Abstract: A communication method and system for communication utilizing modulation of digital signals, such as by targets and/or by use of low-complexity tags is presented. Targets may include any device or object that may alter signals, and tags can include a device with the ability to reflect and/or alter the properties of the signals and, in doing so, impose specific modulations on or alterations of such signals. Modulations can be sensed or detected using a receiver or receivers implementing processing algorithms derived from passive radar detection operations or other processes.

Abstract: A communication method and system for communication utilizing modulation of digital signals, such as by targets and/or by use of low-complexity tags is presented. Targets may include any device or object that may alter signals, and tags can include a device with the ability to reflect and/or alter the properties of the signals and, in doing so, impose specific modulations on or alterations of such signals. Modulations can be sensed or detected using a receiver or receivers implementing processing algorithms derived from passive radar detection operations or other processes.

Abstract: A system for the passive location of non-cooperating vehicles using satellite-based transmitters with ionospheric compensation. The system is a light-weight, low-cost, portable, and field-deployable station to supplement deficiencies in the National Airspace System (NAS) and homeland security surveillance networks. The system accommodates observation modes having long “integration” times that potentially are greater than one second. The system utilizes satellite-based transmitters as illuminators. The passive system measures two radio waves (e.g., a direct path and an illumination plus reflection path), and applies time-difference techniques that can compensate for the ionosphere since the ionospheric delay is applied to both signals. This also has the advantage of compensating for other uncertainties such as exist in the position of the satellite.