug 2007 11:42:55 -0400, "Dana" wrote in :

It's doubtful that anyone could really make it work.

Using Wi-Fi for police and fire is a Really Bad Idea(tm)!

No kidding!

Free and muni are the problems. The free market works much better.

Better to let private business do it.

Not necessarily. Only time will tell.

Sure it's a bad idea. Police, fire and other emergency response units need a reliable means of communication. You get a couple of file-sharing users on and the whole thing goes to pot.

That is why the FCC assigned the 4.9 GHz spectrum, in 2003, known as the 'Public Safety' band.

Works fine if you don't try and make it free... Check out skynet of spokane

them for a few years... Hotspots are HUNDREDS of square miles, and work with laptops/pdas/etc with 802.11b.... Does cost a few bucks a month, but for the few years I used it (till I sold my house and moved), worked great with stuff many people already have.... Wonder why they try and make things supposedly free, or require you to buy something new?

Sorta depends on what you are doing. P/F/ER could probably make good use of a WiFi system for non-emergency routine things like using IM to contact supply for needed replacements, calling on/off shift, chatter between stations, sending reports back and forth, there are probably others. The REAL question is do you want to strip money from the Public Safety budget to underwrite the system. Seems like it maybe should be general public subsidizing Public Safety.

On Mon, 1 Oct 2007 12:36:59 -0400, "Dana" wrote in :

Unfortunately, there's really no way to do that with standard Wi-Fi.

Fortunately bandwidth modeling for WiFi is very easy...when you are a professional in the biz.

Sure there is. It is called proper design and engineering.

Yet people tend to insist that it cannot be done, only because they lack a complete understanding of the technology and how to make it work like we want. Like you said above, "when you are a pro in the biz". People like John just make our job a tad more difficult with customers and users of the systems, when they spout bogus info, based on a lack of complete knowledge of the capabilities.

snipped-for-privacy@gmail.com hath wroth:

Ahem. I beg to differ. I've done quite a bit of modeling wireless data systems for various customers in the past. Strangely, I've never done a Wi-Fi system as all of them were various proprietary schemes designed to compensate for the deficiencies of Wi-Fi.

I've looked at Wi-Fi with Mathcad 2000 and had problems because of the large number of outside influences that are difficult to include. For example, reflections, interference, multipath, proprietary enchancements, and creative implimentations, are all common with Wi-Fi systems. I was interested in simulating various mesh network topologies, mostly to verify how close test results followed theory. Mesh adds additional complexity with routing algorthms, geographic routing, and long range timing problems. Throw in various fading models for moving clients, and life becomes really complex. I could ignore all the outside influences in the simulation, but then it wouldn't resemble reality.

Unfortunately, I may have hit the limits of my abilities with Mathcad. If I ever get inspired to resurrect the exercise, I may to need an update to the latest version (13?), a copy of Simulink, and to get some qualified advice on where I screwed up and on how to continue. I'm also tempted to switch to MATLAB, which offers a library of models to plagerize: "IEEE 802.11a WLAN model"

"Simulation of an 802.11 Wireless Network"

"802.11b PHY MATLAB Code"

"Modeling Multpath in 802.11 Systems"

Ugh... power going up and down. Later...

Jeff Liebermann hath wroth:

One more: "Mathworks Communications Toolbox (74 Files)"

Sounds like a typical day in the office for cellular engineers. Ray tracing methods are now becoming popular in rf propagation software solutions.

I was interested in simulating various mesh network

"Dana" hath wroth:

Methinks we're talking about two different types of simulations here. snipped-for-privacy@gmail.com said: "Fortunately bandwidth modeling for WiFi is very easy...when you are a professional in the biz." which I took to mean simulating bit/packet error rates, retransmission algorthm effects, thruput, error correction effects, carrier to jamming ratio, doppler damage, Eb/No falloff, power control effects, and reliability/availability. You seem to have interpreted the original statement as coverage area, which really is a trivial exercise until you get down to urban jungles and indoor propagation. (Incidentally, thanks for the Wavecall link. I was trying to remember their URL).

What I use for propagation is Radio Mobile:

using SRTM data for the wide areas, and some "borrowed" LADAR data for the local urban jungle. It blows up in the near field, but then I don't care much about that. I should finish this web site one of these daze:

Simulating Wi-Fi is far more complicated. With a propagation and coverage model, there are really only a few variables, which are mostly signal strength and postion. All the other variables are static for a given map. With modulation and data simulation, there are a huge number of variables, most of which I listed previously. However, the purposes are very similar, which it to calculate how many radios can function in a given geographic area, and at what performance levels. That's not very easy as witnessed by none of the MATLAB models I posted go beyond the idealized RF model (no interference, no reflections, no multipath, no doppler, no MIMO, no mesh, no long distance timing, etc).

Incidentally, I don't think I'll be buying MATLAB. $1,900 for MATLAB, $3,000 for SIMULAB and my guess is about $7,000 for all the RF/COMM modules I'll need.

I was reply> "Fortunately bandwidth modeling for WiFi is very easy...when you

I took his statement in the context of the ongoing thread, about preserving bandwidth for certain users.

You seem to have interpreted the

No problem about the url. When I read your reply which included multipath and other rf impairments, I thought you were saying rf planning fro mesh networks is almost impossible.

Yep. for those of us not lucky enough, mathlab is kind of out of reach on the affordability scale.

On Wed, 5 Sep 2007 19:46:43 -0400, "Dana" wrote in :

I beg to differ -- Wi-Fi lacks the kind of facilities needed for guaranteeing "bandwidth" (a serious misnomer -- tsk tsk:) or even any sort of communication at all -- all it takes is one bad apple to spoil the Wi-Fi barrel, which is why it's definitely not "mission critical".

On Wed, 5 Sep 2007 19:46:43 -0400, "Dana" wrote in :

p.s. Thanks for finally fixed your computer clock. Was that a good example of proper design and engineering? Or just cockpit error? ;)

On Thu, 30 Aug 2007 20:14:23 -0400, "Peter Pan" wrote in :

And that's the point.

Only because you lack the knowledge of the technology.

I beg to differ...WiFi is nothing more than another type of radio communications, albeit with more limitations. With proper traffic control facilites, i.e. limiting how much pipe a user can have access to, it can take out that "bad apple".

Please refrain from spouting misleading misinformation. Hire a professional that deals with "mission critical" applications as part of his professional venue.

Proper design will ensure that the bandwidth for police, fire, etc is preserved.