What the spread spectrum technique is.
The classifications of the spread spectrum technique.
The advantages of the spread spectrum technique.
The spread spectrum technique is used for all sorts of wireless communication
Initially, spread spectrum techniques were only used in military communications. However, due to advantages like anti-jamming and reduced crosstalk interference, spread spectrum technologies were adopted for wireless communication technologies as well. From mobile communication to WiFi connectivity, the spread spectrum technique is now used as a significant technology in systems design. In this article, we will explore the advantages of the spread spectrum technique as well as its classifications and applications.
What Is the Spread Spectrum Technique?
In the spread spectrum technique, the frequency of the signal to be transmitted is varied by injecting pseudo-random noises into it. This injection increases the bandwidth of signal transmission, and thereby reduces the effects of interference, noise, and signal fading. The pseudo-random noise is generated using codes, and these codes are known only to the sender and receiver. At the receiving end, the pseudo-random codes are used to de-spread the signals for retrieving the original data. This increases the security of signal transmission.
Classifications of the Spread Spectrum Technique
The spread spectrum technique can be further classified as follows:
1. Frequency hopping spread spectrum (FHSS) - In frequency hopping, available bandwidth is divided into channels, and channels are divided into slots. Each slot is used for a given time for signal modulation.
FHSS is subdivided into:
a) Slow hopping - Multiple bits of information are transmitted on a specific frequency.
b) Fast hopping - Individual bits are transmitted on different frequencies.
FHSS is used in wireless local area networks (WLAN) and wireless personal area networks (WPAN).
2. Direct sequence spread spectrum (DSSS) - The spread spectrum signals of DSSS are of shorter duration than original signal bits, which makes the bandwidth of transmitted signals wider than the information bandwidth.
DSSS is subdivided into:
a) Wideband spread spectrum - This spread spectrum technique uses wide bandwidth spreading signals.
b) Narrowband spread spectrum - In this technique, a spread spectrum-like signal is generated from narrowband signals.
DSSS is used in LAN technology and satellite communication technology.
Advantages of the Spread Spectrum Technique
Several advantages of the spread spectrum technique encourage designers to use it in wireless communication technologies. These advantages include:
High signal integrity with less static noise: The spread spectrum technology offers digital processing with high processing gain, which makes the technology immune to electromagnetic interference or noise. With the use of spread spectrum technologies, induced static noise in electronic devices is drastically reduced compared to analog wireless communication systems.
Minimized crosstalk: The processing gain of the spread spectrum technique helps in attenuating the crosstalk in wireless communication. The spread spectrum technique suppresses the crosstalk with digital processing. When the signal undergoes digital processing, the noises below the threshold values are considered negligible errors that do not affect wireless communication.
Immunity to multipath fading: The wideband spread spectrum technique offers frequency diversity properties, which makes the signal transmission immune to multipath fading. Signal frequencies separated by several MHz do not fade simultaneously. The frequency hopping spread spectrum technique limits fading and related communication failures by separating signals.
Secure communication: In the spread spectrum technique, pseudo-random noise is used to modulate the signal either in the time domain or in the frequency domain. The random nature of the signal randomizes the signal transmitted and establishes secure transmission compared to analog wireless communication systems. The receiver retrieves the signal by using the same pseudo-random noise while de-spreading.
Difficulty to demodulate: In the spread spectrum technique, only the sender and receiver have the knowledge of pseudo-random noise injected. To retrieve the data, a pseudo-random noise sequence is necessary. Without the knowledge of the pseudo-random noise, deciphering the signal transmission and demodulating the signal is impossible. The pseudo-random noise is long and quick so that it is impossible to generate the code by any hacker and interception is difficult.
Anti-jamming properties: The spread spectrum technique widens the bandwidth of the signal until it equals the original bandwidth plus the bandwidth of the pseudo-random noise injected. The pseudo-random noise added to the spread spectrum technique prevents jamming and interference in wireless systems.
Co-existence of spread spectrum systems: With a proper design, multiple spread spectrum techniques can co-exist in the same environment without interfering with each other. The susceptibility to interference is less for spread spectrum systems in comparison with non-spread spectrum systems. The system capacity of spread spectrum-based wireless communication is more than analog wireless communication systems.
Increase in operating distances: Spread spectrum modulated signals possess non-interference properties and have higher transmit power. With these higher transmit power capabilities, spread spectrum signals can be transmitted to longer distances compared to analog wireless communication.
Difficult to detect: Spread spectrum modulated signals are wider in bandwidth compared to conventional narrowband transmission. As the bandwidth is wider, low power transmission is possible without being affected by background noise. During de-spreading, the noise frequencies are rejected and the original signals are retrieved.
The advantages of the spread spectrum technique make this technology superior to analog wireless communication. Whenever there is a threat of jamming, signal fading interferences, or hacking, the spread spectrum technique is the best mitigation technique to use. Cadence software offers assistance in designing wireless communication systems utilizing spread spectrum modulation.
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