Joint Turbo Decoding and Carrier Synchronisation

Exploiting Decoder Outputs for Carrier Synchronisation

Satellite communication systems are generally dimensioned for having an excellent downlink performance. However, recently more and more applications like interactive television demand an uplink channel from the terminal via the satellite to the provider's gateway (DVB-RCS standard). Since these terminals have antennas with small diameters, the channel SNR remains rather low. Hence, strong error correcting codes, like Turbo Codes, need to be applied. The downside of Turbo Codes is that they require almost ideal carrier synchronisation at the receiver, which gets the more erroneous the lower the SNR is.

The DVB-RCS standard provides preceding training data before each data burst, a so called preamble, used by the receiver to estimate the channel parameters. As this preamble diminishes the energy efficiency of the transmission by reducing the amount of employed data symbols, it is kept rather short. With this short preamble the receiver is not able to adequately track dynamic channel parameters. Thus, in order to iteratively reduce the estimation errors, it is possible to re-use the soft information provided by the decoder. In this context, convergence must be maintained.

It is our goal to develop a common iterative synchronisation and decoding algorithm and afterwards to extend its applicability to higher order modulations