SG Undersea Cable System: Requirements and Performance

Requirements and Performance By S. T. BREWER, R. L. EASTON, H. SOULIER, and S. A. TAYLOR (Manuscript received September 8, 1977) This paper reviews the major parameters of the SG Undersea Cable System. SG transmission goals and signal statistics were established, which led to a specific system and equalization design. As the SG design evolved, information on cable aging led to the introduction of four shore-controlled equalizers in the SG transatlantic link (TAT-6). Performance delivered by the TAT-6 link has been generally satisfactory, though some excess noise was encountered in the top third of the high band. Equalization results permit the link to handle 4200 two-way voice channels, 200 more than the objective. I. INTRODUCTION AND BACKGROUND* 1.1 Traffic growth and forecast Since 1956, when voice communication across the Atlantic by undersea cable began, growth in traffic has continued at a rapid rate.1'2-4,5 The two upper curves of Fig. 1 indicate the growth of (i) total U.S. overseas phone messages and (ii) transatlantic phone messages. Data plotted here include traffic by satellite and radio, as well as by cable. Between 1960 and 1976, annual overseas phone messages have increased from 3.7 to 87.7 million. This represents an exponential growth of 22 percent per year. Transatlantic phone messages to Europe have increased from 1.0 million in 1960 to 29.7 million in 1976. Thus, Atlantic basin growth rate is 24 percent per year. Projecting 1976 traffic at growth rates experienced to date yields an expected 520 million total overseas phone messages in * This paper broadly covers all aspects of the SG system.