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本文提出一种改进现有增量调制或脉码调制的帧同步系统性能的新方法。帧同步码采用1010交替码。它用一种新型的帧码提取器从输入信码中检测同步信道,帧码提取器由两个容量为1帧的 PMOS 移存器和少量 TTL 集成电路组成。它可同时依次检测一帧中的所有码位,并记录每个码位的码型与本地帧码码型一致的次数,同时删除不适合作帧同步码的码位。当发现第1个码位不适合作帧码之后,其余不适合作帧码的码位能很快移位过去而不需重新计数,直至同步建立。采用此项技术使系统的捕捉性能大为改善。例如在1帧中有512个码位的系统中,建立帧同步大约需要十帧的时间;即在信码速率为115.2Kb/s,帧码速率为225b/s 的系统中,帧同步建立时间大约为50毫秒。而 CCITT 建议115.2Kb/s 的增量调制;帧码速率为2.4Kb/s;1.544Kb/s 的脉码调制,帧码速率为8Kb/s。本方案可以将增量调制的帧码速率降低至原来的1/10,并可改善同步性能,脉码调制的系统也可作相应的改善。本同步系统能够在帧码发生误码的情况下提取帧码井建立同步,本方案克服了现有方案帧码速率高建立时间长的缺点并且可以方便地纳入现有帧同步系统。本文介绍该同步系统的工作原理,帧码提取器的电路组成以及初步试验结果。
In this paper, we propose a new method to improve the performance of the frame synchronization system of existing delta-modulation or pulse-code modulation. Frame synchronization code using 1010 alternating code. It uses a new type of frame code extractor to detect synchronization channels from incoming code, which consists of two PMOS shifters with a capacity of one frame and a small number of TTL integrated circuits. It can detect all the code bits in a frame at the same time and record the number of patterns of each code bit consistent with the local frame code pattern and delete the code bits unsuitable for the frame synchronization code at the same time. When it is found that the first code bit is not suitable for frame coding, the rest of the code bits unsuitable for frame coding can be quickly shifted without recounting until synchronization is established. The use of this technology greatly improves the system’s capture performance. For example, in a system with 512 code bits in one frame, it takes approximately ten frames to establish frame synchronization. That is, in a system with a code rate of 115.2 Kb / s and a frame rate of 225 b / s, a frame synchronization establishment time About 50 milliseconds. The CCITT recommends 115.2Kb / s delta modulation; frame rate 2.4Kb / s; pulse code modulation 1.544Kb / s, frame rate 8Kb / s. The scheme can reduce the frame rate of incremental modulation to the original 1/10 and improve the synchronization performance. The pulse code modulation system can also be improved correspondingly. The present synchronization system can extract the frame code and set up the frame synchronization when the frame error occurs, and overcomes the shortcomings of the existing scheme that the frame rate is high and can be easily incorporated into the existing frame synchronization system. This article describes the working principle of the synchronization system, the frame of the code extractor circuit and preliminary test results.