9,949 research outputs found
Cooperative Multi-Cell Block Diagonalization with Per-Base-Station Power Constraints
Block diagonalization (BD) is a practical linear precoding technique that
eliminates the inter-user interference in downlink multiuser multiple-input
multiple-output (MIMO) systems. In this paper, we apply BD to the downlink
transmission in a cooperative multi-cell MIMO system, where the signals from
different base stations (BSs) to all the mobile stations (MSs) are jointly
designed with the perfect knowledge of the downlink channels and transmit
messages. Specifically, we study the optimal BD precoder design to maximize the
weighted sum-rate of all the MSs subject to a set of per-BS power constraints.
This design problem is formulated in an auxiliary MIMO broadcast channel (BC)
with a set of transmit power constraints corresponding to those for individual
BSs in the multi-cell system. By applying convex optimization techniques, this
paper develops an efficient algorithm to solve this problem, and derives the
closed-form expression for the optimal BD precoding matrix. It is revealed that
the optimal BD precoding vectors for each MS in the per-BS power constraint
case are in general non-orthogonal, which differs from the conventional
orthogonal BD precoder design for the MIMO-BC under one single sum-power
constraint. Moreover, for the special case of single-antenna BSs and MSs, the
proposed solution reduces to the optimal zero-forcing beamforming (ZF-BF)
precoder design for the weighted sum-rate maximization in the multiple-input
single-output (MISO) BC with per-antenna power constraints. Suboptimal and
low-complexity BD/ZF-BF precoding schemes are also presented, and their
achievable rates are compared against those with the optimal schemes.Comment: accepted in JSAC, special issue on cooperative communications on
cellular networks, June 201
Precoding and Decoding Schemes for Downlink MIMO-RSMA with Simultaneous Diagonalization and User Exclusion
In this paper, we consider the precoder design for downlink multiple-input
multiple-output (MIMO) rate-splitting multiple access (RSMA) systems. The
proposed scheme with simultaneous diagonalization (SD) decomposes the MIMO
channel matrices of the users into scalar channels via higher-order generalized
singular value decomposition for the common message (CM) and block
diagonalization (BD) for the private messages, thereby enabling low-complexity
element-by-element successive interference cancellation (SIC) and decoding at
the receivers. Furthermore, the proposed SD MIMO-RSMA overcomes a critical
limitation in RSMA systems, whereby the achievable rate of the CM is restricted
by the users with weak effective MIMO channel for the CM, by excluding a subset
of users from decoding the CM. We formulate a non-convex weighted sum rate
(WSR) optimization problem for SD MIMO-RSMA and solve it via successive convex
approximation to obtain a locally optimal solution. Our simulation results
reveal that, for both perfect and imperfect CSI, the proposed SD MIMO-RSMA with
user exclusion outperforms baseline MIMO-RSMA schemes and linear BD precoding.Comment: 7pp, 2 figures, accepted to the Workshop on Rate-Splitting Multiple
Access for 6G at the IEEE Intl. Commun. Conf. (ICC) 202
Large-System Analysis of Correlated MIMO Multiple Access Channels with Arbitrary Signaling in the Presence of Interference
Presence of multiple antennas on both sides of
a communication channel promises significant improvements in
system throughput and power efficiency. In effect, a new clas
s
of large multiple-input multiple-output (MIMO) communication
systems has recently emerged and attracted both scientific and
industrial attention. To analyze these systems in realistic scenarios,
one has to include such aspects as co-channel interference,
multiple access and spatial correlation. In this paper, we study
the properties of correlated MIMO multiple-access channels in
the presence of external interference. Using the replica method
from statistical physics, we derive the ergodic sum-rate of the
communication for arbitrary signal constellations when the numbers
of antennas at both ends of the channel grow large. Based
on these asymptotic expressions, we also address the problem of
sum-rate maximization using statistical channel information and
linear precoding. The numerical results demonstrate that when
the interfering terminals use discrete constellations, the resulting
interference becomes easier to handle compared to Gaussian
signals. Thus, it may be possible to accommodate more interfering
transmitter-receiver pairs within the same area as compare
d
to the case of Gaussian signals. In addition, we demonstrate
numerically for the Gaussian and QPSK signaling schemes that it
is possible to design precoder matrices that significantly improve
the achievable rates at low-to-mid range of signal-to-noise ratios
when compared to isotropic precoding
Beam Focusing for Near-Field Multiuser MIMO Communications
Large antenna arrays and high-frequency bands are two key features of future wireless communication systems. The combination of large-scale antennas with high transmission frequencies often results in the communicating devices operating in the near-field (Fresnel) region. In this paper, we study the potential of beam focusing, feasible in near-field operation, in facilitating high-rate multi-user downlink multiple-input multiple-output (MIMO) systems. As the ability to achieve beam focusing is dictated by the transmit antenna, we study near-field signalling considering different antenna structures, including fully-digital architectures, hybrid phase shifter-based precoders, and the emerging dynamic metasurface antenna (DMA) architecture for massive MIMO arrays. We first provide a mathematical model to characterize near-field wireless channels as well as the transmission pattern for the considered antenna architectures. Then, we formulate the beam focusing problem for the goal of maximizing the achievable sum-rate in multi-user networks. We propose efficient solutions based on the sum-rate maximization task for fully-digital, (phase shifters based-) hybrid and DMA architectures. Simulation results show the feasibility of the proposed beam focusing scheme for both single- and multi-user scenarios. In particular, the designed focused beams provide a new degree of freedom to mitigate interference in both angle and distance domains, which is not achievable using conventional far-field beam steering, allowing reliable communications for uses even residing at the same angular direction
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