5,220 research outputs found
Near-Capacity Turbo Coded Soft-decision Aided DAPSK/Star-QAM for Amplify-and-Forward based Cooperative Communications
Full text linkMultilevel Differential Amplitude and Phase-Shift Keying (DAPSK) schemes do not require any channel estimation, which results in low complexity. In this treatise we derive the soft-output probability formulas required for a soft-decision based demodulation of high-order DAPSK, in order to facilitate iterative detection by exchanging extrinsic information with an outer Turbo Code (TC). Furthermore, when the TC block size is increased, the system operates closer to the channel capacity. Compared to the identical-throughput TC assisted 64-ary Differential Phase-Shift Keying (64-DPSK) scheme, the 4-ring based TC assisted 64-ary DAPSK arrangement has a power-efficiency improvement of 2.3 dB at a bit error rate (BER) of 10-5 . Furthermore, when the TC block size is increased, the system operates closer to the channel capacity. More specifically, when using a TC block length of 400 modulated symbols, the 64 DAPSK (4, 16) scheme is 7.56 dB away from its capacity curve, while it had a reduced gap as low as 2.25 dB, when using a longer TC block length of 40 000 modulated symbols. Finally, as a novel application example, the soft-decision M-DAPSK scheme was incorporated into an Amplify-and-Forward (AF) based cooperative communication system, which attains another 4.5 dB SNR improvement for a TC block length of 40 000 modulated symbols
Polaron Bands in the Far- and Mid-Infrared Spectra of e-doped Cuprates
No full textEditors E. K. H. Salje, A. S. Alexandrov, and W. Y. Liang (Cambridge university Press, Cambridge
Magnetic proximity-enhanced Curie temperature of Cr-doped Bi2Se3 thin films
Full text linkBeam time awarded on ID32 at the ESRF (Proposal No. HC-1282) and on I10 at the Diamond Light Source (Proposal No. SI-10207) are acknowledged. T.H. acknowledges the John Fell Oxford University Press (OUP) Research Fund. A.A.B. was supported by Diamond Light Source and together with L.J.C.M. by EPSRC through Doctoral Training Awards.We report a study on the transition temperature TC of Cr-doped topological insulator thin films, where an increase in the ferromagnetic onset can provide a pathway towards low-power spintronics in the future. Arrott plots, measured by surface-sensitive x-ray magnetic circular dichroism at the Cr L2,3 edge as a function of field at various low temperatures, give a TC ≈ 7K for the pristine surface. This is comparable to the bulk value of the film, which means that there is no indication that the spontaneous magnetization is different near the surface. Evaporation of a thin layer of Co onto the pristine surface of the in-situ cleaved sample increases the ordering temperature near the surface to ∼19K, while in the bulk it rises to ∼10K. X-ray absorption spectroscopy shows that Cr enters the Bi2Se3 host matrix in a divalent state, and is unchanged by the Co deposition. These results demonstrate a straightforward procedure to increase the transition temperature of doped topological insulators.Peer reviewe
Mechanisms for accumulation and migration of technetium-99 in saltmarsh sediments
No full textThis thesis describes the development of analytical methods for both the bulk determination of 99Tc, and determination of 99Tc in sequential extracts from sediments. These methods have been used to collect data, which, along with trace and major element data have been used to interpret the mechanisms for 99Tc input, migration and accumulation in saltmarshes. The inventory of 99Tc stored in the Thornflatt Saltmarsh, Esk Estuary has also been determined. The routine determination of 99Tc in bulk samples uses 99mTc as a yield monitor. Samples are ignited stepwise to 550°C and the 99Tc is extracted using 8M nitric acid. Many contaminants are precipitated with Fe(OH)3 and the Tc in the supernant is pre-concentrated and further purified using anion-exchange chromatography. Final separation of Tc from Ru is achieved by extraction of Tc into 5% TnOA in xylene from 2M sulphuric acid. The yield is determined by γ-spectrometric analysis of 99mTc. Determination of 99Tc is made by liquid scintillation counting. Typical recoveries are in the order of 70-95% and the method has a detection limit of 1.7 Bq/kg for a sample size of 10g. Determination of Tc in sequential extracts uses operationally defined procedures to extract: exchangeable Tc, reducible Tc and oxidisable Tc. An initial water wash is used to extract any occluded Tc and a final leach in 8 M nitric acid is used to dissolve any residual Tc. The isolation of 99Tc uses TEVA resin for Extracts 1-4 and the decontamination procedure developed for bulk analysis for Extract 5. 99mTc was used as a yield monitor, and determination of 99Tc is by liquid scintillation counting. Limits of detection were dependent on the amount of 99mTc tracer used but were found to be as low as 2.4 Bq/kg for a sample size of 2g. A study was made of the mechanisms responsible for the accumulation and migration of Tc in estuarine sediments using sediments collected from saltmarshes at Thornflatt, Carlaverock and the Ribble Estuary. 99Tc was present at determinable activities in all the sediment cores taken from these sites. Good correlations between Tc and CaO as well as CO3 concentrations and poor correlation between Tc and radionuclides adsorbed to inorganic detritus infer a direct input of 99Tc to marsh sediments. Determination of 99Tc in biota living on the marsh also showed that this was not a significant pathway for input of Tc to the sediments. Sequential extraction data imply sorption to an organic fraction of the sediment. Stable element and sequential extraction data indicates that Tc is readily oxidised and remobilised before reprecipitation where redox conditions are favourable. Data indicate a reduction potential between those of the MnIV to MnII reaction and the FeIII to FeII reaction is necessary for re-accumulation to occur, as suggested by published thermodynamic data. Data collected from reducing sediments imply that similar mechanisms are responsible for the accumulation of Mn (e.g. reduction by sulphate reducing bacteria) and the accumulation of Tc. The inventory of 99Tc held within the Thornflatt saltmarsh is proportionally less than that of 137Cs or 241Am when compared to discharges from Sellafield. However a higher proportion of 99Tc is transferred from Seliafield and incorporated into saltmarsh sediments than is suggested by previously published standard distribution coefficient data. Saltmarsh sediments are therefore a more important sink of 99Tc than extrapolations made from inventories of other radionuclides would suggest
Service-oriented models for audiovisual content storage
No full textWhat are the important topics to understand if involved with storage services to hold digital audiovisual content? This report takes a look at how content is created and moves into and out of storage; the storage service value networks and architectures found now and expected in the future; what sort of data transfer is expected to and from an audiovisual archive; what transfer protocols to use; and a summary of security and interface issues
T0-Berekening: Status Quo van UNIBEST-TC
No full textDit rapport gaat in op de ontwikkelingen bij het UNIBETS-TC model. Met dit model wordt het cross-shore en longshore sediment transport berekend. Om inzicht te krijgen in de verbeteringen in het model wordt er in dit rapport een T0-berekening (een berekening op tijdstip T=0) gemaakt. Dit maakt het mogelijk de ontwikkelingen te evalueren door het te vergelijken met een dergelijke exercitie op het moment T1. Met de berekening wordt er antwoord gegeven op de vragen of het UNIBEST-TC model één heel jaar de ontwikkeling van het kustprofiel kan doorrekenen en in hoeverre het model de werkelijkheid beschrijft. Geconcludeerd wordt dat het (nieuwe) UNIBEST-TC model het dwarstransport in de goede orde van grootte bepaald, maar dat het model geen rekening houdt met het ontstaan van banken. Verder onderzoek is nodig. Het model houdt verder goed rekening met de interactie tussen langs- en dwarstransport en biedt daarnaast een goede mogelijkheid om het lot van een zandsuppletie te bestuderen
Quantitation of anionic sites in glomerular capillar basement-membranes of Samoyed dogs with hereditary glomerulopathy
No full textPT: J; NR: 39; TC: 8; J9: VIRCHOWS ARCH A PATH ANAT HIS; PG: 7; GA: G8940Source type: Electronic(1
Coherent and non-coherent coded modulation for cooperative communications
No full textThe design trade-offs of coherent versus non-coherent coded modulation conceived for cooperative communications are explored. More specifically, coherent versus non-coherent coded modulation designed for traditional point-to-point communications is investigated first, before we extend the application of coded modulation to cooperative communications. Firstly, we focus our attention on coherent coded modulation, when communicating over Additive White Gaussian Noise (AWGN) and uncorrelated Rayleigh fading channels, followed by the investigation of the adaptive coded modulation (ACM), when transmitting over both quasistatic as well as over shadow-and-fast Rayleigh fading channels. Furthermore, soft-decision aided non-coherent coded modulation designed both for fixed modes and adaptive modes is proposed. More specifically, we conceive soft decision aided Differential Amplitude and Phase-Shift Keying (DAPSK) for low-complexity wireless communications, since it dispenses with high-complexity channel estimation. We commence by designing soft-decision based demodulation for 16-level DAPSK, or l6-level Star Quadrature Amplitude Modulation, which is then invoked for iterative detection aided Bit-Interleaved Coded Modulation (BICM-ID). It is shown that the proposed 16- DAPSK based BICM-ID scheme achieves a coding gain of approximately 14 dBs in comparison to the identical-throughput 16-level Differential Phase-Shift Keying (16DPSK) assisted BICM scheme at a Bit Error Ratio (BER) of 10-6. Then, we derive the soft-output probability formulas required for a soft-decision based demodulation of high-order DAPSK, in order to facilitate iterative detection by exchanging extrinsic information with an outer Turbo Code (TC). Furthermore, when the TC block size is increased, the system operates closer to the channel capacity. Offset DAPSK is also considered in order to facilitate the employment of a less stringent linear power amplifier specification at the transmitter. Compared to the identical-throughput TC assisted 64-ary Differential Phase-Shift Keying (64-DPSK) scheme, the 4-ring based TC assisted 64-ary DAPSK arrangement has a power-efficiency improvement of 4.2 dB at a BER of 10-5. Furthermore, when the TC block size is increased, the system operates closer to the channel capacity. More specifically, when using a TC block length of 400 modulated symbols, the 64 DAPSK(4, 16) scheme is 11.25 dB away from its capacity curve, while it operates within 2.7 dB of the capacity, when using a longer TC block length of 40 000 symbols. Furthermore, for the sake of an improved energy efficiency, we proposed the adaptive modes for non-coherent coded modulation.Then, we considered coded modulation schemes designed for cooperative communications. Firstly, an attractive hybrid method of mitigating the effects of error propagation that may be imposed by the relay node (RN) on the destination node (DN) is proposed in Chapter 4. We select the most appropriate RN location for achieving a specific target BER at the relay and signalled the RN-BER to the DN. The knowledge of this BER is then exploited by the decoder at the destination. Our simulation results show that when the BER encountered at the RN is low, we do not have to activate the RN-BER aided decoder at the DN. However, when the RN-BER is high, significant system performance improvements may be achieved by activating the proposed RN-BER based decoding technique at the DN. For example, a power-reduction of up to about 19 dB is recorded at a DN BER of 10-4. Secondly, the basic principle of ACM invoked for cooperative communications is detailed in the context of three main structures: single RN aided ACM, twin RN aided ACM and single RN aided ACM additionally combined with the source-to-destination (SD) link at the DN. Then we propose an adaptive TTCM (ATTCM) aided Distributed Space-Time Trellis Coding (STTC) scheme for cooperative communication over quasi-static Rayleigh fading channels.Specifically, an ATTCM scheme is employed by the source node during the first transmission period for reliably conveying the source bits to N RNs by appropriately adjusting the code-rate and modulation mode according to the near-instantaneous channel conditions. It is shown that the proposed ATTCM-DSTTC scheme requires 12 dBs less transmission power in comparison to a standard TTCM scheme when aiming for a Frame Error Ratio (FER) of 10-3.Finally, we focus our attention on non-coherent coded modulation conceived for cooperative communications. Firstly, we investigate a 16-StQAM-TC assisted NC scheme relying on the popular butterfly network topology. As expected, the achievable BER performance is affected by the location of the RN. More specifically, when the transmit powers at the SNs and RN are identical, the RN located at the centre of the butterfly network topology achieves the best performance. However, when the appropriately designed power sharing approach is invoked in Section 5.2.1.2, the optimum RN location is closer to the DNs, and another 1 dB of power gain can be attained. Then, the NC capacity was quantified and the simulation results of Figure 5.5 showed that the achievable capacity of the NC scenario is improved compared to the single-link scenario. Secondly, as a novel application example, our soft-decision M-DAPSK scheme is incorporated into an AF based cooperative communication system. We found that an AF based cooperative communication system obtains a 4.5 dB SNR improvement for a TC block length of 40 000 modulated symbols, compared to that of the traditional point-to-point transmission. Finally, we propose a low-complexity amalgamated cooperative wireless and optical-fiber communication scheme for uplink communication in a FFR based multicell, multiuser system. The FFR principle is invoked for improving the cell-edge performance without reducing the throughput of the cell center. Each cell is illuminated with the aid of six Remote Antennas (RAs), which are connected to the central base station with the aid of realistically modelled imperfect optical-fiber links. When a Mobile Station (MS) is located at the cell-edge, the two nearest RAs can be invoked for detecting and forwarding the user’s signal to the base-station, based on the Single-Input Multiple-Output (SIMO) principle. Furthermore, we employ both the Digital Fiber Optic (DFO) and Analogue Radio-over-Fiber (AROF) principles for the optical fiber link. We then design a Turbo Coded (TC) 16-level Star-Quadrature Amplitude Modulation (StQAM) scheme for supporting optical-fiber-aided cooperative wireless transmissions, where the receiver does not have to estimate the channel state information. Hence, a lower detection complexity can be achieved, when compared to coherently detected schemes, albeit naturally, at a 3 dB power-loss. We also investigate the effect of phase rotations imposed by imperfect optical-fiber links. Our non-coherent TC-StQAM scheme is robust to both wireless and optical-fiber imperfections. More explicitly, the proposed TC-StQAM-SIMO scheme is capable of removing 6 out of 12 BER peaks at the cell-edge, despite dispensing with CSI for both the wireless and optical-fiber links. As a further improvement, the adaptive turbo-coded soft-decision aided differential detection (ATSDD) scheme is employed by the Mobile Station (MS) for reliably conveying the source bits to a pair of nearby Remote Antennas (RAs) by appropriately adjusting the modulation mode according to the near instantaneous wireless and AROF channel condition. The ATSDD switching thresholds are specifically adjusted for ensuring that the BER remains below 10-5. We also investigated the effect of phase-rotations routinely imposed by practical imperfect Radio-over-fiber (ROF) links. We demonstrate that our ATSDD scheme is robust to both wireless and optical-fiber imperfections
Near-Capacity Turbo Coded Soft-decision Aided DAPSK/Star-QAM
Full text linkLow-complexity non-coherently detected Differential Amplitude and Phase-Shift Keying (DAPSK) schemes constitute an ideal candidate for wireless communications. In this paper, we derive the soft-output probability formulas required for the soft-decision based demodulation of DAPSK, which are then invoked for Turbo Coded (TC) transmissions. Furthermore, the achievable throughput characteristics of the family of M-ary DAPSK schemes are provided. It is shown that the proposed 4-ring based TC assisted 64-ary DAPSK scheme achieves a coding gain of about 4.2 dBs in comparison to the identical-throughput TC assisted 64-ary Differential Phase-Shift Keying (64-DPSK) scheme at a bit error ratio of 10?5
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