New Receivers for Differentially Encoded Offset-QPSK

Before a new mobile radio system will be standardised, an intense process of decision making is required concerning the different aspects of the system. One aspect is the definition of the air interface and in particular the employed modulation method. During the standardisation of the TETRA (Terrestrial Trunked Radio) system, the expert group decided to choose the linear modulation format π/4-QPSK. One important point for decision making was the requirement to support power efficient, nonlinear amplifiers. Although the second candidate, Offset-QPSK (OQPSK) shows further reduced envelope fluctuations, the nonavailibilty of a conventional differential demodulator for OQPSK led to a clear preference for π/4-QPSK. Differential demodulation is an at-tractive combined carrier phase estimation and demodulation technique on fast time selective fading channels. The work presented in the thesis is concerned with the synthesis and analysis of receiver algorithms for differentially encoded OQPSK signals, which fulfil the requirements of modern mobile radio systems. The thesis begins with an overview of the theoretical principles of digital modulation and optimum receivers. A description of mobile radio channels and the theoretical performance of PSK signals complete the basic chapter. A new receiver structure for DOQPSK using differential demodulation followed by a Viterbi decoder is then proposed. On this basis, an advanced algorithm suitable for general roll-off factors and with reduced complexity is derived and investigated. Following the differential demodulation, original algorithms for joint coherent demodulation and equalisation, which are based on the principle of per-survivor processing (PSP) are synthesised and discussed. These receiver structures are extended for the use in time and frequency selective mobile radio channels. With the aid of a computer simulation system the derived receiver structures are investigated. Simulation results on different linear and nonlinear channels are presented and compared with results obtained with standard π/4-DQPSK receivers and the theoretical bounds. The thesis concludes with a description of the simulation tool COSSAP and gives examples of created and implemented simulation models. The results of a fixed-point analysis of one model is presented and the possibilities to synthesise a hardware implementation is discussed

New receivers for differentially encoded Offset-QPSK Investigation in differential demodulation and per-survivor-processing algorithms

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Brain/blood ratios of methadone and ABCB1 polymorphisms in methadone-related deaths

Methadone is an opioid that often leads to fatalities. Interpretation of toxicological findings can be challenging if no further information about the case history is available. The aims of this study were (1) to determine whether brain/blood ratios can assist in the interpretation of methadone findings in fatalities; (2) to examine whether polymorphisms in the gene encoding the P-glycoprotein (also known as multidrug resistance protein 1 (MDR1) or ATP-binding cassette sub-family B member 1 (ABCB1)), which functions as a multispecific efflux pump in the blood-brain barrier, affect brain/blood ratios of methadone. Femoral venous blood and brain tissue (medulla oblongata and cerebellum) from 107 methadone-related deaths were analysed for methadone by gas chromatography-mass spectrometry. In addition, all the samples were genotyped for three common ABCB1 single nucleotide polymorphisms (SNPs rs1045642, rs1128503, and rs2032582) using ion-pair reversed-phase high-performance liquid chromatography-electrospray ionization mass spectrometry (ICEMS). In nearly all cases, methadone concentrations were higher in the brain than in the blood. Inter-individual brain/blood ratios varied (0.6-11.6); the mean ratio was 2.85 (standard deviation 1.83, median 2.35). Moreover, significant differences in mean brain/blood ratios were detected among the synonymous genotypes of rs1045642 in ABCB1 (p = 0.001). Cases with the T/T genotype had significantly higher brain/blood ratios than cases with the other genotypes (T/T vs. T/C difference (d) = 1.54, 95% CI [1.14, 2.05], p = 0.002; T/T vs. C/C d = 1.60, 95% CI [1.13, 2.29], p = 0.004). Our results suggest that the rs1045642 polymorphisms in ABCB1 may affect methadone concentrations in the brain and its site of action and may be an additional factor influencing methadone toxicity