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本文介绍了一种用于一点多址TDMA系统中的高速OQPSK全数字突发MO-DEM的实现。该MODEM采用逆调制载波恢复方案,能同时实现载波的快速恢复和极低的载波跳周率性能。为了实现这些性能,该MODEM采用CCCS(ConcurrentCarrierandClockSynchronization)技术,使得载波和时钟恢复能同时进行,加快捕获和同步时间;同时,采用一种新的报头信息来加快同步速率和消除相位模糊;此外,其数字式载波滤波电路也具有一定的独特性,既能有效的滤除噪声又能减小滤波电路所引人的群时延。计算机模拟结果显示该MODEM在输入中频频差高达17kHz,Eb/No=8dB时,其同步时间不到60个符号,其误比特率接近理论值。这些性能使得该MODEM既有良好的性能又易于实现,很适于一点多址TDMA系统。
This paper presents an implementation of a high-speed OQPSK all-digital burst MO-DEM for a one-point multiple access TDMA system. The MODEM adopts an inverse modulation carrier recovery scheme, which can simultaneously achieve carrier fast recovery and very low carrier hop rate performance. In order to achieve these performances, the MODEM uses the CCCS (ConcurrentCarrierandClockSynchronization) technology so that carrier and clock recovery can be performed at the same time to speed up the capture and synchronization time; at the same time, a new type of header information is used to speed up the synchronization rate and eliminate phase ambiguity. In addition, Digital carrier filter circuit also has a certain unique, both effective noise reduction filter circuit can also reduce the introduction of group delay. Computer simulation results show that the MODEM input IF frequency difference up to 17kHz, Eb / No = 8dB, the synchronization time less than 60 symbols, the bit error rate close to the theoretical value. These properties make the MODEM both good performance and easy to implement, it is suitable for TDMA TDMA system.