Communication system employing turbo codes and a hybrid automatic repeat request scheme
View Patent ↗A communications system employs a HARQ method and, for at least some transmission formats, incremental redundancy (IR) signals. For such formats, the multiple IR signals are derived from a single turbo encoded signal by forming multiple permutations of the encoded signal. The permutations are then converted to the coding rate of the selected transmission format. It is demonstrated by simulation that the present proposal achieves a better performance than the known HARQ techniques, while its implementation is simpler. For certain transmission formats, the transmitted signal in response to a retransmission request is identical to the first transmitted signal.
1. A method of transmitting a message comprising:
(i) receiving a selection of a transmission format from a predetermined plurality of transmission formats associated with a corresponding coding rate, whereby a selected format is obtained;
(ii) generating from the message a first version of encoded data having a first coding rate;
(iii) permuting said first version to obtain a plurality of further versions of said data also having the first coding rate, said plurality of further versions comprising systematic bits and parity bits;
(iv) converting one of said plurality of further versions to a second coding rate, wherein during the conversion, the systematic bits are punctured, the second coding rate being the corresponding coding rate of the selected format, and transmitting, in the selected format, a first signal generated from the converted version;
(v) in response to a retransmission request, if the selected format is one of a predetermined subset of the formats, retransmitting, in the selected format, the first transmitted signal; and
(vi) in response to a retransmission request, if the selected format is not one of a predetermined subset of the formats, retransmitting, in the selected format, a further signal generated from another of said plurality of further versions and having said second coding rate.
2. A method according to claim 1 in which said plurality of further versions are stored at the first coding rate and one of the stored versions is converted to the second coding rate upon receipt of each retransmission request.
3. A transmitter for use in a communication system, the transmitter comprising:
(i) means to register a selection of one of a plurality of predetermined transmission formats, each associated with a corresponding second coding rate;
(ii) an encoder for receiving a message and using the message to generate a first version of encoded data having a first coding rate;
(iii) a permutation unit for permuting said first version to obtain a plurality of further versions of said encoded data also having the first coding rate, said plurality of further versions comprising systematic bits and parity bits and at least one of said plurality of further versions being arranged such that, during conversion to a second coding rate in a rate matching unit, the systematic bits are punctured;
(iv) a rate matching unit for converting data at the first coding rate to the corresponding coding rate of the selected format; and
(v) a signal transmission unit for receiving the output of the rate matching unit and transmitting a corresponding signal, in the selected format; and
the transmitter being arranged to transmit a first signal, in the selected format, derived from one of said versions, and, in response to a retransmission request, if the selected format is one of a predetermined subset of formats, to retransmit the first signal, in the selected format, and in response to a retransmission request, if the selected format is not one of a predetermined subset of formats, to transmit a further signal, in the selected format, generated from another of said plurality of further versions.
4. A transmitter according to claim 3 comprising a buffer for storing said plurality of further versions at the first coding rate and for transmitting a selected one of said plurality of further versions to the rate matching unit upon receipt of a retransmission request.
5. A communication system including at least one transmitter comprising:
(vi) means to register a selection of one of a plurality of predetermined transmission formats, each associated with a corresponding second coding rate;
(vii) an encoder for receiving a message and using the message to generate a first version of encoded data having a first coding rate;
(viii) a permutation unit for permuting said first version to obtain a plurality of further versions of said encoded data also having the first coding rate, said plurality of further versions comprising systematic bits and parity bits and at least one of said plurality of further versions being arranged such that, during conversion to a second coding rate in a rate matching unit, the systematic bits are punctured;
(ix) a rate matching unit for converting data at the first coding rate to the corresponding coding rate of the selected format; and
(x) a signal transmission unit for receiving the output of the rate matching unit and transmitting a corresponding signal, in the selected format; and
the transmitter being arranged to transmit a first signal, in the selected format, derived from one of said versions, and, in response to a retransmission request, if the selected format is one of a predetermined subset of formats, to retransmit the first signal, in the selected format, and in response to a retransmission request, if the selected format is not one of a predetermined subset of formats, to transmit a further signal, in the selected format, generated from another of said plurality of further versions;
and at least one receiver adapted to receive signals from the transmitter and reconstruct messages from them.
6. A receiver for reconstructing a message from encoded signals, the encoded signals being transmitted by a transmitter comprising:
(i) means to register a selection of one of a plurality of predetermined transmission formats, each associated with a corresponding second coding rate;
(ii) an encoder for receiving a message and using the message to generate a first version of encoded data having a first coding rate;
(iii) a permutation unit for permuting said first version to obtain a plurality of further versions of said encoded data also having the first coding rate, said plurality of further versions comprising systematic bits and parity bits and at least one of said plurality of further versions being arranged such that, during conversion to a second coding rate in a rate matching unit, the systematic bits are punctured;
(iv) a rate matching unit for converting data at the first coding rate to the corresponding coding rate of the selected format; and
(v) a signal transmission unit for receiving the output of the rate matching unit and transmitting a corresponding signal, in the selected format; and
the transmitter being arranged to transmit a first signal, in the selected format, derived from one of said versions, and, in response to a retransmission request, if the selected format is one of a predetermined subset of formats, to retransmit the first signal, in the selected format, and in response to a retransmission request, if the selected format is not one of a predetermined subset of formats, to transmit a further signal, in the selected format, generated from another of said plurality of further versions;
the receiver including:
a decoder for decoding signals having a first coding rate;
a signal reception unit for receiving signals at a second coding rate;
a rate dematching unit for converting the received signals from the second coding rate to the first coding rate; and
a permutation unit for permuting the converted signals and passing them to the decoder;
wherein the permutation unit is operative to permute successive received signals representative of a single message in differing ways.
7. A method of reconstructing a message from encoded signals, the encoded signals being transmitted by a transmitter comprising:
(i) means to register a selection of one of a plurality of predetermined transmission formats, each associated with a corresponding second coding rate;
(ii) an encoder for receiving a message and using the message to generate a first version of encoded data having a first coding rate:
(iii) a permutation unit for permuting said first version to obtain a plurality of further versions of said encoded data also having the first coding rate, said plurality of further versions comprising systematic bits and parity bits and at least one of said plurality of further versions being arranged such that during conversion to a second coding rate in a rate matching unit, the systematic bits are punctured;
(iv) a rate matching unit for converting data at the first coding rate to the corresponding coding rate of the selected format; and
(v) a signal transmission unit for receiving the output of the rate matching unit and transmitting a corresponding signal, in the selected format; the transmitter being arranged to transmit a first signal, in the selected format, derived from one of said versions, and in response to a retransmission request, if the selected format is one of a predetermined subset of formats, to retransmit the first signal, in the selected format, and, in response to a retransmission request, if the selected format is not one of a predetermined subset of formats, to transmit a further signal, in the selected format, generated from another of said versions;
the method using a receiver comprising a decoder for decoding signals having a first coding rate; a signal reception unit for receiving signals at a second coding rate; a rate dematching unit for converting the received signals from the second coding rate to the first coding rate; and a permutation unit for permuting the converted signals and passing them to the decoder; wherein the permutation unit is operative to permute successive received signals representative of a single message in differing ways, the method comprising the steps of:
receiving multiple encoded signals, the multiple encoded signals being derived from the message and having a second coding rate;
converting the received signals from the second coding rate to the first coding rate; and
permuting one or more of the converted signals; and passing the converted signals, including the permuted signals, to the decoder.
8. A method according to claim 1 , wherein each of said plurality of further versions comprises systematic bits, first parity bits and second parity bits.
9. A method according to claim 8 , wherein at least one of said plurality of further versions is arranged such that during conversion to a second coding rate in (iv), the systematic bits and the first parity bits are punctured and the second parity bits are not punctured.
10. A method according to claim 8 , wherein at least one of said plurality of further versions is arranged such that during conversion to a second coding rate in (iv), the systematic bits and the second parity bits are punctured and the first parity bits are not punctured.
11. A transmitter according to claim 3 , wherein each of said plurality of further versions comprises systematic bits, first parity bits and second parity bits.
12. A transmitter according to claim 11 , wherein at least one of said plurality of further versions is arranged such that, during conversion to a second coding rate in a rate matching unit, the systematic bits and the first parity bits are punctured and the second parity bits are not punctured.
13. A transmitter according to claim 11 , wherein at least one of said plurality of further versions is arranged such that, during conversion to a second coding rate in a rate matching unit, the systematic bits and the second parity bits are punctured and the first parity bits are not punctured.