| 单词 | cellular radio |
| 释义 | cellular radio A radio system that positions numerous, low-power transmit/receive antennas through- out a metropolitan area, thereby dividing a large area of coverage, or macrocell, into smaller microcells, or even smaller picocells. Allocated spectrum is divided into a number of bands and further subdivided into a number of voice grade channels.The bands are distributed among the cells and each frequency band can be reused in nonadjacent cells. The basic concept of cellular radio dates to 1947, when numerous, low-power transmit/receive antennas were scattered throughout a metropolitan area to increase the effective subscriber capacity of specialized mobile radio (SMR) systems. The first prototype cellular radio system was developed by AT&T and Bell Labs in 1977. The first commercial cellular system was activated in Tokyo, Japan by Nippon Telephone and Telegraph (NTT) in 1979.The first commercial system in the United States was activated in Chicago in 1983. The coverage area of each individual cell overlaps those of neighboring cells, with the cell diameter generally a minimum of about one mile and a maximum of about five miles, sensitive to factors such as topography and traffic density. Approximately in the center of each cell is a fixed antenna known as a base station (BS) that establishes and maintains connections with mobile stations (MSs). As a mobile station moves out of the effective range of one cell, the call switches from one base station to another through a process known as handoff, in order to maintain connectivity at acceptable signal strength. The handoff is controlled through a mobile telephone switching office (MTSO), which is the functional equivalent of a central office in the public switched telephone network (PSTN).The MTSOs generally are interconnected and also provide connections to the PSTN. Cellular radio initially was analog in nature, although contemporary systems are largely digital.Analog standards include Advanced Mobile Phone System (AMPS), Narrowband AMPS (N-AMPS),Total Access Communications System (TACS), and Nordic Mobile Telephone (NMT). Digital standards include Digital AMPS (D-AMPS), Global System for Global Communications (GSM), Personal Communications System (PCS), and Personal Digital Cellular (PDC). See also AMPS, analog, antenna, band, BS, channel, D-AMPS, digital, GSM, handoff, macrocell, microcell, MS, MTSO, N-AMPS, NMT, PCS, PDC, picocell, PSTN, SMR, TACS, and voice grade. |
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