The first generation (1G) of cell phones appeared in the mid-1980s. Known as
the Advanced Mobile Phone System (AMPS) in the U.S., these phones used FM in
30-kHz bands and a frequency-division-duplexing scheme in the 800- to 900-MHz
range. The system worked well, but subscriber demand overwhelmed the capacity
of the spectrum and technology.
To get the kind of growth they wanted, carriers went digital, developing several
second-generation (2G) systems. In the U.S., the IS-54/IS-136 time-division
multiple-access (TDMA) standard managed three calls per 30-kHz channel using
heavy voice compression. Europe developed the Global System for Mobile (GSM)
access, which managed eight calls per 270-kHz channel using a TDMA scheme as
well.
Meanwhile, Qualcomm developed the IS-95 standard. It employed a sophisticated
code-division multiple-access (CDMA) approach also known as spread-spectrum.
With direct-sequence spread-spectrum (DSSS), the system could accommodate up
to 64 subscribers per 1/25-MHz channel.
Carriers eventually phased out the IS-136
standard in favor of GSM and its greater subscriber capacity. At the same time, Motorola
and Nextel developed another TDMA 2G
method known as iDEN.
Once 2G phones achieved digital capability, data capability was the next step. Subscribers wanted e-mail and Internet access,
prompting improvements. Developed for
GSM phones, the General Packet Radio Service (GPRS) provided packet data capability
up to about 115 kbits/s; typical throughput
ranged from 40 to 70 kbits/s.
The Enhanced Data Rate for GSM Evolution (EDGE) further enhanced GSM phones.
It used 8PSK (phase-shift keying) to provide more bits per symbol and data rates
up to 384 kbits/s. (The average ranged from 100 to 200 kbits/s.) Sometimes,
GPRS is called a 2.5G technology, while EDGE is called a 2.5G or 2.75G technology.
Generally known as cdmaOne, the IS95A/B CDMA standards were upgraded with
packet data capability. They eventually morphed into cdma2000, Qualcomm's 2.5G
technology. Also known as 1xRTT (Radio
Transmission Technology) and EV-DO (Evolution-Data Optimized), it boosted data rates
to a maximum of 144 kbits/s with 30 to 70
kbits/s typical.
Today, the two main cell-phone technologies in use are GSM/GPRS/EDGE and
cdma2000. AT&T and T-Mobile use GSM,
while Verizon and Sprint Nextel employ
cdma2000. Sprint Nextel still supports the
iDEN system.
