About Data spreading in CDMA

1. What is spreading in CDMA?
2. How spread spectrum technique is useful in CDMA?
3. What is data rate in CDMA?
4. How do spreading codes work?

What is spreading in CDMA?

A spreading sequence is a binary sequence that appears random but can be reproduced in a deterministic manner by intended receivers. These spreading sequences are used to encode and decode a user's signal in asynchronous CDMA in the same manner as the orthogonal codes in synchronous CDMA (shown in the example above).

How spread spectrum technique is useful in CDMA?

By spreading the spectrum of the transmitted signal, one can reduce its power density such that it becomes less than the power density of the noise. In this way, it is possible to hide the signal in the noise. It can be demodulated if you know the code that was used to send the signal.

What is data rate in CDMA?

The original CDMA standard, also known as CDMA One, offers a transmission speed of only up to 14.4 kilobits per second in its single channel form and up to 115 Kbps in an eight-channel form.

How do spreading codes work?

In DSSS, a spreading code is used to map each data bit in the original signal to multiple bits in the transmitted signal. The pseudorandom code (spreading code) spreads the input data across a wider frequency range compared with the input frequency. In the frequency domain, the output signals appear as noise.