Lab Implementation of 10Gbps/channel Optical Transmitter Diversity Scheme for Geostationary Satellite Feeder Links Ahmad Mustafa, Dr. Dirk Giggenbach, Dr. Juraj Poliak, Amita Shrestha, Dr. Ramon Mata-Calvo, Christian Fuchs German Aerospace Center (DLR), Institute of Communications and Navigation, Oberpfaffenhofen, Germany Contact: ahmad.mustafa@dlr.de Abstract Free-space optical (FSO) communications is an attractive alternative to microwave technology in geostationary (GEO) communication satellite feeder link applications, due to the possibility of transmitting information with high data rate, small antenna size, secure communication, and no spectrum licensing requirements. However, optical links through the atmosphere suffer from scintillation effects caused by index of refraction turbulence of the air. It aggravates stable sig- nal detection in the uplink scenario. The benefits of transmitter diversity to mitigate the fading effects in the uplink GEO feeder link are verified by the recently conducted ArtemEx measurement campaign using unmodulated optical beams. In this paper, the lab implementation of the transmitter diversity technique using a 10Gbps data signal and using measured fading vectors from the ArtemEx campaign is presented. 1 Introduction Many space applications such as Geostationary Commu- nication Satellite Systems will require more than 1Tbps throughput in future. This is difficult to achieve with tra- ditional RF technology as it is approaching the capacity limits and more than 40 ground stations would be re- quired. High-speed optical feeder links can solve this data link bottleneck as optical carrier frequencies, with their higher bandwidths, offer throughput higher than Tbps us- ing Dense Wavelength Division Multiplexing (DWDM) technology [1]. Moreover, because of high directivity, beam tapping is almost impossible and no governmental licensing fee is required to use the optical spectrum. It makes FSO communications an ideal candidate to over- come the limitations of RF transmission systems. However, the performance of optical communication links is highly dependent on the weather conditions. Se- vere weather conditions like clouds can have a detri- mental impact on the performance of the transmission systems which has to be recovered by large scale Ground Station Diversity. One of the main challenges in the long- haul optical links through the atmosphere is turbulence, which is a random process. The laser beam propagating through the atmosphere suffers from scintillation effects caused by the index of refraction turbulence of the air. In ground to satellite links these effects are more dominant in the uplink signal than in the downlink. Spatial diversity is a beneficial method to mitigate the fading on the optical signal. Figure 1 shows a realization of the spatial diversity scheme. By placing two or more transmitter telescopes at moderate spatial separation on ground, the turbulent paths are de-correlated and the fad- ing effects on the uplink signal are reduced using standard diversity schemes. Figure 1: Spatial diversity scheme with two transmitters in a GEO feeder uplink In this paper, the implementation of transmitter diversity using one data signal with data rate R b =10Gbps and a wavelength division scheme with two wavelengths in a GEO feeder uplink is presented. The German Aerospace Center’s Institute of Communica- tions and Navigation is pursuing research in a number of different projects in this context including downlink and uplink applications [2], [3]. 2 Transmitter Diversity Scheme Figure 2 describes the transmitter diversity scheme with wavelength division multiplexing (WDM). The two opti- cal transmitters are fed by the same 10Gbps data signal. The frequency separation between the two optical signals is 50GHz. This minimum separation is kept to avoid opti-