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824 WIRELESSCOMMUNICATIONSAPPLICATIONSUMTS (Universal Mobile
Telecommunications Systems)
UMTS (universal mobile telecommunications systems)
has been the planned European W-CDMA standard since- Its development was spearheaded by the UMTS fo-
rum, an industry and government group charged with
developing a successor to GSM. The UMTS Forum suc-
ceeded in developing a draft W-CDMA proposal that was
compatible with GSM, but it underestimated worldwide
demand for mobile communications. Before a full UMTS
standard could be tested and ratified, the proposal was
picked up by the Japanese. The first W-CDMA networks
are being deployed in Japan by NTT DoCoMo and J-Phone
(Kaaranen, 2001).
CDMA 2000
Of the 2G systems, only CdmaOne is already based on
CDMA. This gives it a head start in the race to 3G, as
operators are able to upgrade their existing networks
with new software of modulation rather than building a
new radio system. These upgrades are collectively known
as CDMA 2000; all are backward compatible with exist-
ing IS-95 systems. Until mid-2000, the upgrade path for
CdmaOne seemed clear. The end result was supposed to
be a system named CDMA 2000 3XMC. It combines three
channels, resulting in a wider band. Unfortunately, this
system was not compatible with the form of W-CDMA.
In 2000, Motorola and Nokia together launched a system
called 1Xtreme, which they claimed can reach speeds sim-
ilar to that of 3XMC, but using only one channel, and
hence a third of the spectrum.EDGE (Enhanced Data Rates
for GSM Evolution)
EDGE (enhanced data rates for GSM evolution) is a tech-
nology based on TDMA. It was a planned upgrade for the
GSM networks. The plan was that GSM operators would
deploy it in their existing networks, while building UMTS
to take advantage of the newly licensed IMT-2000 spec-
trum. Because UMTS can hand over calls to GSM, the
two would even be compatible.
EDGE inherits almost all its main features from GSM
and GPRS, including the eight-user TDMA structure and
even the slot length of 0.577 ms. The only difference is the
modulation scheme of 8-PSK, which triples the capacity
compared to GSM.
EDGE could be applied to a regular GSM system, giv-
ing every user a landline quality voice or data connection,
but it is such a major upgrade that every operator who
installs it will also use GPRS and HSCSD. Because 8-PSK
is more susceptible to errors than GSM, EDGE has nine
different Modulation and Coding Schemes, each designed
for a different quality connection.
To make EDGE deployment easier for a D-AMPS op-
erator, the UWCC (Universal Wireless Communications
Consortium) has defined a simplified stand called EDGE
Compact. This can be used only for data, not voice, and so
omits many of the control channels found in the full-scale
system, which in the context of EDGE compact is referred
to as EDGE Classic.Finally, Table 2 summarizes the evolution of wireless
systems.MOBILE DATA SERVICES
Messaging
Every digital, and even some analog, mobile phone sys-
tems already incorporate some form of messaging. This
allows subscribers to receive and sometimes send short
text messages. This is essentially the same as paging, but
with the data appearing on a mobile phone instead of a
separate page.
In theory, messaging service should allow people to
receive e-mail through their mobile phone and to dis-
pense with pagers altogether. However, in practice, nei-
ther of these objectives has been achieved. Mobile phone
operators are not geared up to deal with the type of ser-
vices offered by paging companies. Most of the messages
sent to a pager originate on the regular telephone net-
work. To page someone, the user calls an operator, who
transcribes the message and transmits it. Operators have
made more progress in interconnecting their own mes-
saging networks so that customers of one operator can
send messages to those of another.
A digital cellular phone uses three types of messaging
services:SMS (short message service)—Only messaging standard
to have achieved widespread acceptance. Began as part
of the original GSM specification, but has since spread
to all the other digital systems. Limited versions must
be standardized for the AMPS and NMT analog sys-
tems.
CBS (cell broadcast service)—If the same information
needs to be sent to many different users, broadcasting
is more efficient than transmitting a separate transmis-
sion. Each message is known as a page and can be only
93 bytes long. Up to 15 pages can be concatenated to-
gether. CBS has not been widely deployed because it
offers operators no way to charge for the services.
USSD (unstructured supplementary services data)—This
service uses the control channel and can operate while
a phone in use. The message is longer than that of
SMS, with a maximum of 182 bytes. One advantage of
USSD is it is connection-oriented. The network estab-
lishes a connection with the phone before sending any
data.The Wireless Web
Transferring the Web to cell phones presents several
changes, including variable latency and input device de-
sign. Two issues that have preoccupied the mobile indus-
try are low capacity and small screens. Most existing cell
phone systems allow data speed of only 13.3 Kbps. Even
more advanced technologies will push this up to 56 Kbps.
Because of the small screen, many cellphones can display
only a few lines of monochrome text, whereas a PDA has
larger displays, but it still has limits. It is not possible to
squeeze a desktop-sized screen into the palm of a user’s
hand.