Wireless Future - Telenor

56
7 Conclusion and
Further Research
The results presented in this paper indicate that it
is possible to obtain a much larger spectral efficiency
in wireless systems than achieved in present-day
systems. The large increase in spectral
efficiency may be obtained by utilizing coding
schemes which adapt the information rates
according to the quality of the wireless links.
This in turn may enable the introduction of novel
bandwidth-intensive multimedia services.
7.1 Planned Research
While we have only considered narrowband
channels with frequency-flat fading, adaptive
coding techniques may also be used on broadband
frequency-selective fading channels.
Orthogonal frequency division multiplexing
(OFDM) can be used to decompose a broadband
frequency-selective fading channel into a set of
parallel narrowband subchannels with flat fading
[24]. Adaptive coding techniques may be utilized
on each individual narrowband subchannel
to achieve broadband OFDM transmission with
large total average spectral efficiency.
The success of ACM/OFDM is ultimately
dependent on reliable knowledge of the subchannel
dynamics at the transmitter. Since the subchannel
states have to be estimated at the receiver,
there will always be a certain degradation
of system performance compared to the idealized
case of perfect subchannel knowledge. It is
important to minimize this degradation by finding
optimal subchannel estimation techniques
for realistic channel models.
In November 2000, the authors started a new
project with the title “Bandwidth-Efficient and
Adaptive Transmission Schemes for Wireless
Multimedia Communications” (BEATS). The
BEATS project is a part of the IKT-2010 research
programme funded by the Norwegian
Research Council. The principal objective of this
project is to develop bandwidth-efficient, adaptive
OFDM schemes for broadband wireless
multimedia communications. More information
about the project may be found on the web-page
http://www.tele.ntnu.no/beats/. As new results
become available, they will be posted on this
page.
The authors also participate in the joint NTNU-
Telenor research project “Turbo Codes, Access,
and Network Technology” (TURBAN). Our
TURBAN project goal is to determine efficient
channel codes for use in adaptive transmission.
References
1 Meyr, H. Algorithm design and system
implementation for advanced wireless communications
systems. In: Proc. International
Zurich Seminar on Broadband Communications
(IZS’2000), Zurich, 2000.
2 Bose, V, Wetherall, D, Guttag, J. Next century
challenges : RadioActive Networks. In:
Proc. ACM/IEEE International Conference
on Mobile Computing and Networking
(MOBICOM’99), Seattle, WA, 1999,
242–248.
3 Stüber, G L. Principles of Mobile Communication.
Norwell, MA, Kluwer Academic
Publishers, 1996.
4 Cover, T M, Thomas, J A. Elements of Information
Theory. New York, Wiley, 1991.
5 Goldsmith, A J, Varaiya, P P. Capacity of
fading channels with channel side information.
IEEE Trans. Inform. Theory, 43 (6),
1986–1992, 1997.
6 Alouini, M-S, Goldsmith, A J. Capacity of
Nakagami multipath fading channels. In:
Proc. 47th IEEE Vehicular Technology
Conference (VTC’97), Phoenix, AZ, 1997,
358–362.
7 Gradshteyn, I S, Ryzhik, I M. Table of Integrals,
Series, and Products. San Diego, CA,
Academic Press, fifth ed., 1994.
8 Webb, W T, Hanzo, L. Modern Quadrature
Amplitude Modulation. Graham Lodge, London,
Pentech Press, 1994.
9 Webb, W T, Steele, R. Variable rate QAM
for mobile radio. IEEE Trans. Commun., 43
(7), 2223–2230, 1995.
10 Goldsmith, A J, Chua, S-G. Variable-rate
variable-power MQAM for fading channels.
IEEE Trans. Commun., 45 (10), 1218–1230,
1997.
11 Alouini, M-S, Goldsmith, A J. Adaptive
M-QAM modulation over Nakagami fading
channels. In: Proc. 6th Communications
Theory Mini-Conference (CTMC VI) in conjunction
with IEEE Global Communications
Conference (GLOBECOM’97), Phoenix,
Arizona, 1997, 218–223.
Telektronikk 1.2001