# Cooperative Reception of Multiple Satellite Downlinks
###### Abstract  
Popular small satellites host individual sensors or sensor networks in space but require ground stations with directional antennas on rotators to download sensors' data. Such ground stations can establish a single downlink communication with only one satellite at a time with high vulnerability to system outages when experiencing severe channel impairments or steering engine failures. To contribute to the area of improving the reception quality of small satellites signals, this paper presents a simple receive diversity scheme with proposed processing algorithms to virtually combine satellite downlink streams collected from multiple omnidirectional receivers. These algorithms process multiple received versions of the same signal from multiple geographically separated receiving sites to be combined in one virtual ground station. This virtual ground station helps detect the intended signal more reliably based only on a network of simple and cooperating software-defined radio receivers with omnidirectional antennas. The suggested receive diversity combining techniques can provide significant system performance improvement if compared to the performance of each individual receiving site. In addition, the probability of system outages is decreased even if one or more sites experience severe impairment consequences. Simulation results showed that the bit error rate (BER) of the combined stream is lower than the BER of the best quality receiving site if considered alone. Moreover, virtual ground stations with cooperative omnidirectional reception at geographically separated receivers also allow data to be received from multiple satellites in the same frequency band simultaneously, as software-defined receivers can digitize a wider portion of the frequency band. This can be a significant conceptual advantage as the number of small satellites transmitting data grows, and it is reasonable to avoid the corresponding necessary increase in the number of fully equipped ground stations with rotators. c 20  
factors [4]. Spatial diversity can be configured at the transmitter, receiver, or even at both sides with multiple antenna arrangements [4]. Numerous publications on multiple-input multiple-output (MIMO) systems have been surveyed in [5] to provide a recapitulated document for newly interested researchers in such promising field. This study, however, focused on the receive diversity technique and how it enhances the wireless system performance without any required modifications at the transmitter side. To catch up with the requirements of new generations' communications as well as the new technology trends, lots of research has been conducted to investigate and utilize the advantages of spatial diversity in general and receive diversity in specific. Receive diversity is a widely deployed antenna configuration in MIMO technology applications [6]. For instance, the navigation precision is improved through receive diversity combining to provide high accuracy location data to the autonomous driving cars [7]. Capable and professional ground stations can utilize a dual-channel global navigation satellite system (GNSS) receiver to receive dual-frequency signals simultaneously as presented in [8] to improve the location accuracy. It was shown in [9] that applying receive diversity combining at the analog feedback communication system (AFCS) improved the power bandwidth efficiency and reduced the detected errors. The same study suggested that such communication system with receive diversity would reach the required error threshold with less iterations compared to the single receiver system. To improve the system performance in the presence of multiple interferers, two models of receive diversity combining were presented in [10] to decrease the error rate.