# Cooperative Reception of Multiple Satellite Downlinks
## 4 Conclusions  
In conclusion, the traditional satellite-to-ground station communication system is highly vulnerable to outages and not in favor of the new generations of wireless communications trends since its performance is significantly degradable when the data rate is high and the received signals are deeply faded. In addition, a ground station in such single radio link can only track one satellite at a time through steerable high-gain antenna. The unexpected mechanical failures of the antenna rotator then create another cause of outages.  
To avoid the consequences of such circumstances, the receive diversity combining was recommended to significantly improve the satellite downlink reception quality. This work proposed a network of ground stations with affordable omnidirectional antennas instead of the high-gain antennas to cooperatively receive multiple replicas of the same downlink signal to be demodulated and then combined. Combining multiple independent and uncorrelated copies of a satellite downlink signal based on maximum likelihood helped reduce detection errors. Deploying the proposed cooperative reception scheme on 14 separate omnidirectional ground stations created sufficient diversity gain to compensate the lesser receiving antenna gain and hence achieved significant reduction in the BER for the combined stream. The combined stream achieved lesser ED to the original data if compared to all other received versions. The suggested combining algorithm neither requires SNR calculations nor involves weightings. However, additional three improvement techniques that require quality metrics were examined and can be utilized for further improvement. Excluding the worst stream in the combining matrix reflected better system performance. Replacing the worst stream with the best stream imposed more weight of the less corrupted signal version and consequently performed even better. The best algorithm was when always tailing the best candidate into the combining matrix which significantly improved the system performance, achieving zero detected errors at the six sites combining trial. The algorithms were tested against different data lengths and showed great scalability with reasonable processing elapsed times.  
The presented cooperative reception scheme of the omnidirectional ground stations along with the virtual combining platform can achieve lower BER with less required \(E_{b}/N_{o}\), track more than a satellite at once, extend the communication window, provide resistance against outages, exploit the available online open source SDR networks for streaming the data out through the Internet, and offer to replace the expensive directive antennas and their steering engines with much affordable omnidirectional antennas.  
H.N.A.-A. and [PERSON] have contributed evenly to this article. All authors have read and agreed to the published version of the manuscript.  
This research has been supported by SGS-2021-005--internal fund at the University of West Bohemia in Pilsen under project name Research, development, and implementation of modern electronic and information systems.  
Not applicable.  
The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Data Length** & **Worst Excluded** & **Worst Replaced** & **Best Tailed** \\ \hline \(1\times 10^{6}\) 1 & 9.439559 & 10.967350 & 19.539677 \\ \(1\times 10^{5}\) & 0.948979 & 1.131833 & 2.061516 \\ \(1\times 10^{4}\) & 0.108183 & 0.130703 & 0.256498 \\ \(1\times 10^{3}\) & 0.043260 & 0.050263 & 0.056976 \\ \(2\times 10^{6}\) & 18.795995 & 21.877629 & 38.563990 \\ \hline \hline \end{tabular}  
* Denotes the used data length in this study.  
\end{table}
Table 2: Elapsed time in (sec.) taken by the algorithms to combine 14 streams.