應用於無線干擾環境與多波單音干擾下結合時空編碼技術及跳頻展頻系統之研究

Abstract

在無線傳輸的環境中，傳輸的信號常遭受到惡意的干擾源及通道衰減效應，導致接收訊號產生嚴重的失真。跳頻展頻系統是一般最常用來抑制干擾效應的技術，而具有分集增益及編碼增益的時空編碼技術可有效的降低通道衰減效應。因此，在本篇論文裡吾人便結合了兩者之優點，提出了時空編碼結合跳頻展頻技術以提升傳輸系統在無線干擾環境中之整體效能。 為了能夠專注於分析時空碼的解碼設計，吾人考慮了兩種較簡單的跳頻方式。第一種定義為所有傳送天線的訊號都跳至相同的頻帶上，稱此為最差跳頻。第二種情形為所有傳送信號皆設計為避免互相發生碰撞，稱此為最佳跳頻。其中最差及最佳跳頻方式分別代表為此系統效能分析的上界與下界。針對上述跳頻方式，吾人推導出在路徑增益已知或未知情況下此系統的最大可能性解碼。吾人亦針對兩種不同的跳頻系統推導出建立適合的空時編碼的準則。此外，吾人亦針對 此系統提出了在無線干擾環境下好的時空碼準則。最後經由模擬結果驗證出，在相同的訊雜比及頻寬效益的考量之下，此系統比傳統單進單出編碼效能來的更佳。

In wireless jamming environments, the transmitted signals usually su?er from hostilejammers and undesired channel impairments, e.g., multipath fading. Conventionally, frequency-hopping spread spectrum (FHSS) systems are most effective anti-jamming techniques, and space-time coding (STC), which introduces temporal and spatial correlation into the transmitted signals to achieve transmitter diversity without sacri?cing the bandwidth, has been shown to provide excellent performance against multipath fading. Therefore, in this thesis, we combine STC with the FHSS to construct a powerful high-rate transmission scheme for wireless jamming channels. Two cases of FH are considered here to simplify the design of STC. One is the worstcase frequency hopping which hops the symbols from all transmitter antennas into the same frequency band, and the other is the perfect frequency hopping which avoids any possible collision of the transmitted symbols. The actual performance of the combined STC/FHSS system with arbitrary hopping patterns can then be upper and lower bounded by the evaluated performance of the worst case and perfect case, respectively. The maximum likelihood decoding of space-time codes is derived with respect to di?erent reception conditions, and the design criteria for constructing good space-time codes with respect to two kinds of FH are also derived. Veri?ed by the simulation results, the proposed system can provide better performance than the conventional schemes in terms of both bandwidth e?ciency and signal-to-noise ratio.