Method and system for free-field optical transmission by means of laser signals

摘要

The invention relates to a method and system for free-field optical transmission by means of laser signals, including setting a rate for encoding information that is useful for transmission on the basis of variations in a signal receiving characteristic belonging to a single communication session. The encoding rate is preferably dynamically adjusted during the communication session. An optimized compromise is thereby created between a useful rate that is high and a post-decoding bit error rate that is low. The method and the related system enable atmospheric conditions that can disrupt laser signal transmission to be taken into account in real time when said laser signals pass through part of the earth's atmosphere.

主权项

1. A method for free-space optical transmission by means of laser signals, between a first and a second optical communications terminal, wherein time variations are evaluated for a reception characteristic of first laser signals which are received by the first terminal and which originate from the second terminal, and wherein a useful information to be sent by the first terminal to the second terminal is encoded before transmission, the method comprising;
varying an encoding rate of the useful information, in second laser signals transmitted by said first terminal to said second terminal, and adjusting the encoding rate on the basis of time variations in the reception characteristic of the first laser signals, said encoding rate of the useful information in the second laser signals, being defined as a number of bits of the useful information before encoding, divided by the number of bits corresponding to the same useful information after encoding, adjusting said encoding rate of the useful information in the second laser signals according to a decreasing function of an amplitude of the time variations in the reception characteristic of the first laser signals, and selecting the reception characteristic of the first laser signals from among a reception direction of said first laser signals or a deviation between a reception direction of said first signals and an optical axis of the first terminal;
wherein the reception characteristic of the first laser signals received by the first terminal is measured at a measurement frequency greater than 100 Hz, and the amplitude of the time variations in said reception characteristic of the first laser signals is evaluated at an analysis frequency of less than 10 Hz.