干擾環境下應用方塊渦輪碼於跳頻系統之研究

由於跳頻(frequency-hopped) 技術具有抗干擾、多重進接等特性，已經廣泛地被應用於無線通訊系統中，尤其是在軍事用途上。大致來說，跳頻系統可分為兩種：一種稱為快跳頻(fast frequency-hopped, FFH) 系統，而另一種則是慢跳頻(slow frequency-hopped, SFH) 系統；由於快跳頻系統可以利用分集組合接收器(diversity combining receiver) 進行接收訊號的檢測，若使用適當的分集組合規則，則可以有相當好的抗干擾(antijam, AJ) 性能。然而選擇慢跳頻系統時，系統為了達到符合規格的抗干擾能力，通常需要額外的機制來強化它，常用的一種方式就是利用正向錯誤更正碼(forward error-correction coding, FEC)。在本論文裡，我們考慮將方塊渦輪碼(block turbo codes, BTCs) 應用於慢跳頻系統中。其編碼的方式是根據建構乘積碼(product codes) 的觀念來而的，一次選用兩組方塊碼(block codes) 來當做它的組成碼(component codes)。由於它具有相當於迴旋渦輪碼(convulotional turbo codes, CTCs) 的高解碼能力，但卻有較低的解碼複雜度，對於系統設計者來說，它是個不錯的選擇。在我們的系統設計中，除了使用方塊渦輪編碼將資料編碼外，還利用了慢跳頻/二位元頻率鍵移(binary frequency-shift keying, BFSK) 作為調變方式。其中我們選用了兩組相同的BCH (Bose–Chaudhuri–Hocquenghem) 碼來當作方塊渦輪碼的組成碼，並且考慮了兩種干擾的環境(jamming environments)：部分頻帶雜訊干擾(partial-band noise jammer, PBNJ) 以及帶頻多波道單音干擾(band multitone jammer, BMTJ)。在接收端的解碼方式，我們利用Chase 演算法來做軟式解調，找出最大可能性(maximum likelihood, ML) 的碼字(codeword)，並搭配遞迴式(iterative) 的軟式輸入/輸出(soft-input/soft-output, SISO) 解碼過程來解BCH–方塊渦輪碼。其中如何從接收訊號取得解碼之軟式輸出(soft output)是本論文主要解決的問題；干擾存在與否的估測及信號可靠度評估也都於本論文中討論。另一方面，軟式解碼通常需要連帶的估計一些信號及通道參數，我們也提出了一個參數估計的演算法及流程來維持解碼的可行性。

關鍵字

Chase 演算法；方塊渦輪碼；遞迴式解碼；跳頻；軟式輸入/輸出解碼器

並列摘要

Owing to the advantages of anti-jam and multiple access, frequencyhopping technique has been widely used in wireless communication systems, especially, in military communication system. In general, there are two classes of frequency-hopped systems. One is the fast frequency-hopped (FFH) system, and the other is the slow frequency-hopped (SFH) system. FFH systems provide better anti-jam (AJ) capability by diversity combining receiver. On the other hand, to acquire a satisfactory AJ capability, SFH systems usually add an extra mechanism of protection such as the forward error-correction coding (FEC). To attain the near optimum performance, a more powerful coding scheme is demanded. Block turbo codes (BTCs) are powerful codes which are based on the conception of product codes. Besides, BTCs give the same performance against convulotional turbo codes (CTCs) with lower decoding complexity. Therefore, BTC is an attractive alternative to CTC. In this thesis, we consider the application of Bose–Chaudhuri–Hocquenghem (BCH)–BTC on an SHF/binary frequency-shift keying (BFSK) system under jamming environments. Two types of jammers, partial-band noise jammer (PBNJ) and band multitone jammer (BMTJ), are discussed. Applying Chase algorithm, soft-decision decoding for a maximum-likelihood (ML) codeword is accomplished, and by using the soft-input/soft-output (SISO) decoder with an iterative way, the optimum performance for BCH–BTC is reached. The major issue presented in our thesis is how to obtain the soft outputs in the decoding process. We also propose a modified detection rule to determine whether the hop is jammed or not and the optimum decoding metric for each received symbols. Finally, we provide a realistic estimation method for signal and channel parameters to support the SISO decoder in the decoding scheme.

並列關鍵字

Chase algorithm ； block turbo code ； frequency hopping ； iterative decodign ； soft-input soft output decoder

參考文獻

[15] William H. Press, Saul A. Teukolsky, William T. Vetterling, Brian P. Flannery, Numerical recipes in C, Cambridge university press, 2nd ed., 2002.

[2] M. B. Pursley and W. E. Stark, ”Performance of Reed-Solomon coded frequency-hop spread-spectrum communications in partial- band interference,” IEEE Trans. Commun., vol. COM-33, pp. 767-774, Aug. 1985.

[3] C. D. Frank and M. B. Pursley, " Concatenated coding for frequencyhop spread-spectrum with partial-band interference,” IEEE Trans. Commun., vol. 44, pp. 377-387, Mar. 1996.

[4] J. H. Kang and W. E. Stark, ”Turbo codes for noncoherent FH-SS with partial-band interference,” IEEE Trans. Commun., vol. 46, pp. 1451- 1458, Nov. 1998.

[5] C. Berrou, A. Glavieux, and P. Thitimajshima, ”Near Shannon limit error-correcting coding and decoding: Turbo-codes (1),” in IEEE Int. Conf. Communications ICC’93, vol.2/3, pp.1064-1071, May 1993.

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干擾環境下應用方塊渦輪碼於跳頻系統之研究

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