New Approaches to Primary Reference Source in Telecommunications Networks

• Main Authors: Jiang-Lin Shi, 施江霖
• Other Authors: Chia-Li Ho
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/96830627940380198181

博士 === 國立中央大學 === 電機工程研究所 === 90 === ABSTRACT With the introduction of high-speed networks, today’s telecommunications networks require a more accurate primary reference source (PRS) than conventional ones. A PRS synchronized to the national frequency standard (NFS) based on the technique of global positioning system (GPS) common view, a powerful means for time and frequency transfer, is proposed in chapter 3. According to ITU-T G.811 [2], the frequency accuracy of a PRS should be better than . At this order, the network is allowed to have not greater than one slip in 70 days for any 64 kbit/s channel. To achieve the same slip rate, the accuracy should be less than for a high-speed network such as synchronous digital network (SONET) or synchronous digital hierarchy (SDH). This is not achievable for most existing schemes [3], [4]. The proposed PRS achieves performance comparable to the NFS, which is at present accurate to better than . Our method achieves performance comparable to the NFS, which has frequency accuracy of the order up to , with a lower cost. Performance results indicate that the frequency offset of the PRS is improved to almost without sacrificing the stability. Indicate that a PRS with frequency offset can be improved to . An optical system for time and frequency transfer via optical fibers, presented in chapter 4. The system used a number of unused overhead bytes of the SONET/SDH frame, in transmitting a timing signal. The system completed the loop-back test in temperature-controlled conditions. Experimental results showed that short-term time stability can be achieved at 5 ps, and long-term frequency stability is better than , regardless of whether the loop-back is a 5 meter or 35 km long optical fiber. Moreover, the delay variation in the 35 km loop-back test was less than 1.4 ns. In this dissertation, a PRS synchronized to the NFS with high performance and lower cost, used optical fiber to transmitted high precise time and frequency are proposed. All got good results.