Modern communications are deliberately designed to resist jamming. Three concepts you will often come across — explained here:
- DSSS (Direct-Sequence Spread Spectrum): each data bit is multiplied by a much faster, secret pseudo-random chip sequence. This makes the signal wide and noise-like, with low power per Hz — it partly "disappears" below the noise floor. Only a receiver that knows the code can "compress" it back together (despread it); a jammer has to spread its power over the entire wide band. This is the technique behind, among other things, the GPS C/A code (GNSS and navigation warfare). See also New concepts in EW.
- FHSS (Frequency-Hopping Spread Spectrum): the transmitter constantly hops between many frequencies according to a pseudo-random code; transmitter and receiver hop in sync. A narrowband jammer only hits occasionally (New concepts in EW).
- The advantage is called processing gain: the wider you spread, the more jamming power is needed to get through — the direct reason why such links are so hard to jam.
On top of that comes the network structure:
- A mesh network is a network in which each node is connected to several others and data "hops" from node to node. If one path drops out (or is jammed), the traffic automatically finds another route. That makes a mesh resilient: taking down one node is not enough.
- A MANET (Mobile Ad-hoc Network) is a mesh that organises itself without fixed infrastructure: every device is both end user and router, and nodes come and go as they move. Many military tactical radios and drone swarms work this way. For COMJAM this means there is no single transmitter or mast to take out — you have to hit several nodes at once, or attack the shared control/sync function (Waveforms and 'smart' jamming).
The answer to this resilience is cognitive/adaptive jamming (New concepts in EW): the jammer characterises the link in real time and chooses or synthesises the most effective technique — the only way to keep pace with hoppers and mesh networks.