Abstract The performance of conventional receivers for wireless communications may severely deteriorate in the presence of unaccounted interference. The effectiveness of methods for mitigating these effects greatly depends on the knowledge that is available about the interference and signal-of-interest (SOI), therefore making the design of robust receivers a great challenge. This thesis focuses on receiver structures for channel coded systems that exploit different levels of knowledge about the SOI and interference in an iterative fashion. This achieves both robustness and overall performance improvement compared to non-iterative receivers. Code division multiple access (CDMA) and spatial division multiple access (SDMA) systems are considered. The overlay of a turbo coded direct-sequence spread-spectrum (DS-SS) system and strong digitally modulated tone interference is studied. An iterative receiver, which is capable of blind cancellation of both wideband and narrowband interference is proposed based on the adaptive self-reconfigurable -filter scheme. Asymptotic performance analysis of the iterative receiver shows that significant iteration gains are possible if the signal-to-interference-plus-noise-ratio (SINR) is relatively large and the processing gain (PG) of the SOI is relatively small. Robust diversity detection in turbo-coded DS-SS system with statistically modeled interference is studied. A non-parametric type-based iterative receiver that estimates the probability density function (PDF) of interference-plus-noise is proposed. Its performance is shown to be rather robust to the number of interferers and their distances from the victim receiver and very similar to the performance of a clairvoyant receiver. Amazingly, this is achievable with no prior knowledge about the interference parameters. Furthermore, iteration gain is shown to significantly reduce the length of the pilot sequence needed for the PDF estimation. A family of iterative minimum-mean-squared-error (MMSE) and maximum-likelihood (ML) receivers for convolutionally and space-time coded SDMA systems is proposed. Joint iterative multiuser-detection (MUD), equalization and interference suppression are proposed to jointly combat co-channel interference (CCI), inter-symbol-interference (ISI) and unknown CCI (UCCI) in broadband single-carrier systems. It is shown that both in convolutional and space-time coded systems the ISI and CCI interference can be completely eliminated if UCCI is absent. This is achievable with a number of receive antennas equal to the number of users of interest and not to the total number of transmit antennas. In case UCCI is present, the effectiveness of CCI and ISI cancellation and UCCI suppression depends on the effective degrees of freedom of the receiver. Receiver robustness can be significantly preserved by using hybrid MMSE/ML detection for the signals of interest, or by using estimation of the PDF of the UCCI-plus-noise. A low complexity hybrid MMSE/ML iterative receiver for SDMA is proposed. It is shown that its performance is not significantly degraded compared to the optimal ML receiver. Its sensitivity to spatial correlation and a timing offset is assessed by using field measurement data. It was shown that the hybrid MMSE/ML receiver is robust against spatial correlation. The sensitivity to the timing offset is significantly reduced if the receiver performs UCCI suppression.

In a telemetry system, it has been frequently proved that multipath channels and transmission noise are the most critical sources of distortion. While equalization allows a strong limitation of the multipath effects, the noise impact can be efficiently reduced if forward error correction is used. This paper proves that the combination of blind equalization and a powerful FEC like LDPC strongly improves bit error rates for the SOQPSK modulation. We also prove that a LDPC code is able to fully correct the residual errors that may persist at the equalizer output. In other terms, the combination of equalization and LDPC code enables quasi-error free transmissions in various channel scenarios that represent the various phases of a telemetry mission.

Drawing on historical case study methodology informed by critical perspectives of education, this study examines the decision by Tucson United School District (TUSD) to ban its nationally recognized Mexican American Studies (MAS) program in 2012. Framing public education as a site of contestation for equality and democratization, the ban is examined within a five-phase historical context of the struggles of Chicanos for equity in the USA. The research questions address the dismantling of the program in terms of the ongoing historical disparities between the education of Chicanos and Anglo Americans in Tucson, diverse stakeholders’ perspectives on equality and inequality in the decision making, and the response of stakeholders who supported the program to the attempts to dismantle it. The theoretical framework of this study intersects Critical Race Theory and its corollary Latino Critical Theory, Critical Multicultural Pedagogy that centers Critical Pedagogy and Historical Discourse Analysis that focuses attention to the use of power in educational decision making. The interview data from nine study participants who were closely affiliated with the MAS program and selected historical documents and archival data were analyzed to uncover Anglo and Chicano perspectives on education for Mexican Americans in Tucson. The analysis revealed that the differences between Chicano and Anglo perspectives on equity and the role of education in facilitating equality for Chicanos laid the groundwork for the conceptualization of the MAS program by its supporters, and the rationale for its banning by its opponents. The interview data revealed that all participants contextualized their work in the MAS within the history of struggle for Chicano education, they represented a cohesive “Dream Team” committed to implementing a program grounded in critical and culturally relevant pedagogies, and that initial marginalization provided them the space for unimpeded development of the program. Participants’ responses further revealed evidence of the deep psychological toll, intellectual energy demands, and civic engagement required of MAS supporters in the face of this particular episode in the ongoing history of the struggle for Chicano educational equity. The implications for critical multicultural education programs operating within culturally hegemonic policy and social contexts are examined. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2021. / FAU Electronic Theses and Dissertations Collection

Dissertation submined in fulfilment of the requirements for the degree Magister Educationis in the Department of Educational Psychology of the Faculty of Education at the University of Zululand, 1998. / The aims of this investigation were: * To pursue a study of relevant literature of the life-world of the black child in the ex-Model *C schools. * In the light of the findings obtained from the literature study formulate recommendations which could serve as guidelines according to which accountable support can be instituted in order to meet the needs of the black learner in "ex-Model *C* schools" who may be experiencing educational distress. As an introduction the nature and dynamics of the black child in ex-Model 'C schools are analyzed and discussed with an aim to state the problem clearly. From a psychopedagogical perspective the black child in ex-Model 'C schools often experience educational distress mainly due to the fact that the black learner has been perpetually subjected to educational neglect. Black learners during the apartheid era developed psychological and emotional problems which manifested in dysfunctional relationships with themselves, educators and educational authorities. The typical black child during the apartheid period was characterised by, inter aliay a sense of inadequacy, inferiority, hatred, envy, jealousy and racial prejudices. The educational products of apartheid education in many black communities, were unemployed, frustrated and highly politicised militant adolescents, who stumble though life with a feeling of insecurity, a lack of self-confidence and opposed to any form of authority. They have a a sense of impending failure, which encourages black learners to wander aimlessly along the road of violence, alcohol and substance abuse as wel! as sexual promiscuity. Education as a true human activity which finds its actualization in the relationship between adult and child is examined more closely. From a psychopedagogical perspective the black learner in ex-Model 'C schools finds himself in a situation of dysfunctional education mainly because his live-experiencing of education in ex-Model *C schools is often without adequate assistance and guidance of a responsible parent, or adult. This results in the psychic life of the black learner in ex-Model 'C schools being under-actualised. The inadequate adult intervention and guidance, which are based on the pedagogical principles of love, trust, understanding and authority, result in the black learner forming relationships within his life-world which are inadequate for his emancipation. Thus, the black learner, more often than not, fails to constitute a meaningful life-world in ex-Model *C* schools. At present, only a few supporting services exist in ex-Model 'C* schools, unfortunately these support services are not compatible or commensurate with the needs of historically, economically and environmentally deprived black learners. Support services which endeavour to rehabilitate family relations, eliminate hindrances to successful learning and supervises those who are offered assistance, are desperately needed. The fact that the black learner is a "child" that should be assisted by parents and the school in his transition process of becoming, is at present not given enough attention in ex-Model 'C* schools. There is a lack of the suitably qualified personnel and funds to offer the needed support by the existing support services. The findings of this research hence recommends the following: * School preparedness of the ex-Model TC school to accommodate all races. * Academic support for black learners at ex-Model *C* schools. * Compulsory guidance and counselling for all black learners at ex-Model X' schools. Establishment of school clinics to assist the black learner in particular. Guidance and involvement programmes at ex-Model 'C schools for black parents. Adequate pre-service and in-service preparation of teachers for ex-Model 'C schools for multi-racial education. Further research into this aspect of multi-cultural education.

No description available.

Sound pressure equalization of audio signals using digital signal processors has been a subject of ongoing study for many years. The traditional approach is to equalize sound at a point in a listening environment, but because of its specific dependence on the room frequency response between a source and receiver position, this equalization generally causes the spectral response to worsen significantly at other locations in the room. This work presents both a time-invariant and a time-varying implementation of an adaptive acoustic energy density equalization filter for a one-dimensional sound field. Energy density equalization addresses the aforementioned challenge and others that relate to sound equalization. The theory and real-time implementation of time-invariant sound pressure and energy density equalizers designed using the least-squares method are presented, and their performances are compared. An implementation of a time-varying energy density equalizer is also presented. Time-invariant equalization results based on real-time measurements in a plane-wave tube are presented. A sound pressure equalizer results in a nearly flat spectral magnitude at the point of equalization. However, it causes the frequencies corresponding to spatial nulls at that point to be undesirably boosted elsewhere in the sound field, where those nulls do not exist at the same frequencies. An energy density equalization filter identifies and compensates for all resonances and other global spectral effects of the tube and loudspeaker. It does not attempt to equalize the spatially varying frequency nulls caused by local pressure nodes at the point of equalization. An implementation of a time-varying energy density equalizer is also presented. This method uses the filtered-x filter update to adjust the filter coefficients in real-time to adapt to changes in the sound field. Convergence of the filter over time is demonstrated as the closed end of the tube is opened, then closed once again. Thus, the research results demonstrate that an acoustic energy density filter can be used to time-adaptively equalize global spectral anomalies of a loudspeaker and a one-dimensional sound field.

No description available.

This thesis describes the use of adaptive equalization techniques to compensate for the intersymbol interference (ISI) that results when digital data is transmitted over a multipath radio channel. The equalization structures covered in this work are the linear transversal equalizer (LTE), the fractionally spaced equalizer (FSE), the decision-feedback equalizer (DFE), and the maximum-likelihood sequence estimation (MLSE) equalizer. This work also covers adaptive algorithms for equalization including both the least mean squares (LMS) and the recursive least squares (RLS) algorithm. All these equalizer structures and algorithms will be modeled using various simulation modules. Equalization for both stationary and mobile radio channels is considered. Stationary channels are modeled with a simple exponentially decaying profile. The mobile radio channel is represented using a two-ray Rayleigh fading model for an outdoor environment. The SIRCIM channel modeling tool is used to create channel profiles for an indoor mobile radio channel. Adaptive arrays and their similarities to linear equalizers are also studied in this thesis. The properties and performance of simple adaptive array systems using the LMS and RLS algorithms are examined through simulation. This thesis concludes with an in-depth study of the use of adaptive equalization for high-speed data systems operating in an indoor environment. Both stationary and slowly varying radio channels are examined. Simulations of DFE and MLSE equalizers operating in such a system show that both equalizer structures provide better BER performance over a system with no equalization. These simulation results also show that the MLSE equalizer provides better performance than the DFE in almost all cases, but requires a great deal more computations. / Master of Science

Cochannel interference (CCI) is a major impairment in narrowband cellular systems. To increase the spectral efficiency of the narrowband systems, identical carrier frequencies are reused in distant cells. The interference rejection capability of the receiver determines this frequency reuse and is therefore critical. In this thesis, we propose an improved demodulation scheme, employing high-resolution frequency estimation techniques, for continuous phase modulated (CPM) signals in presence of CCI. Minimum shift keying (MSK), which is a special case of CPM, is a very popular modulation format around the world. Frequency detectors, such as the limiter-discriminator permit the non-coherent demodulation of MSK signals. High-resolution frequency estimation appears as a very attractive alternative to the conventional non-coherent frequency detectors. The frequency estimation methods that we have studied are based on autoregressive modeling. The contributions of this thesis include the implementation of various demodulation schemes employing parametric frequency estimation. The use of the Viterbi algorithm as a non-linear equalization technique to mitigate intersymbol interference is considered. We verified that the model-based sequence estimation schemes outperform the conventional non-coherent receivers for MSK with AWGN, flat fading, and CCI. Demodulator diversity is also investigated as a way to combat interference. An improved technique combining the proposed model-based receiver and the conventional coherent receiver is implemented and simulated in presence of CCI. / Master of Science

In modern wireless communication systems, such as satellite communications and wireless networks, the need for higher data rates without the need for additional transmit power has made Continuous Phase Modulation (CPM) one of the most attractive modulation schemes in band limited channels. However, as the data rates keep increasing, the spectral width of the CPM signal increases beyond the channel bandwidth and performance becomes constrained by the intersymbol interference (ISI) that results from band-limiting filters. We propose two approaches to the problem of equalization of band-limited CPM signals. First, our efforts are focused on shortening the channel impulse response so that we can use a low complexity MLSE equalizer. We implement the channel truncation structure by Falconer and Magee and adapt it to work with CPM signals. This structure uses a, a more derivable, pre-filter to shape the overall response of the channel, so that its impulse response is of shorter duration. Simulation results show that near-MLSE performance can be obtained while dramatically reducing MLSE equalizer complexity. In our second approach, we focus on eliminating the group-delay variations inside the channel passband using an FIR pre-filter. We assume the channel to be time-invariant and provide a method to design an FIR filter so that -when convolved with the band limiting filter - it results in more constant group-delay over the filter passband. Results show that eliminating the group-delay variations in the band limiting filter passband reduce the amount of ISI and improve bit error rate performance. / Master of Science