5,329 research outputs found
Soft Pilot Reuse and Multi-Cell Block Diagonalization Precoding for Massive MIMO Systems
The users at cell edge of a massive multiple-input multiple-output (MIMO)
system suffer from severe pilot contamination, which leads to poor quality of
service (QoS). In order to enhance the QoS for these edge users, soft pilot
reuse (SPR) combined with multi-cell block diagonalization (MBD) precoding are
proposed. Specifically, the users are divided into two groups according to
their large-scale fading coefficients, referred to as the center users, who
only suffer from modest pilot contamination and the edge users, who suffer from
severe pilot contamination. Based on this distinction, the SPR scheme is
proposed for improving the QoS for the edge users, whereby a cell-center pilot
group is reused for all cell-center users in all cells, while a cell-edge pilot
group is applied for the edge users in the adjacent cells. By extending the
classical block diagonalization precoding to a multi-cell scenario, the MBD
precoding scheme projects the downlink transmit signal onto the null space of
the subspace spanned by the inter-cell channels of the edge users in adjacent
cells. Thus, the inter-cell interference contaminating the edge users' signals
in the adjacent cells can be efficiently mitigated and hence the QoS of these
edge users can be further enhanced. Our theoretical analysis and simulation
results demonstrate that both the uplink and downlink rates of the edge users
are significantly improved, albeit at the cost of the slightly decreased rate
of center users.Comment: 13 pages, 12 figures, accepted for publication in IEEE Transactions
on Vehicular Technology, 201
A New SLNR-based Linear Precoding for Downlink Multi-User Multi-Stream MIMO Systems
Signal-to-leakage-and-noise ratio (SLNR) is a promising criterion for linear
precoder design in multi-user (MU) multiple-input multiple-output (MIMO)
systems. It decouples the precoder design problem and makes closed-form
solution available. In this letter, we present a new linear precoding scheme by
slightly relaxing the SLNR maximization for MU-MIMO systems with multiple data
streams per user. The precoding matrices are obtained by a general form of
simultaneous diagonalization of two Hermitian matrices. The new scheme reduces
the gap between the per-stream effective channel gains, an inherent limitation
in the original SLNR precoding scheme. Simulation results demonstrate that the
proposed precoding achieves considerable gains in error performance over the
original one for multi-stream transmission while maintaining almost the same
achievable sum-rate.Comment: 8 pages, 1 figur
PAR-Aware Large-Scale Multi-User MIMO-OFDM Downlink
We investigate an orthogonal frequency-division multiplexing (OFDM)-based
downlink transmission scheme for large-scale multi-user (MU) multiple-input
multiple-output (MIMO) wireless systems. The use of OFDM causes a high
peak-to-average (power) ratio (PAR), which necessitates expensive and
power-inefficient radio-frequency (RF) components at the base station. In this
paper, we present a novel downlink transmission scheme, which exploits the
massive degrees-of-freedom available in large-scale MU-MIMO-OFDM systems to
achieve low PAR. Specifically, we propose to jointly perform MU precoding, OFDM
modulation, and PAR reduction by solving a convex optimization problem. We
develop a corresponding fast iterative truncation algorithm (FITRA) and show
numerical results to demonstrate tremendous PAR-reduction capabilities. The
significantly reduced linearity requirements eventually enable the use of
low-cost RF components for the large-scale MU-MIMO-OFDM downlink.Comment: To appear in IEEE Journal on Selected Areas in Communication
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