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University of Nebraska - Lincoln

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Articles 31 - 33 of 33

Full-Text Articles in Systems and Communications

Wireless Communications And Cognitive Radio Transmissions Under Quality Of Service Constraints And Channel Uncertainty, Sami Akin May 2011

Wireless Communications And Cognitive Radio Transmissions Under Quality Of Service Constraints And Channel Uncertainty, Sami Akin

Department of Electrical and Computer Engineering: Dissertations, Theses, and Student Research

In this thesis, we study wireless communications and cognitive radio transmissions under quality of service (QoS) constraints and channel uncertainty. Initially, we focus on a time-varying Rayleigh fading channel and assume that no prior channel knowledge is available at the transmitter and the receiver.  We investigate the performance of pilot-assisted wireless transmission strategies. In particular, we analyze different channel estimation techniques, including single-pilot minimum mean-square-error (MMSE) estimation, and causal and noncausal Wiener filters, and analyze efficient resource allocation strategies. Subsequently, we study the training-based transmission and reception schemes over a priori unknown, Rayleigh fading relay channels in which the fading …


Exploration Of Spatial Diversity In Multi-Antenna Wireless Communication Systems, Shichuan Ma May 2011

Exploration Of Spatial Diversity In Multi-Antenna Wireless Communication Systems, Shichuan Ma

Department of Computer Electronics and Engineering: Dissertations, Theses, and Student Research

With increasing demand on wireless internet and personal multimedia, the data rate of wireless communications is expected to increase dramatically. Future wireless networks face challenges of supporting data rates higher than one gigabits per second. Among various technologies, multi-antennas, also known as multiple-input multiple-output (MIMO), are undoubtedly the most promising to enable higher data rates. By employing the extra degrees of freedom in the spatial domain, multi-antenna techniques enhance the wireless communication systems through array gain, spatial diversity, and spatial multiplexing. Although multi-antenna systems have been utilized for more than ten years, a thorough analysis of various aspects of multi-antenna …


Finite Tree-Based Decoding Of Low-Density Parity-Check Codes, Eric T. Psota Jan 2010

Finite Tree-Based Decoding Of Low-Density Parity-Check Codes, Eric T. Psota

Department of Electrical and Computer Engineering: Dissertations, Theses, and Student Research

Low-density parity-check codes are commonly decoded using iterative message-passing decoders, such as the min-sum and sum-product decoders. Computer simulations demonstrate that these suboptimal decoders are capable of achieving low probability of bit error at signal-to-noise ratios close to capacity. However, current methods for analyzing the behavior of the min-sum and sum-product decoders fails to produce usable bounds on the probability of bit error. Thus, the resulting probability of bit error when using these decoders remains largely unknown for signal-to-noise ratios beyond the reach of simulation. For this reason, it is worth considering alternative methods for decoding low-density parity-check codes. New …