DSSS stands for Direct-Sequence Spread Spectrum.
Direct-Sequence Spread Spectrum (DSSS) is a spread-spectrum modulation technique used in telecommunications to combat interference and improve signal security. It achieves this by spreading the original signal over a wider bandwidth than required, using a pseudo-random noise (PN) code. This code is a high-rate bit sequence, also known as a chipping code, that divides the user data according to a spreading ratio.
Here's a breakdown of how DSSS works:
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Data Signal: The original information signal to be transmitted.
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Chipping Code (PN Sequence): A pseudo-random sequence of bits generated by a specific algorithm. This code has a much higher bit rate than the data signal.
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Spreading: The data signal is multiplied by the chipping code, effectively spreading its energy across a wider frequency band. This makes the signal more resistant to narrowband interference and jamming.
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Transmission: The spread signal is transmitted over the wireless channel.
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De-spreading: At the receiver, the received signal is multiplied by the same chipping code used for spreading. This process concentrates the signal energy back into its original bandwidth, while spreading the energy of any interfering signals.
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Data Recovery: The original data signal is then recovered from the de-spread signal.
Key characteristics and benefits of DSSS:
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Interference Resistance: DSSS is highly resistant to narrowband interference and jamming because the interference is spread over a wider bandwidth during de-spreading at the receiver.
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Signal Security: The use of a PN code makes it more difficult for unauthorized parties to intercept and decode the signal. The longer and more complex the PN sequence, the more secure the transmission.
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Code Division Multiple Access (CDMA): DSSS forms the basis for CDMA, a multiple access technique where multiple users can share the same frequency band simultaneously by using different chipping codes.
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Multipath Mitigation: DSSS can help mitigate the effects of multipath fading by spreading the signal over a wide bandwidth, which reduces the correlation between different multipath components.
Example of DSSS application:
- IEEE 802.11b WLAN: An earlier version of the Wi-Fi standard used DSSS for wireless communication. However, modern Wi-Fi standards like 802.11g/n/ac/ax predominantly use Orthogonal Frequency-Division Multiplexing (OFDM).
In summary, DSSS is a robust modulation technique that provides improved resistance to interference, enhanced signal security, and support for multiple access schemes.
