  In the context of satellite communications, random access (RA) methods can
significantly increase throughput and reduce latency over the network. The
recent RA methods are based on multi-user multiple access transmission at the
same time and frequency combined with interference cancellation and iterative
decoding at the receiver. Generally, it is assumed that perfect knowledge of
the interference is available at the receiver. In practice, the interference
term has to be accurately estimated to avoid performance degradation. Several
estimation techniques have been proposed lately in the case of superimposed
signals. In this paper, we present an improved channel estimation technique
that combines estimation using an autocorrelation based method and the
Expectation-Maximization algorithm, and uses Pilot Symbol Assisted Modulation
to further improve the performance and achieve optimal interference
cancellation.
