7 research outputs found
Optimal Power Allocation over Multiple Identical Gilbert-Elliott Channels
We study the fundamental problem of power allocation over multiple
Gilbert-Elliott communication channels. In a communication system with time
varying channel qualities, it is important to allocate the limited transmission
power to channels that will be in good state. However, it is very challenging
to do so because channel states are usually unknown when the power allocation
decision is made. In this paper, we derive an optimal power allocation policy
that can maximize the expected discounted number of bits transmitted over an
infinite time span by allocating the transmission power only to those channels
that are believed to be good in the coming time slot. We use the concept belief
to represent the probability that a channel will be good and derive an optimal
power allocation policy that establishes a mapping from the channel belief to
an allocation decision.
Specifically, we first model this problem as a partially observable Markov
decision processes (POMDP), and analytically investigate the structure of the
optimal policy. Then a simple threshold-based policy is derived for a
three-channel communication system. By formulating and solving a linear
programming formulation of this power allocation problem, we further verified
the derived structure of the optimal policy.Comment: 10 pages, 7 figure
Optimal Control of a Single Queue with Retransmissions: Delay-Dropping Tradeoffs
A single queue incorporating a retransmission protocol is investigated,
assuming that the sequence of per effort success probabilities in the Automatic
Retransmission reQuest (ARQ) chain is a priori defined and no channel state
information at the transmitter is available. A Markov Decision Problem with an
average cost criterion is formulated where the possible actions are to either
continue the retransmission process of an erroneous packet at the next time
slot or to drop the packet and move on to the next packet awaiting for
transmission. The cost per slot is a linear combination of the current queue
length and a penalty term in case dropping is chosen as action. The
investigation seeks policies that provide the best possible average packet
delay-dropping trade-off for Quality of Service guarantees. An optimal
deterministic stationary policy is shown to exist, several structural
properties of which are obtained. Based on that, a class of suboptimal
-policies is introduced. These suggest that it is almost optimal to use a
K-truncated ARQ protocol as long as the queue length is lower than L, else send
all packets in one shot. The work concludes with an evaluation of the optimal
delay-dropping tradeoff using dynamic programming and a comparison between the
optimal and suboptimal policies.Comment: 29 pages, 8 figures, submitted to IEEE Transactions on Wireless
Communication
Resource management in QoS-aware wireless cellular networks
2011 Summer.Includes bibliographical references.Emerging broadband wireless networks that support high speed packet data with heterogeneous quality of service (QoS) requirements demand more flexible and efficient use of the scarce spectral resource. Opportunistic scheduling exploits the time-varying, location-dependent channel conditions to achieve multiuser diversity. In this work, we study two types of resource allocation problems in QoS-aware wireless cellular networks. First, we develop a rigorous framework to study opportunistic scheduling in multiuser OFDM systems. We derive optimal opportunistic scheduling policies under three common QoS/fairness constraints for multiuser OFDM systems--temporal fairness, utilitarian fairness, and minimum-performance guarantees. To implement these optimal policies efficiently, we provide a modified Hungarian algorithm and a simple suboptimal algorithm. We then propose a generalized opportunistic scheduling framework that incorporates multiple mixed QoS/fairness constraints, including providing both lower and upper bound constraints. Next, taking input queues and channel memory into consideration, we reformulate the transmission scheduling problem as a new class of Markov decision processes (MDPs) with fairness constraints. We investigate the throughput maximization and the delay minimization problems in this context. We study two categories of fairness constraints, namely temporal fairness and utilitarian fairness. We consider two criteria: infinite horizon expected total discounted reward and expected average reward. We derive and prove explicit dynamic programming equations for the above constrained MDPs, and characterize optimal scheduling policies based on those equations. An attractive feature of our proposed schemes is that they can easily be extended to fit different objective functions and other fairness measures. Although we only focus on uplink scheduling, the scheme is equally applicable to the downlink case. Furthermore, we develop an efficient approximation method--temporal fair rollout--to reduce the computational cost