The document discusses different types of spread spectrum techniques used in wireless communications including frequency hopping spread spectrum (FHSS), direct sequence spread spectrum (DSSS), and code division multiple access (CDMA). It explains that spread spectrum works by spreading data over a wider bandwidth through techniques like frequency hopping or spreading each bit into multiple bits, making the signal harder to intercept or jam. The receiver is able to recover the original data by using the same spreading code or sequence as the transmitter.

1. Data Communications - Spread Spectrum

4. General Model of Spread Spectrum System

9. Frequency Hopping Example

12. Direct Sequence Spread Spectrum Example

13. Direct Sequence Spread Spectrum Using BPSK Example

15. CDMA Example