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cell that has the strongest signal, usually without interrupting the
call. However, in some areas (usually remote and sparsely popu-
lated) where there is no signal the phone shows the dreaded “no
service” message.
The Growth of Cellular Networks
The switch from analog (first generation or 1G) cellular systems to
digital (second generation or 2G) in the 1990s allowed systems
to accommodate the growing number of users, as well as allow-
ing more data to be transmitted. This is because digital signals,
like other digital data, can be manipulated by computers. In one
system, called TDMA, each piece of data is compressed so it only
takes a third as much time to transmit—meaning a frequency can
handle three times as many calls.
Another widely used approach, called
CDMA, “stamps” each piece of signal
with a unique sequence code and sends
it over the next available frequency. At the
receiving phone the relevant pieces are
identified and stitched back together. All
this happens so fast one normally does
not hear a delay.
The method used in CDMA, called spread spectrum, is rather
like the way the Internet works. On the Internet data is broken up
into identifiable “packets” that are sent over an appropriate con-
nection and then reassembled at the destination computer. Indeed,
at the very time when cell phone service was being designed and
implemented, the Internet was also coming of age. With the devel-
opment of the smartphone, the two technologies would be married
into a device that could take full advantage of both.
It All Comes Together
Cell phones grew rapidly in popularity as the 1990s drew to an end.
The adoption of mobile phones was accelerated by a new business
model. Just as in the early twentieth century Kodak made its cam-
eras popular by selling the devices cheaply and making money on
packets
“Chunks” of data on the
Internet or similar networks.
They can be sent to speci c
addresses and reassembled
into complete les.
