High-Resolution, Low Probability of Detection Links Through SDRs

This paper presents the design and implementation of a low probability of detection (LPD) communication link using a software-defined radio (SDR) platform. The proposed LPD link was tested in an indoor environment using an over-the-air (OTA) network. The transmitter and receiver communicate asynchronously and perform real-time modulation and demodulation. Importantly, the transmitter software minimizes memory usage, operational cost, and computationally-costly resampling is avoided. The receiver software acquires and tracks the transmitted waveform using parallel processing for speed, and uses multiple-layers for error detection to reduce computational resources. Further, the receiver's acquisition and tracking operations were profiled, and bottlenecks were removed by replacing slow calculations and algorithms to achieve faster sampling rates. This novel software design achieves significantly faster sampling rates, on the order of six times as compared to similar research. As a result, wider bandwidths and longer spreading codes are achieved to increase LPD characteristics. The asynchronous operation expands the system's usability to areas that are denied, degraded, or contested.