Covert netted wireless noise radar sensor: OFDMA-based communication architecture

• Authors: Shrawan C. Surender;Ram M. Narayanan
• Venue: MILCOM'06 Proceedings of the 2006 IEEE conference on Military communications
• Year: 2006

We address the need for covert situational awareness by the effective use of random waveforms in ad-hoc networks, wireless communication, and radar sensors. UWB random noise radar is well-known for its LPD and LPI properties. Notch filtering is used to fragment this radar's band-limited random noise transmit signal and the intermediate bandwidth so obtained is used for establishing a covert wireless multi-user communication platform between the radars. This being the primary goal of this paper, we prove that the radar's detection and ranging function can occur simultaneously with data communication. Our results also show that embedding OFDM symbols into the intermediate bandwidth not only preserves the random nature of the transmitted signal but also lets the receiver retrieve the embedded data from the noise-data radar received signal. Next, the CDF of the camouflaged noise-data signal can be made to look very similar to the CDF of a Gaussian random noise signal, by proper adjustments to the number of carriers used in the OFDM symbol. This CDF can be used as a metric to measure the covertness of this system. Further, the effect of this tradeoff on the BER of the system can be brought into allowable limits with the use of OFDM-based data redundancy technique. Now, using this deterministically fragmented noise spectrum as the communication channel and OFDMA/FDD as a multiplexing technique, a number of such noise radars can be configured to form an ad-hoc multi-radar wireless network. An algorithm in this regard is also presented. Thus, as seen by any hostile target, the transmitted noise-data waveform appears random and noise-like. However, for the radar sensors in the network, this noise-like signal contains camouflaged information.