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Frequency Hopping Code Division Multiple Access (FH-CDMA) is a basic modulation technique used in spread spectrum signal transmission. FH-CDMA is the repetitive switching of frequency at the time of radio transmission.
This helps to reduce the strength of electronic warfare, that is, the unauthorized jamming or interception of telecommunications. Spread spectrum allows a signal to be carried over a frequency band, which is considerably wider than the minimum bandwidth needed by the information signal. The energy that is originally centered in the narrowband is spread by the transmitter over many different frequency band channels on a broader electromagnetic spectrum.
Some of the advantages are enhanced privacy, reduced narrowband interference, and improved signal capacity.
In the FH-CDMA technique, a transmitter hops between all available frequencies based on a specific algorithm, which is either preplanned or random. The transmitter functions in synchronization with a receiver, which stays tuned to the exact same center frequency as the transmitter's.
A short data burst is carried on a narrowband. Afterwards, the transmitter tunes to a different frequency and transmits again. Therefore, the receiver has the ability to hop its frequency across a specified bandwidth many times per second, transmitting using one particular frequency for a specific time frame, then hopping to yet another frequency and transmitting again.
Direct Sequence Code Division Multiple Access (DS-CDMA), yet another spread spectrum technique, is considered an alternative of FH-CDMA. DS-CDMA splits the data into tiny pieces and spreads them over the frequency domain.
The devices that make use of FH-CDMA technology consume less power and are usually cost effective; however, DS-CDMA systems are more reliable and perform better. The greatest benefit of FH-CDMA is based on the coexistence of various access points in the same area, which is not possible when using direct sequence.
There are some rules that control the way the frequency-hopping devices are utilized. For example, in North America, the industrial, scientific, and medical wave band (ISM wave band) is split into 75 hopping channels.
The power transmission of these hopping channels does not exceed 1 watt on any channel. This restriction makes sure that an individual device does not consume an excessive amount of bandwidth or remain excessively on a single frequency.