Multimedia applications in wireless communication have shown notable increases over recent years. Specifically, Quality of Service (QoS) has become an important support mechanism in the context of a variety of applications which utilize network resources. The IEEE 802.16 standard for Wireless Metropolitan Area Networks (WirelessMAN) provides a complete QoS control structure designed to enable flow isolation and service differentiation over the common wireless interface. Although the media access control (MAC) mechanisms defined in this standard can offer predefined QoS provisioning on a pre-connection basis (additionally, many algorithms have been addressed to support QoS guarantees for various kinds of applications), the design for a stable, efficient and flexible MAC scheduling algorithm for such QoS provisioning still remains to be discovered. In this paper, we propose a QoS control scheme, Efficient Bandwidth Allocation (EBA), for the WirelessMAN system. Notably, this schedule enables predefined service parameters to control the service provided for each uplink connection and it provides each connection with different service opportunities such that the BS could allocate the most suitable bandwidth constantly for each connection with the various QoS parameters. Moreover, through MAC layer resource allocation, the proposed algorithm is capable of providing QoS guarantee for the SSs under different distance.

Full field characterization is an important issue for ultrafast optoelectronics. By suitable nonlinear constrain, several approaches, such as FROG, SPIDERS, MIIPS and so on, have been developed for providing detail information of optical pulses. However, phase matching bandwidth of nonlinear material limit the functionality for broadband signal. In this thesis, linear approach without limitation of phase matching bandwidth is proposed. Theoretically, we successfully demonstrated the feasibility of proposed method. We analyzed the limitation and discussed the pulse compression power with the proposed method. Besides, we also proposed experimental method for this method.

MPLS, the next-generation backbone architecture, can speed up packet forwarding via label switching. However, if the traversed LSPs (Label Switching Paths) are in congestion, traffic may encounter serious throughput degradation due to packet loss. This performance degradation may become worse and worse unless another forwarding LSP for these traffic flows are allocated. Moreover, in this Thesis, we propose a preemption mechanism for higher-priority flows to obtain necessary resources (the bandwidth of a LSP) by preempting low-priority traffic flows. In the multiple-flow preemption mechanism, several LSPs between Ingress router and Egress router are established to forward traffic flows. Some of these traffic flows are higher priority with stringent QoS requirements. If no satisfactory throughput can be met, Egress router would have to feedback average throughput values to Ingress router, which in turn decides how many lower-priority traffic flows should be preempted and moved to another LSP. Consequently, Ingress router has to send bandwidth reservation messages to reserve bandwidth just released by those lower-priority flows. After that, every core router can process these MPLS packets with specified traffic class to meet their QoS requirements. Finally, for the purpose of demonstration, we embed multiple flow preemption modules into MNS simulator and use it to run some experiments. Since in our scheme, it is not necessary to reserve bandwidth for higher-priority traffic flows in advance, the overall bandwidth utilization can be increased. Furthermore, the higher-priority flows can meet their QoS requirements by preempting the lower-priority flows whenever it is needed.

In this Thesis, we propose a Negotiable RSVP with Multiple Preemption for supporting dynamic bandwidth reservation. With the properties of negotiation and preemption, we can re-allocate bandwidth to effectively increase the probability of successful reservations of flows with higher priority. Different from RSVP, negotiable RSVP uses a priority mechanism with many parameters, such as upper-bound bandwidth and upper-bound priority. Negotiable RSVP transmits these parameters by sending Resv Messages such that every RSVP flow possesses individual priority levels. When the available bandwidth is not enough, the arriving new flows can negotiate with the existing reserved flows that have lower priorities. We then estimate the sum of the available bandwidth and the preemptive bandwidth from the reserved flows. If the sum satisfies the lower-bound bandwidth of the arriving new flow, the reservation is successful. At the best case, if the sum can meet its high-bound bandwidth, the system can reserve the high-bound bandwidth for the flow. However, if the sum is lower than its low-bound bandwidth, it will be rejected. To demonstrate the efficiency and feasibility of negotiable RSVP, we build two simulation models, RSVP and Negotiable RSVP, respectively, and compare their simulation results. We have shown that negotiable RSVP can perform better than RSVP in many ways. For example, the probability of successful reservation and the number of reserved flows are significantly increased. We also implement the negotiable RSVP on FreeBSD platform, and measure the percentages of improvements through various experiments.

In this thesis, we consider a network environment which consists of wired Internet and a wireless broadband network (WiMAX); data from wired or wireless network are all conveyed through WiMAX links to its destination. In order to promise the quality of real-time traffic and allow more transmission opportunity for other traffic types, we propose an Adaptive Bandwidth Allocation (ABA) algorithm for BS to adequately allocate bandwidth. Our ABA algorithm would first reserve required minimum bandwidth for high-priority traffic, such as video streaming. By allocating minimum bandwidth to real-time traffic, the delay time constraint can be satisfied. Other traffic types, such as non-real-time, which have no real-time requirement, may gain extra bandwidth to improve their throughput. For best-effort traffic, the remaining bandwidth can be used to avoid any possible starvation. We build four-dimension Markov chains to evaluate the performance of the proposed ABA algorithm. In the analytical model, we first divide transmission on WiMAX into upload and download phases, and analyze the ABA performance by using Poisson process to generate traffic. At last, by comparing to a previous work, we observe the impacts of different traffic parameters on WiMAX network performance in terms of average delay time, average throughput, and average packet-drop ratio.

In a WiMAX network, four traffic types with different priorities are defined. They are Unsolicited Grant Service (UGS), real-time Polling Service (rtPS), non-real-time Polling Service (nrtPS), and Best Effort (BE). In this thesis, we propose a Dynamic Bandwidth Allocation (DBA) scheme for BS to schedule the four above-mentioned traffic types. By adopting Deficit Round Robin (DRR) scheduling, DBA first assigns minimum quantum to each traffic type for transmission. When rtPS packets exceed their delay constraints, without sacrificing the minimum requirements of nrtPS and BE traffic, DBA borrows some quantum from nrtPS and BE to satisfy the delay requirements of rtPS traffic. When nrtPS packets can not reach the minimum transmission rate, without starving the BE traffic, DBA borrows some quantum from BE to support the required throughput of nrtPS traffic. According to the history record of borrowed quantum, DBA dynamically adjusts the assigned quantum for the three traffic types. For the purpose of evaluation, we use NS-2 to simulate the proposed DBA. We adjust the traffic load to analyze the performance in terms of average packet delay, average throughput, and average packet loss ratio. The simulation results show that the DBA, in comparison to a previous work, can promise the delay constraints of rtPS, maintain the average throughput of nrtPS, and avoid the starvation of BE, when the traffic load is high.

WiMAX (Worldwide Interoperability for Microwave Access) provides wide transmission range and broadband network services. However, in IEEE 802.16 standard, there is no specific definition for SS (Subscriber Station) to select an optimal route in a mesh-based WiMAX network. In this thesis, we propose an Optimal Route Selection Scheme (ORSS) for SS to select a route to its BS (Base Station). ORSS basically considers three influential factors, the bandwidth SS to be assigned, the number of interference nodes around SS, and the hop counts to BS. We also investigate QoS (Quality of Service) issue in a mesh-based WiMAX network; an SS transferring the rtPS traffic type will share bandwidth with the neighboring SS of the same level that transmit the same traffic type. To ensure the selected route that can meet the bandwidth requirements of rtPS and the delay constraints, we estimate the average transmission delay from SS to BS. For the purpose of evaluation, we establish a mathematical model to analyze the proposed ORSS and discuss the impact of varying network parameters on the successful rate of route selection. Through the Matlab simulation, we validate our mathematical model. The simulation results demonstrate that our ORSS, in comparison to a previous work, is more effective in ensuring the delay constraints when selecting a route to transfer rtPS traffic.

Mobile ad hoc networks are without centralized infrastructure, and suitable for the region that difficultly builds the basic network framework, for example, desert and ocean. The bandwidth in mobile ad hoc networks is likely to remain a scarce resource. A call request of a connection in a wireless network is blocked if there exits no bandwidth route. This blocking does not mean that the total system bandwidth capacity is less than the request, but that there is no path in which each link has enough residual unused bandwidth to satisfy the requirement. Like the routing in a datagram network, if packets of a virtual circuit can stream across multiple paths, we can select multiple bandwidth routes such that the total bandwidth can meet the requirement of a source-destination pair. Therefore, even though there is no feasible single path for a bandwidth-constrained connection, we may still have a chance to accept this one if we can find multiple bandwidth routes to meet the bandwidth constraint. In this dissertation, we propose a bandwidth-constrained routing algorithm to aggregate the bandwidth of multiple wireless links by splitting a data flow across multiple paths at the network layer. That is, it allows the packet flow of a source-destination pair to be delivered over multiple bandwidth routes with enough overall resources to satisfy a certain bandwidth requirement. Our algorithm considers not only the QoS requirement, but also the cost optimality of the routing paths to improve the overall network performance. Extensive simulations show that high call admission ratio and resource utilization are achieved with modest routing overheads. This algorithm can also tolerate the node moving, joining, and leaving. We also propose an algorithm, named efficient utilization polling (EUP), to support asynchronous data traffic at MAC layer by using the characteristics of Bluetooth technology. The algorithm uses a single bit in the payload header to carry the knowledge of queues in slaves for dynamically adapting the polling intervals for achieving the goals of high channel utilization and power conserving. In addition, we propose a differentiation mechanism, named shift-polling window (SPW). Based on EUP, the SPW differentiates the throughput from various classes, and still keeps the link utilization high and almost the same as that of the best-effort services. Extensive simulations are experimented on the behavior of the EUP and SPW by tuning the related parameters, such as polling interval, buffer size, and queue threshold level, etc., in order to verify the expectation of these methods.

There have been many different technology advancements with the invention of solid state electronics, leading to the digital era which has changed the way users employ electronic circuits. Antennas are no different; however, they are still analog devices. With the advancements in technology, antennas are being fabricated on much higher frequencies and with greater bandwidths, all while trying to keep size and weight to a minimum. Centimeter and millimeter wave technologies have evolved for many different radio frequency (RF) applications. Microstrip patch antennas have been developed, as wire and tubular antenna elements are difficult to fabricate with the tolerances required at micro-wavelengths. Microstrip patch antennas are continuously being improved. These types of antennas are great for embedded or conformal applications where size and weight are of the essence and the ease of manufacturing elements to tight tolerances is important. One of the greatest benefits of patch antennas is the ease in creating an array. Many simulation programs have been created to assist in the design of patch antennas and arrays. However, there are still discrepancies between simulated results and actual measurements. This research will focus on these differences. It begins with a literature research of patch antenna design, followed by an assessment of simulation programs used for patch antenna design. The resulting antenna design was realized by the fabrication of an antenna from the Genesys software. Laboratory measurements of the real-world antenna are then compared to the theoretical antenna characteristics. This process is used to illustrate deficiencies in the software models and likely improvements that need to be made.

ITC/USA 2013 Conference Proceedings / The Forty-Ninth Annual International Telemetering Conference and Technical Exhibition / October 21-24, 2013 / Bally's Hotel & Convention Center, Las Vegas, NV / Cobham Electronic Systems, Inc. has developed a digital potentiometer circuit to allow for digital compensation of frequency and temperature variations in the VCO/PLL frequency control loop of a telemetry transmitter. The ability to reprogram the RF center frequency of a telemetry transmitter is a useful feature and is required on many telemetry programs. When setting the frequency modulation deviation (FM Modulation Index) of a telemetry transmitter, the exact setting will change with RF center frequency due to the variation of the transfer function of the VCO (Kvco). Typically, a resistor divider is used to set the frequency modulation deviation level by setting the output data signal amplitude. However, since Kvco varies with respect to RF center frequency, a method of adjusting frequency modulation deviation for each frequency setting is required. The shunt resistor in the resistor divider is replaced with a digital potentiometer to provide the necessary adjustment, using the on-board microprocessor to store a look-up table of settings versus frequency. A key feature of the digital potentiometer circuit is a method to increase the frequency bandwidth of the potentiometer. Digital potentiometers typically have frequency bandwidths measured in kiloHertz to MegaHertz, which limits their use in setting the frequency modulation deviation of high data rate telemetry transmitters. The circuit consists of a 256 position digital potentiometer and several resistors that are used to adjust the slope of the resistance vs. digital code curve and to translate the curve up and down along the Y-Axis. Adding external resistors to the digital potentiometer helps to increase the frequency bandwidth of the digital potentiometer. The selection of the maximum resistance range of the digital potentiometer is also important, as the potentiometer bandwidth is greater when a small portion of the total resistance is used. This paper will explore various methods of increasing the effective bandwidth of a digital potentiometer, with the goal of making them suitable for use in dynamically setting the frequency modulation deviation via digital control.