一種符號內跳頻/多頻移鍵解調方法的抗干擾能力之分析

Abstract

如果接收機的解調方式作適當的設計﹐符號內跳頻 (或所謂快速跳頻) /多頻移鍵展頻調變﹐是一種有效的電子反反制 (electronic counter- counter-measures,ECCM)方法。 本篇論文就一種簡單且穩定的接收機﹐ 即限幅多向度結合器 (clipped diversity combiner)﹐對其在多波道單 音干擾 (multitone jamming) 下的系統性能﹐予以詳盡的分析。本文所 考慮的干擾方式包括帶頻式多波道單音干擾 (band multitone jamming) 及獨立式多波道單音干擾 (independent multitone jamming) 。我們同 時討論相關的設計問題及參數﹐諸如限幅器的量化位階 (quantization level)、門檻值 (threshold) 的設定﹐熱雜訊 (thermal noise) 的效 應和附加訊息 ( side information) 的利用等。如果給予適當的系統參 數﹐我們發現整個接收機的抗干擾能力有明顯的改善。固定位元率 (bit rate) 及更實際被採用的(hopping rate)﹐是我們所考慮的兩種模式。如 後者被應用時﹐則沒有所謂最佳向度 (optimum diversity) 存在﹐相較 於傳統的單位位元能量 (energy per bit) ﹐達到一定錯誤率所需要的單 位頻率能量 (energy per hop)﹐應是一種較佳的系統性能量度方式。 Intrasymbol frequency-hopped or fast frequency-hopped (FH) M- ary frequency shifted keyed (MFSK) spread spectrum modulation is an effective electronic counter-counter-measures (ECCM) if the demodulation algorithm is properly designed. Many demodulation algorithms for this class of signals have been proposed and analyzed. This thesis concentrates on the jamming immunity analysis of a simple and robust receiver---the clipped diversity combiner---for intrasymbol FH signals against multitone jamming. We present exact analysis and investigate related design issues and parameters such as quantization level, clipper threshold, the effect of thermal noise, and the use of side information. We demonstrate how significant improvement can be obtained with an appropriate system design. The jamming schemes under consideration include band multitone jamming and independent jamming. We examine the constant bit rate as well as the more practical constant hopping rate operating scenarios. When the latter option is considered, there is no optimum diversity and the required energy per hop to achieve a predetermined bit error rate is a better performance measure than the conventional energy per bit used in a fixed bit rate operation condition.