Spreading Code

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A spreading code is a pseudo-random code that has a narrow ambiguity function, unlike other narrow pulse codes. In CDMA a locally generated code runs at a much higher rate than the data to be transmitted.

To ensure multiple users on a CDMA system cause minimal mutual interference the spreading codes must be orthogonal - various different forms of code can be used.

Although using DSSS it is not possible to decode a signal unless the correct spreading code is used in the receiver, using CDMA, it is also necessary to ensure that the minimum level of mutual interference is caused between different users accessing a base station.

To ensure the minimum levels of interference orthogonal spreading codes must be used. Being orthogonal, the different CDMA signals are able to operative with little mutual interference.

The CDMA spreading codes are used to increase the bandwidth of the signal to gain the benefits of spread spectrum communications, but reducing the mutual interference requires the codes are orthogonal. There are different types of orthogonal code that can be used for CDMA

Thanks

To ensure multiple users on a CDMA system cause minimal mutual interference the spreading codes must be orthogonal - various different forms of code can be used.

Explanation

The concept of CDMA is based on the fact that a data sequence is multiplied by a spreading code or sequence which increases the bandwidth of the signal. Then within the receiver, the same spreading code or sequence is used to extract the required data. Only when the required code is used, does the required data appear from the signal.

The process of extracting the data is called correlation. When a code exactly the same as that used in the transmitter is used, then it is said to have a correlation of one and data is extracted. When a spreading code that does not correlate is used, then the data will not be extracted and a different set of data will appear. This means that it is necessary for the same spreading code to be used within the transmitter and receiver for the data to be extracted.

Types are 

- PIN codes:

- Truly orthogonal codes: