- 2078 Kartik · 3 marks
Compare FDM and FHSS
Short answer
FDM assigns each user a fixed narrow frequency band for continuous use, while FHSS spreads a single user across many frequencies by hopping in a pseudorandom pattern. FDM shares link among multiple users; FHSS resists jamming and interception. Bluetooth uses FHSS.
Compare FDM and FHSS using a suitable time-frequency graph.
FDM gives each user a fixed frequency band all the time; FHSS makes one user jump among many frequencies in a pseudorandom pattern.
FDM FHSS
Freq Freq
f3 |######### f6 | #
f2 |######### f5 | #
f1 |######### f4 |#
+---------> t f3 | #
each channel fixed f2 | #
on its own band f1 | #
+---------> t
one user hops over the whole band
| Point | FDM | FHSS |
|---|---|---|
| Purpose | Share a link among many signals | Spread one signal to resist jamming / interception |
| Carrier | Fixed per channel | Changes every hop period |
| Bandwidth per user | One narrow band | Whole spread band used over time |
| Code needed | No | PN sequence, shared by Tx and Rx |
| Interference | A narrow-band interferer kills the channel | Affects only a few hops |
| Security | Poor | Good |
| Example | Radio/TV channels | Bluetooth |
✓ Answer checked by Claude Sonnet 5.5
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