Spatial Multiplexing for Outdoor MIMO-OFDM Systems
with Limited Feedback Constraint.
Politecnico di Milano,
Politecnico di Milano, and
IEEE International Conference on Communications,
Istanbul, Turkey, 11-15 June 2006.
The use of multiple antennas enables also space-division
multiple access (SDMA), which allows intra-cell bandwidth
reuse by creating spatially multiplexed channels.
A fundamental challenge to be overcome is how the
scheduler should separate and group the users.
focused on the uplink case and suggested clustering
of users based on their mutual spatial correlation, or
alternatively based on their main direction of arrival
in case of moderate angular spread at the base station.
If channel state information (CSI) is perfectly known
to the transmitter then interference-free spatially
multiplexed channels could be set up through
appropriate precoding matrices or vectors.
However, for frequency division duplex (FDD) systems,
this assumption leads to an unacceptable feedback rate requirement
for users at vehicular velocities.
In this paper we propose a spatial multiplexing technique
for the downlink of a multiple-input-multiple-output (MIMO)
orthogonal frequency-division-multiplexing (OFDM) system.
For outdoor environments with a limited angular spread
at the base station, the proposed technique is able to separate
the users streams through a joint spatial processing at
both the transmitter and the receiver requiring only a
limited feedback from each user. Adaptive transmission
is adopted on each stream, designed to attain a
fixed probability of error.
Numerical simulations show that the proposed technique
is able to provide significant throughput gains compared
to fixed-beams based approaches
proposed in the literature.
Journal paper version
IEEE Trans. Wireless Comm., Nov. 2008
Proc. of the IEEE (Dec. 2007)
invited paper on
adaptive transmission in beyond-3G wireless systems.
Reduced-rank Channel Estimation and Tracking in
Time-slotted CDMA Systems,
Reduced-rank channel estimation,
method by Erik Lindskog and Claes Tidestav, IEEE VTC'99.