2017/2

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Now showing 1 - 5 of 24
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    Distributed Matching Algorithms: Maximizing Secrecy in the Presence of Untrusted Relay
    (Společnost pro radioelektronické inženýrství, 2017-06) Ali, Bakhtiar; Zamir, Nida; Ng, Soon Xin; Butt, Muhammad Fasih Uddin
    In this paper, we propose a secrecy sum-rate maximization based matching algorithm between primary transmitters and secondary cooperative jammers in the presence of an eavesdropper. More explicitly, we consider an untrusted relay scenario, where the relay is a potential eavesdropper. We first show the achievable secrecy regions employing a friendly jammer in a cooperative scenario with employing an untrusted relay. Then, we provide results for the secrecy regions for two scenarios, where in the first case we consider no direct transmission between the source and the destination, while in the second case we include a source to destination direct link in our communication system. Furthermore, a friendly jammer helps to send a noise signal during the first phase of the cooperative transmission, for securing the information transmitted from the source. In our matching algorithm, the selected cooperative jammer or the secondary user, is rewarded with the spectrum allocation for a fraction of time slot from the source which is the primary user. The Conventional Distributed Algorithm (CDA) and the Pragmatic Distributed Algorithm (PDA), which were originally designed for maximising the user’s sum rate, are modified and adapted for maximizing the secrecy sum-rate for the primary user. Instead of assuming perfect modulation and/or perfect channel coding, we have also investigated our proposed schemes when practical channel coding and modulation schemes are invoked.
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    DOA Estimation of Uncorrelated, Partly Correlated and Coherent Signals Using Alternating Oblique Projection
    (Společnost pro radioelektronické inženýrství, 2017-06) Hou, Huijun; Mao, Xingpeng
    The problem of direction-of-arrival (DOA) estimation is important in array signal processing. To estimate the DOAs of uncorrelated, partly correlated and coherent signals, a new iterative DOA estimation algorithm, named AOP-DOA, is proposed by using alternating oblique projection (AOP). In each iteration, the oblique projection approach is employed to separate the received signals, then the DOA of each separated signal is estimated one after another. After theoretical analysis on the relationship between the proposed AOP-DOA and the conventional alternating projection based maximum likelihood estimator (AP-MLE), an AOP&AP-DOA algorithm, which is a combination of AOP-DOA and AP-MLE, is developed to reduce the computational complexity of AOP-DOA. Extensive experiments validate the effectiveness and complexity of the proposed two algorithms. Particularly, AOP&AP-DOA keeps the merits of AOP-DOA, but exhibits superiority over AOP-DOA in terms of computational complexity when proper adaptive grid refinement strategy is applied.
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    Detection-Localization Tradeoff in MIMO Radars
    (Společnost pro radioelektronické inženýrství, 2017-06) Nazari Majd, Mohammad; Radmard, Mojtaba; Chitgarha, Mohammad M.; Bastani, Mohammad H.; Nayebi, Mohammad M.
    Two gains play key roles in recently developed‎ MIMO ‎wireless communication systems‎: ‎"spatial diversity‎" ‎gain and "spatial multiplexing‎" ‎gain‎. ‎The diversity gain refers to the capability to decrease the error rate of the MIMO channel‎, ‎while the multiplexing gain implicitly refers to the amount of increase in the capacity of the MIMO channel‎. ‎It has been shown that there is a fundamental tradeoff between these two types of gains‎, ‎meaning interplay between increasing reliability (via an increase in the diversity gain) and increasing data rate (via an increase in the multiplexing gain)‎. ‎On the other hand‎, ‎recently‎, ‎MIMO radars have attracted much attention for their superior ability to enhance the system's performance‎. ‎As a MIMO system‎, ‎it is expected that the mentioned diversity-multiplexing tradeoff exists in a MIMO radar‎, ‎too‎. ‎In this paper‎, ‎this tradeoff is studied and verified in MIMO radars with widely separated antennas‎. ‎In more details‎, ‎it will be shown that increasing dependency between transmit-receive links results in higher diversity gain and lower multiplexing gain‎, ‎and vice versa‎. ‎Then‎, ‎the optimal tradeoff is introduced‎, ‎i.e.‎, ‎the conditions that the MIMO radar system should have‎, ‎so that the diversity-multiplexing tradeoff is at its optimum point‎, ‎are driven‎.
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    Modeling and Link Performance Analysis of Busbar Distribution Systems for Narrowband PLC
    (Společnost pro radioelektronické inženýrství, 2017-06) Hasirci, Zeynep; Cavdar, Ismail Hakki; Ozturk, Mehmet
    Busbar distribution system is used as a modular infrastructure to carry electrical energy in low voltage grid. Due to the widespread usage in industrial areas, the power line communication possibilities should be investigated in terms of smart grid concept. This paper addresses modeling of the busbar distribution system as a transmission line and gives some suggestions on the link performance for narrowband power line communication for the first time in literature. Firstly, S-parameters of different current level busbars were measured up to 500 kHz for all possible two-port signal paths. The utilization of the frequency-dependent model was proposed to extract transmission line characteristics to eliminate the unwanted measurement effects. Particle swarm algorithm was used to optimize the model parameters with a good agreement between measured and simulated S-parameters. Additionally, link performance of busbar distribution system as a power line communication channel at 3 kHz-148.5 kHz band was examined for frequency shift keying and phase shift keying modulations under different network configurations such as varying busbar type, the line length between transmitter and receiver, branch number, and terminating load impedance. Obtained results were presented as bit-error-rate vs. signal to noise ratio graphs.
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    2D DOA Estimation of UCA Correlative Interferometer Based on One Dimensional Sorting Lookup Table-Two Dimensional Linear Interpolation Algorithm
    (Společnost pro radioelektronické inženýrství, 2017-06) Cui, Kaibo; Wu, Weiwei; Huang, Jingjian; Chen, Xi; Yuan, Naichang
    In order to improve the direction-finding efficiency of the correlative interferometer and reduce the size of the lookup table, this paper proposes the one dimensional sorting lookup table-two dimensional linear interpolation (1DSLUT-2DLI) algorithm. Firstly, the uniform circular array (UCA) model is established and the direction finding (DF) theory of the correlative interferometer is analyzed. A new lookup table is obtained by proceeding the ascending order for the first dimensional phase differences and a one dimensional iterative filtering method is used to look up the new table to get the direction of arrival (DOA) estimation. Compared to the exist methods, the 1DSLUT algorithm can reduce the computational complexity greatly. Considering the burden of a big lookup table, this paper proposes the 2DLI algorithm. Through the Taylor expansion, the conclusion that the phase difference is approximately linear in a small angle range is obtained. So, the linear interpolation can be applied to calculate the phase differences in the azimuth direction and elevation direction. On this basis, we conclude the equations to get the DOA estimation using the 2DLI algorithm. In this way, the size of the lookup table is reduced greatly, which decreases the computational complexity greatly also. The numerical simulations verify the effectiveness of the 1DSLUT-2DLI algorithm and it can obtain a pretty high DOA estimation precision with a low computational complexity and a small lookup table.