2018/1

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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.
Perceived Audio Quality Analysis in Digital Audio Broadcasting Plus System Based on PEAQ
(Společnost pro radioelektronické inženýrství, 2018-04) Ulovec, Karel; Smutny, Miroslav
Broadcasters need to decide on bitrates of the services in the multiplex transmitted via Digital Audio Broadcasting Plus system. The bitrate should be set as low as possible for maximal number of services, but with high quality, not lower than in conventional analog systems. In this paper, the objective method Perceptual Evaluation of Audio Quality is used to analyze the perceived audio quality for appropriate codecs --- MP2 and AAC offering three profiles. The main aim is to determine dependencies on the type of signal --- music and speech, the number of channels --- stereo and mono, and the bitrate. Results indicate that only MP2 codec and AAC Low Complexity profile reach imperceptible quality loss. The MP2 codec needs higher bitrate than AAC Low Complexity profile for the same quality. For the both versions of AAC High-Efficiency profiles, the limit bitrates are determined above which less complex profiles outperform the more complex ones and higher bitrates above these limits are not worth using. It is shown that stereo music has worse quality than stereo speech generally, whereas for mono, the dependencies vary upon the codec/profile. Furthermore, numbers of services satisfying various quality criteria are presented.
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.
A Carrier Synchronization Algorithm for SDR-based Communication with LEO Satellites
(Společnost pro radioelektronické inženýrství, 2018-04) Kozlowski, Sebastian
In this work a carrier synchronization algorithm for communication with low Earth orbit (LEO) satellites was proposed. The algorithm has a form of a software routine and is intended to be run on a typical personal computer (PC) providing computational resources for a software defined radio (SDR) receiver. Due to limited computational power of PCs in comparison with other devices, such as FPGAs, the work was focused on providing carrier synchronization with minimal processing. The algorithm includes a nonlinear operation for recovering carrier wave from the received signal, a software 2nd order type 2 phase locked loop for tracking the recovered carrier, and a correction block for removing frequency shift from the received signal. Computer simulations were performed to investigate algorithm’s behavior. Additionally, execution time was measured to determine maximal symbol rate of a signal to be processed.
General Time-Division AltBOC Modulation Technique for GNSS Signals
(Společnost pro radioelektronické inženýrství, 2018-04) Zhou, Zhihui; Tang, Zuping; Wei, Jiaolong; Xia, Xuan
In this paper, a general time-division alternate binary offset carrier (GTD-AltBOC) modulation method is proposed, which is an extension of TD-AltBOC and time-multiplexed offset-carrier quadrature phase shift keying (TMOC-QPSK) with high design flexibility. In this method, binary complex subcarriers and a time-division technique with flexible time slot assignment are used to achieve constant envelope modulation of the signal components with a variable power allocation ratio (PAR). The underlying principle of GTD-AltBOC and the constraints related to the PAR are investigated. For the generation of GTD-AltBOC signals, a lookup table (LUT)-based scheme is presented; the minimum required clock rate is half or less of that for existing non-time-division methods. The receiver processing complexities are analyzed for three typical receiving modes, and the power spectral densities (PSDs), cross-correlation functions, multiplexing efficiencies and code-tracking performance are simulated; the results show that GTD-AltBOC enables a significant decrease in receiving complexity compared with existing methods while maintaining high performance in terms of multiplexing efficiency and code tracking.

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