Distributed space-time block coding in cooperative relay networks with application in cognitive radio

Spatial diversity is an effective technique to combat the effects of severe fading in wireless environments. Recently, cooperative communications has emerged as an attractive communications paradigm that can introduce a new form of spatial diversity which is known as cooperative diversity, that can enhance system reliability without sacrificing the scarce bandwidth resource or consuming more transmit power. It enables single-antenna terminals in a wireless relay network to share their antennas to form a virtual antenna array on the basis of their distributed locations. As such, the same diversity gains as in multi-input multi-output systems can be achieved without requiring multiple-antenna terminals. In this thesis, a new approach to cooperative communications via distributed extended orthogonal space-time block coding (D-EO-STBC) based on limited partial feedback is proposed for cooperative relay networks with three and four relay nodes and then generalized for an arbitrary number of relay nodes. This scheme can achieve full cooperative diversity and full transmission rate in addition to array gain, and it has certain properties that make it alluring for practical systems such as orthogonality, flexibility, low computational complexity and decoding delay, and high robustness to node failure. Versions of the closed-loop D-EO-STBC scheme based on cooperative orthogonal frequency division multiplexing type transmission are also proposed for both flat and frequency-selective fading channels which can overcome imperfect synchronization in the network. As such, this proposed technique can effectively cope with the effects of fading and timing errors. Moreover, to increase the end-to-end data rate, this scheme is extended for two-way relay networks through a three-time slot framework. On the other hand, to substantially reduce the feedback channel overhead, limited feedback approaches based on parameter quantization are proposed. In particular, an optimal one-bit partial feedback approach is proposed for the generalized D-O-STBC scheme to maximize the array gain. To further enhance the end-to-end bit error rate performance of the cooperative relay system, a relay selection scheme based on D-EO-STBC is then proposed. Finally, to highlight the utility of the proposed D-EO-STBC scheme, an application to cognitive radio is studied

Full-rate and full-diversity extended orthogonal space-time block coding in cooperative relay networks with imperfect synchronization

In this paper we present a novel extended orthogonal space-time block coding (EO-STBC) scheme for three and four relay nodes to use in asynchronous cooperative relay networks. This approach attains full-rate and full-diversity in that each hop attains unity rate and all four uncorrelated paths are utilized. Robustness against the effects of random delays at the relay nodes is enhanced through the use of a low-rate feedback channel. A new low complexity phase feedback scheme has been proposed which can retain the advantage of the perfect feedback scheme with substantial reduction in the feedback overhead. Orthogonal frequency division multiplexing (OFDM) with cyclic prefix (CP) is used at the source node to combat the timing errors at the relay nodes, which operate in a simple amplify-and-forward (AF) mode. Simulations show that our new scheme outperforms the previous schemes and uses a very simple symbol-wise maximum-likelihood (ML) decoder

Extended orthogonal space time block codes in wireless relay networks

In this paper we propose complex extended orthogonal space-time block codes (EO-STBCs) with feedback for wireless relay networks with the assumption of quasi-static flat fading channels. Full rate in each stage and full cooperative diversity for distributed EO-STBCs (D-EO-STBCs) are achieved by providing channel state information (CSI) at certain relay nodes. Two closed-loop schemes are proposed which make use of limited feedback from the destination node to a particular number of relay nodes, not exceeding half of the total number of such relay nodes. In our simulations, we use four relay nodes. Simulation results show that these two closed-loop D-EOSTBCs achieve full cooperative diversity in addition to array gain with linear processing. In particular, the proposed D-EO-STBCs designs preserve low decoding complexity and save both transmission power and total transmit time between source and destination

Magneto-forming studies

The paper describes preliminary experimental studies of magneto-forming technology, undertaken at Loughborough University and using the existing 2 MA/100 kJ Quattro capacitor bank as power supply. Different practical arrangements will be detailed and results presented that illustrate magneto-forming in the tap inch geometry: • Magneto-forming stainless steel cylinders • Welding stainless steel cylinders with stainless steel cylinders. • Magneto-forming magnesium cylinders. For each arrangement, the results of magneto-forming are analyzed at the interface as well in the adjoined materials in comparison with their pre-manufacture (as delivered) state. The used characterization techniques include micro and nano-indentation, optical microscopy and scanning electron microscopy

Analysis of pulsed electroplasticity in metals

Application of high-intensity electric fields and/or currents is known to enhance materials’ deformability. For instance, their continuous or in short-pulses application on metals and ceramics may significantly affect their deformation response to external loads. This phenomenon is commonly referred to as electroplasticity (EP) or electroplastic effect. In the present preliminary study, mechanical tensile experiments were carried out in combination with the application of short duration high-intensity electric currents in copper samples. Our study captures the enhanced plasticity induced in the metal due to EP. Postevent microstructural studies highlighted the effect of high-intensity electric current on the material