Site: Lincoln Laboratory
Wood Street
P.O. Box 73
Lexington, MA 01776
http://www.ll.mit.edu

Date Visited: March 20-21, 1997

WTEC: William T. Brandon (report author), John Evans

Hosts:

BACKGROUND

The Lincoln Laboratory Communications Division has conducted a continuous program in communications research since about 1950. The focus of the research, development, and demonstrations has been for military applications, with emphasis on satellite and space communications since about 1960. The program has accomplished many firsts in technology, including the first solid state geostationary satellite, first microwave null-forming satellite antenna, first communications satellite crosslink, first processing repeater, pioneering use of UHF and EHF, leadership in frequency hop waveforms, small terminals and optical satellite crosslink technology. The Lincoln Experimental Satellites (LES) series of satellites, largely built with technology produced in the laboratory, has demonstrated extreme reliability and long life on orbit. The LES8 and LES9, launched in 1978 and powered by radioisotope thermal electric generators, are still operational. The program has spawned many advances in devices, instruments, and techniques, as well as communications applications, theory and experimental implementation of systems. The program features an annual review by the laboratory's Joint Advisory Committee (JAC). Formerly attended by government personnel only, the JAC Seminar has been made available to industry since 1993. This report is a description of the portions of the 1997 JAC Seminar of direct relevance to the WTEC study. The Seminar consists of lectures and tours of experimental facilities; some of the relevant topics and lecturers are identified above.

The laboratory's expertise in optical communications grew from the advanced development of an optical crosslink package for satellite communications applications. While this technology has not been flown in space, it represents the world's most advanced performance in terms of data rate and data rate per weight. Changes in the military environment and growth in fiber optic communications have encouraged extending the optical communications program to include advanced fiber optic terrestrial networks. This work is expressed through a collaborative testbed network with Digital Equipment Corporation, Massachusetts Institute of Technology and Lucent Technologies. Military interests in scalability, interoperability, security and advanced networks are mirrored in similar needs for commercial applications; and the need to extend fiber seamlessly via satellite is similarly of critical interest to both military and commercial communities. The defense communications infrastructure will increasingly be integrated with commercial systems; consequently, it is imperative that the communications program embrace fiber.

While the focus of this WTEC study is on satellite communications, and reporting on the laboratory's program in this area alone would facilitate preparation of a more succinct site report, one of the most striking and potentially significant aspects of the activity is its treatment of the entire communications realm in a holistic and integrated way. The program recognizes the parallel explosive growth in fiber optic terrestrial networks, wireless communications, local area networks, long haul transmission, security and computer technologies, and investigates the vision of an interconnected "seamless web of interoperable communication and information networks." In framing its (size-constrained) program to address many critical problem areas of this vision, the division testifies to an optimism that this vision can be reached. Indeed, it is the integration and engineering for interoperability—considering and using existing systems as well as very new breakthrough technology—that is likely to provide the greatest gains towards global, ubiquitous connectivity. Hence, the program seeks to extend the application of MILSTAR (military) satellite communications by introducing the (commercial) teleport concept; prototyping a UHF paging concept; and also addressing certain improvements through application of optical processing (e.g., control of phased array satellite receive antennas for uplink interference rejection).

Activity in optical terrestrial networks is based on SONET high speed standards combined with wavelength division multiplexing (WDM), envisioned to achieve ultimately wide area networks and trunking capacities of over 100 Tbps. Complementary activity in all-optical time division multiplexed channels operating at 100 Gbps is directed towards low latency, metropolitan area networks, soliton propagation, short pulse sources, optical buffering and switching. Moreover, the protocol and security issues in interconnecting such networks are recognized and addressed in architectural studies.

Advanced EHF

The project in advanced EHF (44/20 GHz) includes studies and component development to advance the capacity, throughput and interconnection of EHF satellite communications with other media. Activities address system transition problems associated with block changes to the space segment, global broadcast transponders, advanced signal processing, use of EHF terminals as teleports, integration with terrestrial networks, EHF protocols, and worldwide paging implementation. An advanced EHF testbed that includes satellite and terminal emulation is used to investigate performance of concepts developed in the studies.

In the area of interference rejection uplink antennas, prior work had achieved 40 dB cancellation over a 2 GHz bandwidth at C-band in a two channel nuller; recent work has shown that translation of this approach to Q-band (44 GHz) is feasible for a seven channel nuller, with similar performance demonstrated.

References

Barry, Richard A. 1996. WDM and TDM All-Optical Network Architectures. Optical Society of America Annual Meeting.

Chan, Vincent W. 1997. Global Information Network. Annotated lecture notes.

Figucia, Robert J. and Don M. Boroson. A System Architecture for the MILSTAR Teleport.

Marek, Todd C. 1996. MILSTAR Communications Gateway. Proceedings, IEEE MILCOM96, MS-11688.

MIT Lincoln Laboratory. 1993. MIT Lincoln Laboratory—Technology In the Public Interest. Cambridge, MA.

Niessen, Charles W. 1996. Tactical Communications via Airborne Nodes. Lincoln Laboratory JAC Seminar, March 20, 1997; see also "High Altitude UAV-Based Military Communications Services," Proceedings of AIAA 16th International Communications Satellite Systems Conference, vol.2, p. 841ff., Washington.


Published: December 1998; WTEC Hyper-Librarian