(signals in a wider band with low power density (power per frequency), appears as background noise to others than the receiver. Used in CDMA and WLANs.)
- DSSS - direct-sequence spread spectrum - a chipping sequence code (digital modulation) creates a chipping sequence (shorter signals than original bits) that is modulated with a carrier signal (radio modulation). 802.11b, CDMA uses DSSS.
- FHSS - frequency-hopping spectrum - first modulates to narrowband signals, then a second modulation uses a hopping sequence of frequency to send the radio signal. Bluetooth uses FHSS.
- OFDM - orthogonal-frequency-division multiplexing - uses multiple subcarriers in parallel to transmit data. The subcarriers are orthogonal in that they are modulated with their own data independently. It is used in ADSL, 802.11a/g wireleess LANs, and WiMax.
- DSSS and FHSS can be multiplexed by CDM.