Aerospace and Electronic Systems Magazine December 2017 - 33

Figure 1.

Proactive Remote Intelligent Spectrum Management System (PRISM).

continuously updated every few seconds as the wideband monitoring data is processed.
The frequency selection logic has four main constructs: 1) utilize the maximum available bandwidth, 2) minimize the revisit rate
to a defined channel, 3) occupy a channel for no more than 20 minutes, and 4) maintain a minimum frequency separation between
the two operating frequencies of the radar. Under this mode of operation, spectral use by the radar is spread equally throughout the
available band, while maintaining the maximum bandwidth and
frequency diversity to maximize radar performance. The utilization of this sense-and-adapt technology allows the radar to optimally perform even in hostile RF environments.
The PRISM system is designed to monitor the two frequency
channels on which the radar is currently operating. The in-band
occupancy processing utilizes orthogonal waveform codes to remove radar target and clutter energy from the in-band dataset. This
process permits reliable detection of users on the same frequency
channel which would typically be masked by the dominant radar
energy from clutter.
The combination of the in-band occupancy detection with a
statistical database of open channels allows the system to react instantly upon detection of an in-band user, by switching to an open
channel, thus minimizing radar downtime. In the event that there
are no available open channels at suitable bandwidths, the PRISM
system can cease transmissions until a suitable channel becomes
available or switch to a defined "safe haven" frequency. This mode
of operation is consistent with the recommended practices for the
operation of HFSWR within the U.S. [3]:
"DOD (Department of Defense) expects to increase HF radar use over time, as does the Coast
Guard. Since there are no HF allocations for the
radiolocation service and new allocations in the
HF bands are unlikely, future HF radars must be
carefully designed with a dynamic channel occupancy analyzer to minimize harmful interference to other systems."

Figure 2.

Spectrum Plot over a 20-hour period showing clear spectrum during
daylight hours (08:00-16:00 hours) and congestion during hours of
darkness.

DECEMBER 2017

An example of a spectrum plot (frequency vs. time) from the
PRISM system is presented in Figure 2. It can be observed that,
during daylight hours, the spectrum is wide open with few local
users of the spectrum being observed. During these times the radar
can operate at its maximum bandwidth and at frequencies that are

IEEE A&E SYSTEMS MAGAZINE

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