Use Slow Frequency Hopping for Reduced Interference in Wireless Communications

Key Takeaways

• A type of spread spectrum technique called frequency hopping is commonly used in wireless personal area networks and local area network applications.

• Slow frequency hopping is a type of frequency hopping primarily used for avoiding multiple access interferences in wireless communication systems.

• The slow frequency hopping spread spectrum technique is a popular technique used in wireless local area networks and wireless personal area network communication.

Frequency hopping is commonly used in wireless personal area networks and local area network applications

When there are multiple uses of the same frequency or frequency band in the same locality, some kind of electromagnetic interference occurs. The signals from different devices interfere with each other and cause glitches in control or disrupt the normal operation of devices. Electromagnetic interference is a severe issue in wireless communication. To ensure secure data transmission, this interference needs to be mitigated. 

The spread spectrum technique is one signal modulation method used to mitigate interference issues. A type of spread spectrum technique called frequency hopping is commonly used in wireless personal area networks and local area network applications. Slow frequency hopping is a sub-classification of frequency hopping that is primarily used for avoiding multiple access interferences in wireless communication systems. 

The Frequency Hopping Spread Spectrum Technique

The frequency hopping spread spectrum (FHSS) technique is a communication technique where the carrier signal randomly hops from one frequency to another. The carrier injected into the signal follows a specific hopping pattern known to only the sender and receiver. The frequency of the hop set varies from f₁ to f_L where L is the number of frequency channels available for frequency hopping. For a given time, called hop period (t_h), the signal transmitted remains in a particular hop frequency slot of bandwidth B. The frequency of the signal transmitted is constant for the given hop time. The spread spectrum bandwidth denoted by W will be much greater than B.

Advantages of the Frequency Hopping Spread Spectrum Technique

The injection of carrier signals into a signal using the frequency hopping spread spectrum technique has the following advantages:

1)  Increased bandwidth - The narrow bandwidth of the signal to be transmitted is changed into a wider bandwidth through the frequency hopping process.

2) Overcome fading - Fading is the variation in the attenuation of the signal. The signal frequencies separated by several MHz do not fade simultaneously. Frequency hopping limits fading and related communication failures by separating the signals. 

3) Multipath channel communication - Multipath channel communications face interference problems often. The use of frequency hopping prevents these channel interferences.

4)  Increased spectral efficiency - In frequency hopping, each channel of bandwidth B includes the single carrier frequency as its center frequency. Most of the information is contained within the given channel spectral region, which increases the spectral efficiency.

5) Prevent jamming - Since the frequency of the carrier signal hops, frequency hopping has strong anti-jamming properties.  

Slow Frequency Hopping

There are two types of frequency hopping spread spectrum techniques: fast frequency hopping and slow frequency hopping. In slow frequency hopping, the carrier frequency is changed on a regular basis. The hopping sequence is created and is known for the sender and receiver. The time taken to send a single signal frequency is greater than the duration to send several bits of digital information. However, the advantage is that the slow frequency spectrum reduces interference and fading in signal transmission.  

In slow frequency hopping, the carrier time period Tc is greater than the symbol time period T_s. In each frequency hopping event, multiple symbols are transmitted. The relationship between T_c and T_s in slow frequency hopping is given as T_c = N T_s. At every T_c seconds, the center frequency of the signals is changed according to the frequency hopping pattern. The slow frequency hopping spread spectrum technique also employs error control coding to help in restoring the loss of bits in the one hop process.

Advantages of Slow Frequency Hopping

Slow frequency hopping offers similar advantages that the frequency hopping technique does. Slow frequency hopping is particularly useful because even when one of the hopped signals is faded at the receiving end due to narrowband interference, other signals are received correctly. The reproduction of original information at the receiving end is possible even with the signal loss in slow frequency hopping.

Consider securing your signal transmission with the slow frequency hopping technique. With this technique, you can prevent interferences, fading, jamming, etc. It also provides multiple access communication possibilities without signal disturbances. Cadence’s suite of design and analysis tools can help you design slow frequency hopping spread spectrum-based wireless communication systems.

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