Secure Non-Coherent Links Using Commercial Software-Defined Radios

A low probability of detection (LPD) communication network is proposed using commercial software-defined radios (SDRs) for transmission and reception. The network utilizes code-division multiple access (CDMA) to simultaneously transmit signals over a shared bandwidth. Four transmitters are used to send unique 20-bit binary sequences to a receiver non-coherently. Each sequence uses Direct Sequence Spread Spectrum (DSSS) to extend the signal's spectrum by a factor of 635 to bury the desired signals below the RF noise floor. The receiver was able to acquire, align, and despread all four signals in real time.