Signal detection plays a critical role in realizing reliable transmission through communication systems. In this dissertation, by applying information theoretic approach, efficient detection schemes and algorithms are designed for three particular communication systems. First, a computation efficient coding and detection algorithm is developed to decode two dimensional inter-symbol interference (ISI) channels. The detection algorithm significantly reduces the computation complexity and makes the proposed equalization algorithm applicable. A new metric, the post-detection mutual information (PMI), is established to quantify the ultimate information rate between the discrete inputs and the hard detected output. This is the first time that the information rate loss caused by the hard mapping of the detectors is considered. Since the hard mapping step in the detector is irreversible, we expect that the PMI is reduced compared to the MI without hard mapping. The conclusion is confirmed by both the simulation and the theoretic results. Random complex field code is designed to achieve the secrecy capacity of wiretap channel with noiseless main channel and binary erasure eavesdroppers' channel. More importantly, in addition to approaching the secrecy capacity, RCFC is the first code design which provides a platform to tradeoff secrecy performance with the erasure rate of the eavesdropper's channel and the secrecy rate.

abstract: The Milky Way galaxy is a powerful dynamic system that is highly efficient at recycling material. Stars are born out of intergalactic gas and dust, fuse light elements into heavier elements in their cores, then upon stellar death spread material throughout the galaxy, either by diffusion of planetary nebula or by explosive events for high mass stars, and that gas must cool and condense to form stellar nurseries. Though the stellar lifecycle has been studied in detail, relatively little is known about the processes by which hot, diffuse gas ejected by dying stars cools and conglomerates in the interstellar medium (ISM). Much of this mystery arises because only recently have instruments with sufficient spatial and spectral resolution, sensitivity, and bandwidth become available in the terahertz (THz) frequency spectrum where these clouds peak in either thermal or line emission. In this dissertation, I will demonstrate technology advancement of instruments in this frequency regime with new characterization techniques, machining strategies, and scientific models of the spectral behavior of gas species targeted by these instruments. I begin this work with a description of radiation pattern measurements and their use in astronomical instrument characterization. I will introduce a novel technique to measure complex (phase-sensitive) field patterns using direct detectors. I successfully demonstrate the technique with a single pixel microwave inductance detectors (MKID) experiment. I expand that work by measuring the APEX MKID (A-MKID) focal plane array of 880 pixel detectors centered at 350 GHz. In both chapters I discuss the development of an analysis pipeline to take advantage of all information provided by complex field mapping. I then discuss the design, simulation, fabrication processes, and characterization of a circular-to-rectangular waveguide transformer module integrated into a circularly symmetric feedhorn block. I conclude with a summary of this work and how to advance these technologies for future ISM studies. / Dissertation/Thesis / Doctoral Dissertation Exploration Systems Design 2018

Reliability of data transmission is a fundamental problem in wireless communications. Fading in wireless channels causes the signal strength to vary at the receiver and this results in loss of data packets. To improve the reliability, automatic repeat request (ARQ) schemes were introduced. However these ARQ schemes suffer from a reduction in the throughput. To address the throughput reduction, conventional ARQ schemes were combined with forward error correction (FEC) schemes to develop hybrid-ARQ (HARQ) schemes. For improving the reliability of data transmission, HARQ schemes are included in the present wireless standards like LTE, LTE-Advanced and WiMAX. Conventional HARQ systems use the same transmission power and the same number of channel uses in different ARQ rounds. However this is not optimal in terms of minimizing the average transmit power or the average energy spent for successful transmission of a data packet. We address this issue in the first part of the dissertation, where we consider optimal resource allocation in HARQ systems with a limit on the maximum number of allowed transmissions for a data packet. Specifically, we consider the problem of minimizing the packet drop probability (PDP) under an average transmit power constraint or equivalently minimizing the average transmit power under a fixed PDP constraint. We consider both incremental redundancy (IR)-based and Chase combining (CC)-based HARQ systems in our work. For an IR-HARQ system, for the special case of two allowed transmissions for each packet, we provide a solution for the optimal number of channel uses and the optimal power to be used in each ARQ round. For a CC-HARQ system, we solve the problem of optimal power allocation in i.i.d. Rayleigh fading channels as well as correlated Rayleigh fading channels. For the CC-HARQ case, we also provide a low complexity geometric programming (GP) solution using an approximation of the outage probability expression. HARQ systems conventionally use one bit acknowledgement (ACK)/negative ACK (NACK) feedback from the receiver to the transmitter. In the 3GPP-LTE systems, one method for sending these HARQ acknowledgement bits is to jointly code them with the other control signaling information using a specified Reed-Muller code consisting of 20 coded bits. Even though the resources used for sending this control signaling information can inherently provide a diversity gain, the Reed-Muller code with such a short block size is not good at extracting all of the available diversity. To address this issue, in the second part of this dissertation, we propose two new methods: i) based on complex-field coding (CFC), and ii) using repetition across frequency bands, to extract the inherent diversity available in the channel resources and improve the error protection for the HARQ acknowledgement bits along with the other control signaling information. In the second part of the dissertation, we also propose a new signal space diversity (SSD) scheme, which results in transmit signals having constant envelope (CE). The proposed CE-SSD scheme results in a better overall power efficiency due to the reduced back-off requirements on the radio frequency power amplifier. Moreover, the proposed CE-SSD technique can be useful for application scenarios involving transmission of small number of information bits, such as in the case of control signaling information transmission. In conventional HARQ systems, during the retransmission phase, the channel resources are exclusively used for the retransmitted data packet. This is not optimal in terms of efficient resource utilization. For efficient utilization of channel resources during the retransmissions, a superposition coding (SPC) based HARQ scheme was proposed in the literature. In an SPC based HARQ system, an erroneous packet is transmitted together with a new data packet by superposition in the Euclidean space. In the final part of this dissertation, we study performance of different bits-to-symbol mappings for such an SPC based HARQ system.

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Today’s communication systems are in need of spectrally efficient and high throughput techniques more than ever because of high data rate applications and the scarcity and expense of bandwidth. To cope with increased data rate demands, more base stations are needed which is not cost and energy efficient in cellular networks. It has been shown that wireless relay networks can provide higher network throughput and increase power efficiency with low complexity and cost. Furthermore, network resources can be utilized more efficiently by using network coding in relay networks. A wireless relay network in which multiple nodes exchange information with the help of relay node(s) is called a multi-way relay channel (MWRC). MWRCs are expected to be an integral part of next generation wireless standards. The main focus of this dissertation is the investigation of transmission schemes in an MWRC to improve the throughput and error performance. An MWRC with full data exchange is assumed in which a half-duplex relay station (RS) is the enabler of communication. One of the challenges with signal demodulation in MWRCs is the existence of ambiguous points in the received constellation. The first part of this dissertation investigates a transmission scheme for full data exchange in MWRC that benefits from these points and improves its throughput by 33% compared to traditional relaying. Then an MWRC is considered where a RS assists multiple nodes to exchange messages. A different approach is taken to avoid ambiguous points in the superposition of user symbols at the relay. This can be achieved by employing complex field network coding (CFNC) which results in full data exchange in two communication phases. CFNC may lead to small Euclidean distances between constellation points, resulting in poor error performance. To improve this performance, the optimal user precoding values are derived such that the power efficiency of the relay constellation is highest when channel state information is available at the users. The error performance of each user is then analyzed and compared with other relaying schemes. Finally, focusing on the uplink of multi-way relay systems, the performance of an MWRC is studied in which users can employ arbitrary modulation schemes and the links between the users and the relay have different gains, e.g. Rayleigh fading. Analytical expressions for the exact average pairwise error probability of these MWRCs are derived. The probability density function (PDF) and the mean of the minimum Euclidean distance of the relay constellation are closely approximated, and a tight upper bound on the symbol error probability is developed. / Graduate