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Distributed Coherent Communications



PROPOSALS ACCEPTED: Phase I and DP2. Please see the 16.2 DoD Program Solicitation and the DARPA 16.2 Direct to Phase II Instructions for DP2 requirements and proposal instructions.


OBJECTIVE: Establish practical approaches to achieve distributed coherent communications between two disaggregated groups of RF communications nodes.

DESCRIPTION: There is a critical Department of Defense (DoD) need to create and exploit distributed coherent communications to enable future defense operations to make greater use of small, disaggregated, collaborative elements in contrast to larger elements. The challenge of communicating between clusters of such nodes becomes more acute as their size, weight, and power is reduced, in all environments (air, ground, maritime). The ability to create and exploit distributed coherent communications can be of great benefit to meeting these challenges. The reason for this is that a phase coherent array of n RF transmitters can enhance the power received at a distant receiver by a factor of n^2 relative to a single radio [1]. If the receiver also contains an array of m elements, a factor of (n^2)m power gain can be achieved in one direction, and (m^2)n in the other direction. In a symmetric system, n^3 gain is possible. For example, a distributed coherent collection of 10 transmitters communicating to 10 receivers can ideally reduce the power required of a single transmitter by a factor of 1000. This project is aimed at maximizing the ability to exploit this phenomena.

In systems that are not physically connected, the separate challenges of 1) phase coherence between the transmitters, 2) RF channel state measurement, and 3) coordinated sharing of the information communicated must be resolved. While topics associated with coherent communications between groups of users and a centralized base station have been considered in the past, the case of communication between two disaggregated groups is more challenging [2,3,4]. Innovative and practically implementable solutions to these challenges are sought such that the size, weight, and power of the communicating clusters is minimized for a given data rate and operating frequency.

PHASE I: Develop an initial concept design and model key elements of all 3 challenges, and analyze the resulting communication systems properties. Phase 1 deliverables shall include a final report that contains design concept and architecture for a group to group communication system; results of simulation and modeling to establish system feasibility; and a plan for an experimental demonstration of a group to group coherent communication system.

PHASE II: Develop and demonstrate the efficacy of a distributed coherent communications system operating between two self-organizing clusters of nodes. An exemplary demonstration would include n airborne nodes over a variety of link ranges exhibiting n^(3/2) range enhancement relative to a single pair of nodes. Such a system will utilize a local network to establish and maintain communicating groups and to coordinate information transmission between the distant groups. A means for establishing and maintaining coherence among participating users and across groups will be developed. Groups of at least 3 members will be shown, with a preferable goal of 10 group members. Groups shall be flexibly assembled and members may join and leave the assembly in an ad hoc fashion. Phase 2 deliverables shall include the demonstration event, the hardware and software used to effect it, and final report describing the results, a comparison to theoretical expectations, identification of steps needed for further maturation of the technology and open issues or challenges to taking them.

PHASE III DUAL USE APPLICATIONS: Emergency responders often have a need to communicate in challenging conditions where conventional cellular communication infrastructure may be damaged or destroyed. In such conditions, the ability to communicate between disparate groups of radio-equipped users may be essential. The use of reach-enhancing techniques may be essential in these conditions.

Ad hoc communicating clusters of airborne nodes can be used to reduce power demands of autonomous unmanned aircraft systems (UAS) swarms or other collections of small disaggregated sensors. In such environments, small, affordable, stand-in platforms may be called upon to communicate results of intelligence, surveillance, and reconnaissance information. The use of distributed coherent group-to-group communications methods may significantly reduce the size, weight, and power burden that would otherwise be required on a single platform. A similar need arises for separated groups of soldiers communicating in austere environments.


  • “MIMO Channel Prediction Results on Outdoor Collected Data,” Patrick Bidigare, D. Brown, S. Kraut, U. Madhow, 2013 Asilomar Conference proceedings.
  • “Massive MIMO for Next Generation Wireless Systems, “E.G. Larsson, O. Edfors, F. Tufvesson, T. Marzetta, IEEE Communications Magazine, Feb. 2014.
  • “Distributed Transmit Beamforming: Challenges and Recent Progress,” R. Mudumbai, D. R. Brown III, U. Madhow, H. V. Poor, IEEE Communications Magazine, Feb. 2009, p. 102
  • “Distributed Transmit Beamforming Using Feedback control,” R. Mudumbai, J. Hespanha, U. Madhow, G. Barriac, IEEE Trans. Information Theory, v.56 (3), 2010, p.411.

KEYWORDS: multiple-input, multiple-output (MIMO), coherent communications, RF systems, data links

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