Decoding method and apparatus

#The present invention is directed to a method and apparatus for decoding data that has been encoded by conventional concatenated block and convolutional encoding. The method and apparatus provide improved system performance in the presence of pulsed and continuous interference. Error correction of conventionally encoded data is improved, and the overhead rate (number of code/parity bits) is not increased.

#Forward Error Correction (FEC) is a common method of achieving data transmission with low error rates. FEC coding techniques transmit data in encoded form by encoding the data with added redundancy or parity data, which is used by a decoding device to detect and correct errors introduced during transmission or passage of the data between a source and a destination. Generally, data does not have to be retransmitted to correct errors.

#The ability of FEC systems to correct errors without retransmission makes them suitable for use in satellite communications systems. Many satellite communications systems use a conventional form of FEC coding; concatenated Viterbi and Reed Solomon coding. Convolutional encoding with Viterbi decoding is capable of correcting disperse, scattered errors, as caused, for example, by white noise. Reed Solomon (block) coding is capable of correcting limited-size burst errors, as caused, for example, by pulsed noise. In combination, concatenated convolutional and Reed Solomon coding improve system performance in the presence of pulse and scattered interference. Nevertheless, communications systems using such coding that are near multiple or high duty cycle radars often suffer from performance degradation. There is a need for a mitigation technique that allows FEC coding systems to compensate for pulse error patterns, as for example, are typically introduced by multiple interfering and/or high duty cycle radars.

#FIG. 1 shows a conventional Forward Error Correction (FEC) coding system.

#FIG. 2 shows a detailed version of a conventional FEC decoder 14.

#FIG. 3 shows a decoding unit 60.

#Before discussing the invention in detail, the operation of a conventional system will be described. FIG. 1 shows a conventional Forward Error Correction (FEC) coding system. Data input 10 is passed to an FEC encoder 12. The FEC encoder 12 includes a first encoder 16, and a second encoder 18. The first encoder 16 and the second encoder 18 perform concatenated linear FEC encoding. The first encoder 16, sometimes called the outside encoder, is typically a block encoder. The data input 10 is block encoded by the first encoder 16, whose output is passed to the second encoder 18. The second encoder 18, sometimes referred to as the inner encoder, typically performs convolutional encoding of the data output by the first encoder 16. The convolutionally and block encoded data 20 is output by the FEC encoder 12.

#The FEC encoded data 20 is transferred across a data transfer path 22. The data transfer path 22 is typically a radio transmission link, a data network path, a databus, etc. Noise is typically introduced in the data transfer path, which makes reception of the correct data difficult. A storage device, such as a digital optical storage disk, may also be used as a data transfer path 22. In such a case, FEC encoded data 20 is stored on the disk, and is read from device and passed to an FEC decoder 14.

#The FEC decoder 14 is equipped with a first decoder 24 and a second decoder 26. The first decoder 24, often referred to as the inner decoder, decodes the FEC encoded data 20 with a decoding process corresponding to the encoding performed by the second encoder 18. Output of the first decoder 24 is processed by the second decoder 26, also known as the exterior decoder. The second decoder 26 performs a decoding process corresponding to the encoding performed by the first encoder 16. The resulting FEC decoded data output 28 is approximately equal to the data input 10, where effects of noise added to the FEC encoded data 20 introduced during transfer across the data transfer path 22 are mitigated by either the first decoder 24 or the second decoder 26. Perfect error correction is not generally guaranteed, and some bits in the decoded data output 28 may not equal their counterparts in the data input 10.