Towards the Terabit/s satellite – interference issues in the user link

Abstract

Present high-capacity geostationary satellites provide throughput in the range of 70 Gb/s (Ka-Sat) up to 140 Gb/s (ViaSat-1, EchoStar 17). In order to keep up with the quickly increasing bit rate requirements of new services and applications, future communication satellites must increase their capacity by an order of magnitude, thus reaching the terabit/s throughput range. The challenge of achieving a terabit/s satellite system requires investigation of a multitude of issues, limitations and problems. This paper discusses the main interference effects occurring in the user uplinks and downlinks of a multi-beam satellite: co-channel interference, adjacent-channel interference and cross-polarisation interference. Different cluster sizes for the beam pattern and use of dual polarisations are considered, and an optimum cluster scheme with regard to throughput is discussed in more detail. Moreover, the influence of beam spacing, interference cancellation for the user uplink as well as rain fading for the uplink and downlink are discussed. For the satellite spot beam antenna, a typical tapered antenna characteristic with side lobes is considered. The investigation is based on Monte Carlo simulation of user positions within the beam pattern, resulting in CDFs of signal-to-noise-plus-interference power ratio and capacity. Besides Shannon capacity, the achievable throughput of Digital Video Broadcasting - Return Channel over Satellite, 2nd Generation (DVB-RCS2), Digital Video Broadcasting over Satellite, 2nd Generation (DVB-S2) and Digital Video Broadcasting over Satellite, 2nd Generation, Extension (DVB-S2X) is evaluated. Considering 200 beams and 1 GHz of bandwidth, it is shown that with efficient uplink and downlink schemes, a total throughput of 1 Tb/s can be approached.