be implemented corresponding to other rotations for instance in systems having more or different axes of symmetry in the signal constellation where such rotations are meaningful if synchronisation is lost during reception this 34 constellation rotate 34 function described above is repeated until a match is detected it will be appreciated that 34 constellation rotate 34 could equally be implemented using a single stored eprom signal with the constellation being physically rotated by signal multiplication as is well known the inventive method encompasses any rotational technique and may be implemented in association with block convolutional trellis or other codings as required in particular applications an illustrative circuit is illustrated in overall block form in fig5 and detailed block diagrams of the inventive system in fig6 fig5 illustrates the transmission and reception components of the modem 50 in overview the embodiment illustrated is in the context of a supergroup modem using a 1024 point qam system particularly adapted for undersea cables this particular application is described in more detail in co pending australian patent application no 72095 91 raw g703 format data enters the transmitter stage 52 and is processed by the transmitter forward error correction txfec unit 60 this unit performs outer scrambling encodes the data preferably via concatenated reed solomon fec encoders inner scrambles the resulting output and encodes the output as complex data points in a 1024 point qam constellation the data rate of the resulting i and q components is then increased via interpolating filters and output to modulator 70 modulator 70 processes the i and q channels to produce an analog g233 output signal for transmission the received g233 signal enters the receiver stage 51 receiver input unit 100 amplifies and bandpass filters the incoming signal and.