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Ensuring Secure Communication With Spread-Spectrum Techniques

Key Takeaways

  • What spread-spectrum techniques are.

  • Where spread-spectrum techniques are commonly used.

  • The different types of spread-spectrum techniques.

 Military communications

Spread-spectrum techniques are used in military communications to ensure secure communication

Secure communication is critical for military communications in hostile environments. To ensure the secure transmission of information, military communications use spread-spectrum techniques. The main advantage of spread-spectrum techniques is the immunity to interference--it is impossible to jam the signals. Wireless communication systems also use this advantageous technique to ensure secure communications for the general public.

Spread-spectrum techniques offer advantages such as increased bandwidth and reduced noise and signal issues. These techniques help maintain the signal-to-noise ratio as a high value, as spread-spectrum signals are difficult to interfere with. Let’s take a look at spread-spectrum techniques and their advantages.

Spread-Spectrum Techniques

In conventional wireless communication, the frequency of a signal is kept constant, and such wireless signals have limited bandwidth. Since the signal frequency and bandwidth are known, anyone can hack into the system using this data and retrieve signal information. Constant frequency signals are often victims of electromagnetic interference and can be easily intercepted. It is not safe to transmit confidential information using constant frequency wireless communication. To offset the disadvantages of conventional constant frequency communication, spread-spectrum techniques are employed in wireless communication.

In wireless communications where spread-spectrum techniques are used, the frequency of transmitted signals is intentionally varied. The variation of the frequency follows a specific and complicated mathematical function that sweeps the frequency of the signal over a wide area of the electromagnetic radiation spectrum. By varying the frequency, increased bandwidth is achieved.  Multiple users can share the same spread-spectrum bandwidth without a problem of interference with one another. The use of the same spread-spectrum bandwidth by multiple users results in multiple access communications.

Spreading Operation

To achieve spread-spectrum techniques in signal transmission, pre-agreed signal sequences that are coded for specific signals are injected into the transmitting chain before the antenna. The process of injecting spread-spectrum signals into the signals being transmitted is called the spreading operation. The spreading operation spreads the information contained in the transmitted signals into larger bandwidth. 

Despreading Operation

The process of removing the spread-spectrum signals at the receive chain is called the despreading operation. The dispreading operation brings the information back to its original bandwidth. The same code is used to inject and remove the spread-spectrum signals in the transmission and receive chain. For secure signal communication, the code will be known only to those transmitting and receiving signals.

Classifying Spread-Spectrum Techniques

Spread-spectrum techniques can be classified into the following types:

1) Frequency-Hopping Spread-Spectrum (FHSS) Technique

In the frequency-hopping spread-spectrum technique, the bandwidth is properly utilized to its maximum. The available bandwidth is divided into channels, and these channels are arranged continuously. The transmitters and receivers select the frequency slots from the channels randomly and use them for a given time in milliseconds. By hopping on channels for a particular amount of time, the FHSS technique implements both frequency-division multiplexing and time-division multiplexing.

The FHSS technique is subdivided into:

  • Slow hopping technique - Multiple bits of information are transmitted on a specific frequency.
  • Fast hopping technique - Individual bits are transmitted on different frequencies.

The application of FHSS is seen in wireless local area networks (WLAN) and wireless personal area networks (WPAN).

2) Direct-Sequence Spread-Spectrum (DSSS) Technique

The direct-sequence spread-spectrum technique is commonly used in telecommunication applications to reduce signal interference. The spread-spectrum signals of DSSS are of shorter duration than original signal bits, which makes the bandwidth of the transmitted signal wider than the information bandwidth. 

The DSSS technique is subdivided into:

  • Wideband spread-spectrum - This spread-spectrum technique uses wide bandwidth spreading signals.
  • Narrowband spread-spectrum - In this technique, the spread-spectrum-like signal is generated from narrowband signals.

The DSSS spread-spectrum technique is used in LAN and satellite communication technologies.

Irrespective of the classification, the main objective of spread-spectrum techniques is to enable secure communication with less interference, noise, or jamming issues. Depending on the application, either frequency-hopping or direct-sequence spread-spectrum techniques should be used for wireless communication security. Cadence’s suite of design and analysis tools can help you in designing wireless communication systems utilizing spread-spectrum techniques.

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