CNR之估計與快速頻率獲取與追蹤之研究

Abstract

本論文包含兩部份。第一部份研究估計攔截載波雜訊比的兩種演算法與它 們在低攔截機率測試上的一些應用; 第二部份討論瞬時都卜勒頻率及相關 高階統計特性的估計。一個軍事通訊系統的LPI規格 ，一般都以單一變 數 - 攔截等效半徑來衡量，但寬頻訊號的可偵測性與訊號波形及偵測器 的結構有一密切關連 ，雖然我們可以利用不同的攔截器各別去測試一種 訊號是否滿足LPI的要求，但此種LPI測試方式甚不經濟 。我們只需要在 不同地點量測訊號的CNR值,便能估計其其CEVR值。這裡我們提出了用迪克 接收器和功率輻射計兩種測量計來定點估計CNR值的法則，並同時研究其 統計特性及可靠度。由於低軌道(LEO)衛星與地面台的相對運動 ，使得衛 星通訊的訊號傳送過程中不可避免地產生都卜勒效應，這種現象將對訊號 獲取造成很大的困擾訊號的載波相位樣本我們以最小平方差估計法對重建 的做估計，週期地修正振盪器輸出頻率以去除訊號中的都卜勒效應。經電 腦模擬後，我們証明這種新方法不但可以很快地獲得接收訊號的頻率且其 估計誤差很小。 This thesis consists of two parts. The first part studies two algorithms for estimating intercepted signal power levels and their application to low-probability-of-intercept (LPI) tests. The second part deals with the estimation of instantaneous doppler frequency and related higher order statistics. The detectability of a wide band signal is a function of both the waveform design and the detector structure. A single parameter measure called Circular Equivalent Vulnerability Radius (CEVR) is often used to characterize the LPI capability of a given signal. To estimate the CEVR of the intercepted carrier-to- noise power ratio (CNR) at various locations are needed. Estimation algorithms for the intercepted CNR are proposed, their statistical properties and reliability are studied. Signals emitted from a platform with high dynamic will unavoidably induce rapid-changing carrier doppler. Using the reconstructed carrier sample phases, we present a least-squares estimation algorithm to periodically update the local VCO output. The proposed algorithm is shown to obtain fast frequency acquisition.