摘要 : Significant and ongoing developments during 1989 are summarized. Satellites are moving into an era of multiple beams and high-gain spot beams, supplementing global communications coverage and permitting the use of very small anten... 展开 Significant and ongoing developments during 1989 are summarized. Satellites are moving into an era of multiple beams and high-gain spot beams, supplementing global communications coverage and permitting the use of very small antennas. Commercial ISDN services have begun. Cellular radio systems around the world are testing digital systems to replace their analog FM equipment. Cordless telephones are moving outside the home and may merge with cellular systems, enabling users to carry their phones with them. In the US, the seven Bell regional operating companies, created when AT&T Co. was dismantled six years ago, are still fighting to be freed from court-mandated restrictions against entering long-distance, manufacturing, or information services markets. 收起