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    ABSTRACT: A full hardware implementation of a Weighted Fair Queuing (WFQ) packet scheduler is proposed. The circuit architecture presented has been implemented using Altera Stratix II FPGA technology, utilizing Reduced Latency DRAM (RLDRAM) II and Quad Data Rate (QDR) II SRAM memory components. The circuit can provide fine granularity Quality of Service (QoS) support at a line throughput rate of 12.8 Gb/s in its current implementation. The authors suggest that, due to the flexible and scalable modular circuit design approach used, the current circuit architecture can be targeted for a full ASIC implementation to deliver 50 Gb/s throughput. The circuit itself comprises three main components; a WFQ algorithm computation circuit, a tag/time-stamp sort and retrieval circuit, and a high throughput shared buffer. The circuit targets the support of emerging wireline and wireless network nodes that focus on Service Level Agreements (SLA's) and Quality of Experience.
    Integration the VLSI Journal 01/2012; 45(1-45):99-109. DOI:10.1016/j.vlsi.2011.01.001
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    ABSTRACT: In this study, the authors analyse the temporal and spatial compression characteristics of retrodirective antenna systems wherein active phase conjugation (APC) is deployed. It is shown that under the APC Hermitian channel matrix properties result and these lead to opportunities for both temporal and spatial signal compression. The effects of additive channel noise, as well as compression assistance given by multipath richness are described. Some general properties of retrodirective antenna systems with respect to linear and circular polarised pilot signals are also discussed. The scheme elaborated here is compliant with a generic channel model and can therefore be easily incorporated into any readily available communication systems analysis or channel modelling software. The work presented in this study provides a theoretical foundation for the previous experimental findings in APC systems.
    IET Microwaves Antennas & Propagation 01/2012; 6(4):482-488. DOI:10.1049/iet-map.2011.0459
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    ABSTRACT: Aggressive MOS transistor size scaling substantially increase the probability of faults in NoC links due to manufacturing defects, process variations, and chip wire-out effects. Strategies have been proposed to tolerate faulty wires by replacing them with spare ones or by partially using the defective links. However, these strategies either suffer from high area and power overheads, or significantly increase the average network latency. In this paper, we propose a novel flit serialization method, which divides the links and flits into several sections, and serializes flit sections of adjacent flits to transmit them on all available fault-free link sections to avoid the complete waste of defective links bandwidth. Experimental results indicate that our method reduces the latency overhead significantly and enables graceful performance degradation, when compared with related partially faulty link usage proposals, and saves area and power overheads by up to 29% and 43.1%, respectively, when compared with spare wire replacement methods.
    Networks on Chip (NoCS), 2012 Sixth IEEE/ACM International Symposium on; 01/2012
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    ABSTRACT: In this paper, we propose a security model to capture active attacks against multipath key establishment (MPKE) in sensor networks. Our model strengthens previous models to capture more attacks and achieve essential security goals for multipath key establishment. In this model, we can apply protocols for perfectly secure message transmission to solve the multipath key establishment problem. We propose a simple new protocol for optimal one-round perfectly secure message transmission based on Reed-Solomon codes. Then, we use this protocol to obtain two new multipath key establishment schemes that can be applied provided that fewer than one-third of the paths are controlled by the adversary. Finally, we describe another MPKE scheme that tolerates a higher fraction (less than half) of paths controlled by the adversary. This scheme is based on a new protocol for a weakened version of message transmission, which is very simple and efficient. Our multipath key establishment schemes achieve improved security and lower communication complexity, as compared to previous schemes.
    IEEE Transactions on Dependable and Secure Computing 01/2012; DOI:10.1109/TDSC.2010.48
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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: This paper presents an analytical performance investigation of the capacity limits of correlated multiple-input single-output (MISO) channels in the presence of quality-of-service (QoS) requirements. Exact closed-form expression for the effective capacity of correlated MISO channels is derived. In addition, simple expressions are obtained at the asymptotic high and low signal-to-noise ratio (SNR) regimes, which provide insights into the impact of various system parameters on the effective capacity of the system. Also, a complete characterization of the impact of spatial correlation on the effective capacity is provided with the aid of a majorization theory result. The findings suggest that antenna correlation reduce the effective capacity of the channels. Moreover, a stringent QoS requirement causes a significant reduction in the effective capacity but this can be effectively alleviated by increasing the number of antennas.
    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; 5(8-5):921 - 927. DOI:10.1049/iet-map.2010.0362
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    ABSTRACT: The quality factor of microwave resonators miniaturised by virtue of periodic loading is assessed. Five X-band resonators in E-plane technology with different miniaturisation factors have been designed to resonate at approximately the same frequency. The loaded quality factor is extracted from the fractional bandwidth and subsequently employed to estimate the unloaded quality factor. The study reveals that the unloaded quality factor drops approximately linearly with the miniaturisation. Subsequently design guidelines for E-plane filters with periodically loaded resonators are provided by means of an example involving a fifth-order filter. Full-wave simulated and experimental results are presented to validate the study.
    IET Microwaves Antennas & Propagation 06/2011; 5(7-5):818 - 822. DOI:10.1049/iet-map.2010.0396
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    ABSTRACT: This paper studies the Demmel condition number of Wishart matrices, a quantity which has numerous applications to wireless communications, such as adaptive switching between beamforming and diversity coding, link adaptation, and spectrum sensing. For complex Wishart matrices, we give an exact analytical expression for the probability density function (p.d.f.) of the Demmel condition number, and also derive simplified expressions for the high tail regime. These results indicate that the condition of complex Wishart matrices is dominantly decided by the difference between the matrix dimension and degree of freedom (DoF), i.e., the probability of drawing a highly ill conditioned matrix decreases considerably when the difference between the matrix dimension and DoF increases. We further investigate real Wishart matrices, and derive new expressions for the p.d.f. of the smallest eigenvalue, when the difference between the matrix dimension and DoF is odd. Based on these results, we succeed to obtain an exact p.d.f. expression for the Demmel condition number, and simplified expressions for the high tail regime.
    IEEE Transactions on Communications 06/2011; 59(5-59):1309 - 1320. DOI:10.1109/TCOMM.2011.040111.100137
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