Relay-Induced Error Propagation Reduction for Decode-and-Forward Cooperative Communications

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. We selected the most appropriate relay location for achieving a specific target Bit Error Ratio (BER) at the relay and signalled the RN-BER to the DN. The knowledge of this BER was then exploited by the decoder at the destination. Our simulation results show that when the BER 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 19dB was recorded at a DN BER of 10-4

Near-Capacity Turbo Coded Soft-decision Aided DAPSK/Star-QAM

Low-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

A Hybrid Approach to Case Teaching

We structure case based teaching using a combination of computer-support echnology and in-class activities. We create and design an on-line learning tool, Case Study On-line (CSOL) that enables instructor to structure the delivery of teaching resources and set up assignment tasks in the system. The tool enables tasks to be set in a way that they can be completed sequentially, and learning resources can be accessed only when required by students. Upon submission of their assignments, students can promptly receive instructor’s explanations to the tasks. Follow up activities take place in class, with the objective to promote active learning. The tool was adopted over two semesters in an undergraduate economics course and surveys were conducted among the students to evaluate the effectiveness of the tool. The results of the survey were very positive, providing support to our belief that a system of well-designed case teaching delivery tool, together with classroom activities, is able to increase the level of students’ engagement and interest. The paper helps to address some concerns about teaching methods in undergraduate economics courses.Technologies-based Instruction, In-class Activities, Scaffolding, Active-based Learning

Near-Capacity Turbo Coded Soft-decision Aided DAPSK/Star-QAM for Amplify-and-Forward based Cooperative Communications

Multilevel 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

Reduced-complexity non-coherent soft-decision-aided DAPSK dispensing with channel estimation

Differential Amplitude Phase Shift Keying (DAPSK), which is also known as star-shaped QAM has implementational advantages not only due to dispensing with channel estimation, but also as a benefit of its low signal detection complexity. It is widely recognized that separately detecting the amplitude and the phase of a received DAPSK symbol exhibits a lower complexity than jointly detecting the two terms. However, since the amplitude and the phase of a DAPSK symbol are affected by the correlated magnitude fading and phase-rotations, detecting the two terms completely independently results in a performance loss, which is especially significant for soft-decision-aided DAPSK detectors relying on multiple receive antennas. Therefore, in this contribution, we propose a new soft-decision-aided DAPSK detection method, which achieves the optimum DAPSK detection capability at a substantially reduced detection complexity. More specifically, we link each a priori soft input bit to a specific part of the channel's output, so that only a reduced subset of the DAPSK constellation points has to be evaluated by the soft DAPSK detector. Our simulation results demonstrate that the proposed soft DAPSK detector exhibits a lower detection complexity than that of independently detecting the amplitude and the phase, while the optimal performance of DAPSK detection is retained

A Hybrid Approach to Case Teaching

We structure case based teaching using a combination of computer-support technology and in-class activities. We create and design an on-line learning tool, Case Study On-line (CSOL) that enables instructor to structure the delivery of teaching resources and set up assignment tasks in the system. The tool enables tasks to be set in a way that they can be completed sequentially, and learning resources can be accessed only when required by students. Upon submission of their assignments, students can promptly receive instructors explanations to the tasks. Follow up activities take place in class, with the objective to promote active learning. The tool was adopted over two semesters in an undergraduate economics course and surveys were conducted among the students to evaluate the effectiveness of the tool. The results of the survey were very positive, providing support to our belief that a system of well-designed case teaching delivery tool, together with classroom activities, is able to increase the level of students engagement and interest. The paper helps to address some concerns about teaching methods in undergraduate economics courses.Technologies-based Instruction, In-class Activities, Scaffolding, Active-based Learning

Experimental and theoretical investigation of the behaviour of brickwork cladding panel subjected to lateral loading

This thesis deals mainly with the resistance of single leaf brickwork cladding panels subjected to uniform lateral pressure. Such panels when supported on three or four sides bend like thin plates and are subjected to bi-axial bending. A bi-axial failure criterion for brickwork, which shows both strength and stiffness orthotropies, is required to predict the strength of the cladding panels. A systematic investigation was undertaken to establish the failure criterion of brickwork in bi-axial bending using a novel test method. A total number of 33 cross-beams in which both vertical and horizontal moments can be applied simultaneously was tested to define the failure criterion. From the tests, it appears that the strength in the weaker direction is enhanced in biaxial bending. In most cases, the load was shed from the weaker to the stronger direction after cracking. Once the section cracks, it is not capable of carrying any moment, which indicates the brittle nature of masonry. A conventional plate bending finite element program was modified incorporating the bi-axial failure criterion which takes into account the load-shedding observed in the tests. A smeared crack modelling technique was used to model the progressive cracking in bi-axial bending. Once the material properties in bi-axial bending were established and numerical modelling was carried out to predict the behaviour, it was essential to apply the theoretical model to walls subjected to lateral loading. A total number of 15 walls with different aspect ratios and boundary conditions was tested for comparison with the numerical method. Good agreement was obtained between the theoretical model and experimental results. All walls were tested under ideal boundary conditions so that rotational restraint at the supports could be avoided. Similar observations of load shedding from the weaker vertical direction to the stronger horizontal direction were observed also in the wall tests. This was confirmed by measuring the drop and increase in the reactions in the weaker and stronger directions. This was also confirmed from strain measurements in two orthogonal directions before and after cracking. These results also indicate without doubt that a cracked section cannot support any moment. This modified finite element program using the bi-axial failure criterion developed in this thesis was also used to compare the results with the wall test carried out by other researchers. A good agreement between the theoretical and the experimental results of wall with and without openings and subjected to lateral loading was also obtained. Hence, this finite element program using the bi-axial failure criterion can be used for the design of laterally loaded brickwork panels with confidence

Transverse Bragg-resonant enhancement of modulation and switching

We demonstrate theoretically that the electrooptic phase retardation, hence, modulation, can be enhanced very substantially in transverse Bragg resonance (TBR) waveguides. This enhancement is due fundamentally to the strong dependence of the dispersion of the TBR waveguide on the Bragg condition. Both theoretical and numerical analysis show that this enhancement can be used to improve the performance of directional coupler switches and electroabsorption modulators, leading potentially to major reductions in the device size or the switching voltage/current

Local auxin transport regulation in the nascent nodule - an overview in nodulating plants and an investigation into the cytokinin receptor, cre1 - mediated control of auxin transport in medicago truncatula

Legumes form a symbiotic relationship with a group of bacteria, collectively known as rhizobia. The bacterial symbiont fixes atmospheric nitrogen within root nodules, thus providing the host with an assimilative nitrogen source. Nodule formation involves a complex signalling pathway within the legume host. The plant hormone auxin is involved in nodule organogenesis, but how auxin regulates nodulation is still poorly described. Several studies have found increased auxin signalling in nodule primordia, but so far auxin metabolites have never been quantified during the early stages of nodulation. Therefore, the first aim of this thesis was to establish methods for auxin quantification in legume roots. The presumed build-up of auxin in nodule primordia has been predicted to be due to inhibition of auxin export from cells at the nodule initiation site, but the regulation of auxin transport has not been tested systematically in different legumes. Therefore, the second aim was to compare auxin concentrations and auxin transport changes during nodulation in different legumes. Third, the regulation of auxin transport and auxin accumulation was placed into the known signalling pathway of nodulation in the model legume, Medicago truncatula. Auxins are naturally present in low quantities in the root. We developed an LC-MS/MS method for the accurate and sensitive quantification of auxins in root tissues. The method was validated and produced sensitive limits of detection / quantification and correlation coefficients. To compare the role of auxin between indeterminate and determinate nodule types, we measured auxin transport and auxin content in M. truncatula (forming indeterminate nodules) and Lotus japonicus (forming determinate nodules). In addition to acropetal auxin transport, basipetal auxin transport was regulated in response to rhizobia inoculation in both legumes. Different auxins with distinct levels of abundance were detected in separate legumes, with some unique to the nodule tissues. Auxin concentrations increased at the early stages of nodule formation in M. truncatula, but not Lotus japonicus. The inhibition of acropetal polar auxin transport by rhizobia occurred only in indeterminate nodule-forming legumes and correlated with the ability of synthetic auxin transport inhibitors to induce pseudonodules in those legumes. Finally, we investigated the role of the cytokinin receptor CRE1 in modulating auxin transport during nodulation in M. truncatula. We found that cytokinin signalling through CRE1 is necessary for inhibition of acropetal auxin transport, increased auxin concentration and auxin signalling in response to rhizobia. The CRE1 receptor was also required for the correct induction of several flavonoids, which could act as endogenous auxin transport inhibitors. External application of those flavonoids rescued nodulation in the cre1 nodulation-deficient mutant. In conclusion, we demonstrated that the auxin transport machinery is a crucial component in the host legume that is regulated in response to rhizobia. Auxin transport changes could explain measured changes in auxin concentrations during nodule initiation of M. truncatula, but not L. japonicus. Auxin transport control is mediated by endogenous flavonoids, and both flavonoid induction and auxin transport control are regulated by cytokinin signalling in M. truncatula