Direct sequence spread spectrum, also known as direct sequence code division multiple access (DS-CDMA), is one of two approaches to spread spectrum modulation for digital signal transmission over the airwaves. In direct sequence spread spectrum, the stream of information to be transmitted is divided into small pieces, each of which is allocated across to a frequency channel across the spectrum.
A type of spread spectrum that spreads its signal continuously over a wide frequency band. DSSS is a transmission technology in which a data signal at the sending station is mapped into a higher data rate bit sequence using a "chipping" code. The chipping code (also known as processing gain) introduces redundancy which allows data recovery if certain bit errors occur during transmission. The FCC rules the minimum processing gain should be 10, typical systems use processing gains of 20.
A modulation technique where a pseudorandom sequence directly phase modulates a (data-modulated) carrier, thereby increasing the bandwidth of the transmission and lowering the spectral power density (i.e. the power level at any given frequency). The resulting RF signal has a noise-like spectrum, and in fact can intentionally be made to look like noise to all but the intended radio receiver. The received signal is despread by correlating it with a local pseudorandom sequence identical to and in synchronization with the sequence used to spread the carrier at the radio transmitter.
A type of spread-spectrum radio transmission that spreads its signal continuously over a wide frequency band.
A modulation scheme that uses a pseudorandom binary sequence to modulate the frequency carrier of a signal. The relative rate between user data and the pseudorandom sequence is typically between 10 and 100 for commercial systems and on the order of 10,000 for military systems.
A WLAN technology that generates a redundant bit pattern for each bit to be transmitted. Frequency Division Multiple Access (FDMA): A digital radio technology that divides the available spectrum into separate radio channels. Generally used in conjunction with Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA).
One of two approaches (with frequency hopping spread spectrum) for sorting out overlapping data signals transmitted via radio waves. Direct sequence spread spectrum is commonly abbreviated to DSSS or DS. 802.11b uses direct sequence spread spectrum.
DSSS is one of two types of spread spectrum radio, the other being frequency hopping spread spectrum (FHSS). DSSS is a transmission technology used in WLAN transmissions where a data signal at the sending station is combined with a higher data rate bit sequence, or chipping code, that divides the user data according to a spreading ratio. The chipping code is a redundant bit pattern for each bit that is transmitted, which increases the signal's resistance to interference. If one or more bits in the pattern are damaged during transmission, the original data can be recovered due to the redundancy of the transmission.
A spread spectrum technique which involves “imprinting” a special digital code onto the RF carrier so that only the intended receiver can decipher it.