Spread spectrum communication system, a clear channel assessment method and related apparatus

The invention discloses a spread spectrum communication system, and the spread spectrum communication system comprises a first antenna, a second antenna, a first carrier wave demodulator, a second carrier wave demodulator, a first analog-digital converter, a second analog-digital converter, a first filter, a second filter, an idle channel estimating device and a selecting device, wherein the carrier wave demodulators respectively convert radio-frequency signals into fundamental-frequency signals; the analog-digital converters respectively convert the fundamental-frequency signals into digital signals; the filters respectively carry out e filtration on the digital signals to generatefiltrated signals; the idle channel estimating device generates a channel estimating signal and a path selecting signal according to the signal characteristics of the filtrated signals; and the selecting device selectively outputs one of the filtrated signals or does not generate any output according to at least one of the channel estimating signal and the path selecting signal.