JP4148944B2 - Signal receiving device - Google Patents

Description

  The present invention relates to a signal receiving apparatus that demodulates a received signal using a modulation method such as an OFDM method.

  In recent years, an OFDM (Orthogonal Frequency Division Multiplexing) scheme has been proposed as a modulation scheme excellent in high-quality transmission. For example, OFDM schemes include modulation schemes such as QPSK (Quadrature Phase Shift Keying) and 16QAM (Quadrature Amplitude Modulation).

  5 and 6 are diagrams illustrating reference points according to the QPSK modulation method. The numerical values in parentheses shown in FIG. 5 are bit data indicating reference points on a complex plane (hereinafter referred to as a complex plane) according to the multilevel modulation method. The numerical value in “” is data indicating the direction and size of the reference value in the complex plane. Here, “+1” shown in FIG. 5 is obtained by an equation of P × (3/4) × (1 / √2). “−1” is obtained by the equation −P × (3/4) × (1 / √2). Note that P means an average value of pilot signals.

  FIG. 7 is a diagram illustrating each reference point according to the 16QAM modulation scheme. The numerical values in parentheses shown in FIG. 7 are bit data indicating the reference point in the complex plane. The numerical value in “” is data indicating the direction and size of the reference value in the complex plane. Here, “+1” shown in FIG. 7 is obtained by an equation of P × (3/4) × (1 / √10). “+3” is obtained by the formula of P × (3/4) × (1 / √10) × 3. “−1” is obtained by the equation −P × (3/4) × (1 / √10). “−3” is obtained by the equation −P × (3/4) × (1 / √10) × 3.

  The reference point shown in FIG. 5 or FIG. 7 is compared with the signal point of the received signal, and any one of the reference points is specified, whereby the received signal is demodulated into bit data. As a processing method for specifying this reference point, a hard decision Viterbi decoding process and a soft decision Viterbi decoding process can be cited. In the hard decision Viterbi decoding process, bit data indicating a reference point closest to the signal point of the received signal is specified. As shown in FIG. 6, when the hard decision Viterbi decoding process is executed, the reference point (01) closest to the signal point A of the received signal is specified.

  On the other hand, in the soft decision Viterbi decoding process, each bit indicating the reference point is expanded by 3 bits. As shown in FIG. 6, in the soft decision Viterbi decoding process, “000”, “001”, “010”, “011”, “ “111”, “110”, “101”, “100” are allocated on the I-axis or the Q-axis from the side closer to “1”, thereby indicating the signal point of the received signal. For example, the signal point A shown in FIG. 6 has a deviation of −2 in the I-axis direction and +2 in the Q-axis direction from the reference point (01) closest to the signal point A. Therefore, the signal point A is indicated by (010101). Thereby, in the soft decision Viterbi decoding process, the reference point is more appropriately specified than in the hard decision Viterbi decoding process.

Here, each of the plurality of receiving units performs the hard-decision Viterbi decoding process or the soft-decision Viterbi decoding process on the received signal. And a diversity synthetic | combination part selects either of the received signals output by the said several receiving part (for example, refer patent document 1). Specifically, the diversity combining unit selects the receiving unit that has calculated the shortest distance between the reference point and the signal point of the received signal, and outputs the received signal from the selected receiving unit.
JP 2003-28359 A

  However, when the reception state in one receiving unit is good and the receiving state in the other receiving unit is worse than the receiving state in the one receiving unit, the diversity combining unit receives the one receiving state in which the receiving state is good. In some cases, the reception signal output by the other reception unit, which is worse than the reception state in the one reception unit, is selected in error instead of the reception signal output by the unit.

  FIG. 8 is a diagram illustrating a state in which signal points of received signals are projected on a complex plane in one receiving unit (hereinafter referred to as a first receiving unit) having a good reception state. FIG. 9 is a diagram illustrating a state in which signal points of received signals are projected on a complex plane in the other receiving unit (hereinafter referred to as a second receiving unit) that is worse than the receiving state in the one receiving unit. K1 and K2 shown in FIGS. 8 and 9 indicate regions where the signal related to (11) transmitted on the transmission side varies in the vicinity of (11) in the complex plane on the reception side.

  As shown in FIG. 8, in the first receiving unit in a good reception state, the signal point B of the received signal is arranged within a range close to the original reference point (11). On the other hand, as shown in FIG. 9, in the second receiving unit in which the reception state is worse than a certain degree, the signal point C of the received signal is separated from the original reference point (11), and an incorrect reference point (hereinafter referred to as an erroneous reference point). May be placed near (01). Therefore, the original reference point (11) close to the signal point B is specified in the first receiving unit, while the erroneous reference point (01) close to the signal point C is specified in the second receiving unit.

  In this case, since the distance L2 between the signal point C and the erroneous reference point (01) is shorter than the distance L1 between the signal point B and the original reference point (11), the diversity combining unit The reception signal output by the second reception unit that has calculated the shortest distance L2 may be selected by mistake. For this reason, if it is determined that there is a high possibility that the signal point of the received signal projected on the complex plane is closer to the erroneous reference point than the original reference point, the diversity combining unit further sets the original reference point to the original reference point. A receiving unit that outputs a signal corresponding to a close signal point can be selected.

  Therefore, the present invention has been made in view of the above points, and whether or not the signal point of the received signal projected on the complex plane is likely to be closer to the erroneous reference point than the original reference point. It is an object of the present invention to provide a signal receiving apparatus that can make a determination.

  In order to solve the above-described problem, the present invention specifies signal points of a received signal projected at a position separated by a predetermined distance or more from an extension of a region surrounding all reference points in a complex plane according to a multi-level modulation method. And a signal point specifying unit; and an abnormality determining unit that determines that the signal point is abnormal when the signal point is specified by the signal point specifying unit.

  Here, as shown in FIG. 9, when the region K2 is larger than the region K1, outside the region K0 separated by a predetermined distance or more from the extension of the region surrounding all the reference points in the complex plane according to the multilevel modulation method. There is a high possibility that the signal points of the received signal increase and within the area K2, the signal point of the received signal exceeds the area of the reference point (11) and approaches the erroneous reference point (01) or the erroneous reference point (10). Become. In the present invention, when there is a signal point of the received signal at a location separated by a predetermined distance or more from the extension of the region surrounding all the reference points in the complex plane according to the multi-level modulation method, the abnormality determination unit detects the signal point. If the signal receiving device determines that the signal point of the received signal is closer to the erroneous reference point than the original reference point in the region separated by the predetermined distance or more, It can be determined whether or not.

  In the above invention, the predetermined distance may be a half distance between adjacent reference points in the complex plane. Here, the predetermined distance from the extension of the region surrounding all the reference points in the complex plane is a half distance between adjacent reference points, and the number of received signals projected on the separated points more than the predetermined distance is The increase in the number of signal points of the received signal that are closer to the erroneous reference point in the region separated by the predetermined distance or more increases. In the present invention, the signal reception device determines that the signal point of the reception signal is higher than the original reference point by determining that the reception signal projected on the portion separated by the predetermined distance or more is abnormal. It is possible to determine with high accuracy whether or not there is a high possibility of approaching the erroneous reference point.

  In the above invention, when the number of abnormalities within the predetermined period determined by the abnormality determination unit does not exceed the predetermined threshold, the signal output by the signal receiving device is selected and the predetermined period determined by the abnormality determination unit When the number of abnormalities in the signal exceeds a predetermined threshold value, a selection unit that does not select a signal output by the signal reception device may be provided. In this case, when the number of abnormalities within the predetermined period determined by the abnormality determining unit exceeds a predetermined threshold, the selection unit does not select the signal output by the signal receiving device, so that the signal selecting device It is possible to prevent selection of a signal from a signal receiving apparatus that has a high possibility that the signal point of the received signal is closer to the erroneous reference point than the original reference point, and to prevent the output of a signal with large quality degradation. be able to.

  In the above-described invention, a selection unit may be provided that selects a signal output by the signal receiving apparatus having the smallest number of abnormalities within a predetermined period determined by the abnormality determination unit. In this case, the signal selection device can select the signal from the signal reception device that has the lowest possibility that the signal point of the reception signal is closer to the erroneous reference point than the original reference point, and the quality deterioration is caused. A small number of signals can be output.

  In the said invention, the frequency | count of abnormality within the predetermined period determined by the abnormality determination part may show the degree of quality degradation of the signal output by a signal receiver. In this case, when the number of abnormalities within the predetermined period determined by the abnormality determining unit exceeds a predetermined threshold, the degree of quality degradation of the signal output by the signal receiving device is increased. The signal output by the signal receiving apparatus can be prevented from being output. Further, the signal selection device can select the signal with the least quality degradation by selecting the signal output by the signal reception device with the smallest number of abnormalities within the predetermined period determined by the abnormality determination unit. .

  In the above-described invention, transmission / reception of signals by the OFDM method may be possible. In this case, even in a signal receiving apparatus capable of transmitting and receiving signals by the OFDM method, the signal point of the received signal is closer to the false reference point than the original reference point in the region separated by the predetermined distance or more. It can be determined whether the possibility is high.

  According to the present invention, it is possible to determine whether or not there is a high possibility that the signal point of the received signal projected on the complex plane is closer to the erroneous reference point than the original reference point.

(First embodiment)
A signal selection apparatus according to the present embodiment will be described with reference to the drawings. FIG. 1 is a diagram illustrating a signal selection device 1 according to the present embodiment. As shown in FIG. 1, the signal selection device 1 can transmit and receive signals using the OFDM method, and includes signal receiving units 100 and 200 (signal receiving device) and a diversity combining unit 300.

  The signal receiving unit 100 includes an antenna 101, a tuner 102, an AGC unit 103, an A / D conversion unit 104, a synchronization unit 105, an FFT unit 106, a demodulation unit 107, a signal point specifying unit 108, an abnormality And a determination unit 109.

  The antenna 101 receives a signal transmitted from a transmission unit (not shown). Tuner 102 specifies a baseband signal based on the signal received by antenna 101. The AGC unit 103 increases or decreases the power value of the signal output from the tuner 102 to approach a specific power value.

  The A / D conversion unit 104 converts the signal output from the AGC unit 103 from analog to digital. Further, the A / D conversion unit 104 generates an I-axis component signal and a Q-axis component signal based on the input signal by using Hilbert transform or the like. The synchronization unit 105 executes synchronization processing of the signal output from the A / D conversion unit 104.

  The FFT unit 106 converts the signal along the time axis output from the synchronization unit 105 into a signal along the frequency axis by executing fast Fourier transform. The demodulation unit 107 demodulates the signal output from the FFT unit 106 by demodulation processing such as differential modulation according to the modulation method. Further, the demodulation unit 107 projects the signal output from the FFT unit 106 as a signal point onto a complex plane (hereinafter referred to as a complex plane) according to the multi-level modulation method.

  The signal point specifying unit 108 is a portion (region R2, which will be described later) separated from the extension of regions (regions R1, R1 ′ which will be described later) surrounding all reference points in the complex plane composed of the I component and the Q component. The signal point of the received signal projected on (outside R2 ′) is specified. The predetermined distance in the present embodiment is a half distance between adjacent reference points in the complex plane.

  Here, FIG. 2 is a diagram illustrating a complex plane of QPSK in the present embodiment. FIG. 3 is a diagram illustrating a complex plane of 16QAM in the present embodiment. As shown in FIGS. 2 and 3, the signal point specifying unit 108 sets the regions R1 and R1 'to a complex plane. These regions R1 and R1 'are regions surrounding all reference points in the complex plane. In the present embodiment, the regions R1 and R1 'are regions surrounding the extensions W1 and w1' where there is no reference point adjacent in any one direction to a specific reference point.

  In addition, when the modulation method is QPSK, the signal point specifying unit 108 sets a distance LW that is half the distance between adjacent reference points (for example, between the reference point (00) and the reference point (01)) to the region R1. A region R2 surrounding the region R1 is set apart from the outer extension W1 (see FIG. 2). Similarly, even when the modulation method is 16QAM, the signal point specifying unit 108 is half the distance LW ′ between adjacent reference points (for example, between the reference point (0000) and the reference point (0001)). A region R2 ′ surrounding the region R1 ′ is set while separating the region from the extension W1 ′ of the region R1 ′. The signal point specifying unit 108 specifies a signal point of the reception signal projected outside the region R2 or the region R2 '.

  The abnormality determining unit 109 determines that the signal point is abnormal when the signal point specifying unit 108 specifies the signal point.

  The signal reception unit 200 (signal reception device) includes an antenna 201, a tuner 202, an AGC unit 203, an A / D conversion unit 204, a synchronization unit 205, an FFT unit 206, a demodulation unit 207, and a signal point specification. Unit 208 and an abnormality determination unit 209. Each unit included in the signal receiving unit 200 has the same function as the unit of the same name included in the signal receiving unit 100.

  Diversity combining section 300 (selecting section) selects a signal output by signal receiving sections 100 and 200 when the number of abnormalities within a predetermined period determined by abnormality determining sections 109 and 209 does not exceed a predetermined threshold. When the number of abnormalities within the predetermined period determined by the abnormality determining units 109 and 209 exceeds a predetermined threshold, the signals output by the signal receiving units 100 and 200 are not selected. Further, the diversity combining unit 300 selects a signal output by the signal receiving unit 100 or the signal receiving unit 200 with the smallest number of abnormalities within the predetermined period determined by the abnormality determining units 109 and 209.

  Here, when there are many signal points of the received signal projected outside the regions R2 and R2 ′ separated by a predetermined distance or more from the extension of the regions R1 and R1 ′ surrounding all the reference points in the complex plane. In the regions R2 and R2 ′, there is a high possibility that the signal point of the received signal approaches the erroneous reference point. In the present invention, when there are signal points of the received signal outside the regions R2 and R2 ′ separated by a predetermined distance from the extension of the regions R1 and R1 ′ surrounding all the reference points in the complex plane, the abnormality determination is performed. When the unit 209 determines that the signal point is abnormal, the signal selection device 1 can cause the signal point of the received signal to be closer to the erroneous reference point than the original reference point in the regions R2 and R2 ′. It can be determined whether or not the property is high.

  Further, since the predetermined distance from the extension of the regions R1 and R1 ′ surrounding all the reference points in the complex plane is half the distance between the adjacent reference points, it is projected to a place separated by more than the predetermined distance. The increase in the number of received signals within a predetermined period means that in the regions R2 and R2 ′ separated by the predetermined distance or more, the signal points of received signals closer to the erroneous reference point can be increased within the predetermined period. Increases nature. In the present invention, when the abnormality determination units 109 and 209 determine that the received signal projected outside the regions R2 and R2 ′ is abnormal, the signal selection device 1 can receive the received signal within the regions R2 and R2 ′. It is possible to determine with high accuracy whether or not there is a high possibility that the signal point is closer to the erroneous reference point than the original reference point.

  Further, when the number of abnormalities within the predetermined period determined by the abnormality determining unit 209 exceeds a predetermined threshold, the diversity combining unit 300 does not select the signal output by the signal receiving units 100 and 200, thereby diversity combining. The unit 300 can prevent a signal from the signal receiving unit having a high possibility that the signal point of the received signal is closer to the erroneous reference point than the original reference point, and outputs a signal having a large quality degradation. You can avoid it.

  Furthermore, the diversity combining unit 300 can select a signal from the signal receiving unit with the lowest possibility that the signal point of the received signal is closer to the erroneous reference point than the original reference point, and the signal with less quality degradation. Can be output.

(Second Embodiment)
FIG. 4 is a diagram illustrating the signal selection device 1 according to the present embodiment. The signal selection device 1 according to this embodiment is different from the first embodiment in that the reliability information generation units 110 and 210 are provided.

  The reliability information generators 110 and 210 indicate the degree of quality deterioration of the signals output by the signal receivers 100 and 200 based on the number of abnormalities determined within the predetermined period determined by the abnormality determiners 109 and 209. Generate sex information. For example, the reliability information generators 110 and 210 indicate that the degree of quality degradation of the signals output from the signal receivers 100 and 200 is high when the number of abnormalities within the determined predetermined period is large. Generate sex information. On the other hand, the reliability information generation units 110 and 210 indicate that the degree of quality degradation of the signals output by the signal reception units 100 and 200 is low when the number of abnormalities within the determined predetermined period is small. Generate sex information.

  In this case, when the number of abnormalities within the predetermined period determined by the abnormality determining units 109 and 209 exceeds a predetermined threshold, the degree of quality degradation of the signals output by the signal receiving units 100 and 200 increases. Therefore, the diversity combining unit 300 can prevent the signals output by the signal receiving units 100 and 200 from being output. Moreover, the diversity combining unit 300 selects the signal output by the signal receiving unit that has determined the smallest number of abnormalities within the predetermined period determined by each abnormality determining unit, thereby causing the least quality degradation. A signal can be selected.

  The contents described in the signal selection device can be realized by executing a dedicated program for using a predetermined program language in a general-purpose computer such as a personal computer. The program may be recorded on a recording medium. Examples of the recording medium include a hard disk, a flexible disk, a compact disk, an IC chip, and a cassette tape. In addition, the signal selection device can be configured by an integrated circuit or the like.

  An example of the present invention has been described above. However, the present invention is not limited to the specific example, and the specific configuration and the like of each unit can be appropriately changed in design. Further, the actions and effects described in the embodiments and the modifications are only listed the most preferable actions and effects resulting from the present invention, and the actions and effects according to the present invention are described in the embodiments and modifications. It is not limited to things.

It is a figure which shows the signal selection apparatus in 1st Embodiment. It is a figure which shows the complex plane of QPSK in 1st Embodiment. It is a figure which shows the complex plane of 16QAM in 1st Embodiment. It is a figure which shows the signal selection apparatus in 2nd Embodiment. It is a figure which shows the complex plane of the conventional QPSK. It is a figure which shows the complex plane of the conventional QPSK. It is a figure which shows the complex plane of 16QAM from the past. It is a figure which shows the area | region where the signal point of the received signal in a complex plane varies. It is a figure which shows the area | region where the signal point of the received signal in a complex plane varies.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Signal selection apparatus, 100, 200 ... Signal receiving part, 101, 201 ... Antenna, 102, 202 ... Tuner, 103, 203 ... AGC part, 104, 204 ... A / D conversion part, 105, 205 ... Synchronizing part, 106, 206 ... FFT unit, 107, 207 ... demodulating unit, 108, 208 ... signal point specifying unit, 109, 209 ... abnormality determining unit, 110, 210 ... reliability information generating unit, 300 ... diversity combining unit

Claims (6)

A signal point specifying unit for specifying a signal point of a received signal projected at a position more than a predetermined distance from the extension of an area surrounding all reference points in a complex plane according to a multi-level modulation method, and a signal by the signal point specifying unit When a point is specified, the signal receiving device having an abnormality determination unit that determines that the signal point is abnormal,
When the number of abnormalities within the predetermined period determined by the abnormality determination unit does not exceed a predetermined threshold, the signal output by the signal receiving device is selected and within the predetermined period determined by the abnormality determination unit A signal selection device including a selection unit that does not select a signal output by the signal reception device when the number of abnormalities in the signal exceeds a predetermined threshold.   The signal selection apparatus according to claim 1, wherein the predetermined distance is a half distance between adjacent reference points in the complex plane.   3. The signal selection according to claim 1, further comprising: a selection unit that selects a signal output by the signal receiving device having the smallest number of abnormalities within the predetermined period determined by the abnormality determination unit. apparatus.   4. The frequency of abnormality within the predetermined period determined by the abnormality determination unit indicates a degree of quality degradation of a signal output from the signal receiving device. The signal selection device described.   5. The signal selection apparatus according to claim 1, wherein a signal can be transmitted / received by an OFDM system. 6. The signal selection apparatus according to claim 3, wherein a signal can be transmitted / received by an OFDM system.

Images