Sung-Hoon Moon

Fast DOA estimation algorithm using pseudocovariance matrix

This paper proposes a new direction of arrival (DOA) estimation algorithm that can rapidly estimate the DOAs of incidence signals using a pseudocovariance matrix even under coherent interference environments. The conventional multiple signal classification (MUSIC) algorithm, which should estimate a covariance matrix, cannot perform a DOA estimation until it acquires the covariance matrix. In addition, the MUSIC algorithm cannot be used under rapidly changing or correlated interference environments. In contrast, the proposed algorithm can obtain a bearing response after acquiring the pseudocovariance matrix based on a single snapshot. Signal incidence angles can then be accurately estimated by combining the bearing response and the location of pattern nulls. Accordingly, the proposed algorithm can rapidly estimate the DOAs of signals even when they are correlated.

Spatial diversity technique for improvement of DTV reception performance

Digital television (DTV) receiver architecture with an antenna array is proposed to improve the reception performance in multipath fading conditions. The proposed DTV receiver uses diversity combining and equalization techniques in the beam-space. Two separate beamformers are forming separate beam patterns to two different signal arriving angles by utilizing a channel estimation technique. Then the outputs of the beamformers are combined with a proper time adjustment. Simulation results show the convergence speed of the proposed architecture is three times faster than that of the receiver using only one branch beamformer.

Monopulse angle estimation with constrained adaptive beamforming using simple mainlobe maintenance technique

A new monopulse radar system is proposed to overcome the difficulties with conventional monopulse techniques under jamming conditions. The proposed system uses a simple mainlobe maintenance technique based on the estimated direction of the mainlobe jammer. Thereafter, an adaptive array is used to create pattern nulls in the incoming directions of jammers, while maintaining the shape of the mainlobe. As a result, the proposed system can track the target angle without any correction of the adaptive sum and difference beam outputs.

Channel capacity enhancement using virtual array elements in smart antenna systems

A smart antenna system using virtual array elements is proposed to increase the channel capacity of mobile communication systems. The proposed smart antenna system increases the degree of freedom using virtual array elements generated by complex conjugations of real array elements signals and sign compensations using the orthogonality between the user identification codes in the I and Q channels. The performance of the proposed system is analyzed under cdma2000 specifications in urban cell environments.

A new GSC using monopulse angle estimation technique for fast target tracking

A new generalized sidelobe canceller (GSC) is proposed to solve the steering error problem caused by fast target maneuvering or array imperfections. The proposed GSC uses the monopulse technique to identify the steering error. Seperate sum and different channels are used for estimating the monopulse ratio. While interferences are removed by adaptive beamforming, fixed-weight sum and difference beampattems are applied to estimate the steering error. Simulation results show that the proposed GSC can solve the steering error and track the target even under severe jamming conditions.

Fast DOA estimation algorithm for improving performance of SPT-LCMV beamformer

To eliminate coherent interferences, a conventional split polarity transformation-linearly constrained minimum variance (SPT-LCMV) beamformer uses the SPT matrix to remove any correlation between the desired signal and coherent interferences. After removing the correlation, an LCMV beamforming is applied to obtain the desired signal. However, it needs to estimate direction of arrivals (DOAs) for all coherent interferences. Conventional algorithms to estimate the DOAs of coherent interferences are computationally complexity. Moreover, the performance of the SPT-LCMV beamformer degraded severely as the estimated DOA errors increased. Accordingly, high-order constraints are required to compensate the DOA estimation errors. As a result, the SPT-LCMV beamformer needs many array elements in proportion to the number of the constraints applied to generate the SPT matrix. This paper proposes a DOA estimation algorithm to overcome the disadvantages of the SPT-LCMV beamformer. The proposed algorithm has a significantly reduced computational complexity and can also reduce the number of the high-order constraints compared to the conventional DOA estimation algorithms.

Sequentially operated SPT-LCMV beamformer to overcome coherent interferences

The paper proposes a sequentially and linearly constrained minimum variance beamformer (SLCMV) based on a split polarity transformation (SPT) called an SPT-SLCMV beamformer. The proposed SPT-SLCMV is an improved version of an SPT-LCMV beam-former as it can minimize the degree of freedom loss and eliminate the desired signal cancellation phenomenon under coherent interference situations. These advantages are obtained by successively applying sub-constraint matrices divided from a whole constraint matrix to remove any correlation between the desired and interference signals. As a result, the proposed beamformer can solve the degree of freedom loss while maintaining the performance of the conventional SPT-LCMV beamformer.

Two-dimensional transform-domain partially adaptive beamformer

This paper proposes a transform-domain partially adaptive beamformer to reduce the computational complexity of conventional transform-domain beamformers, After transforming the input signals, the proposed beamformer adapts only those parts of the weights that correspond to the transformed coefficients expected to contain interference by using the cell averaging constant false alarm rate (CA-CFAR) processor. The false alarm rate of the CA-CFAR processor is also changed adaptively according to the variation of output power.

Adaptive array algorithm using spatial interpolation for the cancellation of coherent interferences

An adaptive array system is a candidate to increase the channel capacity by rejecting interference. However adaptive array systems are hard to remove all the interference when the incident signals are coherent with a desired signal. In this paper, we propose a modified Duvall beamformer, which performs spatial smoothing using spatial interpolation technique to maintain the degree of freedom. The proposed algorithm can minimize the loss in the degree of freedom due to spatial smoothing by forming subarrays with interpolated signals. Simulation results show that the proposed algorithm can remove all the interference while the conventional beamformer cannot.

Frequency-domain partially adaptive array algorithm combined with CFAR technique

A frequency-domain partially adaptive beamformer is proposed to reduce the computational complexity of conventional frequency-domain adaptive beamformers. The proposed beamformer only adapts the weights that correspond to the frequency bins expected to contain interferences using a cell-averaging constant false alarm rate (CA-CFAR) processor. The false alarm rate is also changed adaptively to achieve optimum partial adaptation.