| 单词 | LMDS (Local Multipoint Distribution Service) |
| 释义 | LMDS (Local Multipoint Distribution Service) A wireless local loop (WLL) technology developed by Bernard B. Broussard for wireless cable television (TV), referring to premium wireless subscription TV rather than traditional free broadcast TV or cable TV. Broussard, with Shant and Vahak Hovnanian, formed a firm that provided 49 TV channels in New York City, and later added high speed Internet access. The technical rights to LMDS technology later were spun off into a separate company, and the U.S. Federal Communications Commission (FCC) auctioned the first LMDS radio licenses in early 1998.The A Block has a width of 1.15 GHz in the frequency bands of 27.5–28.35 GHz, 29.1–29.25 GHz, and 31.0–31.15 GHz.The B Block has a width of 150 MHz in the spectrum between 31.15 GHz and 31.3 GHz. Outside of North America, LMDS operates in the 20 GHz and 45 GHz bands. LMDS requires line of sight (LOS), has a maximum cell diameter of 10–15 miles, and compensates for rain fade through the use of adaptive power controls. LMDS can carve a 360° cell into four quadrants of alternating antenna polarity, and supports both point-to-point and point-to-multipoint service configurations. LMDS is flexible enough to support local loops ranging from 1.544 Mbps (T1) to 622 Mbps, and in either symmetric or asymmetric configurations. Multiplexing access methods include frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). TDMA modulation options include phase modulation (BPSK, DQPSK, QPSK, and 8PSK) and amplitude modulation (QAM, 16-QAM, and 64-QAM). LMDS is considered obsolete in the United States, having been replaced by the IEEE 802.16 standards, commonly known as WiMAX. See also 8-PSK, 802.16, asymmetric, antenna, BPSK, CDMA, DQPSK, FCC, FDMA, frequency band, LOS, phase modulation, point-to-multipoint circuit, point-to-point circuit, polarity, QPSK, rain fade, spectrum, symmetric, TDMA, WiMAX, and WLL. |
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