Mitigating Environmental Effects on Free-Space Laser Communications

Abstract

Robust link margin stability is critical to maintaining successful laser communications at long range through the atmosphere. Laser power impinging on the receiver must sufficiently exceed all noise for adequate link closure and bit determination. Losses associated with statistical terms can heavily reduce received signal power, which will cause the bit error rate (BER) to rise. A high BER can lead to unacceptable data loss. Large statistical losses are manifested in platform jitter, and atmospheric scintillation. It is essential for system performance that these combined losses are represented as accurately as possible. A detailed picture of system dynamics is achieved through combining numerical simulation of these two terms and including the mitigating influence of forward error correction (FEC) and interleaving. Trade space analysis is performed that incorporates platform jitter, atmospheric fades and various FEC-interleaver combinations. A sensitivity analysis is shown that illustrates the affects of various signal to noise ratios (SNR) on BER and how link efficiency can be increased through these mitigating techniques. FEC-interleaver combinations show a two order of magnitude decrease in BER when implemented