| 单词 | PCS |
| 释义 | PCS 1. Personal Communications Services. Originating in the United Kingdom, where it is known as PCN (Personal Communications Network), PCS is a service concept for a full range of wireless services accessible through a single device and utilizing one telephone number that will work anywhere and anytime, for life. While the service is technology-dependent and the spectrum allocation varies by country or region, the designated U.S. band designations and frequency allocations are as follows: • Narrowband PCS spectrum is allocated in the 900–901 MHz, 930–931 MHz, and 940–941 MHz bands.This spectrum is intended to extend the capabilities of pagers and cell phones to include acknowledgment paging, two-way messaging, and digital voice. • Broadband PCS spectrum is allocated 120 MHz in the 1.85–1.91 GHz and 1.93–1.99 GHz bands. This spectrum is intended for the delivery of high-tier wireless communications, including wireless local loop (WLL), voice and data services, and cellular-like services for pedestrian traffic in high-density areas. • Unlicensed PCS spectrum is allocated in two bands, with 20 MHz in the 1.91–1.93 GHz range, and 10 MHz in the 2.39–2.40 GHz range.This spectrum serves low-tier applications such as wireless LANs (WLANs) and wireless office telecommunications systems (WOTS). As the spectrum assignments will vary by country, the terminal devices must be multimode, i.e., multi-band, and even cognitive in nature. See also band, broadband, cognitive radio, frequency, high-tier, low-tier, narrowband, spectrum, WLAN, WLL, and WOTS. 2. Personal Communications Services. A cordless telephony service in the United States, based on Wireless Access Communication System (WACS), which subsequently was modified to an industry standard known as Personal Access Communications Services (PACS). PCS derives 32 carriers with spacing of 300 kHz in the 1850–1910 MHz and 1930–1990 bands, and employs frequency division duplex (FDD) to pair 16 downstream and 16 upstream carriers.Within each frequency channel, PCS derives eight time division multiple access (TDMA) channels employing /4 Quadrature Phase Shift Keying (/4 QPSK).Voice encoding is adaptive differential pulse code modulation (ADPCM) at 32 kbps, and the theoretical data rate is 384 kbps per channel. PCS has never gained any traction due largely to the high availability and low cost of cellular telephony. See also ADPCM, carrier, cellular, cordless telephone, downstream, encode, FDD, /4 QPSK, TDMA, and upstream. 3. Personal Communications System. A U.S. term for digital cellular radio systems based on EIA/TIA IS-95a, and also known as cdmaOne and CDMA Digital Cellular. PCS is a 2G upgrade to the analog Advanced Mobile Phone System (AMPS), and the two systems can coexist.The implementation of PCS requires that one or more AMPS frequency bands of 1.25 MHz be converted and subdivided into 20 carriers, each of which supports as many as 798 channels and aggregate bandwidth of up to 1.288 Mbps. The specified signal modulation methods are binary phase shift keying (BPSK) and offset quadrature phase shift keying (OQPSK). Bidirectional communication is supported via frequency division duplex (FDD), with the downlink operating in the 869–894 band and the uplink in the 824–849 band.The variable-rate speech encoding algorithms run at maximum rates of 8 kbps using code excited linear prediction (CELP) or 13 kbps using enhanced variable rate vocoder (EVRC), and varies the rate downward to as low as one-eighth rate if the level of speech activity 74570c16.qxd 9/11/07 12:27 PM Page 369 |
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