摘 要:通過對混沌映射的研究,針對單一映射產生的擴頻序列其系統復雜度低,容易通過反向逆推估計出系統初值的缺點,以Logistic映射為基礎,構造出一種新的映射。該映射容易被數字電路實現,且具有較高的系統復雜度。該序列由兩個不同初始值的兩個Logistic映射復合而成,具有較高的安全性。在此,對復合混沌序列初值敏感性、平衡性、自相關性、功率譜密度進行了分析。研究結果表明,這種新型的序列具有較高的初值敏感性、優良的平衡性、自相關性和偽隨機性,是一種有效和可靠的擴頻序列。
關鍵詞:混沌序列; Logistic映射; 直接序列擴頻; 相關性分析
中圖分類號:TN911文獻標識碼:A
文章編號:1004-373X(2010)15-0015-03
Study on Modified Chaotic Spreading Spectrum Sequence
XIAO Li-li, HE Shi-biao
(Graduate Team, Chongqing Communication Institute, Chongqing 400035, China)
Abstract: Aiming at overcoming the shortcoming that the spreading spectrum sequence(SSS) generated by single map has low complexity and that the initial value is easy to be estimated by inversion, a new map is constructed by the research on the chaotic map based on Logistic-map. This map can be realized easily by digital circuit and has high system complexity. The modified chaotic sequences are compounded by two Logistic maps with two different initial values and more secure for communication. The initial-value sensitivity, self-correlation and power spectral density of the compounded chaotic sequences are analyzed. The results indicate that the new sequences have higher sensitivity to initial conditions, better autocorrelation characters and excellent pseudo randomness. A practical scheme of spreading spectrum is simulated. The simulation results show the effectiveness and reliability of the new-style chaos sequences.
Keywords: chaotic sequence; Logistic map; DSSS; correlation analysis
0 引 言
在傳統的擴頻通信系統中,通常采用PN序列(偽隨機序列)作為擴頻序列。然而,這種擴頻序列具有一定的周期性,所以它的碼數量很有限,抗截獲性也較差?;煦缦到y對初始值有著敏感的依賴性,可以提供數量眾多的、非相關、類隨機而又可再生的信號。因此,混沌序列的研究為選擇擴頻序列開辟了新途徑。近年來,把非線性動態系統的混沌映射用于產生擴頻通信中的擴頻碼,是國內外通信領域研究的熱點[1]。目前,文獻中研究的混沌擴頻通信方案大多基于單一混沌映射進行設計和分析[2-3]。隨著混沌理論的深入研究和廣泛使用,傳統的單一混沌映射產生的序列作為隨機序列的局限性逐漸暴露出來。傳統的混沌序列生成簡單,隨著研究傳統混沌序列的破譯技術逐漸成熟,敵方很可能根據相關信息,得到混沌的結構模型而實現被破譯[4-6]。……