Data link control, multiple access, and flow control for data communication have at last advanced to the state that it is possible for applications that require combining these techniques to be carried out. Therefore, research efforts are now beginning to focus on the performance of these applications, rather than the previous trend of carrying out the performance of each scheme separately. This study analyses the performance of a Very Small Aperture Terminal (VSAT) satellite star network. The network uses roll-call polling as its multiple access scheme, High-level Data Link Control or HDLC, and go-back-N Automatic Repeat Request, for error control. The network is a VSAT packet-switched network, that carries out its communications task on a Time Division Multiplexing (TDM) satellite channel. This research consists of three major parts. First, the performance analysis of the single-hop star architecture network is carried out. This includes the study of a polling communication system for the inbound, VSAT-to-Hub line. The time delay of a packet using the inbound line is evaluated. Secondly, the performance analysis of the TDM outbound Hub-to-VSAT line is represented. The throughput of the multiplexed system for the outbound Hub-to-VSAT line, as well as the average time delay of a packet are determined. Thirdly, both the analysis of the inbound, and outbound lines are combined to provide the performance of the double-hop architecture of the network. The time delay of a VSAT-to-VSAT packet is found. / Master of Science

The current study compared the performance of six commonly used cursor devices (absolute touchpad, mouse, trackball, relative touchpad, force joystick, and displacement joystick) on three types of tasks (target acquisition, text editing, and graphics). Prior to these comparisons, each of the devices was optimized for display/control dynamics in independent experiments. A total of 30 subjects were used in the five optimization studies. For each device, the optimization experiment compared a range of control dynamics using a target acquisition task (i.e., positioning a cross-hair cursor over square targets of varying sizes and screen distances). An analysis of variance procedure was used to determine the best control dynamics, of the range studied, for each device. Performance was based on a time-to-target (TT) measure. A comparison of the six optimized devices was then performed on the three task environments. For the target acquisition, text editing, and graphics tasks, a total of 12, seven, and six subjects were required, respectively. For the target acquisition study, the six devices were compared on a task identical to the optimization task; that is, cursor positioning performance for various target sizes and distances. In addition to the TT dependent measure, bipolar scale and subjective rank data were also collected. The text editing task required subjects to perform document correction on the computer using each of the six devices, with cursor keys added as a baseline device. Task completion time (TCT), bipolar scale response, and subjective rank data were collected. For the graphics task, subjects were required to perform basic graphics editing tasks with the six devices. As with the text editing task, TCT, bipolar scale, and rank data were collected. Results indicated a wide variation in the cursor positioning performance of the devices on the three tasks. Without exception, the mouse and trackball performed the best of the six devices, across all tasks. In addition, these devices were most preferred. In general, the two joysticks performed worse on the target acquisition and graphics tasks than the two touchpads. On the text editing task, however, the rate—controlled joysticks performed better than the touchpads. / Ph. D.

Access to abstract permanently restricted to Ball State community only. / Background : a survey for rate adaptation -- ABEP metric and channell assessment -- ABEP-based adaptive rate control -- Performance evaluation. / Access to thesis permanently restricted to Ball State community only. / Department of Computer Science

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 144-152).

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In this dissertation, we study energy efficient transmission in wireless communication networks. The general problem of energy efficient transmission over wireless networks is formulated into optimization problems for the following distinct (but inter-related) settings: Problem Setting 1: The minimization of energy (power) consumption given a system throughput and other constraints, and Problem Setting 2: The maximization of system throughput given energy (power) constraints. Under Problem Setting 1, we focus on energy efficient transmission problems over wideband channels. The first result we obtain is as follows: We consider a two user multiple access channel. In this multiple access channel, previous research shows that cooperation with respect to block error rate is only possible if two transmitters share their sources completely. However, we find that a modified pulse position modulation with synchronization enables cooperation without complete sharing of their sources between two transmitters if we replace a block error rate requirement with a normalized error rate constraint. Normalized error rate, a quantity that resembles bit error rate, is developed in this work as an error metric that is of value in practical communication systems. We show full cooperation between two transmitters without sharing their sources by deriving that the minimum energy per bit required for reliable transmission reduces by quarter compared with the minimum energy per bit required for point-to-point channels. Next, we generalize this analysis to a cognitive communication framework with a wideband cognitive transmitter, which can causally sense signal levels over multiple frequency bands, and a cognitive receiver. We assume that multiple legitimate users already exist in the system and each one transmits in its own non-overlapping frequency band. In this setting, from order statistical analysis, we show that the wideband cognitive transmit-receive pair is able to communicate reliably with minimum energy as if the legitimate users were absent from the system, while causing negligible interference to bandlimited legitimate users. The wideband cognitive transmit-receive pair employs a strategy defined as opportunistic group orthogonal signaling to achieve the minimum energy per bit. Under Problem Setting 2, we investigate the impact of correlation and transmit and receive strategies on the throughput of multiple antenna broadcast channels in cellular networks. With perfect channel state information at the transmitter, it is well known that dirty paper coding (DPC) is the optimal multi-user broadcast transmission method. However, with partial channel state information at the transmitter, the picture changes significantly. Specifically, since multi-user transmission is unable to employ DPC perfectly, singleuser transmission strategies can have a better performance than multi-user transmission strategies when we have a small number of users and correlated antenna gains. We explore the trade-offs between the single-user and multiuser MIMO transmission strategies. Order statistical analysis provides us with both analytical expressions and insights about these trade-offs. We verify that the analytical framework that we develop is accurate by checking the values obtained against numerical results. From this analysis, we confirm that 'mode switching' between single-user and multi-user MIMO transmission schemes is necessary for maximizing throughput for emerging MIMO solutions. Finally, we suggest an adaptive mode switching algorithm between single-user and multi-user MIMO transmission strategies based on this analytical framework. / text

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Dissertation (PhD)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Though not so prominent as the wide band, high speed, mainstream development of data communication networks, cost and particular bandwidth limitations, still ensure extensive and continuing use of low-speed, half-duplex data link equipment. Most of these applications are radio based and aimed towards telemetry systems serving a wide range of utilities. Experience has shown that systems engineering for this type of installation, is seldom undertaken to a satisfactory analytical level. Investigation of published analyses of CSMA protocols in general, has indicated scope of extension of theoretical work to include system parameters for the type of protocol investigated in this dissertation. This dissertation describes the mathematical modeling of such a strategy by utilising a significantly modified, finite source, transition state-matrix approach derived from queueing theory. The contribution of the dissertation is to include system overhead parameters, such as backoff strategy, channel noise, equipment rise times, propagation- and retry delays, into the abovementioned model. The latter provides a relatively straightforward and readily applicable method for system analysis and performance prediction. A further contribution is the presentation of a software emulation with which different strategies could be simulated, allowing for adjustment of all design parameters. The simulation is intended for parallel and confimatory use with the theoretical model. A dual set of tools, theoretical and emulation based, is thus contributed to assist with the system design, performance prediction and protocol selection process. / AFRIKAANSE OPSOMMING: Alhoewel nie so prominent soos die wyeband, hoëspoed, hoofstroom ontwikkeling van datakommunikasie netwerke nie, verseker koste en spesifieke bandwydte beperkings nog die uitgebreide en voortdurende gebruik van laespoed half-dupleks data verbindingstoerusting. Meeste van die toepassings is radio gebaseer en gerig op telemetriestelsels wat deur 'n wye verskeidenheid diensverskaffers benut word. Stelselontwerp vir hierdie tipe installasies word selde op analitiese vlak benader. Ondersoek van gepubliseerde analises van kontensieprotokolle in die algemeen, het ruimte aangetoon vir die uitbreiding van bestaande teoretiese werk om stelselveranderlikes soos van toepassing op die tipe protokol in hierdie proefskrif ondersoek, in te sluit. Hierdie proefskrif beskryf die wiskundige modelering van sodanige strategie, deur gebruik te maak van 'n beduidend veranderde eindige bron, oorgangs-toestandmatriks benadering, afgelei van touteorie. Die bydrae van hierdie proefskrif is die insluiting van oorhoofse stelselveranderlikes, soos herhaal strategie, kanaalruis, toerusting stygtye, herhaal- en voortplantingsvertragings, in bogenoemde model. Laasgenoemde verskaf 'n relatief eenvoudige en maklik toepasbare metode vir stelselanalise en werkverrigtingvoorspelling. 'n Verder bydrae is die daarstelling van 'n sagteware simulasie waarmee verskillende strategieë nageboots kan word. Verstelling van alle ontwerpparameters word ondersteun. Die simulasie is bedoel vir parallelle en bevestigende gebruik tesame met die teoretiese model. 'n Dubbele, teoreties- en simulasie gebaseerde benadering, word dus aangebied vir gebruik by stelselontwerp, gedragsvoorspelling en optimale protokolseleksie.

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This paper describes the design and simulation of a network interface unit (NIU) for a picture archiving and communication system (PACS) network called PACnet. PACnet is a dual fiber optic ring network under development at the Computer Engineering Research Laboratory of the University of Arizona. This network integrates voice, data, and image communications in a hospital environment and supports a throughput rate between 200-500 megabits per second. At each node in the network, an NIU implements the Data Link Layer and Physical Layer protocols of PACnet. The initial network interface unit design for PACnet was a functional description of NIU protocols and major components. In order to construct a demonstration prototype of PACnet,the NIU description must be refined and an architecture must be specified. The NIU design is specified and simulated using the hardware description language VHDL. Simulation results provide information on NIU timing characteristics and logic families required to implement the NIU.