With the increasing size and complexity of emerging military communication networks, low footprint emulation methods are required to evaluate protocols, algorithms and user performance. In this paper we describe a new emulation architecture that is scalable, modular, and responds to real-time changes in topology and link characteristics. We use this scalable emulation testbed to evaluate system performance in a simple Satcom network topology, and enhance it to emulate Dynamic Resource Allocation using distributed software architecture.
Laser communications advantages include the lack of optical spectral congestion and frequency allocation requirements, and immunity to electromagnetic interference (EMI), collocated iransmitters and RF jammers. It also offers superb lowprobability-of-detection (LPD) for covert communications compared with line-of-sight RF systems. An atmospheric lasercom link over a 4 km path has been implemented between The MITRE Corporation and Lahey Clinic, Bedford, MA. This testbed employs emerging 1550 nm laser and receiver technology for greatly enhanced covertness and eye safety compared to current 820 nm technology. Supporting testhed equipment provides automated monitoring of link performance, correlated with automated data acquisition of the local visibility and precipitation.This report describes the laser link and supporting testbed equipment under IBM P5/2 computer control in which continuous monitoring of the atmospheric conditions, link bit err rate, pointing jitter, and beam wander are accomplished. The bit error rate drives an automated adaptive data rate modem at one of three data rates, depending on weather conditions. Criteria for operation at 1550 nm, such as trade-offs with regard to atmospheric absorption, covertness and eye safety are presented. Characteristics of our custom designed laser transmitter (laser diode, beam parameters, modulation, etc.), and receiver (optics, detector electronics, bit synchronizer) are described. System alignment procedures and transmission performance as a function of temperature, visibility, and precipitation are presented. Finally, conclusions are stated and recommendations are made for further research efforts.
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