JP4847372B2 - QRM-MLD control method and system - Google Patents

Description

  The present invention relates to a QRM-MLD control method and system, and more particularly to a QRM-MLD control method and system that improves transmission efficiency in the QRM-MLD scheme.

  In this type of technical field, research and development for realizing high-capacity high-speed information communication at present and the next generation and beyond are underway. For example, in addition to a single input single output (SISO) method, a single input multiple output (SIMO) method, a multiple input single output (MISO) is used from the viewpoint of increasing communication capacity. Research and development are being conducted on the Output (Multiple Output Multiple Output) system and the like.

  FIG. 7 is a diagram showing an overview of a MIMO communication system. In the figure, 102 is a transmitter and 104 is a receiver. A plurality of transmission antennas 106-1 to 106-N are connected to the transmitter 102, and a plurality of reception antennas 108-1 to 108-N are connected to the receiver 104. In the MIMO system, different signals are transmitted simultaneously from the plurality of transmission antennas 106-1 to 106-N at the same frequency. These transmission signals are received by the plurality of reception antennas 108-1 to 108-N.

  Here, for the sake of simplicity, the number of transmitting antennas and the number of receiving antennas are both N, but they may be different. In the receiver 104, processing for separating a plurality of signals from the transmitter 102 into individual signals is performed based on reception signals received by the respective reception antennas. The separated signal is sent to a subsequent processing circuit for further demodulation processing.

  As one of the signal separation methods performed by the receiver 104, there is a maximum likelihood determination method (MLD: Maximum Likelihood Detect). This method calculates the Euclidean distance or its square for all possible combinations of a plurality of transmission signals and reception signals transmitted from a plurality of transmission antennas, and selects a combination of transmission signals that gives the minimum distance. is there.

  In recent years, the QRM-MLD method, which has a relatively small calculation processing load, has been used in view of the large calculation processing load of the MLD method. This method combines the QR decomposition and the M algorithm with the MLD method to reduce the number of square Euclidean distance calculations.

  FIG. 8 is a block diagram showing a configuration example of a conventional system. In the figure, reference numeral 10 denotes a QRM-MLD unit, which includes a channel estimation unit 1, a power measurement unit 2, a rearrangement unit 3, a QR decomposition unit 4, a z calculation unit 5, an MLD unit 6, and a likelihood calculation unit 7. Yes. Reference numeral 8 denotes a plurality of antennas provided at the input stage of the QRM-MLD unit 10. Here, four antennas 8 are shown. This antenna is used for both transmission and reception. 11 is a decoding unit that decodes a signal modulated by receiving an output from the QRM-MLD unit 10, 12 is an uncorrected error measuring unit that receives an output from the QRM-MLD unit 10 and measures an error before correction, 13 Is a corrected error measuring unit that receives the output of the decoding unit 11 and measures the corrected error. The operation of the system configured as described above will be described as follows.

  The channel estimation unit 1 obtains a channel impulse response value (CIR) or a channel estimation value based on a received signal including a known pilot signal on both transmission and reception sides. The subsequent power measurement unit 2 ranks the received signals received in the order of power. The rearrangement unit 3 determines the arrangement order of the plurality of received signals based on the output signal of the power measurement unit 2. The determined arrangement order of the rearrangement unit 3 enters the subsequent QR decomposition unit 4.

The QR decomposition unit 4 obtains the matrices Q and R so that the channel matrix H obtained by the channel estimation unit 1 is represented by the product of the unitary matrix Q and the upper triangular matrix R. The z calculator 5 performs signal conversion by multiplying a vector having a plurality of received signals as components by a conjugate transpose matrix Q ^H of the unitary matrix Q. Here, H represents conjugate transposition.

  The MLD unit 6 receives the output of the z calculation unit 5 and narrows down the symbol candidates of the transmission signal by the maximum likelihood determination method (MLD method). The likelihood calculation unit 7 receives the output of the MLD unit 6 and calculates the likelihood or likelihood of the symbol candidate. The operation of the system configured as described above will be described as follows.

  The receiver receives transmission signals as reception signals y <b> 1 to y <b> 4 by the four reception antennas 8. They are given to the channel estimation unit 1 and the z calculation unit 5. The order of the plurality of received signals is determined by the channel estimation unit 1, the power measurement unit 2, and the rearrangement unit 3. Here, it is assumed that the received signals are arranged in the order of the magnitude of the received power, and for the sake of simplicity, the received power increases in the order of x1, x2, x3, x4. The received signal is converted by the z calculator 5 such that z = (z1, z2, z3, z4) T = QHy, and the converted signal is input to the MLD unit 6.

  In the first stage in the MLD unit 6, processing corresponding to the initial setting is performed. At this stage, paying attention to the equation regarding z4 and z4 depends only on one transmission signal x4, a symbol candidate generation unit (not shown) generates 16 symbol candidates regarding x4. A square Euclidean distance between these symbol candidates and the fourth received signal z4 is calculated by a square Euclidean distance calculation unit (not shown), and S1 symbol candidates are selected as surviving symbol candidates in order of increasing distance. .

  The second stage focuses on the equation for z3. There are 16 types of candidates for x4, and there are 16 types of signal point candidates for x3. Sixteen signal points are introduced by a symbol candidate generation unit (not shown) as new signal points for x3. Therefore, there can be 16 × 16 = 256 combinations of signal points. The 256 square Euclidean distances between these symbol candidates and the third received signal x3 are calculated, and the symbol candidates are narrowed down by selecting 16 (S2 = 16) combinations in ascending order of the values.

  The third stage focuses on the equation for z2. The combinations of the transmission signals x3 and x4 are narrowed down to 16 candidates in the previous stage, and there are 16 signal point candidates for x2. For this reason, a symbol candidate generation unit (not shown) generates 16 symbol candidates related to x2. In this case as well, symbol candidates are narrowed down by selecting 16 (S3 = 16) candidates having a small square Euclidean distance from among 256 combinations of signal points.

  The fourth stage focuses on the formula for z1. The combinations of the transmission signals x1, x2, x3, and x4 are narrowed down to 16 candidates in the previous stage, and there are 16 signal point candidates for x1. For this reason, a symbol candidate generation unit (not shown) generates 16 symbol candidates related to x1. Also in this case, symbol candidates are narrowed down by selecting 16 (S4 = 16) candidates having a small square Euclidean distance from among 256 combinations of signal points.

  In this way, by limiting the number of symbol candidates to a certain number or less at each stage, it is possible to narrow down the symbol candidates of the transmission signal without calculating the square Euclidean distance for all possible combinations of signal points.

  The output of the MLD unit 6 that performs such an operation enters a subsequent likelihood calculation unit 7 where the likelihood is calculated. Here, the likelihood is a function p having x as a variable when a conditional probability density function p of the reception signal y is given to the transmission signal x.

  The output of the likelihood calculation unit 7 enters the decoding unit 11 where the received signal is decoded. The pre-correction error measurement unit 12 receives a signal from the input / output unit of the decoding unit 11 and performs pre-correction error measurement. On the other hand, the corrected error measurement unit 13 receives the output of the decoding unit 11 and measures the corrected error.

As a conventional system of this type, first determination means for sequentially determining symbol candidates of a plurality of transmission signals by a QRM-MLD method using a plurality of reception signals arranged in a first order; Uses a plurality of received signals arranged in a different second order, a second determining means for sequentially determining symbol candidates of a plurality of transmission signals by the QRM-MLD method, and the first and second determining means. A technique for obtaining symbol candidates and likelihoods of a plurality of transmission signals based on the determination result is known (see, for example, Patent Document 1). In addition, an OFDM symbol synchronization circuit having high accuracy in threshold determination of a plurality of signals is known in symbol synchronization detection in OFDM (see, for example, Patent Document 2).
JP 2006-121348 A (paragraphs 0034 to 0058, FIGS. 5 to 7) Japanese Patent Laying-Open No. 2005-318521 (paragraphs 0014 to 0023, FIGS. 3 and 4)

  In the QRM-MLD system described above, when attention is paid to a certain transmission signal, the number of symbol candidates gradually decreases from the first stage to the second stage and the third stage. That is, the transmission signal assigned to the first stage has a reduced number of symbol candidates as compared with the transmission signal assigned to the third stage, and therefore, the probability of missing a true symbol candidate is increased, resulting in deterioration. Cause.

  As described above, the QRM-MLD scheme has a problem in that variations in characteristics occur between transmission signals after channel separation, and as a result, the overall characteristics deteriorate due to being dragged to the most deteriorated signal. In order to suppress this, it is conceivable to control the received power and assign it from the first stage in descending order of power, but it is difficult to correlate with the actual packet error with the received power. There is a problem of falling.

  The present invention has been made in view of such a problem, and can suppress variation with higher accuracy. By using this characteristic, a specific transmission signal can be preferentially communicated and transmitted. An object of the present invention is to provide a QRM-MLD control method capable of improving the efficiency.

(1) The invention according to claim 1 is a MIMO communication in which a transmission signal is transmitted from a plurality of transmission antennas, signals transmitted from a plurality of reception antennas are received, and a transmission signal is reproduced from the plurality of received signals received. In the method, a plurality of received signals rearranged in order of large number of errors after decoding after decoding are used to determine symbol candidates of a plurality of transmission signals using a QRM-MLD method. In the QRM-MLD control method, the order of the rearrangement is switched according to the number of errors after code correction, according to the number of errors before code correction. Select whether to use the rearrangement method or the method of rearranging by switching between the order with the largest number of errors or the order with the smallest number of errors according to the number of errors after code correction. Characterized in that sort in the order in accordance with the error number.
(2) The invention according to claim 2 is a QRM-MLD unit including a channel estimation unit, a power measurement unit, a rearrangement unit, a QR decomposition unit, a z calculation unit, an MLD unit, and a likelihood calculation unit, and the QRM A plurality of antennas provided at the input stage of the MLD unit, a decoding unit that receives the output from the QRM-MLD unit, decodes the modulated signal, and receives the output of the QRM-MLD unit before correction An error measurement unit before correction that measures an error of the error, and an error measurement unit after correction that receives an output from the decoding unit and measures an error after correction, and the error measurement unit before correction or the error measurement unit after correction The rearrangement unit is configured to control the rearrangement by any one of the outputs .

(1) According to the first aspect of the present invention, variation can be suppressed with higher accuracy, and a specific transmission signal can be preferentially communicated using this characteristic, thereby improving transmission efficiency. be able to. Further, according to the present invention, the method of rearranging the order of the rearrangement by switching from the order of the large number of errors to the order of the small number of errors according to the number of errors before code correction is used, or Depending on the number of errors, select the method of rearrangement by switching between the order with the smallest number of errors and select the method of rearrangement, and by rearranging in the order according to the number of errors of the selected one, between all antennas Variations in transmission signals can be suppressed with high accuracy .
(2) According to the invention described in claim 2, it is possible to suppress variation with higher accuracy, and it is possible to preferentially communicate a specific transmission signal by using this characteristic, thereby improving transmission efficiency. be able to. Therefore, according to the configuration of the present invention, variations in transmission signals among all antennas can be suppressed .

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The present invention has a function of rearranging received signals input by the QRM-MLD method, and has one of the following functions in order to determine the arrangement order.
1) Rearrangement is performed in descending order of the number of errors based on the decoded error before code correction.
2) Rearrangement is performed in the order of the smaller number of errors based on the decoded error before code correction.
3) The above 1) and 2) are switched based on the error before code correction.
4) Rearrangement is performed in the descending order of the number of errors on the basis of errors after code correction after decoding.
5) Rearrangement is performed in the order of the smaller number of errors based on the error after decoding and code correction.
6) Switch the above 4) and 5) based on the error after code correction.
7) Switch the above 1), 4) or 2), 5) based on the number of errors after code correction.
8) The above 3) and 6) are switched based on the number of errors after code correction.
9) Rearrange in the order specified by the control channel from the opposite device.
10) Sorting is performed by the sorting method specified by the control channel from the opposite device.
11) In 9) and 10) above, it is possible to set the rearrangement method when the control channel cannot be received normally.

  FIG. 1 is a block diagram showing a first embodiment of the present invention. The same components as those in FIG. 8 are denoted by the same reference numerals. In the conventional system shown in FIG. 8, the rearrangement of the rearrangement unit 3 is controlled based on the output of the power measurement unit 2, whereas in the embodiment shown in FIG. The rearrangement unit 3 is controlled based on the output (error before code correction). Other configurations are the same as those in FIG.

  In this embodiment, the case of MIMO with four transmission antennas and four reception antennas is shown. In the figure, since the variation of the degradation occurs in the order of transmission signals determined by the rearrangement unit 3, the error measurement unit 12 before correction has a large number of errors based on the number of errors before correction for each transmission signal (transmission antenna). The rearrangement unit 3 rearranges the transmission signals so that the transmission signals are in the order of less deterioration.

  As a result, the number of errors for each transmission signal is averaged, and the occurrence of post-correction errors due to the outstanding errors in the transmission signal and the decrease in transmission efficiency due to retransmission control are suppressed. In a situation where reception characteristics are poor, there is almost an error state. Therefore, priority is given to a signal with less error, and there is a higher possibility of no error, and throughput may be improved. As a result, when the reception characteristics are poor (the number of errors before correction is large), the data is rearranged in the order of the smallest number of errors, and when the reception characteristics are good (the number of errors before correction is small), the data is arranged in the order of the number of errors. By switching, it is possible to obtain the optimum throughput for the reception characteristics. In this embodiment, the operation of the rearrangement unit 3 has been described, but the operation of other parts is the same as that described with reference to FIG. 8 (the same applies hereinafter).

  As described above, when the reception characteristics are poor (when the number of errors before correction is large), the data is rearranged in the order of the small number of errors, so that the number of errors before decoding and before the code correction is small. Even if rearrangement is performed, variations between transmission signals can be suppressed. Also, when the reception characteristics are good (the number of errors before correction is small), it is possible to suppress variations between transmission signals by rearranging in the order of the number of errors.

  Further, according to the present invention, the rearrangement order can be switched by switching between the order with a large number of errors or the order with a small number of errors according to the number of errors after decoding and before code correction. In this way, it is possible to switch between the order in which the number of errors is large or the order in which the number of errors is small according to the number of errors after code decoding and before code correction. Can be suppressed.

  FIG. 2 is a block diagram showing a second embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals. In the embodiment shown in FIG. 1, the rearrangement control of the rearrangement unit 3 is performed by the output of the pre-correction error measurement unit 12. However, in the second embodiment, the rearrangement is performed by the output of the post-correction error measurement unit 13. The unit 3 is controlled.

  In the first embodiment, this is particularly effective when no corrected error has occurred, and when the corrected error has occurred, the calculation of the error before correction becomes inaccurate. It becomes effective. In addition, since retransmission control is operating when an error has occurred after correction, priority is given to the transmission signal for which retransmission control is operating, so that retransmission can be completed early, which is also effective in reducing data delay. There is. In this case, the data are rearranged in the order from the smallest number of errors. In this case, switching the order of arrangement according to the corrected error has the same effect as in the first embodiment.

  As described above, according to the second embodiment, the order of the rearrangement is rearranged in the order in which the number of errors after code correction after decoding is large, so that the variation between the transmission signals can be highly accurate. Can be suppressed. In addition, the rearrangement order can be rearranged in the order of few errors after decoding and code correction. In this way, transmission signal variations among all antennas can be suppressed with high accuracy.

Alternatively, it is possible to switch between rearrangement in the order of the larger number of errors and rearrangement in the order of the smaller number of errors.
FIG. 3 is a block diagram showing a third embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals. In this embodiment, whether the signal of the rearrangement unit 3 is rearranged based on the output of the error measurement unit 12 before correction or whether the signal of the rearrangement unit 3 is rearranged based on the output of the error measurement unit 13 after correction. The selection is made by the selector. Reference numeral 15 in FIG. 15 denotes a selector that selects one of the output from the pre-correction error measurement unit 12 and the output from the post-correction error measurement unit 13 and supplies the selected result to the rearrangement unit 3.

  In this embodiment, when there is no error after correction, rearrangement is performed according to the number of errors before correction, and when there is an error after correction, rearrangement is performed according to the number of errors after correction. An effect of suppressing signal variation can be obtained.

  According to the present invention, the sorting order is selected according to the number of errors after code correction, whether to use the number of errors before code correction or the number of errors after code correction. It can be rearranged in the order according to the number. In this case, the order of the rearrangement is selected depending on the number of errors after code correction, whether to use the number of errors before code correction or the number of errors after code correction, and the number of selected errors By rearranging in the order according to, variations in transmission signals of all antennas can be suppressed with high accuracy.

  Further, according to the present invention, the order of the rearrangement is determined according to the number of errors after code correction, according to the number of errors before decoding and after code correction, or according to the number of errors before decoding. Or select whether to change the order of the number of errors or the order of few errors according to the number of errors after code correction after decoding. Can be rearranged in the order according to the number of errors. In this case, the order of the rearrangement is selected depending on the number of errors after code correction, whether to use the number of errors before code correction or the number of errors after code correction, and the number of selected errors By rearranging in the order according to, variations in transmission signals between all antennas can be suppressed with high accuracy.

  FIG. 4 is a block diagram showing a fourth embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals. In this embodiment, a control channel data extraction unit 16 that receives a reception signal from the antenna 8 is provided, and the rearrangement control of the rearrangement unit 3 is performed by the output of the control channel data extraction unit 16. Other configurations are the same as those shown in FIG.

  In this configuration, information specifying the rearrangement order is transmitted to the control channel from the opposite apparatus (transmitter), and rearrangement is performed on the receiving side based on the information. As a result, it is possible to give priority to the transmission signal that is desired to be given priority on the transmission side.

  FIG. 5 is a block diagram showing a fifth embodiment of the present invention. The same components as those in FIG. 4 are denoted by the same reference numerals. In this embodiment, the rearrangement control of the rearrangement unit 3 is performed by selecting any one of the outputs of the error measurement unit 12 before correction, the error measurement unit 13 after correction, and the output of the control channel data extraction unit 16. It is something to be done. The select signal uses the output of the control channel data extraction unit 16. According to this embodiment, an optimal rearrangement method can be selected according to the situation.

  Further, in the invention, when the control channel is not normally received when specified from the control channel transmitted from the opposite device, it may be rearranged in the order using the preset order determining means. it can. In this way, even when the control channel cannot be normally received, it is possible to rearrange using the preset order determining means.

  FIG. 6 is a diagram showing comparison of on / off characteristics according to the present invention. The vertical axis represents BER, and the horizontal axis represents received power. (A) shows the characteristics when sorting is not performed (when off), and (b) shows the characteristics when sorting is performed (when turned on). In (a), f1 indicates a characteristic based on error measurement before correction, and f2 indicates a characteristic based on error measurement after correction. In (b), f3 indicates a characteristic based on the error measurement before correction, and f4 indicates a characteristic based on the error measurement after correction. It can be seen that the characteristic (f4) when rearranged based on the error measurement after correction shows a preferable characteristic.

(Appendix 1)
In a MIMO communication method of transmitting a transmission signal from a plurality of transmission antennas, receiving a signal transmitted from a plurality of reception antennas, and reproducing a transmission signal from the plurality of received signals received,
Using a plurality of received signals rearranged in the order of the large number of errors after decoding and after code correction, symbol candidates of a plurality of transmission signals are determined using the QRM-MLD method.
The QRM-MLD control method characterized by the above-mentioned.

(Appendix 2)
The QRM-MLD control method according to supplementary note 1, wherein the rearrangement order is rearranged according to the number of errors before or after code correction after decoding.

(Appendix 3)
Depending on the number of errors after code correction, the order of the rearrangement may be switched using a method of rearranging between the order with a large number of errors or the order with a small number of errors according to the number of errors before code correction, or a code correction Select whether to use the rearrangement method by switching between the order with the larger number of errors or the order with the smaller number of errors according to the number of errors later, and rearrange in the order according to the number of errors of the selected one QRM-MLD control method.

(Appendix 4)
The QRM-MLD control method according to supplementary note 1, wherein the rearrangement order is rearranged in an order specified in a control channel transmitted from the opposite apparatus.

(Appendix 5)
A QRM-MLD unit including a channel estimation unit, a power measurement unit, a rearrangement unit, a QR decomposition unit, a z calculation unit, an MLD unit, and a likelihood calculation unit;
A plurality of antennas provided at an input stage of the QRM-MLD unit;
A decoding unit that receives the output from the QRM-MLD unit and decodes the modulated signal;
A pre-correction error measurement unit that receives an output of the QRM-MLD unit and measures an error before correction;
An error measurement unit after correction that receives the output of the decoding unit and measures an error after correction,
And
A QRM-MLD control system configured to control the rearrangement of the rearrangement unit by either the error measurement unit before correction or the output of the error measurement unit after correction.

(Appendix 6)
The QRM-MLD control method according to supplementary note 1, wherein the rearrangement order is rearranged in an order using order determination means specified in a control channel transmitted from the opposite apparatus.

(Appendix 7)
Supplementary note 3 wherein when the control channel is not normally received in the case where the control channel is designated by the control channel transmitted from the opposite apparatus, the control channel is rearranged in the order using the preset order determining means. Or the QRM-MLD control method of 4.

It is a block diagram which shows the 1st Embodiment of this invention. It is a block diagram which shows the 2nd Embodiment of this invention. It is a block diagram which shows the 3rd Embodiment of this invention. It is a block diagram which shows the 4th Embodiment of this invention. It is a block diagram which shows the 5th Embodiment of this invention. It is a figure which shows the comparison of the characteristic at the time of ON / OFF by this invention. It is a figure which shows the outline | summary of the communication system of a MIMO system. It is a block diagram which shows the structural example of a conventional system.

Explanation of symbols

1 Channel estimation unit 3 Rearrangement unit 4 QR decomposition unit 5 z calculation unit 6 MLD unit 7 Likelihood calculation unit 11 Decoding unit 12 Error measurement unit before correction 13 Error measurement unit after correction

Claims (2)

In a MIMO communication method in which a transmission signal is transmitted from a plurality of transmission antennas, a signal transmitted from a plurality of reception antennas is received, and the transmission signal is reproduced from the plurality of reception signals received, before decoding the code after decoding Using a plurality of received signals rearranged in order of large number of errors, and determining symbol candidates of a plurality of transmission signals using a QRM-MLD method.
In a QRM-MLD control method characterized by :
Depending on the number of errors after code correction, the order of the rearrangement may be switched using a method of rearranging between the order with a large number of errors or the order with a small number of errors according to the number of errors before code correction, or a code correction Select whether to use the rearrangement method by switching between the order with the larger number of errors or the order with the smaller number of errors according to the number of errors later, and rearrange in the order according to the number of errors of the selected one QRM-MLD control method . A QRM-MLD unit including a channel estimation unit, a power measurement unit, a rearrangement unit, a QR decomposition unit, a z calculation unit, an MLD unit, and a likelihood calculation unit;
A plurality of antennas provided at an input stage of the QRM-MLD unit;
A decoding unit that receives the output from the QRM-MLD unit and decodes the modulated signal;
A pre-correction error measurement unit that receives an output of the QRM-MLD unit and measures an error before correction;
An error measurement unit after correction that receives the output of the decoding unit and measures an error after correction,
And
A QRM-MLD control system configured to control the rearrangement of the rearrangement unit by either the error measurement unit before correction or the output of the error measurement unit after correction.

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