268 research outputs found
Statistical Multimode Transmit Antenna Selection for Limited Feedback MIMO Systems
This paper was
presented in part at the Asia-Pacific Conference on Communications, Busan,
Korea, August 2006.In a wireless multiple-input multiple-output
(MIMO) system, transmit antenna selection is an effective
means of achieving good performance with low complexity. We
consider spatial multiplexing with linear receivers, and equal
power and equal rate allocation over different selected transmit
antennas in order to reduce feedback overhead. Under these
constraints, we address the problem of statistical multimode
transmit antenna subset selection to improve the capacity
of spatially correlated MIMO fading channels. In particular,
we first derive an analytical closed-form expression for the
expectation of the lower bound on the capacity using the
smallest eigenvalue distribution of a Wishart matrix. Then,
we propose a transmit antenna subset selection criterion of
maximizing this average lower-bound capacity
Joint Hybrid Precoder and Combiner Design for mmWave Spatial Multiplexing Transmission
Millimeter-wave (mmWave) communications have been considered as a key
technology for future 5G wireless networks because of the orders-of-magnitude
wider bandwidth than current cellular bands. In this paper, we consider the
problem of codebook-based joint analog-digital hybrid precoder and combiner
design for spatial multiplexing transmission in a mmWave multiple-input
multiple-output (MIMO) system. We propose to jointly select analog precoder and
combiner pair for each data stream successively aiming at maximizing the
channel gain while suppressing the interference between different data streams.
After all analog precoder/combiner pairs have been determined, we can obtain
the effective baseband channel. Then, the digital precoder and combiner are
computed based on the obtained effective baseband channel to further mitigate
the interference and maximize the sum-rate. Simulation results demonstrate that
our proposed algorithm exhibits prominent advantages in combating interference
between different data streams and offer satisfactory performance improvement
compared to the existing codebook-based hybrid beamforming schemes
Receive Combining vs. Multi-Stream Multiplexing in Downlink Systems with Multi-Antenna Users
In downlink multi-antenna systems with many users, the multiplexing gain is
strictly limited by the number of transmit antennas and the use of these
antennas. Assuming that the total number of receive antennas at the
multi-antenna users is much larger than , the maximal multiplexing gain can
be achieved with many different transmission/reception strategies. For example,
the excess number of receive antennas can be utilized to schedule users with
effective channels that are near-orthogonal, for multi-stream multiplexing to
users with well-conditioned channels, and/or to enable interference-aware
receive combining. In this paper, we try to answer the question if the data
streams should be divided among few users (many streams per user) or many users
(few streams per user, enabling receive combining). Analytic results are
derived to show how user selection, spatial correlation, heterogeneous user
conditions, and imperfect channel acquisition (quantization or estimation
errors) affect the performance when sending the maximal number of streams or
one stream per scheduled user---the two extremes in data stream allocation.
While contradicting observations on this topic have been reported in prior
works, we show that selecting many users and allocating one stream per user
(i.e., exploiting receive combining) is the best candidate under realistic
conditions. This is explained by the provably stronger resilience towards
spatial correlation and the larger benefit from multi-user diversity. This
fundamental result has positive implications for the design of downlink systems
as it reduces the hardware requirements at the user devices and simplifies the
throughput optimization.Comment: Published in IEEE Transactions on Signal Processing, 16 pages, 11
figures. The results can be reproduced using the following Matlab code:
https://github.com/emilbjornson/one-or-multiple-stream
Quantized Multimode Precoding in Spatially Correlated Multi-Antenna Channels
Multimode precoding, where the number of independent data-streams is adapted
optimally, can be used to maximize the achievable throughput in multi-antenna
communication systems. Motivated by standardization efforts embraced by the
industry, the focus of this work is on systematic precoder design with
realistic assumptions on the spatial correlation, channel state information
(CSI) at the transmitter and the receiver, and implementation complexity. For
spatial correlation of the channel matrix, we assume a general channel model,
based on physical principles, that has been verified by many recent measurement
campaigns. We also assume a coherent receiver and knowledge of the spatial
statistics at the transmitter along with the presence of an ideal, low-rate
feedback link from the receiver to the transmitter. The reverse link is used
for codebook-index feedback and the goal of this work is to construct precoder
codebooks, adaptable in response to the statistical information, such that the
achievable throughput is significantly enhanced over that of a fixed,
non-adaptive, i.i.d. codebook design. We illustrate how a codebook of
semiunitary precoder matrices localized around some fixed center on the
Grassmann manifold can be skewed in response to the spatial correlation via
low-complexity maps that can rotate and scale submanifolds on the Grassmann
manifold. The skewed codebook in combination with a lowcomplexity statistical
power allocation scheme is then shown to bridge the gap in performance between
a perfect CSI benchmark and an i.i.d. codebook design.Comment: 30 pages, 4 figures, Preprint to be submitted to IEEE Transactions on
Signal Processin
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