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The Evolution of Cellular Data: On the Road to 3G
Published by Intel Corporation.
Peter Rysavy, Rysavy Research
Copyright 1999. All rights reserved.
Introduction
Wireless phone use is taking off around the world. Many
of us would no longer know how to cope without our cellphones. Always being
connected offers us flexibility in our lifestyles, makes us more productive
in our jobs, and makes us feel more secure. So far, voice has been the
primary wireless application. But with the Internet continuing to influence
an increasing proportion of our daily lives, and more of our work being
away from the office, it is inevitable that the demand for wireless data
is going to ignite. Already, in those countries that have cellular-data
services readily available, the number of cellular subscribers taking advantage
of data has reached significant proportions. We want wireless Internet,
we want our organizational data from anywhere, and we want it now.
But to move forward, the question is whether current
cellular-data services are sufficient, or whether the networks need to
deliver greater capabilities. The fact is that with proper application
configuration, use of middleware, and new wireless-optimized protocols,
today’s cellular-data can offer tremendous productivity enhancements. But
for those potential users who have stood on the sidelines, subsequent generations
of cellular data should overcome all of their objections. These new services
will roll out both as enhancements to existing second-generation cellular
networks, and an entirely new third generation of cellular technology.
Our job here is to describe this road to the third generation (3G), as
well as to show you how these services will allow new applications never
before possible.
The World Today
Before we peek into the future, let’s quickly look at
where we are today. In 1999, the primary cellular-based data services are
Cellular Digital Packet Data (CDPD), circuit-switched data services for
GSM networks, and circuit-switched data service for CDMA networks. Some
brave souls connect their PC Card modems to their analog cellphones, but
this approach is not very popular because it is tricky to configure. All
of these services offer speeds in the 9.6 Kbps to 14.4 Kbps range. Why
such low speeds? The basic reason is that in today’s cellular systems,
data is allocated to the same radio bandwidth as a voice call. Since voice
encoders (vocoders) in current cellular networks digitize voice in the
range of 8 to 13 Kbps, that’s about the amount available for data. Remember,
too, that today’s digital and PCS technology designs started over five
years ago. Back then, 9.6 Kbps was considered more than adequate. Today,
it can seem slow with graphical or multimedia content, though it is more
than adequate for text-based applications and carefully configured applications.
There are two basic ways that the cellular industry
is currently delivering data services. One approach is with smart phones,
which are cellular phones that include a microbrowser. With these, you
can view specially formatted Internet information. The other approach is
through wireless modems, supplied either in PC Card format or by using
a cellphone with a cable connection to a computer. See Figure 1.
Figure 1: Smart phone versus phone connected
to laptop
Both approaches can give you access to Internet sites
and corporate systems, including e-mail, databases, or host-based systems.
But both approaches also require that the user take throughput and latency
of the network into account. In contrast, next generation networks
promise throughput, global coverage, and ease-of-use that will greatly
expand your mobile computing options.
The World Tomorrow
Before diving into details of different network technologies,
we need to realize that from a user perspective, the offerings from all
of these networks will be largely comparable. Introduction dates of services
may vary by up to a year, and exact data rates may differ by 20 or 30%.
But just as voice users today may be hard-pressed to distinguish between
the quality of an IS-136 call using AT&T’s wireless network, a GSM
call using Omnipoint’s network, or a CDMA call using Sprint PCS network,
data users will notice great similarity between the new cellular-data services.
In thinking about the rollout of next generation
services, consider what features can be added to existing networks, and
what features will require vastly new network infrastructure. Since we
refer to the current generation of cellular as second generation, then
new feature advancements to the current network are sometimes called 2.5G.
Generally, 2.5G technologies have been developed for third generation (3G)
networks, but they are applied incrementally to existing networks. This
approach allows carriers to offer new high-speed data and increased voice
capacity at much lower cost than deploying all new 3G networks. Plus, they
can do so using their existing spectrum.
Let’s consider data rates in more detail. The global
standards body for communications is the International Telecommunications
Union (ITU). The 3G standards effort is called International Mobile Telephone
2000 (IMT-2000). IMT-2000 mandates data speeds of 144 Kbps at driving
speeds, 384 Kbps for outside stationary use or walking speeds, and 2 Mbps
indoors. Does this mean that we’ll all be using our cellphones at 2 Mbps?
No. The indoor rate will depend on careful frequency planning within buildings,
and possibly an organization’s commitment to work closely with a carrier.
However, since high-speed services such as wireless LANs already offer
speeds of up to 11Mbps, it’s difficult to predict the expected market demand
for 2Mbps indoor service when 3G networks roll out.
What is of much greater interest is the 384 Kbps
data rate for outdoor use, as this IP protocol-based packet service will
be available over wide areas. This service is the one that will let us
extend our office to any location. And the good news? The technology that
will provide 384 Kbps in 3G networks is the same technology that will be
deployed in 2.5G networks, albeit at slightly lower data rates in the 50
to 150 Kbps range. But this is still some ten times faster than most options
today. More good news? 2.5G services will be released in the year 2000,
well in advance of 3G networks that won’t start rolling out until 2002
at the earliest. See Table One.
Core Technology
|
Service
|
Data Capability
|
Expected Deployment
|
| GSM |
Circuit-switched
data based on the standard GSM 07.07 |
9.6 Kbps or
14.4 Kbps |
Available worldwide
now |
| |
High-speed
circuit-switched data (HSCSD) |
28.8 to 56
Kbps service likely |
Limited deployment
1999 and 2000 as many carriers will wait for GPRS |
| |
General Packet
Radio Service (GPRS) |
IP and X.25
communications over Kbps |
Trial deployments
in 2000, rollout of service 2001 |
| |
Enhanced Data
Rates for GSM Evolution (EDGE) |
IP communications
to 384 Kbps. Roaming with IS-136 networks possible. |
Trial deployment
in 2001, rollout of service 2002 |
| |
Wideband CDMA
(WCDMA) |
Similar to
EDGE but adds 2Mbps indoor capability. Increased capacity for voice. |
Initial deployment
in 2002 or 2003 |
| IS-136 |
Circuit-switched
data based on the standard IS-135 |
9.6 Kbps |
Some carriers
may offer service, but not expected on widespread basis because key carriers
already offer Cellular Digital Packet Data (CDPD) |
| |
EDGE |
IP communications
to 384 Kbps. Roaming with GSM networks possible. |
Initial deployment
2002 or 2003 |
| |
WCDMA or Wideband
TDMA (WTDMA) |
Similar to
EDGE but adds 2Mbps indoor capability |
No stated deployment
plans |
| CDMA |
Circuit-switched
data based on the standard IS-707 |
9.6 Kbps or
14.4 Kbps |
Available by
some carriers now |
| |
IS-95B |
IP communications
to 64 Kbps |
Expected in
Japanese markets by early 2000 |
| |
CDMA2000 -
1XRTT |
IP communications
to 144 Kbps |
Trial deployment
in 2001, rollout of service 2002 |
| |
CDMA2000 -
3XRTT |
IP communications
to 384 Kbps outdoors and 2 Mbps indoors |
Initial deployment
in 2002 or 2003. |
Table One: Summary of forthcoming cellular-data services.
Time estimates by Rysavy Research.
How the three major cellular technologies will provide
these services varies, but all have a similar roadmap. In fact, as we detail
in subsequent sections, these technologies are slowly converging, beginning
with a convergence of IS-136 and GSM data services, and followed by a harmonization
of the 3G versions of GSM and CDMA. By harmonization, we mean that while
differences will continue to exist, the systems will interoperate more
readily.
There are some other important trends to note. The
first is that standards bodies are working not just on radio technologies,
but also on the networking infrastructure. One objective is to allow users
to seamlessly roam from private networks (e.g. Ethernet, WLAN) to public
networks. Such roaming will require the implementation of standards such
as Mobile IP. Another goal is to simplify the connection between mobile
computers and wireless devices through personal-area network (PAN) technologies
such as Bluetooth. Yet another trend is voice over IP. As terrestrial networks
start using IP for voice and multimedia, it will be important for such
IP communications to extend all the way to the wireless device.
Perhaps the most important trend of all is for ubiquitous
coverage. This will be achieved not just by converging wireless standards,
but also by sophisticated new devices that operate in multiple modes and
at multiple frequencies. This is the world of tomorrow. To understand how
we’ll get there, we will look first at GSM and IS-136 networks, and then
CDMA networks.
Networks in Detail
GSM and IS-136
GSM dominates the world today, with over 200 million
users in over a hundred countries. As the most mature digital-cellular
standard, GSM networks offered circuit-switched data services well in advance
of other networks. Now in trials is a service called high-speed circuit-switched
data service (HSCSD), which combines two to four of the time slots (out
of a total of 8 in each frame) to provide service from 28.8 Kbps to 56
Kbps. HSCSD is attractive to carriers because it requires minimal new infrastructure.
Nevertheless, most GSM carriers are putting their bets on a service called
General Packet Radio Service (GPRS), a 2.5G technology. GPRS can combine
up to 8 (out of 8 available) time slots in each time interval for IP-based
packet data speeds up to a maximum theoretical rate of 160 Kbps.
However, a typical GPRS device may not use all 8 time slots. One proposed
configuration is four time slots (80 Kbps maximum, 56 Kbps typical) for
the downlink and one timeslot (20 Kbps maximum, 14.4 Kbps typical) for
the uplink. GPRS supports both IP and X.25 networking. Entering field trials
in 2000, GPRS service should start rolling out in 2001.
GPRS can be added to GSM infrastructures quite readily.
It takes advantage of existing 200 kHz radio channels and does not require
new radio spectrum. The principal new infrastructure elements are called
the Gateway GPRS Support Node (GGSN) and the Serving GPRS Support Node
(SGSN). The GGSN provides the interconnection to other networks such as
the Internet or private networks, while the SGSN tracks the location of
mobile devices and routes packet traffic to them. GPRS capability will
be added to cellphones, and will also be made available in data-only devices
such as PC Card modems. Pricing will either be flat rate or based on the
volume of information communicated. Services such as GPRS are exciting
not only because of their higher data rates, but also because packet service
allows constant "virtual" connections without the need to constantly "dial"
into the network. Click
here for a white paper that discusses GPRS in detail.
The phase after GPRS is called Enhanced Data Rates
for GSM Evolution (EDGE). EDGE, generally considered a 3G technology, introduces
new methods at the physical layer, including a new form of modulation (8
PSK) and different ways of encoding data to protect against errors. Meanwhile,
higher layer protocols, such as those used by the GGSN and SGSN, stay the
same. The result is that EDGE will deliver data rates up to 500 Kbps using
the same GPRS infrastructure. Keep in mind though that 500 Kbps represents
a best case scenario, with a strong signal, no interference, and a user
device accessing the entire 200 kHz radio channel. In addition, this radio
channel must also be shared by multiple users in that sector of the cell
site. Consequently, practical throughputs may be only half the maximum
rate. EDGE data services could start rolling out in 2002, depending on
market demand and actual carrier deployments.
Though developed initially for GSM, the Universal
Wireless Communications Consortium (UWCC), an organization that represents
IS-136 carriers and vendors worldwide, has decided to embrace EDGE for
IS-136 networks. The tricky part of adopting EDGE is that IS-136 networks
use 30 kHz radio channels. Deploying EDGE will require new radios in base
stations to support the 200 kHz data channels. The GGSN and SGSN will be
virtually the same for both GSM and IS-136 networks. EDGE data users
will eventually be able to roam between IS-136 and GSM networks around
the world. EDGE data services for IS-136 networks will probably roll out
shortly after EDGE for GSM networks, possibly in 2002 or 2003. Figure 2
shows the common network technology used by both GSM and IS-136 networks.
Figure 2: The same EDGE wireless device
will be able to communicate
across both IS-136 and GSM networks.
IS-136 networks will also converge with GSM for voice
related functions. For instance, the same vocoder technology will eventually
be used by both networks. Meanwhile, in advance of common vocoders, multi-mode
cellphones are planned that will allow voice operation across IS-136, GSM,
and AMPS networks worldwide.
The 3G version of GSM, Wideband CDMA or WCDMA, is
based on CDMA technology. This version of CDMA deviates from American standards,
although it uses the same spread spectrum principles. For data, WCDMA
adds the capability for 2Mbps data rates indoors. The airlink, using either
5MHz, 10MHz, or 20MHz radio channels, will be completely different from
GSM’s current 200 kHz channels. However, the data networking for WCDMA
will likely be based on EDGE/GPRS infrastructure protocols, such as the
GPRS Tunneling Protocol. The earliest WCDMA deployment is expected in Japan
in 2002. IS-136 carriers might eventually use WCDMA technology, though
a wideband TDMA (WTDMA) approach has also been proposed.
CDMA
CDMA network deployment and subscriber growth have developed
considerable momentum, and data services are now available from a number
of carriers. Currently, these carriers use circuit-switched technology
operating at 14.4 Kbps. As with GSM, CDMA requires a handset that specifically
supports data. Connect the phone to a laptop, and the phone operates just
like a modem, enabling you to establish dial-up connections to the Internet,
your corporate remote access server (RAS), and so on. WAP-based microbrowser
applications are also being made available. Another service for CDMA networks
is called QuickNet Connect. By eliminating conventional modem connections,
this service allows fast connections (of approximately five seconds) to
the Internet. See Figure 3. To the user, the carrier appears like an ISP
offering dial-up Internet service.
Figure 3: QuickNet Connect for CDMA
Today’s CDMA service is based on the IS-95A standard.
A refinement of this standard, IS-95B, allows up to eight channels to be
combined for packet-data rates as high as 64 Kbps. Japanese CDMA carriers,
IDO and DDI, are planning on deploying this higher-speed service by early
2000.
Beyond IS-95B, CDMA evolves into 3G technology in
a standard called CDMA2000. CDMA2000 comes in two phases. The first, with
a specification already completed, is 1XRTT, while the next phase is 3XRTT.
The 1X and 3X refer to the number of 1.25 MHz wide radio carrier channels
used, and RTT refers to radio-transmission technology. CDMA2000 includes
numerous improvements over IS-95A, including more sophisticated power control,
new modulation on the reverse channels, and improved data encoding methods.
The result is significantly higher capacity for the same amount of spectrum,
and indoor data rates up to 2Mbps that meet the IMT-2000 requirements.
The full-blown 3XRTT implementation of CDMA requires a 5MHz spectrum commitment
for both forward and reverse links. However, 1XRTT can be used in existing
CDMA channels since it uses the same 1.25 MHz bandwidth.
1XRTT technology is thus a convenient stepping stone
for CDMA carriers moving to 3G, and it can also be thought of as a 2.5G
technology. 1XRTT can be deployed in existing spectrum to double voice
capacity, and requires only a modest investment in infrastructure. It will
provide IP-based packet-data rates of up to 144 Kbps. Initial deployment
of 1XRTT is expected by US CDMA carriers in 2001, with 3XRTT following
a year or two behind, depending on whether new spectrum becomes available.
But what about the differences between CDMA2000 and
WCDMA? If the goal of IMT-2000 is a single worldwide standard, can these
two versions of CDMA be harmonized into a single standard? That is the
very question being addressed by the CDMA Operators Harmonization Group
that is developing the Global 3G CDMA standard (G3G). Since there are some
irreconcilable differences between CDMA2000 and WCDMA in the radio portion,
the approach is a modular architecture as shown in Figure 4. This approach
allows any of three airlink technologies to be used in a network, including
WCDMA, 3XRTT, and a time-division duplex form of spread spectrum. In addition
to the three types of airlinks, the architecture recognizes that network
infrastructures may be based on either GSM-MAP protocols or ANSI-41 protocols.
G3G will give operators flexibility in choosing the airlink and network
infrastructure that best addresses their particular needs.
Figure 4: Modular approach used in the
Global 3G CDMA architecture
One issue in harmonizing CDMA data is that WCDMA
is based on GPRS protocols, which use the GPRS tunneling protocol (GTP)
to forward IP packets to the mobile station. Mobility management is also
handled by specific GPRS protocols. CDMA2000, however, is based on the
Mobile IP standard. Any harmonized CDMA standard should ideally be based
on the same set of tunneling and mobility standards. For this reason,
the European Telecommunications Standards Institute (ETSI), responsible
for GSM and GPRS, has started an investigation of how GPRS/EDGE could integrate
Mobile IP.
3G In Context
3G cellular technology is a huge technological and market
phenomenon, but it needs to be understood in the context of other developments.
One development is that there will be other high-speed wireless-data solutions
available. For instance, don’t overlook Metricom’s Ricochet network. Though
service is restricted to just several cities today, significant new investment
from Paul Allen and MCI WorldCom, combined with a new high-speed service
at 128 Kbps, will propel this service to much wider availability in 2000.
Consider also the Personal Handyphone System (PHS)
deployed widely in Asia, a form of cellular technology limited to pedestrian
use. PHS will soon offer 64 Kbps data service. Nextel has also recently
unveiled a new data service for its Integrated Dispatch Enhanced Network
(iDEN) – based technology. This service uses Mobile IP to provide both
WAP service and IP-based packet data at about 20 Kbps. Also, some companies
are planning on deploying wireless LAN technology in public places such
as airports. Will all of these developments stifle the demand for cellular-based
data? Probably not, but they will offer options, increase competition,
and help drive down prices.
Finally, some market developments will both shape
the nature of wireless-data networks, and increase the demand for such
services. These include the following:
-
The control network used in telephone
networks today is called Signaling System 7 (SS7). This system will evolve
into an IP-based system, increasing the importance for IP-based control
mechanisms in wireless networks.
-
IP will increasingly be used for voice
communications, so delivery of IP-based voice to cellphones will be critical.
This will require the resolution of difficult, quality-of-service issues
in wireless networks.
-
As E-commerce becomes common, users will
want to safely conduct transactions from their mobile terminals. Such use
will make robust security protocols a must for wireless networks.
-
Mobile users will want to access private
information from anywhere, driving the demand for secure communications
and related technologies such as virtual private networks (VPNs).
-
As a huge population of mobile-data users
emerges, content developers will start producing material specifically
for these users, including items related to travel, entertainment, news,
weather, and recreation. Though such developments are already underway,
they are still in their infancy.
There is no question that a myriad of new applications
will be possible with next-generation, wireless-data networks. But keep
in mind that these are massively complex networks, and it will take both
time and large investments to develop and deploy the technology. Many of
the advantages that these networks will offer are already available using
existing data services. Organizations that gain experience with wireless
technologies today will be the ones best positioned to take advantage of
new networks tomorrow.
Peter Rysavy is president of Rysavy Research, a consulting firm
that helps companies research, develop, and deploy communications technologies.
Rysavy Research home
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