Talk about a high-capacity wireless network. Researchers at DARPA this week will detail a program - with over $18.3 million in funding behind it - that looks to develop wireless communications links capable of supporting 100 Gb/sec capacity at ranges of 125 miles for air-to-air links and about 62 miles for air-to-ground links from an altitude of 60,000 ft.
From DARPA: The goal of the 100 Gb/s RF Backbone (100G) Program is to design, build and test an airborne-based communications link with fiber-optic-equivalent capacity and long reach that can propagate through clouds and provide high availability. Additionally, the system will provide an all-weather (cloud, rain, and fog) capability while maintaining tactically-relevant throughput and link ranges. Size, weight, and power will be limited by the host platforms, which will primarily be high-altitude, long-endurance aerial platforms.
"Backbone communications networks rely on high-capacity links to interconnect the major nodes of the network and to handle the aggregated voice, video, internet, and enterprise data flows. Our nation's telecommunication infrastructure relies heavily on single-mode optical fiber as the data backbone. However, our military can't rely on a fixed infrastructure for deployed operations and instead needs a means of projecting fiber-optic-equivalent capacity anywhere within the area of responsibility.
A logical approach is to use free-space optical (FSO) links to project the capacity. FSO links have been shown to have fiber-optic-equivalent capacity at long ranges and are expected to play a significant role in the implementation of the military's airborne-based data backbone. However, FSO links can't propagate through clouds, which are present 40% of the time in some regions and lead to unacceptable network availability," DARPA stated.
DARPA researchers said potential technology to increase wireless system capacity could include:
- Multiple independent channels, such as spatial multiplexing, polarization multiplexing, and/or orbital angular momentum; some of which require multiple antenna apertures.
- Increased system bandwidth, which usually requires moving to higher frequencies where atmospheric losses can reduce link performance.
- Spectrally-efficient modulation, such as quadrature amplitude modulation, which requires increasing the signal power in order to achieve the signal-to-noise ratio required to demodulate the signal.
The 100G program comprises three phases. Phase 1 will focus on technology development, maturation, and characterization leading to their incorporation into a prototype system in subsequent phases. Phase 2 will develop prototype 100G transceivers and integrate them into aircraft and fixed ground sites. Phase 3 will focus on final prototype development and flight tests involving air-to-air and air-to-ground configurations.
What if your wireless communications just absolutely, positively have to be heard above the din of other users or in the face of massive interference?
The 100G program is the second major wireless move the research agency will make this month. DARPA is expected to detail its Spectrum Challenge - a $150,000 competition that aims to find developers who can create software-defined radio protocols that best use communication channels in the presence of other users and interfering signals.
High priority radios in the military and civilian sectors must be able to operate regardless of the ambient electromagnetic environment, to avoid disruption of communications and potential loss of life. Rapid response operations, such as disaster relief, further motivate the desire for multiple radio networks to effectively share the spectrum without requiring direct coordination or spectrum preplanning. Consequently, the need to provide robust communications in the presence of interfering signals is of great importance, DARPA stated.
DARPA says the Challenge is not focused on developing new radio hardware, but instead is targeted at finding strategies for guaranteeing successful communication in the presence of other radios that may have conflicting co-existence objectives. The Spectrum Challenge will entail head-to-head competitions between your radio protocol and an opponent's in a structured test bed environment. In addition to bragging rights for the winning teams, one team could win as much as $150,000, the agency stated.
"The Spectrum Challenge is focused on developing new techniques for assured communications in dynamic environments - a necessity for military and first responder missions. We have created a head-to-head competition to see who can transmit a set of data from one radio to another the most effectively and efficiently while being bombarded by interference and competing signals," said Dr. Yiftach Eisenberg, DARPA program manager in a statement. "To win this competition teams will need to develop new algorithms for software-defined radios at universities, small businesses and even on their home computers."
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