Cellphone Technology on the Way Out

TDMA: Dramatic Cellular Improvement Being Phased Out

TDMA, or Time Division Multiple Access was one of the first cell phone digital standards available in the United States. It was the first successor to the original AMPS analog service that was popular throughout the country, and was in popular service from the early-mid 1990's up until roughly 2003 when the last of the TDMA carriers, Cingular and AT&T, switched to the GSM digital standard.

TDMA was a significant leap over the analog wireless service that was in place at the time, and it's chief benefit for carriers was that it used the available wireless spectrum much more efficiently than analog, allowing more phone calls to go through simultaneously. An additional benefit to carriers was that it virtually eliminated the criminal cell phone cloning that was popular at the time by encrypting the signal it's wireless signal.

The primary benefit for wireless users of the era was dramatically increased call quality over the scratchy, frequently garbled or "under water" sounds that analog users had become accustomed to. All manufacturers produced TDMA handsets during this period of time, but Nokia's ubiquitous model 5165 is probably the most popular example of TDMA technology.
TDMA was replaced by GSM to permit the use of advanced, data intensive features such as text messaging and picture messaging, and to allow an even more efficient use of bandwidth.

While TDMA is in limited use today it is expected to be fully phased out by 2008.



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What is a WORLD Phone?

You Can Use a Cellphone in Most of the World Without a Giant Dish

In the United States several major cell phone carriers, such as Cingular and T-Mobile, have chosen to use the GSM digital protocol that is popular overseas. Their wireless handsets, as well as other brands sold in the U.S., operate on either 850 mhz or 1900 mhz, while European networks operate on either 900 mhz or 1800 mhz. These frequencies, or bands, are incompatible so in order for a handset to work both in the U.S. and abroad it must be capable of transmitting signal on three or four different frequencies. Therefore a wireless handset capable of operating on three of these bands is called a tri-band, while a handset capable of operating any of the four is called a quad-band.

These multi-band phones are termed "World Phones", though a serious traveller would really only consider a quad-band, as tri-band phones were more of an interim step. While several major manufacturers such as Samsung and Nokia have produced competent world phones, Motorola was the first company to popularize quad-band phones and continues to produce more of them than any other carrier. The Motorola RAZR is an excellent example of the company's recent quad-band efforts.

As GSM is easily the most pervasive wireless protocol worldwide with over one billion current subscribers, a traveller with a quad-band world phone phone should be able to obtain useable wireless signal in most urban areas accross the globe.


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What is an UNLOCKED GSM Cellphone?

and Do I Need to Get a Key?

When purchased from a wireless carrier, such as Cingular or T-Mobile, a GSM cell phone will typically come with a "subsidy-lock" or "sub-lock" code. These software codes are installed in the handsets during the manufacturing process in order to prevent consumers from using a phone purchased from one carrier on another carrier's network.

The logic here is that when selling the phone to a consumer, the carrier subsidized the cost of the phone. Free phones are the perfect example of this strategy. Intuitively, consumers know wireless phones are not free to manufacture, but will nevertheless be tempted by the prospect of not having to actually pay money for a new cell phone. The difference between what a consumer pays for a cell phone versus what it actually cost the carrier (always more) is called the subsidy, and to protect their "investment" carriers lock the phones to only work on their network.

Yes, this is kind of a shady thing for carriers to do as consumers do have to sign up for two years of service or pay a hefty cancellation fee in order to get the "free" phone, but it is not illegal.

However, for every lock there is a key. All of these phones with subsidy locks can be unlocked by third party companies using specialized devices. Unlocked GSM cell phones can then be placed in service with any compatible carrier, allowing the consumer a much wider range of choice.

Unlocking GSM cell phones is completely legal in all 50 states and the service is pretty easy to come by. Simply do a Google search for Unlock GSM Cell Phones and examine your choices.


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GSM, TDMA, CDMA

Wireless Alphabet Soup:What it All Means


CDMA, TDMA, GSM, iDEN, and AMPS, what do they all mean? Since you found this article you likely know that these are acronyms that primarily relate to the cellular phone industry, and this particular alphabet soup of acronyms refers to most of the wireless protocols that are used in the United States. What I will try to do is break down the different protocols into layman's terms starting with AMPS.

Wireless protocols are essentially the methods by which wireless, or cellular, signals are transmitted between a caller and a receiver. An easy way to follow the progression of these technologies is to start at the beginning and work our way throught them in chronological order. AMPS, commonly referred to as Analog, stands for Advanced Mobile Phone System and it was the name given original mobile phone system introduced to the U.S. in 1984. AMPS was a product of Bell Labs, and while analog is no longer considered remotely advanced (AMPS phones are the size of cinder blocks), the cellular switching technology AMPS introduced was cutting edge at the time.

AMPS uses FDMA, or Frequency Division Multiple Access, which is a ten dollar way of saying that each conversation is divided by assigning them separate channels. AMPS made this work better than past technologies were able to by computerizing frequency management, handset transmitter power, and call setup. Are your eyes beginning to glaze over yet?

AMPS was in wide us in the United States from 1984 to the late 1990's, though it did began to get supplanted by an early digital protocol, TDMA or D-AMPS. The writing was on the wall in the early 1990's when phone cloning (c'mon you remember cloning don't you?) became widespread. This was a scheme where unscrupulous individuals could fish AMPS cellular identification pretty much right out of the air and with a little programming create a second phone line that billed to the one they copied. On top of this, as wireless service was permeating the U.S. market the limitations of AMPS (assigning a whole channel to one conversation) became rather apparent, and wireless carriers began to literally run out of space on their networks in major markets.

The switch to digital protocols (TDMA, GSM, CDMA) that began in the early 1990's is now almost complete, and the U.S. Government will allow wireless carriers to terminate their AMPS service entirely on March 1, 2008.

AMPS has brought us some good times, if you think about it. Remember those 80's movies and TV shows that tried to look all high-techy with Sonny Crockett or Michael Knight making calls on a phone the size of a Korean War-era walkie talkie? You got it, that was AMPS. You can also make "You might be a redneck" type jokes about AMPS. For example, "If you're phone is the size of a toaster, you might be using AMPS." or "If you're cell phone tans one side of your face while using it, you might be using AMPS."

The latter joke here refers to the fact that handset transmitter output was, ahem, somewhat higher and less regulated back in the day. But don't worry, even if the phones did transmit enough microwave energy to cook poultry (note to attorneys: we're not saying they did), cell phone minutes were so expensive back then that hardly anyone could afford to talk on them for very long.

Keep an eye out for Alphabet Soup Part 2, The Revenge of TDMA


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