EFFECTS OF MUTUAL COUPLING AND DIRECTIVITY ON DOA ESTIMATION USING MUSIC LOPAMUDRA KUNDU & ZHE ZHANG

Outline of the Presentation  What is DOA?  MUSIC  Parameter study:  Signal-to-noise ratio (SNR)  Inter-element spacing  Mutual coupling  Directivity  Why DOA?  Applications  Scopes of future work

Direction of Arrival (DOA) Estimation  Estimation of direction finding signals in the form of electromagnetic/acoustic waves impinging on a sensor or antenna array.  High resolution DOA can resolve closely spaced frequencies.  Most popular technique is “Subspace method”  Used for locating and tracking signal sources in both military and civilian communications.

4 Multiple Signal Classification (MUSIC)  Steering vectors:  Data model of M signals incident on an array of N elements: Where, k=1,…,K (number of snapshots)  Correlation matrix of x: A: signal correlation matrix σ 2 : noise variance 1 2 N Antenna array d M signals ΦnΦn

MUSIC (contd.)  Eigen value decomposition of R  Since (signal subspace) ⊥ (noise subspace), DOAs are the peak locations of MUSIC power spectrum signal subspace noise subspace M N-MM v vHvH

Parameters Affecting the Performance of MUSIC  Signal-to-Noise Ratio (SNR)  Inter-element Spacing  Mutual Coupling  Antenna Directivity

Normalized Power Spectrum For Different SNR Levels (AWGN)  Simulation Parameters:  Array size=5 (ULA)  Element Spacing=  Number of Signals=2  AOA= 20 ⁰ and 80 ⁰  Number of Snapshots=3  Conclusion:  Broad peaks for SNR<15 dB.  Sharp peaks at SNR ≥ 15 dB and both the signal directions are estimated correctly.

Normalized Power Spectrum For Various Inter-Element Spacing (No Coupling)  Simulation Parameters:  Array size=5 (ULA)  SNR level=30 dB (AWGN)  Number of Signals=2  AOA=20 ⁰ and 80 ⁰  Number of Snapshots=3  Conclusion:  Broad peaks for d<0.5.  Sharp peaks at d ≥0.5 and both the signal directions are estimated correctly.

Normalized Power Spectrum in the Presence of Mutual Coupling  Simulation Parameters:  Array size=5 (ULA)  SNR level=50 dB  Number of Signals=3 (LP)  AOA=20 ⁰, 50 ⁰ and 80 ⁰  Number of Snapshots=10  Conclusion:  Broad peaks for d<0.5.  Sharp peaks at d ≥ 0.5 and all the three signal directions are estimated correctly.

Comparison Between NEC Simulation and MALTLAB Simulation  Simulation Parameters:  Array size=5 (ULA)  SNR level=50 dB  Number of Signals=3 (LP)  AOA=20 ⁰, 50 ⁰ and 80 ⁰  Number of Snapshots=10  Conclusion:  The algorithm works better for no coupling scenario.  Mutual coupling degrades the direction estimation efficiency considerably for same spacing.

Directivity of Antenna  DOA estimation is related not only with the mutual coupling, but also with the directivity of the antennas.  Isotropic antenna: radiates uniformly in all directions.  Directional antenna: radiates more efficiently in some directions than others. Steering vector would be modified by the gain of directional antenna  Goal is to compare the performance of isotropic antenna arrays and directional antenna arrays in DOA estimation.

Structure of Antenna arrays in NEC Isotropic Directional

Simulation Result for Isotropic Array  Analysis:  Incident signals at 3 angles : 20 ⁰, 50 ⁰ and 80 ⁰  All 3 signals are detected accurately.  Isotropic array could detect all the incident signals simultaneously.

Simulation Result for Directional Array  Analysis:  Incident signals at 3 angles: 20 ⁰, 50 ⁰ and 90 ⁰.  Only incoming signal at 90 ⁰ is detected.  Directional array could only detect the signals that fall within the range of its main beam position.  The gain of directional antenna may make the result more accurate.

Why DOA: Applications DOA ESTIMATION radar Sonar Seismic Exploration Electronic Surveillance Wireless Communication

Applications Involving Coupling and Directivity  Applications involving mutual coupling: MIMO system with closely spaced antennas.  Applications involving directivity: Indoor environment with intensive multipath effect and interferences.

Scopes of Future Work  Other types of arrays and antennas.  Effects of other parameters like polarization, antenna gain, delay and ground effects.

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