| 单词 | undocumented feature |
| 释义 | undocumented feature for Mobile Communications (GSM). UMTS is based on code division multiple access (CDMA) and operates over a carrier 5 MHz wide, compared to the 200 kHz carrier used for narrowband CDMA. UMTS specifications provide for both time division duplex (TDD) and frequency division duplex (FDD) modes of operation, with TDD largely used in Europe and FDD in the United States.The FDD specifications call for the downlink to run in the 2110–2200 MHz range and the uplink in the 1885–2025 MHz range. As is the case with all true 3G systems, UMTS specifications include 128 kbps for high-mobility applications, 384 kbps for pedestrian speed applications, and 2 Mbps (1.920 Mbps) for fixed in-building applications. In reality, UMTS currently caps the transmission rate at a theoretical 384 kbps. UMTS was first deployed in Japan (2000), where it is known as Freedom of Mobile Multimedia Access (FOMA). High Speed Downlink Packet Access (HSDPA), sometimes characterized as a 3.5G technology, is an upgrade to UMTS that increases theoretical downlink data rates to 14.4 Mbps. High Speed Uplink Packet Access (HSUPA), which remains in development, is expected to increase uplink speeds to a maximum of 5.76 Mbps. UMTS standards are published by the 3rd Generation Partnership Project (3GPP). See also 3G, 3GPP, carrier, CDMA, cellular radio, digital, downlink, FDD, GSM, HSDPA, HSUPA, narrowband, TDD, uplink, and wideband. |
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