1,284 research outputs found
Resource allocation for transmit hybrid beamforming in decoupled millimeter wave multiuser-MIMO downlink
This paper presents a study on joint radio resource allocation and hybrid precoding in multicarrier massive multiple-input multiple-output communications for 5G cellular networks. In this paper, we present the resource allocation algorithm to maximize the proportional fairness (PF) spectral efficiency under the per subchannel power and the beamforming rank constraints. Two heuristic algorithms are designed. The proportional fairness hybrid beamforming algorithm provides the transmit precoder with a proportional fair spectral efficiency among users for the desired number of radio-frequency (RF) chains. Then, we transform the number of RF chains or rank constrained optimization problem into convex semidefinite programming (SDP) problem, which can be solved by standard techniques. Inspired by the formulated convex SDP problem, a low-complexity, two-step, PF-relaxed optimization algorithm has been provided for the formulated convex optimization problem. Simulation results show that the proposed suboptimal solution to the relaxed optimization problem is near-optimal for the signal-to-noise ratio SNR <= 10 dB and has a performance gap not greater than 2.33 b/s/Hz within the SNR range 0-25 dB. It also outperforms the maximum throughput and PF-based hybrid beamforming schemes for sum spectral efficiency, individual spectral efficiency, and fairness index
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
Bandwidth-Constrained Capacity Bounds and Degrees of Freedom for MIMO Antennas
The optimal spectral efficiency and number of independent channels for MIMO
antennas in isotropic multipath channels are investigated when bandwidth
requirements are placed on the antenna. By posing the problem as a convex
optimization problem restricted by the port Q-factor a semi-analytical
expression is formed for its solution. The antennas are simulated by method of
moments and the solution is formulated both for structures fed by discrete
ports, as well as for design regions characterized by an equivalent current. It
is shown that the solution is solely dependent on the eigenvalues of the
so-called energy modes of the antenna. The magnitude of these eigenvalues is
analyzed for a linear dipole array as well as a plate with embedded antenna
regions. The energy modes are also compared to the characteristic modes to
validate characteristic modes as a design strategy for MIMO antennas. The
antenna performance is illustrated through spectral efficiency over the
Q-factor, a quantity that is connected to the capacity. It is proposed that the
number of energy modes below a given Q-factor can be used to estimate the
degrees of freedom for that Q-factor.Comment: 13 pages, 17 figure
Eigen-Based Transceivers for the MIMO Broadcast Channel with Semi-Orthogonal User Selection
This paper studies the sum rate performance of two low complexity
eigenmode-based transmission techniques for the MIMO broadcast channel,
employing greedy semi-orthogonal user selection (SUS). The first approach,
termed ZFDPC-SUS, is based on zero-forcing dirty paper coding; the second
approach, termed ZFBF-SUS, is based on zero-forcing beamforming. We first
employ new analytical methods to prove that as the number of users K grows
large, the ZFDPC-SUS approach can achieve the optimal sum rate scaling of the
MIMO broadcast channel. We also prove that the average sum rates of both
techniques converge to the average sum capacity of the MIMO broadcast channel
for large K. In addition to the asymptotic analysis, we investigate the sum
rates achieved by ZFDPC-SUS and ZFBF-SUS for finite K, and show that ZFDPC-SUS
has significant performance advantages. Our results also provide key insights
into the benefit of multiple receive antennas, and the effect of the SUS
algorithm. In particular, we show that whilst multiple receive antennas only
improves the asymptotic sum rate scaling via the second-order behavior of the
multi-user diversity gain; for finite K, the benefit can be very significant.
We also show the interesting result that the semi-orthogonality constraint
imposed by SUS, whilst facilitating a very low complexity user selection
procedure, asymptotically does not reduce the multi-user diversity gain in
either first (log K) or second-order (loglog K) terms.Comment: 35 pages, 3 figures, to appear in IEEE transactions on signal
processin
Hybrid Beamforming for Large Antenna Arrays with Phase Shifter Selection
This paper proposes an asymptotically optimal hybrid beamforming solution for
large antenna arrays by exploiting the properties of the singular vectors of
the channel matrix. It is shown that the elements of the channel matrix with
Rayleigh fading follow a normal distribution when large antenna arrays are
employed. The proposed beamforming algorithm is effective in both sparse and
rich propagation environments, and is applicable for both point-to-point and
multiuser scenarios. In addition, a closed-form expression and a lower-bound
for the achievable rates are derived when analog and digital phase shifters are
employed. It is shown that the performance of the hybrid beamformers using
phase shifters with more than 2-bits resolution is comparable with analog phase
shifting. A novel phase shifter selection scheme that reduces the power
consumption at the phase shifter network is proposed when the wireless channel
is modeled by Rayleigh fading. Using this selection scheme, the spectral
efficiency can be increased as the power consumption in the phase shifter
network reduces. Compared to the scenario that all of the phase shifters are in
operation, the simulation results indicate that the spectral efficiency
increases when up to 50% of phase shifters are turned off.Comment: Accepted to Transactions on Wireless Communications, 201
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