| Passband modulation |
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| Analog modulation |
| Digital modulation |
| Hierarchical modulation |
| Spread spectrum |
| See also |
| Multiplexing |
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| Analog modulation |
| Related topics |
In telecommunications, direct-sequence spread spectrum (DSSS) is a spread-spectrum modulation technique primarily used to reduce overall signal interference. The direct-sequence modulation makes the transmitted signal wider in bandwidth than the information bandwidth. After the despreading or removal of the direct-sequence modulation in the receiver, the information bandwidth is restored, while the unintentional and intentional interference is substantially reduced.[1]
Swiss inventor, Gustav Guanella proposed a "means for and method of secret signals".[2] With DSSS, the message symbols are modulated by a sequence of complex values known as spreading sequence. Each element of the spreading sequence, a so-called chip, has a shorter duration than the original message symbols. The modulation of the message symbols scrambles and spreads the signal in the spectrum, and thereby results in a bandwidth of the spreading sequence. The smaller the chip duration, the larger the bandwidth of the resulting DSSS signal; more bandwidth multiplexed to the message signal results in better resistance against narrowband interference.[1][3]
Some practical and effective uses of DSSS include the code-division multiple access (CDMA) method, the IEEE 802.11b specification used in Wi-Fi networks, and the Global Positioning System.[4][5]
- ^ a b Torrieri, Don (2018). Principles of Spread-Spectrum Communication Systems, 4th ed.
- ^ "Espacenet - Bibliographic data". worldwide.espacenet.com. Retrieved December 2, 2020.
- ^ Stuber, Gordon L. (2017). Principles of Mobile Communication, 4th ed.
- ^ Rappaport, Theodore (2002). Wireless Communications Principles and Practice, 2nd ed.
- ^ Pratep, Misra; Enge, Per (2012). Global Positioning System: Signals, Measurements, and Performance, rev. 2nd ed.