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Shortly after cellular first launched, third-party entrepreneurs began offering modems for cellular data transmission. These modems resemble the standard analog modems circa 1985. They transmitted data at 300 baud, used a special cellular protocol called MNP-10, and an AT command set. MNP-10 made
these modems different from regular modems because they had to be fault-tolerant to cellular hand-offs and the in-band signaling tones used in analog cellular. One such modem was created by a Dallas, Texas company, Spectrum Cellular, that actually consisted of a modem set or pair. The land or fixed side modem was installed at the cellular switch. The mobile half was connected to the mobile phone and computer. The connection was circuit-switched, which meant that the phone was connected as long as data was transmitted and the cellular traffic channel was dedicated to that one user.
The next milestone for data over cellular was Cellular Digital Packet Data (CDPD) in 1992. An industry consortium of leading wireless communications companies set out to develop the CDPD specification. Their design objectives were to send digital data over the existing AMPS wireless infrastructure without major changes to the AMPS infrastructure, with reasonable performance (19.2 Kbps), high reliability, and security; and to support seamless roaming. CDPD also had to coexist with voice traffic. Because it was based on standard Internet TCP/IP protocols, service providers that do not have next-generation digital solutions for consumers today can still use CDPD as an Internet connection. The CDPD market is alive for the time being, but this may change as next-generation networks become active.
THE MOVE TO 2G CELLULAR
In 1989, the cellular industry began the task of migrating cellular from an analog technology to one of several digital technologies, primarily to increase capacity in several cities that were in danger of running out of voice capacity (as in New York and Los Angeles). Data was not the overriding concern for the standard bodies, and unfortunately, not every region adopted the same migration path. This created a challenge to the network designers working to maintain uniformity of operation.
The European community chose collectively to migrate their existing networks to Global System for Mobile Communications (GSM) for their first-generation digital networks. Meanwhile North America chose to develop a digital standard in two parts. The first was referred to as Interim Standard-54 (IS-54) or North American Digital Cellular. This standard, based on a version of Time Division Multiple Access (TDMA), is similar to GSM but incompatible. IS-54 was developed during the early 1990s and was soon followed with IS-136. The difference between the two was that IS-54 continued to use analog control channels and used both analog and digital traffic channels. IS-136 contained both digital and analog channels for control and traffic. IS-54 was not widely popular because it lacked clear advantages to the user. The promise of greater battery life with IS-136 alone was inducement enough to win customers over even had it lacked other advantages.
Having two different network architectures wasn’t too bad but wait—there’s a new show in town. Here comes a company out of San Diego that no one has ever heard of before, and they claim to have a better solution to digital cellular. The company was Qualcomm and the solution proposed was Code Division Multiple Access (CDMA). Today, Europe still has GSM and North America has TDMA, CDMA, and a little
GSM for variety. By 2001, GSM occupied about 65 percent of the worldwide cellular market and CDMA held about 17 percent market share.
As far as wireless data is concerned, we have only three choices: CDPD on an analog channel, Short Message Service (SMS) if it is available, or an internal modem in the phone or device. Each choice has its pros and cons. Short Message Service is just that—short—so speed is very important to the user. The rate for CDPD is 19.2 Kbps, which is fine for certain text applications, and because it is packet-based, valuable spectrum is not wasted. The third option is a built-in modem in the phone that connects to a laptop computer by either cable or infrared. Speeds with an internal modem range from 8 Kbps to 9.6 Kbps. The data simply replaces the voice traffic transmitted by the phone; the connection is circuit-switched, so spectrum is wasted. None of these options is satisfactory for real-time access to the Internet or streaming video.
ONWARD TO 2.5G AND 3G
The next step to higher data rates for each technology was dubbed 2.5G and was to be closely followed by 3G. (The “G” of course stands for “generation.”) 3G is not just a standard for higher data rates: It is also meant to bring global standardization to cellular. Our choice of words here is very deliberate: “closely followed” has been defined by some as within two years of 2.5G, whereas others say that the two standards are practically on top of one another. The simple fact is that it costs a lot of time and money to upgrade a cellular system and it may make more business sense to skip interim steps. Just as IS-54 was quickly replaced by IS-136, carriers may find 2.5G unpalatable financially. In other words, they may skip 2.5G and go directly to 3G. That makes sense but what happens when industry skips an interim solution or worse yet, adds another? Do we add a 2.75G?
The truth is that in the interests of harmonizing all of the different proposals for 3G, the cellular industry has skipped some steps or in some cases, changed direction altogether. Like
Qualcomm, NTT DoCoMo, the Japanese telecommunications giant, has proposed a new standard altogether, Wideband Code Division Multiple Access (WCDMA). Three years ago, the roadmaps for GSM, CDMA, and TDMA were clear. GSM would become GSM Phase 2+ with improvements and the addition of High-speed Circuit Switch Data (HSCSD) and rates up to 144 Kbps. Later, it would migrate to Enhanced Data Rate for Global Evolution (EDGE). GPRS would be added along with a more robust modulation scheme; rates of 384 Kbps would offer wireless multimedia IP-based services and applications. At that time there would be an “alignment” with TDMA; each would have an EDGE physical layer.
Meanwhile, TDMA would become IS-136 Plus with the addition of HSCSD. It would then migrate to IS-136HS (EDGE) just like its cousin, GSM. (Not all EDGE is created equal: The European version of EDGE and the North American version share a common standard but different frequencies. A “world” phone would have to cover more bands in order to roam.) The roadmap for GSM and TDMA primarily increases data capabilities, not voice. It is expected that voice transmission would migrate to Voice-over-IP in the future. Until that happens, EDGE is split into two component networks, one for voice and one for data.
The CDMA side was also quite clear three years ago. IS95A would become IS-95B with HSCSD up to 64 Kbps. Later IS-95C and IS-95D (sometimes referred to as IS-2000 Phase I and II) would increase data rates to about 307 Kbps. IS-95C was also referred to as 1xRTT, and IS-95D referred to as 3xRTT. Just to confuse things a little, another standard was created to overlay the other two. High Data Rate (HDR) could go as high as 2.4 Mbps. (The latest acronym for 1xRTT combined with HDR is 1xEV.)
Well, today most of this has changed. NTT DoCoMo proposed a new Wideband CDMA. When the technical and political ramifications were viewed, deals were made between proponents of each standard. GSM Phase II+ survived but IS136 Plus didn’t. For CDMA, 1xRTT survived but IS-95B didn’t
and 3xRTT will most likely be delayed as long as HDR meets users’ needs. As for WCDMA, it will become a component overlaying GSM networks, transforming those networks into Universal Mobile Telephone Service (UMTS).
The last three years have been very confusing to those following the standards process. The only things that remain clear are that CDMA will launch 1xRTT with an HDR overlay to support date rates from 144 Kbps to over 2 Mbps. Both data and voice capacity will benefit from 1xRTT.
Europe will launch EDGE with WCDMA overlaid. Data rates will run from 384 Kbps to over 2.5 Mbps. Both data and voice capacity will be improved. In the United States, the IS136 component of EDGE may be eliminated in favor of the European version of EDGE and WCDMA. AT&T Wireless has announced a decision to do exactly that: overlay the old IS-136 network with a GSM/EDGE/WCDMA version.
In the United States, a fourth cellular technology is deployed by Nextel. It uses a proprietary technology developed by Motorola called iDEN. The Nextel system works as a hybrid design between cellular and dispatch technologies. Calls may be connected like cellular, or members of a group can be connected together in a way similar to two-way radio, without dialing. For roaming outside the United States, Nextel offers a dual mode—iDEN and GSM—phone. For data applications, the Nextel phones include a Java 2 Micro-edition (J2ME) environment and transmit data on a packet network.
Regardless of the details of who implements what, three important things should be remembered:
• High speed packet data will replace circuit-switched data.
• Internet Protocol (IP) will become the standard protocol for all wireless traffic, voice, and data.
• A quasi-global standard will make international roaming easier.
These three changes to mobile communications will open the door to the next generation of wireless applications. | 
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