Performance evaluation of a decoupling inventory for hybrid push-pull systems

Nowadays, companies that oer product variety while maintaining short lead times and competitive quality and cost, gain a competitive edge over their competitors. Therefore, hybrid push-pull systems allow for efficiently balancing lead times and production costs. Raw materials are `pushed' into the semi-finished good warehouse and customers `pull' products by placing orders. As performance of the decoupling stock is critical to the overall performance of the manufacturing system, we define and analyse a Markovian queueing model with two buers, thereby accounting for both the decoupling stock as well as for possible backlog of orders. In particular, our study assesses the eect of variability in the production process and the ordering process on the performance of the decoupling stock

Stochastic modelling of energy harvesting for low power sensor nodes

Battery lifetime is a key impediment to long-lasting low power sensor nodes. Energy or power harvesting mitigates the ependency on battery power, by converting ambient energy into electrical energy. This energy can then be used by the device for data collection and transmission. This paper proposes and analyses a queueing model to assess performance of such an energy harvesting sensor node. Accounting for energy harvesting, data collection and data transmission opportunities, the sensor node is modelled as a paired queueing system. The system has two queues, one representing accumulated energy and the other being the data queue. By means of some numerical examples, we investigate the energy-information trade-off

Setting the parameters right for two-hop IEEE 802.11e ad hoc networks

Two-hop ad-hoc networks, in which some nodes forward traffic for multiple sources, with which they also compete for channel access suffer from large queues building up in bottleneck nodes. This problem can often be alleviated by using IEEE 802.11e to give preferential treatment to bottleneck nodes. Previous results have shown that differentiation parameters can be used to allocate capacity in a more efficient way in the two-hop scenario. However, the overall throughput of the bottleneck may differ considerably, depending on the differentiation method used. By applying a very fast and accurate analysis method, based on steady-state analysis of an QBD-type infinite Markov chain, we find the maximum throughput that is possible per differentiation parameter. All possible parameter settings are explored with respect to the maximum throughput conditioned on a maximum buffer occupancy. This design space exploration cannot be done with network simulators like NS2 or Opnet, as each simulation run simply takes to long.\ud The results, which have been validated by detailed simulations, show that by differentiating TXOP it is possible to achieve a throughput that is about 50% larger than when differentiating AIFS and CW_min.\u

A Maclaurin-series expansion approach to coupled queues with phase-type distributed service times

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