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routing of data based on priority, latency, etc) flows. This means that the systems will be net-centric and
that network services like C2, data management and flow control, etc., will have to be integrated into the
systems and concepts of operations. In-flight entertainment and finance-based systems will not handle
these issues well for military applications. The personal information services providers might provide
technology paths forward, but major portions of the government will need to invest in the net-centric
solutions required by the U.S. Government. One way of addressing bandwidth and spectrum constraints
is by re-using certain communications paths in new ways (e.g. tactical radios used as orderwires for
directional links, tightly coupled RF backup links for free space optics (lasercomm), etc.).
Communications technologies might be repartitioned to address apertures, RF Front ends, software
defined modems/bandwidth efficient waveforms, multiple signals in space, crossbanding, digital
interfaces, new communications approaches (e.g. free space optics), and hybrid approaches.
4.2.1
4.2.2
Data Links
Airborne data link rates and processor speeds are in a race to enable future UA capabilities. Today, and
for the near-term, the paradigm is to relay virtually all airborne data to the ground and process it there for
interpretation and decision-making. Eventually, onboard processing power will outstrip data link
capabilities and allow UA to relay the results of their data to the ground for decision making. At that
point, the requirement for data link rates in certain applications, particularly imagery collection, should
drop significantly. Meanwhile, data compression will remain relevant as long as band-limited
communications exist, but it is unlikely compression algorithms alone will solve the near term throughput
requirements of advanced sensors. A technology that intentionally discards information is not the
preferred technique. For now, compression is a concession to inadequate bandwidth.
In the case of radio frequency (RF) data links, limited spectrum and the requirement to minimize airborne
system size, weight, and power (SWAP) have been strong contributors for limiting data rates. Rates up to
10 Gbps (40 times currently fielded capabilities) are considered possible at current bandwidths by using
more bandwidth-efficient modulation methods. At gigahertz frequencies however, RF use becomes
increasingly constrained by frequency congestion. This is especially true for the 1-8 GHz range which
covers L, S, and C bands. Currently fielded digital data links provide an efficiency varying between 0.92
and 1.5 bps/Hz, where the theoretical maximum is 1.92.
Airborne optical data links, or lasercom, will potentially offer data rates two to five orders of magnitude
greater than those of the best future RF systems. However, lasercom data rates have held steady for two
decades because their key technical challenge was adequate pointing, acquisition, and tracking (PAT)
technology to ensure the laser link was both acquired and maintained. Although mature RF systems are
viewed as lower risk, and therefore attract investment dollars more easily, Missile Defense Agency
funding in the 1990s allowed a series of increasingly complex demonstrations at Gbps rates. The small
apertures (3 to 5 inches) and widespread availability of low power semiconductor lasers explains why
lasercom systems typically weigh 30 to 50 percent that of comparable RF systems and consume less
power. The smaller apertures also provide for lower signatures, greater security, and provide more jam
resistance.
Although lasercom could surpass RF in terms of airborne data transfer rate, RF will continue to dominate
at the lower altitudes for some time into the future because of its better all-weather capability. Thus, both
RF and optical technology development should continue to progress out to 2025.
Network-Centric Communications
There are several areas of networking technology development that should be identified as critical to the
migration path of UAS and their ability to provide network services, whether they be transit networking
or stub networking platforms. Highflying UAS, such as the Global Hawk or Predator, have the ability to
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provide coverage that lends itself well to network backbone and transit networking applications. In order
to provide these services, the networked communications capabilities need to migrate to provide capacity,
stability, reliability and rich connectivity/interoperability options. The following technologies are
essential to this development:
􀂾 High Capacity Directional Data links
􀂾 High capacity routers with large processing capacity - Ruggedized IP enabled Wideband Routers
　
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