Low complexity multi-channel synchronization for satellite systems with adjacent channel interference

In satellite communications, the space segment is a large slice of the operating costs.Therefore every effort should be made to increase the spectral efficiency, thereby reducing the space segment costs. In order to optimize spectral efficiency, channel spacing (CS) should be reduced. Unfortunately, this introduces spectrally overlapping transmissions, thereby creating adjacent channel interference (ACI), which impairs the performance of satellite communication systems. To overcome this problem, intelligent interference mitigation schemes should be considered. This paper considers the problem of multi-channel synchronization of several spectrally overlapping transmissions in a satellite TDMA/frequency division multiple access burst system.The synchronization aims to estimate carrier frequency, carrier phase and symbol timing in the presence of ACI.The potential performance gain of multi-channel processing over conventional single channel processing is shown. Two types of low-complexity algorithms are proposed: 'channelized' expectation maximization and 'channelized' interference cancellation. Both of these algorithms attain this performance gain. Computer simulations show a 78% improvement in spectral efficiency for a wide range of carrier-imbalance values. This translates into a large potential saving in space segment costs compared to conventional CS.