A Comparative Analysis of Spatial Multiplexing
Techniques for Outdoor MIMO-OFDM Systems
with a Limited Feedback Constraint.
Politecnico di Milano,
Politecnico di Milano, and
IEEE Transactions on Vehicular Technology,
vol. 58, no, 1, January 2009, pp. 218-230.
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 analyze spatial multiplexing
techniques for the downlink of a
Our study is focused on outdoor environments
characterized by moderate angular spread.
We consider two techniques that are able to separate
the downlink data streams associated to different users
and to guarantee a fixed error probability by exploiting
a limited feedback from each user.
The proposed Adaptive Grid of Beams (AGoB) and
Grid of Beams (GoB) differ in the way the precoders
are designed (by adaptive or fixed processing)
and in the scheduling policy. The new AGoB is
able to harness a partial knowledge of the downlink
channel spatial structure to better select the users
and adjusts their precoders for downlink transmission.
The performances of GoB and AGoB are compared
in this paper in terms of throughput and cell
coverage capability. The radio interface is adapted
to fit the requirements for the AMC-AAS
(adaptive modulation and coding with advanced
antenna system) mode of the IEEE 802.16-2005
Numerical results show that, as far as the channel
exhibits a limited angular spread at the base station,
the AGoB technique is able to provide significant
throughput gains compared to the fixed GoB approach.
On the other hand, large angular spreads are proved to
have a substantial impact on the system performance
as the benefits of the adaptation are significantly reduced.
Earlier conference paper
at ICC 2006, Istanbul.
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.
entry in list of publications
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