Analysis and optimization of low-earth-orbit communication links

We have completed the development and testing of an algorithm for modeling, analyzing, and optimizing physical aspects of individual laser links in a low-earth-orbit (LEO) communication system. Called NETLINK, the algorithm provides a highly parametrized test bed for confirming system requirements and exploring design alternatives. Although NETLINK is currently configured as a probability processor that computes and propagates probabilities and statistical parameters directly, with minor modifications it can serve as a Monte Carlo simulator where only individual random samples are processed. A simplified form of the algorithm is also intended as a prototype for producing onboard real-time link performance predictions that will be required at the network level to achieve optimal routing and configuration protocols. Our NETLINK software is implemented in the C language, in which network nodes are conventionally represented as structures. These are used to account for detailed dynamic, geometric, and statistical attributes of individual network nodes and for various random and systematic (bias) errors in the associated acquisition, tracking, and pointing (ATP) system. To achieve both mathematical rigor and computational efficiency, we incorporated advanced numerical techniques. We have obtained useful results with NETLINK. For example, a laser peak power of about 40 watts seems adequate to achievemore » a link reliability of 0.999 (i.e., a message error rate of 0.001) over a communication range of 10 to 2000 km. Moreover, link reliability inside the acceptable range interval also appears better than currently believed. Our results also show that on-line detector threshold optimization is both practical and useful, although it is not necessary if communication distances are limited to the interval 20 to 200 km, in which the optimal threshold is 2960 counts. In using the algorithm to optimize message header structure, we found the optimal header length to be four frames.« less