Design and implementation of 1GbpsLaser Ethernet Transceiver (LET) for Free-Space Optical communications

Abstract: Free Space Optical (FSO) communications are an emerging technology. Multiple resources around the world are being dedicated to the study and implementation of associated technologies. The possibility of high data rates, lower masses and more power efficient antennas are the expected advantages of these systems. However FSO channels are highly vulnerable. Atmospheric perturbations as well as pointing misalignments compromise the integrity of the transmitted data. Besides, current data protection architectures for FSO communication systems are not powerful enough to protect the data due to the nature of the perturbations. Therefore, Deutsches Zentrum für Luft- und Raumfahrt (DLR) is working on the implementation of a communication protocol (Laser Ethernet Transceiver protocol, LET) capable of transmitting high bit rates reliably. LET has to overcome the multiple errors induced by the disturbances in the channel (fades in the signal induced by the atmosphere and miss-pointing) and data stream misalignments during transmission. In addition, LET has to provide a framework for transmitting 1GbE (Gigabit Ethernet) payloads. Thus the focus of this MSc Thesis is on the definition and implementation of the abovementioned algorithms and hardware structures. These hardware structures are developed for their integration on Field Programmable Gate Arrays (FPGA) in VHDL language. At the end of this MSc Thesis, a significant improvement of 3.5 dB in the optical gain has been achieved with a Bit-Level Forward Error Correction (BLFEC) implementation. Some of the hardware structures have also been implemented and tested for the next steps. An analysis of the synchronization problems that will affect the system has been done and a technical solution has been provided. Additionally, an improvement of the channel throughput has been achieved in order to comply with the 1GbE Standard.