Acquisition of Direct-Sequence Spread-Spectrum Signals

Abstract

Since early experimentation in the late 1800's, wireless communication has become increasingly important and has been widely adopted by civilian and military markets worldwide. The proliferation of wireless communication systems presents new challenges, threats and opportunities for society and government institutions. Although the possibility of infringing privacy laws exist, electronic surveillance has become an important capability in military, counter-terrorism and law-enforcement operations. Through interception of wireless communication signals, an advantage may be gained by extracting intelligence from, or interfering with, communication signals of an adversary. Interception can only be performed once the presence of the communication signal is detected. However, communication signals are typically not intended for reception by third parties and security mechanisms are often employed to protect communication transmissions from compromise. Sophisticated techniques are therefore required to reliably detect the presence of, and to extract information from, the communication signal of interest. Due to the ubiquitous use of wireless communication devices, techniques to e ciently use and manage system resources, such as the available radio frequency (RF) spectrum, have been developed and are implemented in these devices to ensure co-existence and to limit interference. Communication systems are also designed to minimise transmission power dynamically, which brings about several advantages, such as enhanced battery life for mobile users and lower detection probability in military applications. Techniques to share resources among several users are also employed in order to increase system capacity and availability. Detecting the presence of a certain communication signal within the resultant dense signal environment is therefore challenging, especially if the intercept receiver does not have accurate knowledge of the parameters being used by the target communication