North America goes digital: IS-54
In 1990 North American carriers faced the question -- how do we increase capacity? -- do we pick an analog or digital method? The answer was digital. In March, 1990 the North American cellular network incorporated the IS-54B standard, the first North American dual mode digital cellular standard. This standard won over Motorola's Narrowband AMPS or NAMPS, an analog scheme that increased capacity by cutting down voice channels from 30KHz to 10KHz. IS-54 on the other hand increased capacity by digital means: sampling, digitizing, and then multiplexing conversations, a technique called TDMA or time division multiple access. This method separates calls by time, placing parts of individual conversations on the same frequency, one after the next. It tripled call capacity .
Using IS-54, a cellular carrier could convert any of its systems' analog voice channels to digital. A dual mode phone uses digital channels where available and defaults to regular AMPS where they are not. IS-54 was, in fact, backward compatible with analog cellular and indeed happily co-exists on the same radio channels as AMPS. No analog customers were left behind; they simply couldn't access IS-54's new features. CANTEL got IS-54 going in Canada in 1992. IS-54 also supported authentication, a help in preventing fraud. IS-54, now rolled into IS-136, accounts for perhaps half of the cellular radio accounts in this country.
I should point out that no radio service can be judged on whether it is all digital or not. Other factors such as poorer voice quality must be considered. In America GSM systems usually operate at a higher frequency than it does in most of Europe. As we will see later, nearly twice as many base stations are required as on the continent, leaving gaps and holes in coverage that do not exist with lower frequency, conventional cellular. And data transfer remains no higher than 9.6 kbs, a fifth the speed of an ordinary landline modem. Tremendous potential exists but until networks are built out and other problems solved, that potential remains unfulfilled.
Meanwhile, back on the continent, commercial GSM networks started operating in mid-1991 in European countries. GSM developed later than conventional cellular and in many respects was better designed. Its North American counterpart is sometimes called PCS 1900, operating in a higher frequency band than the original European GSM. But be careful with marketing terms: in America a PCS service might use GSM or it might not. All GSM systems are TDMA based, but other PCS systems use what's known as IS-95, a CDMA based technology. Sometimes GSM at 1900Mhz is called PCS 1900, sometimes it is not. Arrgh.
Advanced Mobile Phone Service contended well with GSM and PCS at first, but it has since declined in market share. While it was still vibrant, David Crowe put it like this:
"The best known AMPS systems are in the US and Canada, but AMPS is also a de facto standard throughout Mexico, Central and South America, very common in the Pacific Rim and also found in Africa and the remains of the USSR. In summary, AMPS is on every continent except Europe and Antarctica. . . due to the high capacity allowed by the cellular concept, the lower power which enabled portable operation and its robust design, AMPS has been a stunning success. Today, more than half the cellular phones in the world operate according to AMPS standards . . . From its humble beginnings, AMPS has grown from its roots as an 800MHz analog standard, to accommodate TDMA and CDMA digital technology, narrowband (FDMA) analog operation (NAMPS), in-building and residential modifications."
"Most recently, operation in the 1800 Mhz (1.8-2.2 GHz) PCS frequency band has been added to standards for CDMA and TDMA. All of these additions have been done while maintaining an AMPS compatibility mode (known as BOA: Boring Old AMPS). It might be boring, but it works, and the AMPS compatibility makes advanced digital phones work everywhere, even if all their features are not available in analog mode." Cellular Networking Perspectives (external link)
This excellent cellular handheld telephone timeline is of NTT models.
