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.
@cite_5: A first aspect of the invention is a method of transmitting data packets over a transmission channel shared by a plurality of users, based on the time and or frequency diversity slotted Aloha technique, in which at least two replicas of each packet to be transmitted are sent over said transmission channel, wherein each replica transports signaling information enabling the other replica(s) of the same packet to be located in the time and or frequency domain. A second aspect of the invention is a method of recovering packets in the receiver, the method exploiting said signaling information to execute an interference cancellation algorithm for recovering packets corrupted by collisions caused by access conflicts. Other aspects of the invention are a transmitter equipment and a receiver packet recovery equipment adapted to use said methods.
use the method of autocorrelation to estimate channel parameters in @cite_5 . However, @math is chosen so small that it induces negligible phase variation during a time slot. Moreover, @cite_5 takes advantage of clean packets in CRDSA to get a good estimation of @math and @math . Difficulties arise, however, in other random access methods like MuSCA, where finding clean packets in the frame is a rare situation. Note that @cite_5 presents a system adapted to an environment affected by high phase noise.