despreads

Despreads refers to the outputs produced by a despreading operation in spread-spectrum communications, or more broadly to the narrowband data streams recovered after despreading. In a direct-sequence spread-spectrum system, a data signal is multiplied by a high-rate pseudo-random code to spread its bandwidth. At the receiver, a locally generated copy of the same code is used to correlate with the received signal. When the code phases align, the correlation yields a despread, narrowband representation of the original data; the resulting signals are often called the despreads or the despread data streams.

Despreading is a key step in direct-sequence systems such as CDMA and GPS. The despreader acts as a matched filter, compressing the spread spectrum into the original data rate while suppressing non-coherent wideband interference. The process provides a processing gain that improves the signal-to-noise ratio for the desired signal relative to interference and noise, particularly when the spreading code length is large. However, the quality of the despreads depends on accurate code and carrier synchronization; misalignment can reduce despreading effectiveness and degrade data recovery.

In practice, despreads are recovered data symbols that are passed to demodulation and error-correction stages. Systems may employ accumulation and integration across multiple chip periods or use specialized receivers, such as rake receivers, to exploit multipath paths that survive the despreading process. Despreads are central to the functionality of many wireless and satellite communication technologies that rely on spread-spectrum techniques.