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In periodic wireless broadcasting, air behaves like a storage medium requiring new data organization and access methods.Due to power limit for the portable units (ex. the palmtop), how to design an energy-saving organization is a key issue.Imielinski et al. have proposed the hashing based schemes, including the Hashing A and Hashing B schemes, to save energy in the progress of getting data of interest. The Hashing B scheme improves the directory miss phenomenon in the Hashing A scheme, where the directory miss is that the client's initial probe comes before the bucket containing his key but after the bucket which contains a proper offset. However, based on these two schemes, if the differences between the minimum overflow and the other overflows are large extremely or the small overflows appear near the rear part of the broadcast file, both schemes have a poor performance. Therefore, in this thesis, we propose four multiple-hashing-functions-based schemes, including the FirstR, FirstL, AvgK and TopK schemes, to overcome such the situations. The basic idea is to use cutlines to divide the broadcast file with N logical buckets into several regions, and then each region may have the different minimum overflow. Since the minimum overflow in each region can be different, we can have different hashing functions for those regions to determine the positions of the designated buckets. Among the proposed schemes, the difference is how to determine the positions of the cutlines. The FirstR scheme finds those cutlines from the right end to the left whenever the difference of overflows of two adjacent logical buckets is greater than or equal to 1. The FirstL scheme finds those cutlines from the left end to the right whenever the difference of overflows of two adjacent logical buckets is greater than or equal to 1. In the AvgK scheme, we first calculate AvgD, the average of the differences of two consecutive overflows whose values are large than or equal to 1. Then we find cutlines from the left end to the right whenever the difference of two adjacent logical buckets is greater than or equal to AvgD. The TopK determines the cutlines by considering the descending order of the differences of overflows. From our performance analysis and simulation study, the performance of the TopK scheme is the best among the proposed schemes. Therefore, we then make a comparison between the TopK scheme and the Hashing B scheme. Since the number of the hashing functions in the TopK scheme is larger than those in the Hashing B, the physical bucket in the TopK scheme is somewhat bigger than that in the m Hashing B scheme. In our simulation, we have considered this factor as well. From our performance analysis and simulation study, we show that the performance of the TopK scheme performs better than that of the Hashing B scheme, even though the above factor about the storage size is considered. The TopK scheme improves the directory miss in the Hashing B scheme; therefore, the average access time is improved excellently.

Efficiency and power conservation are critical issues in the design of cluster systems because these two parameters have direct implications on the user experience and the global need to conserve power. Widely adopted, distributor-based systems forward client requests to a balanced set of waiting servers in complete transparency to the clients. The policy employed in forwarding requests from the front-end distributor to the backend servers plays an important role in the overall system performance. Existing research separately addresses server performance and power conservation. The locality-aware request distribution (LARD) scheme improves the system response time by having the requests served by web servers which have the data in their cache. The power-aware request distribution aims at reducing the power consumption by turning the web servers OFF and ON according to the load. This research tries to achieve power conservation while preserving the performance of the system. First, we prove that using both power-aware and locality-aware request distribution together provides optimum power conservation, while still maintaining the required QoS of the system. We apply the usage of pinned memory in the backend servers to boost performance along with a request distributor design based on power and locality considerations. Secondly, we employ an intelligent-proactive-distribution policy at the front-end to improve the distribution scheme and complementary pre-fetching at the backend server nodes. The proactive distribution depends on both online and offline analysis of the website log files, which capture user navigation patterns on the website. The prefetching scheme pre-fetches the web pages into the memory based on a confidence value of the web page predicted by backend using the log file analysis. Designed to work with the prevailing web technologies, such as HTTP 1.1, our scheme provides reduced response time to the clients and improved power conservation at the backend server cluster. Simulations carried out with traces derived from the log files of real web servers witness performance boost of 15-45% and 10-40% power conservation in comparison to the existing distribution policies.

No description available.

Zheng, Xiaoting. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (p. 64-69). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgement --- p.iii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Rayleigh Fading --- p.1 / Chapter 1.2 --- Transmission Schemes --- p.2 / Chapter 1.2.1 --- Frequency Division Multiple Access(FDMA) --- p.2 / Chapter 1.2.2 --- Time Division Multiple Access(TDMA) --- p.3 / Chapter 1.2.3 --- Code Division Multiple Access(CDMA) --- p.5 / Chapter 1.2.4 --- The Broadcast Channel --- p.5 / Chapter 1.3 --- Cooperative Transmissions --- p.9 / Chapter 1.3.1 --- Relaying Protocols --- p.10 / Chapter 1.4 --- Outline of Thesis --- p.12 / Chapter 2 --- Background Study --- p.13 / Chapter 2.1 --- Superposition Coding --- p.13 / Chapter 2.2 --- Cooperative Transmission --- p.15 / Chapter 2.2.1 --- Single Source Single Destination --- p.15 / Chapter 2.2.2 --- Multiple Sources Single Destination --- p.16 / Chapter 2.2.3 --- Single Source Multiple Destinations --- p.17 / Chapter 2.2.4 --- Multiple Sources Multiple Destinations --- p.17 / Chapter 2.3 --- Power Minimization --- p.18 / Chapter 2.3.1 --- Power Minimization in Code-Multiplexing System --- p.19 / Chapter 2.3.2 --- Power Minimization in Frequency-multiplexing System --- p.19 / Chapter 2.3.3 --- Power Minimization in Time-Multiplexing System --- p.20 / Chapter 3 --- Sum Power Minimization with Superposition Coding --- p.21 / Chapter 3.1 --- System Model --- p.22 / Chapter 3.2 --- Superposition Coding Scheme --- p.22 / Chapter 3.2.1 --- Optimal Superposition Coding Scheme --- p.22 / Chapter 3.2.2 --- Sub-optimal Superposition Coding Scheme --- p.27 / Chapter 3.3 --- Performance Evaluation --- p.30 / Chapter 3.4 --- Assignment Examples for Superposition Coding Scheme --- p.33 / Chapter 4 --- Source-cooperated Transmission in a Wireless Cluster --- p.42 / Chapter 4.1 --- System Model --- p.42 / Chapter 4.2 --- Selection Protocol --- p.44 / Chapter 4.2.1 --- Protocol Description and Problem Formulation --- p.44 / Chapter 4.2.2 --- Distributed Selection Algorithm --- p.46 / Chapter 4.2.3 --- Low Rate Regime --- p.50 / Chapter 4.3 --- Simulation Results --- p.52 / Chapter 4.3.1 --- Simulation Configuration --- p.53 / Chapter 4.3.2 --- Cases with a Smaller Feasible Solution Set --- p.53 / Chapter 4.3.3 --- Cases with a Larger Feasible Solution Set --- p.56 / Chapter 5 --- Conclusion and Future Work --- p.61 / Chapter 5.1 --- Conclusion --- p.61 / Chapter 5.2 --- Future Work --- p.62 / Chapter 5.2.1 --- Fairness --- p.62 / Chapter 5.2.2 --- Distributed Algorithm --- p.63 / Chapter 5.2.3 --- Game Theory --- p.63 / Chapter 5.2.4 --- Distributed Information --- p.63 / Bibliography --- p.64

Wireless sensor networks suffer from limited power resources. Therefore, managing the energy constraints and exploring new ways to minimize the power consumption during the operation of the nodes are critical issues. Conventional MAC protocols deal with this problem without considering the internal properties of the sensor nodes’ batteries. However, recent studies about battery modeling and behaviour showed that the pulsed discharge mechanism and the charge recovery effect may have a significant impact on wireless communication in terms of power saving. In this thesis we propose two battery-aware MAC protocols that take benefit of these factors to save more energy and to prolong the lifetime of the nodes/network without affecting the throughput. In both protocols we measure the remaining battery capacity of the node and use that measurement in the back-off scheme. The first protocol gives the nodes with higher remaining battery capacity more priority to access the medium, while the other one provides more medium access priority to the nodes with lower remaining battery capacity. The objective is to investigate, through simulations, which protocol reduces the power consumption of the nodes, improve the lifetime of the network, and compare the results with the CSMA-CA protocol.

Wireless sensor networks suffer from limited power resources. Therefore, managing the energy constraints and exploring new ways to minimize the power consumption during the operation of the nodes are critical issues. Conventional MAC protocols deal with this problem without considering the internal properties of the sensor nodes’ batteries. However, recent studies about battery modeling and behaviour showed that the pulsed discharge mechanism and the charge recovery effect may have a significant impact on wireless communication in terms of power saving. In this thesis we propose two battery-aware MAC protocols that take benefit of these factors to save more energy and to prolong the lifetime of the nodes/network without affecting the throughput. In both protocols we measure the remaining battery capacity of the node and use that measurement in the back-off scheme. The first protocol gives the nodes with higher remaining battery capacity more priority to access the medium, while the other one provides more medium access priority to the nodes with lower remaining battery capacity. The objective is to investigate, through simulations, which protocol reduces the power consumption of the nodes, improve the lifetime of the network, and compare the results with the CSMA-CA protocol.

Wireless sensor networks suffer from limited power resources. Therefore, managing the energy constraints and exploring new ways to minimize the power consumption during the operation of the nodes are critical issues. Conventional MAC protocols deal with this problem without considering the internal properties of the sensor nodes’ batteries. However, recent studies about battery modeling and behaviour showed that the pulsed discharge mechanism and the charge recovery effect may have a significant impact on wireless communication in terms of power saving. In this thesis we propose two battery-aware MAC protocols that take benefit of these factors to save more energy and to prolong the lifetime of the nodes/network without affecting the throughput. In both protocols we measure the remaining battery capacity of the node and use that measurement in the back-off scheme. The first protocol gives the nodes with higher remaining battery capacity more priority to access the medium, while the other one provides more medium access priority to the nodes with lower remaining battery capacity. The objective is to investigate, through simulations, which protocol reduces the power consumption of the nodes, improve the lifetime of the network, and compare the results with the CSMA-CA protocol.

Wireless sensor networks suffer from limited power resources. Therefore, managing the energy constraints and exploring new ways to minimize the power consumption during the operation of the nodes are critical issues. Conventional MAC protocols deal with this problem without considering the internal properties of the sensor nodes’ batteries. However, recent studies about battery modeling and behaviour showed that the pulsed discharge mechanism and the charge recovery effect may have a significant impact on wireless communication in terms of power saving. In this thesis we propose two battery-aware MAC protocols that take benefit of these factors to save more energy and to prolong the lifetime of the nodes/network without affecting the throughput. In both protocols we measure the remaining battery capacity of the node and use that measurement in the back-off scheme. The first protocol gives the nodes with higher remaining battery capacity more priority to access the medium, while the other one provides more medium access priority to the nodes with lower remaining battery capacity. The objective is to investigate, through simulations, which protocol reduces the power consumption of the nodes, improve the lifetime of the network, and compare the results with the CSMA-CA protocol.

With the developments in computing and communication technologies, wireless sensor networks have become popular in wide range of application areas such as health, military, environment and habitant monitoring. Moreover, wireless acoustic sensor networks have been widely used for target tracking applications due to their passive nature, reliability and low cost. Traditionally, acoustic sensor arrays built in linear, circular or other regular shapes are used for tracking acoustic sources. The maintaining of relative geometry of the acoustic sensors in the array is vital for accurate target tracking, which greatly reduces the flexibility of the sensor network. To overcome this limitation, we propose using only a single acoustic sensor at each sensor node. This design greatly improves the flexibility of the sensor network and makes it possible to deploy the sensor network in remote or hostile regions through air-drop or other stealth approaches. Acoustic arrays are capable of performing the target localization or generating the bearing estimations on their own. However, with only a single acoustic sensor, the sensor nodes will not be able to generate such measurements. Thus, self-organization of sensor nodes into virtual arrays to perform the target localization is essential. We developed an energy-efficient and distributed self-organization algorithm for target tracking using wireless acoustic sensor networks. The major error sources of the localization process were studied, and an energy-aware node selection criterion was developed to minimize the target localization errors. Using this node selection criterion, the self-organization algorithm selects a near-optimal localization sensor group to minimize the target tracking errors. In addition, a message passing protocol was developed to implement the self-organization algorithm in a distributed manner. In order to achieve extended sensor network lifetime, energy conservation was incorporated into the self-organization algorithm by incorporating a sleep-wakeup management mechanism with a novel cross layer adaptive wakeup probability adjustment scheme. The simulation results confirm that the developed self-organization algorithm provides satisfactory target tracking performance. Moreover, the energy saving analysis confirms the effectiveness of the cross layer power management scheme in achieving extended sensor network lifetime without degrading the target tracking performance.