Object handoff – that is, passing an object or tool to another person – is an extremely common activity in collaborative tabletop work. On digital tables, object handoff is typically accomplished by sliding the object on the table surface – but surface-only interactions can be slow and error-prone, particularly when there are multiple people carrying out multiple handoffs. An alternative approach is to use the space above the table for object handoff; this provides more room to move, but requires above-surface tracking. I developed two above-the-surface handoff techniques that use simple and inexpensive tracking: a force-field technique that uses a depth camera to determine hand proximity, and an electromagnetic-field technique called ElectroTouch that provides positive indication when people touch hands over the table. These new techniques were compared to three kinds of existing surface-only handoff (sliding, flicking, and surface-only Force-Fields). The study showed that the above-surface techniques significantly improved both speed and accuracy, and that ElectroTouch was the best technique overall. Also, as object interactions are moved above-the-surface of the table the representation of off-table objects becomes crucial. To address the issue of off-table digital object representation several object designs were created an evaluated. The result of the present research provides designers with practical new techniques for substantially increasing performance and interaction richness on digital tables.

Heterogeneous wireless networks will be dominant in the next-generation wireless networks with the integration of various wireless access networks. Wireless mesh networks will become to a key technology as an economically viable solution for wide deployment of high speed, scalable and ubiquitous wireless Internet services. In this thesis, we consider an interworking architecture of wireless mesh backbone and propose an effective vertical handoff scheme between 802.11 and 802.16 wireless access networks. The proposed vertical handoff scheme aims at reducing handoff signaling overhead on the wireless backbone and providing a low handoff delay to mobile nodes. The handoff signaling procedure in different scenarios is discussed. Together with call admission control, the vertical handoff scheme directs a new call request in the 802.11 network to the 802.16 network, if the admission of the new call in the 802.11 network can degrade quality-of-service (QoS) of the existing real-time traffic flows. Simulation results demonstrate the performance of the handoff scheme with respect to signaling cost, handoff delay, and QoS support.

With recent growth in mobile components and advances in wireless communication technology, mobile computing is an increasingly important area of research. Enabling mobility in IP networks becomes more and more significant. Mobile IP is the only current means for offering seamless roaming to mobile computers in the Internet. It has recently progressed along the ladder to standardization within the Internet Engineering Task Force (IETF). However, Mobile IP suffers from so-called triangular-routing problem and packet loss due to handoff. In this paper, we propose a new architecture to solve these two problems noted above. We assume that network routers such as Home Agent¡BForeign Agent¡BGeneral Router can equip our Pre-Accessing Engine (Mobile IP Engine) to access IP packets before IP routing Engine. With our Mobile IP table established in Mobile IP Engine, we can set up a transmission path for each correspondent node (CN) to transmit data to mobile node (MN). Therefore, we not only solve triangular-routing problem by direct transmission path, but also decrease handoff latency from path updating function. Furthermore, we use retransmission and flush schemes to avoid packet loss and out-of-order problems. Finally, we use simulation to prove our architecture is useful.

Mobile IPv6 supports host mobility by dynamically changing IP addresses while mobile nodes roaming in the Internet. However, there still exist performance problems during handoffs, such as handoff latency, packet loss. When a mobile node increases its mobility, performance degradation induced by frequent handoffs grows drastically. In this thesis, we propose a dual-tunnel with buffering (DTWB) mechanism to reduce packet loss ratio during multiple handoffs. Packet buffering at access routers is initiated by mobile nodes when the received signal strength goes below a predefined threshold. The buffered packets are forwarded through dual tunnels, of which the first tunnel is established between the old access router and the new access router, and the second tunnel is established between the new access router and the mobile nodes. For the purpose of evaluation, we perform experiments on NS-2 simulation. The simulation results demonstrate that our proposed mechanism can minimize the packet loss ratio and increase the throughput during multiple handoffs.

In this dissertation, we present mathematical analyses for a cellular CDMA communication system by investigating two important performance factors, the spreading code reservation periods and the cell coverage in soft handoff. First, an innovative code assignment scheme is presented by fully utilizing the characteristics of voice and data traffic. In other words, a voice terminal has higher priority to reserve a spreading code to transmit packets in multiple talk spurts, while a data terminal can only transmit packets by either employing the unassigned codes or borrowing the codes from the voice terminals during their silent periods. The code assignment scheme is then extended to analyze a priority-based CDMA system where the code reservation periods can be varied. Two performance measures, the average dropping probability for delay-sensitive traffic and the average packet delay for delay-insensitive traffic, are derived from the analytic models based on the equilibrium point analysis (EPA). Finally, for the cellular CDMA system, we study the influences of enlarging or shrinking the soft handoff coverage on the new-call blocking and the handoff-call dropping probabilities. From the mathematical analyses, we reveal that enlarging the outer cell while fixing the inner cell may significantly increase both blocking and dropping probabilities. On the other hand, if we enlarge the inner cell and fix the outer cell, the two probabilities can be reduced slightly. The impact of activating a call admission control on the proposed cellular CDMA system is also discussed.

A growing number of IEEE 802.11-based wireless LANs have been set up in many public places in the recent years. These wireless LANs provide convenient network connectivity to users. Although mobile nodes allowed roaming across wireless LANs, handoff latency becomes an obstacle when mobile nodes migrate between different IP networks. Advanced, the link-layer handoff process disrupts the association when a mobile node moves from one access point to another. Even without discussing the latency of Mobility Protocols, this link-layer handoff latency already made many real time applications can not meet their requirements. In this dissertation, it is proposed three schemes to solve the problems occurred in the different network layers. These schemes not only reduce the latency of whole handoff procedure but also have no violation to the existing specifications in the IEEE 802.11 standard and compatible with existing devices. L2-Optimize and AIL used to minimize the duration of link-layer handoff. With LASP, Mobility handoff can be reduced to an acceptable situation. Therefore, even real time applications can meet their requirements when users are roaming across wireless LANs.

Many different wireless technologies have increased the demand of accessing Internet resources through wireless networks. One of the most popular applications is watching multimedia streaming over wireless. However, when a user is roaming in a heterogeneous network, he needs to acquire adequate bandwidth from different wireless access points. In this Thesis, we propose a Mobile-IP based vertical handoff scheme in a heterogeneous WiMAX and WLAN. When a mobile node is in the overlapped area of WiMAX and WLAN, it may have to execute the vertical handoff based on the received average signal strength, the transmitting queue length of network interface, and the available network bandwidth. Our goal is to reduce the influences of RTP-based video streaming when the network is congested and when a mobile node executes the vertical handoff in the heterogeneous network. We implement the Dynamic Mobile-IP based vertical handoff on Linux platform by modifying handoff decisions between WiMAX and WLAN. The above-mentioned performance parameters are implemented as modules on Linux platform. At last, we prove that our scheme can effectively improve packet loss ratio and system processing ratio. As a result, the frame mosaic phenomenon and frame slow-playing phenomenon in RTP-based video streaming can be significantly improved.

The rapid growth of wireless and cellular technologies in recent years has brought in various applications in our daily life. Thus, the integration between WLAN and cellular networks has attracted more and more attention to researchers. In this Thesis, we proposed a preemptive channel allocation mechanism for WLAN-embedded cellular networks. In such integrated networking environments, frequent handoffs may result in dramatic performance degradation. In our model, a mobile node first utilizes the cellular network for supporting high mobility. However, the capacity of a BS is easily saturated. To minimize session blocking, a mobile node outside the WLAN coverage can preempt the channel(s) occupied by a mobile node inside the WLAN coverage. The preempted mobile node can still get access to the Internet through the AP of WLAN. For the purpose of performance evaluation, we build a three-dimension Markov Chain to analyze the proposed mechanism. We derive the residence time inside the WLAN coverage and outside the WLAN coverage, respectively. Finally, we evaluate the overall network performance in terms of the number of active sessions over WLAN, the channel utilization of a BS, the probability of session blocking, the preemption probability, and the preempted probability. From the evaluation, we observe the relative performance improvements of our proposed channel preemption mechanisms.

Pico-Cellular architecture fully reuses frequency to increase network capacity. However, it will increase the occurance of Handoff due to the small range of cell. Previous works in channel allocations can reduce blocking probability of handoff call, but it may increase blocking probability of new call. As a result, channel utilization is decreased because they can not adapt to network changes. In this thesis, we present a Dynamic Channel Allocation Mechanism with priority support. All channels and calls are divided into high and low priority. If there is no high_priority channel for high_priority call, high_priority call may downgrade its priority by sacrificing some QoS to utilize low_priority channels. We define two new array for network information status, one is next_cell state, and the other is the transition probability. Next_cell state is used to save prior M Cell_Ids where handoff calls may move to. Transition probability is used to save the probabilities for active calls moving to other neighboring cells. According to next_cell state and transition probability, we can accurately predict the probabilities for mobile hosts moving to other neighboring cells. Therefore, we can dynamically adjust bandwidth reservation requests sending to neighboring cells by the latest transition probability and the number of active calls in this cell. We analyze the proposed mechanism through a mathematical model. In the model, we build a four-dimension Markov Chain and use MATLAB[41] tool to evaluate blocking probability, channel throughput and utilization. We found out that blocking probability of handoff call can be decreased and channel utilization can be increased through the proposed channel allocation mechanisms with high and low priority support.

With the rapid growth of communication, applications in traffic sensor network such as the multimedia service Server Push, are indispensable to business advertising. The applications of server push, for example, the service Push Mail provided by ISP (Internet Service Provider), became much more hot and popular. This paper aims to design a mobile vehicular network to let the people who received the advertisement communicate with the providers of the service. Nevertheless, the handoff problem that arises when traveling brings down the quality of communication. Therefore, seamless handoff becomes a very important issue for us to research. This thesis uses the new SCTP (Stream Control Transmission Protocol) to solve the problem. SCTP not only keeps the advantages of TCP/IP but also provides new support. Allowing the user to own several IP addresses at the same time is one of its important characteristics, which allows you to switch to any other available IP immediately if the transmission is interruptted. With this characteristic, the user barely notices any interruption in the process of handoff. Finally, we propose a new design for SCTP to achieve a response time, and can be used in applications that require a fast response time.