Conference Paper

Real-time implications of multiple transmission rates in wireless networks.

DOI: 10.1145/1287853.1287893 Conference: Proceedings of the 13th Annual International Conference on Mobile Computing and Networking, MOBICOM 2007, Montréal, Québec, Canada, September 9-14, 2007
Source: DBLP

ABSTRACT Wireless networks are increasingly being used for latency-sensitive applications that require data delivery to be timely, efficient and reliable. This trend is primarily driven by the proliferation of wireless networks of real-time data-gathering sensor-actuator devices. This has led to a strong need to bring real-time concerns to the forefront of an integrated research thrust into wireless real-time systems. In this paper, we introduce and analyze a specific instance of the rich set of problems in this domain. We consider a wireless network serving real-time flows in which the underlying physical layer provides multiple transmission rates. Higher rates have more stringent SINR requirements and thus represent a trade-off between raw transmission speed and packet error rate. We adopt a first principles approach to the design of optimal real-time scheduling algorithms for such a multi-rate wireless network. We illustrate the inherent complexities of the problem through examples and obtain provably optimal structural results. We then characterize the optimal policy for an approximate model. Our theoretical analysis provides guidelines for heuristic scheduler design. Our initial work indicates that this is a rich problem domain with the potential for a unifying theory that integrates real-time requirements into multi-rate wireless network design.

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    ABSTRACT: Wireless networks are increasingly being used for latency- sensitive applications that require data delivery to be timely, efficient and reliable. This trend is primarily driven by the proliferation of wireless networks of real-time data-gathering sensor-actuator devices. This has led to a strong need to bring real-time concerns to the forefront of an integrated research thrust into wireless real-time systems. In this pa- per, we introduce and analyze a specific instance of the rich set of problems in this domain. We consider a wireless net- work serving real-time flows in which the underlying physi- cal layer provides multiple transmission rates. Higher rates have more stringent SINR requirements and thus represent a trade-off between raw transmission speed and packet error rate. We adopt a first principles approach to the design of optimal real-time scheduling algorithms for such a multi-rate wireless network. We illustrate the inherent complexities of the problem through examples and obtain provably optimal structural results. We then characterize the optimal policy for an approximate model. Our theoretical analysis provides guidelines for heuristic scheduler design. Our initial work in- dicates that this is a rich problem domain with the potential for a unifying theory that integrates real-time requirements into multi-rate wireless network design.
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    ABSTRACT: Motivated by the increasing usage of wireless broadcast networks for multicast real-time applications like video, this paper considers a canonical real-time multicast scheduling problem for a wireless broadcast LAN. A wireless access point (AP) has N latency-sensitive flows, each associated with a deadline and a multicast group of receivers that desire to receive all the packets successfully by their corresponding deadlines. We consider periodic and one-shot models of real-time arrivals. The channel from the AP to each receiver is a wireless erasure channel, independent across users and slots. We wish to find a communication strategy that minimizes the total deadlines missed across all receivers, where a receiver counts a miss if it does not receive a packet by its deadline. We cast this problem as a restless bandit in stochastic control. We use Whittle's relaxation framework for restless bandits to establish Whittle-indexability for multicast realtime scheduling under the assumption of complete feedback from all receivers in every slot. For the Whittle relaxation, we show that for each flow, the AP's decision between transmitting in a slot and idling has a threshold structure. For the homogeneous case where the erasure channel to each receiver is identically distributed with parameter p, the Whittle index of a flow is x<sub>i</sub>(1 - p) , where x<sub>i</sub> is the number of receivers who have yet to receive the current packet of flow i. For the general heterogeneous case in which the erasure channel to receiver j has loss probability p<sub>j</sub>, the Whittle index corresponding to each flow is Sigma<sub>j</sub> (1- p<sub>j</sub>), where the sum is over all multicast receivers who are yet to receive the packet. We bound the performance of the optimal Whittle relaxation with respect to the optimal wireless multicast real-time scheduler. The heuristic index policy that schedules the flow with the maximum Whittle index in each slot is simple. To relax the comple- te feedback assumption, we design a scalable mechanism based on statistical estimation theory that obtains the required feedback from all the receivers using a single ACK per packet transmission. The resultant policy is amenable to low-complexity implementation.
    INFOCOM 2008. The 27th Conference on Computer Communications. IEEE; 05/2008
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    ABSTRACT: We consider the scheduling of multiclass jobs with deadlines to the completion of their service. Deadlines are deterministic and job arrivals in each class occur at the times of deadline expirations in the respective class. Assuming geometric service times with class dependent means, we derive structural properties of preemptive server allocation policies that maximize the expected number of job completions. Our work extends results that have appeared in the real-time wireless scheduling literature.
    Journal of Scheduling 08/2013; 16(4). DOI:10.1007/s10951-012-0293-x · 1.19 Impact Factor

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