JP2007251471A - Diversity receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diversity receiver whose reception antenna is installed in an environment beyond a visual line such as indoor, which has improved reception performance when an error rate after diversity synthesis is deteriorated. <P>SOLUTION: The diversity receiver comprising a plurality of branches (1a, 1b) each with a plurality of antenna elements includes: phase shift sections (2a, 2b) for changing the directivity of the antenna elements of each branch; a noise calculation section (7) for calculating a noise power value of a received signal after the diversity synthesis; and a phase shift control section (3) for controlling a phase shift amount to be changed in the phase shift sections (2a, 2b) on the basis of the noise power value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a receiving apparatus that receives a radio signal with a plurality of directional variable antennas and performs diversity combining.

  For example, when data modulated by an orthogonal frequency multiplexing (hereinafter referred to as OFDM) transmission method is transmitted by radio, multipath and fading occur due to topography in the middle of the transmission path. In the case of the OFDM transmission system, there is a mechanism that can remove the adverse effects of multipath components having a delay time in the guard interval interval that is an invalid signal interval, but if there is a delayed wave that has a delay time that does not fall within the guard interval interval, There is a problem that an error rate increases when a received signal is decoded.

  Conventionally, as an improvement measure, a receiving apparatus receives radio signals with a plurality of antennas, optimizes the direction of the directivity pattern of the receiving antenna, and performs diversity combining to reduce the influence of multipath and fading. When optimizing the antenna directivity pattern at each branch of diversity, beam steering control that directs the maximum beam direction of the directivity pattern to the arrival direction of the desired wave, and the arrival direction of the interference wave with the minimum beam direction of the directivity pattern Null steering control is performed (see, for example, Patent Document 1). These control the directivity of the antenna in a direction where the influence of multipath is small and the reception gain of the desired wave is high. In addition, control is performed so that the maximum beam direction of another branch is directed in a direction in which the beam gain of one branch decreases between the branches of diversity (for example, see Patent Document 2).

JP 2005-269026 A JP-A-10-190539

  When the receiving antenna is installed in an environment outside the line of sight such as indoors, the power of the incoming wave is often lowered due to the influence of walls and reinforcing bars. In addition to the multipath, fading, and the like caused by the topography in the middle of the transmission path, the receiving device receives a large number of delayed waves with short delay times in which the radio signal is irregularly reflected by indoor walls or furniture.

  In such a case, since the power of the incoming wave is reduced, the received signal is diversity-combined even if the directivity pattern of the antenna element of each branch is in the optimum direction with respect to the desired incoming wave. The error rate of the resulting signal may not improve (error data will not disappear).

  As an improvement measure, after diversity combining, control is performed so that the power value of the signal received from one branch antenna is in a phase that compensates for the lower portion of the power value of the signal received from the other branch antenna. It is conceivable to improve the error rate by increasing the signal power value.

  However, especially in an environment where there are many multipaths that are diffusely reflected by walls, etc., and the received power of the incoming wave is low, the received signal for each branch has a phase that compensates for the low received power of each other. From which direction the wave comes is unpredictable and cannot contribute to improving the error rate.

The present invention
In a diversity receiving device comprising a plurality of branches each having an antenna element,
A phase shifter that changes the directivity of the antenna element of each branch;
A noise calculator that calculates the noise power value of the received signal after diversity combining;
There is provided a diversity receiving apparatus comprising: a phase shift control unit that controls a phase shift amount to be changed in the phase shift unit based on a noise power value of the received signal after the diversity combining.

  As an effect of the present invention, since the directivity of the antenna is controlled so that the noise power value of the received signal resulting from the diversity combining is improved, the error rate can be improved even in an indoor environment. .

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a schematic configuration of a diversity receiver according to Embodiment 1 of the present invention. In this embodiment, the number of diversity branches is 2, and the number of antenna elements in each branch is 1.

  In FIG. 1, reference numerals 1a and 1b denote receiving antenna elements installed for each branch. The received signals received by these antenna elements 1a and 1b are output to the phase shift units 2a and 2b. The phase shift units 2 a and 2 b rotate the phase of the received signal based on the phase shift control signal output by the phase shift control unit 3. This is synonymous with directing the antenna directivity pattern in an arbitrary direction. The received signals whose phases have been rotated by the phase shift units 2a and 2b are input to the demodulation units 4a and 4b and subjected to demodulation processing. The demodulated received signal is input to diversity combining section 5. The diversity combining unit 5 combines the demodulated signals of a plurality of branches with a maximum ratio.

  The maximum ratio combining in diversity is generally performed by combining the phases of the signals of a plurality of branches and determining the amplification value from the received signal power ratio so that the specific gravity of the received signal having a high power level is increased. In addition to maximum ratio combining, there are equal gain combining, selective combining, and the like, which can also be used.

The diversity combined reception signal is output to the error correction unit 6 and the noise calculation unit 7. The noise calculator 7 calculates the noise power of the received signal from the variation in the received power of a known signal such as a pilot signal included in the received signal.
The error correction unit 7 corrects and outputs an error in the diversity combined received signal. Error correction is performed by decoding a convolutional code or a Reed-Solomon code that has been encoded in advance by a transmission apparatus.

  The noise power value calculated by the noise calculation unit 7 is output to the phase shift control unit 3. The phase shift control unit 3 receives the noise power value every arbitrary time interval, compares the previously received noise power value with the newly received noise power value, and if the new noise power value is smaller than the previous time, The phase shift direction of each branch is determined so that the phase is rotated in the same direction as, and when the phase becomes larger, the phase is rotated in the opposite direction. Further, the amount of phase shift is determined from the magnitude of the fluctuation of the noise power, and a phase shift control signal is output to the phase shift units 2a and 2b of each branch. For this algorithm, for example, an LMS algorithm is used.

  The LMS algorithm is a general adaptive control algorithm that minimizes the mean square error based on the steepest descent method. It is generally used for adaptive control because it is stable and requires a small amount of calculation.

  Based on the phase control signal output from the phase control unit 3, the phase shift units 2a and 2b of each branch rotate the phase of the reception signal output from the antennas 1a and 1b.

  As described above, the antenna directivity pattern is controlled so that the noise power value after diversity combining is minimized, and as a result of the control, the noise power after diversity combining is reduced. This means that the C / N value of the signal after diversity combining is improved and the gain of the signal power is increased.

  Hereinafter, this point will be described in detail with reference to FIGS.

  2A to 2C, the vertical axis represents the power value Pw of a signal obtained by diversity combining the received signal of each branch or the received signals of a plurality of branches, and the horizontal axis represents a frequency domain signal obtained by OFDM demodulation of the received signal. The frequency value Fd. Pt represents a power value at which no error occurs after error correction decoding. In the figure, it is assumed that received signals Ra and Rb received by antenna elements of two branches are diversity-combined to obtain a combined signal Rc.

  FIG. 2A shows a case where the maximum beam direction of the antenna directivity of each branch is directed to the arrival direction of the desired wave. Since the reception power of each branch is reduced, there is a frequency that does not reach reception power sufficient for decoding without error even for a signal after diversity combining, and as a result, the error rate cannot be improved.

  FIG. 2 (b) shows that the maximum beam direction of one branch other than the arrival direction of the desired wave is controlled by using the steering direction pattern of the branch antenna in the direction in which the gain of one of the branches decreases between the branches. This is the case when facing in the direction. In this case, since the power value of the signal Rb arriving from the direction to which the maximum beam of one branch antenna is directed is low, the received power after combining is not increased even if diversity combining is performed, and as a result, the error rate cannot be improved. Become.

  On the other hand, as shown in FIG. 2 (c), when the power value of the signal received from one branch antenna is a phase that compensates for the low power portion of the signal received from another branch antenna. The signal power value increases after diversity combining, and an improvement in error rate can be expected. In this way, even when the power of the desired wave is low, if the directivity of the antenna of each branch can be directed to the optimum direction, the power value after diversity combining can be increased (the diversity gain is high), and an error occurs. The rate is improved (there is no error data). Specifically, this can be realized by receiving a delayed wave having a high received power at a frequency at which the received power of a desired wave received by a certain branch is lowered, and diversity combining.

  However, especially in an environment where there are many multipaths that are diffusely reflected by walls, etc., and the received power of the incoming wave is low, the received signal for each branch has a phase that compensates for the low received power of each other. It is unpredictable from which direction the wave comes, and it is not possible to increase the diversity gain by using only conventional beam steering control, null steering control, etc., as shown in FIGS. It cannot contribute to the improvement of the rate.

  In the present embodiment, as described above, the antenna directivity is controlled so as to improve the noise power value of the received signal as a result of the diversity combining. ), The received power is increased (diversity gain is improved), and as a result, the error rate is improved.

Embodiment 2. FIG.
FIG. 3 is a block diagram showing a schematic configuration of the diversity receiver according to the second embodiment of the present invention. This embodiment is a case where the number of diversity branches is two and the number of antenna elements in each branch is one, as in the first embodiment.

  The diversity receiving apparatus of the second embodiment is generally the same as the diversity receiving apparatus of the first embodiment, but the phase shift control unit 3 receives the output signal of the error correction unit 6 instead of the output of the noise calculation unit 7. However, phase control is performed based on this.

  In FIG. 3, the signal that has been diversity combined by the diversity combining unit 5 is output to the error correction unit 6. The error correction unit 6 decodes the received signal according to the encoding method and performs error correction processing. In general, Reed-Solomon error correction is often performed for error correction. In Reed-Solomon error correction processing, error bits in a fixed-length data packet are corrected using the parity data added at the time of encoding. However, the number of data that can be corrected by the parity data length is limited, and more If there is an error in the number of data, it cannot be corrected. When a packet that cannot be corrected in the Reed-Solomon error correction process is received, it can be detected that the error cannot be corrected and used as information on the error rate of the received signal.

  The error correction unit 6 calculates the error rate as described above and outputs it to the phase shift control unit 3. The phase shift control unit 3 receives the error rate at every arbitrary time interval, compares the previously received error rate with the newly received error rate, and if the new error rate is smaller than the previous time, it is in the same direction as the previous time. The phase is rotated, and when the phase becomes larger, the phase shift direction of each branch is determined so that the phase is rotated in the opposite direction. Further, the amount of phase shift is determined from the magnitude of the error rate, and a phase shift control signal is output to the phase shift units 2a and 2b of each branch.

  Based on the phase control signal output from the phase control unit 3, the phase shift units 2a and 2b of each branch rotate the phase of the reception signal output from the antennas 1a and 1b.

  In this way, the antenna directivity pattern is controlled so that the error rate of the signal after diversity combining is minimized, so that the diversity gain can be increased, and as a result, the error rate is improved.

Embodiment 3 FIG.
FIG. 4 is a block diagram showing a schematic configuration of the diversity receiver according to the third embodiment of the present invention. This embodiment is a case where the number of diversity branches is 2, and the number of antenna elements in each branch is 1, as in the first and second embodiments.

  The diversity receiving apparatus according to the third embodiment is generally the same as the diversity receiving apparatus according to the first embodiment, but the phase shift control unit 3 performs not only the noise power value calculated from the diversity combined signal but also the diversity combining. The difference is that a noise power value calculated from the reception signal of each previous branch is also received and phase control is performed based on the received noise power value.

  In FIG. 4, the signals output from the demodulation units 4a and 4b of each branch are input to the branch noise calculation units 8a and 8b. Similar to the noise calculator 7, the branch noise calculators 8 a and 8 b calculate the noise power of the received signal from the variation in the received power of the pilot signal included in the received signal. The calculated noise power value is output to the phase shift control unit 3.

  As mentioned above, diversity gain can be increased by controlling the antenna phase shift so that the noise power value calculated from the signal after diversity combining is minimized, but when power is turned on or when the channel is changed, etc. In the initial state, when the phase shift control is first performed using the noise power received from the antenna of each branch, and then the phase shift control is performed using the noise power after diversity combining, the control convergence speed is faster. There is.

  In the present embodiment, in the initial state, first, phase shift control is performed so that the noise power of the demodulated signal of each branch is minimized. Thus, the maximum beam direction of the antenna directivity pattern of each branch is directed to the arrival direction of the desired wave. Even in an indoor environment, if the received power value is large to some extent, the error rate of the received signal may become zero in this state. In such a case, it is not necessary to perform phase shift control according to the noise power value after diversity combining, so phase shift control using the noise power value of each branch is continued.

  On the other hand, if the noise power value after diversity combining does not decrease or the error rate of the signal after diversity combining does not improve even if the maximum beam direction of each branch is in the direction of arrival of the desired wave, after diversity combining The phase shift control based on the noise power is performed.

  As described above, it is possible to shorten the time until the error rate is improved by appropriately switching the noise power value calculated in each branch and the noise power value after diversity combining for the signal used for phase shift control. it can.

Embodiment 4 FIG.
FIG. 5 is a block diagram showing a schematic configuration of the diversity receiver according to the fourth embodiment of the present invention. This embodiment is also a case where the number of diversity branches is 2, and the number of antenna elements in each branch is 1, as in the first to third embodiments.

  The diversity receiving apparatus according to the fourth embodiment is generally the same as the diversity receiving apparatus according to the second embodiment, but not only the error rate information obtained as a result of signal decoding after the diversity combining is performed by the phase shift control unit 3, but also the diversity. The difference is that a noise power value calculated from the received signal of each branch before synthesis is also received and phase control is performed based on the received noise power value.

  Further, the diversity receiving apparatus of the fourth embodiment is also generally the same as the diversity receiving apparatus of the third embodiment, but the phase shift control unit 3 does not use the noise power value after diversity combining, but the signal after diversity combining. The difference is that error rate information obtained as a result of decoding is received and phase control is performed based on this and the noise power value calculated from the received signal of each branch before diversity combining.

  As in the third embodiment, by performing phase shift control using the noise power value of each branch in the initial state, the error rate can be reduced compared to the case where phase shift control is performed using only the error rate. The time until improvement can be shortened. In particular, since the decoding process often takes time, if the phase shift control is performed using the noise power value for each branch in the initial state, the time reduction effect is great.

Embodiment 5 FIG.
FIG. 6 is a block diagram showing a schematic configuration of the diversity receiver according to the fifth embodiment of the present invention. This embodiment is also a case where the number of diversity branches is two and the number of antenna elements in each branch is one, as in the first to fourth embodiments.

  The diversity receiving apparatus according to the fifth embodiment is generally the same as the diversity receiving apparatus according to the fourth embodiment, but the error rate information obtained as a result of signal decoding after diversity combining and the diversity combining before the diversity combining is performed by the phase shift control unit 3. Not only the noise power value calculated from the received signal of each branch but also the noise power value after diversity combining output from the noise calculation unit 7 is received, and the phase control is performed based on these values.

  In the first to fifth embodiments, the phase shift control can be performed in the RF band or after being converted into a digital signal. When phase-shifting control is performed after conversion to a digital signal, adaptive array processing such as that described in Document 1 can be performed.

  In the first to fifth embodiments, an example in which the number of diversity branches is two and the number of antenna elements in each branch is one is shown. However, the number of branches may be any number. Further, there may be a plurality of antenna elements in each branch.

  When there are a plurality of antenna elements in each branch, the reception signals from the plurality of antenna elements may be input to the selector, and one may be selected and demodulated.

  When there are a plurality of antenna elements in each branch and phase shift control is performed after conversion to a digital signal, beamform processing can be performed using fast Fourier transform or discrete Fourier transform as shown in Document 2. When implemented in the RF band, a Butler matrix can be used.

  In the above embodiment, the noise power of each branch and the noise power value after diversity combining are calculated, but the signal-to-noise power ratio (C / N) can also be calculated and used. Similarly, the signal power value is calculated, and phase shift control can be performed so that the received signal power value becomes maximum.

  As an application example of the present invention, the present invention can be applied to a receiving apparatus that receives a radio signal with a plurality of directional variable antennas and performs diversity combining.

It is a schematic block diagram of the diversity receiver which shows Embodiment 1 of this invention. (A)-(c) is the figure which showed the mode of the received power value of the signal which carried out the diversity synthesis | combination signal and the received signal of multiple branches by which directivity control was carried out. It is a schematic block diagram of the diversity receiver which shows Embodiment 2 of this invention. It is a schematic block diagram of the diversity receiver which shows Embodiment 3 of this invention. It is a schematic block diagram of the diversity receiver which shows Embodiment 4 of this invention. It is a schematic block diagram of the diversity receiver which shows Embodiment 5 of this invention.

Explanation of symbols

1a, 1b antenna, 2a, 2b phase shift unit, 3 phase shift control unit, 4a, 4b demodulation unit, 5 diversity combining unit, 6 error correction unit, 7 noise calculation unit, 8a, 8b branch noise calculation unit.

Claims (5)

In a diversity receiving device comprising a plurality of branches each having an antenna element,
A phase shifter that changes the directivity of the antenna element of each branch;
A noise calculator that calculates the noise power value of the received signal after diversity combining;
A diversity receiving apparatus comprising: a phase shift control unit that controls a phase shift amount that is changed in the phase shift unit based on a noise power value of the received signal after the diversity combining. In a diversity receiving device comprising a plurality of branches each having an antenna element,
A phase shifter that changes the directivity of the antenna element of each branch;
An error correction unit that corrects an error in the received signal after diversity combining;
A diversity receiving apparatus comprising: a phase shift control unit that controls a phase shift amount to be changed in the phase shift unit based on an error rate of a received signal calculated by the error correction unit. It further comprises a branch noise calculator that calculates noise power of the received signal of each branch,
The phase shift control unit controls the amount of phase shift to be changed in the phase shift unit based on not only the noise power value of the received signal after diversity combining but also the noise power value of the received signal of each branch. The diversity receiver according to claim 1. It further comprises a branch noise calculator that calculates noise power of the received signal of each branch,
The phase shift control unit controls the amount of phase shift to be changed in the phase shift unit based on not only the error rate of the received signal calculated by the error correction unit but also the noise power value of each branch. The diversity receiver according to claim 2, characterized in that: A noise calculator that calculates the noise power value of the received signal after diversity combining;
The phase shift control unit is based on not only the error rate of the received signal calculated by the error correcting unit and the noise power value of each branch but also the noise power value of the received signal after diversity combining. The diversity receiving apparatus according to claim 4, wherein the amount of phase shift to be changed in the unit is controlled.

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