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<p> In this thesis, we consider a multiuser downlink OFDM system for which the channel state information ( CSI) is known to both the transmitter and the receiver. </p> <p> For such a system, we design an optimal precoder that minimizes the total mean square error (MSE) subject to a total power constraint for which a minimum MSE (MMSE) equalizer is employed. We show that, the MMSE precoder can be obtained by optimally allocating the subcarriers and optimally allocating the power. This problem can be solved by a two-stage process, in which we minimize the lower bound of the MSE to obtain the optimal power for each subcarrier, followed by seeking an optimal precoder to achieve this minimized lower bound. Specifically, our subcarrier allocation strategy states that, each subcarrier should be allocated to only one user that has the largest subchannel gain in that subcarrier. </p> <P> Moreover, based on this subcarrier allocation strategy, we perform an optimal power loading and design the corresponding optimal precoder that minimizes the average bit error rate (BER). Here, the MMSE equalizer is also employed. This optimization problem is solved by two stages. In the first stage, we derive the lower bound of the average BER and minimize this lower bound. After we employ the MMSE subcarrier allocation strategy, the optimal power loading problem can be efficiently solved by interior point methods. In order to reduce computation complexity, an alternative, efficient power loading method is proposed here, which is much more efficient when the number of subcarriers is large. In the second stage, to achieve the minimized lower bound, we seek a design of an optimal precoder. Simulation results show that for moderate to high signal-to-noise ratio (SNR), the performance of the minimum BER {MBER) precoder employed with the MMSE equalizer design is superior to several other design methods, including the MMSE precoder design. </p> / Thesis / Master of Applied Science (MASc)

Thesis (Ed. D.)--East Tennessee State University, 2002. / Originally issued as electronic document. Includes bibliographical references.

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The Decision Feedback Equalizer (DFE) is a known method of channel equalization which has performance superiority over linear equalizer. The best performance of DFE is obtained, commonly, with training period which is used for initial acquisiton of channel or recovering changes in the channel. The training period requires a training sequence which reduces the bit transmission rate or is not possible to send in most of the situations. So, it is desirable to skip the training period. The Unsupervised (Blind) DFE (UDFE) is such a DFE scheme which has no training period. The UDFE has two modes of operation. In one mode, the UDFE uses Constant Modulus Algorithm (CMA) to perform channel acquisition, blindly. The other mode is the same as classical decision-directed DFE. This thesis compares the performances of the classical trained DFE method and the UDFE. The performance comparison is done in some channel environments with the problem of timing error present in the received data bearing signal. The computer aided simulations are done for two stationary channels, a time-varying channel and a frequency selective Rayleigh fading channel to test the performance of the relevant equalizers. The test results are evaluted according to mean square error (MSE), bit-error rate (BER), residual intersymbol interference (RISI) performances and equalizer output diagrams. The test results show that the UDFE has an equal or, sometimes, better performance compared to the trained DFE methods. The two modes of UDFE enable it to solve the absence of training sequence.

ITC/USA 2015 Conference Proceedings / The Fifty-First Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2015 / Bally's Hotel & Convention Center, Las Vegas, NV / The emission of the telemetry signal is required over minimum two different antennas to keep the telemetry link available during a maneuver of a flying object. If nothing is made at the transmitter side, the telemetry link can be fully lost as both signals may have an opposite phase. We here propose a simple solution based on delay diversity to solve this problem. The basic idea is to introduce a delay between both emitted signals to guarantee a non-destructive signal recombination. We then exploit the ability of the blind equalizer developed by ZDS for the PCM/FM modulation to correctly equalize this signal and to recover the initial data. This solution does not require any modification of the on-board and floor set-ups except the introduction of a delay line between both transmitting antennas. It also does not need any pilot sequence and is natively robust to multipath perturbations.

ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada / The main objectives of iNET (Integrated Network Enhanced Telemetry) are increased data rate and improved spectral efficiency [1]. In this paper we propose that transmission scheme for the physical layer is coded 16-QAM OFDM (Quadrature Amplitude Modulation-Orthogonal Frequency Division Multiplexing) which enables high data rate and spectrum efficiency. However in high mobility scenarios, where the channel is time-varying the receiver design is more challenging. Therefore in this paper pilot-assisted channel estimation is used at the receiver, with convolutional coding and error correction to enhance the performance; while the effect of inter symbol interference (ISI) is mitigated by cyclic prefix. The focus of this paper is to evaluate the performance of OFDM with 16-QAM over an aeronautical channel. The 16-QAM with OFDM enables 4 bits/symbol and provides a higher data rate than QPSK hence it is chosen in this paper. The implementation of OFDM is done using Inverse Fast Fourier Transform (IFFT) and the Fast Fourier Transform (FFT). In this paper we simulate how the performance of Coded 16-QAM OFDM is enhanced using equalization to compensate for inter symbol interference, convolutional coding is used for error correction, puncturing for improving data rate and the insertion of cyclic prefix (CP) to avoid inter carrier interference.

Education is considered the single most important factor in determining the economic and social well-being of a state. This statement aptly applies to the State of Georgia which ranks very low among other states in the nation in overall educational financing. Though education is a state responsibility in Georgia, there is a considerable measure of local control. Local financial contribution toward education in the state is met mainly through the property tax which differs markedly among the school districts/systems. This difference reflects in the amount of money available to the schools for educational purposes. An analytical study of randomly selected school districts in Georgia reveals that the wealthy districts spend more on education, levy less property tax, and can afford to support their schools on money derived from their tax base with or without state supplemental funding. The study further shows that disparities in wealth among school districts· create problems for equalizing educational opportunities and makes recommendations aimed at meliorating the situation.

"Widening access" (WA) policies are designed to increase the participation of underrepresented groups into Higher Education generally, and specifically into professions such as medicine. The interpretation, negotiation and enactment of WA policies is determined by key stakeholders, including medical schools, school teachers and potential applicants. In the UK, measurable progress in WA to medicine has been low. This thesis argues this may partly be due to stakeholders' conflicting values, ideologies and interests. The thesis thus aims to explore, analyse and better understand the complex motivations, perceptions and values underlying key stakeholders' behaviour in WA to medicine. Data includes medical school websites, interviews with high school teachers and focus groups with pupils. Analytical methods are qualitative (critical discourse analysis; thematic analysis) and are enriched by discursive and sociological theories (Foucault, Sen, Bernstein and Bourdieu). Analysis focuses on the pathways of mutual influence and communication between key stakeholders. Findings indicate that UK medical schools predominantly situate WA within ideas of social mobility for the individual rather than benefit to the workforce. Medical school webpages frame WA as a 'requirement', a 'value', or a 'service' and communicate distinct impressions of institutional stance to other stakeholders. High school teachers perceive medical school applications as 'risky' and this appears to limit their ability to engage as greater advocates for WA. Pupils in WA high schools perceive medicine as increasingly culturally inclusive and negotiate cultural differences through reference to role models in the profession. High academic entry requirements within a context of substantial educational inequality may now be the largest perceived 'barrier' to medicine. Overall, this thesis identifies the reasons underlying stakeholders' behaviour and evaluates whether these may be helping/hindering WA to medicine. It demonstrates the benefit of including diverse stakeholder's voices in WA research and provides practical recommendations for future research, policy and practice.