Direct sequence spread spectrum (dsss)

Definition

Direct sequence spread spectrum (DSSS) is a modulation technique used in telecommunications where the signal is spread over a wider bandwidth than the minimum necessary. This technique enhances the robustness of the signal against interference and allows multiple users to share the same frequency band by assigning unique spreading codes, which makes it suitable for wireless communication systems.

5 Must Know Facts For Your Next Test

1. DSSS uses a spreading factor, which is the ratio of the chip rate to the data rate, affecting how much the signal is spread across the spectrum.
2. DSSS is robust against multipath fading, which occurs when signals arrive at the receiver via multiple paths due to reflections or obstacles.
3. The unique spreading codes used in DSSS can be orthogonal or pseudorandom, allowing multiple signals to coexist without causing interference.
4. DSSS can provide a level of security, as only receivers with the correct spreading code can decode the transmitted message.
5. Common applications of DSSS include GPS, CDMA cellular networks, and certain types of wireless local area networks (WLANs).

Review Questions

• How does direct sequence spread spectrum enhance signal robustness and what role do spreading codes play in this process?
  • Direct sequence spread spectrum enhances signal robustness by spreading the transmitted data across a wider frequency band, which makes it less susceptible to interference and jamming. The spreading codes are critical in this process as they determine how the original signal is modulated. By using unique codes for each transmission, DSSS allows multiple users to share the same frequency band while minimizing interference between signals, ensuring reliable communication.
• Compare and contrast direct sequence spread spectrum with frequency hopping spread spectrum in terms of their operational mechanisms and use cases.
  • Direct sequence spread spectrum spreads a signal over a wide bandwidth using spreading codes, allowing for multiple transmissions to coexist without interference. In contrast, frequency hopping spread spectrum rapidly changes frequencies during transmission, hopping among different channels to avoid interference. DSSS is often used in systems like GPS and CDMA, while FHSS is common in Bluetooth technology. Both techniques enhance communication reliability but employ different methods for dealing with interference.
• Evaluate the implications of using direct sequence spread spectrum on network security and capacity within wireless communication systems.
  • The use of direct sequence spread spectrum has significant implications for network security and capacity. By utilizing unique spreading codes for each transmission, DSSS provides an additional layer of security since only receivers with the correct code can decode messages. This makes eavesdropping more difficult. Additionally, DSSS enables multiple users to operate within the same frequency band without causing interference, enhancing overall capacity. However, the efficiency of this technique depends on factors like code design and chipping rates, which must be managed to optimize performance.

Related terms

Spreading Code: A sequence of chips used in DSSS to modulate the signal, allowing the original data to be spread over a wider bandwidth.

Chipping Rate: The rate at which chips are transmitted in a DSSS system, influencing the spread of the signal and its resistance to interference.

Frequency Hopping Spread Spectrum (FHSS): Another spread spectrum technique that rapidly changes the carrier frequency among many frequency channels, as opposed to spreading the signal over a wide band.