On Monday the US Navy will fire up its mighty, six-megawatt AN/SPY-1 raygun radar while academics run an LTE mobile-data base station in the same band, so both sides can establish if coexistence is a workable proposition.
AN/SPY-1 is used as part of the Aegis anti-missile system mounted on, amongst other platforms, the US Navy's mighty Ticonderoga-class missile cruisers, probably the most powerful surface combatant warships afloat today. The radar and its associated weapons are sufficiently powerful that they can reach into space itself to track and perhaps shoot down such things as intercontinental missile warheads hurtling ballistically around the planet - or in one case a malfunctioning US spy satellite. There won't be an actual warship involved in Monday's test, however, in which a shore-based trials rig will be used.
Researchers plan to run the test without any of the mitigation technologies proposed to enable spectrum sharing, just to see what happens. MIT Technology Review tells us that the test will establish a worst-case scenario as a prelude to developing the tools necessary to prevent it from coming to that in the real world.
The AN/SPY radar system sends out its pulses between 2 and 4 GHz, avoiding a few bands between the two. This test is interested in the 100MHz-wide band from 3550MHz to 3650MHz, which is used for 4G in the UK (by our little-discussed fifth network operator UK Broadband) but is only used for satellite transmissions in the USA.
If the radar and LTE could coexist then it would open up those additional bands to 4G telephony, assuming potential interference won't result in anyone being accidentally blown up.
With the application of techniques developed for White Space radio the two systems should be able to share the band without ever colliding, but it's still important to know what would happen if they did.
Radar uses massive bands of radio, but generally within limited geographic regions; everywhere else it should be possible to fill those bands with consumer radio signals. The situation is similar to the TV bands, which are tracked by databases that feed locally-empty frequencies to devices requesting them. A mistake in White Space allocation will only take out some TV signals – not a missile-defence system – so a degree of caution is necessary.
The US certainly want to see more spectrum shared and is pouring money into finding ways to do that. Coexistence with AN/SPY-1 in particular is the focus of a four-year project at Virginia Tech's Hume Centre, which in 2011 secured well over a million dollars from the Office of Naval Research to look into it. However, the cash grant is being shared with the Shared Spectrum Company.
But that should cover the cost of next week's jaunt to Wallops Island as the White Space paradigm of sharing radio spectrum expands across the dial, forcing even the mighty US Navy to make space for streaming cat videos. ®