Browsing by Author "Robert, Pablo Maximiliano"

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    Reduction in Coexistent WLAN Interference Through Statistical Traffic Management
    Robert, Pablo Maximiliano (Virginia Tech, 2003-04-17)
    In recent years, an increasing number of devices have been developed for operation in the bands allocated by the Federal Communications Commission (FCC) for license-free operation. Given the rules governing devices in these bands, it is possible for interference created by these devices to significantly reduce the overall capacity of these bands. Two such protocols are Bluetooth and IEEE 802.11b. Several methods have been presented in the literature for managing interference between these two devices. However, these approaches are generally not practical, since they either require the purchase of specialized hardware or do not comply with the current versions of existing protocols. In this dissertation, an approach is presented that is not only backwards-compatible, but requires the algorithm to be implemented in only a small subset of the devices operating in the local environment for the coexistence algorithm to function properly. An analytical solution for this coexistence approach when applied to generic networks is presented. A method is also presented for the backwards-compatible integration of some medium access control (MAC) protocols into Bluetooth devices. A case study of the Bluetooth/IEEE 802.11b coexistence problem is presented in this dissertation, as well as a proposed coexistence mechanism, collision-based multiple access (CBMA). A form of adaptive frequency hopping (AFH) is presented in this dissertation, as well as a combined CBMA/AFH strategy. The CBMA algorithm is shown be able to significantly reduce the impact of a Bluetooth link on an IEEE 802.11b link. The AFH algorithm is shown to have comparable performance to the CBMA algorithm. A combined CBMA/AFH algorithm presented, is shown to not only have an impact on the IEEE 802.11b link that is not greater than the CBMA-only implementation, but the Bluetooth link throughput is shown to be significantly greater than either the CBMA or AFH implementation alone.
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    Simulation Tool and Metric for Evaluating Wireless Digital Video Systems
    Robert, Pablo Maximiliano (Virginia Tech, 1998-09-23)
    This thesis focuses on the interaction between digital video quality and channel coding in a wireless communication system. Digital video is a high-bandwidth, computationally intensive application. The recent allocation of large tracks of spectrum by the FCC has made possible the design and implementation of personal wireless digital video devices for several applications, from personal communications to surveillance. Wireless video research has centered on contextual coding mechanisms; different sections of a video data stream are coded differently based on the perceived importance of the coded bits. Besides the complexity introduced into a system by this type of coding, no metric based solely on physical layer parameters can be used to predict video quality across different system architectures. A tool was built to explore the video/channel coding relationship. This tool simulates a packet-based digital wireless transmission in various noise and interference environments. The basic communications system models the DAVIC (Digital Audio-Visual Council) layout for the LMDS (Local Multipoint Distribution Service) system and includes several error control algorithms and a packetizing algorithm that is MPEG-compliant. This work introduces a statistical approach to monitoring the video quality. The error-event-mean-arrival-rate, lambda_distance, is a metric derived from the physical layer that can be used to predict the expected video quality across systems with different channel coding algorithms. This metric proved to be uniformly consistent in predicting video quality for sequences corrupted by Gaussian and non-Gaussian noise and protected by a variety of error correction techniques.