| 单词 | GSM (Global System for Mobile Communications née Groupe Spéciale Mobile) |
| 释义 | GSM (Global System for Mobile Communications née Groupe Spéciale Mobile) The pan- European digital cellular radio standard developed by the Groupe Spéciale Mobile (Special Mobile Group) formed in 1982 by the Confederation of European Posts and Telecommunications (CEPT). GSM was adopted by the CEPT in 1987 and was commenced commercial operations in 1991. GSM operates in the 800 MHz and 900 MHz frequency bands and is ISDN-compatible. GSM derives 124 carriers of 200 kHz. Frequency division duplex (FDD) is employed to support bidirectional communications, with the 935–960 MHz band supporting downlink transmission and the 890–915 MHz band supporting uplink transmission.Time division multiple access (TDMA) is employed to derive 8 time slots from each carrier. Gaussian minimum-shift keying (GMSK) modulation yields a signaling rate of 270.833 kbps per carrier and a maximum transmission rate of 33.8 kbps per channel. Regular pulse excitation linear predictive coding (RPELPC) supports voice at 13 kbps and vector sum excited linear predictive (VSELP) coding at 8 kbps. Data throughput generally is limited to 9.6 kbps, due to overhead associated with forward error correction (FEC) and encryption. GSM commonly employs a four-cell reuse plan, rather than the seven-cell plan used in AMPS, and divides each cell into 12 sectors. GSM commonly uses frequency hopping and timeslot hopping, which also is used in CDMA systems. 74570c07.qxd 9/11/07 12:21 PM Page 214 |
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