and wireless networks. Figure 1 shows
Issues in three possible architectures: using a mul-
timode device, an overlay network, or a
common access protocol.
Emerging 4G Multimode devices
One conﬁguration uses a single physical
terminal with multiple interfaces to access
services on different wireless networks.
Wireless Networks Early examples of this architecture include
the existing Advanced Mobile Phone
System/Code Division Multiple Access
dual-function cell phone, Iridium’s dual-
Upkar Varshney and Radhika Jain, Georgia State University function satellite-cell phone, and the
emerging Global System for Mobile
Cordless Terminal dual-mode cordless
eployment of International Mo- ure or loss of one or more networks. 4G phone.
bile Telephony 2000 standards networks will also feature IP interoper- The multimode device architecture
for third-generation wireless ability for seamless mobile Internet access may improve call completion and expand
networks may begin this year, and bit rates of 50 Mbps or more. effective coverage area. It should also
with NTT DoCoMo planning Because deployment of 4G wireless provide reliable wireless coverage in case
to have a nationwide 3G network in technology is not expected until 2006 or of network, link, or switch failure. The
Japan this year. These speciﬁcations give even later, developers will hopefully have user, device, or network can initiate
existing 1G and 2G operators the ﬂexi- time to resolve issues involving multiple handoff between networks. The device
bility to evolve their networks, which heterogeneous networks such as itself incorporates most of the additional
support low-bit-rate data and are pri-
marily designed for voice, into 3G sys-
tems. They also help satellite and terres-
trial providers design new 3G systems.
4G wireless networks
Third-generation networks offer mul- support global roaming
timedia transmission, global roaming
across a cellular or other single type of across multiple wireless
wireless network, and bit rates ranging
and mobile networks.
from 384 Kbps to several Mbps. Analysts
expect worldwide migration to 3G to
continue through 2005, depending on
market needs, carrier and operator incen- • access, complexity without requiring wireless
tives, recovery on investments in existing • handoff, network modification or employing
1G and 2G wireless systems, and per- • location coordination, interworking devices. Each network can
ceived threats to monopolistic wireless • resource coordination to add new deploy a database that keeps track of
carriers in many countries. users, user location, device capabilities, net-
• support for multicasting, work conditions, and user preferences.
4G WIRELESS NETWORKS • support for quality of service, The handling of quality-of-service (QoS)
Meanwhile, researchers and vendors • wireless security and authentication, issues remains an open research question.
are expressing a growing interest in 4G • network failure and backup, and
wireless networks that support global • pricing and billing. Overlay network
roaming across multiple wireless and In this architecture, a user accesses an
mobile networks—for example, from a Network architectures will play a key role overlay network consisting of several
cellular network to a satellite-based net- in implementing the features required to universal access points. These UAPs in
work to a high-bandwidth wireless LAN. address these issues. turn select a wireless network based on
With this feature, users will have access availability, QoS speciﬁcations, and user-
to different services, increased coverage, POSSIBLE ARCHITECTURES deﬁned choices. A UAP performs proto-
the convenience of a single device, one bill One of the most challenging problems col and frequency translation, content
with reduced total access cost, and more facing deployment of 4G technology is adaptation, and QoS negotiation-rene-
reliable wireless access even with the fail- how to access several different mobile gotiation on behalf of users. The overlay
network, rather than the user or device,
performs handoffs as the user moves
from one UAP to another. A UAP stores Fixed wireless network Satellite network
user, network, and device information,
capabilities, and preferences. Because
UAPs can keep track of the various
resources a caller uses, this architecture
supports single billing and subscription.
Common access protocol
This protocol becomes viable if wireless
networks can support one or two standard
access protocols. One possible solution,
which will require interworking between
Wireless LAN Cellular network
different networks, uses wireless asyn-
chronous transfer mode. To implement
wireless ATM, every wireless network (a)
must allow transmission of ATM cells with
additional headers or wireless ATM cells
requiring changes in the wireless networks. Fixed wireless network Satellite network
One or more types of satellite-based net-
works might use one protocol while one
or more terrestrial wireless networks use
QUALITY OF SERVICE
Supporting QoS in 4G networks will
be a major challenge due to varying bit
rates, channel characteristics, bandwidth
allocation, fault-tolerance levels, and
handoff support among heterogeneous Wireless LAN Cellular network
wireless networks. QoS support can
occur at the packet, transaction, circuit, (b)
user, and network levels.
• Packet-level QoS applies to jitter, Fixed wireless network Satellite network
throughput, and error rate. Net-
work resources such as buffer space
and access protocol are likely inﬂu-
Figure 1. Possible 4G wireless network archi-
tectures. (a) A multimode device lets the user,
device, or network initiate handoff between
networks without the need for network modiﬁ-
cation or interworking devices. (b) An overlay Wireless LAN Cellular network
network—consisting of several universal
access points (UAPs) that store user, net- (c)
work, and device information—performs a Database
handoff as the user moves from one UAP to Interface
another. (c) A device capable of automatically Location management
switching between networks is possible if
Universal access point
wireless networks can support a common
protocol to access a satellite-based network
and another protocol for terrestrial networks.
June 2001 95
How to Reach
We welcome submissions. For • Transaction-level QoS describes both networks instead of relying on each net-
detailed information, write for a the time it takes to complete a trans- work’s QoS scheme requires study.
Contributors’ Guide (computer@ action and the packet loss rate.
computer.org) or visit our Web site: Certain transactions may be time- Handoff delay
http://computer.org/computer/. sensitive, while others cannot toler- Handoff delay poses another impor-
ate any packet loss. tant QoS-related issue in 4G wireless
News Ideas • Circuit-level QoS includes call block- networks. Although likely to be smaller
Contact Lee Garber at lgarber@ ing for new as well as existing calls. in intranetwork handoffs, the delay can
computer.org with ideas for news It depends primarily on a network’s be problematic in internetwork hand-
features or news briefs. ability to establish and maintain the offs because of authentication proce-
end-to-end circuit. Call routing and dures that require message exchange,
Products and Books location management are two impor- multiple-database accesses, and negoti-
Send product announcements to tant circuit-level attributes. ation-renegotiation due to a signiﬁcant
email@example.com. Contact • User-level QoS depends on user difference between needed and available
Stephanie Kawada at skawada@ mobility and application type. The QoS.
computer.org with book announce- new location may not support the During the handoff process, the user
ments. minimum QoS needed, even with may experience a signiﬁcant drop in QoS
adaptive applications. that will affect the performance of both
Letters to the Editor upper-layer protocols and applications.
Please provide an e-mail address or Deploying a priority-based algorithm
daytime phone number with your Deploying a global QoS and using location-aware adaptive appli-
letter. Send letters to Letters, cations can reduce both handoff delay
Computer, 10662 Los Vaqueros
scheme may support the
and QoS variability.
Cir., PO Box 3014, Los Alamitos, diverse requirements of
When there is a potential for consid-
CA 90720-1314; fax +1 714 821 users with different erable variation between senders’ and
4010; firstname.lastname@example.org. mobility patterns. receivers’ device capabilities, deploying
a receiver-speciﬁc ﬁlter in part of the net-
On the Web work close to the source can effectively
Visit http://computer.org for infor- In a complete wireless solution, the reduce the amount of traffic and pro-
mation about joining and getting end-to-end communication between two cessing, perhaps satisfying other users’
involved with the Society and users will likely involve multiple wireless QoS needs.
networks. Because QoS will vary across
different networks, the QoS for such lthough 4G wireless technology
Magazine Change of Address
Send change-of-address requests
for magazine subscriptions to
users will likely be the minimum level
these networks support. A offers higher bit rates and the abil-
ity to roam across multiple hetero-
geneous wireless networks, several issues
End-to-End QoS require further research and development.
sure to specify Computer.
Developers need to do much more It is not clear if existing 1G and 2G
work to address end-to-end QoS. They providers would upgrade to 3G or wait
Missing or Damaged Copies may need to modify many existing QoS for it to evolve into 4G, completely
If you are missing an issue or schemes, including admission control, bypassing 3G. The answer probably lies
received a damaged copy, contact dynamic resource reservation, and QoS in the perceived demand for 3G and the
email@example.com. renegotiation to support 4G users’ diverse ongoing improvement in 2G networks to
QoS requirements. The overhead of im- meet user demands until 4G arrives. ✸
Reprint Permission plementing these QoS schemes at differ-
To obtain permission to reprint ent levels requires careful evaluation.
an article, contact William Hagen, A wireless network could make its cur- Upkar Varshney is on the faculty of the
IEEE Copyrights and Trademarks rent QoS information available to all Department of Computer Information
Manager, at firstname.lastname@example.org. other wireless networks in either a dis- Systems at Georgia State University.
To buy a reprint, send a query to
tributed or centralized fashion so they can Contact him at email@example.com.
firstname.lastname@example.org or a fax
to +1 714 821 4010. effectively use the available network
resources. Additionally, deploying a
global QoS scheme may support the Radhika Jain is a doctoral student in the
diverse requirements of users with differ- Department of Computer Information
Innovative technology for computer professionals ent mobility patterns. The effect of imple- Systems at Georgia State University.
menting a single QoS scheme across the Contact her at email@example.com.