| 单词 | DSSS (Direct Sequence Spread Spectrum) |
| 释义 | DSSS (Direct Sequence Spread Spectrum) A radio transmission technique that spreads a narrow- band signal across a wider carrier frequency band. Each transmission is assigned a 10-bit pseudorandom binary code sequence, which comprises a series of ones and zeros in a seemingly random pattern known to both the transmitter and receiver.The original code sequence is mathematically self-correlated to yield a code that stands out from all others, at least on average. The paired transmitters and receivers recognize their assigned and correlated code sequences, which look to all others as pseudonoise (PN). DSSS phase-modulates the carrier wave with a continuous string of PN code symbols, or chips, each of which has a much shorter duration than a data bit. So, the chip rate is much faster than the bit rate.Thereby, the noise signal occurs with much greater frequency than the original data signal and spreads the signal energy over a much wider band. DSSS is used in the 802.11b (Wi-Fi) and 802.11g specifications for wireless local area networks (WLANs). See also 802.11b, 802.11g, band, carrier, FHSS, frequency, narrowband, SS, symbol, wideband, Wi-Fi, and WLAN. 74570c04.qxd 9/11/07 12:19 PM Page 148 |
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