spread spectrum doubt

hai,
why we are using BPSK or QPSK in the spread spectrum technique?especially in DSS?

BPSK and QPSK are modulation schemes that are well known to give close to the best power efficiency available along with reasonable bandwidth efficiency.

The direct spread spectrum uses either BPSK or QPSK modulation technique. On the other hand, The Frequency hopping spread spectrum uses FSK which is poor in performance.

For example: a 4-FSK demodulator that uses conventional limiter/discriminator techniques without coding, the expected power efficiency performance will be much worse than QPSK.

In short, DIRECT SPREAD SPECTRUM uses
(1) Efficient modulation (PSK)
(2) Broad modulation bandwidth and continuous transmission.
(3) Quick synchronization
(4) Low power spectral density minimizing interference.

thank you sir