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May 03, 2008

Too Many Bands Playing Too Many Different Tunes

by Matthew

Cell Tower

Not musical bands, rather the bands of frequencies used by wireless providers the world over. We all know everything wireless use a frequency, measured in Hertz (Hz). The confusing part people don't understand which frequencies and where those frequencies are used. Even more confusing and less understood by many is the fact that each frequency can only support so much information within that frequency (channels) whether that is audio, video or data. Based on some of the comments from May 1, 2008 it's obvious to me people are quite confused by 3G frequencies used in North & South America verses those used elsewhere in the world.

Don't feel alone if you don't understand or confuse the bands and where they are used. It is such a convoluted mess; frequency soup if you will, and even those in the know can confuse them. For simplicity I'm not going to go into great detail on why some frequencies are used, why this frequency is used in North America, others Europe, Korea, Japan and all the endless combinations that are often country specific. Instead I will focus on the two main GSM and three main 3G frequencies that are going to be commonly used, mostly because these will be the most common and how it relates to you, our S60 readers.

Before I get into the frequencies understand GSM is 2G, GPRS 2.5G, EDGE 2.75G, UMTS 3G, HSDPA 3.5G, WiMAX and LTE are typically considered to be 4G although WiMax is 3G and LTE has yet to be offically approved as a standard. GPRS and EGDE are both based on GSM, HSDPA and LTE are is based on UMTS which are all forms of W-CDMA. UMTS and HSDPA are frequently referred to as 3G collectively, although there can be quite a large difference in data speeds. WiMAX is separate technology which for the most part I will leave out and only mention it because it has been in the news a lot with the release of the new Nokia N810 WiMAX and is being used advertised and referred to as a 4G technology by some operators however largely used as an alternative to Cable or DSL today.

Let's start with what most of the world knows as GSM. Outside of North & South America, with a few exceptions GSM is used on 900MHz and 1800 MHz and most of North and South America GSM uses 850MHz and 1900MHz. Some might remember TDMA as 800MHz and 1900MHz. When TDMA was changed over the GSM the 800MHz band was more accurately referred to as 850. In reality GSM is another form of TDMA, there are a number of variations.

When Europe and Asia began offering 3G services they began using what is commonly referred to as 2100. As with all wireless services there is a frequency used for transmission from the base (cell tower) and transmission back to the base (mobile device). Up-link is the data transmitted from the handset up to the base, conversely down-link is the data transmitted down to the handset. To achieve high data speeds 3G promises these were further divided into larger up-link and down-link channels. By dividing the data links more data can be passed to more users at a higher rate of speed, bits per second (bps). In Europe and Asia these frequencies are 1900MHz for the up-link and 2100MHz for the down-link.

When 3G was first introduced in North and South America 3G there wasn't another available frequency group as there was in Europe. As such the same 850/1900 frequencies were used and commonly referred to as US 3G, which is not correct or accurate. As I said before there are only so many channels that can be used within each frequency. AT&T was only able to offer 3G services on the existing frequencies because they had acquired such large sum of available channels in the 850/1900 bands through various acquisitions namely the AT&T/Cingular merger. To clarifiy 850/1900 can be used in tandum or independently depending on the carrier.

AT&T had a great deal of trouble offering 3G, so much so they had two launches of the service. Combining the technologies jump started AT&T's 3G offering the disadvantage is data suffers when voice usage is high. Without getting into a big debate about AT&T's choice to use these bands for 3G, there are only so many channels available and for obvious reasons voice needs to take priority over data (although some might disagree). I believe AT&T more than anything has caused a great deal of confusion among consumers, more so than the frequency differences between GSM regions, not to mention making it more difficult for handset manufactures to make compatible devices for so many frequency variations. We already see a great discrepancy in handsets that use US and European/Asian frequencies.

Now let's get down to what confuses people most about 3G. Two years ago the FCC auctioned off a large spectrum of frequencies 1700MHz and 2100MHz. This spectrum was paired as a single unit and collectively referred to as Advance Wireless Services (AWS). That meant if you bought 1710MHz, you also bought 2110Mhz, similar to Europe and Asia's 1900/2100. It would have been easier on the American consumer if AT&T had waited to offer 3G similarly as Europe had done, but it also meant waiting for the spectrum to be cleared. Most of the delay in T-Mobile's 3G launch was due to the US Government's failure to stop using the frequencies.

AWS here in the US and 3G offered in Europe and Asia are so similar that it confuses people. When looking at mobile devices they indicate their operating frequencies so the consumer knows where said device will work. In a world where three variations of 3G are offered, each, obviously, must be referred to differently. When looking at devices for the US they are either going to specifically state UTMS, HSDPA or WCDMA along with 850/1900 (AT&T), Band IV, 1700 or AWS. If a device doesn't indicate one of these and instead state W-CDMA 2100 or only W-CDMA these devices are using European/Asian 3G. Dual, tri and quad-band WCDMA devices are around the corner. Dual-band would mean one of these possible scenarios: WCDMA 850/1900 (available today) and AWS, or AWS & European/Asian 3G. Tri-band would be W-CMDA 850/1900 and AWS, or 850/1900 and European/Asian 3G while quad-band would be W-CDMA 850/1900, AWS and European/Asian 3G. I would expect to see most dual-band 3G devices will likely be as a combination of either 850/1900 or AWS combined with European/Asian 3G. Tri-band WCDMA would be a combination of all three 3G standards.

To further convolute the frequency soup AT&T and Verizon are planning to deploy LTE (4G) using 700MHz they recently purchased in the FCC auction. The FCC in this case is going to require service providers to maintain an open network, which should benefit us all. LTE is at least 3 years away from reality. This frequency currently used for analog TV which will not be clear until February 2009. Additionally LTE equipment is still largely still being developed much less installed.

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Comments

Chris

This text introduces quite a lot of false information for an article that is suppose to clear anything. So let's start clearing of the clearing:

"Before I get into the frequencies understand GSM is 2G, GPRS 2.5G, EDGE 2.75G, UMTS 3G, HSDPA 3.5G, WiMAX and LTE are 4G."

What is 4G is not decided yet. LTE is specified by 3GPP, which clearly indicates it is part of 3G standards. Also WiMAX is 3G, as it has been accepted as IMT-2000 standard. IMT-2000 is a set of ITU's 3G specs. However, taking into account huge technical differences between LTE/WiMAX and UMTS, these associations are being disputed (personally, as a telecom specialist, I would rather see LTE/WiMAX as 4G). So the author should not step in fron of the line of more prominent experts declaring what is 4G...

"GPRS and EGDE are both based on GSM, HSDPA and LTE are based on UMTS which are all forms of W-CDMA."

This is simply a nonsense, moreover a double one in one sentence. First, LTE is _not_ based on UMTS. Actually, UMTS is by more similar to GSM/GPRS than LTE to UMTS/HSxPA (the author places everywhere HSDPA forgetting existence of HSUPA). UMTS inherited form GSM/GPRS the core network, whereas LTE introduces both, new radio interface and new core. That puts us to the second nonsense: LTE is _not_ based on WCDMA, nor any other version of CDMA. It is based on OFDMA in the downlink and SC-FDMA in the uplink.

The rest of the text is all right, except that it forgets that in Europe there are two UMTS bands: besides the 2100 it is deployed also in 900 band (sharing it with GSM).

I recommend some reading before writing...

Michael

"Dual-band would mean one of these possible scenarios: WCDMA 850/1900 and AWS, AWS & European/Asian 3G or 850/1900 and European/Asian 3G."

This seems to imply that the AT&T's network uses one of its bands for uplink, the other for downlink in the same way that AWS is split on 1700/2100MHz. I have never heard anything to suggest that is the case, though. AT&T's 850MHz 3G network and 1900MHz 3G network operate in-band, and independently of each other. Those licenses were not auctioned off as split bands the way that the various 1700/2100MHz AWS band was.

Thus, a 850/1900/2100MHz 3G device would be tri-band, not dual-band.

Freddie Lopez

Since one of the goal of the article is to clarify some of the confusion they have if a UMTS 2100 MHz handset can work on the AWS spectrum based on the comments of your readers from the previous article, it would be beneficial if you have explored more on the "uplink" or "downlink" you've stated on the 5th paragraph. A lot of things also people don't realize is all major mobile phone technology to date has used "paired" spectrum. That means each "band" is actually a pair of bands, with one half being used for towers to transmit to phones, and the other half being used for phones to transmit to towers.

UMTS 2100 phones transmit to towers in 1920-1980 MHz range, which is what towers using the PCS band use to transmit to phones in United States or North America. Therefore UMTS 2100 phones are already designed to not transmit in that range when they're in the U.S., since that would interfere with PCS networks.

Even if that weren't an issue, an AWS network can only "listen" (tower to phone) to the 1710-1755 MHz range, so it could never "hear" (phone to tower) the 1920-1980 MHz transmissions of a UMTS 2100 phone.

daren benzi

After re-reading your somewhat rambling post, it struck me this might be an excellent opportunity to create a matrix or table illustrating the various frequencies, nomenclature and uses worldwide.

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