On the Next-Generation High Throughput Satellite Systems With Optical Feeder Links

Next-generation multibeam high throughput satellite (HTS) systems aim at achieving Terabits/s throughputs with thousands of spot beams. Conventional radio frequency (RF) Ku-/Ka- band feeder links, between gateways and satellites, are unable to achieve such throughputs due to limited spectrum availability in these bands. Free space optical (FSO) feeder links present a promising alternative to RF feeder links and have gained increased attention lately in the satellite community. This article presents performance analysis of multibeam HTS systems where the feeder link operates in the FSO band and the user link, between the satellite and the user terminal, is in the RF Ka-band. We consider that the FSO feeder link is impaired by the scintillation fading due to atmospheric turbulence and the RF Ka-band user link is attenuated by the rain fading. In multibeam HTS systems, frequency reuse in the user link creates interbeam interference (IBI) due to overlapping side lobes of the multibeam antenna radiation pattern. Considering a forward link with a fixed gain transparent satellite payload, we use the zero-forcing precoding technique to mitigate IBI in the user link. We derive exact and approximate statistics of the end-to-end signal-to-interference-and-noise ratio. Also, by capitalizing on these results, we analyze information-theoretic metrics including the outage probability and ergodic capacity. Our results provide various important insights, e.g., 1) outage performance and ergodic capacity is typically restricted by rain fading in the RF link, and 2) outage diversity of rain fading in the RF link is 0, hence outage performance only increases marginally with power at high signal-to-noise ratio.