The High Frequency (HF) band lies within 2-30 MHz of the electromagnetic spectrum. In this part of the spectrum, propagation via direct wave, surface wave, and ionospheric refraction mechanisms provides means of communications from line-of-sight to beyond-line-of-sight ranges. The characteristics of ionospheric channel impose fundamental limitations on the performance of HF communication systems. The major impairment is fading which results in random fluctuations in the received signal level and affects the instantaneous signal-to-noise ratio. This requires the deployment of powerful diversity techniques to mitigate the degrading effects of fading on the performance. The range of wavelengths in HF band unfortunately restricts the use of spatial diversity (i.e., deployment of multiple antennas) for most practical purposes. This thesis focuses on an alternative method to exploit the spatial dimension of the HF channel. Specifically, we aim to extract distributed spatial diversity through relay-assisted transmission. Towards this main goal, we consider multi-carrier HF communication and investigate the performance of cooperative OFDM over HF channels.

Cooperative communication has recently re-emerged as a possible paradigm shift to realize the promises of the ever increasing wireless communication market; how- ever, there have been few, if any, studies to translate theoretical results into feasi- ble schemes with their particular practical challenges. The multiple-input multiple- output (MIMO) technique is another method that has been recently employed in different standards and protocols, often as an optional scenario, to further improve the reliability and data rate of different wireless communication applications. In this work, we look into possible methods and algorithms for combining these two tech- niques to take advantage of the benefits of both. In this thesis, we will consider methods that consider the limitations of practical solutions, which, to the best of our knowledge, are the first time to be considered in this context. We will present complexity reduction techniques for MIMO systems in cooperative systems. Furthermore, we will present architectures for flexible and configurable MIMO detectors. These architectures could support a range of data rates, modulation orders and numbers of antennas, and therefore, are crucial in the different nodes of cooperative systems. The breadth-first search employed in our realization presents a large opportunity to exploit the parallelism of the FPGA in order to achieve high data rates. Algorithmic modifications to address potential sequential bottlenecks in the traditional bread-first search-based SD are highlighted in the thesis. We will present a novel Cooperative Partial Detection (CPD) approach in MIMO relay channels, where instead of applying the conventional full detection in the relay, the relay performs a partial detection and forwards the detected parts of the message to the destination. We will demonstrate how this approach leads to controlling the complexity in the relay and helping it choose how much it is willing to cooperate based on its available resources. We will discuss the complexity implications of this method, and more importantly, present hardware verification and over-the-air experimentation of CPD using the Wireless Open-access Research Platform (WARP). / NSF grants EIA-0321266, CCF-0541363, CNS-0551692, CNS-0619767, EECS-0925942, and CNS-0923479, Nokia, Xilinx, Nokia Siemens Networks, Texas Instruments, and Azimuth Systems.

In wireless transmissions the communication is often degraded by random fades, noise and other performance reducing phenomena. One way of improving the stability and reducing the error rates is to use relaying techniques where several nodes cooperate in a transmission between two of them. This thesis analyzes some of the available Decode-and-Forward relaying schemes for wireless transmission. The investigated schemes are conventional repetition coding, partial repetition coding and non-collaborative direct transmission. I have developed a three-node communication system using an audio channel to test the performance of repetition coding and direct transmission. This audio communication system can also be used to demonstrate some basic phenomena in wireless transmissions and how different scenarios change the performance of the communication. A theoretical performance analysis and computer simulations of the schemes performance over a Rayleigh fading channel are done as a basis for comparison. As a result we see that in the audio communication system repetition coding actually degrades the performance, compared to direct transmission, when using a relatively slow data rate in comparison to the speed of the fading in the audio channel.

The High Frequency (HF) band lies within 2-30 MHz of the electromagnetic spectrum. In this part of the spectrum, propagation via direct wave, surface wave, and ionospheric refraction mechanisms provides means of communications from line-of-sight to beyond-line-of-sight ranges. The characteristics of ionospheric channel impose fundamental limitations on the performance of HF communication systems. The major impairment is fading which results in random fluctuations in the received signal level and affects the instantaneous signal-to-noise ratio. This requires the deployment of powerful diversity techniques to mitigate the degrading effects of fading on the performance. The range of wavelengths in HF band unfortunately restricts the use of spatial diversity (i.e., deployment of multiple antennas) for most practical purposes. This thesis focuses on an alternative method to exploit the spatial dimension of the HF channel. Specifically, we aim to extract distributed spatial diversity through relay-assisted transmission. Towards this main goal, we consider multi-carrier HF communication and investigate the performance of cooperative OFDM over HF channels.

Cooperative communication has recently become a key technology for modern wireless networks such as 3GPP long-term evolution and WiMAX, because in such networks the transmission rate, the communication reliability, and coverage problems could be improved in a cost-effective manner. This, however, faces many design challenges. First, cooperative transmission typically involves a relaying phase which requires extra resources. This may cause a reduction in the spectral efficiency. Second, extra control signaling increases the complexity of operation, which may limit practical implementation. In addition, a wireless channel is time-varying, mainly due to the multipath propagation. As a result, a careful design of efficient cooperative communication systems is required, not only to enhance the spectral efficiency and maintain the quality-of-service (QoS), but also to be practical. In this dissertation, we aim to address the challenges imposed by cooperative communication and wireless transmission, and design the efficient and distributed systems which can be practically implemented in existing wireless systems. The research work is divided into two main topics: 1) adaptive cooperative wireless systems with variable-rate transmission, and 2) cooperative wireless systems with a power consumption constraint. The first topic investigates how the spectral efficiency of cooperative wireless communication systems can be improved while maintaining the QoS in terms of bit error rate and outage probability. The spectral efficiency enhancement is achieved by using three techniques: adaptivity over the relay node (i.e., relay node is active or not), adaptivity over the modulation mode, and relay selection. Based on that, we propose several adaptive cooperative schemes for both the decode-and-forward (DF) and amplify-and-forward (AF) protocols. To evaluate these schemes, we provide performance analysis in terms of average spectral efficiency, average bit error rate (ABER), and outage probability over Rayleigh fading channels. We start with the single-relay cooperative system using DF protocol, in which two adaptive cooperative schemes with variable-rate transmission are proposed. The first scheme, called the minimum error rate scheme (MERS), aims to exploit the transmit diversity to improve the bit error rate. By trading the multiplexing gain against the diversity gain, we propose the second scheme, called the maximum spectral efficiency scheme (MSES), in which cooperative transmission is avoided whenever it is not beneficial. The MERS improves the ABER significantly and achieves equal or better average spectral efficiency compared to the fixed (i.e., non-adaptive) relaying scheme. In contrast, the MSES provides the best average spectral efficiency due to its ability to not only adapt to the channel variation but also to switch between cooperative and non-cooperative transmissions. To further increase the spectral efficiency, we then propose the third scheme, called variable-rate based relay selection (VRRS) scheme, in which a relay node is selected from among the available relay nodes, based on a predefined criterion. Furthermore, we propose two AF adaptive cooperative schemes, mainly to enhance the spectral efficiency. In the first scheme, we introduce a generalized switching policy (GSP) for a single-relay cooperative wireless system that exploits the variable-rate transmission and useful cooperative regions. The second scheme, called the AF efficient relay selection (AFERS) scheme, extends the GSP to also consider the relay selection technique. Analytical and simulation results verify that the AFERS scheme not only outperforms conventional direct transmission in terms of the average spectral efficiency, but also the AF fixed relaying and the outage-based AF adaptive cooperative scheme. The second topic investigates the fair power consumption of the relay nodes for AF cooperative wireless communication systems. The fairness is defined as to achieve equal power consumption over the relay nodes. We focus on how the relay selection process can be controlled in a distributed manner so that the power consumption of the relay nodes can be included in relay selection. We first introduce a simple closed-form expression for the weight coefficient used in order to achieve the considered fairness that depends only on the local average channel conditions of the relay path. We then derive closed-form expressions of the weighted outage probability and ABER and show that our proposed strategy not only has less complexity than the conventional centralized one but also provides better accuracy in distributing the total consumed power equally among the relay nodes without affecting the performance.

The purpose of this study is to investigate the effects of using moral-based cooperative learning on enhancing compassion, responsibility and honesty among elementary school students. A nonequivalent pretest-posttest design is conducted on this study. The experimental group students receive 11-week of ¡§Moral-based Cooperative Learning¡¨; On the other hand, control group students receive traditional teaching method. During the course, all participants response investigator-developed instrument ¡§Elementary School Students Moral Behavior Scale¡¨ . In addition, observation, daily student behavior records and follow-up individual interview are conducted to 6 target students with the high, moderate, and the low scores of moral behavior in the pre-test. Correlation, t-test, ANOVA and ANCOVA are conducted for comparing the similarity and differences between two groups. A theme content analysis is conducted to analyze the qualitative data. The major findings are as following: 1. After the use of ¡§Moral-based Cooperative Learning ¡¨,The experimental group students¡¦ moral behaviors, compassion and honesty are significantly higher than the control group students¡¦. 2. The experimental group students make more significant improvement of their moral behaviors on ¡§compassion¡¨and ¡§honesty¡¨ than ¡§responsibility¡¨. 3. The low score group students make more significant progress of their moral behaviors than the high and moderate score group students. 4. There is no significant difference on moral behaviors among students with different gender, birth order, social-economic status or family structure. 5. There is significant positive correlation among compassion, responsibility and honesty of experimental group students. According to those significant findings, educational recommendation and suggestions provide toward teachers and researchers be discussed .

This thesis proposes an alternative cooperating strategy for cooperative communications through the use of parley algorithm in cooperative communications. When employing parley algorithm in cooperative communications, the relay nodes and the destination node need to disseminate and agree on a common decision throughout the cooperation network via a consensus flooding procedure. In this thesis, a heuristic approach for improving the performance of the parley algorithm is proposed. This heuristic approach is to design power allocation method during each iteration of consensus flooding protocol. Specifically, when distributing the power to each node within the cooperative network, this thesis adopts the criterion of maximum capacity of the broadcast channel used for consensus flooding procedures. The simulation result obtained from the investigation of this thesis shows that the proposed power allocation approach can improve the performance in terms of bit error rate as compared with the parley algorithm with uniform power allocation, and, hence, confirms the proposed idea is useful.

The aim of this study is to investigate the effects of learning styles and cooperative learning on academic achievement of technical university students in calculus. Meanwhile, in order to understand the effectiveness of learning on calculus, we perform item analysis of calculus test conducted in terms of item difficulty and item discrimination analysis. This research is conducted on a quasi-experimental design. Participants in this study are selected from the first year students of two departments in a technical university. Two intact classes of the same department are randomly assigned to be an experimental group and a control group. The experimental group receives the cooperative learning while the other receives the traditional learning. The results show that the learning achievement of active learners is better than reflective learners in the experimental group of information management. On the contrary, the reflective learners have better learning achievement than active learners in the experimental group of computer science and information engineering. The learning achievement of the experimental group is better than the control group in department of information management. The result is opposite in department of computer science and information engineering. But the differences of the learning achievement mentioned above are not statistically significant. Furthermore, item difficulty analysis suggests teachers and students should pay more attentions to those more difficult items and the corresponding calculus sections.

Wireless networks are becoming more and more popular. In current wireless network environments, mobile users can use multiple wireless network interfaces built in their mobile devices to roam around the mobile networks. They can scan the wireless spectrums and utilize the network resources extremely, and they can roam into nearby wireless networks due to the mobility capabilities of the powerful mobile devices. Before connecting to an access point, an authentication process is necessary. There are many interactive wireless authentication protocols which have been proposed in the literature. Under the wireless networks, handover is an important property for a mobile user to change her/his position. However, the existing interactive wireless authentication protocols may cause unstable connection. This is because that a mobile user may perform failed authentications with some nearby invalid access points and thus she/he cannot finish handover in time. Hence, we would like to design a mechanism for a mobile user to determine the validity of access points before the interactive authentication, and the mobile user can choose a valid one when making handover. In our proposed scheme, the mobile user can just scan and receive authentication messages from access points without interactions with them while she/he can determine which one of them is valid. We call this cognitive authentication. Besides, we also propose cooperative defense which allows mobile users to exchange their received authentication messages for detecting illegal access points. Finally, we provide security proofs for our proposed scheme.

This thesis proposes a distributed beamforming technique in wireless networks with half-duplex amplify-and-forward relays. With full channel state information, it has been shown that transmit beamforming is able to achieve significant diversity and coding gain. However, it takes large amount of overhead. First, we adopt the Generalized Lloyd Algorithm to design codebooks which minimize average SNR, and reduce the feedback rate by quantizing the channel state information. Furthermore, we utilize the correlation property of time-varying channels to compress the size of feedback message required to accomplish distributed beamforming. We model time-varying channels as a first-order finite-state Markov chain, namely the emph{channel state Markov chain}. Then, we propose two methods to compress the feedback bits according to the property of the transition probabilities among different channel states. One method is to compress the feedback by discarding some channel states which is less likely to be transited given current state. In the other method, we reserve all channel states and adopt Huffman coding to compress the feedback bits based on the transition probabilities. Simulations also show that distributed beamforming with compressed feedback performs closely to the beamforming with infinite feedback.