調適的束波器主要是利用可動態調整的束波，去增強期望的信號源或是去壓制干擾的信號源，這是非常重要的一個應用，所以會被採用到各個不同的信號處理上。在於我們的論文之中，將要研究廣義旁波帶消除器之子頻帶分解調適束波器的內在缺陷影響，此內在缺陷為廣義旁波帶消除器本身的非零錯誤信號，次非零錯誤信號主要是由於廣義旁波帶消除器本身的期望信號和雜訊所建構而成。另外，如果在實際的情形之下，由於各子頻帶間的重疊現象，會造成不理想的子頻帶分解，這也將會使得廣義旁波帶消除器本身的非零錯誤信號額外的增加。這些非零錯誤信號將會減緩廣義旁波帶消除器本身的收斂速度。

我們為了要去減輕非零錯誤信號對於廣義旁波帶消除器的嚴重影響，本論文要去提出決策迴授子頻帶分解之廣義旁波帶消除器新架構。此一架構要同時去考量我們廣義旁波帶消除器之下端信號與決策迴授之輸出訊號，基於最小平方誤差法則，去設計決策迴授子頻帶分解廣義旁波帶消除器統計上最佳的子頻帶分解，經由這樣設計的調是束波器，不僅具有優越的干擾消除能力，同時也可以提供很快的收斂速度。

為了要更瞭解我們所提供的新分法，本論文之中，將會推導決策迴授廣義旁波帶消除器之子頻帶分解的信號干擾雜訊比率，及對此一信號干擾雜訊比率去作詳細的分析。此外，我們也會去做詳細的收斂速度特性分析，藉以去證明此一新的架構是否真的具有這些優點，最後再經由已完成的電腦模擬結果，我們可以再一次去驗證，所發展提出的決策迴授子頻帶分解之廣義旁波帶消除器會有很好的收斂特性。

Adaptive beamforming, which can dynamically adjust its beampattern to
enhance the desired signal and null out or reduce the interferences, is of importance in various disciplines of signal processing applications. In this thesis, we focus on that the inherent setback of subband generalized sidelobe canceller (GSC), as the traditional GSC, is the nonzero error signal, which consists of both the desireed signal and the noise signal, in the output of the GSC. In addition, the practically imperfect subband decomposition also increases this error signal due to the aliasing between subbands. Such a nonzero error signal will retaliate the convergence rate of GSC.

To alleviate this shortcoming, the thesis proposes a decision feedback subband
GSC, in which the design of the statistically optimum filter bank decomposition
of the signals passing through the lower branch of the GSC as well as the signal after the decision feedback based on the minimum mean-square error
criterion is addressed. The new beamformer not only renders superior interference cancellation capability, but also possesses a fast convergence rate due to the subband processing scheme and the removal of the desired signal subband component in the output of the GSC via the decision feedback. Furthermore, to mitigate the computational overhead in the determination of the subband filter coefficients, an iterative procedure is also addressed.

To provide further insights into the proposed approach, the analytic expressions of the output signal-to-interference-plus-noise ratio (SINR) of the decision feedback subband GSC is derived. The convergence behavior of the proposed beamformer is analyzed as well to justify the advantages of the new scheme. Furnished simulations show that the proposed beamformer can yield superior performance with faster convergence characteristics compated with previous works.

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