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    ABSTRACT: This paper investigates linear precoding designs for cognitive relay assisted transmissions of coexisting radio systems. The aim of this work is to characterise the interference between the primary and secondary systems in the cognitive radio setup when transmission is assisted by a cognitive relay. While conventionally the aim of the relay is to completely remove the interference between primary and secondary transmissions, we explore the potential of making use of interference energy when the interference between the two systems is mutually constructive. In this direction two adaptive linear precoding techniques are proposed for the cognitive relay and compared to conventional precoding. The presented theoretical analysis and simulations show that the proposed outperform conventional techniques, as the existence of constructive interference energy improves the received signal to noise ratio (SNR) at both primary and secondary receivers.
    Communications (ICC), 2011 IEEE International Conference on; 07/2011
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    ABSTRACT: We consider the problem of secret communication over Nakagami-m fading multiple-input single-output (MISO) broadcast channel, where transmitter sends messages to the destination users following two different transmission protocols. In the first transmission protocol, transmitter sends a confidential message to user 1, and user 2 acts as an eavesdropper. In this protocol, at first, we define the ergodic secrecy capacity for the full channel state information (CSI) case and then we consider the case of only main channel CSI at the transmitter. Finally, we define the secrecy capacity in case of open-loop spatial multiplexing transmission scheme and present the analytical expression for the lower bound of ergodic secrecy capacity. In the second transmission protocol, we consider the transmission of two independent messages to user 1 and user 2 with information-theoretic secrecy, where each user would like to obtain its own confidential message in a reliable and safe manner. Under this communication scenario, an achievable secrecy capacity region is developed using secret dirty-paper coding scheme.
    Communications (ICC), 2011 IEEE International Conference on; 07/2011
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    ABSTRACT: Novel V-band substrate integrated waveguide (SIW) filters have been presented. Design procedures for the filters synthesis and mechanisms providing quasi-elliptic response have been explained. The insertion loss of the filters has been measured below 2 dB with microstrip-to-SIW transitions being included.
    IET Microwaves Antennas & Propagation 07/2011;
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    ABSTRACT: Real-time matrix inversion is a key enabling technology in multiple-input multiple-output (MIMO) communications systems, such as 802.11n. To date, however, no matrix inversion implementation has been devised which supports real-time operation for these standards. In this paper, we overcome this barrier by presenting a novel matrix inversion algorithm which is ideally suited to high performance floating-point implementation. We show how the resulting architecture offers fundamentally higher performance than currently published matrix inversion approaches and we use it to create the first reported architecture capable of supporting real-time 802.11n operation. Specifically, we present a matrix inversion approach based on modified squared Givens rotations (MSGR). This is a new QR decomposition algorithm which overcomes critical limitations in other QR algorithms that prohibits their application to MIMO systems. In addition, we present a novel modification that further reduces the complexity of MSGR by almost 20%. This enables real-time implementation with negligible reduction in the accuracy of the inversion operation, or the BER of a MIMO receiver based on this.
    IEEE Transactions on Signal Processing 05/2011;
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    ABSTRACT: A recently introduced power-combining scheme for a Class-E amplifier is, for the first time, experimentally validated in this paper. A small value choke of 2.2 nH was used to substitute for the massive dc-feed inductance required in the classic Class-E circuit. The power-combining amplifier presented, which operates from a 3.2-V dc supply voltage, is shown to be able to deliver a 24-dBm output power and a 9.5-dB gain, with 64% drain efficiency and 57% power-added efficiency at 2.4 GHz. The power amplifier exhibits a 350-MHz bandwidth within which a drain efficiency that is better than 60% and an output power that is higher than 22 dBm were measured. In addition, by adopting three-harmonic termination strategy, excellent second- and third-harmonic suppression levels of 50 and 46 dBc, respectively, were obtained. The complete design cycle from analysis through fabrication to characterization is explained.
    Circuits and Systems I: Regular Papers, IEEE Transactions on 04/2011;
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    ABSTRACT: An antipodal Vivaldi antenna with tuneable band reject capability is presented. The antenna presented has the capability to operate over the bandwidth 1.5-4.3 GHz at return loss <; -10 dB, but with a tuneable rejection band, the centre frequency of which may be varied in the range 1.8-2.8 GHz enabling rejection of cellular and ISM bands. Within this frequency range the return loss at the centre frequency of the rejected band varies from -2.7 to -4.1 dB. Farfield measurements show that radiation patterns are disrupted only within the rejected band and remain largely unaltered outside the rejected band.
    IET Microwaves Antennas & Propagation 03/2011;
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    ABSTRACT: A new design method that greatly enhances the reflectivity bandwidth and angular stability beyond what is possible with a simple Salisbury screen is described. The performance improvement is obtained from a frequency selective surface (FSS) which is sandwiched between the outermost 377 Ω/square resistive sheet and the ground plane. This is designed to generate additional reflection nulls at two predetermined frequencies by selecting the size of the two unequal length printed dipoles in each unit cell. A multiband Salisbury screen is realised by adjusting the reflection phase of the FSS to position one null above and the other below the inherent absorption band of the structure. Alternatively by incorporating resistive elements midway on the dipoles, it is shown that the three absorption bands can be merged to create a structure with a -10 dB reflectivity bandwidth which is 52% larger and relatively insensitive to incident angle compared to a classical Salisbury screen having the same thickness. CST Microwave Studio was used to optimise the reflectivity performance and simulate the radar backscatter from the structure. The numerical results are shown to be in close agreement with bistatic measurements for incident angles up to 40° over the frequency range 5.4-18 GHz.
    IET Microwaves Antennas & Propagation 03/2011;
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    ABSTRACT: Image segmentation is an important task in the analysis of dermoscopy images since the extraction of skin lesion borders provides important cues for accurate diagnosis. In recent years, gradient vector flow based algorithms have demonstrated their merits in image segmentation. However, due to the compromise of internal and external energy forces within the partial differential equation these methods commonly lead to under- or over-segmentation problems. In this paper, we introduce a new mean shift based gradient vector flow (GVF) algorithm that drives the internal/external energies towards the correct direction. The proposed segmentation method incorporates a mean shift operation within the standard GVF cost function. Theoretical analysis proves that the proposed algorithm converges rapidly, while experimental results on a large set of diverse dermoscopy images demonstrate that the presented method accurately determines skin lesion borders in dermoscopy images.
    Computerized medical imaging and graphics: the official journal of the Computerized Medical Imaging Society 03/2011; 35(2):121-7.
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    ABSTRACT: In this paper, the distribution of the ratio of extreme eigenvalues of a complex Wishart matrix is studied in order to calculate the exact decision threshold as a function of the desired probability of false alarm for the maximum-minimum eigenvalue (MME) detector. In contrast to the asymptotic analysis reported in the literature, we consider a finite number of cooperative receivers and a finite number of samples and derive the exact decision threshold for the probability of false alarm. The proposed exact formulation is further reduced to the case of two receiver-based cooperative spectrum sensing. In addition, an approximate closed-form formula of the exact threshold is derived in terms of a desired probability of false alarm for a special case having equal number of receive antennas and signal samples. Finally, the derived analytical exact decision thresholds are verified with Monte-Carlo simulations. We show that the probability of detection performance using the proposed exact decision thresholds achieves significant performance gains compared to the performance of the asymptotic decision threshold.
    IEEE Journal of Selected Topics in Signal Processing 03/2011;
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    ABSTRACT: An experimental investigation of the effect of conductor-to-substrate interface on distributed passive intermodulation (PIM) generation in printed microstrip lines has been undertaken using the custom-designed microwave laminates with removed surface bonding layers and with the commercial adhesion promotion applied to the conductor underside. The study of long-term stability of PIM performance of the printed circuits is reported for the first time. The comprehensive measurement results, observations of the self-improvement of the PIM performance and the effect of panel bending on PIM generation in printed boards with different finishing are presented. A consistent physical interpretation of the observed phenomena is proposed. The results of this study provide new important considerations for the design and characterisation of low-PIM printed circuits.
    IET Microwaves Antennas & Propagation 02/2011;
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