Wireless Future - Telenor

Olaf Røstbakken (32) received
his PhD from Bristol University.
At the time of writing this article
he was a member of the Personal
Communications group
at Telenor R&D, Kjeller. Røstbakken
is currently working for
Inmarsat Ltd., London, and has
previously been employed as an
RF development engineer at
NEC Technologies (UK). His
research interests include antennas,
propagation, MAC protocols
and general radio access issues.
Olaf_Rostbakken@inmarsat.com
Telektronikk 1.2001
HiperLAN/2 – Overview and Evaluation
of its MAC Protocol
OLAF RØSTBAKKEN
1 Introduction
The development in data and telecommunication
during the last decades has by any standard been
formidable, but it is only recently with the introduction
of multimedia communication that these
two “worlds” have started to “merge”. This has
also been the case in wireless communication,
where the mobile systems have traditionally
been concerned with voice communication and
wireless network systems have mainly been used
for non-real time data communication. However,
this divide is soon to become less distinct with
the introduction of UMTS, which has been particularly
designed to handle multimedia applications/services.
This trend is shown in Figure 1.
UMTS – or more correctly UTRAN, as the
access network in UMTS is called – will initially
be designed to offer up to 2 Mbit/s indoors,
384 kbit/s outdoors (urban/suburban) and
144 kbit/s in rural environments. It is expected
that the increase in data rates together with
improved terminal display capabilities will pave
the way for a stream of bandwidth hungry services/
applications like video conferencing,
video clips, gaming, etc. The users will expect
high quality of service, which in turn is related
to delay, data rate and bit error rate requirements.
As the demand increases more pressure
will be put on the access network to transport the
data to the user in an efficient manner (the frequency
spectrum is a scarce resource and the air
link operates in a harsh environment). The challenge
is that it is difficult to implement an access
technology that is efficient in all environments
and for all services. Part of the answer to this
challenge is software flexible radios, but unfor-
Mobile
Systems
Wireless
Network
NMT
Speech
GSM
Speech
Limited data
802.11
Data,
Internett
tunately this technology is still immature and it
will be some time before full-fledged software
radio technology is common. In the meantime a
possible solution may be to use several access
technologies that are individually optimised (or
as much as possible!) for the environment where
they are deployed. For instance, with the introduction
of bandwidth hungry applications (like
video conferencing, browsing, etc.) hotspots (i.e.
areas with large capacity requirements) are
likely to appear in places like city centres, conference
centres, airports, hotels, etc. It will be
unreasonable for UTRAN alone to cover the
whole communication need in these hotspots,
and it will be desirable/beneficial to deploy
alternative access technologies that are specifically
designed to provide short-range wireless
communication. For this purpose Wireless LANs
(WLANs) are suitable, as they are designed to
transport relatively high bit rates over a short
distance. Most of today’s WLANs are based on
the IEEE 802.11 standard, which can deliver
user data rates up to 5–6 Mbit/s and are mainly
used in offices to provide a wireless data network
extension (e.g. Ethernet). A limiting factor
for IEEE 802.11 is that it is primarily designed
for transport of non-real time data traffic. IEEE
802.11 equipment does also operate in the 2.4
GHz ISM frequency band, which means that it
shares the limited frequency spectrum resources
with other systems such as microwave ovens,
garage openers and soon Bluetooth. The performance
is therefore more susceptible to external
disturbances (interference) than systems that use
dedicated frequency bands.
MULTIMEDIA
UMTS
Hiperlan
2
Figure 1 Developments in mobile wireless data networks
73