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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;
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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: 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: 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: 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;
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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: 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: 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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