Interference Management Using Cooperative NOMA in Multi-Beam Satellite Systems

In this paper, we propose overlay coding scheme as the capacity achieving multiple access technique, i.e., transmitting over non-orthogonal channels. We employ the cooperative non-orthogonal multiple access (NOMA) in multi-beam satellite systems with dense frequency reuse. The overlay coding uses the cooperation of the strongest co-channel interference (CCI) as extra source of information, where the data intended for the target user is shared between the cooperating beams. The involved beams cooperate in jointly transmitting the data to the target user at the same time. Thus, the target user receives a signal containing the aggregate of the data streams from cooperating beams, similar to a multiple access channel (MAC). Our proposition is based on the duality theorem of MAC and broadcast channels (BC) capacity regions. Hence, by employing successive interference cancellation (SIC), both data could be recovered, as proposed in NOMA. In order to employ overlay coding in multibeam satellite systems, we propose an approach based on optimized user pairing strategies. We devise an information theoretic framework followed by simulation to compare different strategies by evaluating the aggregate data rate in the beam of interest. Being based on SIC, the existence of residual errors will degrade the spectral efficiency gain in overlay coding. We investigate the effect of channel signal to noise plus interference ratio (SNIR) estimation errors. Finally, it is verified by simulation that these issues can be overcome and overlay coding can reach expected data throughput very close to the cases with perfect channel estimation.