Internet-based radio waveforms that facilitate the US network-centric warfare strategy may soon be splintered into separate technologies for air- and ground-based applications, requiring planners to consider interoperability issues for a core level of the network.
Two such communications channels are now in development -Wideband Networking Waveform (WNW) and Tactical Targeting Network Technology (TTNT).
WNW is a key development project within the Boeing-led Joint Tactical Radio System (JTRS) Cluster 1, focusing on army ground systems, but the waveform is also the designated baseline for all aircraft with internet protocol (IP)-based network connectivity. The Rockwell Collins-developed TTNT waveform emerged more recently, under a contract with the US Defense Advanced Research Projects Agency (DARPA), attracting interest from the US Air Force and Navy.
Both waveforms have separate development tracks, but it is likely the air force and navy will eventually choose just one, says Maj Steve Waller, DARPA's TTNT programme manager.
For aircraft, it is the new waveform that truly enables the concept of network-centric warfare. By 2020, Link 16 will be an archaic reminder of a network that cannot operate like the internet. It cannot send voice and data messages simultaneously and cannot transmit video. To sign on to a Link 16 net may take up to 35min. Data transmission rates range from 28Kb/s to 1.13Mb/s and bandwidth supply starts fading as the demand grows for new nodes.
In 1997, US military officials began pursuing software-defined radio technology - JTRS - that allows each user to serve as an IP router and can communicate using any of at least 32 waveforms, including Link 16 and the WNW.
In the original plan, the WNW is designed to provide up to 5Mb/s on an IP-based channel. Its users would be spread across the battlespace, from ground vehicles to naval vessels to aircraft. Anywhere from 50 to 75 users would be on a WNW network at any one time, although it can expand to hundreds of users. However, the aviation community has long harboured concerns about latency delays and range limitations for WNW networks, which they suspect are optimised for the army's ground-based requirements.
By contrast, TTNT is intended to provide network access to any user within 10s, versus up to 1min for the WNW. Its connectivity rates would offer double the throughput of the WNW, expanding to 10Mb/s out to 185km (100nm), and lower rates out to 555km, says Waller. The increased sign-on and transmission speeds are better suited in an aviation battlespace that covers hundreds of kilometres. In addition, latency delays must be small as guided weapons and UAVs are added to the ConstellationNet strategy within a decade.
TTNT's higher speeds have attracted interest from autonomous refuelling and UAV developers including the Joint Unmanned Combat Air System and the Joint Precision Approach Landing System. TTNT has been under way for three years, having just completed Phase 2 of the DARPA programme. The agency selected Rockwell Collins as prime contractor for Phase 3 development. The current focus is to make TTNT compliant with the software-compliant architecture standard, allowing it to be added to the list of waveforms supported by JTRS. Waller says TTNT would require some hardware development, but could be packaged to slot into a JTRS radio. In parallel, air force and navy officials are forming a draft requirement for a TTNT-like, IP-based waveform for aircraft. TTNT prime Rockwell Collins suggests that TTNT and WNW can avoid interoperability problems.
STEPHEN TRIMBLE & GRAHAM WARWICK / WASHINGTON DC
Source: Flight International
