It copies the original data stream to several parallel data streams, spreads them in both time and frequency domain, then modulates them to orthogonal sub-carriers for transmission.
它先将原始数据流复制成多路并行数据，经频域扩频和时域扩频，再调制到互相正交的子载波上传输。
But this method occupies the special sub-carriers or time slots and then reduces the system spectrum efficiency and data transmission rate.
但该方法占用专门的子载波或时隙，降低了系统的频谱利用率和信息传输速率。
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