Physical Pseudo Random Function in Radio Frequency Sources for Security

There is tremendous market potential for Location-Based Services (LBS), enabled by the rapid growth in the numbers of personal navigation devices and GPS-enabled mobile handsets. One of the major difficulties for LBS applications is accurate and reliable indoor positioning caused by the difficulty of acquiring and tracking GPS satellite signals in the absence of a clear unobstructed path between the satellite and the user. An alternative approach is to use terrestrial signal sources, such as cellular transmitters, TV or FM broadcast, or Wi-Fi access points.