Results of Airborne PCL Under CCI Conditions Using DVB-T Illuminators of Opportunity

Passive radar, or Passive Coherent Location (PCL), has reached a stage of maturity for stationary PCL receivers exploiting stationary transmitters of opportunity. The next logical step is to place PCL receivers on moving platforms. Mounting PCL receivers on airborne platforms poses a challenge to the system designer. One issue that has received little attention in the literature is that airborne PCL receivers can be more susceptible to Cochannel Interference (CCI) than ground based PCL systems due to the receiver operating at higher altitudes (no terrain masking), therefore potentially having a line-of-sight (LOS) to the interfering transmitter, and atmospheric propagation. For efficient spectrum usage the carrier frequency for a cluster of Digital Video Broadcasting-Terrestrial (DVB-T) transmitters in one Single-Frequency-Network (SFN) will be reused in a second more distant SFN. The distance between the two SFNs is designed such that the signals from each SFN will not self-interfere for ground based receivers. However for airborne receivers the combination of higher operating altitude, propagation effects, and intentional suppression of the Direct Path Interference (DPI) can result in the broadcast signal from the more distant SFN interfering with the signal from the intended SFN transmitter of opportunity. The interfering signal can be regarded as wideband noise jamming and if unaccounted for it can impede PCL performance quite severely. To investigate the problem of CCI in the case of airborne PCL, we conducted an airborne experiment to utilize DVB-T signals in a SFN.