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Bluetooth FHSS compared to WLAN DSSS
Original Post: why FHSS (SIG Forum) Date: 2000-07-19
Bluetooth uses the RF-method of FHSS (Frequency Hopping Spread Spectrum).
One might make the point as too why Bluetooth doesn't use DSSS , which is
more powerful in multipath rejection, throughput etc. There is one simple
reasons as to why FHSS is used in place of DSSS : FHSS is simpler:
- Mostly the difference is in the baseband, DSSS has to run on a much more
powerful DSP chip since DSSS uses chip rate (many times higher than the symbol
rate) while FHSS only need to run at the symbol rate, so the power consumption
for FHSS is much lower and the complexity is lower too.
- In the RF part, FHSS use FSK which is relatively easy to build and the noise
immunity is better while DSSS usually use QPSK(for IEEE 802.11 2 Mbps) or CCK
(in IEEE 802.11b 11Mbps) which are more complex and the noise immunity is
inferior to FSK.
However, one major disadvantage of FHSS is that it is slower than DSSS,
mostly due to the fact that FSK need a frequency synthesizer (to hop frequency)
and if you need a greater spread spectrum advantage, it has to be fast but this
is not easy to implement.
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