1,350 research outputs found
Nearly-optimal scheduling of users with Markovian time-varying transmission rates
We address the problem of developing a well-performing and implementable scheduler of users with wireless connections to the central controller, which arise in areas such as mobile data networks, heterogeneous networks, or vehicular communications systems. The main feature of such systems is that the connection quality of each user is time-varying, resulting in time-varying transmission rate corresponding to available channel states. We assume that this evolution is Markovian, relaxing the common but unrealistic assumption of stationary channels. We first focus on the three-state channel and study the optimal policy, showing that threshold policies (of giving higher priority to users with higher transmission rate) are not necessarily optimal. For the general channel we design a scheduler which generalizes the recently proposed Potential Improvement (PI) scheduler, and propose its two practical approximations, whose performance is analyzed and compared to existing alternative schedulers in a variety of simulation scenarios. We suggest and give evidence that the variant of PI which only relies on the steady-state distribution of the channel, performs extremely well, and therefore should be used for practical implementation
A Survey on Delay-Aware Resource Control for Wireless Systems --- Large Deviation Theory, Stochastic Lyapunov Drift and Distributed Stochastic Learning
In this tutorial paper, a comprehensive survey is given on several major
systematic approaches in dealing with delay-aware control problems, namely the
equivalent rate constraint approach, the Lyapunov stability drift approach and
the approximate Markov Decision Process (MDP) approach using stochastic
learning. These approaches essentially embrace most of the existing literature
regarding delay-aware resource control in wireless systems. They have their
relative pros and cons in terms of performance, complexity and implementation
issues. For each of the approaches, the problem setup, the general solution and
the design methodology are discussed. Applications of these approaches to
delay-aware resource allocation are illustrated with examples in single-hop
wireless networks. Furthermore, recent results regarding delay-aware multi-hop
routing designs in general multi-hop networks are elaborated. Finally, the
delay performance of the various approaches are compared through simulations
using an example of the uplink OFDMA systems.Comment: 58 pages, 8 figures; IEEE Transactions on Information Theory, 201
Scheduling of users with Markovian time-varying transmission rates
We address the problem of developing a well-performing and implementable scheduler of users with wireless connection to the base station. The main feature of such real-life systems is that the quality conditions of the user channels are time-varying, which turn into the time-varying transmission rate due to different modulation and coding schemes. We assume that this phenomenon follows a Markovian law and most of the discussion is dedicated to the case of three quality conditions of each user, for which we characterize an optimal index policy and show that threshold policies (of giving higher priority to users with higher transmission rate) are not necessarily optimal. For the general case of arbitrary number of quality conditions we design a scheduler and propose its two practical approximations, and illustrate the performance of the proposed index-based schedulers and existing alternatives in a variety of simulation scenarios
Cross-layer Congestion Control, Routing and Scheduling Design in Ad Hoc Wireless Networks
This paper considers jointly optimal design of crosslayer congestion control, routing and scheduling for ad hoc
wireless networks. We first formulate the rate constraint and scheduling constraint using multicommodity flow variables, and formulate resource allocation in networks with fixed wireless channels (or single-rate wireless devices that can mask channel variations) as a utility maximization problem with these constraints.
By dual decomposition, the resource allocation problem
naturally decomposes into three subproblems: congestion control,
routing and scheduling that interact through congestion price.
The global convergence property of this algorithm is proved. We
next extend the dual algorithm to handle networks with timevarying
channels and adaptive multi-rate devices. The stability
of the resulting system is established, and its performance is
characterized with respect to an ideal reference system which
has the best feasible rate region at link layer.
We then generalize the aforementioned results to a general
model of queueing network served by a set of interdependent
parallel servers with time-varying service capabilities, which
models many design problems in communication networks. We
show that for a general convex optimization problem where a
subset of variables lie in a polytope and the rest in a convex set,
the dual-based algorithm remains stable and optimal when the
constraint set is modulated by an irreducible finite-state Markov
chain. This paper thus presents a step toward a systematic way
to carry out cross-layer design in the framework of âlayering as
optimization decompositionâ for time-varying channel models
Scheduling of Multicast and Unicast Services under Limited Feedback by using Rateless Codes
Many opportunistic scheduling techniques are impractical because they require
accurate channel state information (CSI) at the transmitter. In this paper, we
investigate the scheduling of unicast and multicast services in a downlink
network with a very limited amount of feedback information. Specifically,
unicast users send imperfect (or no) CSI and infrequent acknowledgements (ACKs)
to a base station, and multicast users only report infrequent ACKs to avoid
feedback implosion. We consider the use of physical-layer rateless codes, which
not only combats channel uncertainty, but also reduces the overhead of ACK
feedback. A joint scheduling and power allocation scheme is developed to
realize multiuser diversity gain for unicast service and multicast gain for
multicast service. We prove that our scheme achieves a near-optimal throughput
region. Our simulation results show that our scheme significantly improves the
network throughput over schemes employing fixed-rate codes or using only
unicast communications
On Stability Region and Delay Performance of Linear-Memory Randomized Scheduling for Time-Varying Networks
Throughput optimal scheduling policies in general require the solution of a
complex and often NP-hard optimization problem. Related literature has shown
that in the context of time-varying channels, randomized scheduling policies
can be employed to reduce the complexity of the optimization problem but at the
expense of a memory requirement that is exponential in the number of data
flows. In this paper, we consider a Linear-Memory Randomized Scheduling Policy
(LM-RSP) that is based on a pick-and-compare principle in a time-varying
network with one-hop data flows. For general ergodic channel processes, we
study the performance of LM-RSP in terms of its stability region and average
delay. Specifically, we show that LM-RSP can stabilize a fraction of the
capacity region. Our analysis characterizes this fraction as well as the
average delay as a function of channel variations and the efficiency of LM-RSP
in choosing an appropriate schedule vector. Applying these results to a class
of Markovian channels, we provide explicit results on the stability region and
delay performance of LM-RSP.Comment: Long version of preprint to appear in the IEEE Transactions on
Networkin
A Fast-CSMA Algorithm for Deadline-Constrained Scheduling over Wireless Fading Channels
Recently, low-complexity and distributed Carrier Sense Multiple Access
(CSMA)-based scheduling algorithms have attracted extensive interest due to
their throughput-optimal characteristics in general network topologies.
However, these algorithms are not well-suited for serving real-time traffic
under time-varying channel conditions for two reasons: (1) the mixing time of
the underlying CSMA Markov Chain grows with the size of the network, which, for
large networks, generates unacceptable delay for deadline-constrained traffic;
(2) since the dynamic CSMA parameters are influenced by the arrival and channel
state processes, the underlying CSMA Markov Chain may not converge to a
steady-state under strict deadline constraints and fading channel conditions.
In this paper, we attack the problem of distributed scheduling for serving
real-time traffic over time-varying channels. Specifically, we consider
fully-connected topologies with independently fading channels (which can model
cellular networks) in which flows with short-term deadline constraints and
long-term drop rate requirements are served. To that end, we first characterize
the maximal set of satisfiable arrival processes for this system and, then,
propose a Fast-CSMA (FCSMA) policy that is shown to be optimal in supporting
any real-time traffic that is within the maximal satisfiable set. These
theoretical results are further validated through simulations to demonstrate
the relative efficiency of the FCSMA policy compared to some of the existing
CSMA-based algorithms.Comment: This work appears in workshop on Resource Allocation and Cooperation
in Wireless Networks (RAWNET), Princeton, NJ, May, 201
Opportunistic scheduling of flows with general size distribution in wireless time-varying channels
In this paper we study how to design an opportunistic scheduler when flow sizes have a general service time distribution with the objective of minimizing the expected holding cost. We allow the channel condition to have two states which in particular covers the important special case of ON/OFF channels. We formulate the problem as a multi-armed restless bandit problem, a particular class of Markov decision processes. Since an exact solution is out of reach, we characterize in closed-form the Whittle index, which allows us to define a heuristic scheduling rule for the problem. We then particularize the index to the important subclass of distributions with a decreasing hazard rate. We finally evaluate the performance of the proposed Whittle-index based scheduler by simulation of a wireless network. The numerical results show that the performance of the proposed scheduler is very satisfactory
EUROPEAN CONFERENCE ON QUEUEING THEORY 2016
International audienceThis booklet contains the proceedings of the second European Conference in Queueing Theory (ECQT) that was held from the 18th to the 20th of July 2016 at the engineering school ENSEEIHT, Toulouse, France. ECQT is a biannual event where scientists and technicians in queueing theory and related areas get together to promote research, encourage interaction and exchange ideas. The spirit of the conference is to be a queueing event organized from within Europe, but open to participants from all over the world. The technical program of the 2016 edition consisted of 112 presentations organized in 29 sessions covering all trends in queueing theory, including the development of the theory, methodology advances, computational aspects and applications. Another exciting feature of ECQT2016 was the institution of the TakĂĄcs Award for outstanding PhD thesis on "Queueing Theory and its Applications"
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