Spread spectrum techniques are methods used in wireless communication to spread the signal bandwidth over a wider frequency range than the original information bandwidth. These techniques offer various benefits, including increased resistance to interference, improved security, and more efficient use of the available spectrum. There are two primary types of spread spectrum techniques: Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS). Here’s an overview of both techniques:

1. Frequency Hopping Spread Spectrum (FHSS):
Frequency Hopping Spread Spectrum involves rapidly changing the carrier frequency of a transmitted signal according to a predefined hopping sequence. The key characteristics of FHSS include:

  • Hopping Sequence: FHSS uses a hopping sequence that determines the order and timing of frequency changes. Both the transmitter and receiver are synchronized to the same sequence.
  • Interference Resistance: FHSS is robust against narrowband interference and jamming. This is because the signal frequently hops between different frequencies, making it difficult for an interferer to target a specific frequency.
  • Security: FHSS can provide a level of security by making it challenging for unauthorized receivers to synchronize with the hopping sequence and capture the entire signal.
  • Bluetooth Technology: FHSS is used in Bluetooth technology, where devices hop between frequencies within the 2.4 GHz ISM (Industrial, Scientific, and Medical) band.

2. Direct Sequence Spread Spectrum (DSSS):
Direct Sequence Spread Spectrum involves spreading the signal using a spreading code that is mathematically combined with the original signal. The key characteristics of DSSS include:

  • Spreading Code: DSSS uses a spreading code that consists of a sequence of chips (binary digits). This code is applied to the original data signal, spreading it across a wider frequency band.
  • Interference Resistance: DSSS offers resistance to narrowband interference and fading. The spread signal appears as noise-like interference to other narrowband signals.
  • Signal Recovery: The receiver uses the same spreading code to despread the received signal and recover the original data signal. The spreading code must be known to both the transmitter and receiver.
  • Higher Data Rates: DSSS allows for higher data rates by spreading the signal over a wider bandwidth. This enables more information to be transmitted within the available spectrum.
  • Wi-Fi and CDMA: DSSS is used in some Wi-Fi standards and Code Division Multiple Access (CDMA) cellular systems.

Spread spectrum techniques find applications in various communication systems, including wireless LANs, cellular networks, satellite communication, military communication, and more. These techniques contribute to the efficient and reliable use of the wireless spectrum while mitigating interference and enhancing security.