The frequency spectrum is of vital importance to the military; many warfighting systems including radars, communications and other sensors depend on unfettered access to spectrum for their successful operation in combat. Spectrum also enhances the quality of life for military personnel; like many Americans, they depend on access to broadband for their cellphones and other electronic devices.
But spectrum is a finite resource and continues to be in great demand by the private sector. The wireless industry projects exponential growth in mobile data demand. The spectrum needs of upcoming bandwidth-intensive applications will also contribute to increased demand. The federal government has already committed to making an additional 500 MHz of federal and non-federal spectrum below 6 GHz available by 2020. But some industry sources are forecasting a need for even more available spectrum.
To meet growing industry demands, the federal government and Department of the Navy (DON) can expect continued pressure to vacate or share more of the spectrum frequency bands. In general, industry preference is for an exclusive license for a band. But presidential memoranda and the President’s Council of Advisors on Science and Technology (PCAST) recognize that clearing and reallocating federal spectrum is not a sustainable basis for spectrum policy due to the high cost, lengthy time to implement, and disruption to the federal government mission. Thus, sharing spectrum is preferred.
The Federal Communications Commission (FCC) has also endorsed sharing, and has rolled out a new technology to share the recently available 3.6 GHz band. The Defense Advanced Research Projects Agency (DARPA) is also developing two sharing technologies that show promise in bands below 6 GHz.
Many critical DON systems operate in bands below 6 GHz. Examples include the Joint Tactical Information Distribution System (JTIDS) that operates in the 1 to 2 GHz L-band, and the Navy’s air and missile defense combat systems (AN/SPY-1 and SPY-6) that operate in the 2 to 4 GHz S-band.
In response to a proposed band reallocation, the DON must determine the systems that are operating in the band of interest and their characteristics. The resulting analysis would lead to one of three recommendations. First, the band should be protected from sharing or vacating. Second, the band should be protected from vacating but sharing may be possible. Third, it’s possible or even desirable to vacate the band.
Spectrum Supply and Demand
But how valid is the perceived shortage of broadband spectrum capacity, or supply? If the forecast shortage is overstated, there should be less pressure on the DON and other federal organizations to reallocate more spectrum frequency bands to the broadband industry. Adding more spectrum is only one way to increase supply, or capacity. There are two other ways to increase wireless spectrum supply: adding more cell sites (“densification”) and improving the spectral efficiency of existing technology.
Densification increases capacity by distributing users among a larger number of sites, thus accommodating more simultaneous users. The shift is described as moving “from cell towers to street poles,” and all the wireless carriers are spending heavily to increase the number of cell sites. New technologies are also increasing spectral efficiency, often measured as bits per second per hertz. High-speed wireless technology 4G LTE+ is twice as efficient as 4G, and 5G is projected to provide an increase of three times in capacity and speed over 4G LTE+.
Other technological advances are also increasing capacity. One is multiple-input multiple-output (MIMO) antenna technologies that increase throughput, system capacity and spectral efficiency, reducing fading and improving resistance to interference, according to Gartner Research. MIMO has been described as being as revolutionary to spectrum efficiency as fracking has been to the oil industry.
Forecasting the future is usually problematic, and wireless traffic demand is no exception. In 2010, the FCC predicted a 275 MHz spectrum deficit by 2014. But a subsequent analysis in 2014 actually uncovered a surplus of 298 MHz! One leading company’s annual forecast is widely regarded as the expert source for wireless information. But many industry experts have criticized the accuracy of its forecasts.
There may well be no near-term shortage of spectrum for commercial wireless use. Continuing technological improvements and densification are both increasing capacity. The wave of the future is to share rather than vacate spectrum, and current and future advances will facilitate greater sharing. Nevertheless, the DON will continue to be under pressure to vacate or share spectrum that it’s currently using.