2018/1

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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.
Analytical Evaluation of Chunk-Based Tractable Multi-cell OFDMA system
(Společnost pro radioelektronické inženýrství, 2018-04) Kavitha, Pillappan; Shanmugavel, Sethu
This paper evaluates thoroughly the performance of multi-cell OFDMA system. The two types of deployment in multi-cell OFDMA system, such as Strict Fractional Frequency Reuse (FFR) and Soft FFR (SFR) were evaluated. In order to model the base station locations, homogeneous Poisson point processes were used, i.e. tractable model instead of hexagonal grid was considered. In order to reduce complexity, chunk-based resource allocation scheme was embedded. Each cell divides the users into the users of the central cell area and the users of the cell edge area according to their average received Signal to Interference and Noise Ratio (SINR) compared with FFR threshold. The primary stage of the analysis includes the spectral efficiency’s expression deriving from these two deployment scenarios, followed by the analysis with the use of coverage probability. However, the improvement of spectral efficiency is achieved in the case of SFR. On the contrary, coverage probability is far improved by using strict FFR scheme. Through numerical anaysis, We have shown that the optimal FFR threshold to achieve the highest spectral efficiency was 12 dB for both Strict FFR as well as SFR.

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