Research On DOA Estimation Of Frequency Agility Signals From Multi-sources

DOA (Direction of Arrival) estimation is one of the main contents of signalparameter estimation, which is widely used in radar, communication, sonar andother fields. With the modern warfare environment more and more complex, thefrequency agility technology has been increasingly applied in radar system. But thedirection estimation algorithms before are proposed for narrowband model, thedifferent frequency signals’ array manifolds and signal subspace are different,which causes the narrowband DOA estimation algorithms can not be directly usedin the frequency agility s ignals. And the conventional methods of estimating thesignals’ direction are carried out under the conditions that the power of the differentsignals is same. But in the real environment the amplitute is easily affected byswitch of the beam and cross polarization of the antenna. So the power of thesignals is varying all the time, which is an important focator that affects theestimation performance of the algorithm. Therefore, research on the DOAestimation of frequency agility is very important and useful in practice.Firstly, the MUSIC algorithm is applied in the frequency agility under thecondition that the bandwidth is small. The results of the simulation show that theMUSIC algorithm can achieve the DOA of the signals effectively. Subsequently,two kinds of wideband estimation algorithm are introduced in the case that thebandwidth of the signal is large, one is Incoherent Signal Subspace Method (ISM)and the other one is Coherent Signal Subspace Method (CSM). The ISM algorithmdecomposes the signals into several segments, then applys the narrowband methodin each segment. Finally averages the results to achieve the DOA of signals. But infact the power of signa ls is varying all the time. Averaging the results will cause theestimation errors, different weights are adopted to each result. Experiments showthat the energy weighted ISM algorithm presents better performance than theconventional ISM algorithm. In addition, the ISM algorithm has another problem. Itcan’t achieve the DOA estimation for correlated signals. Aiming at this problem, thespatial smoothing algorithm and the Toeplitz algorithm are combined with ISMalgorithm, and the modified algorithm can be used to estimate coherent signal. Theother kind of wideband DOA estimation algorithm (CSM algorithm) finishsmoothing in frequency, So it has coherent capacity and can be used to estimatecorrelation signals. The simulations show that the calculated amount of CSMalgorithm is much smaller than ISM algorithm, the estimation error is small and t he algorithm presents more stable performance. But CSM algorithm has a fataldrawback that the algorithm need pre-estimate the DOA of signals, which has agreat influence on the performance of the algorithm.Then two modified algorithms are introduced, one is consistent focusingalgorithm and the other one is Jacobi-Anger algorithm. But when the power ofsignals has dramatic changes, the signals whose amplitude is stable can’t beestimated. And this paper adopts the orthogonal projection pretransformation torestrain the estimated signals. The simulations show that the algorithm is effectiveand stable.