Thesis (M.S.)--University of Texas at Dallas, 2007. / Includes vita. Includes bibliographical references (leaves 84-85)

This dissertation is concerned with performance analysis of diversity combining schemes in frequency-hop spread spectrum communications under the worst case partial-band noise and multitone jamming. Performance of a ratio-threshold diversity combining scheme in fast frequency hop spread spectrum systems with M-ary frequency shift keying modulation (FFH/MFSK ) under partial-band noise (PBN) and band multitone jamming without and with the additive white Gaussian noise (AWGN) is analyzed. The analysis is based on exact bit error probabilities, instead of bounds on the bit error probabilities. A method to compute the bit error probability for ratio-threshold combining on jamming channel is developed. Relationship between the system performance and the system parameters, such as ratio-threshold, diversity order, and thermal noise level, is illustrated. The performances under band multitone jamming and under partial-band noise jamming are compared. For binary FSK modulation, the performance under the two types of jamming is almost the same, but for 8-ary FSK modulation, tone jamming is more effective against communications. The structure of the combiner is very simple and easy to implement. Another merit of this combiner is that its output can be directly fed to a soft-decision FEC decoder. Maximum-likelihood diversity combining for an FFH/MFSK spread spectrum system on a PBN interference channel is investigated. The structure of maximum likelihood diversity reception on a PBN channel with AWGN is derived. It is shown that signal-to-noise ratio and the noise variance at each hop have to be known to implement this optimum diversity combining. Several sub-optimum diversity combining schemes, which require the information on noise variance of each hop to operate, are also considered. The performance of the maximum-likelihood combining can be used as a standard in judging the performance of other suboptimum, but more practical diversity combining schemes. The performance of the optimum combining scheme is evaluated by simulations. It is shown that the Adaptive Gain Control (AGC) diversity combining actually achieves the optimum performance when interference is not very weak. But the performance difference between some of the known diversity combining schemes, which do not require channel information to operate, and the optimum scheme is not small when the diversity order is low. An error-correction scheme is proposed for an M-ary symmetric channel characterized by a large error probability Pe. Performance of the scheme is analyzed. The value of Pe can be close to, but smaller than, 1 – 1/M for which the channel capacity is zero. Such a large Pe may occur, for example, in a jamming environment. The coding scheme considered consists of an outer convolutional code and an inner repetition code of length m which is used for each convolutional code symbol. At the receiving end, the m inner code symbols are used to form a soft-decision metric, which is subsequently passed to a soft-decision decoder for the convolutional code. Emphasis is placed on using a binary convolutional code due to the consideration that there exist commercial codecs for such a code. New methods to generate binary metrics from M-ary (M > 2) inner code symbols are developed. For the binary symmetric channel, it is shown that the overall code rate is larger than O.6R0, where R0 is the cutoff rate of the channel. New union bounds on the bit error probability for systems with a binary convolutional code on 4-ary and 8-ary orthogonal channels are presented. Owing to the variable m which has no effect on the decoding procedure, this scheme has a clear operational advantage over some other schemes. For a BSC and a large m, a method presented for BER approximation based on the central limit theorem. / Graduate

The demand for larger user traffic capacity and better service quality for wireless communications has been increasing drastically in the past decade due to the widespread use of internet and smart phones. However, such demand is severely limited by the shortage of radio spectrum. One of the key enabling techniques to enhance spectrum utilization efficiency is spectrum sharing, which allows unlicensed secondary users to access the spectrum of a licensed primary network under interference constraints. Traditional spectrum sharing strategies developed for finite and deterministic networks require accurate information on user locations or channel gains. It is trivial that acquiring such information consumes substantial resources in large-scale and randomly deployed wireless networks. In this thesis, innovative spectrum sharing techniques for large-scale and random geometric wireless networks are explored by utilizing stochastic geometry models. Our study covers situations where each node of both primary and secondary networks is equipped with one or more than one antenna. We also consider the scenario when multiple secondary networks are present in the communication system. / We first review the various important aspects of spectrum sharing between one primary network and one secondary network where each node is equipped with only one single antenna. We analyze the successful transmission probability of each network in this case, and derive the corresponding optimal transmit power for the secondary network. The main technical challenge is to manage intra-network and inter-network interference caused by the stochastic nature of channel propagation and node distribution. Given a decrement limit for the successful transmission probability of each network, the optimal transmit power of the secondary network is determined to boost the spectrum sharing throughput while preventing individual networks from experiencing severe performance degradation. / Secondly, two multiple-input single-output networks are investigated to further improve the performance of spectrum sharing. Multiple transmit antennas manage aggregate interference by strengthening the desired signal and nulling undesired interferers, as far as possible. Partial zero-forcing beamforming is applied to spectrum sharing networks to quantify the possible density increase in the secondary users while meeting the outage requirements of other spectrum sharing users. Furthermore, we analyze the effects of the nulled interferers, and show how spectrum sharing opportunities can be enhanced in large-scale and random geometric wireless networks by wisely allocating the degrees of freedom for interference nulling. / Lastly, motivated by the evolution of wireless networks toward heterogeneity, we study spectrum sharing between one primary network and multiple secondary networks that are distinguished by system parameters, such as network densities and target data rates. A power allocation strategy is developed for the secondary networks to improve the overall spectrum sharing throughput while guaranteeing the quality-of-service of each network. The joint power allocation problem is transformed into a power ratio allocation strategy, and a quasi-closed form solution that allows for water-filling interpretation is obtained. / 由於互网和智能手機的廣泛應用，對於無線通信中更大的用戶傳輸容量以及更好的服務質量的需求在過去十年得到了長足的增長。但是，這些需求嚴重受限于無線頻譜的不足。作為提升頻譜利用率的主要技術之一，頻譜共享允許無執照的次級用戶在干擾受限的條件下使用屬於有執照的主用戶的頻譜。傳統的頻譜共享策略針對于有限的、確定性的網絡，需要準確的用戶位置信息或信道增益信息。在大規模隨機分佈的無線網絡中，獲取這些信息會消耗大量的資源。本論文利用隨機幾何模型對於大規模隨機幾何無線網絡中的頻譜共享新技術進行了探索。我們的研究涵蓋主用戶和次用戶網絡的每個節點配置單天線和多天線的多種情況。我們還考慮了系統中有多個次用戶的情況。 / 我們首先考慮的是一個主要網絡和一個次級網絡之間的頻譜共享問題，其中每個節點配置單天線。我們分析了這個場景中每個網絡的成功傳輸概率，並提出了最優化的次級用戶傳輸功率。主要的技術挑戰是管理由於信道傳播和節點分佈的隨機性而造成的網絡內部和網絡之間的干擾。為了提升頻普共享的吞吐量並且同時防止個體網絡的性能嚴重下降，次級用戶傳輸功率在給定每個網絡的成功傳輸概率的下降限制的情況下進行優化。 / 為了進一步提高頻譜共享的性能，我們進而研究了多輸入單輸出傳輸的雙網絡頻譜共享問題。發送端利用多個天線可以盡量增加倍號強度和削減干擾，從而管理整體的干擾。在符合用戶中斷概率的要求下，利用頻譜共享網絡中的部份迫零波束成形，我們量化了次級用戶的分佈密度增長。我們進一步分析了干擾源消去的影響，其結果顯示合理分配用於干擾消去的自由度可以增加大規模隨機幾何無線網絡中的頻譜共享機會。 / 最後，基於異構無線網絡的發展趨勢，我們考慮了一個主要網絡和多個次要網絡之間的頻譜共享問題。這些網絡的系統參數，如網絡密度和目標數據速率等，不盡相同。在保證個體網絡服務質量的前提下，為了加強頻譜共享的整體吞吐量，我們提出了多個次級網絡間的功率分配策略。我們把功率分配問題轉化為功率比例分配問題，從而得到了基於注水算法的近似解析解。 / Cai, Ran. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 143-155). / Abstracts also in Chinese. / Title from PDF title page (viewed on 09, December, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 84-86). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 84-86). Also available on the Internet.

Thesis (Ph. D.)--Brigham Young University. Dept. of Mechanical Engineering, 2003. / Includes bibliographical references (p. 263-279).

Includes bibliographical references (p. 124-131).

Thesis (LL. M.)--University of Toronto, 2005. / Includes bibliographical references (leaves 49-52).

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 91-98).

Includes bibliographical references (p. 56-60).