CN113507306B - Combined judgment method based on longitudinal mutual information - Google Patents
Combined judgment method based on longitudinal mutual information Download PDFInfo
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- CN113507306B CN113507306B CN202110774085.9A CN202110774085A CN113507306B CN 113507306 B CN113507306 B CN 113507306B CN 202110774085 A CN202110774085 A CN 202110774085A CN 113507306 B CN113507306 B CN 113507306B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
- H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
- H04B7/0842—Weighted combining
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
- H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
- H04B7/0842—Weighted combining
- H04B7/0848—Joint weighting
- H04B7/0854—Joint weighting using error minimizing algorithms, e.g. minimum mean squared error [MMSE], "cross-correlation" or matrix inversion
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- H04B7/00—Radio transmission systems, i.e. using radiation field
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- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
- H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
- H04B7/0842—Weighted combining
- H04B7/0848—Joint weighting
- H04B7/0857—Joint weighting using maximum ratio combining techniques, e.g. signal-to- interference ratio [SIR], received signal strenght indication [RSS]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0045—Arrangements at the receiver end
- H04L1/0047—Decoding adapted to other signal detection operation
- H04L1/0048—Decoding adapted to other signal detection operation in conjunction with detection of multiuser or interfering signals, e.g. iteration between CDMA or MIMO detector and FEC decoder
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
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- H04L1/0071—Use of interleaving
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Abstract
The invention belongs to the technical field of communication, and particularly relates to a joint judgment method based on longitudinal mutual information. The method of the invention mainly comprises that when Nr paths of signals are received, nr paths of soft information LLR can be obtained after equalization and demodulation, and one of equal gain combination and combination mode selection is selected as the optimal combination judgment mode by comparing the quality of the Nr paths of received signals. The invention relates to a single carrier frequency domain iterative equalization, space diversity, mutual information joint judgment mode and other principles. The scheme introduces space diversity, performs joint judgment on longitudinal mutual information between SISO equalization and SISO decoding, and can adaptively select one mode of equal gain combination and selective combination according to signal quality so as to improve the performance of the system to the greatest extent.
Description
Technical Field
The invention belongs to the technical field of communication, and particularly relates to a joint judgment method based on longitudinal mutual information.
Background
Diversity combining encompasses two implications: firstly, the receiving terminal can obtain a plurality of fading signals carrying the same information by scattered receiving, namely, the receiving terminal is equivalent to receiving a plurality of signal copies from different array sites; and secondly, the centralized processing is that the receiving end properly combines a plurality of received fading signal copies, thereby reducing the influence of fading and improving the performance of the system.
In the joint decision mode, the weighting coefficients of the longitudinal mutual information are required to be combined, namely diversity combination. When the receiving end receives N r How to jointly process the distributed received signals of the channel to reduce the influence of channel fading requires the introduction of joint decisions. A linear joint decision device is generally adopted to receive N r The independent fading signals are weighted and combined to obtain the output y (t) of the combiner
Wherein a is k For the weighting coefficient of the kth signal, selecting different weighting coefficients can form different diversity combining modes, and common combined judging modes include: equal gain combining, maximum ratio combining, selective combining.
(1) Select merge
The selection combining is to detect all distributed receiving signals and select one path of receiving signal with the highest signal-to-noise ratio as the output of the joint decision device. In the formula (1), only one corresponding coefficient of the combination is selected to be 1, and the other coefficients are all 0, and the decision mode is simple to realize, but the fading resistance is poor because other unselected branch signals are discarded.
(2) Equal gain combining
The equal gain combining is to set the weighting coefficients of the branches to be the same and then add the weighted coefficients. The method superimposes the received signals of all the branches by equal gain, thereby effectively avoiding the influence of deep fading on a single branch by utilizing the mutual independence of the signals of all the branches. After equal gain combination, the signal-to-noise ratio gamma of the system and the signal-to-noise ratio p of each branch signal k In relation, the combined signal-to-noise ratio γ can be expressed as:
when the signal-to-noise ratios of the received signals are the same, the combined signal-to-noise ratio is:
as can be seen from the above, when the signal to noise ratios of the received signals of the branches are similar, the signal to noise ratio gamma of the signal is increased by about N compared with the single-path signal P after equal gain combination r -1 times. If the signal to noise ratio of a certain branch before combining is very low, the same gain combination is carried out on the branchThe influence of low signal-to-noise ratio is amplified, so that the total combined signal-to-noise ratio is reduced, and the error code performance is influenced, so that when the signal-to-noise ratio of one or more paths of signals in the multipath distributed receiving signals is very low, different weighting coefficients can be set, on one hand, the specific weight of the signal with high signal-to-noise ratio can be increased, and on the other hand, the specific weight of the signal with low signal-to-noise ratio is reduced, so that the gain obtained by the score aggregation is optimal.
(3) Maximum ratio combining
The maximum ratio combining is an optimal combining mode, and compared with equal gain combining, the maximum ratio combining utilizes different weighting coefficients to combine the received signals:
the weighting factor of the maximum ratio combining is related to the received signal envelope and the noise power of the path.
Disclosure of Invention
According to the signal quality condition received at the receiving end, the invention flexibly adopts different joint judgment modes for the longitudinal mutual information, thereby improving the sensitivity of the receiver. The invention relates to a single carrier frequency domain turbo iterative equalization, space diversity, longitudinal mutual information joint judgment mode and other principles. The equalizer and the decoder are SISO (soft input and soft output), and according to the definition of soft information, the equal gain combination and the maximum ratio combination have the same effect on the soft information, so the invention only considers the equal gain combination and the selective combination.
The invention introduces space diversity and provides a scheme for adaptively selecting a joint judgment mode for longitudinal mutual information, which is different from a traditional distributed receiver, performs joint judgment for the longitudinal mutual information between SISO equalization and SISO decoding, and can adaptively select equal gain combination or a combination mode according to the quality of multipath signals. The invention realizes mutual information longitudinal joint judgment between the equalizer and the decoder, carries out iterative detection on the SISO equalizer and the SISO decoder, ensures mutual independence of external information and prior information by utilizing the thought of space diversity, exchanges soft information between the equalizer and a single decoder, thereby obtaining iterative gain, also obtaining joint gain of iteration and diversity combination, and improving the performance of a receiver.
The steps of the invention are described in detail:
s1, firstly, each path of signal y [ j ] of Nr paths of signals is received]A priori information of Nr and SISO equalizer
Together feed into equalizer, wherein a priori information +.>
Is the extrinsic information generated by the decoder +.>
Obtained by interleaving. In the first iteration the decoder does not generate extrinsic information, which can be considered a priori +.>
Zero. After passing through the equalizer, the posterior information L is output E (x n ) According to formula (6), use L E (x n ) Subtracting a priori information of the equalizer
Get the external information of equalizer->
Then sent to a de-interleaver to obtain prior information input by a decoder
Thus, it is possible toObtaining priori information of Nr-path decoder
I.e. longitudinal mutual information. Wherein x is n Representing the corresponding coded bits after interleaving c n Indicating the corresponding code bit before interleaving and j indicating the j-th received signal.
S2, according to a formula (7), outputting prior information to each path of interleaver
Is averaged to obtain a [ j ]]. And then, averaging the array a according to the formula (8) to obtain b.
Where N represents the length of each frame data and Nr represents the number of received multipath signals.
S3, setting a threshold value xi, when a 1],a[2],...,a[Nr]Is a value of a [ j ]]When the value is smaller than the xi times of b, the Nr path prior information is obtained
Selecting a [ j ] by selecting a merging mode]Maximum one-path priori information
As the best joint decision output. Otherwise, equal gain combination is carried out on the obtained Nr path prior information according to a formula (9) to obtain the optimal joint judgment output +.>
S4, outputting the optimal joint judgment
Is sent to a decoder to obtain corresponding bit soft information L before coding D (a k ) And bit soft information L corresponding to the coded bit soft information L D (c n )，a k Representing the corresponding bits before encoding. According to formula (10), the bit soft information L corresponding to the code is used D (c n ) Decoder prior information minus joint decision output +.>
Obtain the extrinsic information of the decoder->
Then the external information is sent to an interleaver for interleaving to obtain the prior information which is used for updating the equalizer fed back in the next iteration>
So far one iteration is completed.
The invention is more suitable for practical environment, can ensure that the receiving end fully and effectively utilizes multipath received signals, and improves the error code performance of the system.
Drawings
FIG. 1 illustrates a longitudinal mutual information joint detection scheme
Fig. 2 compares the error performance of two joint decision modes when the quality of a received signal is very poor.
Fig. 3 compares the error performance of two joint decisions when the quality of the two received signals is comparable.
Detailed Description
The technical scheme of the invention is described in detail below with reference to the accompanying drawings and examples:
in this example, nr=2 is set, that is, only two paths of received signals are set, so that error code performance of combining and equal gain combining under different conditions in a short wave channel is simulated. The specific simulation parameters are set as follows:
fig. 1 shows a block diagram of a receiver processing two signals, i.e. two received signals y1, y2 are equalized, soft demodulated and soft descrambled to obtain soft information corresponding to the two signals
And->
Then de-interleaving to obtain two paths of longitudinal mutual information +.>
And->
The two paths of mutual information are combined and judged by adopting an equal gain combination or selective combination mode, so that optimal judgment soft information is obtained>
Feeding the best decision soft information into a decoder to obtain posterior soft information L for decision D (a k ) And encoded corresponding bit soft information L for updating a priori information D (c n ) According to the formula->
Can obtain the external information of decoder output +.>
And after interleaving, feeding back to the equalizer as priori information of the next iteration of the equalizer, and finishing one soft information iteration update.
Fig. 2 compares the bit error rates of the select combining and the equal gain combining when there is a poor signal quality for both signals. The result shows that when the signal-to-noise ratio is low, the combination is better than the equal gain combination mode, because when the quality of a certain branch received signal is poor, if the equal gain combination is adopted, the influence of a signal with poor signal quality is amplified, and the signal-to-noise ratio of the total combined signal is reduced. On the contrary, the receiving signal with the highest signal-to-noise ratio can be effectively selected by adopting selective combination as the output of the joint decision device, so that the influence of the path with low signal-to-noise ratio is avoided.
Fig. 3 compares the bit error rates of the select combining and equal gain combining modes when the signal quality of the two signals is comparable. The results show that equal gain combining is better than the selective combining mode. The reason is that the decision combiner only outputs the strongest received signal of one path, discards other branch signals, and does not effectively utilize information of other branches, so that the decision combiner has no combining gain and has poor fading resistance. And the equal gain combination fully utilizes the information of the multipath signals, so that not only the combination gain is obtained, but also the iterative and combined gain is obtained.
Claims (1)
1. The joint judgment method based on the longitudinal mutual information is characterized by comprising the following steps of:
s1, firstly, each path of signal y [ j ] of Nr paths of signals is received]A priori information of Nr and SISO equalizer
Together feed into equalizer, wherein a priori information +.>
Is the extrinsic information generated by the decoder +.>
Is obtained by interweaving; in the first iteration the decoder does not generate extrinsic information, the prior information is +>
Zero, after passing through the equalizer, the posterior information L is output E (x n ) According to formula (1), use L E (x n ) Subtracting a priori information of equalizer->
Get the external information of equalizer->
Then fed into a de-interleaver to obtain a priori information +.>
Thus, a priori information of the Nr-way decoder is obtained
I.e. longitudinal mutual information, where x n Representing the corresponding coded bits after interleaving c n Representing the corresponding code bit before interleaving, j representing the j-th path of received signal;
s2, according to the formula (2), outputting prior information to each path of de-interleaver
Is averaged to obtain a [ j ]]The method comprises the steps of carrying out a first treatment on the surface of the Then the array a [ j ] is assembled according to the formula (3)]Obtaining a mean value to obtain b;
wherein, N represents the length of each frame data, and Nr represents the number of received multipath signals;
s3, setting a threshold value xi, when a 1],a[2],...,a[Nr]Is a value of a [ j ]]When the value is smaller than the xi times of b, the Nr path prior information is obtained
Selecting a [ j ] by selecting a merging mode]Maximum one-path priori information
As the best joint decision output; otherwise, equal gain combination is carried out on the obtained Nr path prior information according to a formula (4) to obtain the optimal joint judgment output +.>
S4, outputting the optimal joint judgment
Is sent to a decoder to obtain corresponding bit soft information L before coding D (a k ) And bit soft information L corresponding to the coded bit soft information L D (c n )，a k Representing the corresponding bits before encoding, according to equation (5), using encodingBit soft information L corresponding to the latter D (c n ) Decoder prior information minus joint decision output +.>
Obtain the extrinsic information of the decoder->
Then the external information is sent to an interleaver for interleaving to obtain prior information which is used for updating the equalizer and fed back to the equalizer in the next iteration
So far one iteration is completed. />
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