FHSS — Frequency Hopping Spread Spectrum
When you listen to your favorite radio station or watch your favorite TV channel, you tune-in to a specific channel. This is a traditional narrow-band radio and TV communications.
3 problems arise with this type of communication:
In wireless communication, interference and jamming slow down the transmission, and Interception becomes a huge security problem.
NOTE: Suppose you are a pirate and a ship comes through your way daily, you can easily make the loot, similarly if data is constantly being transmitted over a band say 2.4 GHz, it can easily be hacked and intercepted.
So, how to tackle these issues? Signal Modulation Methods come in to save our data. Frequency Hopping Spread Spectrum (FHSS) is one of those.
FHSS was introduced in IEEE 802.11 base version.
IEEE 802.11 is part of the IEEE 802 set of local area network technical standards, and specifies the set of media access control and physical layer protocols for implementing wireless local area network computer communication
FHSS uses spread spectrum techniques by which, a signal of specific bandwidth is deliberately spread within the frequency band. Think of yourself as a captain of the ship now, you know the pirate mindset, so you change routes each day. Thus, reducing the chances of interference, jamming and preventing interception. Let’s see this at work!
Let’s first divide our beloved 2.4 GHz frequency band into 79 narrow frequency channels, each of which is 1 MHz wide →
Now, let’s also divide the data travel time, into smaller time segments →
Now let’s observe a single data packet as it goes from a sender to its receivers. Our data packet will now travel not in a single channel, but it will hop between channels up and down. Like a monkey hopping tree-by-tree (Try catching it).
The packet at T1, is at F2 channel, and as soon as it hits T2, it hops to some other channel, say F5 and travels through this channel for the whole duration T2. And the packets goes on hopping in a random looking fashion.
FHSS sends data on one frequency at a time and changes the frequency over time. The hopping pattern is unknown to an attacker this way. This type of modulation is also used by military, cordless phones, GPS etc..