This thesis addresses handoff issues in a WCDMA system with space-time block coded transmit antenna diversity. Soft handoff has traditionally been used in CDMA systems because of its ability to provide an improved link performance due to the inherent macro diversity. Next generation systems will incorporate transmit diversity schemes employing several transmit antennas at the base station. These schemes have been shown to improve downlink transmission performance especially capacity and quality. This research investigates the possibility that the diversity obtained through soft handoff can be compensated for by the diversity obtained in a transmit diversity system with hard handoff. We analyze the system for two performance measures, namely, the probability of bit error and the outage probability, in order to determine whether the improvement in link performance, as a result of transmit diversity in a system with hard handoffs obviates the need for soft handoffs.

Conventional TCP is window based, which exploits the sliding window mechanism to conduct the flow control. It increases the sending window additively and decreases the sending window multiplicatively in response to successful transmission and, packet loss/timeout events respectively. While the mechanism works quite well in normal networks, TCP can hardly reach the ideal bandwidth utilization in long fat networks (LFNs) due to long delay and bursts of packet losses. Besides, as wireless and mobile computing has become popular today, packet loss in such networks may occur due to noise, interference and handoff across different domains. TCP could not react to different situations effectively as it sees all packet losses as an indication of network congestion. In this thesis, we proposed a new transmission control mechanism called Active Rate Anchoring TCP (ARCH-TCP). In ARCH-TCP, we explicitly integrate bandwidth measurement into TCP to solve the aforementioned problem. Specifically, we exploit packet-pair measurement to quickly estimate bandwidth share and then RTT variation is observed to compensate measurement error. We built the model in J-Sim network simulator to evaluate the effectiveness of our proposal. We found that ARCH-TCP can react to network conditions quickly and precisely in both wired and wireless networks and both in the normal networks and LFNs.

An adaptive resource reservation and handoff priority scheme, which jointly considers the characteristics from the physical, link and network layers, is proposed for a packet switching Multicode (MC)-CDMA cellular network supporting multimedia applications. A call admission region is derived for call admission control (CAC) and handoff management with the satisfaction of quality of service (QoS) requirements for all kinds of multimedia traffic, where the QoS parameters include the wireless transmission bit error rate (BER), the packet loss rate (PLR) and delay requirement. The BER requirement is guaranteed by properly arranging simultaneous packet transmissions, whereas the PLR and delay requirements are guaranteed by the proposed packet scheduling and partial packet integration scheme. To give service priority to handoff calls, a threshold-based adaptive resource reservation scheme is proposed on the basis of a practical user mobility model and a proper handoff request prediction scheme. The resource reservation scheme gives handoff calls a higher admission priority over new calls, and is designed to adjust the reservation-request time threshold adaptively according to the varying traffic load. The individual reservation requests form a common reservation pool, and handoff calls are served on a first-come-first-serve basis. By exploiting the transmission rate adaptability of video calls to the available radio resources, the resources freed from rate-adaptive high-quality video calls by service degradation can be further used to prioritize handoff calls. With the proposed resource reservation and handoff priority scheme, the dynamic properties of the system can be closely captured and a better grade of service (GoS) in terms of new call blocking and handoff call dropping probabilities(rates) can be achieved compared to other schemes in literature. Numerical results are presented to show the improvement of the GoS performance and the efficient utilization of the radio resources.

An adaptive resource reservation and handoff priority scheme, which jointly considers the characteristics from the physical, link and network layers, is proposed for a packet switching Multicode (MC)-CDMA cellular network supporting multimedia applications. A call admission region is derived for call admission control (CAC) and handoff management with the satisfaction of quality of service (QoS) requirements for all kinds of multimedia traffic, where the QoS parameters include the wireless transmission bit error rate (BER), the packet loss rate (PLR) and delay requirement. The BER requirement is guaranteed by properly arranging simultaneous packet transmissions, whereas the PLR and delay requirements are guaranteed by the proposed packet scheduling and partial packet integration scheme. To give service priority to handoff calls, a threshold-based adaptive resource reservation scheme is proposed on the basis of a practical user mobility model and a proper handoff request prediction scheme. The resource reservation scheme gives handoff calls a higher admission priority over new calls, and is designed to adjust the reservation-request time threshold adaptively according to the varying traffic load. The individual reservation requests form a common reservation pool, and handoff calls are served on a first-come-first-serve basis. By exploiting the transmission rate adaptability of video calls to the available radio resources, the resources freed from rate-adaptive high-quality video calls by service degradation can be further used to prioritize handoff calls. With the proposed resource reservation and handoff priority scheme, the dynamic properties of the system can be closely captured and a better grade of service (GoS) in terms of new call blocking and handoff call dropping probabilities(rates) can be achieved compared to other schemes in literature. Numerical results are presented to show the improvement of the GoS performance and the efficient utilization of the radio resources.

The promising development of wireless technologies has brought in an increasing demand of multimedia traffic. Since various types of traffic are inherently distinct in bandwidth requirements, delay sensitivities, and error tolerances, an adequate bandwidth allocation scheme is essential for the limited radio resource to fulfill different QoS (quality of service) requirements in mobile wireless networks. In this dissertation, we present a generalized channel preemption scheme (the GCPM) and a jamming-based medium access control with dynamic priority adjustment (the JMDPA) for the two different medium access models of a mobile wireless network, grant/request-based and contention-based, respectively. In the proposed GCPM, a mobile call is identified by four parameters, call type, traffic class, channel requirement, and preemption ratio. To effectively reduce dropping probability, high-priority handoff calls are allowed to fully or partially preempt low-priority ongoing calls when the mobile network becomes congested. An analytical model with multi-dimensional Markov chains is introduced to simultaneously investigate the effect of full and partial preemptions on the performance of a mobile wireless network. On the other hand, the proposed JMDPA scheme prioritizes a mobile node with two priorities, local and global; both of the local and global priorities can be dynamically changed based on the outcome in every contention round. Thus, any possible starvation of low-priority traffic or any ineffective contention of high-priority traffic can be avoided. A multi-dimensional Markov model, together with the scalability analysis, is introduced to evaluate the performance of the proposed JMDPA. The analytical results provide very useful guidelines to tune the QoS parameters for supporting prioritized multimedia traffic.

Today¡¦s mobile IP supports host mobility by dynamic changing IP addresses while the mobile host roaming in the Internet. However, There still exists performance problems during handoffs, such as packet loss, throughput degradation, and so on. In this Thesis, we propose a mechanism to reduce packet loss during handoff. The packet buffering mechanism at a home agent is initiated by mobile hosts when the signal-to-noise ratio of the wireless link falls below some predefined threshold. Once the handoff has completed, the home agent immediately delivers the first packet in the buffer to the mobile host. The home agent then clears the buffered packets already received by the mobile host through the returned ACK such that no further duplicate packets are sent out. In addition, we propose a route-selection policy to reduce end-to-end transmission delay by sending out probe packets along the paths. For the purpose of demonstration, we implement the mechanism on Linux platform. Through the measurements from the experiment, we have shown that the proposed mechanism can improve the throughput and solve the packet retransmission problem while handoffs.

This thesis addresses handoff issues in a WCDMA system with space-time block coded transmit antenna diversity. Soft handoff has traditionally been used in CDMA systems because of its ability to provide an improved link performance due to the inherent macro diversity. Next generation systems will incorporate transmit diversity schemes employing several transmit antennas at the base station. These schemes have been shown to improve downlink transmission performance especially capacity and quality. This research investigates the possibility that the diversity obtained through soft handoff can be compensated for by the diversity obtained in a transmit diversity system with hard handoff. We analyze the system for two performance measures, namely, the probability of bit error and the outage probability, in order to determine whether the improvement in link performance, as a result of transmit diversity in a system with hard handoffs obviates the need for soft handoffs.

With the advance of wireless access technologies, the IEEE 802.11 wireless local area network (WLAN) has gained significant increase in popularity and deployment due to the substantially improved transmission rate and decreased deployment costs. However, this same widespread deployment makes WLANs an attractive target for network attacks. Several vulnerabilities have been identified and reported regarding the security of the current 802.11 standards. To address those security weaknesses, IEEE standard committees proposed the 802.11i amendment to enhance WLAN security. The 802.11i standard has demonstrated the capability of providing satisfactory mutual authentication, better data confidentiality, and key management support, however, the design of 802.11i does not consider network availability. Therefore, it has been suggested that 802.11i is highly susceptible to malicious denial-of-service (DoS) attacks, which exploit the vulnerability of unprotected management frames. This research first investigates common DoS vulnerabilities in a Robust Security Network (RSN), which is defined in the 802.11i standard, and presents an empirical analysis of such attacks – in particular, flooding-based DoS attacks. To address those DoS issues, this thesis proposes a novel design and implementation of a lightweight stateless authentication scheme that enables wireless access points (APs) to establish a trust relationship with an associating client and derive validating keys that can be used to mutually authenticate subsequent layer-2 (link layer) management frames. The quality of service provisioning for real-time services over a WLAN requires the total latency of handoff between APs to be small in order to achieve seamless roaming. Thus, this thesis further extends the proposed link-layer authentication into a secure fast handoff solution that addresses DoS vulnerabilities as well as improving the existing 802.11i handoff performance. A location management scheme is also proposed to minimise the number of channels required to scan by the roaming client in order to reduce the scanning delay, which could normally take up 90% of the total handoff latency. In order to acquire practical data to evaluate the proposed schemes, a prototype network has been implemented as an experimental testbed using open source tools and drivers. This testbed allows practical data to be collected and analysed. The result successfully demonstrated that not only the proposed authentication scheme eradicates most of the DoS vulnerabilities, but also substantially improved the handoff performance to a level suitable for supporting real-time services.

Communication competence and medical communication competence served as the theoretical framework for this research that seeks to identify specific communication behaviors associated with what nurses say constitute a communicatively competent patient handoff at the nursing change of shift. Data collected from 286 nurses responding to an online modified Medical Communication Competence Scale posted at www.allnurses.com supported the hypotheses that information exchange (information giving, seeking and verifying) and socioemotional communication behaviors are rated more highly in the best patient handoffs than in the worst ones. Research questions found that the incoming nursing role rated behaviors associated with information verifying and socioemotional communication higher than did the outgoing nursing role, and that the worst handoffs were those in which the incoming nursing role gave the lowest ratings for information-giving behaviors. Additional insight into other communication-related characteristics associated with quality handoffs were provided as well, including location, tools/type and environment for the patient handoff at the nursing change of shift. These findings offer a foundation for future research into development of communication-based standardized patient handoff processes and training that ultimately may reduce patient care errors caused by communication failures during the patient handoff at the nursing change of shift.

The recent advancements in the communication area have enabled the Internet of Things, a paradigm which extends the Internet to everyday objects. The Internet of Things enables many new applications, but also comes with great challenges; effective communication under limited power supply being the perhaps most important one. This thesis presents the design, implementation, and evaluation of an energy-efficient handover algorithm for the main building block in the creation of the Internet of Things: wireless sensor networks. Our low-power handover design is based on a careful breakdown and analysis of the potential power consumption of different components of the handover process. With the scanning part of the process being identified as the main drain of energy, the algorithm is designed to place the majority of the scanning responsibility on the mains powered access points, rather than on the low-power mobile nodes. The proposed algorithm has been implemented and its functionality and low power consumption have been empirically evaluated. We show that the design can reduce the energy consumption by several orders of magnitude compared to existing handover algorithms for wireless sensor networks. In addition, interesting fading effects were discovered in a sparsely deployed network scenario with limited access point coverage; most likely due to multipath propagation. For this case the handover performance was greatly reduced, relative our more normal coverage scenario. While these results illustrate that the absolute energy savings will differ from scenario to scenario, the potential energy savings made possible by the proposed algorithm significantly reduce the battery requirements of the devices in the emerging landscape of the Internet of Things; potentially even opening the door for new devices to connect.