Doctor of Philosophy (PhD) / This thesis considers transmission techniques for current and future wireless and mobile communications systems. Many of the results are quite general, however there is a particular focus on code-division multiple-access (CDMA) and multi-input multi-output (MIMO) systems. The thesis provides analytical techniques and results for finding key performance metrics such as signal-to-interference and noise power ratios (SINR) and capacity. This thesis considers a large-system analysis of a general linear matrix-vector communications channel, in order to determine the asymptotic performance of linear fixed and adaptive receivers. Unlike many previous large-system analyses, these results cannot be derived directly from results in the literature. This thesis considers a first-principles analytical approach. The technique unifies the analysis of both the minimum-mean-squared-error (MMSE) receiver and the adaptive least-squares (ALS) receiver, and also uses a common approach for both random i.i.d. and random orthogonal precoding. The approach is also used to derive the distribution of sums and products of free random matrices. Expressions for the asymptotic SINR of the MMSE receiver are derived, along with the transient and steady-state SINR of the ALS receiver, trained using either i.i.d. data sequences or orthogonal training sequences. The results are in terms of key system parameters, and allow for arbitrary distributions of the power of each of the data streams and the eigenvalues of the channel correlation matrix. In the case of the ALS receiver, we allow a diagonal loading constant and an arbitrary data windowing function. For i.i.d. training sequences and no diagonal loading, we give a fundamental relationship between the transient/steady-state SINR of the ALS and the MMSE receivers. We demonstrate that for a particular ratio of receive to transmit dimensions and window shape, all channels which have the same MMSE SINR have an identical transient ALS SINR response. We demonstrate several applications of the results, including an optimization of information throughput with respect to training sequence length in coded block transmission.

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With the increasing demand of higher data rate for telecommunication, the IEEE802.11n standard was constituted in 2009. Themost important character of the standard is MIMO-OFDM, which not only improves the throughput but also the spectrumefficiency and channel capacity. This report focuses on the physical layer IEEE802.11n model. By utilizing an existingSimulink based IEEE802.11n system, functionalities like MIMO (up to 4*4), OFDM, STBC, Beamforming, and MMSEdetector are simulated. The results such as bit error rate, packet error rate and bit rate with different system settings are given.Furthermore, the channel estimation process is clarified, and a DSP builder based MMSE detector is realized, which can fulfillexactly the same function as the Simulink model.

Doctor of Philosophy (PhD) / This thesis considers transmission techniques for current and future wireless and mobile communications systems. Many of the results are quite general, however there is a particular focus on code-division multiple-access (CDMA) and multi-input multi-output (MIMO) systems. The thesis provides analytical techniques and results for finding key performance metrics such as signal-to-interference and noise power ratios (SINR) and capacity. This thesis considers a large-system analysis of a general linear matrix-vector communications channel, in order to determine the asymptotic performance of linear fixed and adaptive receivers. Unlike many previous large-system analyses, these results cannot be derived directly from results in the literature. This thesis considers a first-principles analytical approach. The technique unifies the analysis of both the minimum-mean-squared-error (MMSE) receiver and the adaptive least-squares (ALS) receiver, and also uses a common approach for both random i.i.d. and random orthogonal precoding. The approach is also used to derive the distribution of sums and products of free random matrices. Expressions for the asymptotic SINR of the MMSE receiver are derived, along with the transient and steady-state SINR of the ALS receiver, trained using either i.i.d. data sequences or orthogonal training sequences. The results are in terms of key system parameters, and allow for arbitrary distributions of the power of each of the data streams and the eigenvalues of the channel correlation matrix. In the case of the ALS receiver, we allow a diagonal loading constant and an arbitrary data windowing function. For i.i.d. training sequences and no diagonal loading, we give a fundamental relationship between the transient/steady-state SINR of the ALS and the MMSE receivers. We demonstrate that for a particular ratio of receive to transmit dimensions and window shape, all channels which have the same MMSE SINR have an identical transient ALS SINR response. We demonstrate several applications of the results, including an optimization of information throughput with respect to training sequence length in coded block transmission.

This paper investigates the effect of parameter selection for the decision feedback equalization (DFE) on communication performance through a dispersive underwater acoustic wireless channel (UAWC). A DFE based on minimum mean-square error (MMSE-DFE) criterion has been employed in the implementation for evaluation purposes. The output from the MMSE-DFE is input to the decoder to estimate the transmitted bit sequence. The main goal of this experimental simulation is to determine the best selection, such that the reduction in the computational overload is achieved without altering the performance of the system, where the computational complexity can be reduced by selecting an equalizer with a proper length. The system performance is tested for BPSK, QPSK, 8PSK and 16QAM modulation and a simulation for the system is carried out for Proakis channel A and real underwater wireless acoustic channel estimated during SPACE08 measurements to verify the selection.

Alzheimer´s disease (AD) is today the world’s most common disease within dementia as it affects most number of people that are demented. There are no cure to AD, just symptomatic treatment are available. Scientists are still discussing the reason behind AD and many different theories exist. The most popular one is the amyloid cascade hypothesis. To diagnose AD many different types of scales are used to determine a person´s cognitive skills, also blood- and spinal cord samples are taken. One of the most popular scale that is used to diagnose AD is named mini mental state exam (MMSE). MMSE consists of several domains including: orientation, reading, mental arithmetic, writing and figure copying. The maximum of points are 30 and a score of 24 or less indicates some type of dementia. Today acetylcholinesteraseinhibitors like donepezil, rivastigmine and galantamine are used to treat people with mild to moderate AD. People with severe AD are recommended treatment with a NMDA-receptor-antagonist, memantine. The result from this study includes a summary of results from five studies. All of them studied the effect of donepezil over time and three of them also studied donepezils effect compared to placebo. Patients that were included had mild- moderate AD and in one study they measured a continued treatment with donepezil. All studies measured the results with scales and tests, including MMSE, that assessed patient’s cognitive ability. The results showed that patients treated with donepezil had significantly improved their scores on the scale MMSE at the end of the studies compared from baseline in three studies. When compared with placebo patients treated with donepezil got significantly better scores on MMSE. These changes were small even if significantly proven. The conclusion of this work was that MMSE is not optimal for measuring changes in AD if the patient is treated with donepezil because of the small changes. MMSE have difficulties to detect the small changes (a change of ≤ 3 points) and therefore other scales and tests are in need. Donepezil showed a significantly improvement in the beginning of the studies but after a few weeks that improvement had decreased or disappeared. It could be in everyone´s favor to start medication in an early stage of the disease and then after a while make a new assessment of the patient’s health.

This thesis investigates the performance of a multi-user multiple-input single- output (MISO) system considering maximum ratio transmission (MRT) downlink precoding. The transmitted signal from the base station (BS) to each user is as- sumed to experience the double scattering channel. We adopt the minimum-mean- square-error (MMSE) channel estimator for the proposed model. Within this setting, we are interested in deriving tight approximations of the ergodic rate assuming the number of BS antennas, users, and scatterers grow large with the same pace. Under the special multi-keyhole channels, these deterministic equivalents are expressed in more simplified closed-form expressions. The simplified expressions reveal that unlike the standard Rayleigh channel in which the SINR grows as as O(N/k), the SINR associated with a multi-keyhole channel scales as O(S/N). This particularly shows that the K reaped gains of the large-scale MIMO over double scattering channels do not linearly increase with the number of antennas and are limited by the number of scatterers. We further show that the derived asymptotic results match the simulation results closely under moderate system dimensions and provide some useful insights into the interplay between N, K and S.

Orthogonal Frequency Division Multiplexing (OFDM) has recently gained a lot of attention and is a potential candidate for Fourth Generation (4G) wireless systems because it promises data rates up to 10Mbps. A variation of OFDM is Multi-Carrier CDMA (MC-CDMA) which is an OFDM technique where the individual data symbols are spread using a spreading code in the frequency domain. The spreading code associated with MC-CDMA provides multiple access technique as well as interference suppression. Often times in cellular and military environments the desired signal can be buried below interference. In such conditions, the processing gain associated with the spreading cannot provide the needed interference suppression. This research work investigates multi-antenna receivers for OFDM and MC-CDMA systems; specifically this works investigates adaptive antenna algorithms for MC-CDMA for very different channel conditions. Frequency domain beamforming is studied in this research predominantly through simulation. As an alternative a time domain beamforming is also studied. Time variations in the channel can disrupt the orthogonality between subcarriers. Minimum Mean Square Error (MMSE) detection coupled with MMSE beamforming is proposed for time varying channels. Semi-analytic results are derived to study the Bit Error Rate (BER) performance. These results show significant performance improvement in the presence of interference. Joint MMSE weights in space and frequency is also investigated and semi-analytic results are derived to study their BER performance. / Master of Science

Background: Parkinson’s disease (PD) is often accompanied by non-motor complications, such as dementia, depression, and psychotic symptoms, which worsen the prognosis and increase the personal and socioeconomic burden of disease. Prevalence estimates of these complications are quite variable and are lacking for the outpatient care sector. Methods: As part of a larger, nationwide, cross-sectional epidemiological study in n=315 neurological outpatient settings in Germany, this paper estimates the frequency of dementia and cognitive impairment in n=873 outpatients meeting the UK Brain Bank criteria for idiopathic PD. Assessments were based on a clinical interview and neuropsychological assessments, including the Hoehn & Yahr rating and Unified Parkinson’s Disease Rating Scale (UPDRS). Cognitive impairment was assessed by the Mini-Mental State Exam (MMSE), Clock Drawing Test (CDT) and the Parkinson Neuropsychometric Dementia Assessment (PANDA) and the clinician’s diagnosis of dementia was based on the diagnostic criteria of DSMIV. Results Using standardized cutoff scores, the prevalence of cognitive impairment in the study sample as measured by various methods was 17.5% by MMSE (≤ 24), 41.8% by CDT (≥ 3), 43.6% by PANDA (≤ 14), and 28.6% met the DSM-IV criteria for dementia. All estimates increased with age and PD severity. Gender was an inconsistent contributor while illness duration had no significant impact on cognition. Multiple regression analyses revealed PD severity to be the strongest predictor of dementia risk (OR=4.3; 95 % CI: 2.1–9.1), while neuropsychiatric syndromes had independent, although modest additional contributions (OR=2.5, 95% CI: 1.6–3.8). Conclusion: Estimates of cognitive impairment and dementia in PD patients are largely dependent on the diagnostic measure used. Using established clinical diagnostic standards for dementia the overall rate on routine outpatient neurological care is 28.6%, but using more sensitive neuropsychological measures, rates for cognitive impairment might be up to 2-fold higher. The MMSE revealed strikingly low sensitivity. Neuropsychiatric syndromes, in addition to PD severity and age, have an independent – although modest – additional contribution to patients’ risk for cognitive impairment and dementia.

In this thesis, multiuser receivers for code division multiple-access (CDMA) downlink are studied under frequency selective fading channel conditions. The receivers investigated in this thesis attempt to estimate desired symbol as a linear combination of chip-rate sampled received signal sequence. A common matrix-vector representation of signals, which is similar to the model given by Paulraj et. al. is constructed in order to analyze the receivers studied in this thesis. Two receivers already well known in the literature are introduced and derived by using the common signal model. One of the receivers uses traditional matched filter and the other uses symbol-level linear minimum mean square error (MMSE) estimation. The receiver that uses traditional matched filter, also known as the conventional RAKE receiver, benefits from time diversity by combining the signal energy from multiple paths. The conventional RAKE receiver is optimal when multiple-access interference (MAI) is absent. Linear MMSE based receivers are known to suppress MAI and to be more robust to noise enhancement. The optimal symbol-level linear MMSE based receiver requires inversion of large matrices whose size is determined by either number of active users or spreading factor. These two parameters can be quite large in many practical systems and hence the computational load of this receiver can be a problem. In this thesis, two alternative low-complexity receivers, which are chip-level linear MMSE equalizer proposed by Krauss et. al. and interference-suppressing RAKE receiver proposed by Paulraj et. al., are compared with the linear full-rank MMSE based receiver and with the conventional RAKE receiver in terms of bit-error-rate performance. Various simulations are performed to evaluate the performance of the receivers and the parameters affecting the receiver performance are investigated.