Wireless systems are one of the key components for enabling
the information society. Wireless networks and related services will become as pervasive
as microprocessors are today. Therefore it is expected that the demand for wireless
services will continue to increase in the near and medium term, calling for more
capacity and putting more and more pressure on the spectrum availability. To efficiently
employ the scarce radio resources and ensure a certain degree of fairness there
is need to develop techniques that explore in a quasi-optimal way all the dimensions
provided by the space / time and frequency domains.
In wireless communications the path towards high spectral
efficiency transmission techniques has been through the use of the diversity provided
by the rich scattering wireless channels. Diversity is inherent and well known in
the physical layer and either time, frequency, space (antenna) or polarization diversity
has been used to combat the fading by trying to stabilize the channel. Diversity
can also be achieved in the MAC or higher layer, which is termed network diversity,
which can be divided in multiuser diversity (by scheduling or routing) and cooperative
diversity (by cooperative transmission). This type of diversity exploits the channel
fluctuations to ‘ride the peaks’.
There has been in the recent past significant research
activity concerning both aspects, but while research concerning the first topic
has already taken a very practical flavor with proposals / technological evaluation
and integration of solutions that combine the spatial diversity with the ones provided
in the frequency and time domains, research on cooperative channels has been mainly
addressed within the information theory community. Since both aspects provide potential
gains, and considering that for achieving broadband wireless communications it will
be necessary to explore in a quasi-optimal way all the dimensions provided by the
space / time and frequency domains, we feel that there is still significant need
for research in order to design wireless terminals and base stations that integrate
and explore all the potentialities associated with the wireless
medium and user´s resources. These provided the main impetus for this project
proposal whose key objectives are:
To develop and optimize
combinations of physical and
network diversity to increase network capacity, robustness and fairness, and
demonstrate their feasibility.
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