AMPS is an analog technology. It uses radio frequencies in the 800 to 900MHz range, as allocated and regulated by the FCC. The frequency range is divided, with half used for incoming signal transmissions and half used for outgoing signals. These bands are further divided into 30KHz channels, and each call uses one channel dedicated to that call. This allows multiple users to share a cell (actually, the base station for that cell) without interference. However, AMPS uses standard FM radio waves, and anyone with an FM scanner tuned to these frequencies can hear calls. In fact, crooks with the right equipment can capture anyone’s account information onto their phones (a technique referred to as cloning) and run up huge bills, which are sent to the unsuspecting customer.

In its first year, the new cellular mobile system in the U.S. had 92,000 subscribers. Early industry projections had forecast the potential user base for mobile telephones topping out at 900,000. In 1987, the countrywide subscriber base passed the 1 million mark, and by 1995, there were more than 33 million users. By that time, the next generation of mobile telephony was well into development.

A new system was needed because the world had gone digital. Analog AMPS was launched two years after the introduction of the personal computer. By 1995, the Internet was all the rage. Netscape’s Mozilla Web browser had just hit the market, and email was taking over business communications. Business travelers were lugging heavyweight portable computers around airports so they would have access to both of these technologies. Cell phone technology developers had already seen the potential of providing that access via the cell phone, and they were on the case.

Also, it had become apparent that the growing customer base for mobile phones was nowhere near peaking. Digital technology would allow base stations to handle many more users at once. It was time for the second generation of cellular technology.

2G: Mobile Telephony Goes Digital

There are two basic digital mobile technologies, GSM (Global System for Mobile Communications) and CDMA (Code-Division Multiple Access). GSM was developed in Europe by the Groupe Spécial Mobile in the 1980s with the intention of building a trans-European mobile system. It is now the most widely used mobile system in the world. GSM networks can use four radio frequencies: 850MHz, 900MHz, 1800MHz, and 1900MHz. Most existing foreign networks use the 900MHz and 1800MHz ranges. In the U.S., GSM services use the 850MHz and 1900MHz frequencies. Qualcomm developed CDMA in the late ’80s and launched it in the mid-’90s. CDMA is the most widely used digital mobile telephony system in the U.S. Transmission speeds were exciting at launch, though 2G’s 9.6Kbps download speeds don’t seem so thrilling today.

Digital cellular has several key advantages over analog service. First, because it’s digital, it’s harder to intercept calls, and the cloning of digital accounts is not possible. Digital systems allow multiple calls to ride on the same channel, so providers are able to handle more calls. Most importantly from the end user’s perspective, carriers were able to add services such as email and text messaging (via SMS [Short Message Service]), and later, image transmission. Text messaging has become a worldwide phenomenon. It is extremely popular in Europe and especially in Japan, where more users, primarily teens, use their phones for messaging than for talking. In 2002, the first camera phone was released in the U.S. Users could take submegapixel-quality pictures and email them around the world or post them to Web sites. There was some controversy over privacy issues when unauthorized candid images appeared on the Internet, but this was a technology that would not be stopped. Today, 5MP-plus camera phones are on the market; Samsung’s SCH-B600 camera phone houses a 10MP camera. Some market projections forecast there being more than 1 billion camera phones in use by the end of this year.

Many of these digital services are add-ons to the digital cellular infrastructure rather than integrated apps, but it is the 2G digital systems that give them life.

One of the coolest features of GSM phones and service is the SIM (subscriber identity module) card. It is a digital ID card, a bit smaller than an SD Card, which holds all your personal subscriber information, your address book, and your text messages. When you get a new phone, or if you want to use multiple phones, you simply transfer the card from one phone to the other and you’re good to go. Your phone service access is based on the card, not the phone. CDMA phones don’t offer this feature.

After phones went digital, manufacturers could make them smaller and less expensive. Those features combined with the digital access phone makers promised caused phone sales to skyrocket. There were two big hassles related to the 2G versions of GSM and CDMA, however.

The first problem was that the two technologies aren’t compatible. U.S. travelers to Europe and Japan using 2G phone service cannot use their phones in either location. Even those with U.S.-based 2G GSM service are affected because their phones use different frequencies than European and Japanese GSM networks.

The second annoyance was familiar to users who still used dial-up connections to access the Internet from their computers. The transfer of digital information to and from your phone took a long time, and you were paying for minutes used as you executed the transfer. The need for speed quickly became apparent to users and providers alike. Technology came to the rescue once again, in stages.

2.5G: Revving Up To Speed

The first improvement to 2G technology was an enhancement of the GSM system. Called HSCDS (High-Speed Circuit-Switched Data), 2.5G had real-world speeds of 30Kbps or so, which was an improvement over the original GSM technology. It was circuit-based, as is obvious from the name, and was hardly available in the U.S. before the first full GSM upgrade, known as GPRS (General Packet Radio System) launched. GPRS transmits data at rates up to 114Kbps (maximum rated, not actual), compared with HSCSD rates of 38.4Kbps (maximum rated). GPRS works only on GSM systems, and you must have a GPRS-ready phone to reap the benefits of the technology.

Before GPRS, all cell phone service was circuit-switched, meaning that any one call was given a complete circuit. When all circuits were full, access was denied to anyone else until a circuit became available. In this respect, the system was similar to the land-based telephone system. GPRS allowed the digital signals of a call to be broken out into packets and sent along one or multiple channels along with other packets for other calls. The packets are created at the sender’s base station, sent to the receiver’s base station, and reassembled for delivery to the receiver. It works much like a standard computer network. The benefits are more capacity on the network and faster transmission times.

The CDMA network was similarly upgraded. In 2002, Verizon Wireless introduced a retooled version in the U.S. called CDMA2000. The initial release, called 1xRTT, provided real-world speeds of 40 to 60Kbps. It was rated as having a theoretical maximum speed of 144Kbps, which is the minimum speed for designation as a 3G technology. However, because interference, traffic congestion, and network overhead make it virtually impossible ever to hit the maximum rated speed (witness the real-world speeds given above, at less than half the maximum rated), most industry insiders consider 1xRTT a 2.5G technology.

Nokia is another major player in the development of cell phone technology. The company’s original cellular phones were car mounted, not handheld. This Mobira Senator is an early model (1982) Nokia cellular car phone.

EDGE speeds are rated at 384Kbps, but carriers don’t promise more than 70 to 80Kbps. The GSM proponents say this is enough for downloading music and video, sending email on the move, and full Web browsing. Apple seems to agree. It released the iPhone with EDGE technology rather than opting for 3G. EDGE speeds are often better than GPRS, especially in areas with strong network coverage, yet satisfaction is subjective, and providers tend to be more easily satisfied than their customers.

Because of its boost in speed over GPRS and its real-world below-3G speeds vs. its rated 3G speeds, EDGE is often listed as 2.75G.

3G: The State Of The Art

Today, the third generation of cellular technology is being rolled out across the country and has been available in many major markets for several years. Speed ratings reach more than 2Mbps, but as always, reality delivers much less. Experience proves that even today’s best is but a stepping stone to the holy grail of 4G. Under optimum real-world conditions, your 3G network might deliver 384Kbps for stationary systems and 128Kbps when in motion—not bad. Better video downloads and data transmission speeds are the reasons to go for 3G.

The important technologies of 3G mobility, as you’d guess, align with the two major underlying protocols, GSM and CDMA. The GSM version of 3G is UMTS (Universal Mobile Telecommunications System). Rather than an overlay technology such as EDGE, UMTS is an evolution of GSM and replaces it as a basis for mobile communications. UMTS employs W-CDMA (Wideband CDMA) for signal transmission across the air. Despite the closeness of the names, W-CDMA and CDMA2000 networks are not compatible.

In the CDMA corner, the 3G contender is EVDO (Evolution Data Only or, often, Evolution Data Optimized). As the name implies, EVDO is a data-specific technology. It is an overlay to CDMA and offers download speeds of 400Kbps, which is quite impressive. Upload speeds, as usual, are much slower, less than 100Kbps. An enhanced version has already rolled out in some areas. Called EVDO Rev A, it is much faster—perhaps four to six times—than the standard version.

Not to be outdone, UMTS has an enhanced set of protocols that boost its performance. It is called HSPA (High-Speed Packet Access), and there is a set for improving downloads (HSDPA [High-Speed Downlink Packet Access]; rated at 7.2Mbps) and one for boosting upload speeds (HSUPA [High-Speed Uplink Packet Access]; rated at 384Kbps). To date, only HSDPA is available in the market, and providers often restrict speeds to 1.4Mbps so as not to encourage bandwidth-clogging downloading that could choke out voice calls across their networks.

Next Up: 4G

When it comes to speed, more is always better, and what we have is never enough. Today’s high-speed 3G phone networks are merely one more bend in the path to 4G, leading to the goal of full-speed video downloading and even true video streaming. The plans are already off the drawing board and in production. The industry markets 4G as the final step. Whether or not that’s true we should know in just a few short years.

by David Finck