NORTHWEST RESEARCH ASSOCIATES, INC. — Department of Defense SBIR Phase II: DTRA202-005

Description

The ongoing development of new, improved technology for both hardware and software leads to the almost constant upgrade of existing strategic sensor and communications systems and the development and deployment of new systems.  This work addresses warfighter concerns raised in the area of satellite communications and radar, where burst-produced ionospheric disturbances can cause scintillation of a propagating signal.  The signal can experience fading of amplitude and phase, as well as rapid variation in time-of-arrival and angle-of-arrival.  Without mitigation, these disturbances can cause increased error rate and degraded communications and sensor performance. All these propagation channel disturbances are mathematically described by the channel impulse response function (CIRF).  The CIRF can vary in time for a particular propagation channel due to movement of the ionization or movement of the transmitter or receiver which causes motion of the propagation path with respect to the ionization.  The objective of this work is to determine, in real time, the time-varying ionospheric transfer function (or channel filter) (the transfer function is the Fourier transform of the CIRF).  In the proposed work, the transfer function is used to obtain the “matched channel filter (MCF).”  The MCF can be applied to the received signal to precisely compensate for the effects of the disturbance.  Determination of the MCF is thus a first step towards full mitigation of SATCOM link disturbances.  Under this work, we will continue to optimize and refine the MCF developed under Phase I and to transition the algorithms to operate in real-time using software radios.