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1977年,库柏(Cooper)和尼特利顿(Nettleton)提出了一个使用跳频多路、哈德马(Hadamard)纠错编码和差分移相键控调制(DPSK)的扩频移动无线电系统,并声称这个系统在频谱利用率方面比频分调频(FD—FM)系统要高。经后来分析证明,与信道间隔为80kHz的FD—FM系统比较起来,DPSK系统的频谱利用率可提高百分之八点四。古德曼(Goodman)等人在1980年提出了利用多电平移频键控(MFSK)调制方案,使效率提高了百分之三十。本文总结了扩频移动无线电的研究成果,并论述了商用系统投入使用之前某些有待进一步探讨的问题。
In 1977, Cooper and Nettleton proposed a spread spectrum mobile radio system that uses frequency hopping multiplexed, Hadamard error correction coding, and differential phase shift keying modulation (DPSK) , Claiming that the system is more spectrum efficient than a frequency-division-modulation (FD-FM) system. Later analysis shows that the spectral efficiency of DPSK system can be increased by 8.4% compared with that of FD-FM with channel spacing of 80kHz. In 1980, Goodman et al. Proposed the use of multi-level shift keying (MFSK) modulation scheme to increase the efficiency by 30%. This article summarizes the research results of spread spectrum mobile radios and discusses some issues to be further explored before commercial systems are put into use.