Experience with Ranging Buried Cable Sensing

Abstract

The next generation of Guided Radar (GUIDAR) is based on Ultra Wide Band (UWB) radar signal processing. Just as spread spectrum technology has revolutionized the communications industry, UWB is dramatically changing radar signal processing. These advanced signal-processing techniques are adapted to leaky coaxial cable technology in the next generation GUIDAR to provide new features and enhanced performance. At the core of the new technology is an ultra high-speed digital correlator implemented in a Field Programmable Gate Array (FPGA). Complementary orthogonal codes based on Golay codes are used to produce thumbtack correlation functions simultaneously in multiple range bins. The net result is "near continuous wave (CW)" performance in forty to eighty 11.6-meter long-range bins with targets located within one meter along the length of cable. This is a dramatic improvement over the 3% duty cycle of the original GUIDAR and the typical 100 to 200 meter-long zones of current CW leaky cable sensors. Uncorrelated complementary codes are transmitted on each of two leaky coaxial cables. The responses from two parallel receive cables are digitized directly and down converted to baseband using quarter rate translation. The uncorrelated nature of the code allows the A and B sides of the processor to operate without interfering with each other. Synchronous sampling at twice the chip rate ensures that each target is observed in three adjacent sample bins. The phase and amplitude response in the three adjacent samples are combined to precisely pinpoint (within 1 meter) the locations of targets along the length of each of the two cables. The ability to precisely locate and track multiple simultaneous targets on each of two cables leads to numerous new features and performance benefits relative to existing leaky cable sensors. With a separate calibrated threshold for every meter of cable, the sensor sensitivity is much more uniform and installation restrictions on burial depth, cable spacing and medium homogeneity can be relaxed. Potential sources of nuisance alarms can easily be located and overcome. The pinpoint location can be used to provide better CCTV assessment, target capture for video motion sensors and more effective response to intrusions. Through the use of parallel cables the sensor can be used to detect the direction of crossing and to classify targets such as small animals, people and vehicles. This patented next generation of GUIDAR technology represents a dramatic step forward from that which was introduced at the 1976 Carnahan Conference in Lexington Kentucky and the numerous CW leaky coaxial cable sensors that evolved from that work. This technology effectively addresses residential, commercial, industrial and governmental requirements, including those relating to Homeland Security, military operations and prisons.