隨著高頻（High Frequency， HF）通訊系統於軍事通信、遠距離通信及緊急 通訊等領域之應用日益廣泛，如何在有限頻寬與複雜通道環境下維持穩定可靠 之資料傳輸能力，已成為重要研究課題。由於 HF 通道受多徑傳播、頻率選擇 性衰落及加性白高斯雜訊（Additive White Gaussian Noise， AWGN）等因素影 響，容易造成訊號失真與位元錯誤，進而降低通訊系統之整體效能。 本研究以高頻通信資料調複機（Modem/Demodulator）為研究對象，針對 不同資料速率之基頻訊號處理方法進行分析與效能評估。研究內容建立 75 bps、150 bps 與 300 bps 三種資料傳輸架構，系統採用Convolutional Code、 Walsh Mapping、重複映射（Repetition Mapping）以及 Viterbi 解碼等技術，以 提升資料傳輸之可靠度。 為評估各資料速率模式之效能，本研究於 AWGN 通道環境下進行模擬分 析，透過位元錯誤率（Bit Error Rate， BER）與訊號雜訊比（Signal-to-Noise Ratio， SNR）關係曲線比較不同系統架構之傳輸性能。模擬結果顯示，75 bps 模式因採用較高展頻增益與較多取樣點進行累積，在相同 BER 條件下具有最 佳抗雜訊能力；150 bps 模式次之；300 bps 模式則因每位元對應之傳輸符元數 較少，需較高之 SNR 才能達到相同錯誤率表現。 研究結果驗證不同資料處理架構對 HF 通信系統效能具有顯著影響，並說 明低資料速率系統在惡劣通道環境下可提供較佳之通訊可靠度。本研究成果可 作為高頻通信資料調複機設計與效能優化之參考依據。;With the increasing application of High Frequency (HF) communication systems in military communications， long-distance communications， and emergency communications， maintaining stable and reliable data transmission under limited bandwidth and complex channel conditions has become an important research topic. However， HF channels are affected by multipath propagation， frequency-selective fading， and Additive White Gaussian Noise (AWGN)， which can easily result in signal distortion and bit errors， thereby degrading the overall performance of communication systems. This study focuses on the performance evaluation of a HF modem/demodulator by analyzing the baseband signal processing methods under different data rate configurations. Three transmission modes， namely 75 bps， 150 bps， and 300 bps， are established and evaluated. The proposed system employs Convolutional Coding， Walsh Mapping， Repetition Mapping， and Viterbi Decoding. These techniques are incorporated into the transmission framework to enhance the reliability of data transmission. To evaluate the performance of different data rate modes， simulations are conducted over an Additive White Gaussian Noise (AWGN) channel. The transmission performance of each system is compared using Bit Error Rate (BER) versus Signal-to-Noise Ratio (SNR) curves. The simulation results show that the 75 bps mode achieves the best noise immunity because of its higher spreading gain and the accumulation of more received samples. The 150 bps mode provides intermediate performance， whereas the 300 bps mode requires a higher SNR to achieve the same BER performance due to the smaller number of transmitted symbols corresponding to each information bit. The results demonstrate that different baseband signal processing architectures significantly affect the performance of HF communication systems. Lower data rate transmission modes provide better communication reliability under severe channel conditions. The findings of this study provide a valuable reference for the design and performance optimization of HF modem/demodulator systems.
