2014/4

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    Invariance of the Null Distribution of the Multiple Coherence
    (Společnost pro radioelektronické inženýrství, 2014-12) Bortel, Radoslav; Sovka, Pavel
    In this paper we investigate the invariance of the null distribution of the multiple coherence (MC) to the statistics of the examined signals. We show that when the MC is computed between a group of signals x_i[n], i=1,...,K and a signal y[n], the null distribution of the MC is independent of the distribution of x_i[n] and y[n] if at a given frequency the joint distribution of the spectra of the segments of x_i[n] and y[n] is rotationally symmetric with respect to the rotation of the spectra of the segments of x_i[n] or y[n]. The significance of this result lies in the improvement of the multiple coherence analysis. Hitherto, the null distribution of the MC was known only for signals with the multivariate Gaussian distribution; therefore, an MC estimate could be evaluated for its statistical significance only in this limited case. With the results presented in this paper, it will be possible to evaluate the statistical significance of MC estimates for much wider class of signals.
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    On Amplify-and-Forward Relaying Over Hyper-Rayleigh Fading Channels
    (Společnost pro radioelektronické inženýrství, 2014-12) Alvi, Sajid H.; Wyne, Shurjeel
    Relayed transmission holds promise for the next generation of wireless communication systems due to the performance gains it can provide over non-cooperative systems. Recently hyper-Rayleigh fading, which represents fading conditions more severe than Rayleigh fading, has received attention in the context of many practical communication scenarios. Though power allocation for Amplify-and-Forward (AF) relaying networks has been studied in the literature, a theoretical analysis of the power allocation problem for hyper-Rayleigh fading channels is a novel contribution of this work. We develop an optimal power allocation (OPA) strategy for a dual-hop AF relaying network in which the relay-destination link experiences hyper-Rayleigh fading. A new closed-form expression for the average signal-to-noise ratio (SNR) at destination is derived and it is shown to provide a new upper-bound on the average SNR at destination, which outperforms a previously proposed upper-bound based on the well-known harmonic-geometric mean inequality. An OPA across the source and relay nodes, subject to a sum-power constraint, is proposed and it is shown to provide measurable performance gains in average SNR and SNR outage at the destination relative to the case of equal power allocation.
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    Performance Analysis of a Dual-Hop Cooperative Relay Network with Co-Channel Interference
    (Společnost pro radioelektronické inženýrství, 2014-12) Lin, Min; Wei, Heng; Ouyang, Jian; An, Kang; Yuan, Can
    This paper analyzes the performance of a dual-hop amplify-and-forward (AF) cooperative relay network in the presence of direct link between the source and destination and multiple co-channel interferences (CCIs) at the relay. Specifically, we derive the new analytical expressions for the moment generating function (MGF) of the output signal-to-interference-plus-noise ratio (SINR) and the average symbol error rate (ASER) of the relay network. Computer simulations are given to confirm the validity of the analytical results and show the effects of direct link and interference on the considered AF relay network.
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    A Novel FastICA Method for the Reference-based Contrast Functions
    (Společnost pro radioelektronické inženýrství, 2014-12) Zhao, Wei; Wei, Yimin; Shen, Yuehong; Yuan, Zhigang; Xu, Pengcheng; Jian, Wei
    This paper deals with the efficient optimization problem of Cumulant-based contrast criteria in the Blind Source Separation (BSS) framework, in which sources are retrieved by maximizing the Kurtosis contrast function. Combined with the recently proposed reference-based contrast schemes, a new fast fixed-point (FastICA) algorithm is proposed for the case of linear and instantaneous mixture. Due to its quadratic dependence on the number of searched parameters, the main advantage of this new method consists in the significant decrement of computational speed, which is particularly striking with large number of samples. The method is essentially similar to the classical algorithm based on the Kurtosis contrast function, but differs in the fact that the reference-based idea is utilized. The validity of this new method was demonstrated by simulations.
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    First Order Sea Clutter Cross Section for HF Hybrid Sky-Surface Wave Radar
    (Společnost pro radioelektronické inženýrství, 2014-12) Zhu, Yongpeng; Wei, Yinsheng; Li, Yajun
    This paper presents a modified method to simulate the first order sea clutter cross section for high frequency (HF) hybrid sky-surface wave radar, based on the existent model applied in the bistatic HF surface wave radar. The modification focuses on the derivation of Bragg scattering frequency and the ionosphere dispersive impact on the clutter resolution cell. Meanwhile, an analytic expression to calculate the dispersive transfer function is derived on condition that the ionosphere is spherical stratified. Simulation results explicate the variance of the cross section after taking account of the influence triggered by the actual clutter resolution cell, and the spectral width of the first order sea clutter is defined so as to compare the difference. Eventually, experiment results are present to verify the rationality and validity of the proposed method.