Browsing by Subject "Channel estimation"
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Item A Performance Comparison between Oversampled Filter Banks and the 3GPP Long Term Evolution(2013-05) Riley, Matthew E; Karp, Tanja; Nutter, BrianRecent attention is being paid in the field of wireless communications to the Long Term Evolution (LTE) standard developed by the Third Generation Partnership Project (3GPP). The LTE downlink uses an efficient transmission scheme called orthogonal frequency-division multiplexing (OFDM). Despite many advantages to OFDM, the system suffers from poor stopband attenuation, making it susceptible to inter-carrier interference (ICI). This thesis presents a multicarrier system based on oversampled filter banks (OFB) that is comparable to LTE in terms of occupied bandwidth and symbol transmission rate while achieving superior stopband attenuation and subcarrier separation. In addition, a new treatment of the LTE pilot symbol configuration is proposed that simplifies the interpolation process. Using the new pilot symbol treatment, the channel equalization performance of the two systems will be measured using the 1-tap equalizer through symbol error rate (SER) curves. The channel estimation process uses two different estimation and interpolation techniques. An initial channel estimate is obtained using the least squares (LS) estimator or the normalized least mean squared (NLMS) algorithm, and the full estimate is obtained using linear or cubic spline interpolation between pilot symbols. The goal is to provide a performance evaluation of oversampled filter banks in comparison to the LTE standard.Item Graphical models and message passing receivers for interference limited communication systems(2013-08) Nassar, Marcel; Evans, Brian L. (Brian Lawrence), 1965-In many modern wireless and wireline communication networks, the interference power from other communication and non-communication devices is increasingly dominating the background noise power, leading to interference limited communication systems. Conventional communication systems have been designed under the assumption that noise in the system can be modeled as additive white Gaussian noise (AWGN). While appropriate for thermal noise, the AWGN model does not always capture the interference statistics in modern communication systems. Interference from uncoordinated users and sources is particularly harmful to communication performance because it cannot be mitigated by current interference management techniques. Based on previous statistical-physical models for uncoordinated wireless interference, this dissertation derives similar models for uncoordinated interference in PLC networks. The dissertation then extends these models for wireless and powerline interference to include temporal dependence among amplitude samples. The extensions are validated with measured data. The rest of this dissertation utilizes the proposed models to design receivers in interference limited environments. Prior designs generally adopt suboptimal approaches and often ignore the problem of channel estimation which limits their applicability in practical systems. This dissertation uses the graphical model representation of the OFDM system to propose low-complexity message passing OFDM receivers that leverage recent results in soft-input soft-output decoding, approximate message passing, and sparse signal recovery for joint channel/interference estimation and data decoding. The resulting receivers provide huge improvements in communication performance (more than 10dB) over the conventional receivers at a comparable computational complexity. Finally, this dissertation addresses the design of robust receivers that can be deployed in rapidly varying environments where the interference statistics are constantly changing.Item Relay-aided communications with partial channel state information(2011-08) Yazdan Panah, Ali; Heath, Robert W., Ph. D.; Evans, Brian L.; Hasenbein, John; Vikalo, Haris; Andrews, Jeffrey G.Modern wireless communication systems strive to enable communications at high data rates, over wide geographical areas, and to multiple users. Unfortunately, this can be a daunting task in practice, as natural laws governing the wireless medium may hinder point-to-point transmissions. Communications over large distances (path loss), and physical obstructions in line-of-sight signals (shadowing) are prime examples of such impediments. One promising solution is to deploy intermediary terminals to help reestablish such broken point-to-point communication links. Such terminals are called relay nodes, and the corresponding systems are referred to as being relay-aided. As in the case of point-to-point communication, design of efficient transmission and reception techniques in relay-aided systems depends on the availability of propagational channel state information. In practice, such information is only accurate to a certain degree which is governed by overhead constraints, feedback delay, and channel fluctuations due to mobility. Understanding the impacts of such partial channel state information, and devising transmission and reception methods based on such understandings, is the main topic of this dissertation. The transmission protocol classifies relays as either one-way, where the relay receives signals from one terminal, or two-way, where the relay receives signals from more than one terminal. Designs and solutions for both one- and two-way relaying systems are presented in this dissertation. Emphasis is placed on two-way relaying systems given their superior efficiency in utilizing channel resources. For one-way relaying this dissertation presents power loading strategies for multiuser-multicast systems derived based on the availability of full or partial channel state information at the terminals. In the case of two-way relaying, both single and multi-user systems are analyzed. For single-user two-way relaying, this dissertation presents optimal methods of acquiring partial channel state information via pilot-aided channel estimation methods. This includes an analysis of the effects of channel estimation upon the system sum-rate. Also, the design of channel equalizers exhibiting robustness to partial channel state information is proposed. For multi-user two-way relaying, this dissertation presents several precoding strategies at the relay terminal(s) to combat the effects co-channel interference in light of the existence of self-interference inherent to two-way relaying operations.