#### In-depth

## Direct sequence CDMA

In direct sequence CDMA, the narrowband signals from individual users are spread continuously and thinly over a wide bandwidth using a spreading sequence. By mixing the narrowband user data signal with a locally generated well-defined wideband signal, the user energy is spread to occupy roughly the same bandwidth as the wideband source. The wideband spreading signal is generated using a pseudo-random sequence generator (see in-depth) clocked at a very high rate (termed the chipping rate). |

De-spreading of the signal is necessary in the receiver in order to recover the narrowband user data modulation and this is accomplished by mixing the received signal with an identical, accurately timed pseudo-random sequence. This correlation process has the effect of reversing the spreading action in the transmitter. De-spreading will only occur, however, if the correct sequence is used at both ends of the link, and if the two sequences are time aligned (see in-depth).

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