| Summary: | 碩士 === 國立臺灣大學 === 電信工程學研究所 === 94 === With the characteristics of omni-directional coverage, Uniform Circular Array(UCA) is a suitable structure for base-station.
Thesis focuses on adaptive narrowband/broadband UCA beamforming, the difference between narrowband and broadband UCA is that each sensor of broadband UCA beamformer is connected with a tap-delay-line FIR filter.
Under ideal conditions, UCA with adaptive beamformer such as Linearly Constrained Minimum Variance (LCMV) has the ability of maintaining output power gain of desired signals while it could suppress output noise and reject interference signals.
Two conditions, Direction of Arrival(DOA) mismatch and coherent interference, which make adaptive beamforming fail, are considered in this thesis.
For overcoming DOA mismatch problem, a gradient method proposed by Cheng[1] is applied to narrowband UCA.
For coherent interference, Spatial-DFT is applied to transforming
narrowband UCA to virtual ULA and ITAM is applied to all signals without elevation angle.
As to signals with elevation angle under coherent conditions. 2-stage Spatial Smoothing and 2-stage Without Spatial Smoothing are applied to both narrowband/broadband UCA beamformer.
|
|---|
