{'fraction_non_alphanumeric': 0.025238362310712283, 'fraction_numerical': 0.01430173864273696, 'mean_word_length': 4.8861386138613865, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Mutual Interference Between Adjacent Analog Scwbled Signal And 64 Qam Signal In Caw System

On mutual interference between an analog sync. pulse compressed (scrambled) signal and an adjacent 64 QAM signal, experimental results, their cause, and guide of designing equipment6 was described. INTRODUCTION Specifications of digital CATV system have been standardized as ITU (International Telecommunication Union)-Telecommunication Standardization Sector 5.83, and practical digital CATV services have been launching. Newly constructed systems may have enough frequency band to have separated bands for digital channels and conventional analog channels. Since existing facilities, however, have some difficulties to extend their frequency band, increase of channels by the digital CATV signals is desired, and in this case, digital signal channels are possibly allocated between existing analog signal channels. (Fig. 1) For this allocation, mutual interference should be considered carefully. We described experiments on the mutual interferences between especially an analog sync. pulse compressed (scrambled) signal and a 64 QAM (Quadrature Amplitude Modulation) signal, and cause of the interferences. ANALOG SCRAMBLE SYSTEM In analog CATV systems, exclusive or restricted programs are handled by scrambling signals so that neither the sound nor video can be recovered unless subscribers are equipped with a descrambler. Although there are several scrambling ways, sync. pulse compression is generally used because of its balance of complexity and effect. 64 QAM RECEIVER As a digital CATV signal, a ITU-T 5.83 Annex C type 64QAM signal was used. Basic performance of a 64QAM receiver, such as C/N vs BER (Bit Error Rate) and single carrier interference at BER=104 were shown in Fig. 2 and Fig. 3. Degradation of C/N from the theoretical curve was about 1.5 dB at C/N=26 dB in Fig. 2. Allowable D/U is 25 dB in band, and -30 dB out of band. EXPERIMENTAL RESULTS OF MUTUAL INTERFERENCE For interference from the analog scrambled signal to the 64QAM signal, BER was measured as shown in Fig. 4. In case that a lower adjacent analog signal level was, more than 5dB, larger than the 64QAM signal level, an upper adjacent 64QAM signal was degraded in BER by a key signal which is multiplexed with a sound carrier of the analog signal. Leakage of frequency spectrum to the adjacent channel by the modulation of the key signal was shown in Fig. 5. CAUSE OF INTERFERENCE For interference from the 64QAM signal to the analog scrambled signal, degradation of S/N of signal and two types of synchronization error of video signal were observed as table 1. One of the synchronization error was caused when regenerated key signal increased jitter by leakage from the upper adjacent 64QAM signal and then decompression point became wrong. (Fig.6) The other was caused when a non-scrambled signal was received by a home terminal which was set to receive a scrambled signal at the channel. Inserting short-period nonscrambled signal into a scrambled channel is often used for advertisement and etc.. In this case, if a home terminal continue to seek the key signal, misregeneration of the key signal may occur by increase of leakage from the adjacent 64QAM signal. CONCLUSIONS Out-band rejection of a digital set-top-box should be carefully designed taking account of adjacent analog scrambled signal. On the other hand, CATV operators should control or adjust both signal level properly. These results are utilized for recommendation of introducing the digital CATV signal in Japan.