1,330 research outputs found
Scheduling for next generation WLANs: filling the gap between offered and observed data rates
In wireless networks, opportunistic scheduling is used to increase system throughput by exploiting multi-user diversity. Although recent advances have increased physical layer data rates supported in wireless local area networks (WLANs), actual throughput realized are significantly lower due to overhead. Accordingly, the frame aggregation concept is used in next generation WLANs to improve efficiency. However, with frame aggregation, traditional opportunistic schemes are no longer optimal. In this paper, we propose schedulers that take queue and channel conditions into account jointly, to maximize throughput observed at the users for next generation WLANs. We also extend this work to design two schedulers that perform block scheduling for maximizing network throughput over multiple transmission sequences. For these schedulers, which make decisions over long time durations, we model the system using queueing theory and determine users' temporal access proportions according to this model. Through detailed simulations, we show that all our proposed algorithms offer significant throughput improvement, better fairness, and much lower delay compared with traditional opportunistic schedulers, facilitating the practical use of the evolving standard for next generation wireless networks
Resource Allocation in Ad Hoc Networks
Unlike the centralized network, the ad hoc network does not have any central administrations and energy is constrained, e.g. battery, so the resource allocation plays a
very important role in efficiently managing the limited energy in ad hoc networks.
This thesis focuses on the resource allocation in ad hoc networks and aims to develop
novel techniques that will improve the network performance from different network
layers, such as the physical layer, Medium Access Control (MAC) layer and network
layer.
This thesis examines the energy utilization in High Speed Downlink Packet Access (HSDPA) systems at the physical layer. Two resource allocation techniques,
known as channel adaptive HSDPA and two-group HSDPA, are developed to improve the performance of an ad hoc radio system through reducing the residual
energy, which in turn, should improve the data rate in HSDPA systems. The channel adaptive HSDPA removes the constraint on the number of channels used for
transmissions. The two-group allocation minimizes the residual energy in HSDPA
systems and therefore enhances the physical data rates in transmissions due to adaptive modulations. These proposed approaches provide better data rate than rates
achieved with the current HSDPA type of algorithm.
By considering both physical transmission power and data rates for defining the
cost function of the routing scheme, an energy-aware routing scheme is proposed
in order to find the routing path with the least energy consumption. By focusing
on the routing paths with low energy consumption, computational complexity is
significantly reduced. The data rate enhancement achieved by two-group resource
allocation further reduces the required amount of energy per bit for each path. With
a novel load balancing technique, the information bits can be allocated to each path
in such that a way the overall amount of energy consumed is minimized.
After loading bits to multiple routing paths, an end-to-end delay minimization
solution along a routing path is developed through studying MAC distributed coordination function (DCF) service time. Furthermore, the overhead effect and the
related throughput reduction are studied. In order to enhance the network throughput at the MAC layer, two MAC DCF-based adaptive payload allocation approaches
are developed through introducing Lagrange optimization and studying equal data
transmission period
Improving the Performance of Wireless LANs
This book quantifies the key factors of WLAN performance and describes methods for improvement. It provides theoretical background and empirical results for the optimum planning and deployment of indoor WLAN systems, explaining the fundamentals while supplying guidelines for design, modeling, and performance evaluation. It discusses environmental effects on WLAN systems, protocol redesign for routing and MAC, and traffic distribution; examines emerging and future network technologies; and includes radio propagation and site measurements, simulations for various network design scenarios, numerous illustrations, practical examples, and learning aids
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