263 research outputs found
Autonomous Algorithms for Centralized and Distributed Interference Coordination: A Virtual Layer Based Approach
Interference mitigation techniques are essential for improving the
performance of interference limited wireless networks. In this paper, we
introduce novel interference mitigation schemes for wireless cellular networks
with space division multiple access (SDMA). The schemes are based on a virtual
layer that captures and simplifies the complicated interference situation in
the network and that is used for power control. We show how optimization in
this virtual layer generates gradually adapting power control settings that
lead to autonomous interference minimization. Thereby, the granularity of
control ranges from controlling frequency sub-band power via controlling the
power on a per-beam basis, to a granularity of only enforcing average power
constraints per beam. In conjunction with suitable short-term scheduling, our
algorithms gradually steer the network towards a higher utility. We use
extensive system-level simulations to compare three distributed algorithms and
evaluate their applicability for different user mobility assumptions. In
particular, it turns out that larger gains can be achieved by imposing average
power constraints and allowing opportunistic scheduling instantaneously, rather
than controlling the power in a strict way. Furthermore, we introduce a
centralized algorithm, which directly solves the underlying optimization and
shows fast convergence, as a performance benchmark for the distributed
solutions. Moreover, we investigate the deviation from global optimality by
comparing to a branch-and-bound-based solution.Comment: revised versio
Joint User Scheduling and Beamforming Design for Multiuser MISO Downlink Systems
In multiuser communication systems, user scheduling and beamforming (US-BF)
design are two fundamental problems that are usually studied separately in the
existing literature. In this work, we focus on the joint US-BF design with the
goal of maximizing the set cardinality of scheduled users, which is
computationally challenging due to the non-convex objective function and the
coupled constraints with discrete-continuous variables. To tackle these
difficulties, a successive convex approximation based US-BF (SCA-USBF)
optimization algorithm is firstly proposed. Then, inspired by wireless
intelligent communication, a graph neural network based joint US-BF (J-USBF)
learning algorithm is developed by combining the joint US and power allocation
network model with the BF analytical solution. The effectiveness of SCA-USBF
and J-USBF is verified by various numerical results, the latter achieves close
performance and higher computational efficiency. Furthermore, the proposed
J-USBF also enjoys the generalizability in dynamic wireless network scenarios.Comment: 31 pages, 9 figures, submit to IEEE Transactions on Wireless
Communication
Interference-Aware RZF Precoding for Multi Cell Downlink Systems
Recently, a structure of an optimal linear precoder for multi cell downlink
systems has been described in [1, Eq (3.33)]. Other references (e.g., [2,3])
have used simplified versions of the precoder to obtain promising performance
gains. These gains have been hypothesized to stem from the additional degrees
of freedom that allow for interference mitigation through interference
relegation to orthogonal subspaces. However, no conclusive or rigorous
understanding has yet been developed. In this paper, we build on an intuitive
interference induction trade-off and the aforementioned precoding structure to
propose an interference aware RZF (iaRZF) precoding scheme for multi cell
downlink systems and we analyze its rate performance. Special emphasis is
placed on the induced interference mitigation mechanism of iaRZF. For example,
we will verify the intuitive expectation that the precoder structure can either
completely remove induced inter-cell or intra-cell interference. We state new
results from large-scale random matrix theory that make it possible to give
more intuitive and insightful explanations of the precoder behavior, also for
cases involving imperfect channel state information (CSI). We remark especially
that the interference-aware precoder makes use of all available information
about interfering channels to improve performance. Even very poor CSI allows
for significant sum-rate gains. Our obtained insights are then used to propose
heuristic precoder parameters for arbitrary systems, whose effectiveness are
shown in more involved system scenarios. Furthermore, calculation and
implementation of these parameters does not require explicit inter base station
cooperation.Comment: Accepted for publication in IEEE Transactions on Signal Processing,
201
- …