Browsing by Subject "Relaying"
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Item Low-overhead cooperation to mitigate interference in wireless networks(2013-05) Peters, Steven Wayne; Heath, Robert W., Ph. D.Wireless cellular networks, which serve a large area by geographically partitioning users, suffer from interference from adjacent cells transmitting in the same frequency band. This interference can theoretically be completely mitigated via transceiver cooperation in both the uplink and downlink. Optimally, base stations serving the users can utilize high-capacity backbones. to jointly transmit and receive all the data in the network across all the base stations. In reality, the backbone connecting the base stations is of finite capacity, limiting joint processing to localized clusters. Even with joint processing on a small scale, the overhead involved in sharing data between multiple base stations is large and time-sensitive. Other forms of cooperation have been shown to require less overhead while exhibiting much of the performance benefit from interference mitigation. One particular strategy, called interference alignment (IA), has been shown to exploit all the spatial degrees of freedom in the channel provided data cannot be shared among base stations. Interference alignment was developed for the multi-user interference channel to exploit independent channel observations when all of the links in the network have high signal-to-noise ratio, and assumes all the nodes utilizing the physical resources are participating in the cooperative protocol. When some or all of the links are at moderate signal-to-noise ratio, or when there are non-cooperating users, IA is suboptimal. In this dissertation, I take three approaches to addressing the drawbacks of IA. First, I develop cooperative transmission strategies that outperform IA in various operationg regimes, including at low-to-moderate SNR and in the presence of non-cooperating users. These strategies have the same complexity and overhead as IA. I then develop algorithms for network partitioning by directly considering the overhead of cooperative strategies. Partitioning balances the capacity gains of cooperation with the overhead required to achieve them. Finally, I develop the shared relaying model, which is equivalent to the interference channel but with a single multi-antenna relay mediating communications between transceivers. The shared relay requires less overhead and cooperation than interference alignment but requires added infrastructure. It is shown to outperform conventional relaying strategies in cellular networks with a fixed number of total relay antennas.Item Time-domain modeling and validation of overcurrent/reclosing relay operation(2013-08) Lwin, Min Naing; Santoso, SuryaThe primary goal of this work is to develop a PSCAD/EMTDC simulation model which can emulate the reclosing capabilities of an actual reclosing relay. The first part of this work will demonstrate the capabilities of a commercially available, microprocessor-based reclosing relay, the SEL-551c. Next, a computer simulation model of this relay's reclosing capability will be developed in PSCAD/EMTDC and validated. The performance of the model will be compared to the performance of the SEL-551c. Because it is impractical to test the relay operation under fault conditions in a real distribution system, fault characteristics will be determined in PSCAD. Utilizing a test system for the SEL relay, we can show the accuracy of the PSCAD recloser model compared to the SEL-551c relay for similar fault scenarios. The validation is done by analyzing the data from the simulation and experiment. The results show that both the PSCAD recloser model and SEL-551c operate close to the expected theoretical values. The primary contribution of this work is the development of a PSCAD recloser model and validation with a real world reclosing relay. In previous works where recloser analysis was done in PSCAD, such as [14], recloser operation was manually accomplished. However, the recloser model developed in this work allows the user to enter any standard TCC equation that may be programmed into an actual relay and achieve similar results. The model is useful when analyzing larger distribution systems with multiple reclosers. Additionally, validating the PSCAD recloser model with a real world device provides confidence that the simulations provide reasonable and meaningful results.