The next step to higher data rates for each technology was
dubbed 2.5G and was to be closely followed by 3G. (The “G”
of course stands for “generation.”) 3G is not just a standard for
higher data rates: It is also meant to bring global standardization
to cellular. Our choice of words here is very deliberate:
“closely followed” has been defined by some as within two
years of 2.5G, whereas others say that the two standards are
practically on top of one another. The simple fact is that it
costs a lot of time and money to upgrade a cellular system and
it may make more business sense to skip interim steps. Just as
IS-54 was quickly replaced by IS-136, carriers may find 2.5G
unpalatable financially. In other words, they may skip 2.5G and
go directly to 3G. That makes sense but what happens when
industry skips an interim solution or worse yet, adds another?
Do we add a 2.75G?
The truth is that in the interests of harmonizing all of the
different proposals for 3G, the cellular industry has skipped
some steps or in some cases, changed direction altogether. Like Qualcomm, NTT DoCoMo, the Japanese telecommunications
giant, has proposed a new standard altogether, Wideband Code
Division Multiple Access (WCDMA). Three years ago, the
roadmaps for GSM, CDMA, and TDMA were clear. GSM
would become GSM Phase 2+ with improvements and the
addition of High-speed Circuit Switch Data (HSCSD) and
rates up to 144 Kbps. Later, it would migrate to Enhanced
Data Rate for Global Evolution (EDGE). GPRS would be
added along with a more robust modulation scheme; rates of
384 Kbps would offer wireless multimedia IP-based services
and applications. At that time there would be an “alignment”
with TDMA; each would have an EDGE physical layer. Figure
1-9 shows the most recent roadmap for 3G.
Meanwhile, TDMA would become IS-136 Plus with the
addition of HSCSD. It would then migrate to IS-136HS
(EDGE) just like its cousin, GSM. (Not all EDGE is created
equal: The European version of EDGE and the North
American version share a common standard but different frequencies.
A “world” phone would have to cover more bands in
order to roam.) The roadmap for GSM and TDMA primarily
increases data capabilities, not voice. It is expected that voice
transmission would migrate to Voice-over-IP in the future.
Until that happens, EDGE is split into two component networks,
one for voice and one for data.
The CDMA side was also quite clear three years ago. IS-
95A would become IS-95B with HSCSD up to 64 Kbps. Later
IS-95C and IS-95D (sometimes referred to as IS-2000 Phase I
and II) would increase data rates to about 307 Kbps. IS-95C
was also referred to as 1xRTT, and IS-95D referred to as
3xRTT. Just to confuse things a little, another standard was
created to overlay the other two. High Data Rate (HDR) could
go as high as 2.4 Mbps. (The latest acronym for 1xRTT combined
with HDR is 1xEV.)
Well, today most of this has changed. NTT DoCoMo proposed
a new Wideband CDMA. When the technical and political
ramifications were viewed, deals were made between
proponents of each standard. GSM Phase II+ survived but IS-
136 Plus didn’t. For CDMA, 1xRTT survived but IS-95B didn’t
and 3xRTT will most likely be delayed as long as HDR meets
users’ needs. As for WCDMA, it will become a component
overlaying GSM networks, transforming those networks into
Universal Mobile Telephone Service (UMTS).
The last three years have been very confusing to those following
the standards process. The only things that remain clear
are that CDMA will launch 1xRTT with an HDR overlay to
support date rates from 144 Kbps to over 2 Mbps. Both data
and voice capacity will benefit from 1xRTT.
Europe will launch EDGE with WCDMA overlaid. Data
rates will run from 384 Kbps to over 2.5 Mbps. Both data and
voice capacity will be improved. In the United States, the IS-
136 component of EDGE may be eliminated in favor of the
European version of EDGE and WCDMA. AT&T Wireless has
announced a decision to do exactly that: overlay the old IS-136
network with a GSM/EDGE/WCDMA version.
In the United States, a fourth cellular technology is
deployed by Nextel. It uses a proprietary technology developed
by Motorola called iDEN. The Nextel system works as a hybrid
design between cellular and dispatch technologies. Calls may
be connected like cellular, or members of a group can be connected
together in a way similar to two-way radio, without dialing.
For roaming outside the United States, Nextel offers a dual
mode—iDEN and GSM—phone. For data applications, the
Nextel phones include a Java 2 Micro-edition (J2ME) environment
and transmit data on a packet network.
Regardless of the details of who implements what, three
important things should be remembered:
• High speed packet data will replace circuit-switched data.
• Internet Protocol (IP) will become the standard protocol for
all wireless traffic, voice, and data.
• A quasi-global standard will make international roaming easier.
These three changes to mobile communications will open
the door to the next generation of wireless applications.