Doppler estimation for DVB-T based Passive Radar systems on moving maritime platforms

PR (Passive Radar) systems using digital broadcasting services such as DVB-T (Digital Versatile Broadcasting - Terrestrial) transmission as illuminators represent surveillance solutions which have rapidly evolved and matured over recent years. PR systems typically use coherent integration time in the order of a few hundred milliseconds to acquire enough dynamic for the detection of moving objects. This is done under the assumption that both the illuminator of opportunity and the receiver stay static during this time period. However, advances in miniaturization of high performing computers and data storage devices allowed the design of PR systems that are compact enough to be operated onboard of moving platforms such as cars [1] and airplanes [2], [3]. Deploying PR systems on maritime platforms could enable covert surveillance of small land or sea based targets in littoral environment. A receiver mounted on such a platform may be subjected to highly non-linear motions. In this case a reference signal generated under the assumption of a static scenario may de-correlate from measured Doppler shifted surveillance channel and consequently degrade the PR systems detection performance. Compensation of these detrimental effects requires highly sampled and accurate measurements of the vessels Doppler shift with respect to the transmitter. To study these effects a two channel PR system for DVB-T broadcast reception has been deployed on a small boat to acquire platform motion data in a littoral environment. Based on the data gathered in this trial, a robust method for the Doppler estimation was developed, which uses the DVB-T standards OFDM (Orthogonal Frequency Division Multiplexing) signal features. The validity of this approach is verified with data gathered simultaneously from onboard IMU (Internal Motion Units) data.