The problem of locating and finding radiating sources with sensor arrays has been a central topic of research in signal processing. Sensor array processing has found numerous applications in radar, sonar, wireless communications, speech processing and seismology. The aim of Direction of Arrival (DOA) estimation is to use the data received by the sensor array and to estimate the DOA of the incoming signal. The main research area in array signal processing is high resolution DOA estimation methods and algorithms. Determination of signal sources has been used in radar systems, location finding systems in military, electronic warfare systems and various applications such as mobile communication systems. The research in this topic had begun during the 1960s. Firstly, Maximum Likelihood (ML) estimation came into existence in such a way to estimate more than one signal. Earlier, the subarray-based estimation methods were used after Pisarenko’s method. Pisarenko gave this method in 1973 while examining the problem of estimating the frequencies of complex signals in white noise. Then, Multiple Signal Classification (MUSIC) method was developed by Schmidt. Roy and Kailath (1987) developed the Estimation of Signal Parameters via Rotational Invariance technique (ESPRIT) to avoid the disadvantages of MUSIC algorithm. This paper presents a reveiw of such techniques.

To estimate the number of incoming signals is a very difficult task because there is unknown number of incident signals impinging on the antenna array simultaneously with unknown directions and with unknown amplitudes. The received signal is corrupted with noise also. There are several methods to estimate the number of signals and their directions (Honghao and Sven Nordebo, 2014; and Direction of Arrival Estimation).

The DOA estimation method (Schmidt, 1986; Rao and Hari, 1989; Lal, 1996; Hamid and Mats, 1996; Van, 2002; Khan et al., 2008; Andy and Arpad, 2010; Reaz et al., 2012; Honghao and Sven, 2014; and Direction of Arrival Estimation) estimates the linear spectrum which is based on the method of Fourier transform. This basically includes the periodogram method (Honghao Tang and Sven Nordebo, 2014; and Direction of Arrival Estimation). The periodogram method was affected by the Rayleigh limit. This could not acquire a high resolution performance or resist the noise, so it did not obtain satisfactory performance. After that the research was in the field of DOA estimation based on the statistical analysis of Maximum Likelihood (ML) spectrum estimation. This method has a high resolution performance and robust character. The method needs to search for a high dimensional parameter, which requires more calculations. Therefore, this method is not put into practice.

Electrical and Electronics Engineering Journal, Direction of Arrival (DOA, Maximum Likelihood (ML), Multiple Signal Classification (MUSIC), Sensor Array, Estimation of Signal Parameters via Rotational Invariance technique (ESPRIT).