應用時空碼於無線干擾通道之研究

Space-Time Coding for Wireless Jamming Channels

陳尚輝(Shang-Hui Chen)

指導教授 ： 王忠炫

中原大學/工學院/電子工程研究所/碩士(2003年)

https://doi.org/10.6840/cycu200300761

摘要

在無線傳輸的環境中，由於通道衰減的效應以及其他信號有意或無意的干擾，使得在接收端所收到的信號產生嚴重的失真。由於時空碼(space-time codes)具有分集增益(diversity gain)和編碼增益(coding gain)可以有效的降低通道衰減的效應；而展頻系統中跳頻(frequency-hopped)的技術能避免那些有意或無意的干擾以及防止他人竊聽的優點。為了解決此問題，若資料傳送於平坦衰減通道(flat fading channels)的環境並受到部分頻帶雜訊干擾(partial-band noise jamming)及由接收機所產生的熱雜訊干擾時，藉由使用時空碼及跳頻/M-陣列頻率鍵移(FH/MFSK)的技術來保護所傳送的資料，提高系統的效能。因此，在本論文裡我們提出了一個具有空間、時間及頻率維度的系統並探討其效能。
在接收端的解碼上，我們提出了此系統的最大可能性解碼(maximum likelihood decoding)在路徑增益(path gain)已知的情況下，並利用維特比演算法(Viterbi algorithm)進行解碼。不過，對接收機而言，路徑增益往往不易獲得，因此，我們也提出了在路徑增益未知的情況下的最大可能性解碼；並考慮了在干擾狀態(jamming state)已知及未知的情況下的最大可能性解碼。然而，基於複雜度和實現難易程度的考量，在路徑增益已知的情況下我們提出了最小歐幾里德距離(minimum Euclidean distance)及改良式解碼(modified decoding)等幾個複雜度較低的次最佳解碼方式；當接收機無法準確的獲得路徑增益時，提出了封值偵測(envelope detecting)解碼和簡化式解碼(simplified decoding)等幾個較簡單的次最佳解碼方式，並模擬其在多重傳送及接收天線架構下的效能，經由模擬結果證明出我們的系統確實能提高系統的效能，而且所提出的次最佳解碼方式不管在信號雜訊比(signal-to-noise ratio)較高或較低時其效能也不會太差，並且還比較了時空籬柵碼和迴旋碼在一些情況下的效能。此外，我們還推導出時空籬柵碼在路徑增益未知的情況下的最大可能性解碼並將其模擬的結果和差分時空碼作比較。

關鍵字

部分頻帶雜訊干擾 ； 衰減通道 ； 時空碼 ； 跳頻/M-陣列頻率鍵移

並列摘要

In wireless communication environments, the reliability of received signals degrade seriously at the receiver because of the effects of fading channels and intentional or accidental jamming from other signals. Space-time codes can provide good performance in fading channels, and FH/MFSK (frequency-hopped/M-ary frequency shift keying) technologies can effectively avoid the partial-band noise jamming. Therefore, in this thesis, we combine space-time codes with FH/MFSK technologies and investigate the corresponding performance in wireless jamming environments.
On decoding, we provide the the maximum likelihood decoding when the path gains are known or unknown at the receiver. We also consider the maximum likelihood decoding for the cases that the jamming state is available and unavailable at the receiver. However, considering about its complexity and feasibility, we present several sub-optmal decoding methods with low complexity such as the minimum Euclidean distance decoding and the modified decoding when the path gains are known. When the the path gains are not available, we propose the envelope detecting and the simplified decoding which are simple and sub-optimal decoding schemes. Verified by the simulation results, the system can provide excellent performance, and the proposed sub-optimal decoding methods can provide near optimum performance at both of low and high signal-to-noise ratios.

並列關鍵字

space-time codes ； frequency-hop/M-ary frequency-shift keying ； fading channel ； partial-band noise jamming

參考文獻

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