SBIR-STTR Award

Co-channel interference remains a persistent and pervasive annoyance for most HF band communications. The multirate orthogonal sampling (MOS) technique presented is an innovative, yet intuitively straight- forward approach to the problem of co-channel interference. The premise of the MOS technique relies on two fundamental properties of communication signals: (1) The signals are carrier-borne I.E. the information signal has been modulated on to a high frequency carrier, and (2) The bandwidth of the information signal is significantly less than carrier frequency. MOS diverges from conventional demodulation/ suppression methods by recasting the problem to one involving multiple waveform estimation. MOS derives a solution by considering the demodulation/suppression simultaneously as one optimal parameter estimation problem. For two interfering sinusoids, the best estimate of one waveform is obtained when the composite waveform is sampled at a zero-crossing of the other. MOS is conveniently implemented as a set of multi-rate samplers that cooperatively develop optimal sample clocks to provide interference suppressed estimates. MOS is esily implemented using inexpensive components, easily integrated into existing hf modems, and doesn't require complex antennas or demodulation circuitry.

Co-channel interference remains a persistent and pervasive annoyance for most HF band communications. The Phase I program, Co-channel Interference Suppression Using Multirate Orthogonal Sampling (MOS), demonstrated a quasi-linear, non-uniform sampled data system approach for separating co-channel signals. The degree of success has provided a promising enabling technology for addressing the co-channel problem in HF data modems. The Phase 11 effort will apply the results of the technical feasibility study to the development and validation for co-channel suppression technique for specific data modulation formats including FSK, PSK, and QAM. The HF modem "applique" to be developed will be integrated/interfaced with Army JF radios and modems and tested using " live" transmissions. Measures of effectiveness of the equipment, categorized by interference severity and type will be reported. A baseband variation of the Phase I MOS technique will be evaluated. This baseband approach facilitates interfacing MOS suppression to existing radios. Due to the pervasiveness and deleterious effects of co-channel interference in Army communication, the benefits to be derived are substantial. Successful demonstration will enable the immediate manufacturing of low-cost HF modem "add-ons" which will permit better utilization of the HF resources. Additionally, Phase m commercialization of a co-channel interference capable data modem will be addressed.