4 research outputs found
Hybrid Scheduling/Signal-Level Coordination in the Downlink of Multi-Cloud Radio-Access Networks
In the context of resource allocation in cloud-radio access networks, recent
studies assume either signal-level or scheduling-level coordination. This
paper, instead, considers a hybrid level of coordination for the scheduling
problem in the downlink of a multi-cloud radio-access network, as a means to
benefit from both scheduling policies. Consider a multi-cloud radio access
network, where each cloud is connected to several base-stations (BSs) via high
capacity links, and therefore allows joint signal processing between them.
Across the multiple clouds, however, only scheduling-level coordination is
permitted, as it requires a lower level of backhaul communication. The frame
structure of every BS is composed of various time/frequency blocks, called
power-zones (PZs), and kept at fixed power level. The paper addresses the
problem of maximizing a network-wide utility by associating users to clouds and
scheduling them to the PZs, under the practical constraints that each user is
scheduled, at most, to a single cloud, but possibly to many BSs within the
cloud, and can be served by one or more distinct PZs within the BSs' frame. The
paper solves the problem using graph theory techniques by constructing the
conflict graph. The scheduling problem is, then, shown to be equivalent to a
maximum-weight independent set problem in the constructed graph, in which each
vertex symbolizes an association of cloud, user, BS and PZ, with a weight
representing the utility of that association. Simulation results suggest that
the proposed hybrid scheduling strategy provides appreciable gain as compared
to the scheduling-level coordinated networks, with a negligible degradation to
signal-level coordination
Coordinated Scheduling for the Downlink of Cloud Radio-Access Networks
This paper addresses the coordinated scheduling problem in cloud-enabled
networks. Consider the downlink of a cloud-radio access network (C-RAN), where
the cloud is only responsible for the scheduling policy and the synchronization
of the transmit frames across the connected base-stations (BS). The transmitted
frame of every BS consists of several time/frequency blocks, called power-zones
(PZ), maintained at fixed transmit power. The paper considers the problem of
scheduling users to PZs and BSs in a coordinated fashion across the network, by
maximizing a network-wide utility under the practical constraint that each user
cannot be served by more than one base-station, but can be served by one or
more power-zone within each base-station frame. The paper solves the problem
using a graph theoretical approach by introducing the scheduling graph in which
each vertex represents an association of users, PZs and BSs. The problem is
formulated as a maximum weight clique, in which the weight of each vertex is
the benefit of the association represented by that vertex. The paper further
presents heuristic algorithms with low computational complexity. Simulation
results show the performance of the proposed algorithms and suggest that the
heuristics perform near optimal in low shadowing environment
A Tutorial on Clique Problems in Communications and Signal Processing
Since its first use by Euler on the problem of the seven bridges of
K\"onigsberg, graph theory has shown excellent abilities in solving and
unveiling the properties of multiple discrete optimization problems. The study
of the structure of some integer programs reveals equivalence with graph theory
problems making a large body of the literature readily available for solving
and characterizing the complexity of these problems. This tutorial presents a
framework for utilizing a particular graph theory problem, known as the clique
problem, for solving communications and signal processing problems. In
particular, the paper aims to illustrate the structural properties of integer
programs that can be formulated as clique problems through multiple examples in
communications and signal processing. To that end, the first part of the
tutorial provides various optimal and heuristic solutions for the maximum
clique, maximum weight clique, and -clique problems. The tutorial, further,
illustrates the use of the clique formulation through numerous contemporary
examples in communications and signal processing, mainly in maximum access for
non-orthogonal multiple access networks, throughput maximization using index
and instantly decodable network coding, collision-free radio frequency
identification networks, and resource allocation in cloud-radio access
networks. Finally, the tutorial sheds light on the recent advances of such
applications, and provides technical insights on ways of dealing with mixed
discrete-continuous optimization problems
COORDINATED SCHEDULING FOR WIRELESS BACKHAUL NETWORKS WITH SOFT FREQUENCY REUSE
Coordinated resource allocation is a topic of significant interest for emerging wireless networks. This paper proposes and examines the benefits of coordinated scheduling in soft frequency reuse (SFR) based systems. Consider the downlink of a 3-sector-per-cell SFR-based wireless backhaul network consisting of N access nodes (ANs), each serving K remote terminals (RTs) multiplexed across the K time/frequency zones, with frequency reuse one between the sectors. Assuming a fixed transmit power, the paper considers the resource allocation problem of optimally scheduling each of the NK RTs to one of the NK power-zones, on a one-to-one basis, and in a coordinated manner, as opposed to conventional systems which schedule the RTs one at a time in an uncoordinated way. The paper solves the problem using the auction method, which offers a close-to-global-optimal solution. The paper further proposes heuristic methods with lower computational complexity. Simulation results show that coordinated scheduling offers significant performance improvement as compared to non-coordinated systems. 1