Detailed Description
In the LTE system, in order to improve the performance and throughput of the system, the data transmission generally adopts the HARQ transmission mechanism. HARQ is a communication scheme that combines Forward Error Correction (FEC) with automatic repeat Request (ARQ).
The specific process is as follows: the sending end carries out error correction coding processing on the data, the receiving end carries out error correction decoding according to a certain algorithm, successful response information is fed back after the decoding is successful, and otherwise, failed response information is fed back. And the sending end transmits a new data packet or retransmits the failed data packet sent before according to the fed-back successful response information or the fed-back failure information. If a new data packet is sent, the receiving end caches the soft information before decoding. If the data packet which is sent before retransmission fails, the receiving end combines the cached soft information with the newly received soft information before decoding, and then the combined soft information is cached as new soft information, and then decoding is carried out on the combined soft information.
The following describes in detail a HARQ soft combining method and apparatus based on an LTE system according to an embodiment of the present invention with reference to the accompanying drawings.
Fig. 1 is a flowchart of a HARQ soft combining method based on an LTE system according to an embodiment of the present invention.
Referring to fig. 1, in step S101, a threshold value of transmission effectiveness is selected according to a modulation scheme.
Here, the threshold value for Quadrature Phase Shift Keying (QPSK) Modulation is 0.3, and the threshold values for 16 Quadrature Amplitude Modulation (QAM) and 64QAM are 1.0.
In step S102, a measure of the transmission effectiveness is calculated from the received signal.
Here, the metric includes at least one of the following information: equivalent signal-to-noise ratio, received signal quality, and hard decision accuracy.
In step S103, if the metric is greater than the threshold, the data of different redundancy versions are soft-combined.
Here, in the LTE system, the HARQ transmission employs IR combining and RV, there are four versions of RV, which are 0, 2, 3 and 1, respectively, and the data of different redundancy versions carry different information bits and redundancy bits.
In the LTE system, the conversion of the transport channel into physical information capacity is achieved by a rate matching module. In rate matching, bit selection is to select the corresponding number of bits for transmission according to the physical channel capacity. When selecting bits, the value of the start position needs to be calculated according to the RV value, so as to select the corresponding bit number for transmission.
The solution bit selection is the reverse process of the receiving end. When the receiving end carries out soft combination, after the bit is selected, the data of each version is weighted and combined and then sent to the decoding unit for decoding.
Further, the method further comprises:
if the metric is less than the threshold, the base station requests the user terminal to retransmit the data.
Here, the base station may also request the user terminal to transmit a new data packet.
Further, the soft combining of the data of different redundancy versions includes:
judging the version number of the redundancy version;
if the version number is a first version number, forming a first sequence according to the first version number;
if the version number is a second version number, forming an updated first sequence according to the second version number;
and respectively weighting and combining the weight corresponding to each data segment in the updated first sequence and the weight corresponding to each data segment of the soft information to obtain weighted information.
Here, the first version number is 0, and the second version number is 2 or 3 or 1.
Further, if the version number is a first version number, forming a first sequence according to the first version number includes:
if the version number is the first version number, calculating a value of a first starting position and a value of a first ending position according to the first version number;
the values of the first start position and the first end position are arranged in a first order and constitute the first sequence.
Further, if the version number is a second version number, forming an updated first sequence according to the second version number includes:
if the version number is the second version number, calculating a value of a second starting position and a value of a second ending position according to the second version number;
inserting the values of the second start position and the second end position into the first sequence in the first order, thereby constituting the second sequence.
Here, the first order is arranged in order from small to large. The second version number is 2 or 3 or 1, and the composition of the second sequence can be divided into three cases: the first case is composed of version 0 and version 2; the second case is composed of version 0, version 2 and version 3; the third case is composed of version 0, version 2, version 3, and version 1.
Specifically, the weight corresponding to each data segment in the updated first sequence and the weight corresponding to each data segment of the soft information are respectively weighted and combined to obtain weighted information, which may specifically refer to a schematic diagram of the weighted and combined process provided by the implementation of the present invention as shown in fig. 2. As shown in fig. 2, Softbuffer refers to soft information in the cache, and RV ═ 3 refers to information received when the version number is 3. Firstly, if the version number is 0, calculating the value of a first starting position and the value of a first ending position according to the version number 0, and arranging the two values in the order from small to large so as to form a first sequence; secondly, if the version number is 2, calculating a value of a third starting position and a value of a third ending position according to the version number 2, and inserting the two values into the first sequence from small to large so as to form a third sequence; if the version number is 3, the value of the second start position and the value of the second end position are calculated according to the version number 3, and the two values are inserted into the third sequence from small to large, thereby forming the second sequence.
The second sequence is divided into 7 sample intervals, each sample interval has a corresponding weight, and the sample intervals in the soft information also have corresponding weights, so that the weights corresponding to the sample intervals of the second sequence and the weights corresponding to the sample intervals in the soft information are weighted and combined, and a sample interval 1 to a sample interval 7 can be obtained, wherein the sample interval 1 can be known by a formula (1):
the sample interval 2 is given by equation (2):
the sample interval 3 is given by equation (3):
the sample interval 4 is given by equation (4):
the sample interval 5 is given by equation (5):
A=A (5)
the sample interval 6 is given by equation (6):
fig. 3 is a schematic diagram of a weight updating process according to an embodiment of the present invention.
Referring to fig. 3, by updating the weighting information in the buffer, that is, by updating the weight of each data, it can be seen that when RV is 0, the updated weight corresponding to the sample interval is 0, 1, and 0; when RV is 2, the updated sample interval corresponds to weights of 1, 2, 1, 2 and 1, respectively, where 1 indicates that only 1 version has data, and 2 indicates that two versions have data merged; when RV is 3, the weights corresponding to the updated sample interval are 2, 3, and 2, respectively, where 2 denotes the combination of two version data, and 3 denotes the combination of three version data; when RV is equal to 1, the weights corresponding to the updated sample interval are 3, 4, and 3, respectively, where 3 denotes a combination of three version data and 4 denotes a combination of four version data.
Fig. 4 is a graph illustrating throughput performance versus different levels of random interference according to an embodiment of the present invention.
Referring to fig. 4, the abscissa is signal-to-noise ratio and the ordinate is throughput, which is significantly improved by the present method at a random interference of 20db, and also at a random interference of 40db, as can be seen in fig. 5. Therefore, by calculating the judgment measurement of the transmission effectiveness and comparing the judgment measurement with the threshold value, the data information with strong interference is abandoned, the error transmission caused by the strong interference is avoided, and the throughput of the system under the condition of the strong interference is effectively improved.
Fig. 6 is a schematic diagram of an apparatus for HARQ soft combining based on an LTE system according to an embodiment of the present invention. Referring to fig. 6, the apparatus includes a threshold value selecting unit 10, a metric calculating unit 20, and a soft combining unit 30.
A threshold selecting unit 10, configured to select a threshold of transmission effectiveness according to a modulation scheme.
A metric calculation unit 20, configured to calculate the metric of the transmission effectiveness according to the received signal.
A soft combining unit 30, configured to perform soft combining on the data of different redundancy versions if the metric is greater than the threshold.
Further, the soft combining unit 30 includes:
a determining unit 31, configured to determine a version number of the redundancy version;
a first sequence constituting unit 32 configured to constitute a first sequence according to a first version number when the version number is the first version number;
a second sequence forming unit 33, configured to form an updated first sequence, that is, a second sequence, according to a second version number when the version number is the second version number;
and a weighting and combining unit 34, configured to perform weighting and combining on the weight corresponding to each data segment in the latest first sequence and the weight corresponding to each data segment of the soft information, respectively, to obtain weighted information.
Further, the first sequence composing unit 32 includes:
if the version number is the first version number, calculating a value of a first starting position and a value of a first ending position according to the first version number;
the values of the first start position and the first end position are arranged in a first order and constitute the first sequence.
Further, the second sequence composing unit 33 includes:
if the version number is the second version number, calculating a value of a second starting position and a value of a second ending position according to the second version number;
inserting the value of the second start position and the value of the second end position into the first sequence in the first order and constituting the second sequence.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.