Communication method and apparatus
In a frame sync method, a receiver searches for the presence of an N-symbol long unique word pattern. For each possible frame sync detected, the receiver proceeds to demodulation and FEC processing. After each iteration of the FEC decoder, the detected unique word pattern is compared to the expected one and the frame sync is detected if the number of unique word errors has decreased.
1. A method of generating a frame of forward error corrected data, comprising:
receiving data;
convolutionally encoding said data together with a synchronisation pattern, wherein said synchronisation pattern is input before said data is input, so as to generate, in a first encoding step, a first encoded output which is dependent on the synchronisation pattern and independent of the data and, in a second encoding step, a second encoded output which is dependent on said data, wherein said second encoding step includes interleaving said data together with the synchronization pattern;
convolutionally encoding the output of the interleaving step in parallel with the first encoding step; and
generating said frame of forward error corrected data from said output of the encoding step and from said synchronisation pattern in unencoded form.
2. A method according to claim 1 , wherein the encoding step begins from a predetermined initial state before the data and synchronisation pattern are encoded.
3. A method according to claim 1 or 2 , including puncturing some of the second encoded output so that it is not included in said generated frame, while including all of said first encoded output in said generated frame.
4. A method according claim 3 , wherein said synchronisation pattern comprises at least one of the bit patterns of the hexadecimal numbers E4564ADA, BED8B3EA, F2F5F496, C9113642, F9A42BB1, D4E35729, 4CB9D9D1, 6AAF7A6E, AE7E4BB5, 514BB8BA, B5896CCD, A87B0DA6, 5A1A679D, 61FEA549, A32AD281, 775D1B05 and DFB2880E.
5. Apparatus for generating a frame of forward error corrected data, comprising:
a convolutional encoder arranged to encode data together with a synchronisation pattern, wherein the encoder is arranged such that said synchronisation pattern is input to the convolutional encoder before said data is input, so as to generate as output a first encoded output from a first convolutional encoder which is dependent on the synchronisation pattern and independent of the data and a second encoded output from a second convolutional encoder which is dependent on said data;
a frame generator; and
a bit interleaver arranged to interleave the data and the synchronization pattern;
wherein said second convolutional encoder is arranged to encode the data output from the bit interleaver; and
wherein the frame generator is arranged to generate said frame of forward error corrected data from the output of said first and second encoders and from said synchronization pattern in unencoded form.
6. Apparatus according to claim 5 , wherein the encoder is arranged to begin encoding the data and synchronisation pattern from a known state.
7. Apparatus according to claim 5 or 6 , wherein said frame generator is arranged to puncture selected portions of the second encoded output so that it is not included in said generated frame, while including all of said first encoded input in said generated frame.
8. Apparatus according to claim 7 , wherein said synchronisation pattern comprises at least one of the bit patterns of the hexadecimal numbers E4564ADA, BED8B3EA, F2F5F496, C9113642, F9A42BB1, D4E35729, 4CB9D9D1, 6AAF7A6E, AE7E4BB5, 514BB8BA, B5896CCD, A87B0DA6, 5A1A679D, 61FEA549, A32AD281, 775D1B05 and DFB2880E.