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Wireless Local Area Networks (WLANs) have gained popularity at an unprecedented rate, at home, at work and in public hot spot locations. In this thesis, a Selectivity Function Scheduler (SFS) is proposed for IEEE 802.11e WLANs. The SFS aims at providing Quality of Service (QoS) assurance for different traffic types such as delay bound and throughput while maintaining fairness among flows and accommodating fluctuations of real-time applications. The SFS defines several functionalities that accurately analyze and compute the number of data frames at each traffic stream’s transmission queue, and allocate adaptive transmission opportunities (TXOPs) to traffic streams based on online observed physical rate instead of minimum physical rate. Moreover, the SFS incorporates a selectivity function (SF) that differentiates between traffic streams and assigns polling priorities accordingly. SFS appropriately calculates variable service interval lengths depending on actual traffic conditions. The SFS scheme is evaluated under different mixes of traffic and for various characteristics of the IEEE 802.11e and compared with the performance of the standard scheduler. Simulation results indicate that the SFS scheme achieves better system performance in terms of high throughput and low packet drop ratio, succeeds in providing QoS assurance for both constant bit rate (CBR) and variable bit rate (VBR) traffic. The SFS scheme also shows higher fairness among users of a same class, as well as between different classes. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2008-08-27 14:20:34.806

Real-time systems are those whose correctness depends not only on logical results of computations, but also on the time at which the results are produced. This thesis provides a formal definition for real-time systems and includes the following original contributions on real-time scheduling algorithms. The first topic studied in the thesis is minimizing the total penalty to be paid in scheduling a set of soft real-time tasks. The problem is NP-hard. We prove the properties of any optimal scheduling algorithm. We also derive a number of heuristic algorithms which satisfy the properties obtained. Moreover, we obtain a tight upper bound for the optimal solution to the problem. Numerical results that compare the upper bound with the optimal solution and the heuristic algorithms are provided. In the second part of this thesis, we study the problem of minimizing the number of processors required for scheduling a set of periodic preemptive independent hard real-time tasks. We use a partitioning strategy with an EDF scheduling algorithm on each processor. The problem is NP-hard. We derive lower and upper bounds for the number of processors required to satisfy the constraints of the problem. We also compare a number of heuristic algorithms with each other and with the bounds derived in this research. Numerical results demonstrate that our lower bound is very tight. In the third part of the thesis, we study the problem of uplink scheduling in telecommunication systems with two dimensional resources. Our goal is to maximize the total value of the packets sent in uplink subframe such that system constraints and requirements are satisfied. The packets have various QoS requirements and have either soft or hard deadlines. We take two approaches, namely 0-1 and fractional approaches, to model the problem. Considering the properties of the application, we derive globally optimal solutions in polynomial time for the models. We also present a method to fine-tune the models. Numerical results are provided to compare the performance of the various optimal algorithms each corresponding to a model. / Thesis (Ph.D, Computing) -- Queen's University, 2009-04-24 08:22:04.238