FHS (Frequency hopping synchronization)

Frequency hopping is a spread spectrum technique that is widely used in wireless communication systems to enhance the performance and security of wireless networks. In frequency hopping, the frequency of the transmitted signal is changed periodically over a wide range of frequencies according to a predetermined pattern. The pattern of frequency hopping is known as a hopping sequence or a hop pattern. The frequency hopping synchronization (FHS) is a technique used to synchronize the transmitter and the receiver in frequency hopping systems.

In frequency hopping systems, the transmitter and the receiver need to be synchronized in order to communicate with each other effectively. This synchronization is required because the frequency of the transmitted signal changes periodically, and the receiver needs to know when and where to look for the signal. The frequency hopping synchronization is achieved by using a synchronization signal, which is transmitted by the transmitter at a fixed frequency and time interval.

The FHS procedure involves the following steps:

1. Transmission of a synchronization signal: The transmitter sends a synchronization signal at a fixed frequency and time interval. This signal is used by the receiver to synchronize its hopping sequence with that of the transmitter.
2. Detection of the synchronization signal: The receiver continuously monitors the received signal to detect the synchronization signal. Once the synchronization signal is detected, the receiver can synchronize its hopping sequence with that of the transmitter.
3. Calculation of the frequency offset: Once the receiver is synchronized with the transmitter, it calculates the frequency offset between its own hopping sequence and that of the transmitter. This is done by comparing the received synchronization signal with the expected synchronization signal.
4. Correction of the frequency offset: The receiver corrects the frequency offset by adjusting its hopping sequence according to the calculated offset. This ensures that the receiver and the transmitter are synchronized in terms of frequency hopping.

There are different methods that can be used for frequency hopping synchronization, including time division multiple access (TDMA), code division multiple access (CDMA), and frequency division multiple access (FDMA). In TDMA, the synchronization signal is transmitted in a dedicated time slot, while in CDMA, the synchronization signal is spread over a wide bandwidth using a code. In FDMA, the synchronization signal is transmitted at a specific frequency channel.

One of the main advantages of frequency hopping is its resistance to interference and jamming. Since the frequency of the transmitted signal changes rapidly over a wide range of frequencies, it is difficult for an attacker to jam or interfere with the signal. Moreover, frequency hopping can improve the reliability of wireless communication by reducing the effects of fading and multipath propagation.

In summary, frequency hopping synchronization is a crucial technique used in frequency hopping systems to synchronize the transmitter and the receiver. The FHS procedure involves the transmission of a synchronization signal, detection of the synchronization signal, calculation of the frequency offset, and correction of the frequency offset. Frequency hopping is a powerful technique that can enhance the security and reliability of wireless communication systems.