Abstract
This paper presents a method for the joint detection and direction of arrival (DOA) estimation of low probability of detection (LPD) signals. The proposed approach is based on using the antenna array to receive spread-spectrum signals hidden below the noise floor. Array processing exploits the spatial correlation between phase-delayed copies of the signal and allows us to evaluate the parameter used to make the decision about the presence of LPD transmission. The DOA estimation is based on the covariance between signals received by sensors for the fixed geometry of the antenna array. Moreover, the paper provides a method for mitigating narrowband interferences prior to signal detection. The presented methods were verified through simulations which proved that the confident detection of a one-second transmission in an additive white Gaussian noise channel is possible even when the noise is 24 dB higher than the power of the received signal. The performance of DOA estimation is analyzed in a wide range of signal-to-noise and interference-to-noise ratios. It is found that the DOA may be estimated with an RMS error not exceeding 10 degrees, even if interference occupies 15% of the analyzed frequency band.
Highlights
The covert transmission of radio frequency (RF) signals is required in various wireless systems, and mainly used for military purposes
This paper shows that it is possible to detect pseudorandom low probability of detection (LPD) transmissions at signal-to-noise ratio (SNR) considerably lower than −20 dB and estimate their direction of arrival with root mean square error (RMSE) not exceeding 10◦ in presence of narrowband interference
It is assumed that LPD transmission has a form of direct-sequence spread spectrum (DS-SS) signal, where the carrier phase is keyed with a sequence being a modulo-2 sum of a data sequence and a pseudorandom code sequence
Summary
The covert transmission of radio frequency (RF) signals is required in various wireless systems, and mainly used for military purposes. The analyses provided in these papers mainly focus on the possibility of transmitting a finite amount of data through an additive white Gaussian noise (AWGN) channel with given energyper-bit, depending on the extent of warden’s knowledge about channel parameters [5,6,7,8,9,10] Such highly theoretic research provides useful information about the limits of undetected communication; still, it does not cover the methodology of detecting LPD signals. This paper shows that it is possible to detect pseudorandom LPD transmissions at SNR considerably lower than −20 dB and estimate their direction of arrival with root mean square error (RMSE) not exceeding 10◦ in presence of narrowband interference.
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