Serdar Ozgur Ata

High-Resolution Direction-of-Arrival Estimation via Concentric Circular Arrays

Estimating the direction of arrival (DOA) of source signals is an important research interest in application areas including radar, sonar, and wireless communications. In this paper, the problem of DOA estimation is addressed on concentric circular antenna arrays (CCA) in detail as an alternative to the well-known geometries of the uniform linear array (ULA) and uniform circular array (UCA). We define the steering matrix of the CCA geometry and investigate the performance analysis of the array in the DOA-estimation problem by simulations that are realized through varying the parameters of signal-to-noise ratio, number of sensors, and resolution angle of sensor arrays by using the MUSIC (Multiple Signal Classification) algorithm. The results present that CCA geometries provide higher angle resolutions compared to UCA geometries and require less physical area for the same number of sensor elements. However, as a cost-increasing effect, higher computational power is needed to estimate the DOA of source signals in CCAs compared to ULAs.

Joint Relay and Antenna Selection in MIMO PLNC Inter-vehicular Communication Systems over Cascaded Fading Channels

We investigate the joint relay and antenna selection performance in a multiple input multiple output (MIMO) Vehicle-to-Vehicle (V2V) communication system employing physical layer network coding (PLNC) with amplify-and-forward (AF) scheme at the relay antenna. Analytic results are derived under the cascaded Nakagami-m fading channel model assumption, which covers cascaded Rayleigh and conventional cellular channel models as well. We evaluate the performance of the system in terms of joint outage probability of sources and derive closed-form expressions for lower and upper bounds while an exact expression is found as a single integral form. Besides, the asymptotic diversity order is analyzed and quantified as a function of number of relays and antennas installed on the source and relay vehicles, and channel parameters. Finally, we verify the analytic derivations by computer simulations. Our results show that the outage probability performance decreases with the increasing cascading degrees of the channels but joint relay and antenna selection enhances the performance of the system superbly with the increasing number of relays and antennas. Also it is shown throughout all the simulation results, the lower bound for the joint outage probability seems to consistently be well tight for large SNR. Therefore it can be used for practical design of inter-vehicular communication systems which contain multiple relays and antennas.

Relay antenna selection for V2V PLNC system

This paper focuses on the relay antenna selection problem in a Vehicle-to-Vehicle (V2V) communication system employing physical layer network coding (PLNC) with amplify-and-forward (AF) scheme over double-Nakagami-m fading channels. We obtain lower and upper bounds of end-to-end signal-to-noise ratio (E2E-SNR) and their cumulative density functions (CDF). Employing the CDFs, the performance of the system is evaluated in terms of outage probabilities. We analize asymptotic diversity order of the system and express it as a function of number of relay antenna and channels parameters. Finally the analytical results are verified by the simulations.

Secrecy Performance Analysis over Cascaded Fading Channels

In this study, the authors investigate the secrecy performance at the physical layer of wireless communication systems where the channels are modelled as cascaded fading channels, in which the fading effects are worse than those in the cellular communication channels like Rayleigh and Nakagami- m . Analytic results are derived for the cascaded Nakagami- m fading channel model comprising the cascaded Rayleigh, 2*Nakagami- m , the generalised- K , and the conventional cellular channel models as well. By evaluating the information-theoretic physical layer security performance, they obtain the closed-form expressions of the average secrecy capacity and probability of the positive secrecy capacity in case of that channel-state-information of the eavesdropper is known by the source. Then they obtain the exact closed-form secrecy outage probability (SOP) when the eavesdropper is passive. Analytic results are computed in terms of the bivariate and univariate Meijers G functions and later on are successfully validated through Monte Carlo simulations. The simulation results show that the secrecy performance worsens with the increasing cascading degree of the fading channels. For example, in 2*Nakagami- m fading channels where the cascading degree is 2, extra 4 dB signal-to-noise ratio is required to achieve the same SOP value in comparison with the classical Nakagami- m fading channels.

Analog network coding over cascaded fast fading Rayleigh channels in the presence of self-interference

We propose an mobile-to-mobile (M2M) communication system employing analog network coding (ANC) with fixed gain amplify-and-forward (AF) scheme on relay, and investigate performance of the system for the case of imperfect self-interference cancellation proceeded by the the receiver. For this purpose, first we find the expression of end-to-end signal-to-interference-noise-ratio (E2E-SINR) at the receiver. Then, we derive the closed form expression of the cumulative density function (CDF) of E2E-SINR for the fast fading cascaded Rayleigh channel conditions. Using this CDF, we obtain the closed-form expression of outage probability. Finally, we verify the analytic results by comparing with computer simulations. Our results show that the outage probability increases when the success of the self-interference cancellation by the receiver decreases. Also it is shown that the increasing cascading degree of the channels decreases the outage performance of the system.

Signal detection based on linear trend in the noise-originated eigenvalues of the correlation matrix for cognitive radio

Cognitive Radio introduces the opportunistic usage of unoccupied frequency bands by unlicensed users without disturbing the Quality-of-Service of the licensed users. The first problem to be solved by a Cognitive Radio terminal is sensing the signals of the licensed users. In our study, we offer a new sensing method based on the eigenvalue decomposition of the covariance matrix of received signals. The method defines a test statistic on the distribution of eigenvalues to give a “Yes or No” decision about the signals in the band-of-interest. The main idea behind the method is that eigenvalues belonging to the noise subspace of the covariance matrix tend to exhibit a linear trend of decrease in case of limited number of samples of the received signals. The proposed method presents a realistic approach, and due to its robustness to sensing without suffering from noise power uncertainty, it has advantages against the energy level comparison based detectors that are highly influenced by the noise.

Direction-of-arrival estimation via concentric circular antenna arrays

The estimation of direction-of-arrival (DOA) of source signals has been well-studied research area in both military and civil applications. The MUSIC (Multiple SIgnal Classification) algorithm based on the signal subspace separation idea has already been investigated and employed for uniform linear arrays (ULA) and uniform circular arrays (UCA) in DOA estimation extensively. However, an important disadvantage of the ULA geometry in DOA estimation is that it can only estimate the azimuth angle. To estimate the elevation angle, UCA geometries are employed in many applications. As the concentric circular arrays (CCA) that are discussed in this paper have better angle resolutions compared to ULAs, and as they require smaller physical area compared to UCAs with the same number of array elements, CCAs are proposed to be used in mobile applications as a preferable alternative. The DOA estimation problem for CCAs is defined and the steering matrix is expressed in this paper, moreover the performance analysis is investigated by simulations.