- 2076 Asoj · 4 marks
Short note: DSSS versus FHSS
Short answer
DSSS spreads each bit by multiplying with a high-chip-rate pseudo-noise sequence, occupying the whole band continuously. FHSS spreads by rapidly hopping the carrier among many frequencies. DSSS provides higher data rate but requires precise chip-level sync; FHSS has easier hop-level sync and is used in Bluetooth.
Write a short note on DSSS versus FHSS.
Both are spread spectrum techniques that spread a narrow-band signal over a wider bandwidth to resist jamming and interference, but they spread in different ways.
- DSSS multiplies each data bit by a high-rate chip sequence, so the signal occupies the whole wide band at once.
- FHSS keeps a narrow carrier but moves it among many frequencies in a pseudorandom order.
| Point | DSSS | FHSS |
|---|---|---|
| Spreading | By chip code (XOR with PN sequence) | By hopping carrier frequency |
| Bandwidth use | Whole band continuously | One narrow channel at a time |
| Synchronisation | Needs accurate chip-level sync | Easier, hop-level sync |
| Interference | Averaged out by processing gain | Only the hops that collide are lost |
| Near-far problem | Severe | Less |
| Data rate | Higher | Lower |
| Complexity | Needs high chip rate | Needs fast frequency synthesizer |
| Examples | 802.11b, GPS, CDMA | Bluetooth, early 802.11 |
✓ Answer checked by Claude Sonnet 5.5
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