Conference Paper

A Theory of QoS for Wireless

Dept. of Comput. Sci., Univ. of Illinois Urbana, Urbana, IL
DOI: 10.1109/INFCOM.2009.5061954 Conference: INFOCOM 2009, IEEE
Source: IEEE Xplore


Wireless networks are increasingly used to carry applications with QoS constraints. Two problems arise when dealing with traffic with QoS constraints. One is admission control, which consists of determining whether it is possible to fulfill the demands of a set of clients. The other is finding an optimal scheduling policy to meet the demands of all clients. In this paper, we propose a framework for jointly addressing three QoS criteria: delay, delivery ratio, and channel reliability. We analytically prove the necessary and sufficient condition for a set of clients to be feasible with respect to the above three criteria. We then establish an efficient algorithm for admission control to decide whether a set of clients is feasible. We further propose two scheduling policies and prove that they are feasibility optimal in the sense that they can meet the demands of every feasible set of clients. In addition, we show that these policies are easily implementable on the IEEE 802.11 mechanisms. We also present the results of simulation studies that appear to confirm the theoretical studies and suggest that the proposed policies outperform others tested under a variety of settings.

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    • "The packets not delivered by the end of the interval are dropped by the BS. The timely throughput measures the average number Fig. 2. Time model of a user for the timely throughput framework. of packets delivered before their deadlines, which handles the delay requirement and reliability performance jointly [34]. "
    IEEE Transactions on Wireless Communications 12/2015; · 2.50 Impact Factor
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    • "It actually measures the mean probability that a user's packet is delivered before its transmission deadline, which evaluates the reliability performance under a delay constraint of τ time slots. According to the definition, the user timely throughput is given by [10] T "
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    ABSTRACT: Network densification via deploying dense small cells is one of the dominant evolutions towards future cellular network to increase spectrum efficiency. Packet transmission delay and reliability in the resultant interference-limited heterogeneous cellular network (HCN) are essential performance metrics for system design. By modeling the locations of base stations (BSs) in HCN as superimposed of independent Poisson point processes, we propose an analytical framework to derive the timely throughput of HCN, which captures both the delay and reliability performance. In the analysis, the BS activity and temporal correlation of transmissions are taken into consideration, both of which have significant effect on network performance. The effect of mobility, BS density, and association bias factor is investigated through numerical results, which shows that network performance derived ignoring the temporal correlation of transmissions is optimistic.
    IEEE International Conference on Communications (ICC), London, UK; 06/2015
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    • "is the number of packets delivered for the n-th client by time t, as in (1).) The WDD policy has been known to be " timely-throughput " optimal (see [10] for discussion). Fig. 3 shows the costs incurred by these four wireless scheduling policies for different risk-sensitive parameters. "
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    ABSTRACT: In cyber-physical systems such as automobiles, measurement data from sensor nodes should be delivered to other consumer nodes such as actuators in a regular fashion. But, in practical systems over unreliable media such as wireless, it is a significant challenge to guarantee small enough inter-delivery times for different clients with heterogeneous channel conditions and inter-delivery requirements. In this paper, we design scheduling policies aiming at satisfying the inter-delivery requirements of such clients. We formulate the problem as a risk-sensitive Markov Decision Process (MDP). Although the resulting problem involves an infinite state space, we first prove that there is an equivalent MDP involving only a finite number of states. Then we prove the existence of a stationary optimal policy and establish an algorithm to compute it in a finite number of steps. However, the bane of this and many similar problems is the resulting complexity, and, in an attempt to make fundamental progress, we further propose a new high reliability asymptotic approach. In essence, this approach considers the scenario when the channel failure probabilities for different clients are of the same order, and asymptotically approach zero. We thus proceed to determine the asymptotically optimal policy: in a two-client scenario, we show that the asymptotically optimal policy is a "modified least time-to-go" policy, which is intuitively appealing and easily implementable; in the general multi-client scenario, we are led to an SN policy, and we develop an algorithm of low computational complexity to obtain it. Simulation results show that the resulting policies perform well even in the pre-asymptotic regime with moderate failure probabilities.
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