2018/1

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Fractional Delayer Utilizing Hermite Interpolation with Caratheodory Representation
(Společnost pro radioelektronické inženýrství, 2018-04) Du, Qiang; Song, Yaoliang; Ahmad, Zeeshan
Fractional delay is indispensable for many sorts of circuits and signal processing applications. Fractional delay filter (FDF) utilizing Hermite interpolation with an analog differentiator is a straightforward way to delay discrete signals. This method has a low time-domain error, but a complicated sampling module than the Shannon sampling scheme. A simplified scheme, which is based on Shannon sampling and utilizing Hermite interpolation with a digital differentiator, will lead a much higher time-domain error when the signal frequency approaches the Nyquist rate. In this letter, we propose a novel fractional delayer utilizing Hermite interpolation with Caratheodory representation. The samples of differential signal are obtained by Caratheodory representation from the samples of the original signal only. So, only one sampler is needed and the sampling module is simple. Simulation results for four types of signals demonstrate that the proposed method has significantly higher interpolation accuracy than Hermite interpolation with digital differentiator.
Novel Sparse Algorithms based on Lyapunov Stability for Adaptive System Identification
(Společnost pro radioelektronické inženýrství, 2018-04) Pogula, Rakesh; Kumar, T. Kishore; Albu, Felix
Adaptive filters are extensively used in the identification of an unknown system. Unlike several gradient-search based adaptive filtering techniques, the Lyapunov Theory-based Adaptive Filter offers improved convergence and stability. When the system is described by a sparse model, the performance of Lyapunov Adaptive (LA) filter is degraded since it fails to exploit the system sparsity. In this paper, the Zero-Attracting Lyapunov Adaptation algorithm (ZA-LA), the Reweighted Zero-Attracting Lyapunov Adaptation algorithm (RZA-LA) and an affine combination scheme of the LA and proposed ZA-LA filters are proposed. The ZA-LA algorithm is based on ℓ1-norm relaxation while the RZA-LA algorithm uses a log-sum penalty to accelerate convergence when identifying sparse systems. It is shown by simulations that the proposed algorithms can achieve better convergence than the existing LMS/LA filter for a sparse system, while the affine combination scheme is robust in identifying systems with variable sparsity.
Asymmetric Image Encryption Approach with Plaintext-Related Diffusion
(Společnost pro radioelektronické inženýrství, 2018-04) Oravec, Jakub; Turan, Jan; Ovsenik, Lubos; Ivaniga, Tomas; Solus, David; Marton, Michal
This paper deals with topic of image encryption based on chaotic maps. A solution which has advantage of robustness against chosen-plaintext attacks is proposed. Permutations of image pixels are carried out in a way that enables operations on grayscale images with arbitrary resolution. All calculations done with user key and also all diffusion processes employ the same chaotic map. This feature enables usage of look-up tables which reduce computational times. The paper includes several experiments which verify achieved results and also briefly describes advantages and drawbacks of proposed solution.
Analysis of Three-Dimensional Spatial Selectivity for Rician Channel
(Společnost pro radioelektronické inženýrství, 2018-04) Du, Derong; Zeng, Xiaoping; Jian, Xin; Yu, Feng; Miao, Lijuan
The spatial selectivity of multipath fading determines the spatial diversity strategy to increase the performance of the communication system. This paper analyses the three-dimensional (3-D) spatial selectivity of Rician channel to strive to alleviate the current lack of analytical studies. A~3-D multipath angular power density (APD) model for Rician channel is proposed. Analytical expressions of the 3-D multipath shape factors are given based on the APD using the multipath shape factors theory. Finally, some important spatial fading statistics like the fading rate variance, level crossing rate (LCR), average fade duration (AFD), spatial correlation and coherence distance are derived, and the analysis on the impact of 3-D spatial angular directions on these spatial fading statistics is presented through simulations. The results would provide useful insight on quantifying and simplifying the analysis and design of the 3-D multiple input multiple output (MIMO) beamforming technology and smart antenna arrays.
A Spectrum Efficient Self-Admission Framework for Coexisting IEEE 802.15.4 Networks under Heterogeneous Traffics
(Společnost pro radioelektronické inženýrství, 2018-04) Zhao, Nan; Chi, Xuefen; Zhao, Linlin; Zhu, Yuhong
Due to the limited bandwidth resource and the interference among networks, it is challengeable to coordinate the bandwidth resource of multiple IEEE 802.15.4-based wireless personal area networks (WPANs) with heterogeneous traffics, especially in a distributed mode. In this paper, to handle this problem, we first propose a renewal carrier sense multiple access (CSMA)-based self-admission access mechanism for coexisting WPANs in order to maximize the frequency resource utilization and satisfy the diverse rate requirements of heterogeneous traffics. Secondly, we propose the time-space-hard core point process (TS-HCPP) to abstract the renewal CSMA-based self-admission access process for the IEEE 802.15.4 network with multi-channels. TS-HCPP considers the correlation of time and space, and appropriately judges the strong interference between coexisting WPANs, which can solve the density underestimation problems of traditional HCPP. Finally, relying on the TS-HCPP, we obtain the optimum combination of access parameters, which meets the minimum service rate requirements for heterogeneous traffics and maximizes the frequency resource utilization. The simulation results show that the density of coexisting WPANs evaluated by the TS-HCPP matches the experimental results, and an improvement in spectral efficiency of coexisting WPANs can be achieved in our proposed self-admission framework.

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