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Thesis (doctoral)--Stockholm University, 2001. / Includes bibliographical references (p. 602-604).

This dissertation provides methods to utilize chaos efficiently in secure communications. Chaos has many desirable characteristics such as ergodicity and sensitivity to initial conditions, and is considered an ideal candidate for use in cryptography and secure communications. On the other hand, it suffers from sensitivity to noise and fading if it is used for physical layer transmission, and errors due to the finite precision of the numerical algorithms in digital systems. This limits the use of chaos in cryptographic applications. Accordingly, this dissertation proposes new algorithms to enhance the security of modern communication systems using chaos. The focus is on developing chaotic cryptosystems for wireless systems that are reliable, secure, and have good performance. / Graduate / mharoun@uvic.ca

Accurate channel knowledge is indispensable to the practical success of channel-aware wireless communication technologies. However, channel estimates obtained from pilot symbols rapidly become outdated due to fast time variations of multipath fading channels. To reduce system cost, antenna subset selection reduces radio frequency (RF) chain components. For systems selecting a subset of a plurality of antennas for reception, this outdated channel information is a significant impediment to selection and data decoding reliability. In this thesis, training-based schemes for antenna selection (AS) for time-varying channels which account for practical constraints such as training, packetization and antenna switching time are proposed based on discrete prolate spheroidal sequences. They only operate with knowledge or estimates of the Doppler frequency and the channel signal-to-noise ratio (SNR), but do not require detailed statistical correlation knowledge. A pilot-based AS scheme for time-varying frequency-flat channels for single input-multiple output (SIMO) systems selecting one of a plurality of antennas using packet or symbol-rate antenna switching is first proposed. It is demonstrated that the presented scheme provides significant performance gain over AS methods using Fourier-based orthogonal training as well as over single antenna systems with perfect channel knowledge. Analytical expressions for the symbol error probability (SEP) of M-ary phase-shift keying (MPSK) for systems employing the suggested techniques are provided. The second part of this thesis investigates the more general case of selecting a subset of a plurality of receive antennas. A new pilot-based receive antenna subset selection algorithm for time-varying frequency-flat channels is presented. The proposed AS algorithm is shown to outperform AS methods based on Fourier prediction/estimation as well as SIMO systems with perfect channel knowledge. Analysis of MPSK and quadrature amplitude modulation (MQAM) SEP for systems with receive AS is provided. The combination of AS and orthogonal frequency division multiplexing (OFDM) over the more realistic time-varying and frequency-selective fading scenario is examined in the final part. Training schemes for receive AS using packet-rate antenna switching for SIMO and multiple input-multiple output (MIMO) OFDM systems are developed. The suggested schemes exhibit a superior performance over AS methods using either linear interpolation/extrapolation or Fourier prediction/estimation techniques. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2013-01-30 16:47:06.057

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New interactive communication technologies, envisaged as the dominant media of tomorrow, is predicted to alter the fabric of human society and our understanding of communication. Against the backdrop of these new technologies, attempts are already being made to redefine communication in horizontal terms. However, the present state of new media research has not yet come to grips with this theoretical shift. This study focuses on a prominent dimension of the new media research that deals with media choice. This study argues that the present research has not accounted for the role of the communication partner in the horizontal process of communication. Based on the distinction between the relational and content dimensions of communication made by relational communication research, the study argues that participants in communication can have different goals which may either be competitive or complementary with those of the communication partner. The study hypothesizes that relational control would be a significant factor in communication situations when the relational dimension of communication goals is competitive and content control would be a significant factor when content dimension is competitive. / The hypotheses were tested with personal interviews conducted among a self-selected sample of 70 persons who regularly communicate with any of the four media of communication--face-to-face, telephone, e-mail and written media. The interview schedule sought to find the reasons for respondents' media choice in different situations. A content analysis of the responses supported the hypotheses that in situations of relational competitiveness, relational control is a significant factor. Content control figured as a significant variable in all the situations that were tested. Among the four modes of communication, face-to-face was most often used for persuasion, while telephone and e-mail were more often used to position oneself relationally vis a vis the other. / Source: Dissertation Abstracts International, Volume: 54-07, Section: A, page: 2371. / Major Professor: C. Edward Wotring. / Thesis (Ph.D.)--The Florida State University, 1993.