8.4 Spread spectrum communication systems The major objective is often the efficient ultilization of transmission power and BW.Engineers make tradeoff between them. A spread spectrum (SS)system expands the BW of the signal largely to overcome various interferences.And more,using of the random-like codes in the expansion makes the signal hard to listen for an unintended user. Rooted in military communications,it was developed to provide resistance to jamming and to hide signals from enemies by transmitting at very low power. UESTC-Wireless communicatons Prof李晓峰 4