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Ultra-wideband (UWB) communications has emerged as a promising technology for high data rate wireless personal area networks (WPANs). Several proposals for UWB-based WPANs have been made. One widely popular proposal is based on multi-channel OFDM. This proposal was recently standardized by European Computer Manufacturers Association (ECMA). In this dissertation, we address several important aspects that impact the performance of OFDM-based UWB systems. First, we propose an interference management distributed reservation protocol (IMDRP) for these communications. IM-DRP aims at reducing interference between uncooperative beacon groups that operate simultaneously over the same area. We then integrate IM-DRP into the design of a rate adaptation strategy that exploits the multi-rate capability of OFDM-based UWB systems. Besides maintaining a target packet error rate, our proposed strategy attempts to reduce the required reservation time over a link, hence allowing more links to be concurrently activated. Second, we propose a novel overhearing-aware joint routing and rate selection (ORRS) scheme. For a given source-destination pair, ORRS aims at selecting a path and its transmission rates that achieve the minimum channel reservation time, leading to low blocking rate for prospective reservations and high network throughput. At the same time, ORRS takes advantage of packet overhearing, a typical characteristic of broadcast communications. Finally, we propose a novel resource utilization mechanism (RUM) for improving the throughput in multi-rate UWB-based WPANs. RUM exploits opportunistic-relaying and time-spreading techniques to improve link reliability and increase the transmission rate, and hence network throughput. Simulation results indicate that our proposed protocols and schemes achieve significant throughput improvement compared with other protocols.

No description available.

No description available.

No description available.

In wireless networking, receivers are typically assumed to be utilizing single-user decoding. Still, for more than twenty years we know that we can take advantage of interference by multi-user decoding. The Interference Cancellation (IC) technique has, of late, gained interest in the wireless networking context. Previous works [3] have shown considerable potential gains by leveraging optimal collaborative rate control to enable IC, focusing on the low Signal-to-Noise Ratio (SNR) regime. Here, we present centralized and distributed rate control algorithms, enabling IC, to increase system throughput. We consider a system where the receivers can apply multi-user decoding to perform IC and the rates are provided by a step-wise function of the Signal to Interference-and-Noise Ratio (SINR), in realistic conditions. We conduct a thorough simulation study comparing the proposed algorithms using two IC techniques, and deliver results that indicate significant system throughput gains.

International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Group delay variations are a potential problem in many communication systems. This paper is slanted towards the effects of group delay variations in analog magnetic recorder/reproducer systems but the results are applicable in general. Because it is difficult to get an arbitrary group delay profile at the output of a recorder/reproducer, a method of generating arbitrary group delays for bit error probability (BEP) testing was developed. A 32-bit pattern in which all five-bit sequences appear with equal probability was selected as the test signal. The amplitude and phase of the discrete Fourier components were calculated for both non-return-to-zero-level (NRZ-L) and biphase-level (BI -L) waveforms. Filtering and group delay variations were computer generated by varying the amplitude and phase of the Fourier components. The modified signals were then programmed into an arbitrary waveform generator. Noise was added and the composite signal was applied to a bit synchronizer and bit error detector. BEPs were measured for various noise levels and group delay profiles.

Wireless Local Area Networks (WLANs) extend the usage of wired LANs from specific places within a building to the many mobile users whether in the building or outside. The wireless data is not only used by authorized users but also might be intercepted and altered by other unauthorized users. Therefore, the power of the transmitter is kept as low as possible to make it difficult for the others to intercept the signal. In the absence of interception, adversaries might attempt to jam the signal so that the network cannot operate properly. The purpose of present study is to investigate the effects of noise jamming against a WLAN in a high-rise building. The building model was created by Rhino, a well known Windows-based computer drawing software. The jamming effects are simulated using Urbana. The LAN transmitter operates with an omni-directional antenna and 100 mW of power. The noise jammer has variable power levels of 10 W and 100 W. It uses a directional antenna. The signal-to jam-ratio (SJR) is computed for several floors in the building to determine if the jammer will disrupt the WLAN.

The study of metacognition is rooted in the observation of behaviors under states of uncertainty (e.g., Smith et al., 1995). Individuals who are more responsive to uncertainty tend to show greater interference effects in a Stroop color-word naming task compared to those who are less responsive to uncertainty (Washburn, Smith, & Taglialatela, 2005). Individual differences in Stroop interference also have been shown to reflect relative differences in response competition (Washburn, 1994) and rule-maintenance ability (Kane & Engle, 2003). Why would individuals who respond to uncertainty most adaptively be characterized by the worst attention-control skills? The current study was designed to measure the individual contribution of sensitivity to response competition and rule maintenance ability to the pre-established relationship between Stroop interference and uncertainty responsiveness. Though participants performed as expected in both tasks, the previously reported relationship between Stroop interference and uncertainty responsiveness was not observed.

With the advent of resource shared environments such as the Cloud, virtualization has become the de facto standard for server consolidation. While consolidation improves utilization, it causes performance-interference between Virtual Machines (VMs) from contention in shared resources such as CPU, Last Level Cache (LLC) and memory bandwidth. Over-provisioning resources for performance sensitive applications can guarantee Quality of Service (QoS), however, it results in low machine utilization. Thus, assuring QoS for performance sensitive applications while allowing co-location has been a challenging problem. In this thesis, we identify ways to mitigate performance interference without undue over-provisioning and also point out the need to model and account for performance interference to improve the reliability and accuracy of elastic scaling. The end goal of this research is to leverage on the observations to provide efficient resource management that is both performance and cost aware. Our main contributions are threefold; first, we improve the overall machine utilization by executing best-effort applications along side latency critical applications without violating its performance requirements. Our solution is able to dynamically adapt and leverage on the changing workload/phase behaviour to execute best-effort applications without causing excessive interference on performance; second, we identify that certain performance metrics used for elastic scaling decisions may become unreliable if performance interference is unaccounted. By modelling performance interference, we show that these performance metrics become reliable in a multi-tenant environment; and third, we identify and demonstrate the impact of interference on the accuracy of elastic scaling and propose a solution to significantly minimise performance violations at a reduced cost. / <p>QC 20160927</p>