Replies to This Discussion

Permalink Reply by Kirit Soheliya on October 2, 2007 at 5:57am

Hello Kishan, Which vendor equipemnts u used for this trial? what freq? 2.5G? was it 802.16e?

▶ Reply to This

Permalink Reply by Muhammad Khan on December 6, 2007 at 11:03am

WiFi and Wimax are two different technology and are meant to address different markets. While leading to 4G or beyond 4G, Wifi and all short-ranging technlogoies like Bluetooth will keep playing their rols in Person Wireless Communication context. For example Wifi phone, Bluetooth Keyboards, Mouse, WiFi access to Printers etc are just a few.

While Wimax will be more for long haul communication, providing customers triple play services on theri mobile phone, high speed downloads on mobile devices and cost efficient and quick setup to provide voice, video and data services.

▶ Reply to This

Permalink Reply by Rodrigo on December 6, 2007 at 2:03pm

Great topic, Michael!

I usually find very difficult to know which characteristics the different wireless technology have and are true. Is there any trustable source of information for WiMAX, WiFI and others mobile communications standards?

▶ Reply to This

Permalink Reply by Anas on February 19, 2008 at 5:16am

Hi there,

I’m working on wimax capacity, and I’m looking for a capacity expression vs user numbers, cell radius or other cell interference. I’d be greatly appreciated your help. I’m looking forward hearing from you shortly.

Regards

anas

▶ Reply to This

Permalink Reply by Davor Virkes on March 5, 2008 at 7:46am

As mentioned in comments on my page, a way to calculate it in "green field" calculations is nicely depicted in a presentation:

http://www.tra.gov.eg/presentations/TRA%20Wireless%20Broadband%20So...

It gives (somewhere at the end of presentation) an approximate look at cell size/capacity performance for suburban and urban environments, and if you need something better try modeling it using Monte Carlo in some serious planning software.

▶ Reply to This

Permalink Reply by Zain Shah on March 6, 2008 at 3:41pm

Michael,

I think Mythbusters is a great way to showcase WiMAX without all the unnecessary hype that surrounds the technology. Hopefully, this section will provide WiMAX360 members with the facts and nothing more. Even the though WiMAX is a great technology, we should still try and keep it real!

▶ Reply to This

Permalink Reply by Daniel Humire on March 26, 2008 at 2:16pm

I think there is a misconception in how radio propagation works. Increasing range is not dependent on technology. Increasing throughput for a given distance is a function of the FSR calculation.

The FSR calculation, however, is always based on the same laws of propagation physics. In the case of NLOS systems (typically frequencies below 5 GHZ) this can include: diffraction, refraction, reflection (atmospheric/surface), penetration, fading, free space loss, troposcatter, ducting, etc.. In the case of LOS systems (typically frequencies above 5 GHZ) this would include: free space loss, climate attenuations (rain, gas, fog), clearance, etc.)

Basically, the higher frequency you go, the more dependent you are in modeling the details of the physical environment (buildings, trees, etc.) as the Fresnel ellipse decreases and the technology becomes more of a LOS application. So WiMAX at 5.8 GHZ should strictly be modeled as a LOS application and so strictly be used for back haul design. In theory a typical WiMAX BS should reach up to 20 km in range (about when the curvature of the earth starts to become a factor). This is assuming the transmitter antennas can be mounted so that they have LOS communications with the other back haul tower(s). This is really no different than modeling any other P2P system.

Now for NLOS frequencies, WiMAX is offering improved throughput given sufficient signal strength is achieved. The WiMAX TS to the WiMAX SS/CPE range is also been theorized to be up to 20 UL/DL km but over flat earth! ATDI's experience with operators have shown that it is rare to see greater than 7km range in major cities. This is due to the signal strength requirement in order to achieve that higher level throughput that a WiMAX radio can offer via OFDM modulation, MIMO antenna systems, increased FFT size, etc. It is also offering improved spectrum reuse for OFDMA systems via subchannelization permutations. Now a SFN can group the bandwidth into permutation zones in order to allow for frequency reuse between sectors (aka Fractional Frequency Reuse). This minimizes interference issues, but the result can also mean less throughput support. Increasing subchannels decreases number of subcarrier thus decreasing throughput availability. The point of a WiMAX 802.16e equipment is that it is supposed to be able to 'judge' when to implement subchannelization to minimize interference (thus optimizing the signal range) at the expense of throughput. This is based on the SS/CPE SNR/CNR value it sends to the WiMAX TS when it roams into the network.

So you see, WiMAX isn't doing anything 'special' in increasing the range of a TS or BS or SS/CPE. It is integrating previously developed technologies to optimize the throughput and minimize interference/optimize spectrum usage of an IP based network.

On a further note, I seriously doubt WiMAX will serve any threat for voice services providers (AT&T, Verizon's mobile phone division, etc.) in the immediate future. In the US at least, there is no killer app that will convince anyone to jump from one provider to the other just because their cell phone connects to the internet faster. The only killer app with cell phones in the US is texting and e-mails which don't need high speed service. Cell phones just aren't great devices for roaming the internet. ISP related services on a handset are limited to what US customers want right now. However, what will be immediately successful, if Sprint/Nextel can pull it off, is provision of internet service to business professionals that live from city to city, airport to airport. WiMAX will compete with ISPs in the immediate future, not LTE, not HSDPA/HSUPA, EDGE, CDMA, GPRS, GSM or other mobile technologies. Unless the telco switches over to pure VoIP service (and their partners as well) I just don't see WiMAX offering much in terms of mobile phone advantage to the average US customer. In the future maybe, when a killer app urges US customers to want to switch over (gaming, uploading video data to content sites like youtube.com, downloading movie trailers, tv reruns) we may see WiMAX dominating the mobile phone market.

All these modeling considerations have been integrated into ICS telecom, by far the most sophisticated WiMAX modeling platform on the market. Feel free to e-mail me if you have more questions:

dhumire@atdi.com

▶ Reply to This

Permalink Reply by Davor Virkes on March 29, 2008 at 3:26pm

Daniel Humire says: "The WiMAX TS to the WiMAX SS/CPE range is also been theorized to be up to 20 UL/DL km but over flat earth!"
You've got a very big point here. In reality a slightly rolling hilly situation with otherwise clear path should provide a stable 10 km link. But think twice - it IS a NLOS by all means, and it is easily checked for Fresnel violations by any tool. Even when you actually see a BS tower with your bare eyes, your system's Fresnel ellipse may be buried deep under ground.

▶ Reply to This

Permalink Reply by Daniel Humire on March 29, 2008 at 3:38pm

Yeah very few tools effectively model the attenuation impact of below LOS obstructions. ITU-526-12 I believe includes some recommendation on modeling this aspect of NLOS systems.

Then you must also consider the 3D aspect, where most tools model the straight path in 2D but don't consider the partial obstructions due to terrain or tree tops or the edges of buildings. All of this contributes to the reduction of the coverage range. So yes, WiMAX equipment should deliver high data rate up to 20 km over flat earth but in reality, in urban environments I have never heard of further than 7 km delivering 5 mbps DL.

Then, you must also consider the gain due to multipath reflection (urban canyoning). And you must also consider the absorption loss through building materials.

Very few tools consider all of this.

▶ Reply to This

Permalink Reply by Davor Virkes on April 16, 2008 at 5:39am

My strong belief is that too many engineers believe blindly to the mess that occurs when one is relying to Walfisch-Ikegami approach. For several reasons this is a "bad science" that mostly stem out of ignoring the basic assumptions of this model. These are: high tower (>30m), high urban environment, and short distance (up to 5 km). Only with this approach it "works" with loss exponent of 2.6.

Now, if you "reverse engineer" it what you get is:
- flat Earth
- incredible coverage
- no obstructions other than buildings

And gee, no clutters :)

BTW, I measured propagation for UTRAN in Zagreb, Croatia (comparable in layout to most European towns) and I was unable to confirm any urban canyoning. You might consider it as a valid propagation mechanism only when you are able to confirm it by measurements, otherwise it is just another urban legend. For real urban canyons check the streets of New York :lol:

▶ Reply to This

Permalink Reply by Daniel Humire on April 16, 2008 at 9:10am

Yeah measurements is the only way to 'see' the evidence of a particular propagation phenomenon although setting up the environment to generate certain phenomenon is not always straight forward especially when one doesn't know what is causing the phenomenon to occur. You might go out on a measurement campaign for a maritime network to gather evidence of ducting, and not gather any. That is not to say ducting does not occur, but you have to know in what conditions and range you can detect it.

I have never seen the urban canyoning effect happen in suburban areas or towns made up of mostly 6-15m tall buildings. Or the DTOA of the multipath arrays was too great (exceed the GI) for the receiver being used. The impact is more clearly seen in very dense urban city centers like Manhattan or center Montreal, certain districts in Paris, Buenos Aires, etc. where the DTOA is small about 1 microsecond or less. Also, you need a receiver with a GI that can be set (by the manufacturer at least) to accept multipath in the appropriate DTOA range (microseconds) for that technology to see the effect of constructive field strength due to multipath. Working with Earthlink on their MuniWiFi deployments we saww several cases of urban canyoning in Philadelphia, Anaheim, parts of New Orleans but almost none in less dense cities like Pasadena or the suburbs of Texas.

▶ Reply to This

Permalink Reply by Davor Virkes on April 16, 2008 at 9:22am

Exactly. However, the concept of urban canyoning is passed on as a granted thing.

▶ Reply to This

• 1
• 2
• 3