Master-Arbeit Univ. St. Gallen, 2009.

Master-Arbeit Univ. St. Gallen, 2009.

No description available.

No description available.

Forward osmosis (FO) is an osmotically driven process that uses a high concentration draw solution to pull water across a semipermeable membrane from a feed solution. Wastewater, seawater, or other contaminated water sources may be used as a feed solution. In FO, the final product is not clean water but a diluted draw solution. However, FO may be combined with another process, e.g. reverse osmosis (RO). The resulting hybrid process offers advantages compared to the RO process in, for example, seawater desalination. Thin-film composite (TFC) membranes have been used in pressurized processes such as RO due to their thick porous support layer and their ability to endure high hydrostatic pressures. However, the presence of a thick porous layer is detrimental for FO processes. It is responsible for the internal concentration polarization (ICP) inside the membrane, reducing the osmotic driving force and the overall water flux. The characterization of membranes in FO applications is key for understanding how different intrinsic parameters affect membrane performance. In this work, a previously developed methodology for characterizing TFC membranes was improved. Experimental data was obtained from a laboratory-scale FO system, and the experimental data was used to determine three intrinsic transport parameters, namely the water permeance, the salt permeance and the porous layer structural parameter. With this method, the characterization of TFC membranes can be achieved based exclusively on FO data. A sensitivity analysis has highlighted the impact of the intrinsic transport parameters on an FO membrane performance.

In cooperative communications systems, multiple relays selection scheme and adaptive relay selection scheme are usually adopted. In both schemes, the system makes selections based on instantaneous channel status. However, such schemes have an extremely high computational complexity. In particular, when the channels experience fast fading, the systems do not have sufficient to make a correct decision. In this thesis, statistical channel properties are utilized in deciding whether cooperative transmission should be adopted or not. In our investigations, the cooperative mechanism includes direct transmission (DT), decode-and-forward (DF) relaying and amplify-and-forward (AF) relaying. The Ergodic capacity is adopted throughout the theoretical analyses. In addition, a number of approximated thresholds are derived to assist the decision process. Simulation experiments are conducted to verify the derived results. It is shown that the proposed transmission scheme using the cooperative thresholds is effective in deciding when the cooperative communication is necessary.

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This thesis presents packet-level channel modeling, spectrum efficiency optimization and channel estimation for wireless cooperative communication systems with diversity combining. Cooperative transmission in a wireless network allows neighboring nodes to share their communication resources to create a virtual antenna array by distributed transmission and signal processing, which is useful to exploit spatial diversity, increase channel capacity, and attain wider service coverage with single-antenna terminals. How to exploit spatial diversity and leverage the multi-hop channel structure is an important research issue for the cooperative network. In this thesis, two cooperative schemes are considered, amplify and forward (AF) and demodulation and forward (DMF). For AF cooperative systems, finite state Markov chain (FSMC) models are designed in analyzing the system performance considering time-varying channel behaviors and facilitating fast channel simulation. For DMF cooperative systems, first we formulate the optimization problem that jointly chooses the modulation schemes at the source and relay nodes, to maximize the throughput of cooperative systems under the BER constraint. Second, we propose to use the soft values of each bit to devise a simple and effective combining scheme, which can be applied for both AF and DMF cooperative systems. Third, as the soft values from demodulation process can also be used for measuring the channel estimation accuracy, a soft value-assisted channel estimation has been proposed by iteratively utilizing soft values to refine the accurate channel estimation. In addition, we also implement the soft value module in OFDM-based transceiver system based on a GNU Radio/USRP2 platform, and verify the effectiveness and performance improvement for the proposed SVC systems. As considering wireless cooperative systems has attracted increasing attentions from both academic and industry to meet the demanding of the high data rate transmission, the packet-level channel modeling, adaptive modulation, spectrum efficiency improvement frameworks based on soft value combining and accurate channel estimation algorithms proposed in this thesis are essential for future proliferation of high data rate, reliable and efficient wireless communication networks. / Graduate / 0537 / 0544 / 0984

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This study was to mechanically analyze the short forward pass and the long forward pass as used in football by a right-handed passer. The study will determine the basic mechanical movements utilized in executing each pass and present a comparative analysis of the two types of forward passes and illustrate the fundamental differences. It also will present a mechanical description of the forward pass that my be used by a quarterback for the purpose of improving his passing ability or by a coach as a teaching resource.