Feedback error control system

Claim 2

In a data transmission system having a transmitting terminal, a receiving terminal, and a source of information sequences, a method of correcting errors in transmitted data comprising the steps of encoding information sequences into an (n,k) error-correcting block code. generating a flag prefix for each code block indicating whether or not the block contains previously transmitted information, transmitting each block with its corresponding flag prefix from said transmitting terminal to said receiving terminal, replacing erroneous information previously received and stored at the receiving terminal with the parity section of the most recently received code block if the flag prefix of said most recently received block indicates that the block contains previously transmitted information, coding the information section of said most recently received block into a data word of <k digits and in accordance with a second code, and transmitting said data word to said transmitting terminal.

Claim 3

A method as in claim 1 further comprising the steps of decoding the most recently received code block at the receiving terminal to determine if the number of errors in the block is within the error-correcting capability of said (n,k) block code, and correcting errors in the information section of said most recently received code block if it is determined that the number of errors in the block is within the error-correcting capability of the (n,k) block code and if the flag prefix of the block indicates that the block does not contain previously transmitted information.

Claim 4

if the flag signal indicates that the block''s parity bits have not been replaced, (a) correcting the errors in the block if such errors are correctable, generating a parity word in accordance with said second code for the corrected information bits, and transmitting such parity word to the receiving terminal, or (b) detecting the errors in the block if such errors are detectable and not correctable and transmitting to the transmitting terminal, a word requesting retransmission of the block, comparing, at the transmitting terminal, the word received from the receiving terminal with a parity word previously generated by the transmitting terminal for said transmitted block and in accordance with said second code, and replacing the parity bits of subsequently transmitted blocks with the information bits of the block in question if the words compared do not match.

Claim 5

if the flag signal indicates that the block''s parity bits have not been replaced, (a) correcting the errors in the block if such errors are correctable, generating a parity word in accordance with said second code for the corrected information bits, and transmitting such parity word to the receiving terminal, or (b) detecting the errors in the block if such errors are detectable and not correctable and transmitting to the transmitting terminal, a word requesting retransmission of the block, comparing, at the transmitting terminal, the word received from the receiving terminal with a parity word previously generated by the transmitting terminal for said transmitted block and in accordance with said second code, and replacing the parity bits of subsequently transmitted blocks with the information bits of the block in question if the words compared do not match.

Claim 6

A method as in claim 2 further comprising the step of inverting said data word prior to its transmission thereof if it is determined that the number of errors in said most recently received code block is not within the error-correcting capability of said (n,k) block code and if the flag prefix of said most recently received code block indicates that the block does not contain previously transmitted information.

Claim 7

A method as in claim 3 further comprising the steps of coding, at the transmitting terminal, said information sequences into data words of <k digits in accordance with said second code, comparing the data word received from the receiving terminal with the corresponding data word which shall have been generated at the transmitting terminal from the same information sequence from which said received data word was generated, and if the data words compared differ by a predetermined amount, replacing the parity sections of the most recently encoded block and certain subsequently encoded blocks with different portions of the information sequence from which said data words were generated, generating a first flag prefix for the most recently encoded block indicating that said block contains previously transmitted information, and transmitting said first flag prefix and said most recently encoded block to said receiving terminal.

Claim 8

A method as in claim 4 further comprising the steps of generating a second flag prefix for the most recently encoded block if the data words compared do not differ by said predetermined amount, said second flag prefix indicating that said block does not contain previously transmitted information, and transmitting said second flag prefix and said most recently encoded block to said receiving terminal.

Claim 9

A method as in claim 5 further comprising the steps of encoding the data word generated at said receiving terminal into a code word of a third code prior to transmission thereof to said transmitting terminal, and decoding said encoded data word at said transmitting terminal to correct errors therein.

Claim 12

A method as in claim 7 wherein the step of transmitting a word requesting retransmission comprises the steps of generating a parity word for the information bits of the block, inverting the bits of said parity word, and transmitting the inverted parity word to the receiving terminal.

Claim 13

A method as in claim 8 further comprising the steps of encoding the parity word or inverted parity word, as the case may be, at the receiving terminal into a code word of a third code prior to transmission thereof to the receiving terminal, and decoding said encoded parity or inverted parity word at the transmitting terminal to correct errors therein.

Claim 14

In a data transmission system having a transmitting terminal, a receiviNg terminal, and a source of information sequences, said transmitting terminal comprising means for encoding said sequences into an (n,k) block code, where k/n < (b- 1)/b and b is an integer, means for storing (b- 1)l of the most recently encoded blocks, where l is an integer designating the constraint length of the system, means for encoding said sequences into first data words of <k digits in accordance with a second code, means for comparing each of said first data words with a corresponding second data word received from the receiving terminal, said second data word having been generated at the receiving terminal in accordance with said second code from the same information sequence from which the corresponding first data word was generated, said same information sequence having been transmitted to the receiving terminal, means responsive to signals from said comparing means for replacing the parity sections of the block most recently encoded into said (n,k) block code and various like subsequently encoded blocks with different portions of the information sequence transmitted l blocks previously in response to a first outcome from comparing the first and second data words generated from such sequence, flag insertion means responsive to said first outcome for generating a flag prefix for said most recently encoded block indicating that the block contains previously transmitted information, and means responsive to signals from said flag insertion means for transmitting each block with its corresponding flag prefix to said receiving terminal.

Claim 15

In a data transmission system having a transmitting terminal, a receiviNg terminal, and a source of information sequences, said transmitting terminal comprising means for encoding said sequences into an (n,k) block code, where k/n < (b- 1)/b and b is an integer, means for storing (b- 1)l of the most recently encoded blocks, where l is an integer designating the constraint length of the system, means for encoding said sequences into first data words of <k digits in accordance with a second code, means for comparing each of said first data words with a corresponding second data word received from the receiving terminal, said second data word having been generated at the receiving terminal in accordance with said second code from the same information sequence from which the corresponding first data word was generated, said same information sequence having been transmitted to the receiving terminal, means responsive to signals from said comparing means for replacing the parity sections of the block most recently encoded into said (n,k) block code and various like subsequently encoded blocks with different portions of the information sequence transmitted l blocks previously in response to a first outcome from comparing the first and second data words generated from such sequence, flag insertion means responsive to said first outcome for generating a flag prefix for said most recently encoded block indicating that the block contains previously transmitted information, and means responsive to signals from said flag insertion means for transmitting each block with its corresponding flag prefix to said receiving terminal.

Claim 16

A system as in claim 10 wherein said flag insertion means further comprises means responsive to a second outcome from said means for comparing for generating a different flag prefix for the most recently encoded block indicating that the block does not contain previously transmitted information.

Claim 17

A system as in claim 11 wherein said comparing means comprises means for generating a resultant word indicating the difference between each pair of compared first and second data words, a threshold detector means for generating a first signal when said difference exceeds a certain predetermined threshold value for generating a second signal when said difference does not exceed said predetermined threshold value, and a first error tracer unit for storing the (b- 1)l signals most recently generated by said threshold detector means and having b- 1 output taps, the input signals to said first error tracer unit appearing at the mth output tap thereof at a time equal to the time necessary to transmit ml blocks minus the round trip transmission delay time of the system, where m 1,. . ., b- 1.

Claim 18

A system as in claim 12 wherein said replacing means comprises retransmission storage means for storing the most recent information sequence from said information source and n- k other digits, logic means responsive to a said first signal on the mth output tap of said first error tracer unit for transferring the mth portion of k/(b- 1) digits of the mlth block stored in said block storing means to said retransmission storage means, where mlth block indicates mlth most recently stored block in said block storing means, and means for applying said most recent information sequence and said mth portion of the mlth block to said transmitting means.

Claim 19

A system as in claim 10, said receiving terminal comprising means for receiving blocks transmitted by said transmitting terminal, means for storing the information sections of the (b- 1)l blocks most recently received, a flag prefix decoder for generating a ''''1'''' output signal in response to the flag prefiX of the most recently received block indicating that the block contains previously transmitted information and for generating a ''''0'''' output signal in response to such flag prefix indicating that the block does not contain previously transmitted information, and means responsive to the ''''1'''' output signal of said prefix decoder for replacing a portion of the information section of the block received l blocks previously with the parity section of said most recently received block and various subsequently received blocks.

Claim 20

A system as in claim 14 further comprising means for coding the information section of the most recently received block into a second data word of <k digits and in accordance with said second code, and means for transmitting said second data word to said transmitting terminal.

Claim 21

A system as in claim 15 further comprising means for decoding the most recently received block to determine if the number of errors in the block is within the error-correcting capability of said (n,k) block code, and means responsive to a ''''0'''' output signal from said flag prefix decoder and to said block decoding means determining that the number of errors in the most recently received block is within the error-correcting capability of said (n,k) block code for correcting errors in the information section of said most recently received block.

Claim 22

A system as in claim 16 further comprising means responsive to a ''''0'''' output signal from said flag prefix decoder and to said block decoding means determining that the number of errors in the most recently received block is not within the error-correcting capability of said (n,k) block code for inverting said second data word prior to transmission thereof to said transmitting terminal.

Claim 23

A system as in claim 17 further comprising means at said receiving terminal for encoding said second data word into a code word of a third code prior to transmission thereof to said transmitting terminal, and means at said transmitting terminal for correcting errors in said encoded second data word.

Claim 24

A system as in claim 18 wherein said receiving terminal replacing means comprises a second error tracer unit for storing the (b- 2)l output signals most recently generated by said flag prefix decoder and having b- 1 output taps, the jth such tap being from the jlth signal position from the input of said second error tracer unit, said input constituting the 0th such tap, where j 0,. . ., b- 2, and a logic circuit responsive to a ''''1'''' signal on the jth tap of said second error tracer unit for applying the parity section of the most recently received block to the jth group of k/(b-1) digit position of the jlth section of k digit positions in said (b- 1)l block storing means, where the jlth section contains the jlth most recently stored information section.

Claim 25

A system as in claim 19 further comprising an l-bit storage unit, means responsive to ''''0'''' signals being stored in every lth position of said second error tracer unit and to said block decoding means determining that the number of errors in the most recently received block is not within the error-correcting capability of said (n,k) block code for applying a ''''1'''' signal to said l-bit storage unit and responsive to a ''''1'''' signal stored in one of the jlth positions of said second error tracer unit or to said block decoding means determining that the number of errors in the most recently received block is within the error-correcting capability of said (n,k) block code for applying a ''''0'''' signal to said l-bit storage unit, and means responsive Either to a ''''1'''' output signal from said flag prefix decoder or to a ''''1'''' signal stored in the lth position of said l-bit storage unit for applying a ''''1'''' to said second error tracer unit, where said lth position contains the earliest received signal of the l signals currently stored in said l-bit storage unit.